[Is lactate a good indicator of brain tissue hypoxia in the acute phase of traumatic brain injury? Results of a pilot study in 21 patients]

Lactate and the lactate-pyruvate index (LPI) are two hypoxia markers widely used to detect brain tissue hypoxia in patients with acute traumatic brain injury. These two markers have a more complex behavior than expected as they can be abnormally high in circumstances with no detectable brain hypoxia. This condition must be considered in the differential diagnosis because it also reflects an alteration of brain energy metabolism.

OBJECTIVES

1. To describe cerebral energy metabolism characteristics observed in the acute phase of traumatic brain injury (TBI) based on two traditional indicators of anaerobic metabolism: lactate and LPI, 2. To determine the concordance between these two biomarkers in order to classify the incidence of anaerobic metabolism and 3. To classify the different types of metabolic abnormalities found in patients with moderate and severe TBI using both lactate and LPI.

MATERIALS AND METHODS

Twenty-one patients were randomly selected from a cohort of moderate or severe TBI patients admitted to the neurotraumatology intensive care unit. All of them who underwent both cerebral microdialysis and brain tissue oxygen monitoring (PtiO(2)). We analyzed the levels of lactate and the LPI for every microvial within the first 96 hours after head trauma. These data were correlated with PtiO(2) values.

RESULTS

Lactate levels and the LPI were respectively increased during 49.5% and 38.4% of the monitoring time. The incidence and behavior of high levels of both markers were extremely heterogeneous. The concordance between these two biomarkers to determine episodes of dysfunctional metabolism was very weak (Kappa Index=0.29; IC 95%: 0.24-0.34). Based on the levels of lactate and the LPI, we defined four metabolic patterns: I: L>2.5 mmol/L and LPR>25; II: L>2.5 mmol/L and LPR< or = 25; III: L< or = 2.5 mmol/L and LPR< or = 25; IV: L< or = 2.5 mmol/L and LPR>25). In more than 80% of cases in which lactate or LPI were increased, PtiO(2) values were within the normal range (PtiO(2)> 15 mmHg).

CONCLUSIONS

Increased lactate and LPI were frequent findings after acute TBI and in most cases they were not related to episodes of brain tissue hypoxia. Furthermore, the concordance between both biomarkers to classify metabolic dysfunction was weak. LPI and lactate should not be used indistinctly in everyday clinical practice because of the weak correlation between these two markers, the difficulty in their interpretation and the heterogeneous and complex nature of the pathophysiology. Other differential diagnoses apart from tissue hypoxia should always be considered when high lactate and/or LPI are detected in the acute injured brain.

[High-resolution microdialysis. methodological issues and application to the study of inflammatory brain response]

Cerebral microdialysis is a tool that provides very relevant information in the metabolic monitoring of brain injured patients. It is a particularly effective technique for the detection and analysis of small molecules, given that the pores of the dialysis membrane act as a barrier to restrict the transport of larger species, such as proteins and other macromolecules. The recent availability of microdialysis catheters with membrane pores of larger size, termed "high resolution" catheters, would widen the spectrum of molecules detectable in the dialisate. However, there are technical complications related to the use of these catheters for such purposes, and therefore, this potential capacity for the recovery of proteins needs to be validated, in order to begin its application as a tool in studies of proteomics associated with brain injuries. The following review depicts the basic principles of microdialysis, and describes some of the issues involved in the recovery of molecules in the dialisate, including the physical properties of the dialysis membrane and of the molecules of interest.

[Utilization of a post-anesthetic recovery index]

OBJECTIVES

1. To introduce use of the postanesthesia recovery score (assessing consciousness, mobility, ventilation, hemodynamics and blood analysis) as a good method for evaluating and classifying recovery from anesthesia in the postoperative care unit. 2. To determine overall patient progress and assess the influence of various patient, anesthetic and surgical factors.

PATIENTS AND METHODS

This was a multicenter study of 1,227 patients. We excluded all patients who were to be transferred to intensive care units after surgery. A score of 10 or more, with no single item score equal to 0, was considered optimal for discharge from the postanesthesia care unit.

RESULTS

The lowest score upon admission to the unit was among patients who had undergone high abdominal surgery (16.4%). Scores over 9 belonged to patients who had undergone lower abdominal and perineal surgery (87.5 and 95.3%, respectively). Scores were < or = 9 in patients who received inhaled anesthetics (42%). Intravenous anesthesia patients (84.4%) had scores over 9. The local-regional anesthetic procedures with the best scores were axilar blocks and local infiltrations. Patients staying longer in the recovery unit were those classified as ASA III, those whose procedures lasted longer than 120 minutes, those undergoing surgery on the upper abdomen or on extremities, those receiving isoflurane and pancuronium, and those suffering adverse events during and after the procedure. Factors influencing perioperative events were age, duration of procedure and history of intraoperative events.