Intracranial pressure and brain redox balance in rabbits

Hyperoxia for accidental hypothermia and increased mortality: a post-hoc analysis of a multicenter prospective observational study

BACKGROUND

Supraphysiologic oxygen administration causes unfavorable clinical outcomes in various diseases, including traumatic brain injury, post-cardiac arrest syndrome, and acute lung injury. Accidental hypothermia is a critical illness that reduces oxygen demands, and excessive oxygen is likely to emerge. This study aimed to determine whether hyperoxia would be associated with increased mortality in patients with accidental hypothermia.

METHODS

A post-hoc analysis of a nationwide multicenter prospective observational study (ICE-CRASH study) on patients with accidental hypothermia admitted in 2019-2022 was conducted. Adult patients without cardiac arrest whose core body temperature was < 32 °C and whose arterial partial pressure of oxygen (PaO₂) was measured at the emergency department were included. Hyperoxia was defined as a PaO₂ level of 300 mmHg or higher, and 28-day mortality was compared between patients with and without hyperoxia before rewarming. Inverse probability weighting (IPW) analyses with propensity scores were performed to adjust patient demographics, comorbidities, etiology and severity of hypothermia, hemodynamic status and laboratories on arrival, and institution characteristics. Subgroup analyses were conducted according to age, chronic cardiopulmonary diseases, hemodynamic instability, and severity of hypothermia.

RESULTS

Of the 338 patients who were eligible for the study, 65 had hyperoxia before rewarming. Patients with hyperoxia had a higher 28-day mortality rate than those without (25 (39.1%) vs. 51 (19.5%); odds ratio (OR) 2.65 (95% confidence interval 1.47-4.78); p < 0.001). IPW analyses with propensity scores revealed similar results (adjusted OR 1.65 (1.14-2.38); p = 0.008). Subgroup analyses showed that hyperoxia was harmful in the elderly and those with cardiopulmonary diseases and severe hypothermia below 28 °C, whereas hyperoxia exposure had no effect on mortality in patients with hemodynamic instability on hospital arrival.

CONCLUSIONS

Hyperoxia with PaO₂ levels of 300 mmHg or higher before initiating rewarming was associated with increased 28-day mortality in patients with accidental hypothermia. The amount of oxygen to administer to patients with accidental hypothermia should be carefully determined.

TRIAL REGISTRATION

The ICE-CRASH study was registered at the University Hospital Medical Information Network Clinical Trial Registry on April 1, 2019 (UMIN-CTR ID, UMIN000036132).

Hyperoxemia during resuscitation of trauma patients and increased intensive care unit length of stay: inverse probability of treatment weighting analysis

Background

Information on hyperoxemia among patients with trauma has been limited, other than traumatic brain injuries. This study aimed to elucidate whether hyperoxemia during resuscitation of patients with trauma was associated with unfavorable outcomes.

Methods

A post hoc analysis of a prospective observational study was carried out at 39 tertiary hospitals in 2016–2018 in adult patients with trauma and injury severity score (ISS) of > 15. Hyperoxemia during resuscitation was defined as PaO₂ of ≥ 300 mmHg on hospital arrival and/or 3 h after arrival. Intensive care unit (ICU)-free days were compared between patients with and without hyperoxemia. An inverse probability of treatment weighting (IPW) analysis was conducted to adjust patient characteristics including age, injury mechanism, comorbidities, vital signs on presentation, chest injury severity, and ISS. Analyses were stratified with intubation status at the emergency department (ED). The association between biomarkers and ICU length of stay were then analyzed with multivariate models.

Results

Among 295 severely injured trauma patients registered, 240 were eligible for analysis. Patients in the hyperoxemia group (n = 58) had shorter ICU-free days than those in the non-hyperoxemia group [17 (10–21) vs 23 (16–26), p < 0.001]. IPW analysis revealed the association between hyperoxemia and prolonged ICU stay among patients not intubated at the ED [ICU-free days = 16 (12–22) vs 23 (19–26), p = 0.004], but not among those intubated at the ED [18 (9–20) vs 15 (8–23), p = 0.777]. In the hyperoxemia group, high inflammatory markers such as soluble RAGE and HMGB-1, as well as low lung-protective proteins such as surfactant protein D and Clara cell secretory protein, were associated with prolonged ICU stay.

Conclusions

Hyperoxemia until 3 h after hospital arrival was associated with prolonged ICU stay among severely injured trauma patients not intubated at the ED.

Trial registration

UMIN-CTR, UMIN000019588. Registered on November 15, 2015.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13017-021-00363-2.

Neuroendoscopic surgery in empty ventricular system under continuous gas infusion experimental study of pressure changes and complications

INTRODUCTION

The most important limitations to endoscopic procedures in the ventricular system of the brain are due to the constraint of working inside a fluid. The evacuation of cerebrospinal fluid (CSF) from the ventricles is performed often in microsurgical interventions using a surgical microscope. This study aimed at studying the evacuation of CSF during neuroendoscopic surgery in animals while infusing gas to avoid ventricular collapse.

MATERIALS AND METHODS

Hydrocephalus was provoked in five adult New Zealand rabbits by intracisternal injection of kaolin. Endoscopic intervention was performed later; fluid was given as a continuous infusion at constant speed into the CSF for 3 min. In the next stage, CSF was evacuated from the ventricles, which were infused with gas at a stable rate for the same amount of time. The intracranial pressure (ICP) of the rabbits was recorded during both operations. The animals were sacrificed and the brain subjected to pathology examination at the end of the experiment.

