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John Douglas Pickard, David Spiegelhalter, and Marek Czosnyka

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Lawrence F. Marshall, Andrew I. R. Maas, Sharon Bowers Marshall, Albino Bricolo, Michael Fearnside, Fausto Iannotti, Melville R. Klauber, Jacques Lagarrigue, Ramiro Lobato, Lennart Persson, John D. Pickard, Jürgen Piek, Franco Servadei, Georgios N. Wellis, Gabrielle F. Morris, Eugene D. Means, and Bruno Musch

Object. The authors prospectively studied the efficacy of tirilazad mesylate, a novel aminosteroid, in humans with head injuries.

Methods. A cohort of 1120 head-injured patients received at least one dose of study medication (tirilazad or placebo). Eighty-five percent (957) of the patients had suffered a severe head injury (Glasgow Coma Scale [GCS] score 4–8) and 15% (163) had sustained a moderate head injury (GCS score 9–12). Six-month outcomes for the tirilazad- and placebo-treated groups for the Glasgow Outcome Scale categories of both good recovery and death showed no significant difference (good recovery in the tirilazad-treated group was 39% compared with the placebo group in which it was 42% [p = 0.461]; death in the tirilazad-treated group occurred in 26% of patients compared with the placebo group, in which it occurred in 25% [p = 0.750]). Subgroup analysis suggested that tirilazad mesylate may be effective in reducing mortality rates in males suffering from severe head injury with accompanying traumatic subarachnoid hemorrhage (death in the tirilazad-treated group occurred in 34% of patients; in the placebo group it occurred in 43% [p = 0.026]). No significant differences in frequency or types of serious adverse events were shown between the treatment and placebo groups.

Conclusions. Striking problems with imbalance concerning basic prognostic variables were observed in spite of the large population studied. These imbalances concerned pretreatment hypotension, pretreatment hypoxia, and the incidence of epidural hematomas. In future trials of pharmacological therapy for severe head injury, serious consideration must be given to alternative randomization strategies. Given the heterogeneous nature of head injury and the identification of populations that do relatively well with standard therapy, target populations with a higher risk for mortality and morbidity may be more suitable for clinical trials of such agents.

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Marek Czosnyka, Piotr Smielewski, Stefan Piechnik, Eric A. Schmidt, Pippa G. Al-Rawi, Peter J. Kirkpatrick, and John D. Pickard

Object. Plateau waves of intracranial pressure (ICP) are often recorded during intensive care monitoring of severely head injured patients. They are traditionally interpreted as meaningful secondary brain insults because of the dramatic decrease in cerebral perfusion pressure (CPP). The aim of this study was to investigate both the hemodynamic profile and the clinical consequences of plateau waves.

Methods. One hundred sixty head-injured patients were studied using continuous monitoring of ICP; almost 20% of these patients exhibited plateau waves. In 96 patients arterial pressure, ICP, and transcranial Doppler (TCD) blood flow velocity were studied daily for 20 minutes to 3 hours. Sixteen episodes of plateau waves in eight patients were recorded and analyzed.

The dramatic increase in ICP was followed by a profound fall in CPP (by 45%). In contrast, flow velocity fell by only 20%. Autoregulation was documented to be intact both before and after plateau but was disturbed during the wave (p < 0.05). Pressure-volume compensatory reserve was always depleted before the wave. Cerebrovascular resistance decreased during the wave by 60% (p <0.05) and TCD pulsatility increased (p <0.05). Plateau waves did not increase the probability of an unfavorable outcome following injury.

Conclusions. The authors have confirmed that the plateau waves are a hemodynamic phenomenon associated with cerebrovascular vasodilation. They are observed in patients with preserved cerebral autoregulation but reduced pressure-volume compensatory reserve.

