Continuous chest compressions improve survival and neurologic outcome in a swine model of prolonged ventricular fibrillation

Continuous compression with asynchronous ventilation improves CPR prognosis? A meta-analysis from human and animal studies

BACKGROUND

The cardiopulmonary resuscitation (CPR) compression to ventilation strategy remains controversial. We conducted a meta-analysis to compare the outcomes between continuous chest compressions CPR with asynchronous ventilation (CCC-CPR) and interrupted chest compressions CPR with synchronous ventilation (ICC-CPR) in cardiac arrest.

METHODS

PubMed, Web of Science, Embase, MEDLINE (Ovid/LWW) and the Cochrane Libraries were searched up from inception to July 31, 2022. Human and animal studies comparing CCC-CPR versus ICC-CPR were included. Outcome variables were return of spontaneous circulation (ROSC), time to ROSC, survival to discharge, 1-month survival, survival at 4 h, good neurological function, mean arterial pressure (MAP) and other clinical parameters. Jadad Scale and Newcastle-Ottawa Scale were used to assess the study quality and risk of bias.

RESULTS

The systematic search identified eight studies on humans and twelve studies on animal trials. There were no significant differences in ROSC (odd ratios [OR] 1.07; 95% confidence interval [CI]: 0.86-1.32; P = 0.55), survival to hospital discharge (OR 1.04; 95%CI 0.77-1.42; P = 0.79), 1-month survival (OR 1.07; 95%CI 0.84-1.36; P = 0.57), and good neurological outcome (OR 0.92; 95%CI 0.84-1.01, P = 0.09) between CCC-CPR and ICC-CPR in human studies. In animal trials, CCC-CPR had significantly higher rate of ROSC (OR = 1.81; 95% CI: 0.94-3.49; P = 0.07), survival at 4 h (OR 2.57; 95% CI: 1.16-5.72; P = 0.02) and MAP (mean difference [MD] 0.79, 95% CI: 0.04-1.53; P = 0.04), even though no significant differences in ROSC time, arterial potential of hydrogen (pH) and partial tension of carbon dioxide (PaCO2).

CONCLUSION

CCC-CPR did not show superiority in human outcomes compared with ICC-CPR, but its effect value was significantly increased in animal experiments. We should take the positive outcomes from animals and apply them to human models, and more physiological mechanisms need to be confirmed in CPR patients with different compression-ventilation strategies to improve the prognosis of cardiac arrest.

Physiology of neonatal resuscitation: Giant strides with small breaths

The transition of a fetus to a newborn involves a sequence of well-orchestrated physiological events. Most neonates go through this transition without assistance but 5-10% may require varying degrees of resuscitative interventions at birth. The most crucial event during this transition is lung inflation with optimal concentrations of oxygen. Rarely, extensive resuscitation including chest compressions and medication may be required. In the past few decades, significant strides have been made in our understanding of the cardiorespiratory transition at birth from a fetus to a newborn and the subsequent resuscitation. This article reviews the physiology behind neonatal transition at birth and various interventions during neonatal resuscitation.

Inadequate Bioavailability of Intramuscular Epinephrine in a Neonatal Asphyxia Model

BACKGROUND

Over half a million newborn deaths are attributed to intrapartum related events annually, the majority of which occur in low resource settings. While progress has been made in reducing the burden of asphyxia, novel approaches may need to be considered to further decrease rates of newborn mortality. Administration of intravenous, intraosseous or endotracheal epinephrine is recommended by the Newborn Resuscitation Program (NRP) with sustained bradycardia at birth. However, delivery by these routes requires both advanced skills and specialized equipment. Intramuscular (IM) epinephrine may represent a simple, low cost and highly accessible alternative for consideration in the care of infants compromised at birth. At present, the bioavailability of IM epinephrine in asphyxia remains unclear.

METHODS

Four term fetal lambs were delivered by cesarean section and asphyxiated by umbilical cord occlusion with resuscitation after 5 min of asystole. IM epinephrine (0.1 mg/kg) was administered intradeltoid after 1 min of positive pressure ventilation with 30 s of chest compressions. Serial blood samples were obtained for determination of plasma epinephrine concentrations by ELISA.

RESULTS

Epinephrine concentrations failed to increase following administration via IM injection. Delayed absorption was observed after return of spontaneous circulation (ROSC) in half of the studies.

