In Vitro Evaluation of a Micro-Doppler Catheter for Detection and Aspiration of Venous Air Emboli

Abstract

Venous air embolism (VAE) is a potentially fatal complication of surgery when open veins at a surgical site are exposed to ambient air pressure which exceeds the pressure in the venous system. Common techniques of detecting VAE are precordial Doppler monitoring and transesophogeal echocardiography. Precordial Doppler monitoring has poor accuracy and transesophogeal echocardiography is expensive and user-intensive. In both methods, a separate catheter must be inserted into the vena cava so that an embolus may be aspirated if it is detected. We created a micro-Doppler assembly using two ceramic transducers fitted over a 5.8F multiorifice central venous catheter. This micro-Doppler catheter (MDC) was tested in vitro using a static tank and an artificial vena cava (AVC). The MDC was also tested for acoustic pressure and current leakage in the static tank and for heat generation and cavitation in the AVC. The MDC was able to detect bubbles more than 2 mm in diameter with 100% accuracy. A blinded observer was able to identify the onset of vapor lock in 10 of 10 trials. The same observer was able to terminate vapor lock in 10 of 10 trials. The acoustic pressures measured were <1.8 MPa. There was no increase in temperature in the AVC over 24 h and there was no evidence of cavitation in the AVC over 4 h. We have created a MDC that can detect air emboli and relieve vapor lock in a simulated vena cava and atrium. This catheter could be placed percutaneously in the vena cava. Based on the measurements of acoustic pressure, temperature in the AVC and lack of cavitation in the AVC, the device appears to be safe for use in humans. More studies are required to determine if the catheter could be used to detect and aspirate VAE during surgeries where VAE is likely, such as sitting craniotomy.