[Cerebral microdialysis in the current clinical setting]

Ten physiological commandments for severe head injury

Advances in multiparametric brain monitoring have allowed us to deepen our knowledge of the physiopathology of head injury and how it can be treated using the therapies available today. It is essential to understand and interpret a series of basic physiological and physiopathological principles that, on the one hand, provide an adequate metabolic environment to prevent worsening of the primary brain injury and favour its recovery, and on the other hand, allow therapeutic resources to be individually adapted to the specific needs of the patient. Based on these notions, this article presents a decalogue of the physiological objectives to be achieved in brain injury, together with a series of diagnostic and therapeutic recommendations for achieving these goals. We emphasise the importance of considering and analysing the physiological variables involved in the transport of oxygen to the brain, such as cardiac output and arterial oxygen content, together with their conditioning factors and possible alterations. Special attention is paid to the basic elements of physiological neuroprotection, and we describe the multiple causes of cerebral hypoxia, how to approach them, and how to correct them. We also examine the increase in intracranial pressure as a physiopathological element, focussing on the significance of thoracic and abdominal pressure in the interpretation of intracranial pressure. Treatment of intracranial pressure should be based on a step-wise model, the first stage of which should be based on a physiopathological reflection combined with information on the tomographic lesions rather than on rigid numerical values.

Ten physiological commandments for severe head injury

Advances in multiparametric brain monitoring have allowed us to deepen our knowledge of the physiopathology of head injury and how it can be treated using the therapies available today. It is essential to understand and interpret a series of basic physiological and physiopathological principles that, on the one hand, provide an adequate metabolic environment to prevent worsening of the primary brain injury and favour its recovery, and on the other hand, allow therapeutic resources to be individually adapted to the specific needs of the patient. Based on these notions, this article presents a decalogue of the physiological objectives to be achieved in brain injury, together with a series of diagnostic and therapeutic recommendations for achieving these goals. We emphasise the importance of considering and analysing the physiological variables involved in the transport of oxygen to the brain, such as cardiac output and arterial oxygen content, together with their conditioning factors and possible alterations. Special attention is paid to the basic elements of physiological neuroprotection, and we describe the multiple causes of cerebral hypoxia, how to approach them, and how to correct them. We also examine the increase in intracranial pressure as a physiopathological element, focussing on the significance of thoracic and abdominal pressure in the interpretation of intracranial pressure. Treatment of intracranial pressure should be based on a step-wise model, the first stage of which should be based on a physiopathological reflection combined with information on the tomographic lesions rather than on rigid numerical values.

Lactate and lactate clearance in critically burned patients: usefulness and limitations as a resuscitation guide and as a prognostic factor

OBJECTIVE

Lactate levels to guide resuscitation in critically burned patients are controversial. The purpose of our study was to determine whether absolute lactate values or lower lactate clearance predict mortality, and whether these are useful tools in the resuscitation phase.

METHODS

We conducted a prospective, unicentric, observational study of a cohort of 214 burn patients admitted in the Burn Intensive Care Unit. We collected demographic and laboratory data, complications, absolute lactate levels and lactate clearance every 8 h since admission to 72 h. In critical patients we monitored hemodynamic parameters with transpulmonary thermodilution. We used Student's t-test or nonparametric tests, mixed models and Pearson and Spearman methods, Fisher's exact and chi-squared test.

RESULTS

Of the 214 patients, 76.6% were male, mean age were 46 ± 15 years and 23.0 ± 19.5% of Total Basal Surface Area (TBSA) burned. Initial mean absolute levels of lactate were 2.02 ± 1.62 mmol/L in survivors vs. 4.05 ± 3.90 mmol/L in nonsurvivors. Initial elevated lactate levels increased mortality (p < .001), length of ICU stay, mechanical ventilation and shock. In the subgroup of burned TBSA < 20%, lowering the lactate cut-off point from 2.0 to 1.8 mmol/L improved the mortality prediction (OR:9.3). We found no relationship between lactate clearance in the first 24 h and mortality. In more severe patients (> 20% TBSA burned and initial lactate levels > 2), a good correlation was found between lactate and cardiac index; but not with intrathoracic blood volume index (ITBVI). Patients with low ITBVI preload (< 600 mL/m²) did not show significant differences in lactate clearance compared with those with ITBVI > 600.

CONCLUSIONS

Initial elevated lactate levels are a factor of poor prognosis and the cut-off point that best predicts mortality should be adjusted in the patients with TBSA burned < 20%. The global clearance of lactate in the first 24 h, unlike what occurs in other injuries, does not correlate with mortality. Monitoring lactate can ensure adequate peripheral perfusion during resuscitation with lower than normal fluid preload values.