CONCLUSIONS

Inadequate absorption of epinephrine occurs with IM administration during asphyxial cardiac arrest, implying this route would be ineffective in infants who are severely compromised at birth. Late absorption following ROSC raises concerns for risks of side effects. However, the bioavailability and efficacy of intramuscular epinephrine in less profound asphyxia may warrant further evaluation.

Continuous chest compressions with asynchronous ventilations increase carotid blood flow in the perinatal asphyxiated lamb model

BACKGROUND

The neonatal resuscitation program (NRP) recommends interrupted chest compressions (CCs) with ventilation in the severely bradycardic neonate. The conventional 3:1 compression-to-ventilation (C:V) resuscitation provides 90 CCs/min, significantly lower than the intrinsic newborn heart rate (120-160 beats/min). Continuous CC with asynchronous ventilation (CCCaV) may improve the success of return of spontaneous circulation (ROSC).

METHODS

Twenty-two near-term fetal lambs were randomized to interrupted 3:1 C:V (90 CCs + 30 breaths/min) or CCCaV (120 CCs + 30 breaths/min). Asphyxiation was induced by cord occlusion. After 5 min of asystole, resuscitation began following NRP guidelines. The first dose of epinephrine was given at 6 min. Invasive arterial blood pressure and left carotid blood flow were continuously measured. Serial arterial blood gases were collected.

RESULTS

Baseline characteristics between groups were similar. Rate of and time to ROSC was similar between groups. CCCaV was associated with a higher PaO₂ (partial oxygen tension) (22 ± 5.3 vs. 15 ± 3.5 mmHg, p < 0.01), greater left carotid blood flow (7.5 ± 3.1 vs. 4.3 ± 2.6 mL/kg/min, p < 0.01) and oxygen delivery (0.40 ± 0.15 vs. 0.13 ± 0.07 mL O₂/kg/min, p < 0.01) compared to 3:1 C:V.

CONCLUSIONS

In a perinatal asphyxiated cardiac arrest lamb model, CCCaV showed greater carotid blood flow and cerebral oxygen delivery compared to 3:1 C:V resuscitation.

IMPACT

In a perinatal asphyxiated cardiac arrest lamb model, CCCaV improved carotid blood flow and oxygen delivery to the brain compared to the conventional 3:1 C:V resuscitation. Pre-clinical studies assessing neurodevelopmental outcomes and tissue injury comparing continuous uninterrupted chest compressions to the current recommended 3:1 C:V during newborn resuscitation are warranted prior to clinical trials.

Chest compressions during ventilation in out-of-hospital cardiopulmonary resuscitation cause fragmentation of the airflow

INTRODUCTION

When a patient suffers an out-of-hospital cardiac arrest, ventilation and chest compressions are often given simultaneously during cardiopulmonary resuscitation. These simultaneous chest compressions may cause a fragmentation of the airflow, which may lead to an ineffective ventilation. This study focusses on the occurrence and quantification of this fragmentation and its effect on ventilation.

MATERIALS AND METHODS

This study is a single-center observational study, held at Ghent University Hospital. A custom-built bidirectional flow sensor was used to quantify the volumes of ventilation. Adult cardiac arrest patients who were prehospitally intubated and resuscitated by the medical emergency team were eligible for inclusion. Data of the patients who were ventilated and received simultaneous chest compressions, was used to calculate the volumes of ventilation and the amount and volumes of fragmentation. All data in this study is reported as mean (standard deviation; range).

RESULTS

Data of 10 patients (7 male) with a mean age of 71 years (14;51-87) was used in this study. The mean ventilation frequency was 12/min (2;9-16), the mean minute volume and tidal volume were respectively 6.21 L (1.51;3.79-8.15) and 514 mL (99;422-682). Fragmentation of the airflow was observed in all patients, with an average of 3 (1;2-5) fragments per inspiration and a mean volume of 214 mL (65;112-341) per fragment.

DISCUSSION AND CONCLUSION

Chest compressions during ventilation caused fragmentation of the airflow in all patients. There was wide variation in the number and volume of the fragments between patients. The importance of quantification of airflow volumes and the effect fragmentation of the airflow on the efficacy of ventilation can be essential in improving cardiopulmonary resuscitation techniques and therefore needs further investigation.

