Types of incandescent laryngoscope: an incandescent bulb-in-handle device with fiberoptic blade (A) and an incandescent bulb-on-blade device, with bulb mounted distally on blade (B). Xenon light source: a Dedo laryngoscope (Pilling-Teleflex) is attached via fiber optic cable (C). Measurement apparatus: a laryngoscope mounted for measurement (D) and a light meter control (E).
Volsky PG, Murphy MK, Darrow DH. Laryngoscope Illuminance in a Tertiary Children’s HospitalImplications for Quality Laryngoscopy. JAMA Otolaryngol Head Neck Surg. 2014;140(7):603-607. doi:10.1001/jamaoto.2014.676
Laryngoscopes are used by otolaryngologists in a variety of hospital emergency and critical care settings. However, only rarely have quality-related aspects of laryngoscope function and application been studied.
To compare the illuminance of laryngoscopes commonly used in a hospital setting to established standards and to assess the potential effects of maintenance practices on laryngoscope illuminance.
Design, Setting, and Participants
Observational study of laryngoscope light output and cross-sectional survey of individuals charged with laryngoscope maintenance in a tertiary care children’s hospital.
Illuminance was chosen as the unit of measurement (lux). Laryngoscopes in the operating room, emergency department, and pediatric intensive care unit were tested according to a standard technique. Illuminance standards for laryngoscopes, published by the International Organization for Standardization (ISO) (500 lux) and in the medical literature (867 lux) were used as benchmarks.
Main Outcomes and Measures
Mean laryngoscope illuminance by type of laryngoscope and light source and percentage of laryngoscopes with illuminance below established standards as well as nonfunctioning units. Maintenance practices were evaluated as a secondary outcome.
A total of 319 laryngoscopes were tested; 283 were incandescent bulb units used by anesthesiologists, emergency physicians, and intensivists and 36 were xenon light units used by otolaryngologists. Mean (SD) illuminance was 1330 (1160) lux in the incandescent group and 16 600 (13 000) lux in the xenon group (P < .001). Substandard illuminance was observed only in the incandescent group, in 29% to 43% of laryngoscopes; 5% of the incandescent group did not turn on at all. Maintenance of laryngoscopes was performed on a reactive rather than a preventive basis.
Conclusions and Relevance
At our facility, approximately one-third of incandescent laryngoscopes exhibited substandard light output. On the basis of these findings, our hospital has converted all of its incandescent laryngoscopes to light-emitting diode (LED) devices. Such changes, as well as the institution of a quality-control program including scheduled laryngoscope inspection and battery and bulb replacement for incandescent laryngoscopes, may reduce adverse events associated with poor-quality direct laryngoscopy.
In recent years, assessment of the quality and safety of medical devices and procedures has become critically important. In hospitals, laryngoscopes are used ubiquitously from operating rooms (ORs) to emergency settings, and otolaryngologists are among their most frequent users. However, despite the central role of laryngoscopy in emergency and anesthesia care and in otolaryngology, no study has analyzed hospital-wide laryngoscope quality characteristics and maintenance practices.
In 1996, Skilton et al1 asked a cohort of anesthesiologists to identify the minimum adequate light output for safe and effective laryngoscopy. The subjects used adjustable-brightness laryngoscopes for intubation in elective surgical cases. The measured minimum acceptable brightness was 100 candela (cd)/m2. Eleven years later, Cheung et al2 developed a similar but portable measurement apparatus, finding that the 100 cd/m2 equated to an illuminance of 867 lux. A similar benchmark was established by Milne and Brosseau,3 who reported a minimum illuminance of 600 to 900 lux based on the output of laryngoscopes sent for repair by anesthesiologists at their institution. In contrast, studies of laryngoscope light required for intubation of a manikin have found much lower minimum illuminances of 34 lux4 and 92 lux.5 The International Organization for Standardization (ISO), a group composed of volunteer representatives from various national standards organizations, has established that the illumination of laryngoscopes should exceed 500 lux for at least 10 minutes.6
Our purpose was to carry out a performance improvement study to determine how the illuminance of laryngoscopes commonly used in our hospital setting compared with established standards. We chose to investigate this topic when the senior author (D.H.D.) observed that anesthesia laryngoscopes, used by one of his partners for intubation and bronchoscope insertion, appeared dim compared with those used by most otolaryngologists. A cursory examination of a group of these scopes suggested that illumination from these scopes was poor and potentially substandard. Our study also sought to assess the potential effects of laryngoscope maintenance practices on illuminance.
