Research background
Intermittent positive pressure ventilation (IPPV) can have an adverse impact on the outcomes of resuscitation by increasing intrathoracic pressure. As an alternative, continuous flow insufflation of oxygen (CFIO) has been researched, but evidence supporting the superiority of CFIO to IPPV in all cardiac arrest situations is thin.

Study aim
This study aims to compare the effects of CFIO using a novel one-way valve, which was designed to induce a intrathoracic pressure reduction during CPR with the conventional IPPV in a rat model of respiratory cardiac arrest caused by oxygenation  failure.  

Study animal
Male Sprague-Dawley rats weighing 400-450 g were used.

Characteristics of novel device (Figure 1)
The CFIO method applied in this study was designed such that endotracheal inspiratory flow is strengthened during chest decompression by the oxygen accumulated in the opening channel as a result of the closed valve. Further, during chest compression, there is no collision between oxygen running toward the valve and gas pushed out, as the valve is not located in the channel connecting to the trachea, and instead, the outflow of gas from the airway is actually facilitated because the valve is opened due to the pressure in the opening channel and the oxygen flow is directed toward the valve.

Method
Thirty  rats were randomly assigned to the sham, IPPV, and CFIO group, with 10 in each group. Respiratory cardiac arrest was induced by blocking the endotracheal tube. Arterial blood gas analysis (ABGA) was performed one minute after CPR to compare the level of oxygenation. Neurological assessment was performed 24 hours and 48 hours after return of spontaneous circulation (ROSC) using the neurologic deficit score (NDS) to compare the degree of hypoxic brain injury. Then, tissue specimens were taken to analyse the degree of pulmonary barotrauma and ischemic brain injury according to the ventilation method.  Although the methods are described well and in detail, please reduce the word count to be more brief.

Results
ROSC was restored in six rats in the IPPV group and five rats in the CFIO group. At one minute after CPR, oxygen partial pressure was significantly higher in the CFIO group (IPPV vs CFIO: PaO2 56.10 (54.68–58.25) mmHg vs 83.10 (81.05–87.50) mmHg, p<0.001) (Table 2). The NDSs at 24 hours and 48 hours after  ROSC were significantly higher in the CFIO group (NDS at 24 h, CFIO vs IPPV, 76 (75-77) vs 70 (67–70.5), p=0.004; NDS at 48 h, CFIO vs IPPV, 78 (76–80) vs 74 (71.35–76.5), p=0.001) (Figure 3). Lung biopsy performed at 48 hours after ROSC showed a greater level of inflammatory cells and marked thickening of the alveolar wall in the IPPV group, and the IPPV group also had a higher frequency and percentage of neuroglial cells and apoptotic bodies of pyramidal cells  caused by an ischemic brain injury (Figure 4-5).

Conclusion
The CFIO method using a novel one-way valve applied on a rat model of cardiac arrest led to a greater level of oxygenation and less lung and brain cell injuries compared to that of the IPPV method.

8 - Comparison of the constant flow insufflation of oxygen with a one-way valve and intermittent positive pressure ventilation during cardiopulmonary resuscitation in asphyxic cardiac arrest