Effect of mild hypothermia on cerebral microcirculation in a murine cardiopulmonary resuscitation model

The Effects of Temperature Management on Brain Microcirculation, Oxygenation and Metabolism

Purpose: Target temperature management (TTM) is often used in patients after cardiac arrest, but the effects of cooling on cerebral microcirculation, oxygenation and metabolism are poorly understood. We studied the time course of these variables in a healthy swine model.Methods: Fifteen invasively monitored, mechanically ventilated pigs were allocated to sham procedure (normothermia, NT; n = 5), cooling (hypothermia, HT, n = 5) or cooling with controlled oxygenation (HT-Oxy, n = 5). Cooling was induced by cold intravenous saline infusion, ice packs and nasal cooling to achieve a body temperature of 33–35 °C. After 6 h, animals were rewarmed to baseline temperature (within 5 h). The cerebral microvascular network was evaluated (at baseline and 2, 7 and 12 h thereafter) using sidestream dark-field (SDF) video-microscopy. Cerebral blood flow (laser Doppler MNP100XP, Oxyflow, Oxford Optronix, Oxford, UK), oxygenation (PbtO₂, Licox catheter, Integra Lifesciences, USA) and lactate/pyruvate ratio (LPR) using brain microdialysis (CMA, Stockholm, Sweden) were measured hourly. Results: In HT animals, cerebral functional capillary density (FCD) and proportion of small-perfused vessels (PSPV) significantly decreased over time during the cooling phase; concomitantly, PbtO₂ increased and LPR decreased. After rewarming, all microcirculatory variables returned to normal values, except LPR, which increased during the rewarming phase in the two groups subjected to HT when compared to the group maintained at normothermia. Conclusions: In healthy animals, TTM can be associated with alterations in cerebral microcirculation during cooling and altered metabolism at rewarming.

Effects of Methylprednisolone on Myocardial Function and Microcirculation in Post-resuscitation: A Rat Model

Background

Previous studies have demonstrated that inflammation and impaired microcirculation are key factors in post-resuscitation syndromes. Here, we investigated whether methylprednisolone (MP) could improve myocardial function and microcirculation by suppressing the systemic inflammatory response following cardiopulmonary resuscitation (CPR) in a rat model of cardiac arrest (CA).

Methods

Sprague-Dawley rats were randomly assigned to (1) sham, (2) control, and (3) drug groups. Ventricular fibrillation was induced and then followed by CPR. The rats were infused with either MP or vehicle at the start of CPR. Myocardial function and microcirculation were assessed at baseline and after the restoration of spontaneous circulation. Blood samples were drawn at baseline and 60-min post-resuscitation to assess serum cytokine (TNF-α, IL-1β, and IL-6) levels.

Results

Myocardial function [estimated by the ejection fraction (EF), myocardial performance index (MPI), and cardiac output (CO)] improved post-ROSC in the MP group compared with those in the control group (p < 0.05). MP decreased the levels of the aforementioned pro-inflammatory cytokines and alleviated cerebral, sublingual, and intestinal microcirculation compared with the control (p < 0.05). A negative correlation emerged between the cytokine profile and microcirculatory blood flow.

Conclusion

MP treatment reduced post-resuscitation myocardial dysfunction, inhibited pro-inflammatory cytokines, and improved microcirculation in the initial recovery phase in a CA and resuscitation animal model. Therefore, MP could be a potential clinical target for CA patients in the early phase after CPR to alleviate myocardial dysfunction and improve prognosis.

High-resolution respirometry for evaluation of mitochondrial function on brain and heart homogenates in a rat model of cardiac arrest and cardiopulmonary resuscitation

