Analysis of risk factors for venous air embolism in the semisitting position and its impact on outcome in a consecutive series of 740 patients

Shadi Al-AfifDepartment of Neurosurgery, Medical School Hannover, Germany;

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Hesham ElkayekhDepartment of Neurosurgery, Medical School Hannover, Germany;

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Mazin OmerDepartment of Neurosurgery, Medical School Hannover, Germany;

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Hans E. HeisslerDepartment of Neurosurgery, Medical School Hannover, Germany;

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Dirk ScheinichenDepartment of Anesthesiology and Intensive Care, Medical School Hannover, Germany; and

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Thomas PalmaersDepartment of Anesthesiology and Intensive Care, Medical School Hannover, Germany; and

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Makoto NakamuraDepartment of Neurosurgery, University of Witten/Herdecke, Cologne Merheim Medical Center, Cologne, Germany;

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Elvis J. HermannDepartment of Neurosurgery, Medical School Hannover, Germany;

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Madjid SamiiInternational Neuroscience Institute, Hannover, Germany

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Joachim K. KraussDepartment of Neurosurgery, Medical School Hannover, Germany;

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OBJECTIVE

Routine use of the semisitting position, which offers several advantages, remains a matter of debate. Venous air embolism (VAE) is a potentially serious complication associated with the semisitting position. In this study, the authors aimed to investigate the safety of the semisitting position by analyzing data over a 20-year period.

METHODS

The incidence of VAE and its perioperative management were analyzed retrospectively in a consecutive series of 740 patients who underwent surgery between 1996 and 2016. The occurrence of VAE was defined by detection of bubbles on transthoracic Doppler echocardiography (TTDE) or transesophageal echocardiography (TEE) studies, a decrease of end-tidal CO2 (ETCO2) by 4 mm Hg or more, and/or an unexplained drop in systolic arterial blood pressure (≥ 10 mm Hg). From 1996 until 2013 TTDE was used, and from 2013 on TEE was used. The possible risk factors for VAE and its impact on surgical performance were analyzed.

RESULTS

There were 404 women and 336 men with a mean age at surgery of 49 years (range 1–87 years). Surgery was performed for infratentorial lesions in 709 patients (95.8%), supratentorial lesions in 17 (2.3%), and cervical lesions in 14 (1.9%). The most frequent pathology was vestibular schwannoma. TEE had a higher sensitivity than TTDE. While TEE detected VAE in 40.5% of patients, TTDE had a detection rate of 11.8%. Overall, VAE was detected in 119 patients (16.1%) intraoperatively. In all of these patients, VAE was apparent on TTDE or TEE. Of those, 23 patients also had a decrease of ETCO2, 18 had a drop in blood pressure, and 23 had combined decreases in ETCO2 and blood pressure. VAE was detected in 24% of patients during craniotomy before opening the dura mater, in 67% during tumor resection, and in 9% during wound closure. No risk factors were identified for the occurrence of VAE. Two patients had serious complications due to VAE. Surgical performance in vestibular schwannoma surgery was not affected by the presence of VAE.

CONCLUSIONS

This study shows that the semisitting position is overall safe and that VAE can be managed effectively. Persistent morbidity is very rare. The authors suggest that the semisitting position should continue to have a place in the standard armamentarium of neurological surgery.

ABBREVIATIONS

ETCO2 = end-tidal CO2; PEEP = positive end-expiratory pressure; PFO = patent foramen ovale; TEE = transesophageal echocardiography; TTDE = transthoracic Doppler echocardiography; TTE = transthoracic echocardiography; VAE = venous air embolism.

OBJECTIVE

Routine use of the semisitting position, which offers several advantages, remains a matter of debate. Venous air embolism (VAE) is a potentially serious complication associated with the semisitting position. In this study, the authors aimed to investigate the safety of the semisitting position by analyzing data over a 20-year period.

METHODS

The incidence of VAE and its perioperative management were analyzed retrospectively in a consecutive series of 740 patients who underwent surgery between 1996 and 2016. The occurrence of VAE was defined by detection of bubbles on transthoracic Doppler echocardiography (TTDE) or transesophageal echocardiography (TEE) studies, a decrease of end-tidal CO2 (ETCO2) by 4 mm Hg or more, and/or an unexplained drop in systolic arterial blood pressure (≥ 10 mm Hg). From 1996 until 2013 TTDE was used, and from 2013 on TEE was used. The possible risk factors for VAE and its impact on surgical performance were analyzed.

RESULTS

There were 404 women and 336 men with a mean age at surgery of 49 years (range 1–87 years). Surgery was performed for infratentorial lesions in 709 patients (95.8%), supratentorial lesions in 17 (2.3%), and cervical lesions in 14 (1.9%). The most frequent pathology was vestibular schwannoma. TEE had a higher sensitivity than TTDE. While TEE detected VAE in 40.5% of patients, TTDE had a detection rate of 11.8%. Overall, VAE was detected in 119 patients (16.1%) intraoperatively. In all of these patients, VAE was apparent on TTDE or TEE. Of those, 23 patients also had a decrease of ETCO2, 18 had a drop in blood pressure, and 23 had combined decreases in ETCO2 and blood pressure. VAE was detected in 24% of patients during craniotomy before opening the dura mater, in 67% during tumor resection, and in 9% during wound closure. No risk factors were identified for the occurrence of VAE. Two patients had serious complications due to VAE. Surgical performance in vestibular schwannoma surgery was not affected by the presence of VAE.

CONCLUSIONS

This study shows that the semisitting position is overall safe and that VAE can be managed effectively. Persistent morbidity is very rare. The authors suggest that the semisitting position should continue to have a place in the standard armamentarium of neurological surgery.

In Brief

In this study, the authors aimed to investigate the safety of the semisitting position and the incidence of venous air embolism in a cohort of 740 patients over a 20-year period. Venous air embolism was detected in 119 surgeries. No specific risk factors were found, and serious complications were rare, occurring in only 2 instances. Surgical performance during vestibular schwannoma surgery was not affected by the presence of venous air embolism.

