Mild hypercapnia improves brain tissue oxygen tension but not diffusion limitation in asphyxial cardiac arrest: an experimental study in pigs

Monitoring of Brain Tissue Oxygen Tension in Cardiac Arrest: a Translational Systematic Review from Experimental to Clinical Evidence

BACKGROUND

Cardiac arrest (CA) is a sudden event that is often characterized by hypoxic-ischemic brain injury (HIBI), leading to significant mortality and long-term disability. Brain tissue oxygenation (PbtO2) is an invasive tool for monitoring brain oxygen tension, but it is not routinely used in patients with CA because of the invasiveness and the absence of high-quality data on its effect on outcome. We conducted a systematic review of experimental and clinical evidence to understand the role of PbtO2 in monitoring brain oxygenation in HIBI after CA and the effect of targeted PbtO2 therapy on outcomes.

METHODS

The search was conducted using four search engines (PubMed, Scopus, Embase, and Cochrane), using the Boolean operator to combine mesh terms such as PbtO2, CA, and HIBI.

RESULTS

Among 1,077 records, 22 studies were included (16 experimental studies and six clinical studies). In experimental studies, PbtO2 was mainly adopted to assess the impact of gas exchanges, drugs, or systemic maneuvers on brain oxygenation. In human studies, PbtO2 was rarely used to monitor the brain oxygen tension in patients with CA and HIBI. PbtO2 values had no clear association with patients' outcomes, but in the experimental studies, brain tissue hypoxia was associated with increased inflammation and neuronal damage.

CONCLUSIONS

Further studies are needed to validate the effect and the threshold of PbtO2 associated with outcome in patients with CA, as well as to understand the physiological mechanisms influencing PbtO2 induced by gas exchanges, drug administration, and changes in body positioning after CA.

Cerebral monitoring in a pig model of cardiac arrest with 48 h of intensive care

Background

Neurological injury is the primary cause of death after out-of-hospital cardiac arrest. There is a lack of studies investigating cerebral injury beyond the immediate post-resuscitation phase in a controlled cardiac arrest experimental setting.

Methods

The aim of this study was to investigate temporal changes in measures of cerebral injury and metabolism in a cardiac arrest pig model with clinically relevant post-cardiac arrest intensive care. A cardiac arrest group (n = 11) underwent 7 min of no-flow and was compared with a sham group (n = 6). Pigs underwent intensive care with 24 h of hypothermia at 33 °C. Blood markers of cerebral injury, cerebral microdialysis, and intracranial pressure (ICP) were measured. After 48 h, pigs underwent a cerebral MRI scan. Data are presented as median [25th; 75th percentiles].

Results

Return of spontaneous circulation was achieved in 7/11 pigs. Time to ROSC was 4.4 min [4.2; 10.9]. Both NSE and NfL increased over time (p < 0.001), and were higher in the cardiac arrest group at 48 h (NSE 4.2 µg/L [2.4; 6.1] vs 0.9 [0.7; 0.9], p < 0.001; NfL 63 ng/L [35; 232] vs 29 [21; 34], p = 0.02). There was no difference in ICP at 48 h (17 mmHg [14; 24] vs 18 [13; 20], p = 0.44). The cerebral lactate/pyruvate ratio had secondary surges in 3/7 cardiac arrest pigs after successful resuscitation. Apparent diffusion coefficient was lower in the cardiac arrest group in white matter cortex (689 × 10^–6 mm²/s [524; 765] vs 800 [799; 815], p = 0.04) and hippocampus (854 [834; 910] vs 1049 [964; 1180], p = 0.03). N-Acetylaspartate was lower on MR spectroscopy in the cardiac arrest group (− 17.2 log [− 17.4; − 17.0] vs − 16.9 [− 16.9; − 16.9], p = 0.03).

Conclusions

We have developed a clinically relevant cardiac arrest pig model that displays cerebral injury as marked by NSE and NfL elevations, signs of cerebral oedema, and reduced neuron viability. Overall, the burden of elevated ICP was low in the cardiac arrest group. A subset of pigs undergoing cardiac arrest had persisting metabolic disturbances after successful resuscitation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-022-00475-2.