The study was designated “not human subjects research” by the institutional review board of Eastern Virginia Medical School, and formal review was not required.
An observational study was designed to quantify the light output of all laryngoscopes in a tertiary children’s hospital (Children’s Hospital of The King’s Daughters, Norfolk, Virginia) and to compare the results with established standards. Laryngoscopes in the OR, pediatric intensive care unit, and emergency department (ED) composed all the units in the hospital. Individuals charged with laryngoscope maintenance completed a survey regarding the frequency and method of light output assessment, corrective actions for malfunctioning units, preventive maintenance, and laryngoscope cleaning.
Three types of laryngoscopes are used in our hospital. Bulb-in-handle and bulb-on-blade units both rely on two 1.5-V alkaline batteries to power a self-contained incandescent bulb. Nearly all of these laryngoscopes are manufactured by Welch Allyn (Green Series) and use Macintosh, Miller, or Phillips blades. When a bulb-in-handle unit is activated, light is transmitted from the bulb in the handle to the tip of the laryngoscope blade by a fiber optic bundle (Figure, A). Bulb-on-blade laryngoscopes do not use fiber optics; instead, the handle transfers current via a contact on the blade, which is conducted to an incandescent bulb at the distal end (Figure, B). Our xenon laryngoscopes are used exclusively by otolaryngologists. These 1-piece blade and handle diagnostic units are the Parsons or Benjamin types (Karl Storz) or the Dedo or Holinger designs (Pilling-Teleflex) and use fiber optic cables to transmit light from an external AC (alternating current)-powered xenon light source (Figure, C).
To collect illuminance data, a light-proof apparatus with a sensor was constructed (“dark box”). The apparatus consisted of a large wooden box with a positioning arm for the laryngoscope (Figure, D). The inside of the box was painted flat black and padded to reduce reflection and minimize light infiltration. A light sensor (Figure, E; Tenma, Model #72-6693, Newark Electronics) was contained within. To account for variation in angle and dispersion of light inherent to device type, laryngoscopes were positioned for measurement in 1 of 2 ways. For larger fields of light, the bottom edge of the light field was matched to the cover support wall of the detector body, while smaller fields of light were visually centered on the detector surface. The blade tip was positioned 2 cm from the sensor surface. Data were tabulated using Libre Office Calc spreadsheet software (The Document Foundation) and Microsoft Excel (Microsoft Corporation). Because laryngoscope blades outnumbered handles, testing was performed by pairing the blades to handles in a random fashion determined by the spreadsheet software.
Illuminance data were collected by the following procedure: (1) illuminance meter calibrated to dark box; (2) laryngoscope activated as if for use; (3) laryngoscope positioned in the apparatus; and (4) 3 serial measurements taken at 10-second intervals, averaged to reduce error in producing a final illuminance value. For AC-powered xenon light source laryngoscopes, 9 light boxes were tested to obtain a mean range of source illuminance. The unit closest to the population mean was used for testing all laryngoscopes.
When a laryngoscope failed to turn on at all, the handle-blade pair was detached and reassembled 5 times. If after these 5 attempts the laryngoscope light source did not illuminate, illuminance was set to 0 and the device was classified as “failing.” Blades and handles that had been checked were marked with surgical instrument tape to prevent repeat sampling.
Benchmarks for comparison were the 867-lux standard established by Cheung et al2 and the ISO standard of 500 lux.6 “Failing” units (0 lux) were also counted. Illuminance data are reported as mean (SD). Illuminance data were compared using the independent samples t test.
Laryngoscopes in the OR used by anesthesiologists (n = 195) and 1 otolaryngologist (n = 8), as well as laryngoscopes in the ED (n = 16), were of the bulb-in-handle type. The pediatric intensive care unit used both the bulb-in-handle type (n = 35) and bulb-on-blade type (n = 29). Collectively, these 283 laryngoscopes were considered the incandescent group. The laryngoscopes in the OR powered by external light source (n = 36) were considered the xenon group.