The semisitting position has been used for decades to approach lesions in the posterior cranial fossa or at the craniocervical junction.1–4 There are several advantages of this position compared with the prone position, including less brain swelling due to reduction of intracranial pressure, a cleaner operative field with less bleeding, and gravity-related clearance of CSF, which all result in minimizing the use of a suction device, thus enabling the surgeon to work with both hands in the dissection area around critical neurovascular structures.5,6 In addition, the semisitting position may also reduce the demand for mechanical retraction of the cerebellum, and it provides better anatomical orientation.4,7

Routine use of the semisitting position, however, is a matter of debate.8 Because of the fear of potentially devastating side effects, it has been avoided at many neurosurgical centers that instead favor other positions such as the park-bench or the prone position.9,10 A decline in the number of neurosurgeons who use the semisitting position was reported at the beginning of this century.11,12 One of the most important reasons for not adopting the semisitting position more widely is its inherent risk of venous air embolism (VAE). While several centers abandoned the semisitting position, others continued using it and introduced several preoperative and intraoperative measures to increase its safety.5,13 These measures involved not only better preoperative screening of patients, with the exclusion of those with higher risks of complications associated with the semisitting position, but also improvement of intraoperative monitoring and management of VAE. While there has been a renewed interest in the semisitting position more recently and several studies have reported clinical outcomes and other factors,1,14,15 there is still a paucity of data on possible risk factors for VAE and its impact on surgical performance.16–19

Here, we present our experience with the routine use of the semisitting position over a period of 20 years in a large consecutive series of patients. During this period, transthoracic Doppler echocardiography (TTDE) was replaced by transesophageal echocardiography (TEE) for monitoring the occurrence of VAE intraoperatively.20 We identified the occurrence of VAE and its impact on outcome after surgery. In addition, we analyzed possible risk factors for VAE. As a surrogate measure of its impact on surgical performance, we also compared the frequency and severity of postoperative facial palsy in patients with and without VAE who underwent surgery for vestibular schwannoma.

Methods

The IRB of the Medical School Hannover indicated that formal approval for data analysis of this retrospective study was not required. All patients signed informed consent for data analysis in the frame of a clinical study.

After excluding those who underwent surgery for deep brain stimulation or stereotactic biopsy, 740 patients underwent surgery in the semisitting position in the Department of Neurosurgery at the Medical School Hannover between 1996 and 2016. The majority of surgical procedures were performed by four experienced skull base surgeons (M.S., M.N., E.J.H., and J.K.K.). The clinical, radiological, and operative data were collected from the patients’ files, which were archived electronically (ALIDA) and submitted to a systemic analysis.

The anesthesia records were reviewed to identify all occurrences of intraoperative VAE in the semisitting position. Intraoperative VAE was defined by the following criteria, alone or in combination: 1) detection of bubbles by TTDE or TEE monitoring; 2) decrease in the end-tidal CO2 (ETCO2) level by 4 mm Hg or more; and 3) an otherwise unexplained sudden drop in systolic arterial blood pressure during surgery (by 10 mm Hg or more).

Monitoring was performed with TTDE from 1996 until 2013 and thereafter with TEE. The postoperative records were reviewed to identify any postoperative complications possibly related to the semisitting position.

Risk factor analysis for the occurrence of VAE considered age, height, body weight, sex, tumor size, surgical approach, the presence of accompanying disorders, and American Society of Anesthesiologists (ASA) Physical Classification status. Surgical performance was evaluated in the subgroup of patients who presented with vestibular schwannoma according to the frequency and severity of facial palsy as assessed by the House-Brackmann scale.21

Perioperative Preparation

All patients for whom surgery in the semisitting position was considered underwent transthoracic echocardiography (TTE) with intravenous echo contrast performed by a cardiologist to rule out a patent foramen ovale (PFO) or right-left shunt of another etiology.17 When a PFO was found, surgery was performed in the prone position as a modified "semiconcord" prone position with the head flexed.22

All patients were prepared with a triluminal central line in the right atrium, a peripheral catheter in the radial artery, a peripheral venous catheter, and a bladder catheter. Intraoperative monitoring consisted of TTDE or TEE for the detection of VAE, pulse oximetry, electrophysiology (somatosensory evoked potentials, brainstem auditory evoked potentials, and motor evoked potentials), invasive arterial blood pressure recording, and continuous measurement of ETCO2.23,24

Semisitting Position

Detailed descriptions of the semisitting position used at our institution have been described elsewhere.25–28 Patient positioning was always performed under electrophysiological monitoring of somatosensory evoked potentials to ensure patient safety. In summary, the patient is placed supine on the operating table after intubation, and the head is fixed in the Mayfield clamp. The surgeon then holds the Mayfield clamp with one hand and supports the patient’s neck with the other hand to avoid any injury to the cervical spine. The patient’s upper body and legs are slowly elevated by bending the operating table to achieve the semisitting position. The patient’s legs are positioned at or above the level of the heart. The knees are flexed by approximately 30° to avoid any tension on peripheral nerves. After that, the head is flexed carefully anteriorly and rotated laterally when a lateral approach is planned. Care is taken that a 2-finger space is maintained between the patient’s chin and sternal notch to avoid venous obstruction and to enable compression of the jugular veins during surgery if VAE were to occur in order to prevent further entrance of air and to guide localization of the entry site of air in the surgical field by the surgeon. The patient’s arms are supported with special padded arm rests.

Intraoperative Measures for Prevention and Management of VAE

During surgery, meticulous hemostasis is achieved, and the surgical site is continuously covered with wet gauze. The emissary veins are identified early to be closed by bipolar coagulation and/or bone wax. The opened spongiosa is obliterated by bone wax directly after the craniotomy is performed. The patient’s circulation is protected with intravenous fluid loading before the skin incision is made. Fluid balance is controlled continuously, and the venous pressure in the right atrium is maintained at 5 cm H2O or higher. Ventilation is adjusted accordingly to maintain a positive end-expiratory pressure (PEEP).

In the case of intraoperative VAE, the following measures are applied: 1) generous flushing of the surgical site with 0.9% NaCl solution; 2) gentle compression of the jugular veins by the anesthesiologist to elevate the cranial venous pressure, preventing further air entrance in the venous system and allowing the collapsed vessels to open and bleed, making it easier to identify them and close them; 3) with a persisting VAE, tilting of the operative table so that the patient’s head is lowered and the legs are further elevated; 4) aspiration of intracardial air bubbles with a syrinx from the central line; and 5) rapid correction of arterial hypotension by administration of intravenous fluids and/or catecholamines.

Statistical Analysis

Statistical analysis was performed using Excel (Microsoft Office 2016, Microsoft Corp.) and JMP Pro 14 (SAS Institute Inc.). Unless otherwise specified, metric data are given as mean ± standard deviation and frequencies as numbers. Statistical comparisons were carried out using the Student t-test and chi-square tests; p < 0.05 was considered statistically significant.

Results

Demographics and Clinical Data

A total of 740 patients underwent surgery in the semisitting position at our institution between 1996 and 2016. There were 404 women and 336 men. The mean age at surgery was 49 years (range 1–87 years).

