The effects of hypercapnia and hypocapnia upon the cerebrospinal fluid lactate and pyruvate concentrations and upon the lactate, pyruvate, ATP, ADP, phosphocreatine and creatine concentrations of cat brain tissue

Correlation of Lactate Concentration in Peripheral Plasma and Cerebrospinal Fluid with Glasgow Outcome Scale for Patients with Tuberculous Meningitis Complicated by Acute Hydrocephalus Treated with Fluid Diversions

BACKGROUND

Tuberculous meningitis (TBM) is an endemic infectious disease in developing countries, and it can become a serious illness in children. Treatment of TBM is more difficult and prone to failure than treatment of pulmonary tuberculosis. TBM causes hydrocephalus, cerebral edema, increased intracranial pressure, global ischemia, and neurologic deficits, which disturb cellular metabolism and increase lactate levels. A reliable, widely available clinical indicator of TBM severity is needed. Successful treatment of TBM is assessed using the Glasgow Outcome Scale (GOS).

METHODS

This prospective cohort study included 34 patients with TBM and acute hydrocephalus who had undergone fluid diversions and were admitted to Dr. Hasan Sadikin Hospital in Bandung from 2014 to 2015. A portable machine for blood glucose measurement was used to measure lactate concentrations. Statistical significance was defined as P ≤ 0.05.

RESULTS

Average levels of plasma and cerebrospinal fluid (CSF) lactate were 1.99 ± 0.70 mmol/L and 3.04 ± 1.05 mmol/L, respectively. A significantly higher level of lactate was observed in CSF compared with plasma. Preoperative plasma lactate was negatively correlated to GOS (r = -0.539; P = 0.013), and CSF lactate was negatively correlated to GOS (r = -0.412; P = 0.027). Average lactate levels in CSF (central) were higher than plasma (peripheral) levels. GOS scale of patients decreased with increased plasma and CSF lactate levels.

CONCLUSIONS

Examination of plasma and CSF lactate levels should be included in routine examinations to determine extent of cellular damage and GOS score in patients with TBM and acute hydrocephalus who have undergone fluid diversions.

Potential non-hypoxic/ischemic causes of increased cerebral interstitial fluid lactate/pyruvate ratio: a review of available literature

Microdialysis, an in vivo technique that permits collection and analysis of small molecular weight substances from the interstitial space, was developed more than 30 years ago and introduced into the clinical neurosciences in the 1990s. Today cerebral microdialysis is an established, commercially available clinical tool that is focused primarily on markers of cerebral energy metabolism (glucose, lactate, and pyruvate) and cell damage (glycerol), and neurotransmitters (glutamate). Although the brain comprises only 2% of body weight, it consumes 20% of total body energy. Consequently, the ability to monitor cerebral metabolism can provide significant insights during clinical care. Measurements of lactate, pyruvate, and glucose give information about the comparative contributions of aerobic and anaerobic metabolisms to brain energy. The lactate/pyruvate ratio reflects cytoplasmic redox state and thus provides information about tissue oxygenation. An elevated lactate pyruvate ratio (>40) frequently is interpreted as a sign of cerebral hypoxia or ischemia. However, several other factors may contribute to an elevated LPR. This article reviews potential non-hypoxic/ischemic causes of an increased LPR.

Prostacyclin treatment in severe traumatic brain injury: a microdialysis and outcome study

Prostacyclin (PGI(2)) is a potent vasodilator, inhibitor of leukocyte adhesion, and platelet aggregation. In trauma the balance between PGI(2) and thromboxane A(2) (TXA(2)) is shifted towards TXA(2). Externally provided PGI(2) would, from a theoretical and experimental point of view, improve the microcirculation in injured brain tissue. This study is a prospective consecutive double-blinded randomized study on the effect of PGI(2) versus placebo in severe traumatic brain injury (sTBI). All patients with sTBI were eligible.

INCLUSION CRITERIA

verified sTBI, Glasgow Coma Score (GCS) at intubation and sedation of <or=8, age 15-70 years, a first-recorded cerebral perfusion pressure (CPP) of >or=10 mm Hg, and arrival within 24 h of trauma. All subjects received an intracranial pressure (ICP) measuring device, bilateral intracerebral microdialysis catheters, and a microdialysis catheter in the abdominal subcutaneous adipose tissue. Subjects were treated according to an ICP-targeted therapy based on the Lund concept. 48 patients (mean age of 35.5 years and a median GCS of 6 [3-8]) were included. We found no significant effect of prostacyclin (epoprostenol, Flolan) on either the lactate-pyruvate ratio (L/P) at 24 h or the brain glucose levels. There was no significant difference in clinical outcome between the two groups. The median Glasgow Outcome Score (GOS) at 3 months was 4, and mortality was 12.5%. The favorable outcome (GOS 4-5) was 52%. The initial L/P did not prognosticate for outcome. Thus our results indicate that there is no effect of PGI(2) at a dose of 0.5 ng/kg/min on brain L/P, brain glucose levels, or outcome at 3 months.

The role of systemic hemodynamic disturbances in prematurity-related brain injury

Premature infants who experience cerebrovascular injury frequently have acute and long-term neurologic complications. In this article, we explore the relationship between systemic hemodynamic insults and brain injury in this patient population and the mechanisms that might be at play.