The Role of Glycerol-Containing Drugs in Cerebral Microdialysis: A Retrospective Study on the Effects of Intravenously Administered Glycerol

BACKGROUND

Cerebral microdialysis (CMD) is a valuable tool for monitoring compounds in the cerebral extracellular fluid (ECF). Glycerol is one such compound which is regarded as a marker of cell membrane decomposition. Notably, in some acutely brain-injured patients, CMD-glycerol levels rise without any other apparent indication of cerebral deterioration. The aim of this study was to investigate whether this could be due to an association between CMD-glycerol levels and the administration of glycerol-containing drugs.

METHODS

Microdialysis data were retrospectively retrieved from the hospital's intensive care unit patient data management system (PDMS). All patients who were monitored with CMD for ≥ 96 h were included. Administered drug doses were retrieved from the PDMS and converted to exact doses of glycerol. Cross-correlation analyses were performed between the free, metabolized as well as total administered dose of glycerol and the detrended and differenced CMD-glycerol concentration. These analyses were repeated for two sets of subgroups based upon the individual catheter's graphical trend and its location in relation to the lesion.

RESULTS

There was no significant correlation between the differenced CMD-glycerol levels and drug-administered glycerol. Furthermore, there was no significant correlation between CMD-glycerol and catheter location or graphical trend. However, if the CMD-glycerol levels were detrended, significant but clinically non-relevant correlations were identified (maximum correlation coefficient of 0.1 (0.04-0.15, 95% CI) at a lag of 7 h using the total administered dose of glycerol).

CONCLUSIONS

Glycerol-containing drugs routinely administered intravenously in the clinical setting appear to have a minimal and clinically insignificant effect on levels of glycerol in the cerebral ECF.

In vivo and continuous measurement of bisulfide in the hippocampus of rat's brain by an on-line integrated microdialysis/droplet-based microfluidic system

An on-line and continuous approach was demonstrated forin vivomeasurement of bisulfide in rat's brain.

Technological advances in perioperative monitoring: Current concepts and clinical perspectives

Minimal mandatory monitoring in the perioperative period recommended by Association of Anesthetists of Great Britain and Ireland and American Society of Anesthesiologists are universally acknowledged and has become an integral part of the anesthesia practice. The technologies in perioperative monitoring have advanced, and the availability and clinical applications have multiplied exponentially. Newer monitoring techniques include depth of anesthesia monitoring, goal-directed fluid therapy, transesophageal echocardiography, advanced neurological monitoring, improved alarm system and technological advancement in objective pain assessment. Various factors that need to be considered with the use of improved monitoring techniques are their validation data, patient outcome, safety profile, cost-effectiveness, awareness of the possible adverse events, knowledge of technical principle and ability of the convenient routine handling. In this review, we will discuss the new monitoring techniques in anesthesia, their advantages, deficiencies, limitations, their comparison to the conventional methods and their effect on patient outcome, if any.

Impact of static pressure on transmembrane fluid exchange in high molecular weight cut off microdialysis

With the interest of studying larger biomolecules by microdialysis (MD), this sampling technique has reached into the ultrafiltration region of fluid exchange, where fluid recovery (FR) has a strong dependence on pressure. Hence in this study, we focus on the fluid exchange across the high molecular weight cut off MD membrane under the influence of the static pressure in the sampling environment. A theoretical model is presented for MD with such membranes, where FR has a linear dependence upon the static pressure of the sample. Transmembrane (TM) osmotic pressure difference and MD perfusion rate decide how fast FR increases with increased static pressure. A test chamber for in vitro MD under static pressure was constructed and validated. It can hold four MD probes under controlled pressurized conditions. Comparison showed good agreement between experiment and theory. Moreover, test results showed that the fluid recovery of the test chamber MD can be set accurately via the chamber pressure, which is controlled by sample injection into the chamber at precise rate. This in vitro system is designed for modelling in vivo MD in cerebrospinal fluid and studies with biological samples in this system may be good models for in vivo MD.

