Our work has demonstrated that in-hospital CPR providers exhibit a wide range of leaning during chest compression delivery. In addition, the majority of in-hospital cardiac arrest resuscitations in our cohort (91%) demonstrated some degree of leaning. One other investigation has provided data on chest compression leaning from adult, hospital-based, cardiac arrest resuscitations.9
Our finding of 12% overall leaning percentage is similar to the 11% found in their study of CPR performance in an Austrian ED. It is unknown from their data whether leaning was evenly dispersed or concentrated by provider and event. In contrast, an evaluation of out-of-hospital CPR performance in Europe demonstrated no leaning in a cohort of 176 arrest events.2
However, this latter study set the leaning threshold at ≥ 4 kg, instead of the ≥ 2.5 kg level used in our analysis. The use of different techniques to measure leaning may also confound comparison between studies. For instance, while Losert et al.9
used a similar technology and software combination as the current investigation, Aufderheide et al. performed their measurements by way of direct observation and electronically measured airway pressures.11
This difficulty in comparison between studies suggests the need for future standardization of CPR performance definitions.
Laboratory investigations have suggested that leaning during chest compressions (using a threshold of residual leaning force equivalent to 10% of maximal compression force) decreases coronary and cerebral pressures, and that this effect remains in place for a significant period of time after the cessation of leaning.7–8
Therefore, even short periods of leaning during resuscitation may have deleterious effects on tissue perfusion during CPR and resuscitation outcomes.
While a majority of cardiac arrests events in this investigation contained small leaning percentages, many cases did contain a relatively large amount, with leaning affecting as many as 44% of chest compressions in a given episode. This suggests that the overall leaning percentage (12%) does not accurately represent the potential clinical impact on some cardiac arrest victims in our cohort. In an attempt to identify the cause of this wide variation, we found that leaning does not correlate with a set of patient characteristics or external factors other than patient gender, leaving the disparity unexplained by simple univariate analysis. However, it is important to note that CPR quality represents a complex measure with multiple interacting factors, such that any single parameter such as leaning is likely influenced by both other CPR performance and rescuer characteristics. A larger case sample size than contained in our cohort might allow for multivariate regression analysis to better evaluate these factors.
On the other hand, our analysis of initial blocks of chest compressions (representing individual CPR providers) suggests that the wide range of leaning might represent a rescuer-specific phenomenon. Reasons for possible differences between rescuer leaning behaviors remain unclear, but may be related to rescuer training and physical characteristics. An investigation of simulated CPR by Verplancke et al. illustrated that characteristics such as rescuer self-confidence, time from last training, and time from last resuscitation experience affected rescuer CPR quality.15
Further work is needed to examine the relationship between leaning and these factors as well as patient characteristics such as body habitus or chest compliance.
Our data also suggest that leaning may not increase over time when a single rescuer performs continuous chest compressions, contrary to our hypothesis that increasing leaning might represent a fatiguing phenomenon. As a note of caution, this is a small, potentially self-selected group of rescuers who performed chest compressions without pauses, and few continuous blocks were longer than two minutes in any case. Nevertheless, despite previous studies showing that a single rescuer’s CPR quality (e.g., compression depth) worsens over time, our current work indicates that increasing time in a block of continuous chest compressions actually negatively correlates with leaning, at least under conditions of CPR monitoring and corrective feedback.13,16–17
An investigation of CPR quality in pediatric resuscitation by Sutton et al. corroborates this finding of more frequent leaning at the beginning of a rescuer’s chest compression performance.18
Two hypotheses might explain this: one is that rescuers could require some time to establish correct chest compression performance, or alternatively, specific to our study site, perhaps rescuers simply responded to the real-time, automated feedback and corrected any chest compression leaning behavior. Prior work has established that real-time feedback modifies other CPR parameters.19–20
Our analysis found that rescuers exhibited less leaning after feedback messages, suggesting that it indeed may have played a role in decreasing leaning during chest compression delivery.
It is important to note several limitations in our work. First, all of the resuscitation episodes analyzed in this study involved the use of a defibrillator that provided real-time, corrective feedback that may have influenced leaning behaviors. Also, the majority of the cardiac arrest events occurred in the critical care setting, where providers are arguably more experienced in cardiac arrest care than those on most general wards. Finally, the current investigators (and consequently staff at the study hospital) have focused for a number of years on improving hospital-wide cardiac arrest care through education and quality improvement activities.20
Taking these points together, our work likely underestimates the prevalence of leaning compared to other settings of CPR performance.
A second limitation is that our study was not powered to test the relationship between leaning and clinical outcomes. Given the multitude of patient and resuscitation quality factors that influence cardiac arrest outcome, such a relationship would require a much larger cohort. A third limitation lies in the choice of a chest compression leaning threshold of ≥2.5 kg. Despite being based upon animal models and prior clinical work, the quantitative effects of leaning on hemodynamics during clinical CPR are unknown. Further work correlating clinical hemodynamics and chest compression parameters such as leaning is required. Finally, we were unable to gather mattress characteristic data for the resuscitations; other work has demonstrated that mattresses deflection confounds CPR quality measurement.21–22
The effect of mattress compliance on chest compression leaning is unknown.