Permissive hypercapnia to decrease lung injury in ventilated preterm neonates

Lung injury in ventilated premature infants occurs primarily through the mechanism of volutrauma, often due to the combination of high tidal volumes in association with a high end-inspiratory volume and occasionally end-expiratory alveolar collapse. Tolerating a higher level of arterial partial pressure of carbon dioxide (PaCO2) is considered as 'permissive hypercapnia' and when combined with the use of low tidal volumes may reduce volutrauma and lead to improved pulmonary outcomes. Permissive hypercapnia may also protect against hypocapnia-induced brain hypoperfusion and subsequent periventricular leukomalacia. However, extreme hypercapnia may be associated with an increased risk of intracranial hemorrhage. It may therefore be important to avoid large fluctuations in PaCO2 values. Recent randomized clinical trials in preterm infants have demonstrated that mild permissive hypercapnia is safe, but clinical benefits are modest. The optimal PaCO2 goal in clinical practice has not been determined, and the available evidence does not currently support a general recommendation for permissive hypercapnia in preterm infants.

Cerebrovascular injury in premature infants: current understanding and challenges for future prevention

Cerebrovascular insults are a leading cause of brain injury in premature infants, contributing to the high prevalence of motor, cognitive, and behavioral deficits. Understanding the complex pathways linking circulatory immaturity to brain injury in premature infants remains incomplete. These mechanisms are significantly different from those causing injury in the mature brain. The gaps in knowledge of normal and disturbed cerebral vasoregulation need to be addressed. This article reviews current understanding of cerebral perfusion, in the sick premature infant in particular, and discusses challenges that lie ahead.

Lactic acidosis in the brain: occurrence, triggering mechanisms and pathophysiological importance

Brain cells are better protected against systemic acidosis (and alkalosis) than most other cells since they are surrounded by an extracellular fluid which is, in itself, subjected to pH regulation. For all practical purposes, therefore, cerebral intracellular acidosis is endogenous and arises when lactic acid accumulates. This occurs in three main conditions: hypocapnia, epileptic seizures, and hypoxia plus ischaemia. In the first of these, metabolic acidosis is compensatory but in the other two, a moderate or pronounced decrease in pH occurs. In all three, increased glycolytic rate involves activation of phosphofructokinase secondarily to a raised intracellular pH (moderate hypocapnia) or to a perturbation of cerebral energy state (seizures and hypoxia plus ischaemia). In seizure states, accumulation of lactic acid is usually moderate (about 10 mumol g-1). In complete ischaemia, the acidosis is only slightly more pronounced. However, in severe incomplete ischaemia, and in severe hypoxia, the continued substrate supply can lead to excessive accumulation of lactic acid (30-50 mumol g-1). When this occurs, the acidosis contributes to irreversible cell damage.

The role of catecholamines in metabolic acidosis

Catecholamines (noradrenaline and adrenaline) are catabolic hormones secreted during stress. They initiate many metabolic processes including increased production of both ketoacids and lactic acid. Support for a direct participation of these hormones in the development and/or maintenance of ketoacidosis includes: (1) the high incidence of stress (approx. 70%) as a precipitating factor for ketoacidosis; (2) the elevated plasma levels of noradrenaline (norepinephrine) in patients with ketoacidosis; (3) the rise in plasma concentrations of ketone bodies during catecholamine infusion; and (4) the reduction in the incidence of ketoacidosis with beta-adrenergic pharmacological blockade. Support for a direct participation of catecholamines in the development and/or maintenance of lactic acidosis includes: (1) the common association of stress and lactic acidosis; (2) the rise in plasma lactate concentration during adrenaline (epinephrine) infusion; (3) the precipitation of lactic acidosis by adrenaline intoxication and phaeochromocytoma; and (4) the vasoconstrictor effects of catecholamines leading to tissue anoxia and lactic acid production. Thus, in susceptible patients, catecholamines may be principal determinants of whether ketoacidosis and/or lactic acidosis develops.

Long-term neuroprotective effects of carbon dioxide on neonatal rat hypoxic-ischemic brain injury: an experimental study of skilled motor tasks

OBJECTIVE

This study was undertaken to investigate the long-term effect of hypercapnia on neonatal hypoxic-ischemic brain injury, we tested its effect in a neonatal rat hypoxia-ischemia model.

STUDY DESIGN

The rats were subjected to unilateral carotid artery ligation and exposure to 8% oxygen for 30 minutes. Six percent carbon dioxide was administered to the neonatal rats during unilateral hypoxia-ischemia, and the motor function and neurologic outcomes were determined 3 months later.

RESULTS

Significant motor functional improvement was observed in the hypercapnic animals, as judged by the Montoya staircase test. The unilateral brain injury was significantly ameliorated in the hypercapnic animals, and this amelioration was well correlated with the motor functional performance. Cerebral blood flow during hypoxia-ischemia, monitored by laser Doppler flowmetry, was better preserved in the hypercapnic animals.

CONCLUSION

Our results suggest that mild hypercapnia during hypoxia-ischemia may provide long-lasting motor functional as well as neurologic protection for immature brains, possibly by increasing cerebral blood flow during hypoxia.

