Apnoeic oxygenation in adults under general anaesthesia using Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE)- A physiological study

Abstract

Background. Apnoeic oxygenation during anaesthesia has traditionally been limited by the rapid increase in carbon dioxide and subsequent decrease in pH. Using a Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) technique a slower increase in carbon dioxide than earlier studies was seen. Notably, apnoeic oxygenation using THRIVE has not been systematically evaluated with arterial blood gases or in patients undergoing laryngeal surgery. The primary aim of this study was to characterize changes in arterial PO2, PCO2 and pH during apnoeic oxygenation using THRIVE under general anaesthesia. Methods. Adult patients, (ASA I-II), undergoing shorter laryngeal surgery under general anaesthesia, were oxygenated during apnoea using THRIVE, 100% oxygen, 40-70 litres min-1. A cohort was randomized to hyperventilate during preoxygenation. Vital parameters and blood gases were monitored. Results. Thirty-one patients, age 51 (34-76) yr, BMI 25 (4) were included. Mean apnoea time was 22.5 (4.5) min. Patients were well oxygenated, SpO2 was never below 91%. The increase in PaCO2 and end-tidal CO2 during apnoea was 0.24 (0.05) and 0.12 (0.04) kPa min-1, respectively. Hyperventilation during pre-oxygenation generated no difference in PaCO2 at the end of apnoea compared with normoventilation. Conclusions. This physiological study of apnoeic oxygenation using THRIVE during laryngeal surgery shows that this technique is able to keep patients with mild systemic disease and a BMI<30 well oxygenated for a period of up to 30 min. The THRIVE concept makes it possible to extend the apnoeic window but monitoring of CO2 and/or pH is recommended.