The physiology and physiopathology process of mitochondrial function following cardiac arrest remains poorly understood. We aimed to assess mitochondrial respiratory function on the heart and brain homogenates from cardiac arrest rats. The expression level of SIRT1/PGC-1α pathway was measured by immunoblotting. 30 rats were assigned to the CA group and the sham group. Rats of CA were subjected to 6 min of untreated ventricular fibrillation (VF) followed by 8 min of cardiopulmonary resuscitation (CPR). Mitochondrial respiratory function was compromised following CA and I/R injury, as indicated by CIL (451.46 ± 71.48 vs. 909.91 ± 5.51 pmol/min*mg for the heart and 464.14 ± 8.22 vs. 570.53 ± 56.33 pmol/min*mg for the brain), CI (564.04 ± 64.34 vs. 2729.52 ± 347.39 pmol/min*mg for the heart and 726.07 ± 85.78 vs. 1762.82 ± 262.04 pmol/min*mg for the brain), RCR (1.88 ± 0.46 vs. 3.57 ± 0.38 for the heart and 2.05 ± 0.19 vs. 3.49 ± 0.19, for the brain) and OXPHOS coupling efficiency (0.45 ± 0.11 vs. 0.72 ± 0.03 for the heart and 0.52 ± 0.05 vs. 0.71 ± 0.01 for the brain). However, routine respiration was lower in the heart and comparable in the brain after CA. CIV did not change in the heart but was enhanced in the brain. Furthermore, both SIRT1 and PGC-1α were downregulated concurrently in the heart and brain. The mitochondrial respiratory function was compromised following CA and I/R injury, and the major affected respiratory state is complex I-linked respiration. Furthermore, the heart and the brain respond differently to the global I/R injury after CA in mitochondrial respiratory function. Inhibition of the SIRT1/PGC-1α pathway may be a major contributor to the impaired mitochondrial respiratory function.

The Role of Sphingomyelin Metabolism in the Protection of Rat Brain Microvascular Endothelial Cells by Mild Hypothermia

BACKGROUND

Sphingomyelin, composed of ceramide (CER), sphingosine (Sph), and sphingosine-1-phosphate (S1P), is an essential structural component of cellular membranes and plays an important role in the signal transduction regulating cell proliferation, differentiation, and apoptosis. CER is mainly metabolized to Sph, and under the action of sphingosine kinases (SphKs), Sph produces S1P, which can be converted back to Sph by S1P phosphatase. It is suggested that the fate of cells is controlled partly by the interconversion of CER and intracellular S1P. SphK2 is considered the main kinase of S1P synthesis in the central nervous system. The objective of this study was to explore the hypothesis that SphK2 and sphingomyelin metabolism participated in the process of cell apoptosis and the protection of mild hypothermia.

METHODS

Rat brain microvascular endothelial cells were divided into groups for intervention of SphK2 inhibitor, SphK2 small interfering RNA (SiRNA) transfection, ischemia-reperfusion, and mild hypothermia. After interventions, cell apoptosis was detected by 4,6-diamino-2-phenyl indole (DAPI) and flow cytometry, the expression of apoptosis-related protein was detected by Western Blot, and SphK2 enzyme activity and the content of sphingomyelin were determined.

RESULTS

ABC294640 and transfection of SphK2 SiRNA could increase apoptosis, accompanied by the increase of the expression of proapoptotic genes Caspase3 and Bax and the decrease of the expression of BCL-2. This effect could be partially reversed with mild hypothermia. Ischemia-reperfusion injury, transfection of SphK2 SiRNA, and the addition of ABC294640 could significantly inhibit the activity of SphK2, accompanied by the increase of CERs and the decrease of S1P. Mild hypothermia could reverse the changes of sphingolipids but have no significant effect on the activity of sphk2.

CONCLUSIONS

Mild hypothermia can inhibit the occurrence of apoptosis and reverse the changes of apoptosis-related genes and sphingomyelin content induced by ischemia-reperfusion injury, but the effect on sphk2 enzyme activity was not significant.

Targeted temperature management and early neuro-prognostication after cardiac arrest

Targeted temperature management (TTM) is a recommended neuroprotective intervention for coma after out-of-hospital cardiac arrest (OHCA). However, controversies exist concerning the proper implementation and overall efficacy of post-CA TTM, particularly related to optimal timing and depth of TTM and cooling methods. A review of the literature finds that optimizing and individualizing TTM remains an open question requiring further clinical investigation. This paper will summarize the preclinical and clinical trial data to-date, current recommendations, and future directions of this therapy, including new cooling methods under investigation. For now, early induction, maintenance for at least 24 hours, and slow rewarming utilizing endovascular methods may be preferred. Moreover, timely and accurate neuro-prognostication is valuable for guiding ethical and cost-effective management of post-CA coma. Current evidence for early neuro-prognostication after TTM suggests that a combination of initial prediction models, biomarkers, neuroimaging, and electrophysiological methods is the optimal strategy in predicting neurological functional outcomes.