Translational neurochemical research in acute human brain injury: the current status and potential future for cerebral microdialysis

Microdialysis (MD) was introduced as an intracerebral sampling method for clinical neurosurgery by Hillered et al. and Meyerson et al. in 1990. Since then MD has been embraced as a research tool to measure the neurochemistry of acute human brain injury and epilepsy. In general investigators have focused their attention to relative chemical changes during neurointensive care, operative procedures, and epileptic seizure activity. This initial excitement surrounding this technology has subsided over the years due to concerns about the amount of tissue sampled and the complicated issues related to quantification. The interpretation of mild to moderate MD fluctuations in general remains an issue relating to dynamic changes of the architecture and size of the interstitial space, blood-brain barrier (BBB) function, and analytical imprecision, calling for additional validation studies and new methods to control for in vivo recovery variations. Consequently, the use of this methodology to influence clinical decisions regarding the care of patients has been restricted to a few institutions. Clinical studies have provided ample evidence that intracerebral MD monitoring is useful for the detection of overt adverse neurochemical conditions involving hypoxia/ischemia and seizure activity in subarachnoid hemorrhage (SAH), traumatic brain injury (TBI), thromboembolic stroke, and epilepsy. There is some data strongly suggesting that MD changes precede the onset of secondary neurological deterioration following SAH, hemispheric stroke, and surges of increased ICP in fulminant hepatic failure. These promising investigations have relied on MD-markers for disturbed glucose metabolism (glucose, lactate, and pyruvate) and amino acids. Others have focused on trying to capture other important neurochemical events, such as excitotoxicity, cell membrane degradation, reactive oxygen species (ROS) and nitric oxide (NO) formation, cellular edema, and BBB dysfunction. However, these other applications need additional validation. Although these cerebral events and their corresponding changes in neurochemistry are important, other promising MD applications, as yet less explored, comprise local neurochemical provocations, drug penetration to the human brain, MD as a tool in clinical drug trials, and for studying the proteomics of acute human brain injury. Nevertheless, MD has provided new important insights into the neurochemistry of acute human brain injury. It remains one of very few methods for neurochemical measurements in the interstitial compartment of the human brain and will continue to be a valuable translational research tool for the future. Therefore, this technology has the potential of becoming an established part of multimodality neuro-ICU monitoring, contributing unique information about the acute brain injury process. However, in order to reach this stage, several issues related to quantification and bedside presentation of MD data, implantation strategies, and quality assurance need to be resolved. The future success of MD as a diagnostic tool in clinical neurosurgery depends heavily on the choice of biomarkers, their sensitivity, specificity, and predictive value for secondary neurochemical events, and the availability of practical bedside methods for chemical analysis of the individual markers. The purpose of this review was to summarize the results of clinical studies using cerebral MD in neurosurgical patients and to discuss the current status of MD as a potential method for use in clinical decision-making. The approach was to focus on adverse neurochemical conditions in the injured human brain and the MD biomarkers used to study those events. Methodological issues that appeared critical for the future success of MD as a routine intracerebral sampling method were addressed.

Hypocarbia in the ventilated preterm infant and its effect on intraventricular haemorrhage and bronchopulmonary dysplasia

OBJECTIVE

To examine the relationship between PaCO2 levels in ventilated very preterm infants and (i) the incidence of severe intraventricular haemorrhage (IVH) and periventricular leukomalacia (PVL); and (ii) bronchopulmonary dysplasia (BPD).

METHODS

A retrospective cohort analysis of preterm infants comparing PaCO2 levels with the incidence of severe IVH/PVL and BPD was carried out on patients born at less than 29 weeks gestation from 1992 to 1994 and admitted to the tertiary neonatal intensive care unit at the King Edward Memorial Hospital (314 infants). During the first 96 h, PaCO2 levels were examined including lowest and highest PaCO2 levels, mean PaCO2 levels and duration of hypocarbia both pre- and post-surfactant administration.

RESULTS

Of the 314 infants, there were 40 early neonatal deaths (less than 48 h) who were not included in the analysis. Of the 274 surviving infants, 72 (26%) infants had severe IVH. Infants whose PaCO2 fell below 30 mmHg at any stage in the first 48 h of life had an increased risk of severe IVH or PVL (odds ratio 2.38; 95% CI 1.27-4.49; P = 0.007). Of the 265 survivors to 36 weeks corrected gestational age, 134 (51%) had BPD. Infants with at least three PaCO2 values less than 30 mmHg in the first 24 h of life had an increased risk of BPD (odds ratio 2.21; 95% CI 1.05-4.57; P = 0.036).

CONCLUSIONS

The risk of severe IVH/PVL was significantly increased by hypocarbia. There was also an association between hypocarbia and BPD, particularly when hypocarbia was prolonged. These findings suggest that avoidance of hypocarbia may reduce the incidence of severe IVH/PVL and BPD in preterm infants.

Permissive hypercapnia

Although lifesaving, mechanical ventilation can result in lung injury and contribute to the development of bronchopulmonary dysplasia. The most critical determinants of lung injury are tidal volume and end-inspiratory lung volume. Permissive hypercapnia offers to maintain gas exchange with lower tidal volumes and thus decrease lung injury. Further physiologic benefits include improved oxygen delivery and neuroprotection, the latter through both avoidance of accidental hypocapnia, which is associated with a poor neurologic outcome, and direct cellular effects. Clinical trials in adults with acute respiratory failure indicated improved survival and reduced incidence of organ failure in subjects managed with low tidal volumes and permissive hypercapnia. Retrospective studies in low birth weight infants found an association of bronchopulmonary dysplasia with low PaCO(2). Randomized clinical trials of low birth weight infants did not achieve sufficient statistical power to demonstrate a reduction of BPD by permissive hypercapnia, but strong trends indicated the possibility of important benefits without increased adverse events. Herein, we review the mechanisms leading to lung injury, the physiologic effects of hypercapnia, the dangers of hypocapnia, and the available clinical data.