RESULTS

Mean ICP value in the rabbit ventricle was 19.1 while working in CSF and 17.6 when working in air. The difference by a paired test was statistically significant for each individual rabbit except one. The ICP measurement, however, was never lower than the ambient pressure, even while working in continuous gas infusion. No epidural or subdural hematomas were found at autopsy.

CONCLUSIONS

Endoscopic surgery is feasible in a ventricular system that has been insufflated with gas after CSF has been evacuated. During the experiment, however, steadily diminishing ICP values were measured. As a result, new devices, such as small-flow insufflators able to perform sensitive pressure adjustments are needed.

Lack of improvement in cerebral metabolism after hyperoxia in severe head injury: a microdialysis study

OBJECT

The authors investigated the effects of hyperoxia on brain tissue PO2 and on glucose metabolism in cerebral and adipose tissue after traumatic brain injury (TBI).

METHODS

After 3 hours of ventilation with pure O2, 18 tests were performed on different days in eight comatose patients with TBI. Lactate, pyruvate, glucose, glutamate, and brain tissue PO2 were measured in the cerebral extracellular fluid (ECF) by using microdialysis. Analytes were also measured in the ECF of abdominal adipose tissue. After 3 hours of increase in the fraction of inspired O2, brain tissue PO2 rose from the baseline value of 32.7 +/- 18 to 122.6 +/- 45.2 mm Hg (p < 0.0001), whereas brain lactate dropped from its baseline (3.21 +/- 2.77 mmol/L), reaching its lowest value (2.90 +/- 2.58 mmol/L) after 3 hours of hyperoxia (p < 0.01). Pyruvate dropped as well, from 153 +/- 56 to 141 +/- 56 micromol/L (p < 0.05), so the lactate/pyruvate ratio did not change. No significant changes were observed in glucose and glutamate. The arteriovenous difference in O2 content dropped, although not significantly, from a baseline of 4.52 +/- 1.22 to 4.15 +/- 0.76 m/100 ml. The mean concentration of lactate in adipose tissue fell significantly as well (p < 0.01), but the lactate/pyruvate ratio did not change.

CONCLUSIONS

Hyperoxia slightly reduced lactate levels in brain tissue after TBI. The estimated redox status of the cells, however, did not change and cerebral O2 extraction seemed to be reduced. These data indicate that oxidation of glucose was not improved by hyperoxia in cerebral and adipose tissue, and might even be impaired.

Effects of elevated ICP on brain function: can the multiparametric monitoring system detect the 'Cushing Response'?

The 'Cushing Response' is a significant phenomenon associated with elevated ICP. The purpose of our study was to examine the effects of the intracranial hypertension level and duration on the cerebral tissue physiology, using a Multiprobe assembly (MPA). The parameters monitored simultaneously included ICP, CBF, mitochondrial NADH redox state, extracellular K+ and H+ levels, DC potential and ECoG, calculated CPP and blood pressure. Two groups of rats were used. In one group, ICP was elevated to 50-60 mmHg for 13-15 min and, in the second group, ICP was elevated to 20 mmHg for 30 min. The results show that ICP of 50-60 mmHg led to CPP reduction below the lower limits of autoregulation. However, ICP of 20 mmHg, even for a prolonged period of time is completely tolerated. Additionally, we found that the 'Cushing Response', developed in the moderate treatment (ICP = 20 mmHg) is beneficial, assuring high CBF levels under intracranial hypertension. Furthermore, CBF and CPP monitoring, apparently, are not sufficient for autoregulation assessment; more parameters are needed.

[Biomechanics and intracranial hypertension]

Biomechanics can be defined as the physical concepts exploring the effects of mechanical forces in biology. Biomechanics explores the consequences of an alteration in the steady-state normally existing between living tissues and their immediate environment. The application of this science in the field of brain physiopathology and intracranial hypertension is essential to understanding the sequence of events triggered during an alteration of the intracranial volume such as observed with intracranial pathologies. Furthermore, biomechanics allows the development of a logical and rational therapeutic approach, better adapted to the various intracerebral problems anaesthesiologists might be confronted with.

Transcranial Doppler sonography: nitrous oxide and cerebral blood flow velocity in children

To determine the effect of nitrous oxide (N2O) on cerebral blood flow velocity (CBFV) and cerebrovascular resistance index (RI+) in children, ten ASA physical status I or II patients aged one to eight years old, scheduled for urological procedures, were studied. Anaesthesia was induced with thiopentone 2 mg.kg-1, fentanyl 5 micrograms.kg-1 and diazepam 0.3 mg.kg-1. Muscular relaxation was ensured by using vecuronium 0.1 mg.kg-1. After tracheal intubation, anaesthesia was randomly assigned to either a mixture of air in oxygen (N2/O2) or 70% N2O in oxygen (N2O/O2) producing an FIO2 of 30%. Three sets of measurements of CBFV and RI+ were made with both gas mixtures. The CBFV and RI+ were measured in the middle cerebral artery (MCA) with a transcranial Doppler monitor. Measurements were made while using the initial gas mixture, then the second gas mixture was administered, and finally, the patient again was given the initial gas mixture. A continuous caudal epidural or lumbar epidural block was performed before skin incision. Neuromuscular blockade was maintained with vecuronium 0.05 mg.kg-1. Temperature, heart rate, end-tidal CO2, arterial oxygen saturation, haematocrit and arterial blood pressure were maintained constant. Ventilation was adjusted to achieve normocapnia. The CBFV increased when 70% N2/O2 was replaced by 70% N2O/O2 (P less than 0.05) while the CBFV decreased when 70% N2/O2 was readministered (P less than 0.05). Likewise, the CBFV decreased when 70% N2O/O2 was replaced by 70% N2/O2 (P less than 0.05) while the CBFV increased when 70% N2O/O2 was readministered (P less than 0.05).