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

Author(s): Hermez LA, Spence CJ, Payton MJ, Nouraei SAR, Patel A, Barnes TH.

Anaesthesia. 2019; 74: 441-449

Respiratory critical care

Digest Author(s): Marianna Laviola / 20 March, 2019

Several studies have shown that in patients who are anaesthetised and apnoeic the use of high-flow nasal oxygenation can increase apnoea time by delaying hypoxaemia with only small increases in arterial partial pressure of carbon dioxide (CO2) (1-3). However, the physiologic mechanisms involved in CO2 elimination are unclear.In this study, Hermez and co-authors examined the fluid dynamics affecting CO2 clearance from the carina to the mouth in Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) technique, calculating the CO2 clearance.

They used three laboratory airway models to investigate mechanisms of CO2 clearance in apnoeic patients: two-dimensional fluid model used for supraglottis flow visualisation with particle image velocimetry; three-dimensional gas model used to visualise transport of gas between carina and mouth; and three-dimensional model and lung simulator used for turbulence and CO2 clearance measurements. For all experiments, they used a cardiogenic stroke volume of 0-40 ml.

With no cardiogenic oscillations applied, mean (SD) CO2 clearance increased from 0.29 (0.04) ml·min-1 to 1.34 (0.14) ml·min-1 as the THRIVE flow rate was increased from 20 l·min-1 to 70 l·min-1. With a cardiogenic oscillation of 20 ml·beat-1 applied, CO2 clearance increased from 11.9 (0.50) ml.min-1 to 17.4 (1.2) ml·min-1 as THRIVE flow rate was increased from 20 l·min-1 to 70 l·min-1. Turbulence intensity was higher on cardiogenic inspiration phase than on cardiogenic expiration and on inspiration, the turbulent intensity increased with THRIVE flow rate.

This work shows CO2 clearance during THRIVE is mediated by the interaction between supraglottic flow vortices and flow oscillations caused by cardiogenic oscillations. Limitations of the study include the model investigated the clearance only from the carina to the atmosphere and not from the lung periphery and that the models were printed from hard plastic and therefore, they were not compliant.

Key points

  1. THRIVE extends the time until desaturation and significantly decreases the rate of carbon dioxide accumulation, but the physiologic mechanisms involved in carbon dioxide elimination are still under study.
  2. In-vitro laboratory airway models were used to investigate mechanisms of carbon dioxide clearance in apnoeic patients using a THRIVE device.
  3. Carbon dioxide clearance during high-flow nasal oxygenation appears to be explained by an interaction between entrained and highly turbulent supraglottic flow vortices generated by high-flow nasal oxygen and cardiogenic oscillations.
  4. This study is in agreement with a recent published work that uses a computer simulator to ex-plain the physiological mechanisms of apnoeic oxygenation (4).

References

  1. Patel A, Nouraei SA. Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE): a physiological method of increasing apnoea time in patients with difficult airways. Anaesthesia 2015; 70: 323–9
  2. Gustafsson I-M, Lodenius A, Tunelli J, Ullman J, Jonsson Fagerlund M. Apnoeic oxygenation in adults under general anaesthesia using transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) – a physiological study. British Journal of Anaesthesia 2017; 118: 610–17.
  3. To K, Harding F, Scott M, et al. The use of transnasal humidified rapid-insufflation ventilatory exchange in 17 cases of subglottic stenosis. Clinical Otolaryngology 2017; 42: 1407–10.
  4. M. Laviola, A Das, M. Chikhani, D.G. Bates and J.G. Hardman. Computer simulation clarifies mechanisms of carbon dioxide clearance during apnoea. British Journal of Anaesthesia. 2019 Mar;122(3):395-401