Can the SpotOn™ Zero-Heat-Flux-Thermometry Sensor Accurately Measure Core Temperature in Children?

Temperature regulation in the perioperative period is of primordial importance in paediatric population - a particularly sensitive group for thermal variations.

In fact, infants lose a significantly high percentage of their core heat from skin perspiration in comparison to adults (where it approximates roughly 10%). This percentage can go up to 20% in premature infants and relates to the fact that cutaneous heat loss is "grosso modo" proportional to body surface area.

This higher thermal vulnerability is aggravated during the perioperative period, where body exposure to the cold operating room environment is increased, and where anaesthetic interventions impair the compensatory mechanisms to the extent of being unable to sufficiently increase heat production to compensate for hypothermia.

An alternative thermometry method called Zero-heat-flux was developed in the 1970's in an attempt to compensate for the limitations of pure skin temperature, while maintaining its practical character. It is based on the principle that the temperature 1-2 cm below skin surface reasonably approximates core temperature. In order to measure it, it uses 4-layered probe, with the following inside-out structure: patient temperature thermistor, insulating foam layer, heating (flex) circuit, and insulating foam. A servo-controlled system actively warms the probe circuit to the point where, theoretically, temperature equilibrium is achieved between the skin and deeper structures and there is zero heat transfer to the surrounding areas. This concept is commonly exemplified as the creation of a vertical isothermal tunnel between the skin surface and lower dermal layers. Assuming a good tissue perfusion, dermal temperature will reasonably approximate core temperature.

Although a systematic adult population validation is on its way, no data on the paediatric patients exists.

Considering the practical and non-invasive character of this skin surface probe, as well as the abovementioned thermal sensitivity concerns on the paediatric population, it seems that, should the probe indeed prove to be accurate in this age range, it can definitely contribute to the improvement of the perioperative temperature management in children.

Inclusion criteria

• ASA I & II
• Age: 1d - 16 years
• Elective surgery
• Minimum anaesthesia time of 30 minutes

Exclusion criteria

• Fragile skin state in the forehead
• Know allergy to probe adhesive
• Maxillofacial trauma or lesions
• Procedures impeding proper use of SpotOn™ sensor (mostly maxillo-facial)
• Abnormal oesophageal anatomy/gastroesophageal procedures.
• Coagulopathy
• Neurologically impaired children with abnormal thermoregulation
• Extensive Haemodynamic instability
• Need for Vasopression
• Procedures associated with extended use of rinsing fluids (abdominal/thoracic lavages)
• Thoracoscopic/thoracotomic procedures (oesophageal probe cooling)
• Need for use of "over body" forced air warming systems
• Malignant Hyperthermia or family history of malignant hyperthermia
• Fever / Infectious patient
• All conditions that might be judged to alter skin perfusion in an abnormal way
• Anatomical variants (overt hydrocephalus …)
• Calibration/device failure