Cerebral lactate uptake during cardiopulmonary resuscitation in humans

Negative central venous to arterial lactate gradient in patients receiving vasopressors is associated with higher ICU 30-day mortality: a retrospective cohort study

Background

Serum lactate has long been used to evaluate hypoxia and predict prognosis in critically ill patients, however, discrepancy in lactate measurements between different sites have not been recognized as a useful tool for monitoring hypoxia and evaluating outcome.

Methods

Data were obtained from the clinical information system of the intensive care unit (ICU) in a tertiary academic hospital for 1582 ICU patients with vasoactive drug requirement and valid paired blood gas. The mortality rates were compared between patients with sustained negative venous to arterial lactate gradient (VALac) and the others using the Cox proportional hazard model. Predictive factors associated with negative VALac were searched.

Results

A sustained negative VALac was significantly associated with higher 30 day ICU mortality [Adjusted hazard ratio (HR) = 2.31, 95% confidence interval (CI), 1.07–4.99; p = 0.032. Propensity score- weighted HR: 2.57; 95% CI, 1.17–5.64; p = 0.010]. Arterial lactate in the first blood gas pair, 24-h arterial lactate clearance, use of epinephrine, mean positive end-expiratory pressure level, and extracorporeal membrane oxygenation initiation showed statistically significant association with sustained negative VALac during the first 24 h.

Conclusion

The sustained negative VALac in the early stage of treatment may suggest additional information about tissue hypoxia than arterial lactate alone. Critical care physicians should pay more attention to the lactate discrepancy between different sites in their clinical practice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-021-01237-5.

Cerebrospinal Fluid Lactate Levels, Brain Lactate Metabolism and Neurologic Outcome in Patients with Out-of-Hospital Cardiac Arrest

BACKGROUND/OBJECTIVE

Cerebrospinal fluid (CSF) and serum lactate levels were assessed to predict poor neurologic outcome 3 months after return of spontaneous circulation (ROSC). We compared arterio-CSF differences in the lactate (ACDL) levels between two neurologic outcome groups.

METHODS

This retrospective observational study involved out-of-hospital cardiac arrest (OHCA) survivors who had undergone target temperature management. CSF and serum samples were obtained immediately (lactate₀), and at 24 (lactate₂₄), 48 (lactate₄₈), and 72 (lactate₇₂) h after ROSC, and ACDL was calculated at each time point. The primary outcome was poor 3-month neurologic outcome (cerebral performance categories 3-5).

RESULTS

Of 45 patients, 27 (60.0%) showed poor neurologic outcome. At each time point, CSF lactate levels were significantly higher in the poor neurologic outcome group than in the good neurologic outcome group (6.97 vs. 3.37, 4.20 vs. 2.10, 3.50 vs. 2.00, and 2.79 vs. 2.06, respectively; all P < 0.05). CSF lactate's prognostic performance was higher than serum lactate at each time point, and lactate₂₄ showed the highest AUC values (0.89, 95% confidence interval, 0.75-0.97). Over time, ACDL decreased from - 1.30 (- 2.70-0.77) to - 1.70 (- 3.2 to - 0.57) in the poor neurologic outcome group and increased from - 1.22 (- 2.42-0.32) to - 0.64 (- 2.31-0.15) in the good neurologic outcome group.

CONCLUSIONS

At each time point, CSF lactate showed better prognostic performance than serum lactate. CSF lactate₂₄ showed the highest prognostic performance for 3-month poor neurologic outcome. Over time, ACDL decreased in the poor neurologic outcome group and increased in the good neurologic outcome group.

Arterial blood gases during and their dynamic changes after cardiopulmonary resuscitation: A prospective clinical study

PURPOSE

An arterial blood gas analysis (ABG) yields important diagnostic information in the management of cardiac arrest. This study evaluated ABG samples obtained during out-of-hospital cardiopulmonary resuscitation (OHCPR) in the setting of a prospective multicenter trial. We aimed to clarify prospectively the ABG characteristics during OHCPR, potential prognostic parameters and the ABG dynamics after return of spontaneous circulation (ROSC).

METHODS

ABG samples were collected and instantly processed either under ongoing OHCPR performed according to current advanced life support guidelines or immediately after ROSC and data ware entered into a case report form along with standard CPR parameters.

