High PEEP Levels during CPR Improve Ventilation without Deleterious Haemodynamic Effects in Pigs

Chest compression synchronized ventilation during prolonged experimental cardiopulmonary resuscitation improves oxygenation but may cause pneumothoraces

Background

Chest compression synchronized ventilation (CCSV) has been proposed to provide superior ventilation and haemodynamics during cardiac arrest (CA) compared to conventional asynchronous ventilation and compressions. We compared arterial gas exchange, pH, lactate levels and haemodynamics between CCSV and manual asynchronous ventilation during prolonged experimental CA.

Methods

We randomized 30 pigs (weight ca. 55 kg) to receive CCSV with a MEDUMAT Standard2 ventilator or a manual bag valve targeting 10-12 ventilations per minute. Chest compressions were provided with a Lucas® 2 device. Arterial samples were drawn every 5 min and monitoring was recorded continuously. The animals underwent chest CT scans after death.

Results

The median intra-arrest arterial blood gas results for CCSV were PaO2 = 490 (86-570) mmHg, PaCO2 = 20 (10-35) mmHg and pH = 7.39 (7.19-7.53). In the manual ventilation group, the results were PaO2 = 304 (109-379), PaCO2 = 36 (28-47) and pH = 7.24 (7.12-7.34). The oxygen levels were significantly higher in the CCSV group compared to a linear mixed model (p = 0.046). The differences in CO2 and pH levels were not statistically significant. The minute volumes and positive end-expiratory pressures were higher in the CCSV (18.0 [15.3-19.8] l/min; 32.6 [29.2-35.6] cmH2O) group compared to the control group (5.7 [4.9-7.0] l/min; 2.8 [1.8-4.1] cmH2O). The CCSV group had 12 pneumothoraces compared to 3 in the control group (p = 0.008).

Conclusions

The CCSV protocol resulted in higher arterial oxygenation but more pneumothoraces.The study was approved by the Finnish National Animal Experiment Board (ESAVI-26974-2023).

Ventilation during cardiopulmonary resuscitation: A narrative review

Ventilation during cardiopulmonary resuscitation is vital to achieve optimal oxygenation but continues to be a subject of ongoing debate. This narrative review aims to provide an overview of various components and challenges of ventilation during cardiopulmonary resuscitation, highlighting key areas of uncertainty in the current understanding of ventilation management. It addresses the pulmonary pathophysiology during cardiac arrest, the importance of adequate alveolar ventilation, recommendations concerning the maintenance of airway patency, tidal volumes and ventilation rates in both synchronous and asynchronous ventilation. Additionally, it discusses ventilation adjuncts such as the impedance threshold device, the role of positive end-expiratory pressure ventilation, and passive oxygenation. Finally, this review offers directions for future research.

Airway management and ventilation techniques in resuscitation during advanced life support: an update

For many years, ventilation has been an essential part of advanced life support (ALS) in cardiopulmonary resuscitation (CPR). Nevertheless, there is little evidence about the best method of ventilation during resuscitation for both out-of-hospital cardiac arrest (OHCA) and inhospital cardiac arrest (IHCA) patients. Effective ventilation is one of the two main keys to successful resuscitation. In this context, the question always arises as to which airway management, along with which ventilation mode, constitutes the best strategy. Conventional ventilation modes are not designed for cardiac arrest and show important limitations that must be considered when used in CPR. Manual ventilation without the use of an automated transport ventilator (ATV) could be shown to be uncontrolled in applied volumes and pressures and should be avoided. Mechanical ventilation with an ATV is therefore superior to manual ventilation, but both volume- and pressure-controlled ventilation modes are significantly influenced by chest compressions. With the newly designed chest compression synchronized ventilation (CCSV), a special ventilation mode for resuscitation is available. Further research should be conducted to obtain more evidence of the effect of ventilation during CPR on outcomes following OHCA and not only about how to secure the airway for ventilation during CPR.

Oxygenation and ventilation during prolonged experimental cardiopulmonary resuscitation with either continuous or 30:2 compression-to-ventilation ratios together with 10 cmH20 positive end-expiratory pressure

BACKGROUND

In refractory out-of-hospital cardiac arrest, the patient is commonly transported to hospital with mechanical continuous chest compressions (CCC). Limited data are available on the optimal ventilation strategy. Accordingly, we compared arterial oxygenation and haemodynamics during manual asynchronous continuous ventilation and compressions with a 30:2 compression-to-ventilation ratio together with the use of 10 cmH2O positive end-expiratory pressure (PEEP).

