A physiological study to determine the mechanism of carbon dioxide clearance during apnoea when using transnasal humidified rapid insufflation ventilatory exchange (THRIVE)

Abstract

Summary Clinical observations suggest that compared with standard apnoeic oxygenation, transnasal humidified rapid‐insufflation ventilatory exchange using high‐flow nasal oxygenation reduces the rate of carbon dioxide accumulation in patients who are anaesthetised and apnoeic. This suggests that active gas exchange takes place, but the mechanisms by which it may occur have not been described. We used three laboratory airway models to investigate mechanisms of carbon dioxide clearance in apnoeic patients. We determined flow patterns using particle image velocimetry in a two‐dimensional model using particle‐seeded fluorescent solution; visualised gas clearance in a three‐dimensional printed trachea model in air; and measured intra‐tracheal turbulence levels and carbon dioxide clearance rates using a three‐dimensional printed model in air mounted on a lung simulator. Cardiogenic oscillations were simulated in all experiments. The visualisation experiments indicated that gaseous mixing was occurring in the trachea. With no cardiogenic oscillations applied, mean (SD) carbon dioxide clearance increased from 0.29 (0.04) ml.min−1 to 1.34 (0.14) ml.min−1 as the transnasal humidified rapid‐insufflation ventilatory exchange flow rate was increased from 20 l.min−1 to 70 l.min−1 (p = 0.0001). With a cardiogenic oscillation of 20 ml.beat−1 applied, carbon dioxide clearance increased from 11.9 (0.50) ml.min−1 to 17.4 (1.2) ml.min−1 as the transnasal humidified rapid‐insufflation ventilatory exchange flow rate was increased from 20 l.min−1 to 70 l.min−1 (p = 0.0014). These findings suggest that enhanced carbon dioxide clearance observed under apnoeic conditions with transnasal humidified rapid‐insufflation ventilatory exchange, as compared with classical apnoeic oxygenation, may be explained by an interaction between entrained and highly turbulent supraglottic flow vortices created by high‐flow nasal oxygen and cardiogenic oscillations.

Uses and mechanisms of apnoeic oxygenation: a narrative review

“…A paper in this issue of the journal proposes a novel additional mechanism that may be responsible .…”

Carbon dioxide clearance during apnoea with high‐flow nasal oxygen: epiphenomenon or a failure to THRIVE?

“…Subsequently, case series by other groups , randomised trials and widespread international experience have confirmed beyond doubt that this is a highly effective approach to apnoeic oxygenation. However, the data surrounding the concept of carbon dioxide clearance during apnoea with high‐flow nasal oxygen is more limited, raising the possibility that recent modelling and simulation exercises are premature, and that appropriately conducted randomised trials in adults are still required. It is thus timely to re‐examine the strengths and weaknesses of the carbon dioxide data during apnoea, in contrast to the more established benefits associated with high‐flow nasal oxygen.…”

Nasal high‐flow oxygen in pediatric anesthesia and airway management

“…The rate of rise of carbon dioxide using THRIVE was found to be 1.2 mm Hg/min, compared to classic apnoeic oxygenation technique with rate of rise of carbon dioxide of 2.6‐3.3 mm Hg/min. This carbon dioxide clearance mechanism has been suggested to be dependent on flow rate and affected by cardiogenic oscillations . These initial studies have subsequently revolutionized airway management in adult anesthesia providing a safer oxygenation technique allowing a less hurried approach to difficult airways.…”