Different Stratification of Physiological Factors Affecting Cerebral Perfusion Pressure in Hypoxic-Ischemic Brain Injury after Cardiac Arrest According to Visible or Non-Visible Primary Brain Injury: A Retrospective Observational Study

We aimed to explore the stratification of physiological factors affecting cerebral perfusion pressure, including arterial oxygen tension, arterial carbon dioxide tension, mean arterial pressure, intracranial pressure (ICP), and blood-brain barrier (BBB) status, with respect to primary or secondary brain injury (PBI or SBI) after out-of-hospital cardiac arrest (OHCA). Among the retrospectively enrolled 97 comatose OHCA survivors undergoing post-cardiac arrest (PCA) care, 46 (47.4%) with already established PBI (high signal intensity (HSI) on diffusion-weighted imaging (DWI) had higher ICP (p = 0.02) and poorer BBB status (p < 0.01) than the non-HSI group. On subgroup analysis within the non-HSI group to exclude the confounding effect of already established PBI, 40 (78.4%) patients with good neurological outcomes had lower ICP at 24 h (11.0 vs. 16.0 mmHg, p < 0.01) and more stable BBB status (p = 0.17 in pairwise comparison) compared to those with poor neurological outcomes, despite the non-significant differences in other physiological factors. OHCA survivors with HSI on DWI showed significantly higher ICP and poorer BBB status at baseline before PCA care than those without HSI. Despite the negative DWI findings before PCA care, OHCA survivors have a cerebral penumbra at risk for potentially leading the poor neurological outcome from unsuppressed SBI, which may be associated with increased ICP and BBB permeability.

Effect of Epinephrine Administered during Cardiopulmonary Resuscitation on Cerebral Oxygenation after Restoration of Spontaneous Circulation in a Swine Model with a Clinically Relevant Duration of Untreated Cardiac Arrest

Severe neurological impairment was more prevalent in cardiac arrest survivors who were administered epinephrine than in those administered placebo in a randomized clinical trial; short-term reduction of brain tissue O2 tension (PbtO2) after epinephrine administration in swine following a short duration of untreated cardiac arrest has also been reported. We investigated the effects of epinephrine administered during cardiopulmonary resuscitation (CPR) on cerebral oxygenation after restoration of spontaneous circulation (ROSC) in a swine model with a clinically relevant duration of untreated cardiac arrest. After 7 min of ventricular fibrillation, 24 pigs randomly received either epinephrine or saline placebo during CPR. Parietal cortex measurements during 60-min post-resuscitation period showed that the area under the curve (AUC) for PbtO2 was smaller in the epinephrine group than in the placebo group during the initial 10-min period and subsequent 50-min period (both p < 0.05). The AUC for number of perfused cerebral capillaries was smaller in the epinephrine group during the initial 10-min period (p = 0.005), but not during the subsequent 50-min period. In conclusion, epinephrine administered during CPR reduced PbtO2 for longer than 10 min following ROSC in a swine model with a clinically relevant duration of untreated cardiac arrest.

The effect of mild hypercapnia on hospital mortality after cardiac arrest may be modified by chronic obstructive pulmonary disease

BACKGROUND

The main objective was to evaluate the effect of carbon dioxide on hospital mortality in chronic obstructive pulmonary disease (COPD) and non-COPD patients with out-of-hospital cardiac arrest (OHCA).

METHODS

We conducted a retrospective observational study in OHCA patients from the eICU database (eicu-crd.mit.edu). The main exposure was the partial pressure of arterial carbon dioxide (PaCO₂). The proportion of time spent (PTS) within four predefined PaCO₂ ranges (hypocapnia: <35 mmHg, normocapnia: 35-45 mmHg, mild hypercapnia: 46-55 mmHg, and severe hypercapnia: >55 mmHg) were calculated respectively. The primary outcome was hospital mortality. Multivariable logistic regression models were performed to assess the independent relationship between PTS within PaCO₂ range and hospital mortality, and the interaction between PTS within PaCO₂ range and COPD was explored.

RESULTS

A total of 1721 OHCA patients were included, of which 272 (15.8%) had COPD. After adjusted for the confounders, the PTS within mild hypercapnia was associated with lower odds ratio for hospital mortality in COPD patients (OR 0.923; 95% CI 0.857-0.992; P = 0.036); however, it was associated with higher odds ratio for hospital mortality in non-COPD patients (OR 1.053; 95% CI 1.012-1.097; P = 0.012; P_interaction = 0.008). The PTS within normocapnia was not associated with hospital mortality in COPD patients (OR 0.987; 95% CI 0.914-1.067; P = 0.739); however, it was associated with lower odds ratio for hospital mortality in non-COPD patients (OR 0.944; 95% CI 0.916-0.973; P < 0.001; P_interaction = 0.113).

CONCLUSIONS

The effect of carbon dioxide on hospital mortality differed between COPD and non-COPD patients. Mild hypercapnia was associated with increased hospital mortality for non-COPD patients but reduced hospital mortality for COPD patients. It would be reasonable to adjust PaCO₂ targets in OHCA patients with COPD.