RESULTS

During a 22-month observation period, 115 patients had an ABG analysis during OHCPR. In samples obtained under ongoing CPR, an acidosis was present in 98% of all cases, but was mostly of mixed hypercapnic and metabolic origin. Hypocapnia was present in only 6% of cases. There was a trend towards higher paO2 values in patients who reached sustained ROSC, and a multivariate regression analysis revealed age, initial rhythm, time from collapse to CPR initiation and the arterio-alveolar CO2 difference (AaDCO2) to be associated with sustained ROSC. ABG samples drawn immediately after ROSC demonstrated higher paO2 and unaltered pH and base excess levels compared with samples collected during ongoing CPR.

CONCLUSIONS

Our findings suggest that adequate ventilation and oxygenation deserve more research and clinical attention in the management of cardiac arrest and that oxygen uptake improves within minutes after ROSC. Hyperventilation resulting in arterial hypocapnia is not a major problem during OHCPR.

Neurochemical cascade of concussion

PRIMARY OBJECTIVE

The aim of this literature review was to systematically describe the sequential metabolic changes that occur following concussive injury, as well as identify and characterize the major concepts associated with the neurochemical cascade.

RESEARCH DESIGN

Narrative literature review.

CONCLUSIONS

Concussive injury initiates a complex cascade of pathophysiological changes that include hyper-acute ionic flux, indiscriminant excitatory neurotransmitter release, acute hyperglycolysis and sub-acute metabolic depression. Additionally, these metabolic changes can subsequently lead to impaired neurotransmission, alternate fuel usage and modifications in synaptic plasticity and protein expression. The combination of these metabolic alterations has been proposed to cause the transient and prolonged neurological deficits that typically characterize concussion. Consequently, understanding the implications of the neurochemical cascade may lead to treatment and return-to-play guidelines that can minimize the chronic effects of concussive injury.

Stability of cerebral metabolism and substrate availability in humans during hypoxia and hyperoxia

Marked elevations in brain blood flow with progressive hypoxaemia and related reductions in oxygen content resulted in a well-maintained oxygen delivery to the brain. As such, cerebral metabolism is still supported almost exclusively by carbohydrate oxidation during severe levels of hypoxaemia.

Plasma pH does not influence the cerebral metabolic ratio during maximal whole body exercise

Exercise lowers the cerebral metabolic ratio of O2 to carbohydrate (glucose+1/2 lactate) and metabolic acidosis appears to promote cerebral lactate uptake. However, the influence of pH on cerebral lactate uptake and, in turn, on the cerebral metabolic ratio during exercise is not known. Sodium bicarbonate (Bicarb, 1 M; 350-500 ml) or an equal volume of normal saline (Sal) was infused intravenously at a constant rate during a '2000 m' maximal ergometer row in six male oarsmen (23±2 years; mean±S.D.). During the Sal trial, pH decreased from 7.41±0.01 at rest to 7.02±0.02 but only to 7.36±0.02 (P <0.05) during the Bicarb trial. Arterial lactate increased to 21.4±0.8 and 32.7±2.3 mM during the Sal and Bicarb trials, respectively (P <0.05). Also, the arterial-jugular venous lactate difference increased from-0.03±0.01 mM at rest to 3.2±0.9 mM (P <0.05) and 3.4±1.4 mM (P <0.05) following the Sal and Bicarb trials, respectively. Accordingly, the cerebral metabolic ratio decreased equally during the Sal and Bicarb trials: from 5.8±0.6 at rest to 1.7±0.1 and 1.8±0.2, respectively. The enlarged blood-buffering capacity after infusion of Bicarb eliminated metabolic acidosis during maximal exercise but that did not affect the cerebral lactate uptake and, therefore, the decrease in the cerebral metabolic ratio.