Surgery was performed for lesions in the posterior fossa in 709 patients (95.8%), supratentorial lesions in 17 (2.3%), and cervical lesions in 14 patients (1.9%). The most frequent pathology treated in the semisitting position was vestibular schwannoma in 364 patients (49.2%), followed by meningioma in 112 (15.1%), glioma in 62 (8.4%), metastasis in 52 (7%), vascular malformations in 23 (3.1%), ependymoma in 22 (3%), epidermoid cyst in 18 (2.4%), hemangioblastoma in 12 (1.6%), medulloblastoma in 11 (1.5%), tumor of the pineal region in 21 (2.8%), and other entities in 43 (5.8%).

Intraoperative Frequency of VAE in the Semisitting Position

VAE was noted in 119 (16.1%) of the 740 patients intraoperatively (Table 1). In all 119 patients, VAE was apparent on TTDE or TEE. In 23 of these patients, VAE also became evident by a decrease in ETCO2 and in 18 patients by a decrease in blood pressure; in another 23 patients there was a combined drop in ETCO2 and a decrease in blood pressure. VAE occurred in 24% of patients during craniotomy before opening of the dura, in 67% during tumor resection, and in 9% during wound closure.

TABLE 1.

Intraoperative frequency of VAE on TTDE and TEE

No. of Patients (%)p Value
TTDE (n = 629)TEE (n = 111)
Patients w/ VAE74 (11.8)45 (40.5)<0.0001
Patients w/ decrease in ETCO239 (6.2)7 (6.3)0.966
Patients w/ arterial hypotension 31 (4.9)10 (9)0.832

Monitoring with TEE (performed in the last 111 surgeries of this series) detected VAE at a higher rate compared with TTDE (40.5% vs 11.8%; p < 0.0001). There were no statistically significant differences in the occurrence of arterial hypotension or decrease in ETCO2 regardless of the monitoring method (Table 1), indicating a higher sensitivity of TEE as outlined previously.20 The length of stay in intensive care did not differ between the groups.

In all patients, VAE was managed well according to the intraoperative measures as described above, although in one case, surgery had to be aborted due to uncontrollable VAE. There were no systemic or cerebral complications related to the occurrence of VAE except in 2 patients. Prolonged periods of VAE occurred in a 53-year-old man who was undergoing surgery for a brainstem cavernoma. Despite appropriate intraoperative measures, the patient experienced multiple cerebral infarctions that resulted in persistent neurological deficits. In the other case, a 75-year-old woman, VAE resulted in an ischemic infarction with transient hemiparesis and dysphagia. Surprisingly, postoperative workup revealed a PFO, which had not been noted on preoperative routine TTE.

Analysis of Possible Risk Factors Associated With VAE

There were no significant differences between patients with VAE and those without regarding age, height, weight, BMI, preoperative hemoglobin concentration, and a history of chronic cardiovascular disorders (Table 2). With regard to the ASA physical status, there was a tendency (p = 0.0532) for patients in higher classes (III and IV) to less frequently develop VAE compared with those in lower classes (I and II). There were no instances of VAE with occipital approaches and only one instance in a patient undergoing a cervical approach. The frequency of VAE did not depend on whether a medial or a lateral suboccipital approach was performed.

TABLE 2.

Analysis of possible risk factors associated with VAE

Patients w/ VAEPatients w/o VAEp Value
Age, yrs46.9 ± 20.049.3 ± 17.40.2189
Body height, cm169.7 ± 18.2168.4 ± 13.70.4588
Body weight, kg75.4 ± 23.374.8 ± 19.40.7908
BMI, kg/m225.5 ± 5.526.1 ± 5.80.2726
Hb (g/dl)13.6 ± 1.3413.8 ± 6.40.5229
Sex, F/M58/61346/2750.1614
Tumor diameter, cm2.50 ± 1.152.48 ± 1.260.8648
Arterial hypertension241260.9758
Coronary heart disease3220.5720
Diabetes mellitus3250.982
COPD120.1990
Bronchial asthma 38
Approach
Lateral suboccipital924660.214
Medial suboccipital26124
Occipital017
Cervical114
ASA classI & II vs III & IV: 0.0532
I41224
II65284
III11112
IV21

COPD = chronic obstructive pulmonary disease, Hb = hemoglobin.

Values are presented as the number of patients or mean ± SD unless stated otherwise.

With regard to histopathological findings, VAE occurred more often in patients who underwent surgery for pathologies in the pineal region. Overall, however, there was no significant correlation of the type of tumor with the manifestation of VAE (Table 3).

TABLE 3.

VAE and histopathological findings

Histopathological FindingNo. of PatientsNo. of Patients w/ VAE (%)No. of Patients w/o VAE (%)p Value
Vestibular schwannoma36453 (14.6)311 (85.4)
Meningioma11224 (21.4)88 (78.6)
Glioma6212 (19.4)50 (80.6)
Pineal tumor218 (38.1)13 (61.9)
Epidermoid cyst184 (22.2)14 (77.8)
Metastasis525 (9.6)47 (90.4)0.116
Ependymoma222 (9.1)20 (90.9)
Hemangioblastoma122 (16.7)10 (83.3)
Vascular malformation233 (13)20 (87.0)
Medulloblastoma111 (9.1)10 (90.9)
Other435 (11.6)38 (88.4)

Impact of VAE on Operative Performance and Postoperative Outcome

The duration of surgery tended to be longer in patients with intraoperative VAE (p = 0.0513). There were no significant differences with regard to other factors (Table 4). The duration of hospital stay or intensive care unit stay did not differ significantly between patients with VAE and those without. There was no significant increase in side effects of surgery such as postoperative CSF fistula, hematoma, coma, or motor deficits. No patient with VAE died within 30 days after surgery; however, 4 patients without VAE died during this time period (all due to their tumor).

TABLE 4.

Impact of VAE on operative performance and postoperative outcome

Patients w/ VAEPatients w/o VAEp Value
Duration of op, mins261.8 ± 125.3237.5 ± 114.00.0513
Amount of intravenous crystalloids, ml2837.3 ± 988.52684.2 ± 1097.50.2136
Amount of intravenous colloids, ml962.0 ± 584.61043 ± 649.00.1752
Hospital LOS, days16.4 ± 11.116.3 ± 9.80.9066
ICU LOS, days3.5 ± 8.52.4 ± 6.00.1823
Postop motor deficit713
Postop CSF fistula629
Postop hematoma07
Transferred to rehabilitation in coma21
Revision op19
Mortality (w/in 24 hrs)00
Thickness of intracranial air on postop CT, cm1.19 ± 0.951.03 ± 0.940.1018

LOS = length of stay.

