Elsevier

Resuscitation

Volume 35, Issue 2, October 1997, Pages 145-148
Resuscitation

A comparison of the end-tidal-CO2 documented by capnometry and the arterial pCO2 in emergency patients

https://doi.org/10.1016/S0300-9572(97)00043-9Get rights and content

Abstract

Satisfactory artificial ventilation is defined as sufficient oxygenation and normo- or slight arterial hypocarbia. Monitoring end tidal CO2 values with non-invasive capnometry is a routine procedure in anaesthesia, emergency medicine and intensive care. In anaesthesia the ventilation volume is adjusted to the capnometric end tidal CO2 (ETCO2), taking into account a normal variation from the pACO2 of 3–8 mmHg. We evaluated the usefulness and practicability of using ETCO2 for correctly adjusting ventilation parameters in prehospital emergency care, by comparing arterial pCO2 and ETCO2 of 27 intubated and ventilated patients. We used the side-stream capnometry module of the Defigard 2000 (Bruker, ChemoMedica Austria) and a portable blood gas analyzer (OPTI 1, AVL Graz, Austria). Evaluation of the group of patients as a whole showed that there was no correlation whatsoever between the end expiratory and arterial CO2. Dividing the patients into three subgroups (I, During CPR; II, respiratory disturbances of pulmonary and cardiac origin; III, extrapulmonary respiratory disturbances), we found that only patients without primary cardiorespiratory damage showed a slight, but not statistically significant, correlation. This can be explained by the fact that almost any degree of cardiorespiratory failure causes changes of the ventilation–perfusion ratio, impairing pulmonary CO2 elimination. We conclude, that the ventilation of emergency patients can only be correctly adjusted according to values derived from an arterial blood gas analysis and ETCO2 measurements cannot be absolutely relied upon for accuracy except, perhaps, in patients without primary cardiorespiratory dysfunction.

Introduction

The measurement of end tidal CO2 with capnometry is a well-established method for the continuous monitoring of ventilation in routine anaesthesia and in emergency care. Several devices are available for emergency patients, some of them combined with ECG (electrocardiography) or pulse oximetry. Since May 1995 a transportable blood gas analyzer has made measurements of blood gas values in emergency situations possible.

The aim of this study was to determine whether capnometry is a useful method for correctly adjusting ventilation parameters in prehospital emergency care, compared with blood gas analysis.

Section snippets

Patients and methods

The study was performed in Graz, Austria, which has a population of about 250 000. The emergency care service is organized by the Austrian Red Cross which provides a staff of highly qualified emergency technicians, comparable to the American paramedics, supported by emergency physicians from the University Hospital of Graz. Thus, in an emergency situation up to six experts could attend the victim who is seriously ill or injured [1]. The participants of this study were the anaesthesiologists of

Results

During the observation period, from May 1995 to September 1996, 27 emergency patients (15 males, 12 females; mean age, 66.1 years, range, 23–93 years) were included in the study. A total of 61 arterial blood gas samples were taken (five patients, four samples; six patients, three samples; seven patients, two samples; and nine patients, one sample). Thirty-nine samples were taken during cardiopulmonary resuscitation, 11 in the presence of cardiorespiratory insufficiency, and 11 in patients with

Discussion

Our study shows, that although widely used and useful in intraoperative monitoring, the regulation of ventilatory values based on capnometry, which is applicable during routine anaesthesia, seems to carry considerable problems in emergency cases. A positive aspect of capnometry is the assessment of airway continuity. Disconnection or dislocation of the tracheal tube can be detected immediately. Cardiac arrest can also be rapidly diagnosed.

All ETCO2 measurements in our study were made using the

Conclusions

Though it may serve as a `safety belt' enabling an immediate diagnosis of airway occlusion or tracheal tube dislocation, capnometry is not reliable to estimate accurately the quality of ventilation in most emergency patients. Only patients without primary cardiac or pulmonary dysfunction (isolated head injury or respiratory disturbance of extrapulmonary origin) can be ventilated correctly by observation of the ETCO2. Thus, to correctly assess the ventilation values, it is advisable to perform

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