The competitive NMDA antagonist, CGS-19755, improves postischemic hypoperfusion in selectively vulnerable regions in gerbils

We attempted to clarify the effects of an NMDA antagonist on postischemic hypoperfusion in gerbils with 10 min forebrain ischemia and to relate it to postischemic metabolic recovery. We administered 10 mg/kg of CGS-19755, a competitive NMDA antagonist, or the same volume of saline intraperitoneally 30 min before the vascular occlusion. In 26 gerbils, we measured local cerebral blood flow (LCBF) 60 min after the reperfusion using [14C]iodoantipyrine autoradiography. In 20 gerbils, the effects on metabolic recovery were determined by serial measurements of intracellular pH, adenosine triphosphate (ATP) and the ratio between phosphocreatine and inorganic phosphate (PCr/Pi) until 60 min after reperfusion using 31P-magnetic resonance spectroscopy. In another group of 24 gerbils, we determined histopathological damage 24 h after the ischemia. The LCBF autoradiograms in the control group consistently demonstrated a typical postischemic hypoperfusion, i.e. homogeneous 50-75% reduction of blood flow in all forebrain structures. In contrast, CGS-19755 pretreatment animals showed highly heterogeneous LCBF declines, and significantly higher LCBF values were observed in the frontoparietal cortex and thalamus both of which were the most vulnerable area in this model. No significant LCBF change was observed in sham operated animals with or without CGS-19755 pretreatment. The postischemic recovery of PCr/Pi in gerbils pretreated with CGS-19755 was significantly better than that in the control animals. No significant differences in the recovery of ATP and intracellular pH were observed. The histological damage in the CGS-19755-treated group was less extensive than those in the saline-treated group. CGS-19755 pretreatment improved postischemic hypoperfusion and PCr/Pi recovery in the 10-min forebrain ischemia model in gerbils. The improvement of postischemic hypoperfusion in selectively vulnerable regions suggests that the activation of NMDA receptors may be related to the mechanism of developing postischemic hypoperfusion.

Long-term monitoring of CSF lactate levels and lactate/pyruvate ratios following subarachnoid haemorrhage

Ventricular cerebrospinal fluid (CSF) lactate concentrations and lactate/pyruvate (L/P) ratios were measured daily in 20 patients from day 1 to day 12 after subarachnoid haemorrhage due to ruptured aneurysms. Patients without symptomatic vasospasm were classified in Group 1, patients with symptomatic vasospasm were classified in Group 2, and patients who were Hunt and Kosnik grade 4 on admission clinically were classified in Group 3. Patients in all three groups had high CSF lactate concentrations on day 1, and, especially in Group 3, the high lactate was accompanied by an increased L/P ratio and a decreased CSF bicarbonate. Lactate concentrations in Group 1 decreased throughout the observation period. Lactate concentrations in Group 2 also decreased but then began to increase again on days 5 to 7, correlating well with the onset of cerebral vasospasm. The delayed increase of CSF lactate in Group 2 was also accompanied by increases in the CSF pyruvate level and the CSF L/P ratio. Daily monitoring of CSF lactate may thus serve as a chemical marker for cerebral vasospasm.

Chemical monitoring of neurosurgical intensive care patients using intracerebral microdialysis

The authors have used intracerebral microdialysis to develop a method for routine monitoring of disturbances in brain energy metabolism in patients in the neurosurgical intensive care unit. Microdialysis was conducted for periods ranging from 2.3 to 8.3 days in four patients (three with severe head injuries and one with severe subarachnoid hemorrhage). Altogether, 4447 chemical analyses from 587 dialysis samples were carried out. Concentrations of the energy-related metabolites lactate, pyruvate, and hypoxanthine were measured, and the lactate:pyruvate ratio was calculated. In addition, the acids glutamate, aspartate, taurine, glutamine, asparagine, and glycine were measured in one patient. The microdialysis data were matched with various clinical events, including intracranial hypertension and therapeutic interventions such as initiation or withdrawal of barbiturates and cerebrospinal fluid drainage. The present study shows that microdialysis can be used for long-term measurement of extracellular fluid (ECF) energy-related metabolites and amino acids in the frontal cortex of neurosurgical patients in a clinical setting. Fluctuations of the measured ECF energy-related substances corresponded to various clinical events presumably involving hypoxia/ischemia. The authors found a 25-fold increase in ECF glutamate, aspartate, and taurine under conditions of energy perturbation, as indicated by high levels of the lactate:pyruvate ratio, lactate, and hypoxanthine. The use of long-term intracerebral microdialysis in patients opens a new field of clinical research, with many possibilities for improving insight into intracranial dynamics in acute cerebral conditions.

Does acute hyperventilation provoke cerebral oligaemia in comatose patients after acute head injury?

In 27 comatose patients with acute head injury, 45 paired studies of regional cerebral blood flow (rCBF) were performed before and after hyperventilation. In total 676 regions were studied, and rCBF was calculated as initial slope index using the intracarotid washout technique of 133 Xe. The tests were applied from one day to three weeks after the acute trauma. In total hyperventilation from PaCO2 averaging 4.8 to 3.5 kPa increased the frequency of regions with oligaemia defined CBF less than 20 ml/100 g/min from 5 to 16%. Before hyperventilation oligaemia was observed in 11 of 45 studies (9 of 27 patients); after hyperventilation the frequency increased to 21 studies (15 patients). The frequency of severe oligaemia (CBF less than 15 ml) increased from 0.1 to 3% of all regions, or from 2 to 8 of all studies (from 2 to 9 patients). The increased frequency of oligaemia after hyperventilation was correlated to a poor outcome (dementia, vegetative survival or death), where it was observed in 21% of all regions, in 16 of 26 studies and 11 of 15 patients, whereas the frequency in patients with a good recovery was found to be 7% of all regions and observed in 5 of 19 studies (4 of 12 patients). The high frequency of oligaemia after hyperventilation was associated to a low hemispheric CBF before hyperventilation, but not to the level of PaCO2, the level of intracranial pressure, cerebral perfusion pressure or CSF-pH or lactate.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic significance of ventricular CSF lactic acidosis in severe head injury