Values are presented as the number of patients or mean ± SD unless stated otherwise.

There was no significant difference between the groups regarding the occurrence of postoperative pneumocephalus detected on routine postoperative cranial CT, which was measured as the largest thickness of the subdural air collection. When analyzing the postoperative occurrence and severity of facial nerve palsy in patients who underwent surgery for vestibular schwannoma, there was a similar distribution of both frequency and severity according to the House-Brackmann scale between the groups (Table 5).

TABLE 5.

Impact of VAE on frequency and severity of postoperative facial palsy after vestibular schwannoma surgery

House-Brackmann GradePatients w/ VAE (n = 53)Patients w/o VAE (n = 311)p Value
I23169Incidence of facial palsy (I vs II–VI): 0.18; severity of facial palsy (II & III vs IV–VI): 0.8376
II643
III834
IV1145
V415
VI15

House-Brackmann grading was performed within the first 72 hours postoperatively. Grade I, normal; grade II, slight dysfunction; grade III, moderate dysfunction; grade IV, moderately severe dysfunction; grade V, severe dysfunction; and grade VI, total paralysis.

Adult Compared With Pediatric Surgery

Of the 740 patients, 53 were younger than 18 years of age at the time of surgery. There were no significant differences in the incidence of VAE between the adult and pediatric groups (Table 6). The duration of surgery and length of hospital stay did not differ significantly between adults and children who had intraoperative VAE.

TABLE 6.

VAE in adult versus pediatric surgery

Adults (n = 687)Children (n = 53)p Value
Incidence of VAE109 (15.9)10 (18.9)0.57
Duration of op, mins240.8 ± 117.1248.8 ± 105.40.60
Hospital LOS, days16.1 ± 10.018.6 ± 9.7<0.076

Values are presented as the number of patients (%) or mean ± SD unless stated otherwise.

Patients 70 Years or Older Versus Patients Younger Than 70 Years

At the time of surgery, 76 patients were 70 years of age or older. VAE did not occur more often in the older age group. The duration of surgery and length of hospital stay also did not significantly differ (Table 7).

TABLE 7.

VAE in patients older than 70 years versus patients younger than 70 years

Age <70 yrs (n = 664)Age ≥70 yrs (n = 76)p Value
Incidence of VAE103 (15.5)16 (21)0.213
Duration of op, mins238.9 ± 115.5262.9 ± 121.40.105
Hospital LOS, days16.0 ± 9.918.6 ± 10.90.054

Values are presented as the number of patients (%) or mean ± SD unless stated otherwise.

Discussion

Our study shows that the semisitting position is overall safe and that its most dreaded complication, VAE, can be managed in almost all instances by experienced neurosurgical and neuroanesthesiological teams after careful preoperative screening of appropriate patients. Persistent morbidity due to VAE occurred in only 2 of 740 patients over a period of 20 years, and, in at least one instance, it could have been avoidable. While the results of our study are in line with those of a few other recent studies,1,12,29–31 we show that no specific risk factors for the occurrence of VAE could be identified and that VAE does not have an impact on surgical performance.

We suggest that it is time to reconsider and discuss the value of the semisitting position according to the results presented here and those of other contemporary series.1,29–31 The semisitting position not only yields several benefits during surgery but also may be advantageous in terms of operative time and surgical outcome.32 Recently, a prospective multicenter study on patient positioning for vestibular schwannoma surgery showed superior operative results (higher rate of complete removal and better facial nerve function) when patients underwent surgery in the semisitting position compared with the supine position.29 In another study, the semisitting position resulted in reduction of the duration of surgery and was associated with reduced blood loss.31

The incidence of VAE in the semisitting position has been highly variable in different studies, ranging between 5% and 76%.14–16,20 These wide differences may be attributed to different patient selection criteria, but they are also related to the criteria used for the definition of VAE and intraoperative monitoring methods. While VAE in the semisitting position is clinically irrelevant in the majority of cases, serious complications have been described.30

Several classifications have been suggested to define the occurrence and the severity of intraoperative VAE, taking into account both the decrease in ETCO2 and arterial hypotension.13,16,33,34 Almost all newer classifications also consider the detection of intracardial air in the right atrium. One of the scales used more often is the Tübingen VAE Grading Scale, in which a drop in ETCO2, arterial hypotension, and heart rate are used as indicators for VAE severity.16 With this classification, detection of air bubbles by TEE or TTDE is mandatory to establish a diagnosis of intraoperative VAE.

In the present study, all 119 patients with VAE in the semisitting position had air bubbles detected by TTDE or TEE. As reported previously, TEE had a much higher sensitivity than TTDE.20 This explains the significant differences in the detection of VAE in our patients; that is, VAE occurred in 40.5% of patients when TEE was used for monitoring as opposed to 11.7% when TTDE was applied. As outlined, however, there were no statistically significant differences in the occurrence of a drop in ETCO2 and arterial hypotension between the two different monitoring groups, which indicates that, through the higher sensitivity of TEE, more incidences of clinically irrelevant VAEs are detected. On the other hand, the early notion of air bubbles with TEE might also be helpful to immediately counteract and prevent the occurrence of symptomatic VAE.

The incidence of symptomatic VAE has varied considerably in different studies. Feigl et al. noted a decrease in ETCO2 of more than 3 mm Hg in 3.8% and arterial hypotension of more than 20 mm Hg in 1.9% of patients in their series of 200 patients.16 In the series of Pandia et al., however, there was an incidence of 21.6% for an ETCO2 drop of more than 5 mm Hg and an incidence of 14.3% of arterial hypotension with a decrease of 10% or more in systolic blood pressure.35 Remarkably, in our study, a subgroup of patients (18/119) with VAE had a decrease in systolic blood pressure of more than 10 mm Hg without a decrease in ETCO2. The question of which factors make VAE clinically symptomatic has not yet been finally resolved.