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Magdalena Hiler, Marek Czosnyka, Peter Hutchinson, Marcella Balestreri, Peter Smielewski, Basil Matta, and John D. Pickard

Object

The authors explored the relationship between computerized tomography (CT) scan findings and intracranial pressure (ICP) measurements obtained in the first 24 hours of monitoring to identify parameters predicting outcome in patients with severe traumatic brain injury (TBI).

Methods

Intracranial pressure, mean arterial blood pressure, cerebral perfusion pressure (CPP), and pressure reactivity index were measured continuously in 126 patients with severe TBI who were admitted to a neuroscience critical care unit. Mean values in the initial 24 hours of monitoring and in the total period of monitoring were compared with types of injury categorized on the basis of the initial CT scan according to the classification of Marshall, et al., and with Glasgow Outcome Scale scores.

The initial CT scan classification correlated significantly but weakly with ICP measured during the first 24 hours of monitoring (p = 0.036) but not with mean ICP over the total time of intensive care. Both midline shift and the ratio of frontal horn diameter to internal diameter correlated with ICP in the first 24 hours (p < 0.007) and with ICP over the total monitoring period (p < 0.03). Outcome score correlated with initial CT scan findings (p = 0.018), ICP over the total monitoring period (p < 0.0023), pressure reactivity over the total monitoring period (p < 0.0002), and pressure reactivity in the first 24 hours (p < 0.0001) but not with ICP in the first 24 hours. Patients with disturbed pressure reactivity in the first 24 hours after injury had a significantly higher mortality rate than patients with intact pressure reactivity (28.6% compared with 9.5%; p < 0.001).

Conclusions

Patients with severe TBI who have early loss of autoregulation have a worse prognosis. Mean ICP values in patients with diffuse TBI cannot be predicted by using the Marshall CT scan classification.

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Stephen J. Whitaker, Colin I. Meanock, Gillian F. Turner, Patricia J. Smythe, John D. Pickard, Alan R. Noble, and Valerie Walker

✓ Hyponatremia developing some days after transsphenoidal pituitary adenectomy is a treacherous complication of uncertain cause. Of 19 patients monitored in a pilot study at the Wessex Neurological Centre, plasma sodium fell below 125 mmol/liter in three patients at times ranging from 6 to 9 days postoperatively. One patient had evidence of inappropriate secretion of arginine vasopressin (AVP), and the other two probably had steroid insufficiency despite apparently adequate steroid cover. In a more detailed study, the fluid and sodium balance of a further 16 patients was monitored for 7 to 11 days following transsphenoidal surgery together with plasma cortisol, renin, and AVP concentrations. No patient became severely hyponatremic. Three developed partial diabetes insipidus. Two patients with Cushing's disease had evidence of postoperative corticosteroid insufficiency despite normal steroid protection. An inappropriately low plasma cortisol concentration was recorded in both. Plasma AVP concentrations did not show a delayed surge postoperatively. Delayed hyponatremia appears to occur most often in patients with hypoadrenalism, as glucocorticoid cover is decreased. It results from water retention combined with natriuresis, and is reversed by glucocorticoid treatment.

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Peter J. Hutchinson, Mark T. O'Connell, Pippa G. Al-Rawi, Lynn B. Maskell, Rupert Kett-White, Arun K. Gupta, Hugh K. Richards, David B. Hutchinson, Peter J. Kirkpatrick, and John D. Pickard

Object. Clinical microdialysis enables monitoring of the cerebral extracellular chemistry of neurosurgical patients. Introduction of the technique into different hospitals' neurosurgical units has resulted in variations in the method of application. There are several variables to be considered, including length of the catheter membrane, type of perfusion fluid, flow rate of perfusion fluid, and on-line compared with delayed analysis of samples. The objects of this study were as follows: 1) to determine the effects of varying catheter characteristics on substance concentration; 2) to determine the relative recovery and true extracellular concentration by varying the flow rate and extrapolating to zero flow; and 3) to compare substance concentration obtained using a bedside enzyme analyzer with that of off-line high-performance liquid chromatography (HPLC).