Brain-tissue acidosis inferred by cerebrospinal fluid (CSF) lactic acidosis is considered to play an important role in the clinical course of severe head injury. Ventricular CSF lactate concentration was studied in 19 patients during the first 5 days after severe head injury. All patients were intubated, paralyzed, and artificially ventilated so that PaCO2 was kept at 33.2 +/- 5.0 mm Hg and PaO2 at 122 +/- 18 mm Hg (mean +/- standard deviation). The mean Glasgow Coma Scale score on admission was 5.73 +/- 2.42. The first CSF sample was drawn within 18 hours after head injury. Over the first 4 days postinjury, patients with a poor outcome had significantly higher ventricular CSF lactate levels than did those with moderate disabilities or a good outcome. Patients showing favorable outcome had a significant decrease in ventricular CSF lactate levels 48 hours after injury. This decrease was not observed in patients with a poor outcome. Increased ventricular CSF lactate concentration was also reliably associated with increased intracranial pressure (ICP). Ventricular CSF lactate levels did not correlate with the magnitude of intraventricular bleeding. Arterial and jugular venous blood lactate levels, although high after head injury, were usually lower than the levels in the ventricular CSF and reached a normal range by the 3rd day following head trauma. At that time, the ventricular CSF lactate concentration was still above normal in patients with a poor outcome but had decreased to normal in patients with moderate disabilities or a good outcome. Ventricular CSF pH did not generally correlate with the ventricular CSF lactate concentration in patients under controlled ventilation; however, in a few patients close to death or with ventricular infection, a correlation was noted. Ventricular CSF lactate levels were not related to cerebral blood flow. In this study, profiles of ventricular CSF lactate concentration are defined in relation to the patients' clinical course and outcome. High ventricular CSF lactate concentration is present within 18 hours after severe head injury. Its decrease to normal in the following 48 hours is a reliable sign of clinical improvement; however, ventricular CSF lactate levels that are persistently high or that increase over time indicate the patient's deterioration. Serial assessment of ventricular CSF for acid-base status and metabolites in head-injured patients with a ventricular catheter already placed for ICP monitoring is useful in the evaluation of prognosis and clinical course.

Relationship between metabolic recovery and the EEG prolonged ischemia of cat brain

In normothermic cats, cerebral blood flow was arrested for 1 hour followed by blood recirculation for 5-6 hours. Functional recovery was evaluated by qualitative and quantitative EEG analysis, and metabolic recovery by measuring metabolite and electrolyte levels in tissue samples taken from the cerebral cortex. In 5 out of 12 animals EEG activity did not recover after ischemia (group I); in 3 animals, intermittent EEG activity (group II) and in 4 animals continuous EEG activity returned during the observation period (group III). In group I the energy state was severely disturbed and an increase of calcium was detected, in group II this disturbance was much less pronounced, and in group III changes in energy metabolism and ion concentration were absent with the only exception of lower ADP levels. During recovery, the total intensity of EEG correlated positively with ATP (p less than 0.01) and inversely with lactate (p less than 0.05), and the intensity of the delta band inversely with sodium content (p less than 0.05). The results obtained demonstrate that electrophysiological recovery after prolonged ischemia is closely correlated with the restoration of the energy state and of electrolyte homeostasis of the brain. The inverse relationship of EEG intensity with lactate and sodium are interpreted as evidence for the adverse effects of ongoing post-ischemic glycolysis, resulting in the activation of the H+/Na+ antiporter for the regulation of intracellular pH.

Cerebral physiological and metabolic effects of hyperventilation in the neonatal dog

To clarify the changes that occur during marked hypocarbia in the neonate, we measured brain blood flow and metabolite levels after 90 minutes of hyperventilation in neonatal dogs. Brain blood flow decreased significantly in diencephalon, brainstem, and spinal cord but not in cerebral cortex or white matter. There was no substantial change in the electroencephalogram. Lactate concentrations, both in telencephalon and in superior sagittal sinus blood, increased significantly, although there was no alteration in levels of ATP or phosphocreatine. Marked hypocarbia in the neonatal dog produces an elevated brain lactate level that may be related to changes in glycolytic rate rather than to tissue ischemia or hypoxia.

Metabolic and hemodynamic response to hyperventilation in patients with head injuries

The effects of controlled moderate hyperventilation (paCo2 approximately 31 mmHg) on cardiovascular parameters and whole-body-oxygen-uptake (VO2) was studied in 10 patients with head injuries, who were unconscious and artificially ventilated at the time of the investigation. VO2 was measured with the Beckmann Metabolic Measurement Cart and also calculated from cardiac output and arterio-mixed venous oxygen content difference. A mean increase in VO2 (+ 19.6% of control) was observed after 2 h of hyperventilation. Cardiac output remained unchanged. This resulted in a decrease of venous oxygen content and impaired full oxygenation of the blood. Our results indicate that hyperventilation should not be a routine procedure. Close monitoring of arterial and venous blood gases is recommended, when hyperventilation is applied.

