Abstract

BackgroundDuring anesthesia, as compared with intensive care, the time of the tracheal intubation is much shorter. An inhaled gas minimum humidity of 20 mgH2O.L-1 is recommended to reduce the deleterious effects of dry gas on the airways during anesthesia with tracheal intubation. The Fabius GS Premium® anesthesia workstation (Dräger Medical, Lübeck, Germany) has a built-in hotplate to heat gases in the breathing circuit. A heat and moisture exchanger (HME) is used to further heat and humidify the inhaled gas. The humidity of the gases in the breathing circuit is influenced by the ambient temperature. We compared the humidity of the inhaled gases from a low-flow Fabius anesthesia workstation with or without thermal insulation (TI) of the breathing circuit and with or without an HME.MethodsWe conducted a prospective randomized trial in 41 adult female patients who underwent elective abdominal surgery. The patients were allocated into four groups according to the devices used to ventilate their lungs using a Dräger Fabius anesthesia workstation with a low gas flow (1 L.min-1): control, with TI, with an HME or with TI and an HME (TIHME). The mean temperature and humidity of the inhaled gases were measured during 2-h after connecting the patients to the breathing circuit.ResultsThe mean inhaled gas temperature and absolute humidity were higher in the HME (29.2±1.3°C; 28.1±2.3 mgH2O·L-1) and TIHME (30.1±1.2°C; 29.4±2.0 mgH2O·L-1) groups compared with the control (27.5±1.0°C; 25.0±1.8 mgH2O·L-1) and TI (27.2±1.1°C; 24.9±1.8 mgH2O·L-1) groups (P = 0.003 and P<0.001, respectively).ConclusionsThe low-flow Fabius GS Premium breathing circuit provides the minimum humidity level of inhaled gases to avoid damage to the tracheobronchial epithelia during anesthesia. TI of the breathing circuit does not increase the humidity of the inhaled gases, whereas inserting an HME increases the moisture of the inhaled gases closer to physiological values.

Highlights

  • In physiological conditions, inhaled air is warmed and humidified while passing through the nose and upper airways, reaching the subglottic space with a temperature of 31.2 ̊C to 33.6 ̊C, a relative humidity (RH) of 95%-100% and an absolute humidity (AH) of 33 mg H2O.L-1[1,2,3]

  • The mean inhaled gas temperature and absolute humidity were higher in the heat and moisture exchanger (HME) (29.2 ±1.3 ̊C; 28.1±2.3 mgH2OÁL-1) and TI and an HME (TIHME) (30.1±1.2 ̊C; 29.4±2.0 mgH2OÁL-1) groups compared with the control (27.5±1.0 ̊C; 25.0±1.8 mgH2OÁL-1) and thermal insulation (TI) (27.2±1.1 ̊C; 24.9±1.8 mgH2OÁL-1) groups (P = 0.003 and P

  • TI of the breathing circuit does not increase the humidity of the inhaled gases, whereas inserting an HME increases the moisture of the inhaled gases closer to physiological values

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Summary

Introduction

In physiological conditions, inhaled air is warmed and humidified while passing through the nose and upper airways, reaching the subglottic space with a temperature of 31.2 ̊C to 33.6 ̊C, a relative humidity (RH) of 95%-100% and an absolute humidity (AH) of 33 mg H2O.L-1[1,2,3]. These functions are bypassed when a patient’s trachea is intubated or a supraglottic airway device is placed in situ [4]. We compared the humidity of the inhaled gases from a low-flow Fabius anesthesia workstation with or without thermal insulation (TI) of the breathing circuit and with or without an HME

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