Cardiac right-to-left shunts, including PFO, harbor the risk of inducing a direct cerebral injury, even with small amounts of paradoxical air embolism. PFO is the most common cause of a cardiac right-to-left shunt, occurring in 5%–35% of patients.17,36 At our institution, PFO is considered a contraindication for the semisitting position, and the prone position is used for these patients. TEE with contrast has been considered the gold standard with the highest sensitivity.37 Nevertheless, some groups consider patients with PFO for surgery in the semisitting position,16,29,38 and some even recommend postponing surgery until closure of the PFO has been achieved.17

Contrary to our expectations, we did not identify preoperative and intraoperative risk factors for the occurrence of VAE: patient-related factors, including age, sex, BMI, body height, body weight, and history of chronic disease; pathology-related features, including tumor size and histopathological nature of the operated tumor; or surgery-related factors, such as supratentorial versus infratentorial craniotomy or median versus lateral approaches. This is in line with several, but not all, previous studies. Yonekawa, for example, reported a higher incidence of VAE with lateral than with median approaches.39 Another study reported a significant increase of VAE in patients undergoing surgery for meningiomas.40 Astonishingly, there was a marked tendency for a lower occurrence of VAE in patients in higher ASA classes than in those in lower ASA classes. The reason for this remains unclear; however, it might well be that both neuroanesthesiological and neurosurgical teams worked more carefully during each step, with an increased awareness of a possibly higher overall risk of surgery.

We did not encounter any relevant differences in the incidence of VAE when comparing different age groups. In line with other studies, the semisitting position could by performed with ease in pediatric neurosurgery.7,18,35,41,42 The lower age limit for the semisitting position has been quite variable; the youngest patient in our series was a 1-year-old child who underwent surgery for ganglioglioma in the fourth ventricle. There was also no significant increase in VAE in patients 70 years or older compared with those who were younger. Remarkably, however, in both the pediatric and geriatric groups, hospital stay tended to be longer.

While early studies reported on severe persistent side effects due to VAE,2,43 such sequelae have rarely been described in more recent series.15,34 Such persistent morbidity included cardiopulmonary problems, quadriplegia, and other neurological deficits.2,43 Postoperative neurological deficits directly related to VAE were observed in two patients in our study and were persistent in one instance. Presumably the cause for the unexpected cerebral infarctions was the occurrence of paradoxical VAE in both patients. As outlined, in one patient, neither preoperative TTE nor intraoperative TEE had detected a PFO; rather, it was found on postoperative TTE. Of course, the question arises regarding whether the PFO had simply not been noted during the preoperative evaluation or whether it only became evident during surgery in the semisitting position. The cause for the paradoxical VAE in the second patient could not be identified despite extensive workup.

The occurrence of intraoperative VAE in the semisitting position is stressful for both the neurosurgeon and the neuroanesthesiological team. We had hypothesized that the increased pressure on the surgeon having to take care to identify the source of VAE and to prevent further deterioration would have a possible impact on surgical performance. Fortunately, this was not the case, and in the subgroup of patients with vestibular schwannoma, the occurrence of intraoperative VAE did not increase the incidence or the severity of postoperative facial palsy.

It is important to take perioperative measures to prevent the occurrence of VAE by avoiding negative venous pressure. Certainly, perioperative intravenous fluid loading is of utmost importance.13 Furthermore, Türe et al. described a significant reduction in severe VAE when the head was less elevated (30° vs 45°).40 Also, maintaining positive PEEP ventilation throughout surgery has become standard in reducing the risk of VAE.13,44

Early detection of VAE enables the neurosurgical and anesthesiological teams to undertake measures to prevent further air entry in the venous system. Therefore, regarding the higher sensitivity of detecting early VAE with TEE, we suggest that TEE should be the preferred method for intraoperative monitoring instead of TTDE. While findings on TEE and TTDE may not be helpful to determine whether to stop surgery or reposition a patient, they are certainly useful to prevent further intraoperative deterioration. The decision to abort surgery intraoperatively may be extremely challenging, but the surgical team has to consider hemodynamic aspects as well.45 A limitation of this study is the retrospective nature of data collection, which may have led to underestimation of the true frequency of VAE.

Conclusions

The semisitting position is an option with many advantages that should continue to have a place in the standard armamentarium of neurological surgery. Department-specific factors are important in selecting the appropriate nuances of this multifaceted approach. In our series, severe complications related to VAE were very rare. Surgical performance was not affected by the occurrence of VAE. Our results suggest that the semisitting position is safe and that the overall advantages outweigh the associated risks.

Acknowledgments

We thank our operating room staff for their expertise help in the routine use of the semisitting position over the decades, in particular, Christopher Macasero and Peter Weinkauf.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Al-Afif, Elkayekh, Krauss. Acquisition of data: Al-Afif, Elkayekh, Omer. Analysis and interpretation of data: Al-Afif, Elkayekh, Krauss. Drafting the article: Al-Afif, Elkayekh, Krauss. Critically revising the article: Al-Afif, Scheinichen, Palmaers, Nakamura, Hermann, Samii, Krauss. Reviewed submitted version of manuscript: Al-Afif, Krauss. Approved the final version of the manuscript on behalf of all authors: Al-Afif. Statistical analysis: Al-Afif, Elkayekh, Heissler, Krauss. Administrative/technical/material support: Krauss. Study supervision: Al-Afif, Krauss.

References

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    Himes BT, Abcejo AS, Kerezoudis P, Bhargav AG, Trelstad-Andrist K, Maloney PR, et al. Outcomes in single-level posterior cervical spine surgeries performed in the sitting and prone positions. J Neurosurg Spine. 2020;33:667673.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2

    Matjasko J, Petrozza P, Cohen M, Steinberg P. Anesthesia and surgery in the seated position: analysis of 554 cases. Neurosurgery. 1985;17(5):695702.

  • 3

    Lobato EB, Black S, De Soto H. Venous air embolism and selective denervation for torticollis. Anesth Analg. 1997;84(3):551553.

  • 4

    Spektor S, Fraifeld S, Margolin E, Saseedharan S, Eimerl D, Umansky F. Comparison of outcomes following complex posterior fossa surgery performed in the sitting versus lateral position. J Clin Neurosci. 2015;22(4):705712.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5

    Hernesniemi J, Romani R, Albayrak BS, Lehto H, Dashti R, Ramsey C III, et al. Microsurgical management of pineal region lesions: personal experience with 119 patients. Surg Neurol. 2008;70(6):576583.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6

    Ganslandt O, Merkel A, Schmitt H, Tzabazis A, Buchfelder M, Eyupoglu I, Muenster T. The sitting position in neurosurgery: indications, complications and results. A single institution experience of 600 cases. Acta Neurochir (Wien). 2013;155(10):18871893.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7

    Orliaguet GA, Hanafi M, Meyer PG, Blanot S, Jarreau MM, Bresson D, et al. Is the sitting or the prone position best for surgery for posterior fossa tumours in children?. Paediatr Anaesth. 2001;11(5):541547.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8

    Porter JM, Pidgeon C, Cunningham AJ. The sitting position in neurosurgery: a critical appraisal. Br J Anaesth. 1999;82(1):117128.

