Does MRI of different regions lead to different temperature changes in children done under anaesthesia? – A cross sectional study

Abstract              Background: Both general anaesthesia and low-ambient temperature in the magnetic resonance imaging (MRI) suite makes the paediatric patient vulnerable to fall in body temperature. But the radiofrequency radiations cause increase in body temperature. Studies have shown both increase and decrease in body temperature in children undergoing MRI under anaesthesia.  But previously done studies have not shown if there is a difference in temperature changes because of different MRI scan regions. Aim: To determine if MRI of different regions cause different temperature changes in children undergoing MRI under anaesthesia and to find the predominant direction of temperature change. Setting: Prospective observational cross-sectional study. Methods: Two hundred and fifty children of age between birth and 16 years of age scheduled for MRI under anaesthesia were recruited. A baseline (pre-scan) and post-scan axillary temperature was recorded with the digital thermometer before and after the scan respectively both in the induction room. Results: There is a decrease in axillary temperature in children undergoing MRI under anaesthesia The median temperature fall in children across different MRI regions range from 0.8 to 1.1°C. Different MRI scan regions do not cause significant differential temperature changes.

Keywords: paediatric, MRI, scan regions, axillary temperature.

INTRODUCTION

Magnetic resonance imaging (MRI) has become a quintessential diagnostic tool, especially in children, because it is a nonionizing technique for accurately diagnosing soft tissue abnormalities. For a child it is a nightmare as the position in the gantry cause claustrophobia. In addition to this, the long scan duration time which requires the child to stay immobile, necessitates anesthesia/sedation. General anesthesia per se and low ambient temperature requirements for the functioning of MRI scanner makes children vulnerable to hypothermia while in the MRI suite.^1,2 Sedation/anesthesia causes loss of thermoregulatory control which can cause significant drop in the core body temperature.^3,4 Conversely, the MRI scanner generates radio-frequency radiation (RFR), which is absorbed by the patient. Due to differential specific absorption rate of different regions, the different body parts get heated differentially which is more likely to be more exaggerated in children.^5,6,7 Studies done previously in children have shown mixed results with core temperature showing both rise and fall^8,9 but hardly few studies are there to compare temperature changes across MRI of different regions. Monitoring temperature during MRI scans can be challenging, and active warming equipment and MRI compatible monitoring systems are both expensive. This makes temperature control for children in the MRI suite a complex process. We aim to determine whether MRI of different regions cause different temperature changes due to differential specific absortion rate.

METHODOLOGY

This is an observational cross sectional study done in a tertiary care teaching institute in south India. After getting approval from the institutional review board, (IRB no. 10907) we recruited consecutive 250 children of age between birth and 16 years scheduled for MRI under anesthesia during the 7-month period between October 2017 to April 2018. Children having hyperthermia of temperature of greater than 37.2°C or hypothermia of temperature less than 36°C, were excluded. Written informed consent was obtained from all parents/guardians. None of the patients were given sedative premedication prior to the procedure. All eligible patients were subjected to inhalational induction in the anesthesia room of the MRI suite. Intravenous access was achieved following which anesthesia was maintained with propofol total intravenous anesthesia (TIVA) or LMA with inhalational anaesthetic according to the preference of the consultant anaesthesiologist. The dose of propofol used was 100–150 mcg/kg/min. A baseline axillary temperature (pre-scan) was recorded by the consultant anaesthesiologist with the digital thermometer after induction holding it in the armpit in an immobile anaesthetised child for a minute. All patients were wearing light clothing and were covered with a single blanket before, during, and after the scan. The MRI room temperature was maintained between 20 and 24°C. MRI of various regions was done either with 1.5T or 3T (Philips, Achieva) scanners. Once the MRI scan was over, the patient was shifted to the anesthesia room for recovery, wherein post-scan axillary S temperature was immediately measured and the scan region was noted. If the child was found to be hypothermic, additional blankets were used. Descriptive statistics were given as frequencies for sex, age less than/equal to 6 years or greater than 6 years, weight less than/equal to 20 kg or greater than 20 kg. The temperature change across different regions during MRI were given as median and interquartile range. Box plot were used to show graphically. All statistical output was done using R software.

RESULTS

The demographic characteristics of the study population are given in Table 1. The majority of the children belonged to the <6year age group, male sex, and less than 20 kg weight category. The mean age was 4 (±2.6) years and weight was 14.83 (±6.78) kg. The average duration was around one hour.

Table 1: Patient Demographics

Table 2: Temperature decrease in different regions of MRI

                                                Figure 1: Distribution of decrease in      Figure 2: Distribution of decrease in temperature 

                                                     temperature in different regions       among different MRI regions

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