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Maria A. Poca, Juan Sahuquillo, Anna Vilalta and Angel Garnacho

Object

Ischemic lesions are highly prevalent in patients with traumatic brain injuries (TBIs) and are the single most important cause of secondary brain damage. The prevention and early treatment of these lesions is the primary aim in the modern treatment of these patients. One of the most widely used monitoring techniques at the bedside is quantification of brain extracellular level of lactate by using arteriojugular venous differences of lactate (AVDL). The purpose of this study was to determine the sensitivity, specificity, and predictive value of AVDL as an indicator of increases in brain lactate production in patients with TBIs.

Methods

Arteriojugular venous differences of lactate were calculated every 6 hours using samples obtained though a catheter placed in the jugular bulb in 45 patients with diffuse head injuries (57.8%) or evacuated brain lesions (42.2%). Cerebral lactate concentration obtained with a 20-kD microdialysis catheter implanted in undamaged tissue was used as the de facto gold standard.

Six hundred seventy-three AVDL determinations and cerebral microdialysis samples were obtained simultaneously; 543 microdialysis samples (81%) showed lactate values greater than 2 mmol/L, but only 21 AVDL determinations (3.1%) showed an increase in brain lactate. No correlation was found between AVDL and cerebral lactate concentration (ρ = 0.014, p = 0.719). Arteriojugular venous differences of lactate had a sensitivity and specificity of 3.3 and 97.7%, respectively, with a false-negative rate of 96.7% and a false-positive rate of 2.3%.

Conclusions

Arteriojugular venous differences of lactate do not reliably reflect increased cerebral lactate production and consequently are not reliable in ruling out brain ischemia in patients with TBIs. The clinical use of this monitoring method in neurocritical care should be reconsidered.

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Juan Sahuquillo, Maria-Antonia Poca, Mercedes Arribas, Angel Garnacho and Enrique Rubio

Object. It is generally accepted that the intracranial compartment behaves as a unicameral space in which intracranial pressure (ICP) is uniformly distributed. However, this concept has been challenged many times. Although there is general agreement on the existence of craniospinal and suprainfratentorial gradients, the existence of interhemispheric gradients is still a matter of debate. The object of this study was to reexamine the issue of interhemispheric supratentorial ICP gradients in patients with head injuries and the clinical significance of these gradients in their management.

Methods. The authors present the results of a prospective study conducted in 50 head-injured patients to determine the clinical significance of supratentorial ICP gradients. In each case a concurrent bilateral frontal intraparenchymatous device was implanted within the 6-hour window after computerized tomography (CT) scanning. According to CT criteria, each patient was categorized into one of three different groups: 1) diffuse lesions, in which no unilaterally measured volumes greater than 25 ml were present and the midline shift was 3 mm or less; 2) Focal A, in which added hemispheric volumes were greater than 25 ml and midline shift was 3 mm or less; and 3) Focal B, in which all patients with a midline shift greater than 3 mm were included. From the results of the entire group the authors were able to distinguish four different patterns of supratentorial ICP. In Pattern I, the intracranial compartment behaved as a true unicameral space with similar mean ICPs and pulse amplitudes in both hemispheres; in Pattern II, different mean ICPs and amplitudes were observed although ICP increases or decreases were congruent; and in Pattern III, patients with different mean ICPs, different ICP amplitudes, and no congruent increases or decreases of ICP were included. All (15 cases) but one patient with a diffuse lesion presented with ICP Pattern I. Fifteen patients with focal lesions showed a Type II pattern, whereas only one patient presented with a Type III pattern. In 10 patients, of whom all but one presented with a focal lesion, transient gradients that disappeared in less than 4 hours were also observed.

Conclusions. In many patients with focal lesions, clinically important interhemispheric ICP gradients exist. In this subset, transient gradients that disappear with time are frequently observed and may indicate an increase in the size of the lesion. The clinical relevance of such gradients is discussed and guidelines for adequately monitoring ICP are suggested to optimize head injury management and to avoid suboptimal or even harmful care in patients with mass lesions.