Hyperventilation in Severe Traumatic Brain Injury Has Something Changed in the Last Decade or Uncertainty Continues? A Brief Review

Short-term mild hyperventilation on intracranial pressure, cerebral autoregulation, and oxygenation in acute brain injury patients: a prospective observational study

Current guidelines suggest a target of partial pressure of carbon dioxide (PaCO2) of 32-35 mmHg (mild hypocapnia) as tier 2 for the management of intracranial hypertension. However, the effects of mild hyperventilation on cerebrovascular dynamics are not completely elucidated. The aim of this study is to evaluate the changes of intracranial pressure (ICP), cerebral autoregulation (measured through pressure reactivity index, PRx), and regional cerebral oxygenation (rSO2) parameters before and after induction of mild hyperventilation. Single center, observational study including patients with acute brain injury (ABI) admitted to the intensive care unit undergoing multimodal neuromonitoring and requiring titration of PaCO2 values to mild hypocapnia as tier 2 for the management of intracranial hypertension. Twenty-five patients were included in this study (40% female), median age 64.7 years (Interquartile Range, IQR = 45.9-73.2). Median Glasgow Coma Scale was 6 (IQR = 3-11). After mild hyperventilation, PaCO2 values decreased (from 42 (39-44) to 34 (32-34) mmHg, p < 0.0001), ICP and PRx significantly decreased (from 25.4 (24.1-26.4) to 17.5 (16-21.2) mmHg, p < 0.0001, and from 0.32 (0.1-0.52) to 0.12 (-0.03-0.23), p < 0.0001). rSO2 was statistically but not clinically significantly reduced (from 60% (56-64) to 59% (54-61), p < 0.0001), but the arterial component of rSO2 (ΔO2Hbi, changes in concentration of oxygenated hemoglobin of the total rSO2) decreased from 3.83 (3-6.2) μM.cm to 1.6 (0.5-3.1) μM.cm, p = 0.0001. Mild hyperventilation can reduce ICP and improve cerebral autoregulation, with minimal clinical effects on cerebral oxygenation. However, the arterial component of rSO2 was importantly reduced. Multimodal neuromonitoring is essential when titrating PaCO2 values for ICP management.

Prevalence of secondary insults and outcomes of patients with traumatic brain injury intubated in the prehospital setting: a retrospective cohort study

BACKGROUND

Prehospital neuroprotective strategies aim to prevent secondary insults (SIs) in traumatic brain injury (TBI). This includes haemodynamic optimisation in addition to oxygenation and ventilation targets achieved through rapid sequence intubation (RSI).The primary aim was to report the incidence and prevalence of SIs (prolonged hypotension, prolonged hypoxia and hyperventilation) and outcomes of patients with TBI who were intubated in the prehospital setting.

METHODS

A retrospective cohort study of adult patients with TBI who underwent RSI by a metropolitan road-based service in South-East Queensland, Australia between 1 January 2017 and 31 December 2020. Patients were divided into two cohorts based on the presence or absence of any SI sustained. Prolonged SIs were defined as occurring for ≥5 min. The association between SIs and mortality was examined in multivariable logistic regression and reported with adjusted ORs (aORs) and 95% CIs.

RESULTS

277 patients were included for analysis. Median 'Head' Abbreviated Injury Scale and Injury Severity Score were 4 (IQR: 3-5) and 26 (IQR: 17-34), respectively. Most episodes of prolonged hypotension and prolonged hypoxia were detected with the first patient contact on scene. Overall, 28-day mortality was 26%. Patients who sustained any SI had a higher mortality than those sustaining no SI (34.9% vs 14.7%, p<0.001). Prolonged hypoxia was an independent predictor of mortality (aOR 4.86 (95% CI 1.65 to 15.61)) but not prolonged hypotension (aOR 1.45 (95% CI 0.5 to 4.25)) or an end-tidal carbon dioxide <30 mm Hg on hospital arrival (aOR 1.28 (95% CI 0.5 to 3.21)).

CONCLUSION

SIs were common in the early phase of prehospital care. The association of prolonged hypoxia and mortality in TBI is potentially more significant than previously recognised, and if corrected early, may improve outcomes. There may be a greater role for bystander intervention in prevention of early hypoxic insult in TBI.