Lactate and pyruvate content of the human cisternal cerebrospinal fluid. Normal values, age and sex dependency, correlations with glucose concentrations

Cisternal CSF specimens were obtained from 144 fasted individuals free from organic brain disease (42 males and 102 females; mean age 41 +/- 10.3 years, range 16-69 years). In 30 cases a simultaneous lumbar puncture was also performed. The concentration of CSF glucose (G1) was measured by the o-toluidine method, and that of lactate (La) and pyruvate (Py) by enzymatic tests. No significant difference was found between the mean G1 and Py values of the lumbar and cisternal CSF but the lumbar La was somewhat higher than the cisternal one (P less than 0.10). In the cisternal CSF the frequency distribution of G1, La and Py samples was a Gaussian one (P less than 0.05). The normal ranges, as mean +/- 2SD, were for La 0.680-2.100 mM/1, and for Py lower limits of the range (between mean +/- 2 SD and mean +/- 1 SD) are considered to be potentially pathological. No significant difference was found between the mean G1, La and Py values in males and females. Consistent age-related changes could not be detected either in the G1 or Py levels, however, a tendency for La increase was observed in the oldest-age-group (over 54 years). A negative correlation was found between the G1 and La concentrations of the cisternal CSF (r = 0.375; P less than 0.001).

Effects of hyperventilation on cerebral blood flow and brain tissue metabolism in normotensive and spontaneously hypertensive rats

Cerebral vascular carbon dioxide (CO2) reactivities were compared in normotensive (NTR) and hypertensive (SHR) rats. Cerebral blood flow (CBF) in cortex and thalamus were evaluated before and during one hour of hyperventilation. After one hour of hyperventilation brain lactate, pyruvate, and ATP concentrations were also determined. Significant and similar reductions of CBF due to hyperventilation induce hypocapnia were found in both NTR and SHR groups. In contrast the percent increase in cerebrovascular resistance (CVR) per unit decrease in paCO2 was significant, indicating that hypocapnia induced vasoconstriction is greater in NTR than in SHR groups. During hyperventilation the average value for lactate in the NTR group was 3.98 mM/kg. In contrast it was 3.15 mM/kg in the SHR group, a significant difference (p less than 0.05). When paCO2 fell below 15 mm Hg the cerebral lactate increased strikingly in the NTR group and cortical CVR was reduced suggesting that an accumulation of the ischemic metabolites caused dilatation of the constricted cerebral vessels. In contrast the SHR group disclosed no such changes. The increase CVR characteristic of SHR appeared to diminish the cerebral vasoconstrictive response to hypocapnia. As a result ischemic metabolites in the brain do not increase in this group to the degree that they do in NTR.

The young-adult and normally aged brain. Its blood flow and oxidative metabolism. A review--part I

Blood flow and oxidative metabolism of the mature and healthy young-adult human brain account for about 20% of the cardiac output and about 20 and 25% of the requirements of oxygen and glucose, respectively, for the whole body. Normal cerebral aging is associated with only smaller reductions in the cerebral metabolic rates of oxygen and glucose while cerebral blood flow would seem to be unchanged. The age-dependent reduction in oxidative brain metabolism may be related to a decline in glycolytic flux due to a diminution of enzyme activities also involving acetylcholine synthesis. This metabolic reduction with age may be tentatively accounted for by a physiologically occurring loss of neurons, dendrites and dendritic spines in distinct brain areas. The mechanisms of autoregulation of cerebral blood flow, of CO2 reactivity of the brain vessels, of arterial hypoxemia on cerebral blood flow and their effects on oxidative and energy metabolism are well documented in young-adult brain. There is, however, no or only minimal information on the responsiveness of the normally aged brain to changes of these important biological parameters controlling and influencing brain blood flow and metabolism.

Intracranial pressure changes following aneurysm rupture. Part 2: associated cerebrospinal fluid lactacidosis

Lactate concentrations and pH were measured serially in the cerebrospinal fluid (CSF) of 52 patients with ruptured intracranial aneurysms. Measurements were made during continuous monitoring of the intraventricular pressure (IVP) in the first 12 days after the initial subarachnoid hemorrhage. A total of 226 samples of CSF were analyzed. The clinical condition of the patients was graded according to the Hunt and Hess system. The degree of cerebral arterial spasm was measured on angiograms taken on admission and again approximately 7 days later. Results showed that the lactate concentrations in hemorrhagic and xanthochromic CSF were significantly higher than in clear CSF, indicating lactate production from shed blood cells. However, regardless of the degree of blood admixture to CSF, lactate increased with deteriorating clinical condition. Patients with a moderately increased IVP (20 to 40 mm Hg) had lactate levels of about 3 mmol/liter. A rising IVP or the development of severe spasm was accompanied by a persistent elevation or an increase in lactate. These results suggest that increased CSF concentrations of lactate reflected an increased production of lactate by partially ischemic cerebral tissue. A CSF lactate value above 3.5 mmol/liter was associated with a poor prognosis.

Effects of severe arterial hypocapnia on regional blood flow regulation, tissue PO2 and metabolism in the brain cortex of cats

The effect of a stepwise decrease in PaCO2 from 3.9-1.6 kPa on rCBF, rCMRO2, tissue PO2 and concentrations of glucose, lactate, pyruvate, ATP, ADP, AMP and phosphocreatine in the brain cortex was studied in cats lightly anaesthetized with sodium pentobarbital. 1. Moderate lowering of PaCO2 to 2.5 kPa induced in all animals a homogeneous decrease of rCBF in corresponding areas of the right and left hemisphere. Mean rCBF fell from 129.2 to 103.1 ml X 100 g-1 X min-1, while rCMRO2 remained unchanged (12.7-12.9 ml X 100 g-1 X min-1). The tissue PO2 frequency histograms showed a shift to lower values without indicating the presence of brain tissue hypoxia. 2. Severe arterial hypocapnia (PaCO2 = 1.6 kPa) caused an inhomogeneous blood flow reaction. Both further decreased as well as increased rCBF values were measured simultaneously in the brain cortex of individual animals (mean rCBF = 97.6 ml X 100 g-1 X min-1). At the same time tissue PO2 measurements and metabolite assays indicated the presence of pronounced brain tissue hypoxia. The tissue concentrations of lactate and pyruvate and the lactate/pyruvate ratio were significantly increased, while the phosphocreatine concentration was significantly reduced. In addition, rCMRO2 decreased to 11.3 ml X 100 g-1 X min-1. The results provide conclusive evidence that severe arterial hypocapnia leads to an insufficient O2 supply of the brain cortex, which in turn seems to counteract the influence of hypocapnia on cortical blood flow regulation.