Lactate kinetics in human tissues at rest and during exercise

Lactate production in skeletal muscle has now been studied for nearly two centuries and still its production and functional role at rest and during exercise is much debated. In the early days skeletal muscle was mainly seen as the site of lactate production during contraction and lactate production associated with a lack of muscle oxygenation and fatigue. Later it was recognized that skeletal muscle not only played an important role in lactate production but also in lactate clearance and this led to a renewed interest, not the least from the Copenhagen School in the 1930s, in the metabolic role of lactate in skeletal muscle. With the introduction of lactate isotopes muscle lactate kinetics and oxidation could be studied and a simultaneous lactate uptake and release was observed, not only in muscle but also in other tissues. Therefore, this review will discuss in vivo human: (1) skeletal muscle lactate metabolism at rest and during exercise and suggestions are put forward to explain the simultaneous lactate uptake and release; and (2) lactate metabolism in the heart, liver, kidneys, brain, adipose tissue and lungs will be discussed and its potential importance in these tissues.

Blood lactate is an important energy source for the human brain

Lactate is a potential energy source for the brain. The aim of this study was to establish whether systemic lactate is a brain energy source. We measured in vivo cerebral lactate kinetics and oxidation rates in 6 healthy individuals at rest with and without 90 mins of intravenous lactate infusion (36 mumol per kg bw per min), and during 30 mins of cycling exercise at 75% of maximal oxygen uptake while the lactate infusion continued to establish arterial lactate concentrations of 0.89+/-0.08, 3.9+/-0.3, and 6.9+/-1.3 mmol/L, respectively. At rest, cerebral lactate utilization changed from a net lactate release of 0.06+/-0.01 to an uptake of 0.16+/-0.07 mmol/min during lactate infusion, with a concomitant decrease in the net glucose uptake. During exercise, the net cerebral lactate uptake was further increased to 0.28+/-0.16 mmol/min. Most (13)C-label from cerebral [1-(13)C]lactate uptake was released as (13)CO(2) with 100%+/-24%, 86%+/-15%, and 87%+/-30% at rest with and without lactate infusion and during exercise, respectively. The contribution of systemic lactate to cerebral energy expenditure was 8%+/-2%, 19%+/-4%, and 27%+/-4% for the respective conditions. In conclusion, systemic lactate is taken up and oxidized by the human brain and is an important substrate for the brain both under basal and hyperlactatemic conditions.

Cerebral glucose and oxygen metabolism in patients with fulminant hepatic failure

Hyperammonemia and hyperventilation are consistent findings in patients with fulminant hepatic failure (FHF), which may interfere with cerebral glucose and oxygen metabolism. The aim of the present study is to evaluate whether cerebral oxidative metabolism is preserved early in the course of FHF and whether hyperventilation has an influence on this. We included 16 patients with FHF, 5 patients with cirrhosis of the liver, and 8 healthy subjects. Concomitant blood sampling from an arterial catheter and a catheter in the jugular bulb and measurement of cerebral blood flow by the xenon 133 wash-out technique allowed calculation of cerebral uptake of glucose (CMRgluc) and oxygen (CMRO2). Both CMRgluc and CMRO2 were reduced in patients with FHF compared with those with cirrhosis and healthy subjects, i.e., 11.8 +/- 2.7 v 18.3 +/- 5.5 and 28.5 +/- 6.6 micromol/100 g/min (P <.05) and 86 +/- 18 v 164 +/- 42 and 174 +/- 27 micromol/100 g/min (P <.05). Arteriovenous difference in oxygen and oxygen-glucose index were normal in patients with FHF. Institution of mechanical hyperventilation did not affect glucose and oxygen uptake and hyperventilation did not affect lactate-pyruvate ratio or lactate-oxygen index. In conclusion, we found that cerebral glucose and oxygen consumption are proportionally decreased in patients with FHF investigated before clinical signs of cerebral edema. Our data suggest that cerebral oxidative metabolism is retained at this stage of the disease without being compromised by hyperventilation.

A reduced cerebral metabolic ratio in exercise reflects metabolism and not accumulation of lactate within the human brain

