Lack of utility of arteriojugular venous differences of lactate as a reliable indicator of increased brain anaerobic metabolism in traumatic brain injury.

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 modem 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 (p = 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.

Influence of extraneurological insults on ventricular enlargement and neuropsychological functioning after moderate and severe traumatic brain injury.

Extraneurological insults secondary to TBI such as hypotension or hypoxia have been associated with mortality and morbidity. The purpose of this study was to investigate the influence of systemic complications on both neuropsychological outcome and cerebral atrophy. Fifty-seven patients selected from 122 consecutive admissions were studied. Data on the type and severity of injury as well as other systemic insults were collected prior to and during the first 3 days of hospitalization. These data included the presence or absence of a hypoxic episode during the pre-hospital period, the presence and degree of hypoxia, hypercapnia, anemia, hypotension and intracranial hypertension, pupillary reactivity, Glasgow Coma Scale score and coma duration. From the last control CT scan image, performed 6 months post-injury, four different indexes of ventricular dilatation were calculated. Neuropsychological assessment at 6 months included tests of verbal and visual memory, visuoconstructive functions, fine motor speed, and frontal lobe functions. Our results showed that hypoxia and hypotension were related to neuropsychological outcome and long-term ventricular enlargement. Hypoxic episodes prior to hospitalization were related to third ventricle dilatation and to adverse neurological and cognitive outcomes, especially to attention, motor speed, mental flexibility, fluency and verbal memory impairments, suggesting fronto-striatal and hippocampal dysfunction. We conclude that the effect of extraneurological insults on brain structure and function may be as important as the severity of the primary injury.

Morphological features in human cortical brain microvessels after head injury: a three-dimensional and immunocytochemical study.

We studied the morphology of cortical microvessels in the brains of 10 patients who had died after receiving a traumatic head injury (THI). Scanning electron microscopy (SEM) of vascular corrosion casts, confocal microscopy of histological sections after immunocytochemistry, and detection of apoptosis by terminal dUTP nick end labeling (TUNEL) were used. Microvascular casts showed an angioarchitectonic distribution that was defined as normal according to results obtained in a previous, nontraumatic series of subjects. However, when we compared them with previous works, the cast surface of some of the microvessels showed three types of morphological alterations: longitudinal folds, sunken surfaces with craters, and a significant flattening with reduction of lumen. The vessels that were primarily affected were the arterioles and capillaries of the middle and deep cortical vascular zones. Immunostaining with the monoclonal antibody MAS-336 against endothelial cells also showed the presence of longitudinal folds with a thinning of the vascular lumen, cytoplasmic round bodies, and a thickening of the endothelial cell membrane. The TUNEL technique revealed a positive staining of some endothelial cells. The structural alterations we observed indicate that microvessels undergo endothelial cell damage after THI. We suggest that this kind of lesion and the secondary functional injury to the blood-brain barrier (BBB) could play an important role in the development of the secondary lesions that these patients show in the subacute phase.

Normobaric hyperoxia in traumatic brain injury: does brain metabolic state influence the response to hyperoxic challenge?

This study sought to investigate whether normobaric hyperoxia (NH) improves brain oxygenation and brain metabolism in the early phase of severe and moderate traumatic brain injury (TBI) and whether this effect occurs uniformly in all TBI patients. Thirty patients (9 women and 21 men) with a median initial Glasgow Coma Score (GCS) of 6 (range, 3-12) were monitored using a brain microdialysis (MD) catheter with a brain tissue oxygen sensor (PtiO(2)) placed in the least-injured hemisphere. The inspired oxygen fraction was increased to 100% for 2 h. Patients were divided into two groups: Group 1: patients with baseline brain lactate ≤3 mmol/L and Group 2: patients with baseline brain lactate >3 mmol/L, and therefore increased anaerobic metabolism in the brain. In Group 1, no significant changes in brain metabolic parameters were found after hyperoxic challenge, whereas a significant increase in glucose and a decrease in the lactate-pyruvate ratio (LPR) were found in Group 2. In this latter group of patients, brain glucose increased on average by 17.9% (95% CI, +9.2% to +26.6%, p<0.001) and LPR decreased by 11.6% (95% CI, -16.2% to -6.9%, p<0.001). The results of our study show that moderate and severe TBI may induce metabolic alterations in the brain, even in macroscopically normal brain tissue. We observed that NH increased PaO(2) and PtiO(2) and significantly decreased LPR in patients in whom baseline brain lactate levels were increased, suggesting that NH improved the brain redox state. In patients with normal baseline brain lactate levels, we did not find any significant changes in the metabolic variables after NH. This suggests that the baseline metabolic state should be taken into account when applying NH to patients with TBI. This maneuver may only be effective in a specific group of patients.