With respect to the absolute amount of light produced, comparing bulb-in-handle and bulb-on-blade incandescent laryngoscope revealed that bulb-on-blade laryngoscopes were on average 32% brighter (mean [SD], 1280  lux vs 1690  lux, respectively), but this difference was not statistically significant (P = .06, unpaired t test). While the laryngoscopes were drawn from 3 different locations within the hospital, all groups contained roughly the same devices and received the same maintenance. For these reasons, the incandescent units were treated as a single group. Comparing incandescent and xenon groups, the xenon group produced significantly more light, by a factor of approximately 12.5 (mean [SD], 1330  lux vs 16 600 [13 000] lux, respectively) (P < .001, unpaired t test).
Illuminance data were compared with the minimum standards reported in the scientific literature. In the incandescent group, 43% were below the threshold of 867 lux, 29% fell below the ISO threshold of 500 lux, and 5% failed to illuminate at all. None of the xenon units fell below either threshold (Table 1).
Surveys regarding maintenance protocol were completed by staff familiar with laryngoscope care in the OR, pediatric intensive care unit, and ED (Table 2). In all departments, laryngoscope blades were sterilized after each use, using a highly disinfectant chemical soak performed by the sterile processing department. Personnel reported that the sterilization process had changed over the preceding few years from steam sterilization because the latter process seemed to increase the likelihood of damage to the scopes. Laryngoscope handles were cleaned separately in each department with hand wipes containing Cidex OPA (Johnson & Johnson) (OR and ED) or Oxivir (pediatric intensive care unit).
No departments reported scheduled or preventive assessments of laryngoscope light output. Rather, maintenance was only performed in response to a reported malfunction. Inspection of laryngoscope performance was on a qualitative basis (ie, no current meters or light meters used to quantify the integrity of the batteries, current, or light output).
To our knowledge, this study is the first to examine the illuminance of laryngoscopes throughout a children’s hospital. We discovered that 43% of our incandescent laryngoscopes fell short of the most stringent benchmark for light output, whereas all of our xenon light laryngoscopes were more than adequate. Failure rates based on the ISO standard of 500 lux were lower but still significant, with 29% falling below the standard and 5% failing completely. A review of the literature suggests that a high failure rate among laryngoscopes in use is not uncommon. Previously published laryngoscope illuminance failure rates using standards established by anesthesiologists ranged from 27% to 86% when using the 867-lux or equivalent benchmark.1,2,7 Another children’s hospital audit of 18 anesthesia department laryngoscopes found that half did not meet these literature standards, and only 1 device met the ISO standard.8 In a manikin study, a group of anesthesiologists found only 1 of 16 laryngoscopes produced the median acceptable light on each reading and the minimum acceptable light for all testers.9
In most cases, the amount of light required to intubate an airway is less than that required for an otolaryngologist to characterize airway pathologic conditions. Indeed, prior research in manikin intubations (perhaps due to reflection off the artificial laryngeal and pharyngeal structures) demonstrated no difference in successful intubations across 3 light levels (600, 200, and 50 lux)10 and lower minimum illuminances of 34 lux4 and 92 lux.5 Nevertheless, the rates of failure in the present study are still concerning because the literature standards were determined by anesthesiologists in the operative setting. Should an intubation become challenging, the obstacles to successful intubation may be difficult to ascertain if the light output of the laryngoscope is insufficient.
The disparity in output between xenon and incandescent laryngoscopes is explained by differences in energy and light source. Xenon light boxes are designed to provide light comparable to the sun in spectrum and magnitude. Xenon bulbs used in the light boxes are rated for hundreds of watts in power consumption. The difference in energy requirements of the light sources reflects this, as xenon light sources are powered by 125 V AC, while handheld anesthesia units use 3 V DC. However, it is worth considering whether, in the OR setting, the convenience of using a battery-powered, handheld laryngoscope justifies the huge difference in illuminance provided by these units compared with those used with xenon light sources.