The feasibility of emergency medical technicians performing intermittent high-quality cardiopulmonary resuscitation

Background: Whether intermittent chest compressions have an effect on the quality of CPR is worthy of discussion. The purpose of this study was to investigate differences in the chest compression quality of emergency medical technicians (EMTs) performing cardiopulmonary resuscitation (CPR) with different rest intervals. Methods: Seventy male firefighters with EMT licenses participated in this study. Participants completed body composition measurements and three CPR quality tests, as follows: (1) CPR-uninterrupted for 10 minutes; (2) after 2 days of rest, CPR 10s-intermittent (CPR-10s), for 2 minutes each time and 5 cycles; (3) after another 2 days of rest, CPR 20s-intermittent (CPR-20s), for 2 minutes each time and 5 cycles. Results: Body composition results showed that body mass (BM), body mass index (BMI), upper limb muscle mass (ULMM), core muscle mass (CMM), and upper limb-core muscle mass (UL+CMM) were positively correlated with chest compression depth (CCD) (p < 0.05). Analysis of the three different modes of CPR quality analysis indicated significant differences in the chest compression fraction (CCF, F = 6.801, p = 0.001), chest compression rebound rate (CCRR, F = 3.919, p = 0.021), and ratings of perceived exertion (RPE, F = 23.815, p < 0.001). Among the different performance cycles of CPR-10s, significant differences were found in CCF, CCD, CCR (chest compression rate), and RPE (p < 0.05). On the other hand, among the different performance cycles of CPR-20s, significant differences were found in CCD, CCR, and RPE (p < 0.05). Moreover, the CCF, CCD, and RPE scores of the two tests reached significant differences in specific phases (p < 0.05). Conclusions: This study confirmed that the upper limb muscle mass or the weight of the upper body of EMTs is positively correlated with the quality of CPR. In addition, intermittent chest compressions with safe interruption intervals can reduce fatigue caused by long-term chest compressions and maintain better chest compression quality.

Comparison of standard and over-the-head method of chest compressions during cardiopulmonary resuscitation - a simulation study

Background

Maintaining highly effective cardiopulmonary resuscitation (CPR) can be particularly difficult when artificial ventilation using a bag-valve-mask device, combined with chest compression have to be carried out by one person. The aim of the study is to compare the quality of CPR conducted by one paramedic using chest compression from the patient’s side with compression conducted from the ‘over-the-head’ position.

Methods

The subject of the study were two methods of CPR – ‘standard’ (STD) and ‘over-the-head’ (OTH). The STD method consisted of cycles of 30 chest compressions from the patient’s side, and two attempts at artificial ventilation after moving round to behind the patient’s head. In the OTH method, both compressions and ventilations were conducted from behind the patient’s head.

Results

Both CPR methods were conducted by 38 paramedics working in medical response teams. Statistical analysis was conducted on the data collected, giving the following results: the average time of the interruptions between compression cycles (STD 9.184 s, OTH 7.316 s, p < 0.001); the depth of compression 50–60 mm (STD 50.65%, OTH 60.22%, p < 0.001); the rate of compression 100–120/min. (STD 46.39%, OTH 53.78%, p < 0.001); complete chest wall recoil (STD 84.54%, OTH 91.46%, p < 0.001); correct hand position (STD 99.32%, OTH method 99.66%, p < 0.001). A statistically significant difference was demonstrated in the results to the benefit of the OTH method in the above parameters. The remaining parameters showed no significant differences in comparison to reference values.

Conclusions

The higher quality of CPR in the simulated research using the OTH method by a single person justifies the use of this method in a wider range of emergency interventions.

Gastric insufflation during cardiopulmonary resuscitation: A study in human cadavers

INTRODUCTION

Bag-valve-mask ventilation is the first-line ventilation method during cardiopulmonary resuscitation (CPR). Risks include excessive volume delivery and gastric insufflation, the latter increasing the risk of pneumonia. The efficacy of ventilation can also be reduced by airway closure. We hypothesized that continuous chest compression (CC) could limit the risk of gastric insufflation compared to the recommended 30:2 interrupted CC strategy. This experimental study was performed in human "Thiel" cadavers to assess the respective impact of discontinuous vs. continuous chest compressions on gastric insufflation and ventilation during CPR.

METHODS

The 30:2 interrupted CC technique was compared to continuous CC in 5 non-intubated cadavers over a 6 min-period. Flow and Airway Pressure were measured at the mask. A percutaneous gastrostomy allowed measuring the cumulative gastric insufflated volume. Two additional cadavers were equipped with esophageal and gastric catheters instead of the gastrostomy.