Intravascular cooling for rapid induction of moderate hypothermia in severely head-injured patients: results of a multicenter study (IntraCool).

OBJECTIVES: To evaluate the feasibility, safety and effectiveness of a new method of intravascular temperature management for inducing moderate hypothermia (MHT). DESIGN AND SETTINGS: Prospective, international-multicenter clinical trial conducted in four university hospitals. PATIENTS: In a 2-year period 24 patients with severe head injury and refractory high ICP were treated with MHT (32.5 degrees C) by intravascular methods. RESULTS: Seventeen were males and seven females, with a median age of 25 years (range 15-60). The median Glasgow Coma Scale upon admission was 7 (range 3-13) and the median Injury Severity Score was 22 (range 13-43). A total of 75% of patients presented a diffuse lesion in the pre-enrollment computed tomography. Median time from injury until reaching refractory high ICP was 71.5 h after injury (minimum 14 h, maximum 251 h). Twelve patients (50%) reached this situation within the first 72 h after injury. MHT was attained in a median time of 3 h. Pre-enrollment median ICP was 23.8 mmHg and was reduced to 16.8 mmHg upon reaching target temperature. At 6 months after injury, nine patients had died (37.5%), six were severely disabled (25%), two moderately disabled (8.3%) and seven had a good recovery (29.2%). Of the nine patients who died, in four the cause was rebound ICP during rewarming, one death was attributed to accidental potassium overload, two to septic shock, one to cardiac arrest of unknown origin and the ninth to a pulmonary embolism. CONCLUSION: Intravascular methods to induce MHT combined with precooling with cold saline at 4 degrees C appear to be feasible and effective in reducing ICP in patients with high ICP refractory to first-line therapeutic measures.

Risk and prognostic factors of ventilator-associated pneumonia in trauma patients.

OBJECTIVE: To assess the risk and prognostic factors of ventilator-associated pneumonia in trauma patients, with an emphasis on the inflammatory response. DESIGN: Case-control study. SETTING: Trauma intensive care unit. PATIENTS: Of 190 consecutive mechanically ventilated patients, those with microbiologically confirmed pneumonia (n = 62) were matched with 62 controls without pneumonia. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Clinical, microbiological, and outcome variables were recorded. Cytokines were measured in serum and blind bronchoalveolar lavage specimens at onset of pneumonia. Multivariate analyses of risk and prognostic factors for ventilator-associated pneumonia were done. Increased severity of head and neck injury (odds ratio, 11.9; p < .001) was the only independent predictor of pneumonia. Among patients with pneumonia, serum levels of interleukin-6 (p = .019) and interleukin-8 (p = .036) at onset of pneumonia were higher in nonresponders to treatment. Moreover, serum levels of tumor necrosis factor-alpha (p = .028) and interleukin-6 (p = .007) at onset of pneumonia were higher in nonsurvivors. Mortality in the intensive care unit was 23% in cases and controls. Nonresponse to antimicrobial treatment (odds ratio, 22.2; p = .001) and the use of hyperventilation (p = .021) were independent predictors of mortality in the intensive care unit for patients with pneumonia. CONCLUSIONS: Severe head and neck trauma is strongly associated with ventilator-associated pneumonia. A higher inflammatory response is associated with nonresponse to treatment and mortality among patients with pneumonia. Although pneumonia did not influence mortality, nonresponse to treatment independently predicted mortality among these patients.

Influence of Angiotensin-converting enzyme polymorphism on neuropsychological subacute performance in moderate and severe traumatic brain injury.

Traumatic brain injury (TBI) frequently results in cerebrovascular lesions that may increase secondary damage and cause neuropsychological impairment. Previous studies suggest an association among the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE), cardiovascular disease, and cognitive performance. Clinical and experimental studies have demonstrated the beneficial effects of ACE inhibitor treatment on vascular injury, hypertension, brain ischemia, and cognitive functioning. In a sample of 73 moderate and severe TBI patients, the authors assessed whether cognitive sequelae differed in relation to the ACE I/D polymorphism. D allele carrier patients performed worse than those with I/I polymorphism on tests involving attention and processing speed. Findings suggest that the physiopathological changes associated with TBI may have greater consequences in ACE D allele carriers.