  • 9

    Elton RJ, Howell RS. The sitting position in neurosurgical anaesthesia: a survey of British practice in 1991. Br J Anaesth. 1994;73(2):247248.

  • 10

    Schaffranietz L, Günther L. The sitting position in neurosurgical operations. Results of a survey. Article in German. Anaesthesist. 1997;46(2):9195.

  • 11

    Schaffranietz L, Grothe A, Olthoff D. Use of the sitting position in neurosurgery. Results of a 1998 survey in Germany. Article in German. Anaesthesist. 2000;49(4):269274.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    Leonard IE, Cunningham AJ. The sitting position in neurosurgery—not yet obsolete! Br J Anaesth. 2002;88(1):13.

  • 13

    Jadik S, Wissing H, Friedrich K, Beck J, Seifert V, Raabe A. A standardized protocol for the prevention of clinically relevant venous air embolism during neurosurgical interventions in the semisitting position. Neurosurgery. 2009;64(3):533539.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Breun M, Nickl R, Perez J, Hagen R, Löhr M, Vince G, et al. Vestibular schwannoma resection in a consecutive series of 502 cases via the retrosigmoid approach: technical aspects, complications, and functional outcome. World Neurosurg. 2019;129:e114e127.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15

    Himes BT, Mallory GW, Abcejo AS, Pasternak J, Atkinson JLD, Meyer FB, et al. Contemporary analysis of the intraoperative and perioperative complications of neurosurgical procedures performed in the sitting position. J Neurosurg. 2017;127(1):182188.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Feigl GC, Decker K, Wurms M, Krischek B, Ritz R, Unertl K, Tatagiba M. Neurosurgical procedures in the semisitting position: evaluation of the risk of paradoxical venous air embolism in patients with a patent foramen ovale. World Neurosurg. 2014;81(1):159164.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Fathi AR, Eshtehardi P, Meier B. Patent foramen ovale and neurosurgery in sitting position: a systematic review. Br J Anaesth. 2009;102(5):588596.

  • 18

    Cucchiara RF, Bowers B. Air embolism in children undergoing suboccipital craniotomy. Anesthesiology. 1982;57(4):338339.

  • 19

    Safdarian M, Safdarian M, Chou R, Hashemi SMR, Rahimi-Movaghar V. A systematic review about the position-related complications of acoustic neuroma surgery via suboccipital retrosigmoid approach: sitting versus lateral. Asian J Neurosurg. 2017;12(3):365373.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20

    Günther F, Frank P, Nakamura M, Hermann EJ, Palmaers T. Venous air embolism in the sitting position in cranial neurosurgery: incidence and severity according to the used monitoring. Acta Neurochir (Wien). 2017;159(2):339346.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21

    House JW, Brackmann DE. Facial nerve grading system. Otolaryngol Head Neck Surg. 1985;93(2):146147.

  • 22

    Hatipoglu Majernik G, Al-Afif S, Heissler HE, Cassini Ascencao L, Krauss JK. Microvascular decompression: is routine postoperative CT imaging necessary?. Acta Neurochir (Wien). 2020;162(5):10951099.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23

    Matthies C, Samii M. Management of vestibular schwannomas (acoustic neuromas): the value of neurophysiology for intraoperative monitoring of auditory function in 200 cases. Neurosurgery. 1997;40(3):459468.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 24

    Matthies C, Samii M. Direct brainstem recording of auditory evoked potentials during vestibular schwannoma resection: nuclear BAEP recording. Technical note and preliminary results. J Neurosurg. 1997;86(6):10571062.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25

    Samii M, Matthies C. Management of 1000 vestibular schwannomas (acoustic neuromas): surgical management and results with an emphasis on complications and how to avoid them. Neurosurgery. 1997;40(1):1123.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 26

    Hermann EJ, Rittierodt M, Krauss JK. Combined transventricular and supracerebellar infratentorial approach preserving the vermis in giant pediatric posterior fossa midline tumors. Neurosurgery. 2008;63(1)(suppl 1):ONS30ONS37.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 27

    Hong B, Biertz F, Raab P, et al. Normobaric hyperoxia for treatment of pneumocephalus after posterior fossa surgery in the semisitting position: a prospective randomized controlled trial. PLoS One. 2015;10(5):e0125710.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 28

    Hermann EJ, Petrakakis I, Polemikos M, Raab P, Cinibulak Z, Nakamura M, et al. Electromagnetic navigation-guided surgery in the semi-sitting position for posterior fossa tumours: a safety and feasibility study. Acta Neurochir (Wien). 2015;157(7):12291237.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 29

    Scheller C, Rampp S, Tatagiba M, Gharabaghi A, Ramina KF, Ganslandt O, et al. A critical comparison between the semisitting and the supine positioning in vestibular schwannoma surgery: subgroup analysis of a randomized, multicenter trial. J Neurosurg. 2020;133(1):249256.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 30

    Saladino A, Lamperti M, Mangraviti A, Legnani FG, Prada FU, Casali C, et al. The semisitting position: analysis of the risks and surgical outcomes in a contemporary series of 425 adult patients undergoing cranial surgery. J Neurosurg. 2017;127(4):867876.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 31

    Schackert G, Ralle S, Martin KD, Reiss G, Kowalski M, Sobottka SB, et al. vestibular schwannoma surgery: outcome and complications in lateral decubitus position versus semi-sitting position-a personal learning curve in a series of 544 cases over 3 decades. World Neurosurg. 2021;148:e182e191.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 32

    Roessler K, Krawagna M, Bischoff B, Rampp S, Ganslandt O, Iro H, et al. Improved postoperative facial nerve and hearing function in retrosigmoid vestibular schwannoma surgery significantly associated with semisitting position. World Neurosurg. 2016;87:290297.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 33

    Ammirati M, Lamki TT, Shaw AB, Forde B, Nakano I, Mani M. A streamlined protocol for the use of the semi-sitting position in neurosurgery: a report on 48 consecutive procedures. J Clin Neurosci. 2013;20(1):3234.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 34

    Luostarinen T, Lindroos AC, Niiya T, Silvasti-Lundell M, Schramko A, Hernesniemi J, et al. prone versus sitting position in neurosurgery-differences in patients’ hemodynamic management. World Neurosurg. 2017;97:261266.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 35

    Pandia MP, Bithal PK, Dash HH, Chaturvedi A. Comparative incidence of cardiovascular changes during venous air embolism as detected by transesophageal echocardiography alone or in combination with end tidal carbon dioxide tension monitoring. J Clin Neurosci. 2011;18(9):12061209.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 36