Methods. A specially designed bolt was used to conduct two adjacent microdialysis catheters into the frontal cortex of patients with head injury or poor-grade subarachnoid hemorrhage who were receiving ventilation. One reference catheter (10-mm membrane, perfused with Ringer's solution at 0.3 µl/minute) was constant for all studies. The other catheter was varied in terms of membrane length (10 mm or 30 mm), perfusion fluid (Ringer's solution or normal saline), and flow rate (0.1–1.5 µl/minute). The effect of freezing the samples on substance concentration was established by on-line analysis and then repeated analysis after storage at −70°C for 3 months. Samples assayed with the bedside enzyme analyzer were reassessed using HPLC for the determination of glutamate concentrations.

Conclusions. Two adjacent microdialysis catheters that were identical in membrane length, perfusion fluid, and flow rate showed equivalent results. Variations in perfusion fluid and freezing and thawing of samples did not result in differences in substance concentration. Catheter length had a significant impact on substance recovery. Variations in flow rate enabled the relative recovery to be calculated using a modification of the extrapolation-to-zero-flow method. The recovery was approximately 70% at 0.3 µl/minute and 30% at 1 µl/minute (10-mm membrane) for all analytes. Glutamate results obtained with the enzyme analyzer showed good correlation with those from HPLC.

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Christian Zweifel, Andrea Lavinio, Luzius A. Steiner, Danila Radolovich, Peter Smielewski, Ivan Timofeev, Magdalena Hiler, Marcella Balestreri, Peter J. Kirkpatrick, John D. Pickard, Peter Hutchinson, and Marek Czosnyka

Object

Cerebrovascular pressure reactivity is the ability of cerebral vessels to respond to changes in transmural pressure. A cerebrovascular pressure reactivity index (PRx) can be determined as the moving correlation coefficient between mean intracranial pressure (ICP) and mean arterial blood pressure.

Methods

The authors analyzed a database consisting of 398 patients with head injuries who underwent continuous monitoring of cerebrovascular pressure reactivity. In 298 patients, the PRx was compared with a transcranial Doppler ultrasonography assessment of cerebrovascular autoregulation (the mean index [Mx]), in 17 patients with the PET–assessed static rate of autoregulation, and in 22 patients with the cerebral metabolic rate for O2. Patient outcome was assessed 6 months after injury.

Results

There was a positive and significant association between the PRx and Mx (R2 = 0.36, p < 0.001) and with the static rate of autoregulation (R2 = 0.31, p = 0.02). A PRx > 0.35 was associated with a high mortality rate (> 50%). The PRx showed significant deterioration in refractory intracranial hypertension, was correlated with outcome, and was able to differentiate patients with good outcome, moderate disability, severe disability, and death. The graph of PRx compared with cerebral perfusion pressure (CPP) indicated a U–shaped curve, suggesting that too low and too high CPP was associated with a disturbance in pressure reactivity. Such an optimal CPP was confirmed in individual cases and a greater difference between current and optimal CPP was associated with worse outcome (for patients who, on average, were treated below optimal CPP [R2 = 0.53, p < 0.001] and for patients whose mean CPP was above optimal CPP [R2 = −0.40, p < 0.05]). Following decompressive craniectomy, pressure reactivity initially worsened (median −0.03 [interquartile range −0.13 to 0.06] to 0.14 [interquartile range 0.12–0.22]; p < 0.01) and improved in the later postoperative course. After therapeutic hypothermia, in 17 (70.8%) of 24 patients in whom rewarming exceeded the brain temperature threshold of 37°C, ICP remained stable, but the average PRx increased to 0.32 (p < 0.0001), indicating significant derangement in cerebrovascular reactivity.

Conclusions

The PRx is a secondary index derived from changes in ICP and arterial blood pressure and can be used as a surrogate marker of cerebrovascular impairment. In view of an autoregulation–guided CPP therapy, a continuous determination of a PRx is feasible, but its value has to be evaluated in a prospective controlled trial.