Do heat and moisture exchangers in the anaesthesia breathing circuit preserve body temperature in dogs undergoing anaesthesia for magnetic resonance imaging?

Objective:  To investigate whether use of a Heat andMoisture Exchanger (HME) preserve body temperature in dogs weighing < 10kg anaesthetisedfor MRI.

Study design:prospective, randomised, clinical trial.

Animals:Thirty one client owned dogs (17 females, 14 males), 8 months-11 years old,weighing between 2.5 kg and 10 kg.

Methods:Dogs were randomly assigned to a treatment group (HME (n= 16) or no HME(n=15)). Dogs were pseudorandomized according to the premedication theyreceived, either dexmedetomidine or no dexmedetomidine. Induction agents werenot standardised. General anaesthesia was maintained with isoflurane vaporisedin 100% oxygen delivered using a T- piece and a fresh gas flow of 600 ml kg^-1minute^-1. Rectal temperature was measured before premedication (T1),after induction (T2), before moving to the MRI unit (T3) and at the end of theMRI scan (T4). Ambient temperatures were measured in the induction room,outside and inside the MRI unit. Data were analysed using a General LinearModel (GLM) with T4, as the outcome variable. Linear correlations were performed between T1, T2, T3 and T4 and variablesthat predicted T4 were investigated.

 

Results:   Gender, ageor body mass were not significantly different between groups. There were nosignificant differences in rectal temperature between groups at any time point(HME_{end MRI}= 36.26 ± 1.05 °C, No HME_{end MRI} =36.24 ± 1.41 °C)but dogs receiving dexmedetomidine (DEX_{end MRI}  =36.6 ± 0.7 °C) had a higherrectal temperature compared to dogs that did not receive dexmedetomidine (NoDEX_{end MRI} = 35.9 ± 1.6 °C) for premedication. Rectal temperature varieddirectly with ambient temperature in MRI scanning room and inversely withanaesthetic duration.   

 

Conclusions and Clinical Relevance: Using a HME did not alter body temperature in dogs weighing less than 10 kgundergoing an MRI but including dexmedetomidine in the premedication regimencan preserve the bodytemperature during anaesthesia.