TRACHEAL intubation is commonly performed on sick babies in the neonatal intensive care unit (NICU). Direct laryngoscopy before tracheal intubation can cause complications, including bradycardia, increased intracranial pressure, desaturation, trauma to the pharynx, injuries to the gum, and perturbances of cardiorespiratory measurements. 1,2Here we describe a previously unreported complication that was most likely caused by overheating in a laryngoscope during intubation of a newborn baby.
A term baby weighing 3.6 kg was born covered in thick meconium. The Apgar score was 5 and 7 at 1 and 5 min, respectively. Gentle suction of the mouth was performed, and the baby was tracheally intubated at approximately 1 min of age using a Welch Allyn light-bulb laryngoscope (model WA 685; Welch Allyn, Skaneateles Falls, NY). The findings on chest radiograph were supportive of a diagnosis of meconium aspiration. A septic screen that included blood culture did not suggest infection. The baby needed positive pressure ventilation for pulmonary hypertension caused by aspiration of meconium. On day 2 of life, the baby had blood-stained secretions from the mouth. Examination of the oropharynx revealed a 5-mm ulceration (fig. 1), The doctor who intubated the baby was surprised because the procedure was easy and did not involve any force or repeated attempts. These comments were supported by the nurse who was present at the time. The baby made an uneventful recovery and was discharged homeon day 7.
During resuscitation of a baby in our NICU 6 months later, we left a Welch Allyn light-bulb laryngoscope accidentally switched on for a few minutes. On picking up the laryngoscope, the light bulb on the blade of the laryngoscope was noted by the specialist (T. H. H. G. K.) to be so hot that he dropped it. On questioning, the resident involved in the aforementioned case recalled that the Welch Allyn laryngoscope was left switched on for a while before the baby was intubated. We therefore suspect that the lesion in the case reported here may have been caused by a burn sustained from an overheated light bulb of the laryngoscope.
Methods and Results
We performed a telephone survey of the 22 NICUs in Australia to ascertain the incidence of use of laryngoscopes with a light bulb and laryngoscopes with fiberoptic-conveyed light source. We found that 18 of 22 NICUs use light laryngoscopes only, one unit uses fiberoptic laryngoscopes only, and three units use a combination of the two.
Ten laryngoscopes (nine Welch Allyn 68470 and one Atom Medical fiberoptic “O”[Mitcham, Australia]) in current use in the delivery suites and the NICU of our hospital were assessed. The laryngoscope blade and a thermocouple were held in separate bench vices that were positioned such as to bring the thermocouple tip into contact with the surface of the laryngoscope light bulb. Thermal contact was optimized by the application of a small spot of transistor heat-sink compound at the point of contact. A regulated power supply was used to apply 2.5 V to the laryngoscope lamp. Each laryngoscope light source was activated, and the temperature at the face of the light source was recorded every 30 s for 7 min.
We measured the temperature of the light bulb at 1-min intervals for 3 min from when the laryngoscopes were switched on. For one light-bulb laryngoscope, there was an increase in temperature at 1 min to a maximum recorded temperature of 70°C and a further increase at 2 min to 78°C (fig. 2); this was hot enough to evoke a painful withdrawal when placed on the palms of the investigators. It was then confirmed that the bulbs that overheated drew more than the normal current. This suggests that the filaments may have become partly overlapped, resulting in a greater current consumption and hence greater heating. Our findings were confirmed by the manufacturer (Michael Lynch, Product Manager, Welch Allyn Medical Division). In contrast, the temperature of the distal end of the fiberoptic bundle in the blade of the fiberoptic laryngoscope remained unchanged (the bottom line in fig. 2).
One of the challenges facing the neonatal team is to minimize iatrogenic problems. Tracheal intubation is a common procedure performed in delivery suites and NICUs. Unusual complications associated with laryngoscopes include tracheal perforation 3and ingestion of the laryngoscope light bulb. 4
We have shown that a light-bulb laryngoscope, in contrast to a fiberoptic laryngoscope, can reach temperatures that could result in burns to the oropharynx. This is the first reported case of oropharyngeal burns caused by an overheated light-bulb laryngoscope. The preterm newborn baby with an immature mucosa may be at increased risk from such burns. Such injuries may have easily passed undetected because examination of the oropharynx in intubated newborn babies is not routinely performed. Our case emphasizes the importance of routine examination of the oropharynx to identify both congenital abnormalities but also iatrogenic lesions in the palate of babies who have been intubated. It may be argued that the lesion in our baby was caused by the suction catheter; however, this is unlikely because the doctor did not perform any suctioning of the oropharynx.
There is one report of thermal skin burn from a laryngoscope that was switched on while leaning against the flank of a 5-month-old infant during orthopedic surgery. 5The laryngoscope used was a Harris-Lake Miller-1, and temperature measurements from three laryngoscopes showed an increase of up to 55°C at 1 min after the laryngoscope has been switched on. Malposition of the blade on the laryngoscope handle can produce a short circuit that leads to rapid heating of the handle. 6
We recommend that all light-bulb laryngoscopes be switched on for <1 min. If left switched on, the temperature of the bulb should be checked with the hand before usage. We would advise that all light-bulb laryngoscopes in use undergo an annual check for overheating tendencies. We recommend that only fiberoptic laryngoscopes be used in NICUs. However, fiberoptic laryngoscopes also have a light bulb located in the handle. If the blade is disconnected from the handle and pressure is placed on the connection adjacent to the light bulb, the light bulb is activated and can become hot. Although heat generated from a handle of the fiberoptic laryngoscope can cause burns to the limbs or torso, 5we believe that it is unlikely in the context of injury to the orophraynx.
The authors thank Welch Allyn for their report on light-bulb testing.
To the best of my knowledge, the article and Mr. Lynch’s response accurately describe the event and our subsequent findings. By the nature of their operation, lamps get hot during illumination. As they approach end of life, the filament relaxes, and it is common for two or more of the coils to touch. This reduces the resistance of the lamp, and the current, in turn, increases, thereby increasing the operating temperature further. Some institutions have made recommendations that only fiberoptic laryngoscopes be used in neonatal intubation procedures. To the best of my knowledge, this is the only report of such an incident that we have ever received. However, the potential of a patient burn from a laryngoscope lamp is recognized, and there is now a requirement in the ISO standard for laryngoscopes: the instructions for use contain a warning that “lamps in an exposed position may generate heat sufficient to burn human tissue.”
Senior Quality Engineer
Welch Allyn, Inc.
Skaneateles Falls, NY 13153-0220