METHODS

Intubated and anaesthetized landrace pigs with electrically induced ventricular fibrillation were left untreated for 5 min (n = 31, weight ca. 55 kg), after which they were randomized to either the CCC group or the 30:2 group with the the LUCAS® 2 piston device and bag-valve ventilation with 100% oxygen targeting a tidal volume of 8 ml/kg with a PEEP of 10 cmH2O for 35 min. Arterial blood samples were analysed every 5 min, vital signs, near-infrared spectroscopy and electrical impedance tomography (EIT) were measured continuously, and post-mortem CT scans of the lungs were obtained.

RESULTS

The arterial blood values (median + interquartile range) at the 30-min time point were as follows: PaO2: 180 (86-302) mmHg for the 30:2 group; 70 (49-358) mmHg for the CCC group; PaCO2: 41 (29-53) mmHg for the 30:2 group; 44 (21-67) mmHg for the CCC group; and lactate: 12.8 (10.4-15.5) mmol/l for the 30:2 group; 14.7 (11.8-16.1) mmol/l for the CCC group. The differences were not statistically significant. In linear mixed models, there were no significant differences between the groups. The mean arterial pressures from the femoral artery, end-tidal CO2, distributions of ventilation from EIT and mean aeration of lung tissue in post-mortem CTs were similar between the groups. Eight pneumothoraces occurred in the CCC group and 2 in the 30:2 group, a statistically significant difference (p = 0.04).

CONCLUSIONS

The 30:2 and CCC protocols with a PEEP of 10 cmH2O resulted in similar gas exchange and vital sign outcomes in an experimental model of prolonged cardiac arrest with mechanical compressions, but the CCC protocol resulted in more post-mortem pneumothoraces.

Ultra-low tidal volume ventilation during cardiopulmonary resuscitation shows no mitigating effect on pulmonary end-organ damage compared to standard ventilation: insights from a porcine model

OBJECTIVE

This study aimed to determine whether ultra-low tidal volume ventilation (ULTVV) applied during cardiopulmonary resuscitation (CPR) compared with standard ventilation (intermittent positive pressure ventilation, IPPV) can reduce pulmonary end-organ damage in the post-resuscitation period.

METHODS

A prospective, randomized trial was conducted using a porcine model (n = 45). The animals were divided into three groups: IPPV, ULTVV, and a sham control group. Juvenile male pigs underwent CPR after inducing ventricular fibrillation and received the designated ventilation intervention [IPPV: tidal volume 6-8 ml per kilogram body weight (ml/kg BW), respiratory rate 10/min, FiO2 1.0; ULTVV: tidal volume 2-3 ml/kg BW, respiratory rate 50/min, FiO2 1.0]. A 20-h observation period followed if return of spontaneous circulation was achieved. Histopathological examination using the diffuse alveolar damage scoring system was performed on postmortem lung tissue samples. Arterial and venous blood gas analyses and ventilation/perfusion measurements via multiple inert gas elimination technique (MIGET) were repeatedly recorded during the experiment.

RESULTS

Out of the 45 experiments conducted, 28 animals were excluded based on predefined criteria. Histopathological analysis showed no significant differences in lung damage between the ULTVV and IPPV groups. ULTVV demonstrated adequate oxygenation and decarboxylation. MIGET measurements during and after resuscitation revealed no significant differences between the intervention groups.

CONCLUSION

In the short-term follow-up phase, ULTVV demonstrated similar histopathological changes and functional pulmonary parameters compared to standard ventilation. Further research is needed to investigate the long-term effects and clinical implications of ULTVV in resuscitation settings.

Analysis of cerebral Interleukin-6 and tumor necrosis factor alpha patterns following different ventilation strategies during cardiac arrest in pigs

Hypoxia-induced neuroinflammation after cardiac arrest has been shown to be mitigated by different ventilation methods. In this prospective randomized animal trial, 35 landrace pigs were randomly divided into four groups: intermittent positive pressure ventilation (IPPV), synchronized ventilation 20 mbar (SV 20 mbar), chest compression synchronized ventilation 40 mbar (CCSV 40 mbar) and a control group (Sham). After inducing ventricular fibrillation, basic life support (BLS) and advanced life support (ALS) were performed, followed by post-resuscitation monitoring. After 6 hours, the animals were euthanized, and direct postmortem brain tissue samples were taken from the hippocampus (HC) and cortex (Cor) for molecular biological investigation of cytokine mRNA levels of Interleukin-6 (IL-6) and tumor necrosis factor alpha (TNFα). The data analysis showed that CCSV 40 mbar displayed low TNFα mRNA-levels, especially in the HC, while the highest TNFα mRNA-levels were detected in SV 20 mbar. The results indicate that chest compression synchronized ventilation may have a potential positive impact on the cytokine expression levels post-resuscitation. Further studies are needed to derive potential therapeutic algorithms from these findings.