Inspired anaesthetic gas humidification improves thermal uniformity during canine whole body hyperthermia

Abstract

Supplying warmed saturated water vapour in anaesthetic gases during whole body hyperthermia (WBH) could potentially improve thermal uniformity in the trachea and esophagus. Four normal dogs were anaesthetized for WBH at 42°C. A Puritan Bennett Cascade humidifier was used to supply anaesthetic gases saturated with water vapour at an average airway temperature of either 42°C or 38°C. Esophageal temperature was monitored at the thoracic inlet and 5 cm cephalad. Thermal dose was estimated by calculating equivalent minutes for an isoeffect at 43°C (CEM 43° T_x, where T_x is the site of temperature measurement). Endotracheal mucociliary transport velocity (MCTV) was determined before and 48 h following WBH by ^99mTc-MAA scintigraphy. Compared to the 38°C humidified gas group, dogs receiving 42°C humidified gas reached 42°C faster (p = 0·02) and had CEM 43° T_esophageal values equivalent to the target CEM 43° T_rectal. Endotracheal MCTV with 42°C humidified gas, however, was reduced 53% from baseline 48 h following WBH (p = 0·02). With 38°C humidified gas, endotracheal mucociliary transport velocity was unchanged from baseline 48 h post WBH. Tracheal histology was examined using light and electron microscopy in four additional dogs euthanatized following 90 min of 42°C humidified gas combined with WBH. There was no histological evidence of tracheal or lung thermal damage with 42°C humidified gas in these four dogs. However, a moderate increase in tracheal goblet cell secretory granule staining was observed. This change could imply temporary heat-induced ciliary microtubule dysfunction, rather than decreased mucus production, as the likely mechanism of reduced mucociliary transport velocity 48 h following WBH. Administration of 42°C humidified anaesthetic gases with WBH improves heating rate and esophageal thermal uniformity but temporarily depresses tracheal mucociliary transport velocity.

Key Words:

• Mucociliary transport velocity
• Cascade humidifier
• whole body hyperthermia
• anaesthesia