Pediatric Temperature Variation in the MRI Scanner Under General Anesthesia
Condition: Children Requiring MRI
Study type: Observational

Summary: 
      The number of children undergoing MRI imaging has increased significantly in the past years,
      because many young children cannot stay still for the duration of the scan, have difficulty
      tolerating the confined space and the noise produced by the Magnetic Resonance Imaging (MRI)
      machine, sedation or General Anesthesia is required in these cases. In the investigators
      institution, the investigators use General Anesthesia for children undergoing MRI.

      Because children have a larger surface area to body weight ratio; hypothermia from passive
      heat loss is one of the anesthesiologists' concerns.

      MRI requires a cool environment with low humidity; this specialized environment represents a
      significant thermal challenge to the anesthetized children. Since most temperature devices
      are not compatible with the MRI, the simple task to measure temperature change has never been
      investigated.
    

Detailed description: 
      It is known that following the induction of anesthesia, core hypothermia occurs in three
      stages;

        1. Redistribution

        2. Linear phase

        3. Plateau phase Redistribution This accounts for the largest drop in core temperature of
           the three stages. Vasodilatation causes redistribution of heat from the core to the
           periphery.

      Linear Phase This begins at the start of surgery as the patient is exposed to cold cleaning
      fluids and cool air flow in the theatre. Heat loss exceeds heat production, and most surgery
      does not extend past the linear phase.

        -  Radiation contributes the most (40%) and is proportional to environment/core,
           temperature difference to the power of four.

        -  Convection contributes up to 30% and is proportional to air velocity.

        -  Conduction contributes up to 5% and is proportional to the difference in surface
           temperatures.

        -  Evaporation contributes up to 15% and occurs from cleaning fluids, skin, respiratory and
           wound. A laparotomy can contribute up to 50% of the total.

        -  Respiratory contributes 10% (8% evaporation of water; 2% heating of air) and is enhanced
           by the cooling effect of cold anesthetic gases.

        -  Cold intravenous fluids. Plateau Phase Once core temperature falls below the
           thermoregulatory threshold, peripheral vasoconstriction increases and acts to limit the
           heat loss from the core department. When core heat production = heat loss to the
           peripheral compartment, core temperature reaches a plateau. Patients with an autonomic
           neuropathy (diabetics) have impaired sympathetic vasoconstriction and are unable to
           establish a core plateau in phase 3. Combined general and regional anesthesia will have
           a similar effect as the regional anesthetic (spinal/epidural) will prevent
           vasoconstriction in the legs; i.e. failure to establish a core plateau.

      The ability to maintain body temperature is also compromised because anesthesia impairs
      intrinsic thermoregulatory response.

      Heating devices including fluid warmers and bear huggers, commonly used in the Operating Room
      theaters, are incompatible with MRI.

      On the other hand, MRI produces Radiofrequency Energy that transforms into heat within the
      patient's tissues. This may partially offset the heat loss.

      The purpose of our study is to determine if children undergoing MRI under General Anesthesia
      become hypothermic and whether aggressive measures should be taken to prevent passive heat
      loss during MRI studies.

      Study Design This is an observational, prospective non blinded study.
    

Intervention name(s): axillary temperature before MRI and after the MRI
Intervention type(s): Other
Intervention description(s): observation of body temperature changes with axillary temperature measurement with MRI compatible device
Observational model: Case-Only
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Children 6 months to 8 years
      
Keywords: Children MRI General Anesthesia