RESULTS

For the 7 cadavers studied (4 women) median age of death was 79 [74-84] years. After 6 min of CPR, the cumulative gastric insufflation measured in 5 cadavers was markedly reduced during continuous CC compared to the interrupted CC strategy: (1.0 [0.8-4.1] vs. 5.9 [4.0-5.6] L; p < 0.05) while expired minute ventilation was slightly higher during continuous than interrupted CC (1.9 [1.4-2.8] vs. 1.6 [1.1-2.7] L/min; P < 0.05). In 2 additional cadavers, the progressive rise in baseline gastric pressure was lower during continuous CC than interrupted CC (1 and 2 cmH₂O vs. 12 and 5.8 cmH₂O).

CONCLUSION

Continuous CC significantly reduces the volume of gas insufflated in the stomach compared to the recommended 30:2 interrupted CC strategy. Ventilation actually delivered to the lung is also slightly increased by the strategy.

Continuous Chest Compressions During Sustained Inflations in a Perinatal Asphyxial Cardiac Arrest Lamb Model

OBJECTIVE

Continuous chest compressions are more effective during resuscitation in adults. Sustained inflation rapidly establishes functional residual capacity in fluid-filled lungs at birth. We sought to compare the hemodynamics and success in achieving return of spontaneous circulation in an asphyxial cardiac arrest lamb model with transitioning fetal circulation and fluid-filled lungs between subjects receiving continuous chest compressions during sustained inflation and those receiving conventional 3:1 compression-to-ventilation resuscitation.

DESIGN

Prospective, randomized, animal model study.

SETTING

An experimental laboratory.

SUBJECTS

Fourteen newborn term gestation lambs.

INTERVENTIONS

Lambs were randomized into two groups: 3:1 compression-to-ventilation (control) and continuous chest compressions during sustained inflation. The umbilical cord was occluded to induce asphyxia and asystole. The control group was resuscitated per NRP guidelines. In the sustained inflation + continuous chest compressions group, sustained inflation at 35 cm H2O was provided for 30 seconds with 1-second interruptions before another sustained inflation was provided. One hundred twenty chest compressions/min started after the initial sustained inflation. The first dose of IV epinephrine was given at 6 minutes if return of spontaneous circulation was not achieved and then every 3 minutes until return of spontaneous circulation or for a total of four doses.

MEASUREMENT AND RESULTS

All lambs achieved return of spontaneous circulation in a comparable median time (interquartile range) of 390 seconds (225-405 s) and 345 seconds (204-465 s) in the sustained inflation + continuous chest compressions and control groups, respectively. Four of seven (sustained inflation + continuous chest compressions) and three of six (control) lambs required epinephrine to achieve return of spontaneous circulation. Diastolic blood pressures were lower in the sustained inflation + continuous chest compressions (4 ± 2 mm Hg) compared to the control group (7 ± 2 mm Hg), p < 0.05. PaCO2, PaO2, and lactate were similar between the groups during the study period.

CONCLUSION

In this perinatal cardiac arrest lamb model with transitioning fetal circulation and fluid-filled lungs, sustained inflation + continuous chest compressions is as effective as 3:1 compression-to-ventilation resuscitation in achieving return of spontaneous circulation. Half the lambs achieved return of spontaneous circulation without epinephrine. continuous chest compressions during sustained inflation reduced diastolic pressures but did not alter gas exchange or carotid blood flow compared to 3:1 compression-to-ventilation resuscitation.

Sudden cardiac death

INTRODUCTION

Sudden cardiac arrest continues to be the leading cause of death in the industrialized world.

SOURCES OF DATA

Original papers, reviews and guidelines.

AREAS OF AGREEMENT

Community programs for lay bystander cardiopulmonary resuscitation (CPR) and automatic external defibrillation improve outcomes. Post-arrest care, including targeted temperature management (TTM) combined with early coronary angiography and percutaneous coronary intervention, is helpful for those suffering cardiac arrest during an ST-segment elevation myocardial infarction.

AREAS OF CONTROVERSY

(1) The optimal approach to encourage lay bystanders to assist with resuscitation efforts. (2) Whether TTM combined with early coronary angiography is cost effective for those without ST elevation on their post-arrest ECG is unknown.

GROWING POINTS

Increasing data show that chest compression-only CPR is preferred by lay rescuers and improves local survival rates.

AREAS TIMELY FOR DEVELOPING RESEARCH

Randomized clinical trials are underway to examine the utility of early coronary angiography in the treatment of post-arrest patients without ST-segment elevation.

