Thermal injuries in three children caused by an electrical warming mattress

D. J. Dewar1, J. F. Fraser2,*, K. L. Choo3 and R. M. Kimble4

1 University of Queensland, Brisbane, Australia. 2 Intensive Care Medicine, Prince Charles Hospital and Department of Paediatrics and Child Health, Royal Children's Hospital, Brisbane, Queensland, Australia. 3 Paediatric Surgery and 4 Burns, Royal Children's Hospital, Brisbane, Queensland, Australia

* Corresponding author: J. Fraser, University of Queensland, Department of Paediatrics and Child Health, 3rd Floor, RCH Foundation Building, Royal Children's Hospital, Queensland 4029, Australia. E-mail: j.fraser{at}uq.edu.au

Accepted for publication June 14, 2004.


    Abstract
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 Abstract
 Introduction
 Case report
 Discussion
 References
 
Peroperative hypothermia is recognized to increase mortality and morbidity, and the paediatric anaesthetist faces specific challenges resulting from the increased body surface to volume ratio, particularly in smaller children. We describe three children who were consecutive patients on one operating list and sustained severe thermal injuries. These were due to a malfunctioning electrical heating mat, despite appropriate use and monitoring by the attending anaesthetist. It is rare for thermal warming devices to cause injury. We review the use of heating mats, and suggest modifications in their manufacture which may minimize the risks associated with heating devices.

Keywords: anaesthesia, paediatric ; burns ; equipment, warming mattress ; measurement techniques ; monitoring


    Introduction
 Top
 Abstract
 Introduction
 Case report
 Discussion
 References
 
Prevention of peroperative hypothermia is an important consideration in anaesthesia and the use of a variety of patient warming devices has become standard protocol in operating theatres.13 It has become standard practice in paediatric hospitals to use heating devices during all anaesthetics. In rare cases, these devices have resulted in burns to patients.2 48 We report three paediatric patients who sustained thermal injury as a direct result of a faulty thermal mattress. Two of the three cases required skin grafting and long-term scar management.


    Case report
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 Abstract
 Introduction
 Case report
 Discussion
 References
 
The three operations reported here occurred consecutively on one dental surgical list. The injuries were noted at completion of the list, and all injuries corresponded to a fault in an isolated area on the thermal mattress used (Klimamed® Technology Thermal Mat System, Germany).

Case 1 was a 2-yr-old male who underwent emergency dental extraction without complication. His estimated exposure time to the thermal mattress was between 10 and 15 min. Blistering was noticed on the exterior surface of the right forearm (2.5x1.5 cm) on the same day, after discharge from hospital. He returned to hospital, where the resultant superficial partial thickness wound was treated with simple dressings. No long-term scar management was necessary.

Case 2 was a 9-yr-old male who underwent dental extraction. The injury was noted during the third case, but was initially thought to be a pressure injury. His estimated exposure time to the thermal mattress was approximately 90 min. It resulted in a 3x5 cm full-thickness burn located on the posterior surface of the right elbow, which required subsequent split skin grafting and scar management (Fig. 1).



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Fig 1 Full-thickness burn 4 days after injury (case 2).

 
Case 3 was a 10-yr-old female, whose estimated exposure to the thermal mattress was greater than 60 min. At the end of the operation, a full-thickness burn area of 10x2 cm was noted on her right arm. Split skin grafting and subsequent scar therapy were required.

On completion of the third case, physical examination of the patients revealed that the injuries in cases 2 and 3 were thermal in nature, and the position was similar in the two patients. Subsequent palpation of the warming mattress indicated that there was a hot area well above the monitored temperature of 33°C. This hot spot directly matched the position of injury in all three children. External inspection revealed no sign of damage to the warming device and no fault had been indicated by the integrated Klimamed® digital temperature monitoring equipment. The mattress and its monitoring device were immediately removed from the clinical area and sent to the hospital medical equipment technicians, and functional tests were conducted. Investigations using a FlukeTM 75 multimeter (Carlton-Bates, Little Rock, AR, USA) confirmed that a small area of the mat overheated to dangerously high temperatures (maximum 103.3°C), when a temperature of only 32.4°C was being displayed on the Klimamed digital temperature monitoring equipment (Fig. 2).