The critical importance of PaCO2 during intracranial aneurysm surgery. Case report

In a patient undergoing craniotomy for clipping of an anterior communicating artery aneurysm, sodium nitroprusside was used to lower systemic arterial blood pressure to 80/35 mm Hg (mean arterial blood pressure (MABP) = 50 mm Hg), at which time the electroencephalogram (EEG) changed abruptly from normal to a burst suppression pattern. At the onset of burst suppression, PaCO2 was 18 mm Hg. After PaCO2 had been increased to 28 mm Hg, the patient tolerated a blood pressure of 45/25 mm Hg (MABP = 32 mm Hg) during aneurysm clipping without EEG change. The observations reported here support the conclusion that, with moderate hypotension, hypocarbia may cause brain ischemia and that the level of PaCO2 may influence the degree of hypotension that may be safely used during aneurysm surgery. The importance of repeated arterial blood gas measurements when induced hypotension is employed for berry aneurysm surgery is stressed. Intraoperative EEG monitoring may be employed to help judge safe levels of intraoperative hypotension during intracranial aneurysm surgery.

Effects of prolonged N2O and barbiturate anesthesia on brain metabolism and pH in the dog

The brain acid-base status and metabolites were measured in 17 mongrel dogs that were anesthetized with pentobartital (20-25 mg/kg initially and 2-4 mg/kg every 2 h thereafer), or initially anesthetized with sodium pentothal (20 mg/kg) and placed on nitrous oxide (70% N2O-30% 02) for 5-51/2 h under normoxic, normocapnic conditions. In comparison with the awake, unrestrained state, both anesthetics caused a significant metabolic acidosis in both plasma and cisternal CSF. No significant differences between anesthetics were found with: (1) acid-base status in plasma or brain ECF and ICF; (2) cerebral tissue energy charge potential; or (3) creatine and phosphocreatine levels and the creatine to phosphocreatine ratios. No differences were found in the ATP to ADP ratios, but lactate to pyruvate ratios were significantly lower. Within pentobarbital anesthesia, citrate levels were higher, while other TCA metabolites measured were lower. Further, the citrate to alpha-ketoglutarate and malate to oxaloacetate ratios were significantly increased. We propose that pentobarbital anesthesia lowers metabolic activity in brain tissue and the primary site of 'crossover' inhibition is between citrate and alpha-ketoglutarate.

Brain energy metabolism in global brain oedema

Different degrees of severity in global brain oedema were induced by varying amounts of water intoxication (50, 100, 150, and 200 ml Aqua dest./kg b.wt. intravenously) in groups of six cats, which were functionally nephrectomized. Animals loaded with physiological saline and sham-operated served as controls. Two hours following the water load, the tissue concentrations of CrP, ATP, ADP, AMP, pyruvate, glucose, and lactate were determined by optical enzymatic analysis. The results show disturbances in brain energy metabolism dependent on the severity of the brain oedema. The high energy compounds and in consequence the ATP/ADP-ratio, and respectively the energy charge potential, fall in direct relationship to the severity of the brain oedema. Lactate and lactate-pyruvate ratio increase. The energy source of the cell, glucose as well as pyruvate, significantly falls in the group with severe brain oedema. The results of the brain energy metabolism were compared with our previous study concerning the brain water content, rCBF and CPP in global brain oedema (Meinig et al. 1973). The results show that the disturbances of energy metabolism are directly related to the rCBF and are not dependent on CPP over a wide range.

Cerebrospinal fluid acid-base status and lactate and pyruvate concentrations after short (less than 30 minutes) first febrile convulsions in children

Twenty-nine infants and children with short (less than 30 minutes) first febrile convulsions were studied between 3 and 22 hours after convulsive episodes. Arterial and CSF acid-base variables, lactate and pyruvate concentrations, and lactate/pyruvate ratios were measured. Biochemical signs of cerebral hypoxia were found in only 2 patients, one of whom had short, repeated convulsions. Our findings indicate that hypoxic damage is unlikely to result from a short-duration febrile convulsion.

A case of industrial carbon dioxide poisoning

A case of poisoning by carbon dioxide from an overhead fire-extinguishing apparatus is reported, and the subsequent rapid reversal of blood-gas and acid-base changes during the recovery phase described. A possible explanation of these changes is discussed.

Cerebrospinal fluid lactate and lactate/pyruvate ratios in hydrocephalus

Cerebral metabolism in 21 hydrocephalic patients was studied. Preoperative and postoperative specimens of cerebrospinal fluid (CSF) were obtained and the cerebral perfusion pressure (CPP) was calculated in each instance. The specimens of CSF were analyzed for lactate and pyruvate and the lactate/pyruvate (L/P) ratio was calculated for each sample. The L/P ratio, which reflects the redox state of the cell, was used to determine the extent of anaerobic metabolism. An inverse relationship was noted between CPP and lactate as well as the L/P ratio. In general, the level of anaerobic metabolism was decreased after insertion of a shunt.