Combined administration of hyperbaric oxygen and hydroxocobalamin improves cerebral metabolism after acute cyanide poisoning in rats

Hyperbaric oxygen therapy (HBOT) or intravenous hydroxocobalamin (OHCob) both abolish cyanide (CN)-induced surges in interstitial brain lactate and glucose concentrations. HBOT has been shown to induce a delayed increase in whole blood CN concentrations, whereas OHCob may act as an intravascular CN scavenger. Additionally, HBOT may prevent respiratory distress and restore blood pressure during CN intoxication, an effect not seen with OHCob administration. In this report, we evaluated the combined effects of HBOT and OHCob on interstitial lactate, glucose, and glycerol concentrations as well as lactate-to-pyruvate ratio in rat brain by means of microdialysis during acute CN poisoning. Anesthetized rats were allocated to three groups: 1) vehicle (1.2 ml isotonic NaCl intra-arterially); 2) potassium CN (5.4 mg/kg intra-arterially); 3) potassium CN, OHCob (100 mg/kg intra-arterially) and subsequent HBOT (284 kPa in 90 min). OHCob and HBOT significantly attenuated the acute surges in interstitial cerebral lactate, glucose, and glycerol concentrations compared with the intoxicated rats given no treatment. Furthermore, the combined treatment resulted in consistent low lactate, glucose, and glycerol concentrations, as well as in low lactate-to-pyruvate ratios compared with CN intoxicated controls. In rats receiving OHCob and HBOT, respiration improved and cyanosis disappeared, with subsequent stabilization of mean arterial blood pressure. The present findings indicate that a combined administration of OHCob and HBOT has a beneficial and persistent effect on the cerebral metabolism during CN intoxication.

[An experimental model of mass-type brain damage in the rat: expression of brain damage based on neurospecific enolase and protein S100B]

OBJECTIVE

To determine whether a model of transient mass-type brain damage (MTBD) in the rat produces early release of neurospecific enolase (NSE) and protein S100B in peripheral blood, as an expression of the induced brain injury.

DESIGN

An experimental study with a control group.

SETTING

Experimental operating room of the Institute of Biomedicine (IBiS) of Virgen del Rocío University Hospital (Seville, Spain).

PARTICIPANTS

Fourteen adult Wistar rats.

INTERVENTIONS

Blood was sampled at baseline, followed by: MTBD group, a trephine perforation was used to insert and inflate the balloon of a catheter at a rate of 500 μl/20 sec, followed by 4 blood extractions every 20 min. Control group, the same procedure as before was carried out, though without trephine perforation.

PRIMARY STUDY VARIABLES

Weight, early mortality, serum NSE and S100B concentration.

RESULTS

Differences in NSE and S100B concentration were observed over time within the MTBD group (P<.001), though not so in the control group. With the exception of the baseline determination, differences were observed between the two groups in terms of the mean NSE and S100B values. Following MTBD, NSE and S100B progressively increased at all measurement timepoints, with r=0.765; P=.001 and r=0.628; P=.001, respectively. In contrast, the control group showed no such correlation for either biomarker.

CONCLUSIONS

Serum NSE and S100B concentrations offer an early indication of brain injury affecting the gray and white matter in an experimental model of mass-type MTBD in the rat.

Clinical variables and neuromonitoring information (intracranial pressure and brain tissue oxygenation) as predictors of brain-death development after severe traumatic brain injury

BACKGROUND AND PURPOSE

The aim of this study was to ascertain the role of clinical variables and neuromonitoring data as predictors of brain death (BD) after severe traumatic brain injury (TBI).

PATIENTS AND METHODS

This prospective observational study involved severe TBI patients admitted to the intensive care unit between October 2009 and May 2011. The following variables were recorded: gender, age, reference Glasgow Coma Scale after resuscitation, pupillary reactivity, prehospital hypotension and desaturation, injury severity score, computed tomography (CT) findings, intracranial hypertension, and low brain tissue oxygenation (Pti02) levels (<16 mm Hg), as well as the final result of BD.

RESULTS

Among 61 patients (86.9% males) who met the inclusion criteria, the average age was 37.69 ± 16.44 years. Traffic accidents were the main cause of TBI (62.3%). The patients at risk of progressing to BD (14.8% of the entire cohort) were those with a mass lesion on CT (odds ratio [OR] 33.6; 95% confidence interval [CI]: 3.75-300.30; P = .002), altered pupillary reaction at admission (OR 25.5; 95% CI: 2.27-285.65; P = .009), as well low Pti02 levels on admission (OR 20.41; 95% CI: 3.52-118.33; P < .001) and during the first 24 hours of neuromonitoring (OR 20; 95% CI: 2.90-137.83; P < .001). Multivariate logistic regression showed that a low Pti02 level on admission was the best independent predictor for BD (OR 20.41; 95% CI: 3.53-118.33; P = .001).

CONCLUSIONS

Clinical variables and neuromonitoring information may identify TBI patients at risk of deterioration to BD.