O-29 End-tidal carbon dioxide is a reliable non-invasive parameter in acute pulmonary embolism

Abstract

Introduction. The clinical presentation of acute pulmonary embolism (PE) ranges from shock or sustained hypotension to mild dyspnoea. The diagnosis is confirmed by objective testing in only about 20%. We hypothesized that end-tidal carbon dioxide (ET-CO2) is a reliable non-invasive parameter in the development of acute PE. Method. Twenty adult female Landrace pigs (-90 Kg) were anaesthetized and ventilated. A pulmonary catheter and a large bore catheter (tracheal tube 8.5 mm ID with the cuff removed) were inserted into the jugular veins. An arterial catheter was inserted into the carotid artery. ET-CO2 was measured with capnography and peripheral oxygen saturation with pulse oxim-etry (SpO2). All parameters were collected every five seconds. Autologous blood mixed with bovine thrombin formed clots in 50 mL syringes used for the embolus. An embolus was injected into the large bore catheter every 5 minutes until circulatory collapse was seen after 4 or 5 injections. This animal model is described in details in an earlier publication [1]. Parametric statistics were used with a significance level of P<0.05. Results. The development of a great central and fatal PE was very reproducible. After % of the emboli were given the arterial pressure, pulse and SpO2 were still within normal ranges. Pulmonary pressure significantly increased whereas ET-CO2 significantly decreased to very low values with each embolus given and reached zero at the time of circulatory collapse. The sensitivity as well as the specificity of ET-CO2 measurements was 100%. The arterial pressure of CO2 was unchanged. Conclusion. With the development of acute PE an increase in pulmonary pressure was seen, but another very reliable parameter was the decrease in ET-CO2 caused by an increased ven-tilatory dead space due to non-perfused regions in the lungs. ET-CO2 is non-invasive and may be essential in the diagnosis of acute PE.