During maximal exercise lactate taken up by the human brain contributes to reduce the cerebral metabolic ratio, O(2)/(glucose + 1/2 lactate), but it is not known whether the lactate is metabolized or if it accumulates in a distribution volume. In one experiment the cerebral arterio-venous differences (AV) for O(2), glucose (glc) and lactate (lac) were evaluated in nine healthy subjects at rest and during and after exercise to exhaustion. The cerebrospinal fluid (CSF) was drained through a lumbar puncture immediately after exercise, while control values were obtained from six other healthy young subjects. In a second experiment magnetic resonance spectroscopy ((1)H-MRS) was performed after exhaustive exercise to assess lactate levels in the brain (n = 5). Exercise increased the AV(O2) from 3.2 +/- 0.1 at rest to 3.5 +/- 0.2 mM (mean +/-s.e.m.; P < 0.05) and the AV(glc) from 0.6 +/- 0.0 to 0.9 +/- 0.1 mM (P < 0.01). Notably, the AV(lac) increased from 0.0 +/- 0.0 to 1.3 +/- 0.2 mm at the point of exhaustion (P < 0.01). Thus, maximal exercise reduced the cerebral metabolic ratio from 6.0 +/- 0.3 to 2.8 +/- 0.2 (P < 0.05) and it remained low during the early recovery. Despite this, the CSF concentration of lactate postexercise (1.2 +/- 0.1 mM; n= 7) was not different from baseline (1.4 +/- 0.1 mM; n= 6). Also, the (1)H-MRS signal from lactate obtained after exercise was smaller than the estimated detection limit of approximately 1.5 mM. The finding that an increase in lactate could not be detected in the CSF or within the brain rules out accumulation in a distribution volume and indicates that the lactate taken up by the brain is metabolized.

Energy dysfunction as a predictor of outcome after moderate or severe head injury: indices of oxygen, glucose, and lactate metabolism

The purpose of this study was to determine if the relationship between abnormalities in glucose, lactate, and oxygen metabolism were predictive of neurologic outcome after moderate or severe head injury, relative to other known prognostic factors. Serial assessments of the cerebral metabolic rates for glucose, lactate, and oxygen were performed using a modified Kety-Schmidt method. In total, 31 normal control subjects were studied once, and 49 TBI patients (mean age 36+/-16 years, median GCS 7) were studied five times median per patient from postinjury days 0 to 9. Univariate and multivariate analyses were performed. Univariate analysis showed that the 6-month postinjury Glasgow Outcome Scale (GOS) was most strongly associated with the mean cerebral metabolic rate of oxygen (CMRO2) (P = 0.0001), mean arterial lactate level (P = 0.0001), mean arterial glucose (P = 0.0008), mean cerebral blood flow (CBF), (P = 0.002), postresuscitation GCS (P = 0.003), and pupillary status (P = 0.004). Brain lactate uptake was observed in 44% of all metabolic studies, and 76% of patients had at least one episode of brain lactate uptake. By dichotomized GOS, patients achieving a favorable outcome (GOS 4-5) were distinguished from those with an unfavorable outcome (GOS1-3) by having a higher CMRO2 (P = 0.003), a higher rate of abnormal brain lactate uptake relative to arterial lactate levels (P = 0.04), and lesser degrees of blood-brain barrier damage based on CT findings (P = 0.03).

CONCLUSIONS

During the first 6 days after moderate or severe TBI, CMRO2 and arterial lactate levels are the strongest predictors of neurologic outcome. However, the frequent occurrence of abnormal brain lactate uptake despite only moderate elevations in arterial lactate levels in the favorable outcome patients suggests the brain's ability to use lactate as a fuel may be another key outcome predictor. Future studies are needed to determine to what degree nonglycolytic energy production from alternative fuels such as lactate occurs after TBI and whether alternative fuel administration is a viable therapy for TBI patients.

Lactate as a pivotal element in neuron-glia metabolic cooperation

Lactate has been considered for a long time as a metabolic waste and/or a sign of hypoxia in the central nervous system. Nevertheless, clear evidence that lactate can constitute an adequate energy substrate for brain tissue has been provided as early as in the 1950s with the pioneering work of McIlwain in brain slices. Over the years, several studies using different approaches have confirmed that lactate is efficiently oxidized by brain cells in vitro. Moreover, lactate has been shown under certain circumstances to have a neuroprotective effect and support neuronal activity. Similar confirmation of lactate utilization in vivo as well as putative neuroprotection in various excitotoxic models has been provided. Lactate was even shown to restore cognitive performance upon an hypoglycemic episode in humans. More recently, it was proposed that lactate could be produced by astrocytes and released in the extracellular space to form a pool readily available for neurons in case of high energy demands. Several elements support the concept of a lactate shuttle between astrocytes and neurons in the central nervous system. Among them, the description of specific monocarboxylate transporters found on both astrocytes and neurons is an important observation consistent with this concept. Interestingly, lactate shuttles between different cell types within the same organ have been described outside the central nervous system, notably in muscle and testis. Thus, lactate is emerging as a valuable intercellular exchange molecule in different systems including the brain where it might be an essential element of neuron-glia metabolic interactions.