Lactate and pyruvate concentrations, and acid-base balance of cerebrospinal fluid in experimentally induced intracerebral and subarachnoid hemorrhage in dogs

The effect of blood injected into either subarachnoid space or subcortical brain tissue upon lactate and pyruvate concentrations as well as acid-base balance of cerebrospinal fluid (CSF) was studied in the anesthetized dog. CSF lactate and lactate/pyruvate ratio (L/P ratio) increased progressively following the intracranial injection of blood and reached the maximum level at six hours after injection. These changes were significantly greater in animals with intracerebral hematoma than in those with subarachnoid hemorrhage (SAH). An increase in CSF lactate and L/P ratio in hemorrhagic CSF seems to be caused by two different factors. Shed blood cells per se produce lactate and pyruvate, and blood in the subarachnoid space and intracerebral hematomas cause secondary changes in brain tissue metabolism by a probable reduction of cerebral blood flow. Therefore, an increase in CSF lactate with a concomitant rise in CSF L/P ratio is a useful indicator for brain tissue hypoxia, even when CSF is hemorrhagic. The association of an increase in CSF lactate to a disproportionate decrease in CSF HCO-3 was also observed in these animals.

Cerebrospinal fluid and arterial lactate, pyruvate and acid-base balance in patients with intracranial hemorrhages

Lactate and pyruvate concentrations and acid-base balance in cerebrospinal fluid (CSF) and arterial blood were determined in patients with intracranial hemorrhages (28 subarachnoid hemorrhages and 15 intracerebral hemorrhages). A greater increase in CSF lactate and lactate-pyruvate ratio (L/P ratio) was observed in patients with impairment of consciousness, focal neurological deficits, poor prognosis, or CSF pressures higher than 300 mm H2O. A combination of CSF lactate greater than 2.5 mM per liter, L/P ration above 20, bicarbonate less than 20.4 mEq per liter, pH below 7.276, or arterial PCO2 below 31.5 mm Hg seems to indicate poor prognosis from intracranial hemorrhage. The mechanism of hyperventilation in acute cerebrovascular diseases and of CSF pH regulation in acid-base disturbances was also discussed.

Ventricular fluid lactate, pyruvate, bicarbonate and ph in unconscious brain-injured patients subjected to controlled ventilation

In 35 unconscious patients suffering from traumatic brain injury and subjected to controlled hyperventilation within 12 hours of the acute trauma, we measured continuously the intraventricular pressure (IVP), ventricular fluid lactate, pyruvate, L/P ratio, pH and bicarbonate during the first 4 posttraumatic days, and related the findings to the clinical course. In patients in whom the follow-up study did not reveal severe mental impairment or dementia, the ventricular fluid lactate never exceeded 4 mmol/litre. In this group, the IVP level never exceeded 40 mmHg/hour, and the mean pressure/day never exceeded 20 mmHg. In half of the patients in whom dementia, vegetative survival or death occurred, ventricular fluid lactate exceeded 4 mmol/litre; the IVP level/hour exceeded 40 mmHg in two of 23 patients, and the mean pressure/day exceeded 20 mmHg in nine of 23 patients. The prognostic value of pyruvate was of less importance, although a significant increase in patients with a poor outcome was seen. No prognostic conclusions could be drawn from ventricular fluid, L/P ratio, pH and bicarbonate.

Effect of experimental pneumococcal meningitis on respiration and circulation in the rabbit

Pathophysiological studies in bacterial meningitis in man have been limited by clinical variability and the necessity for immediate therapy. After the development of a reliable animal model of pneumococcal meningitis, we studied respiration and circulation in 25 anesthetized New Zealand white rabbits during untreated pneumococcal meningitis and in 33 healthy controls. In meningitis, we found increased lactic acid in cerebrospinal fluid (CSF). Increased ventilation, perhaps due to CSF lactic acid accumulation, resulted in respiratory alkalosis; the concomitant lowering of Pco(2) acted as a homeostatic mechanism to restore pH toward normality in the CSF. Hyperventilation increased with the duration of the illness. Cardiac output was also increased with decreased peripheral vascular resistance but with only slight reduction in mean systemic and pulmonary arterial pressures. In the final hour of life, peripheral vascular resistance fell further; ventilation declined and then abruptly ceased while cardiac activity continued. Lactic acid accumulation in the CSF, found in both experimental and human pneumococcal meningitis, may cause the hyperventilation found in this disease and may contribute to death.

Energy state and glycolysis in human cerebral edema

✓ A new freeze-stop device using a liquid nitrogen reservoir and an automatic biopsy mechanism has been developed, suitable for rapid, sterile, and standardized sampling of cerebral tissue in man. In animal experiments a 200 mg piece of cerebral cortex was cooled from a room temperature of 18°C to −40°C within 7 sec which is twice as fast as when it was immersed in liquid N2. The method was then applied to metabolic tissue studies of perifocal edematous cortex from patients undergoing neurosurgery for intracranial tumors. Energy-rich phosphate compounds or parameters of the energy state were found to be less affected in this type of brain edema than the glycolytic activity which was markedly enhanced, indicated by lactic and pyruvic acid determinations. The tissue water content correlated closely with the lactic acid concentration, and very little with measurements of the energy state such as the energy charge potential or the adenosinetriphosphate-adenosinediphosphate (ATP/ADP) ratio. It is suggested that in perifocal brain edema increased levels of lactic acid are associated with mechanisms leading to an increased water uptake.