The subject of numerous studies related to CPR has been the length of interruptions between chest compressions. Perkins et al. [5] claimed that effective treatment of patients with out-of-hospital cardiac arrest is dependent on the length of time between chest compressions necessary for the other resuscitation actions. Other authors are of the same opinion [17,19], and indicate that any interruptions in chest compression, including those for artificial ventilation, have a significant negative effect on a patient’s chances of survival.
Our research has shown that the average length of time between chest compression cycles resulting from the necessity to conduct two attempts at ventilation is significantly shorter in the OTH method than when the STD method is used (p<0.001). Similar results were obtained by Maisch et al. [8] in their research comparing the effectiveness of CPR carried out using several methods. Our research shows that as a person conducting CPR using the OTH method is not required to change position, this significantly shortens the length of time between chest compressions, resulting in an increase in chest compressions applied compared to the STD method.
Irrespective of whether the person conducting chest compressions is at the patient’s side or behind their head, they must adjust the pressure on the sternum in order to achieve the correct depth of compression. This depth has been assessed in numerous scientific studies [1, 21–23]. In their research, Maisch et al. [8] compared CPR conducted by paramedics from the patient’s side and from behind the patient’s head in terms of the depth of chest compressions. The author did not find significant differences between the frequency of insufficient and excessive chest compression depths and the reference values. The research results demonstrated that during over-the-head CPR, when the paramedic does not change position, it is easier to adjust the pressure on the sternum to ensure that compressions of the correct depth are made.
The quality of CPR is affected by the rate with which chest compressions are made. Perkins et al. [5] recommend conducting chest compressions on adults at a rate of 100–120 compressions per minute. Scientific studies have proved that rates of compression of below 100/min. and above 120/min. result in a drop in cardiac capacity, and a subsequent increase in patient mortality [2,24]. Our research has shown that in CPR conducted using the OTH method, chest compression cycles of the correct rate are made significantly more often than in the STD method. Chest compressions of insufficient and excessive rate occurred significantly more often in CPR cycles using the STD method.
During CPR, it is extremely important to conduct chest compressions when the chest is complete recoil. Monsieurs et al. [25] recommend that the person conducting chest compressions should take care not to press on the chest in the relaxation phase, thus allowing the chest walls to return to their anatomical shape. Fried et al. [26] assessed cardiopulmonary resuscitation carried out on 108 patients with SCA. In the group studied, a total of 112,569 compressions were made, of which 12% were conducted without complete recoil. In our research, we analyzed chest compressions made with complete and incomplete recoil using the STD and OTH methods. It was shown that compressions with incomplete recoil were made significantly more often during chest compressions using the STD method.
An important factor that affects the quality of CPR is the place where chest compressions are made. In Perkins et al. [5] meta-analysis, they recommend conducting chest compressions in the centre of the patient’s chest to ensure quick identification of the correct place for compressions on the bottom half of the sternum. Our study has shown that a very small percentage of chest compressions were made in the incorrect place by research participants—in the ‘standard’ method 0.68%, and in the ‘over-the-head’ method 0.34% (p<0.001). These results suggest that due to the lower percentage of compressions made in the incorrect place, using the OTH method can have a more beneficial influence on the hemodynamic effect of CPR than the STD method.
Based on scientific studies, it has been determined that the person conducting cardiopulmonary resuscitation should maintain the correct ratio of the time the chest is compressed to the total time from one compression to the next [5,27,28]. Our research showed no statistically significant differences for this parameter between the STD and OTH methods (p>0.001).
The authors of numerous studies have demonstrated that during cardiopulmonary resuscitation, optimal blood flow through the organs is ensured by chest compressions and artificial ventilation at a ratio of 30 to 2 [5,29]. The research showed that for both methods there was no significant difference in maintaining the recommended ratio of chest compressions to artificial ventilation.
Excessive or insufficient ventilation volumes can have negative consequences for a patient with SCA. ERC and AHA guidelines define the volume of air for artificial ventilation as 6–7 ml/kg of patient body mass [25,30]. This value was adopted in our research as a ventilation volume reference parameter. It was demonstrated that the percentage of correct volume ventilations did not differ significantly in both methods (p>0.05). Ventilation with insufficient volume was conducted significantly more often in the STD method (p<0.001). Ventilation with excessive volume was conducted significantly more often in the OTH method (p<0.001).
Conducting artificial ventilation can result in air finding its way into the stomach, causing regurgitation and inhaling of stomach contents into the airways. If the stomach is full of air, this can put pressure on the diaphragm and cause problems with ventilation. Studies by numerous authors have confirmed the importance of reducing the frequency of ventilation and inspiratory pressure so as to minimize the risk of blowing air into the stomach during positive pressure ventilation in patients with unprotected airways [5,31–33]. Our research showed that the percentage of artificial breaths where air found its way into the stomach did not differ significantly in both methods (p>0.05).
Conclusions
Our research has shown that when CPR is conducted using the STD method, there can be significantly more difficulties in maintaining the correct resuscitation parameters than when applying the OTH method. The research results have shown that the STD method does not ensure significantly higher quality CPR for any of the designated ERC parameters. The values of five of the nine parameters tested are significantly closer to the reference values when using the OTH method. The results of our study conducted in simulated conditions suggest that the over-the-head method can be used to a wider extent than only in CPR conducted in confined spaces.