Plasma anion gap and risk of in-hospital mortality in patients with spontaneous subarachnoid hemorrhage

Background

The association between the serum anion gap (AG) and prognosis of patients with spontaneous subarachnoid hemorrhage (SAH) remains unknown. Thus, this study aimed to explore the association between AG levels and mortality in patients with SAH in the intensive care unit (ICU).

Methods

This was a retrospective analysis of data stored in the Medical Information Mart for Intensive Care–IV and eICU Collaborative Research databases. Critically ill patients diagnosed with spontaneous SAH were included. The primary outcome measure was in-hospital all-cause mortality. A multivariate Cox proportional hazards regression model and a restricted cubic spline were used to evaluate the relationship between AG concentration and outcomes. Kaplan–Meier curves were used to compare cumulative survival among patients with AG levels.

Results

A total of 1,114 patients were enrolled. AG concentration was significantly associated with in-hospital all-cause mortality [hazard ratio ([HR], 1.076 (95% confidence interval (CI), 1.021–1.292; p = 0.006)]. The risk of mortality was higher in the Category 2 group (AG ≥10 mmol/L and <13 mmol/L; HR, 1.961; 95% CI, 1.157–3.324; p = 0.0) and the Category 3 group (AG ≥13 mmol/L; HR, 2.151; 95% CI, 1.198–3.864; p = 0.010) than in the Category 1 group (AG < 10 mmol/L). Cumulative survival rates were significantly lower in patients with higher AG levels (log-rank p < 0.001).

Conclusions

In-hospital and ICU mortalities increase with increasing AG concentration in patients with SAH. An increased serum AG level is an independent, significant, and robust predictor of all-cause mortality. Thus, serum AG levels may be used in the risk stratification of SAH.

Second- and Third-Tier Therapies for Severe Traumatic Brain Injury

Intracranial hypertension is a common finding in patients with severe traumatic brain injury. These patients need treatment in the intensive care unit, where intracranial pressure monitoring and, whenever possible, multimodal neuromonitoring can be applied. A three-tier approach is suggested in current recommendations, in which higher-tier therapies have more significant side effects. In this review, we explain the rationale for this approach, and analyze the benefits and risks of each therapeutic modality. Finally, we discuss, based on the most recent recommendations, how this approach can be adapted in low- and middle-income countries, where available resources are limited.

Optimal Targets of the First 24-h Partial Pressure of Carbon Dioxide in Patients with Cerebral Injury: Data from the MIMIC-III and IV Database

BACKGROUND

It is generally believed that hypercapnia and hypocapnia will cause secondary injury to patients with craniocerebral diseases, but a small number of studies have shown that they may have potential benefits. We assessed the impact of partial pressure of arterial carbon dioxide (PaCO₂) on in-hospital mortality of patients with craniocerebral diseases. The hypothesis of this research was that there is a nonlinear correlation between PaCO₂ and in-hospital mortality in patients with craniocerebral diseases and that mortality rate is the lowest when PaCO₂ is in a normal range.

METHODS

We identified patients with craniocerebral diseases from Medical Information Mart for Intensive Care third and fourth edition databases. Cox regression analysis and restricted cubic splines were used to examine the association between PaCO₂ and in-hospital mortality.

RESULTS

Nine thousand six hundred and sixty patients were identified. A U-shaped association was found between the first 24-h PaCO₂ and in-hospital mortality in all participants. The nadir for in-hospital mortality risk was estimated to be at 39.5 mm Hg (p for nonlinearity < 0.001). In the subsequent subgroup analysis, similar results were found in patients with traumatic brain injury, metabolic or toxic encephalopathy, subarachnoid hemorrhage, cerebral infarction, and other encephalopathies. Besides, the mortality risk reached a nadir at PaCO₂ in the range of 35-45 mm Hg. The restricted cubic splines showed a U-shaped association between the first 24-h PaCO₂ and in-hospital mortality in patients with other intracerebral hemorrhage and cerebral tumor. Nonetheless, nonlinearity tests were not statistically significant. In addition, Cox regression analysis showed that PaCO₂ ranging 35-45 mm Hg had the lowest death risk in most patients. For patients with hypoxic-ischemic encephalopathy and intracranial infections, the first 24-h PaCO₂ and in-hospital mortality did not seem to be correlated.

CONCLUSIONS

Both hypercapnia and hypocapnia are harmful to most patients with craniocerebral diseases. Keeping the first 24-h PaCO₂ in the normal range (35-45 mm Hg) is associated with lower death risk.