Optimal Chest Compression Rate and Compression to Ventilation Ratio in Delivery Room Resuscitation: Evidence from Newborn Piglets and Neonatal Manikins

Cardiopulmonary resuscitation (CPR) duration until return of spontaneous circulation (ROSC) influences survival and neurologic outcomes after delivery room (DR) CPR. High quality chest compressions (CC) improve cerebral and myocardial perfusion. Improved myocardial perfusion increases the likelihood of a faster ROSC. Thus, optimizing CC quality may improve outcomes both by preserving cerebral blood flow during CPR and by reducing the recovery time. CC quality is determined by rate, CC to ventilation (C:V) ratio, and applied force, which are influenced by the CC provider. Thus, provider performance should be taken into account. Neonatal resuscitation guidelines recommend a 3:1 C:V ratio. CCs should be delivered at a rate of 90/min synchronized with ventilations at a rate of 30/min to achieve a total of 120 events/min. Despite a lack of scientific evidence supporting this, the investigation of alternative CC interventions in human neonates is ethically challenging. Also, the infrequent occurrence of extensive CPR measures in the DR make randomized controlled trials difficult to perform. Thus, many biomechanical aspects of CC have been investigated in animal and manikin models. Despite mathematical and physiological rationales that higher rates and uninterrupted CC improve CPR hemodynamics, studies indicate that provider fatigue is more pronounced when CC are performed continuously compared to when a pause is inserted after every third CC as currently recommended. A higher rate (e.g., 120/min) is also more fatiguing, which affects CC quality. In post-transitional piglets with asphyxia-induced cardiac arrest, there was no benefit of performing continuous CC at a rate of 90/min. Not only rate but duty cycle, i.e., the duration of CC/total cycle time, is a known determinant of CC effectiveness. However, duty cycle cannot be controlled with manual CC. Mechanical/automated CC in neonatal CPR has not been explored, and feedback systems are under-investigated in this population. Evidence indicates that providers perform CC at rates both higher and lower than recommended. Video recording of DR CRP has been increasingly applied and observational studies of what is actually done in relation to outcomes could be useful. Different CC rates and ratios should also be investigated under controlled experimental conditions in animals during perinatal transition.

Quality of continuous chest compressions performed for one or two minutes

OBJECTIVES

This study was designed to assess cardiopulmonary resuscitation quality and rescuer fatigue when rescuers perform one or two minutes of continuous chest compressions.

METHODS

This prospective crossover study included 148 lay rescuers who were continuously trained in a cardiopulmonary resuscitation course. The subjects underwent a 120-min training program comprising continuous chest compressions. After the course, half of the volunteers performed one minute of continuous chest compressions, and the others performed two minutes, both on a manikin model. After 30 minutes, the volunteers who had previously performed one minute now performed two minutes on the same manikin and vice versa.

RESULTS

A comparison of continuous chest compressions performed for one and two minutes, respectively, showed that there were significant differences in the average rate of compressions per minute (121 vs. 124), the percentage of compressions of appropriate depth (76% vs. 54%), the average depth (53 vs. 47 mm), and the number of compressions with no errors (62 vs. 47%). No parameters were significantly different when comparing participants who performed regular physical activity with those who did not and participants who had a normal body mass index with overweight/obese participants.

CONCLUSION

The quality of continuous chest compressions by lay rescuers is superior when it is performed for one minute rather than for two minutes, independent of the body mass index or regular physical activity, even if they are continuously trained in cardiopulmonary resuscitation. It is beneficial to rotate rescuers every minute when performing continuous chest compressions to provide higher quality and to achieve greater success in assisting a victim of cardiac arrest.

Neonatal resuscitation: evolving strategies

Birth asphyxia accounts for about 23% of the approximately 4 million neonatal deaths each year worldwide (Black et al., Lancet, 2010, 375(9730):1969-87). The majority of newborn infants require little assistance to undergo physiologic transition at birth and adapt to extrauterine life. Approximately 10% of infants require some assistance to establish regular respirations at birth. Less than 1% need extensive resuscitative measures such as chest compressions and approximately 0.06% require epinephrine (Wyllie et al. Resuscitation, 2010, 81 Suppl 1:e260–e287). Transition at birth is mediated by significant changes in circulatory and respiratory physiology. Ongoing research in the field of neonatal resuscitation has expanded our understanding of neonatal physiology enabling the implementation of improved recommendations and guidelines on how to best approach newborns in need for intervention at birth. Many of these recommendations are extrapolated from animal models and clinical trials in adults. There are many outstanding controversial issues in neonatal resuscitation that need to be addressed. This article provides a comprehensive and critical literature review on the most relevant and current research pertaining to evolving new strategies in neonatal resuscitation. The key elements to a successful neonatal resuscitation include ventilation of the lungs while minimizing injury, the judicious use of oxygen to improve pulmonary blood flow, circulatory support with chest compressions, and vasopressors and volume that would hasten return of spontaneous circulation. Several exciting new avenues in neonatal resuscitation such as delayed cord clamping, sustained inflation breaths, and alternate vasopressor agents are briefly discussed. Finally, efforts to improve resuscitative efforts in developing countries through education of basic steps of neonatal resuscitation are likely to decrease birth asphyxia and neonatal mortality.