    Papadopoulos G, Kuhly P, Brock M, Rudolph KH, Link J, Eyrich K. Venous and paradoxical air embolism in the sitting position. A prospective study with transoesophageal echocardiography. Acta Neurochir (Wien). 1994;126(2-4):140143.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 37

    Pearson AC, Labovitz AJ, Tatineni S, Gomez CR. Superiority of transesophageal echocardiography in detecting cardiac source of embolism in patients with cerebral ischemia of uncertain etiology. J Am Coll Cardiol. 1991;17(1):6672.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 38

    Klein J, Juratli TA, Weise M, Schackert G. A systematic review of the semi-sitting position in neurosurgical patients with patent foramen ovale: how frequent is paradoxical embolism? World Neurosurg. 2018;115:196200.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 39

    Yonekawa Y. Operative neurosurgery: personal view and historical backgrounds (8) suboccipital craniotomy-sitting position-linear incision. Article in Japanese. No Shinkei Geka. 2011;39(8):789809.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 40

    Türe H, Harput MV, Bekiroğlu N, Keskin Ö, Köner Ö, Türe U. Effect of the degree of head elevation on the incidence and severity of venous air embolism in cranial neurosurgical procedures with patients in the semisitting position. J Neurosurg. 2018;128(5):15601569.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 41

    Bithal PK, Pandia MP, Dash HH, Chouhan RS, Mohanty B, Padhy N. Comparative incidence of venous air embolism and associated hypotension in adults and children operated for neurosurgery in the sitting position. Eur J Anaesthesiol. 2004;21(7):517522.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 42

    Baro V, Lavezzo R, Marton E, Longatti P, Landi A, Denaro L, d’Avella D. Prone versus sitting position in pediatric low-grade posterior fossa tumors. Childs Nerv Syst. 2019;35(3):421428.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 43

    Hitselberger WE, House WF. A warning regarding the sitting position for acoustic tumor surgery. Arch Otolaryngol. 1980;106(2):69.

  • 44

    Voorhies RM, Fraser RAR, Van Poznak A. Prevention of air embolism with positive end expiratory pressure. Neurosurgery. 1983;12(5):503506.

  • 45

    Abcejo AS, Pasternak JJ, Perkins WJ. Urgent repositioning after venous air embolism during intracranial surgery in the seated position: a case series. J Neurosurg Anesthesiol. 2019;31(4):413421.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • Collapse
  • Expand

Illustration from Morshed et al. (pp 1–8). Copyright Ken Probst. Published with permission.

  • 1

    Himes BT, Abcejo AS, Kerezoudis P, Bhargav AG, Trelstad-Andrist K, Maloney PR, et al. Outcomes in single-level posterior cervical spine surgeries performed in the sitting and prone positions. J Neurosurg Spine. 2020;33:667673.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2

    Matjasko J, Petrozza P, Cohen M, Steinberg P. Anesthesia and surgery in the seated position: analysis of 554 cases. Neurosurgery. 1985;17(5):695702.

  • 3

    Lobato EB, Black S, De Soto H. Venous air embolism and selective denervation for torticollis. Anesth Analg. 1997;84(3):551553.

  • 4

    Spektor S, Fraifeld S, Margolin E, Saseedharan S, Eimerl D, Umansky F. Comparison of outcomes following complex posterior fossa surgery performed in the sitting versus lateral position. J Clin Neurosci. 2015;22(4):705712.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5

    Hernesniemi J, Romani R, Albayrak BS, Lehto H, Dashti R, Ramsey C III, et al. Microsurgical management of pineal region lesions: personal experience with 119 patients. Surg Neurol. 2008;70(6):576583.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6

    Ganslandt O, Merkel A, Schmitt H, Tzabazis A, Buchfelder M, Eyupoglu I, Muenster T. The sitting position in neurosurgery: indications, complications and results. A single institution experience of 600 cases. Acta Neurochir (Wien). 2013;155(10):18871893.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7

    Orliaguet GA, Hanafi M, Meyer PG, Blanot S, Jarreau MM, Bresson D, et al. Is the sitting or the prone position best for surgery for posterior fossa tumours in children?. Paediatr Anaesth. 2001;11(5):541547.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8

    Porter JM, Pidgeon C, Cunningham AJ. The sitting position in neurosurgery: a critical appraisal. Br J Anaesth. 1999;82(1):117128.

  • 9

    Elton RJ, Howell RS. The sitting position in neurosurgical anaesthesia: a survey of British practice in 1991. Br J Anaesth. 1994;73(2):247248.

  • 10

    Schaffranietz L, Günther L. The sitting position in neurosurgical operations. Results of a survey. Article in German. Anaesthesist. 1997;46(2):9195.

  • 11

    Schaffranietz L, Grothe A, Olthoff D. Use of the sitting position in neurosurgery. Results of a 1998 survey in Germany. Article in German. Anaesthesist. 2000;49(4):269274.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    Leonard IE, Cunningham AJ. The sitting position in neurosurgery—not yet obsolete! Br J Anaesth. 2002;88(1):13.

  • 13

    Jadik S, Wissing H, Friedrich K, Beck J, Seifert V, Raabe A. A standardized protocol for the prevention of clinically relevant venous air embolism during neurosurgical interventions in the semisitting position. Neurosurgery. 2009;64(3):533539.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Breun M, Nickl R, Perez J, Hagen R, Löhr M, Vince G, et al. Vestibular schwannoma resection in a consecutive series of 502 cases via the retrosigmoid approach: technical aspects, complications, and functional outcome. World Neurosurg. 2019;129:e114e127.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15

    Himes BT, Mallory GW, Abcejo AS, Pasternak J, Atkinson JLD, Meyer FB, et al. Contemporary analysis of the intraoperative and perioperative complications of neurosurgical procedures performed in the sitting position. J Neurosurg. 2017;127(1):182188.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Feigl GC, Decker K, Wurms M, Krischek B, Ritz R, Unertl K, Tatagiba M. Neurosurgical procedures in the semisitting position: evaluation of the risk of paradoxical venous air embolism in patients with a patent foramen ovale. World Neurosurg. 2014;81(1):159164.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Fathi AR, Eshtehardi P, Meier B. Patent foramen ovale and neurosurgery in sitting position: a systematic review. Br J Anaesth. 2009;102(5):588596.

  • 18

    Cucchiara RF, Bowers B. Air embolism in children undergoing suboccipital craniotomy. Anesthesiology. 1982;57(4):338339.

