Difference in end-tidal carbon dioxide changes during cardiopulmonary resuscitation between cardiac arrest due to asphyxia and VF/VT cardiac arrest

Introduction

In recent years there has been an increased interest in the use of capnometry, the noninvasive continuous measurement of partial pressure of end-tidal carbon dioxide (petCO₂) in expired air. petCO₂ monitoring has been useful in determining the effectiveness of cardiopulmonary resuscitation. During cardiopulmonary reanimation (CPR) the petCO₂ correlates with cardiac output and efficacy of cardiac compressions and as such has been shown to have prognostic value in CPR. This study was undertaken to compare initial petCO₂ and petCO₂ after 1 min during CPR in cardiac arrest due to asphyxia versus cardiac arrest due to ventricular fibrillation (VF).

Methods

This prospective study was conducted at the Center of Emergency Medicine – Pre-hospital Unit Maribor, Slovenia. The study included two groups of patients. The first group represented patients who suffered from heart arrest due to asphyxia. The causes of asphyxia included foreign body in the airway, aspiration, suicide with hanging, drowning, edema or tumor of airway and acute asthma attack. The initial rhythm was either asystole or pulse-less electrical activity. We compared this group of patients with those whose cause of heart arrest was AMI or malignant arrhythmias (VF or pulseless VT). petCO₂ measurements were made by infrared side stream capnometer (BCI Capnocheck Model 20600A1; BCI international, Waukesha, WI, USA). petCO₂ was measured for both groups immediately after intubation (first measurement) and then repeatedly every minute. Thus the initial, average and end petCO₂ was detected for both groups. We performed the same procedure for the patients with return of spontaneous circulation (ROSC) and for those without ROSC. Statistics used: Student's t test, χ² test, P < 0.05 was considered significant.

Results

From February 1998 to February 2002 we analyzed 126 patients with cardiac arrest (initial rhythm VF/pulseless VT) and 36 patients with cardiac arrest due to asphyxia (initial rhythm asystolia or PEA). Patients with cardiac arrest caused by asphyxia were younger than patients whose cardiac arrest was provoked by VF (50.7 ± 21.4 vs 64.5 ± 15.4; P < 0,05). Time spent from beginning of the arrest to start of CPR was not significantly different (patients with ROSC: 8.2 ± 5.2 min vs 9.1 ± 4.6 min, P = 0,79; patients without ROSC: 14.1 ± 4.6 min vs 13.6 ± 5.2 min, P = 0.83). The mean value of EtCO₂ for all patients (with and without ROSC) is presented in Table 1. In the group of patients who presented with arrest due to asphyxia there was no significant difference in initial values of petCO₂, even when compared with those with and without ROSC (72.4 ± 13.4 mmHg vs 67.4 ± 14.6 mmHg). However, there was a significant difference in petCO₂ after 1 min of CPR between those patients with ROSC and those without ROSC (34.5 ± 9.7 mmHg vs 18.1 ± 8.3 mmHg).

Table 1 The value of initial, average, final and petCO₂ after 1 min of CPR for arrest due to asphyxia and VT/VF cardiac arrest

Conclusions

In cardiac arrest caused by asphyxia, the initial petCO₂ is much higher than in cardiac arrest due to VF and does not correlate with ROSC.

After 1 min of CPR, petCO₂ correlates with ROSC and it is an important method for noninvasive monitoring of the effectiveness of CPR.