The initial success rate of cardiopulmonary resuscitation and its associated factors in patients with cardiac arrest within 24 hours after anesthesia for an emergency surgery

PURPOSE

To determine the initial success rate and its associated factors on cardiopulmonary resuscitation (CPR) in patients with cardiac arrest within 24 hours after receiving anesthesia for an emergency surgery.

PATIENTS AND METHODS

After the hospital ethical committee gave approval for this study, the anesthesia providers recorded all relevant data regarding CPR in patients with cardiac arrest within 24 hours after anesthesia for emergency surgery at Maharaj Nakorn Chiang Mai Hospital, a university hospital in Northern Thailand. Only data from the cardiac arrest patients who received the first CPR attempt were included in the analysis. The end point of the initial success of CPR was return of spontaneous circulation (ROSC). Factors related to ROSC were determined by univariate analyses and multiple logistic regression analysis. The odds ratios (OR) and 95% confidence intervals (CI) were used to calculate the strength of the factors associated with the ROSC.

RESULTS

Of the 96 cardiac arrest patients, 44 patients (45.8%) achieved ROSC. Factors associated with ROSC were electrocardiogram monitoring for detected cardiac arrest (OR =4.03; 95% CI =1.16-14.01; P=0.029), non-shock patients before arrest (OR =8.54; 95% CI =2.13-34.32; P=0.003), timing to response of activated CPR team within 1 minute (OR =9.37; 95% CI =2.55-34.39; P<0.001), having trained CPR teams (OR =8.76; 95% CI =2.50-30.72; P<0.001), and administration of more than one dose of epinephrine (OR =5.62; 95% CI =1.32-23.88; P<0.019).

CONCLUSION

Patients undergoing anesthesia for an emergency surgery are at risk for perioperative cardiac arrest with high mortality which requires immediate CPR. Our results have confirmed that early detection of cardiac arrest by vigilant electrocardiogram monitoring and prompt management with a qualified team are important factors in improving the success of CPR. Emergency surgical patients at risk for cardiac arrest should be promptly managed, with facilities available not only during the operation but also during the pre- to postoperative period.

Hypoxia/reoxygenation-induced myocardial lesions in newborn piglets are related to interindividual variability and not to oxygen concentration

OBJECTIVE

Evaluation of myocardial histological changes in an experimental animal model of neonatal hypoxia-reoxygenation.

METHODS

Normocapnic hypoxia was induced in 40 male Landrace/Large White piglets. Reoxygenation was initiated when the animals developed bradycardia (HR <60 beats/min) or severe hypotension (MAP <15 mmHg). The animals were divided into four groups based on the oxygen (O(2)) concentration used for reoxygenation; groups 1, 2, 3, and 4 received 18%, 21%, 40%, and 100% O(2), respectively. The animals were further classified into five groups based on the time required for reoxygenation: A: fast recovery (<15 min); B: medium recovery (15-45 min); C: slow recovery (45-90 min); D: very slow recovery (>90 min), and E: nine deceased piglets.

RESULTS

Histology revealed changes in all heart specimens. Interstitial edema, a wavy arrangement, hypereosinophilia and coagulative necrosis of cardiomyocytes were observed frequently. No differences in the incidence of changes were observed among groups 1-4, whereas marked differences regarding the frequency and the degree of changes were found among groups A-E. Coagulative necrosis was correlated with increased recovery time: this condition was detected post-asphyxia in 14%, 57%, and 100% of piglets with fast, medium, and slow or very slow recovery rates, respectively.

CONCLUSIONS

The significant myocardial histological changes observed suggest that this experimental model might be a reliable model for investigating human neonatal cardiac hypoxia-related injury. No correlation was observed between the severity of histological changes and the fiO(2) used during reoxygenation. Severe myocardial changes correlated strictly with recovery time, suggesting an unreported individual susceptibility of myocardiocytes to hypoxia, possibly leading to death after the typical time-sequence of events.