When it comes to complications from tracheal intubation, mucosal burns are not often at the forefront of anesthesiologists’ concerns, but perhaps they should be. Research has concluded that the bulbs in older laryngoscopes can quickly and easily generate temperatures that can cause mucosal damage, a problem obviated by the use of LED bulbs.
According to Michael H. Harris, MD, stable and bright light sources are critical for visualizing the larynx, thereby facilitating patient intubation. Although laryngoscopes often are analyzed according to their light production, heat production is rarely considered in their analysis. “When you think of laryngoscopes, you think of ease of use and visualizing structures,” said Dr. Harris, a postdoctoral research fellow at Wake Forest University School of Medicine, in Winston-Salem, N.C. “You don’t think of all the other inherent risks.” Nevertheless, airway burns associated with laryngoscope use have been reported in both adults and children, prompting the researchers to assess four different types of laryngoscopes for their heat-producing characteristics.
To that end, the researchers measured bulb temperatures using a thermistor placed 1 mm from the light source on each laryngoscope blade. Temperature was measured over 10 minutes recorded at one-minute intervals for the following devices: five disposable MAC #3 laryngoscopes; a Welch Allyn MAC #3 LED Fiber Optic (Green Top) laryngoscope; a Welch Allyn MAC #3 standard laryngoscope; and a halogen “demo” light source blade. Standard battery sources were used, and each battery was tested using a voltmeter to ensure accurate baseline voltage.
“After three minutes, the halogen ‘demo’ bulb was nearly at 44 C,” Dr. Harris reported at the 2014 annual meeting of the American Society of Anesthesiologists (abstract A2168). “At four minutes, it was almost at 50 C. An important point is that human tissue necrosis begins at 43 C and gets faster with higher temperatures [Int J Hyperthermia 2003;19:267-294].”
The highest recorded temperature was 50 C in the halogen demo bulb at 10 minutes. Although no recordings were made beyond 10 minutes, the demo bulb never reached a plateau. By comparison, the standard laryngoscope reached a plateau temperature of 39 C at four minutes and then held this temperature. The LED fiber-optic laryngoscope held constant at 23 C.
Dr. Harris told Anesthesiology News that some practitioners have tried replacing traditional incandescent bulbs with xenon bulbs in an attempt to further improve visualization. “Those bulbs actually get hotter,” he said, “and can reach 70 C to 80 C.
“There have been a few case studies that looked at endoscopes that use the xenon bulbs,” he continued. “One paper used a 33% power setting in endoscopes, noting a bulb temperature of 45 C fairly quickly. By the time they hit 100% power setting [maximum brightness], it was almost 100 C. So there’s a real risk in using the xenon bulbs.”
Although a mucosal burn may not pose a significant risk in a healthy adult patient, it is quite a different story in immunocompromised adults and children, Dr. Harris said. “We want people to be aware of the risks when they replace the bulbs with nonstandardized bulbs, as [these bulbs] pose safety risks.”
Given these results, the switch to LED-based laryngoscopes was a no-brainer for Dr. Harris, not only because of the decreased risk for injury, but also because they have the potential for clearer visualization. “Our recommendation would be to phase out the old laryngoscopes for newer LED-based scopes,” he said. “And if you’re using reusable laryngoscopes, do not replace the bulbs with anything other than the factory-standard bulbs.”
D. John Doyle, MD, chief of general anesthesiology at Cleveland Clinic Abu Dhabi in Abu Dhabi, United Arab Emirates, expected that the news regarding laryngoscope bulb heat would be surprising to many clinicians. “This gives us all the more reason to use LED bulb designs, which generate less heat, consume less energy per unit of light and last longer. It’s a no-brainer to me too: We should be changing over to LED laryngoscopes as the old incandescent models are retired from practice.
“By the way,” Dr. Doyle added, “not all laryngoscope designs place the bulb near the oral mucosa, such as the ‘green line’ models, where the bulb is in the handle, not the blade. These models would not be expected to offer a burn hazard.”
Leave a Reply
You must be logged in to post a comment.