Feeding active neurons: (re)emergence of a nursing role for astrocytes

Despite unquestionable evidence that glucose is the major energy substrate for the brain, data collected over several decades with different approaches suggest that lactate may represent a supplementary metabolic substrate for neurons. Starting with the pioneering work of McIlwain in the early 1950s which showed that lactate can sustain the respiratory rate of small brain tissue pieces, this idea receives confirmation with more recent studies using nuclear magnetic resonance spectroscopy undoubtedly demonstrating that lactate is efficiently oxidized by neurons, both in vitro and in vivo. Not only is lactate able to maintain ATP levels and promote neuronal survival but it was also found to support neuronal activity, at least if low levels of glucose are present. Despite the early suggestion for a role of astrocytes in metabolic supply to neurons, it is only recently however that they have been considered as a potential source of lactate for neurons. Moreover, it has been proposed that astrocytes might provide lactate to neurons in response to enhanced synaptic activity by a well-characterized mechanism involving glutamate uptake. The description of specific transporters for lactate on both astrocytes and neurons further suggest that there exist a coordinated mechanism of lactate exchange between the two cell types. Thus it is proposed that astrocytes play a nursing role toward neurons by providing lactate as an additional energy substrate especially during periods of enhanced synaptic activity. The importance of this metabolic cooperation within the central nervous system, although not unique if compared to other organs, still remains to be explored.

Lactate, glucose and O2 uptake in human brain during recovery from maximal exercise

The metabolic activity of the brain has not been evaluated during physical exercise. In six volunteers substrate uptake by the brain was determined during graded exercise and recovery from maximal exercise by measuring the arterial-internal jugular venous concentration differences(a-v differences). The a-v difference for lactate increased from 0.02 +/- 0.08 mmol l-1 at rest to 0.39 +/- 0. 13 mmol l-1 during exercise and remained positive during 30 min of recovery (P < 0.05). The a-v difference for glucose (0.55 +/- 0.06 mmol l-1 at rest) did not change significantly during exercise, but during the initial 5 min of recovery it increased to 0.83 +/- 0.10 mmol l-1 (P < 0.05). The O2 a-v difference at rest of 3.11 +/- 0.30 mmol l-1 remained stable during exercise, then increased during the initial 5 min of recovery (3.77 +/- 0.52 mmol l-1) and remained high during the subsequent 30 min recovery period (3.62 +/- 0.64 mmol l-1; P < 0.05). Thus the O2/glucose uptake ratio did not change during exercise (pre-exercise 5.95 +/- 0.68; post-exercise 6.02 +/- 1.39) but decreased to 4.93 +/- 0.99 during the initial 5 min of recovery (P < 0.05). When lactate uptake was included, the resting O2/carbohydrate uptake ratio of 5.84 +/- 0.73 was reduced to 4.42 +/- 0.25 during exercise and decreased further during the recovery phase (to 3.79 +/- 0.30; P < 0.05). In contrast, in the resting and immobilised rat, lactate infusion to a level similar to that obtained during maximal exercise in humans did not affect the a-v difference for lactate. The large carbohydrate uptake by the brain during recovery from maximal exercise suggests that brain glycogen metabolism is important in the transition from rest to exercise, since this would explain the significant post-exercise decrease in the O2/carbohydrate uptake ratio.

Mastering pediatric cardiopulmonary resuscitation

Premature and unexpected death, especially in children, is tragic and very unacceptable. Effective treatments for sudden death of pediatric patients continue to emerge. Modern cardiopulmonary resuscitation function began with the widespread introduction of closed-chest cardiac massage in 1960; however, despite 35 years of research and refinement, more than 90% of children who receive cardiopulmonary resuscitation do not survive. This article summarizes and expands on current treatment concepts for pediatric sudden death. Emphasis is placed on procedures and techniques that likely are accessible in most medical centers caring for critically ill and injured children.