The interplay between bystander cardiopulmonary resuscitation and ambient temperature on neurological outcome after cardiac arrest: A nationwide observational cohort study

BACKGROUND

At lower ambient temperature, patients with out-of-hospital cardiac arrest (OHCA) easily experience hypothermia. Hypothermia has shown to improve the rate of successful return of spontaneous circulation (ROSC) in animal models. We hypothesized that lower temperature affects the impact of bystander cardiopulmonary resuscitation (CPR) on the increased odds of a favorable neurological outcome post-OHCA.

METHODS

This study used information collected by the prospective, nationwide, Utstein registry to examine data from 352,689 adult patients who experienced OHCA from 2012 to 2016 in Japan. The primary outcome was a 1-month favorable neurological outcomes. Multivariable logistic regression analyses were conducted to test the impact of bystander CPR according to the temperature on the favorable outcome.

RESULTS

A total of 201,111 patients with OHCA were included in the complete case analysis. The lower temperature group had lower proportions of receiving bystander CPR (46.5 vs. 47.9%) and having favorable outcome (2.1 vs 2.8%) than those in the higher group. Multivariable analysis revealed that bystander CPR at lower temperatures was significantly associated with favorable outcomes (adjusted odds ratio, 1.22; 95% CI, 1.09-1.37), whereas bystander CPR at higher temperatures was not associated with favorable outcomes (1.02; 0.92-1.13). The nonlinear relationship using a spline curve in the multivariable model revealed that odds ratio of favorable neurological outcomes associated with bystander CPR increased as the temperature decreased.

CONCLUSION

Bystander CPR was associated with favorable neurological outcomes at lower temperatures. The odds of a favorable outcome associated with bystander CPR increased as the temperature decreased.

The risk factors for postoperative cerebral complications in patients with Stanford type a aortic dissection

Background

Postoperative cerebral complications (PCC) are common and serious postoperative complications for patients with Stanford type A aortic dissection (AAD). The aim of this study was to evaluate the risk factors for PCC in these patients and to provide a scientific basis for effective prevention of PCC.

Methods

In this retrospective case-control study, 125 patients with AAD who underwent thoracotomy in our department from October 2017 to October 2018 in the department of cardiovascular surgery, Fujian Medical University Union Hospital were divided into two groups: patients with PCC (n = 12), and patients without PCC (n = 113). The general clinical data, the types of corrective surgeries, the intraoperative situations, the postoperative complications, and the midterm outcomes of the patients were analyzed.

Results

The patients with PCC were significantly older than the patients without PCC (P = 0.016), and the incidence of the preoperative cerebral disease history in the patients with PCC was significantly higher than those of the PCC (−) group (P = 0.024). The Euro SCORE II of patients with PCC was dramatically higher than the patients without PCC (P = 0.005). There were significant differences between the two groups in terms of the duration of cardiopulmonary bypass (CPB) (P = 0.010) and the length of moderate hypothermic circulatory arrest (MHCA) combined with selective cerebral perfusion (SCP) (P = 0.000). The monitoring of rcSO₂ indicated that there was significant difference between the two groups in terms of the bilateral baseline (P = 0.000). Patients with PCC were observed to have experienced significantly longer intubation times (P = 0.000), ICU stays (P = 0.001), and postoperative hospital stays (P = 0.009), and they also had dramatically higher rates of pulmonary infection (P = 0.000), multiple organ dysfunction syndrome (P = 0.041) and tracheotomy (P = 0.022) after surgeries. The duration of MHCA+SCP (OR:9.009, P = 0.034) and the average baseline value of rcSO₂ (OR:0.080, P = 0.009) were ultimately identified as significant risk factors.

Conclusions

PCC has a serious influence on the prognoses of patients following surgical treatment with AAD. The duration of MHCA+SCP and the average baseline value of rcSO₂ were the independent risk factors for PCC.