Chu SE, Huang CY, Cheng CY, Chan CH, Chen HA, Chang CH, Tsai KC, Chiu KM, Ma MH, Chiang WC, Sun JT. Cardiopulmonary Resuscitation Without Aortic Valve Compression Increases the Chances of Return of Spontaneous Circulation in Out-of-Hospital Cardiac Arrest: A Prospective Observational Cohort Study. Crit Care Med. 2024 Sep 1;52(9):1367-1379. doi: 10.1097/CCM.0000000000006336. Epub 2024 May 23. PMID: 38780398.
https://pubmed.ncbi.nlm.nih.gov/38780398
Synopsis Provided By
Manuel Boller, Dr. med. vet., MTR, DACVECC
Synopsis
This recent article by Chu and colleagues published in Critical Care Medicine in September 2024 elegantly illustrates that rescuer hand placement during CPR is of significant hemodynamic importance: chest compressions employing the cardiac pump mechanism must be administered over the ventricles and not the heart base (Chu 2024). In this study, Chu et al. examined the impact of aortic valve (AV) compression/deformation during CPR in adults on relevant outcomes. They found that narrowing or deformation of the AV during chest compressions was associated with a marked reduction in CPR efficacy.
This prospective observational study included adults with out-of-hospital cardiac arrest in whom CPR was initiated in the field and continued in the emergency department. In the emergency department, the investigators used transesophageal echocardiography (TEE) to visualize the AV during chest compressions. This allowed them to study the effect of AV compression versus no such compression on sustained return of spontaneous circulation (ROSC; i.e., ROSC > 20 minutes) and other relevant outcomes. Based on the presence of AV narrowing/deformation, the investigators allocated patients to an “AV uncompressed group” (n = 39) or an “AV compressed group” (n = 37). Patients in the AV uncompressed group achieved higher diastolic arterial blood pressure (DIA) (33.4 vs. 11.5 mm Hg; P = 0.002), a higher proportion reaching the critical DIA for ROSC (93.8% vs. 33.3%; P < 0.001), a nearly 5-fold increase in the probability of sustained ROSC (53.8% vs. 24.3%; adjusted odds ratio [aOR], 4.72; P = 0.009) and a more than 6-fold increase in the probability of survival to ICU admission (33.3% vs. 8.1%; aOR, 6.74; P = 0.010). However, there was no difference in survival to hospital discharge (5.1% vs. 0%, P = NS) or in discharge with favorable neurologic outcome (0% vs 0%, P = NS), as there were very few survivors (n = 2). Although there are limitations due to study design and the inherent challenges of conducting such studies in emergency settings, the overall message remains clear: chest compressions that deform or narrow the heart’s outflow tract severely compromise CPR efficacy. These clinical findings are supported by 2 recent studies in swine, which also reported the detrimental effects of AV compression during CPR (Anderson 2017, Teran 2023).
What does this mean for small animal CPR? The key takeaway is that when performing chest compressions using the cardiac pump approach (e.g., in keel-chested dogs, small dogs, and cats), it is essential for the rescuer to position their hands over the ventricles rather than over the heart base. This may be particularly important in cats, given their generally highly compressible chests. The RECOVER 2024 guidelines have updated recommended compression techniques for cats and small dogs, in part to prevent over-compression and also to promote compression over the ventricles (Burkitt-Creedon 2024). Anatomically, the heart in dogs and cats typically occupies the ventral half of the chest, with the ventricles located in the bottom third. While the optimal compression point in dogs and cats undergoing CPR remains an important knowledge gap, compressing the ventral aspect of the chest of the keel-chested dog, small dog, or cat in lateral recumbency is crucial to avoid compressing the outflow tract of the ventricles.
References
Chu SE, Huang CY, Cheng CY, Chan CH, Chen HA, Chang CH, Tsai KC, Chiu KM, Ma MH, Chiang WC, Sun JT. Cardiopulmonary Resuscitation Without Aortic Valve Compression Increases the Chances of Return of Spontaneous Circulation in Out-of-Hospital Cardiac Arrest: A Prospective Observational Cohort Study. Crit Care Med. 2024 Sep 1;52(9):1367-1379. doi:10.1097/CCM.0000000000006336. Epub 2024 May 23. PMID: 38780398.
Teran F, Owyang CG, Martin-Flores M, Lao D, King A, Palasz J, Araos JD. Hemodynamic impact of chest compression location during cardiopulmonary resuscitation guided by transesophageal echocardiography. Crit Care. 2023 Aug 19;27(1):319. doi: 10.1186/s13054-023-04575-7. PMID:37598201; PMCID: PMC10439621