  • 19

    Safdarian M, Safdarian M, Chou R, Hashemi SMR, Rahimi-Movaghar V. A systematic review about the position-related complications of acoustic neuroma surgery via suboccipital retrosigmoid approach: sitting versus lateral. Asian J Neurosurg. 2017;12(3):365373.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20

    Günther F, Frank P, Nakamura M, Hermann EJ, Palmaers T. Venous air embolism in the sitting position in cranial neurosurgery: incidence and severity according to the used monitoring. Acta Neurochir (Wien). 2017;159(2):339346.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21

    House JW, Brackmann DE. Facial nerve grading system. Otolaryngol Head Neck Surg. 1985;93(2):146147.

  • 22

    Hatipoglu Majernik G, Al-Afif S, Heissler HE, Cassini Ascencao L, Krauss JK. Microvascular decompression: is routine postoperative CT imaging necessary?. Acta Neurochir (Wien). 2020;162(5):10951099.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23

    Matthies C, Samii M. Management of vestibular schwannomas (acoustic neuromas): the value of neurophysiology for intraoperative monitoring of auditory function in 200 cases. Neurosurgery. 1997;40(3):459468.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 24

    Matthies C, Samii M. Direct brainstem recording of auditory evoked potentials during vestibular schwannoma resection: nuclear BAEP recording. Technical note and preliminary results. J Neurosurg. 1997;86(6):10571062.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25

    Samii M, Matthies C. Management of 1000 vestibular schwannomas (acoustic neuromas): surgical management and results with an emphasis on complications and how to avoid them. Neurosurgery. 1997;40(1):1123.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 26

    Hermann EJ, Rittierodt M, Krauss JK. Combined transventricular and supracerebellar infratentorial approach preserving the vermis in giant pediatric posterior fossa midline tumors. Neurosurgery. 2008;63(1)(suppl 1):ONS30ONS37.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 27

    Hong B, Biertz F, Raab P, et al. Normobaric hyperoxia for treatment of pneumocephalus after posterior fossa surgery in the semisitting position: a prospective randomized controlled trial. PLoS One. 2015;10(5):e0125710.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 28

    Hermann EJ, Petrakakis I, Polemikos M, Raab P, Cinibulak Z, Nakamura M, et al. Electromagnetic navigation-guided surgery in the semi-sitting position for posterior fossa tumours: a safety and feasibility study. Acta Neurochir (Wien). 2015;157(7):12291237.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 29

    Scheller C, Rampp S, Tatagiba M, Gharabaghi A, Ramina KF, Ganslandt O, et al. A critical comparison between the semisitting and the supine positioning in vestibular schwannoma surgery: subgroup analysis of a randomized, multicenter trial. J Neurosurg. 2020;133(1):249256.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 30

    Saladino A, Lamperti M, Mangraviti A, Legnani FG, Prada FU, Casali C, et al. The semisitting position: analysis of the risks and surgical outcomes in a contemporary series of 425 adult patients undergoing cranial surgery. J Neurosurg. 2017;127(4):867876.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 31

    Schackert G, Ralle S, Martin KD, Reiss G, Kowalski M, Sobottka SB, et al. vestibular schwannoma surgery: outcome and complications in lateral decubitus position versus semi-sitting position-a personal learning curve in a series of 544 cases over 3 decades. World Neurosurg. 2021;148:e182e191.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 32

    Roessler K, Krawagna M, Bischoff B, Rampp S, Ganslandt O, Iro H, et al. Improved postoperative facial nerve and hearing function in retrosigmoid vestibular schwannoma surgery significantly associated with semisitting position. World Neurosurg. 2016;87:290297.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 33

    Ammirati M, Lamki TT, Shaw AB, Forde B, Nakano I, Mani M. A streamlined protocol for the use of the semi-sitting position in neurosurgery: a report on 48 consecutive procedures. J Clin Neurosci. 2013;20(1):3234.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 34

    Luostarinen T, Lindroos AC, Niiya T, Silvasti-Lundell M, Schramko A, Hernesniemi J, et al. prone versus sitting position in neurosurgery-differences in patients’ hemodynamic management. World Neurosurg. 2017;97:261266.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 35

    Pandia MP, Bithal PK, Dash HH, Chaturvedi A. Comparative incidence of cardiovascular changes during venous air embolism as detected by transesophageal echocardiography alone or in combination with end tidal carbon dioxide tension monitoring. J Clin Neurosci. 2011;18(9):12061209.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 36

    Papadopoulos G, Kuhly P, Brock M, Rudolph KH, Link J, Eyrich K. Venous and paradoxical air embolism in the sitting position. A prospective study with transoesophageal echocardiography. Acta Neurochir (Wien). 1994;126(2-4):140143.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 37

    Pearson AC, Labovitz AJ, Tatineni S, Gomez CR. Superiority of transesophageal echocardiography in detecting cardiac source of embolism in patients with cerebral ischemia of uncertain etiology. J Am Coll Cardiol. 1991;17(1):6672.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 38

    Klein J, Juratli TA, Weise M, Schackert G. A systematic review of the semi-sitting position in neurosurgical patients with patent foramen ovale: how frequent is paradoxical embolism? World Neurosurg. 2018;115:196200.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 39

    Yonekawa Y. Operative neurosurgery: personal view and historical backgrounds (8) suboccipital craniotomy-sitting position-linear incision. Article in Japanese. No Shinkei Geka. 2011;39(8):789809.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 40

    Türe H, Harput MV, Bekiroğlu N, Keskin Ö, Köner Ö, Türe U. Effect of the degree of head elevation on the incidence and severity of venous air embolism in cranial neurosurgical procedures with patients in the semisitting position. J Neurosurg. 2018;128(5):15601569.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 41

    Bithal PK, Pandia MP, Dash HH, Chouhan RS, Mohanty B, Padhy N. Comparative incidence of venous air embolism and associated hypotension in adults and children operated for neurosurgery in the sitting position. Eur J Anaesthesiol. 2004;21(7):517522.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 42

    Baro V, Lavezzo R, Marton E, Longatti P, Landi A, Denaro L, d’Avella D. Prone versus sitting position in pediatric low-grade posterior fossa tumors. Childs Nerv Syst. 2019;35(3):421428.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 43

    Hitselberger WE, House WF. A warning regarding the sitting position for acoustic tumor surgery. Arch Otolaryngol. 1980;106(2):69.

  • 44

    Voorhies RM, Fraser RAR, Van Poznak A. Prevention of air embolism with positive end expiratory pressure. Neurosurgery. 1983;12(5):503506.

  • 45

    Abcejo AS, Pasternak JJ, Perkins WJ. Urgent repositioning after venous air embolism during intracranial surgery in the seated position: a case series. J Neurosurg Anesthesiol. 2019;31(4):413421.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation

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