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Fig 2 The Klimamed digital temperature monitor displaying 32.4°C (left), while the Fluke 75 multimeter records a hot-spot temperature of 103.3°C (right).

 
X-ray of the thermal mattress identified a break in one of the conductive strips running internally through it. The resultant elevation in local current density surrounding the break resulted in a hot spot in the mattress (Fig. 3).



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Fig 3 X-ray showing fractured element (arrow) at the site of the hot spot.

 
The Klimamed mattress uses an electric current and contains a resistive circuit. When functioning appropriately, temperatures above 37.7°C are not attainable with this device. It is not possible to manually turn up the temperature of the Klimamed warming mattress to reach a level high enough to produce a burn injury in an anaesthetized patient through operator error.

The hospital medical equipment technicians have reported the fault to the manufacturer and to the Therapeutic Goods Association of Australia.


    Discussion
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 Abstract
 Introduction
 Case report
 Discussion
 References
 
It requires less than 1 s of contact time at a temperature of 70°C for a significant burn to be sustained.9 Given the temperature the hot spot on this mattress reached, it is not surprising that our patients sustained serious burns. Two children in particular incurred considerable morbidity, needing surgical grafting and prolonged scar prevention therapy with the attendant pain, discomfort and cosmetic defect.

Anaesthesia and surgery impair thermoregulation.3 4 Prevention of intraoperative hypothermia reduces mortality, wound infection rates and blood loss, enhances clotting capacity and avoids prolonged recovery time.21014 Thus, it is accepted as best practice to maintain intraoperative normothermia unless hypothermia is specifically indicated. Evidence has supported peroperative warming using forced warm air as the gold standard, but this method has also been reported to cause burn injury and has recently been challenged by a resurgence in controlled circular water warming systems.1517

Measures to avoid hypothermia and minimize the reliance on a heating device can be separated into passive insulation and active cutaneous heating. Passive insulation reduces cutaneous heat loss by 20–30%, and varies only slightly depending on the insulating fabric (heating blankets, plastic bags/cotton blankets, etc.). Active heating maintains normothermia much more effectively than passive heating, and heating mattresses are one of the most important methods of active heating. When considering the effectiveness of any form of intraoperative warming device, the anaesthetist also needs to assess the device's potential to produce injury in the case of malfunction or inappropriate operation.7 8 1820

Electrical resistive circuit heaters include heated water circuits, forced air warmers (remote heating element) and electrical blankets (direct heating source). Whilst burns have been reported with all types of heating blankets, devices with the heat source in direct contact with the patient may have a higher risk of causing significant thermal injury, as any significant rise in temperature will be directly transferred to the patient with minimal dissipation. This has also been seen with a forced air warmer.

This report highlights the dangers of a warming mattress which uses a direct resistive electrical circuit for heat generation. In this instance, the circuit of the mattress became damaged at a single location, resulting in an invisible fault that caused extreme temperature elevation in a small area of the mat. We have identified two design faults with regard to the thermal mattress in question, which we believe should be addressed by the manufacturer. First, the hot spot was too remote from the single temperature sensor in the mattress to be detected. Consideration should be given to monitoring temperature in multiple locations within such a mattress, which would increase the likelihood of identifying a hot spot. It should include an automatic shut-off that activates if any one sensor detects changes outside the set tolerance limits. However, small hot spots could still occur and not be detected. A second level of safety in electrical devices such as these mattresses would be obtained if there was an inbuilt ability to monitor current, voltage and impedance across the circuit. Any damage to the circuit similar to that which occurred in this thermal mattress would then result in automatic deactivation, and thus prevent a thermal injury regardless of temperature readings.


    References
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 Abstract
 Introduction
 Case report
 Discussion
 References
 
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14 Winkler M, Akca O, Birkenberg B, et al. Aggressive warming reduces blood loss during hip arthroplasty. Anesth Analg 2000; 91: 978–84

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20 Zeitlin GL. Burns from warming devices in anesthesia, 1910. Anesthesiology 1994; 81: 788[Medline]





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