Elsevier

Resuscitation

Volume 81, Issue 11, November 2010, Pages 1571-1576
Resuscitation

Experimental paper
Extended series of cardiac compressions during CPR in a swine model of perinatal asphyxia

https://doi.org/10.1016/j.resuscitation.2010.06.007Get rights and content

Abstract

Background

The rationale for a compression to ventilation ratio of 3:1 in neonates with primary hypoxic, hypercapnic cardiac arrest is to emphasize the importance of ventilation; however, there are no published studies testing this approach against alternative methods. An extended series of cardiac compressions offers the theoretical advantage of improving coronary perfusion pressures and hence, we aimed to explore the impact of compression cycles of two different durations.

Materials and methods

Newborn swine (n = 32, age 12–36 h, weight 2.0–2.7 kg) were progressively asphyxiated until asystole occurred. Animals were randomized to receive compressions:ventilations 3:1 (n = 16) or 9:3 (n = 16). Return of spontaneous circulation (ROSC) was defined as a heart rate ≥100 beats min−1.

Results

All animals except one in the 9:3 group achieved ROSC. One animal in the 3:1 group suffered bradycardia at baseline, and was excluded, leaving us with 15 animals in each group surviving to completion of protocol. Time to ROSC (median and interquartile range) was 150 s (115–180) vs. 148 s (116–195) for 3:1 and 9:3, respectively (P = 0.74). There were no differences in diastolic blood pressure during compression cycles or in markers of hypoxia and inflammation. The temporal changes in mean arterial blood pressure, heart rate, arterial blood gas parameters, and systemic and regional oxygen saturation were comparable between groups.

Conclusion

Neonatal pigs with asphyxia-induced cardiac arrest did not respond to a compression:ventilation ratio of 9:3 better than to 3:1. Future research should address if alternative compression:ventilation ratios offer advantages over the current gold standard of 3:1.

Introduction

Unfortunately, many of the recommendations for newborn resuscitation are supported by limited evidence. In particular, the 2005 guidelines of the International Liaison Committee on Resuscitation (ILCOR) acknowledge that the ideal ratio of chest compressions to ventilations (C:V ratio) during neonatal CPR is unknown.1 Asphyxia is the most common cause of arrest in the newborn and thus the reversal of asphyxia via adequate ventilation is critical. Proper positive pressure ventilation alone is, according to ILCOR guidelines, effective for resuscitating almost all apneic or bradycardic newborns.2 Chest compressions should be given in a ratio of 3 compressions to 1 breath if the pulse is <60 beats min−1 and not increasing despite at least 30 s of effective ventilation.3 In contrast, recommendations for older children and adults include longer compression sequences with less interruption for ventilation.1 This is in part due to the fact that the cause of arrest in older age groups is more frequently due to ventricular fibrillation where animal data suggest that adequately oxygenated blood can be circulated for the initial 4–6 min, even without ventilatory efforts.4 In addition, non-neonatal paediatric and adult animal data demonstrate better coronary perfusion pressures (CPP) with less interruption of the cardiac compressions.5, 6, 7, 8 Whether longer sequences of uninterrupted compressions in concert with continued intermittent ventilation would result in better responses to neonatal CPR is unknown.

The primary aim of this study was to compare the effect of 9:3 vs. 3:1 compressions to ventilations on time to return of spontaneous circulation (ROSC) during neonatal CPR. 9:3 was chosen in an attempt to meet the equally important goals of achieving sufficient CPP via less interruption of compressions while simultaneously achieving adequate ventilation. Secondary outcomes of interest included the effect of compression cycle length on mean arterial blood pressure (MAP), diastolic blood pressure (DBP) as a rough estimate of CPP, acid/base status, the proinflammatory cytokine interleukin-1β, lactate/pyruvate ratios, systemic and regional cerebral oxygen saturation and survival. We hypothesized that a 9:3 C:V ratio would lead to a faster ROSC than the recommended 3:1 ratio during resuscitation from asphyxia-induced cardiac arrest. Secondary hypotheses were that use of the 9:3 ratio during neonatal CPR would be accompanied by better haemodynamic status following successful resuscitation with less evidence of hypoxic/inflammatory damage.

Section snippets

Experimental protocol

The experimental protocol (Fig. 1) was approved by the Norwegian Council for Animal Research. Animals were cared for and handled in accordance with the European Guidelines for Use of Experimental Animals by certified category C researchers of the Federation of European Laboratory Animals Science Associations.

Animal preparation (see Appendix)

Thirty-two Noroc pigs of both sexes, 12–36 h of age (2.0–2.7 kg) were anaesthetized and mechanically ventilated. Surgical instrumentation for the measurement of arterial blood pressure, blood

Results

Of 16 animals in the 3:1 group, one suffered bradycardia (HR < 100 beats min−1) throughout the 1 h stabilization period and was excluded. Of 16 pigs randomized to the 9:3 group, one did not achieve ROSC. Time to ROSC for this animal was set arbitrarily to 1000 s for statistical calculations using the Mann–Whitney test.

Discussion

In this study we compared the C:V ratios of 3:1 and 9:3 in a piglet model of asphyxia-induced cardiac arrest. There were no differences in time to ROSC, haemodynamic parameters, oxygen saturation indices, IL-1β in BALF and CSF; or lactate/pyruvate ratios in CSF and blood between the groups. Lactate/pyruvate ratios are elevated by hypoxia, and high levels of cord plasma lactate and lactate/pyruvate ratios at birth are associated with abnormal neurodevelopmental outcome.10 IL-1β in BALF and CSF

Conclusions

A C:V ratio of 9:3 did not lead to a faster ROSC than the recommended 3:1 ratio in newborn pigs with cardiac arrest resulting from asphyxia. There were no differences between the groups in the number of compressions achieved per min, and the groups were comparable in terms of haemodynamic parameters during and after resuscitation.

Conflict of interest statement

The study was partially funded through a grant from the Laerdal Foundation of Acute Medicine.

Acknowledgments

We thank Camilla Skjæret and Tonje Sonerud for help in optimizing cytokine-measurements, Anne Syrrist for the analysis of lactate and pyruvate and Geir Aamodt for statistical assistance. We express gratitude towards Respiratory Covidien Norway AS for lending the INVOS cerebral oximeter; and the Laerdal Foundation of Acute Medicine and University of Oslo's Foundation at Akershus University Hospital for significant economic contributions to the study.

References (18)

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    Citation Excerpt :

    Animal models have been used to compare CV ratios of 3:1 with other ratios. Using a newborn piglet asphyxia-induced arrest model, time to return of spontaneous circulation (ROSC) with a 3:1 ratio was compared with ratios of 9:3 and 15:2, the latter CV ratio being that often used on neonates resuscitated outside a delivery unit [42,43]. No disadvantage for the 3:1 ratio was found when compared to higher ratios with respect to short-term survival, time to ROSC, gas exchange during CPR and markers of tissue injury.

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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2010.06.007.

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