Department maintenance surveys revealed that there was regular visual but not quantitative testing of the laryngoscopes. However, individuals assigned to maintain laryngoscopes are not usually trained to determine what constitutes an appropriately bright laryngoscope or to compare laryngoscope light output with accepted standards. As a result, the poor light output of a laryngoscope may not have been identified until it was well below established minimum thresholds. This reactive approach to maintenance meant that a corrective action occurred only after flawed equipment was discovered at the time of use. Although repairs including some combination of battery, bulb, or blade replacement were made as failures occurred, such corrections may have been too late to avoid difficulties or complications during intubation. This approach to laryngoscope maintenance may also result in a single repair that improves the laryngoscope output, when some combination of repairs may in fact be more likely to generate a greater light output for a longer period. Using 867 lux as the minimum acceptable illumination in a test of 51 laryngoscopes, Cheung et al2 found that changing both the batteries and the bulb increased the “pass” rate from 14% to 92%. The authors also reported that illuminance did not significantly differ among brands of blades. Light loss has also been reported as a result of looseness or gap between the handle and blade and by damage and debris involving the surface of the fiberoptic bundle at the base of the blade.1,7,11 These data suggest that regular inspection and preventive maintenance are important quality improvement measures that can improve the performance of incandescent laryngoscopes. Furthermore, this improvement suggests that a low “pass” rate is far more likely related to laryngoscope age and maintenance than to characteristics of a particular laryngoscope brand.
Disinfection techniques have been shown to affect the intensity of laryngoscope light.12,13 In one study, 300 cycles of machine washing and disinfection at 90°C decreased mean light output of fiberlight laryngoscopes by 34.6%, while washing and steam sterilization at 134°C resulted in an output loss of 86.5% and, as noted at our facility, damage to the fiber bundle and its casing.13 As a result, despite recommendations for steam sterilization of most endoscopic equipment and accessories,14 the minimum standard of washing and disinfection at 90°C may be preferable from the standpoint of equipment longevity.15 Disposable laryngoscope blades have been used as an alternative.
No adverse events have been reported at our hospital as a result of using dim laryngoscopes. However, the findings from this study served to motivate a change at our facility toward preventive maintenance. Following a presentation of our data to the hospital’s Performance Improvement Committee, our facility replaced all of its incandescent laryngoscopes with LED (light-emitting diode) devices. LEDs are more efficient than light bulbs in converting energy into light and automatically shut off when the battery voltage drops to a certain level. As a result, with insufficient battery power, the LED does not dim to unacceptable levels but rather is unable to light. This ultimately reduces maintenance requirements, acting as a self-regulating output threshold.
There were several potential sources of error in this study. One such source is the accuracy of the light meter itself, which depends on its internal error and relies on calibration by the manufacturer and our calibration of the sensor in a dark environment. The manufacturer (Tenma) specifies that the sensor is accurate to ±2.5%. In addition, our light meter measurements were recorded with significant figures intrinsic to the meter (ie, <2000, the sensor resolution was 1 lux; from 2000-20 000, resolution was 10 lux; and >20 000, resolution was 100 lux). Another potential source of error was the cradle used to position the laryngoscope during measurement. It is possible that small changes in the position of the cradle, which was held in place by friction, may have allowed the device to move closer to the detector, thereby inflating the recorded output. Finally, variable light fields produced by different blades also potentially introduced error in our measurements.
Laryngoscopes are relied on heavily in emergency and intensive care, anesthesia care, and otolaryngology. To our knowledge, this is the first study of the quality of laryngoscope light output throughout a tertiary care children’s hospital, revealing that 29% to 43% of incandescent laryngoscopes exhibit substandard light output. The implications for patient care are noteworthy and, in our medical center, these data have resulted in the procurement of new, brighter laryngoscopes.
We recommend preventive laryngoscope maintenance, including scheduled, quantitative device inspection and battery or bulb replacement to improve laryngoscope light output. In addition, wherever practical, the use of more efficient laryngoscope light sources (such as LED) should be explored. Such practices are certain to improve the quality of direct laryngoscopy and may reduce airway-related adverse events.
Submitted for Publication: January 7, 2014; final revision received March 5, 2014; March 25, 2014.
Corresponding Author: David H. Darrow, MD, DDS, Department of Otolaryngology–Head & Neck Surgery, Eastern Virginia Medical School, 600 Gresham Dr, Norfolk, VA 23507 (firstname.lastname@example.org).
Published Online: May 15, 2014. doi:10.1001/jamaoto.2014.676.
Author Contributions: Mr Murphy and Dr Darrow had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: All authors.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: All authors.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: All authors.
Obtained funding: Murphy.
Administrative, technical, or material support: Murphy, Darrow.
Study supervision: Volsky, Darrow.
Conflict of Interest Disclosures: None reported.
Previous Presentations: Portions of this study were presented at the Society for Ear, Nose, and Throat Advances in Children (SENTAC) annual meeting; December 2, 2012; Charleston, South Carolina; the completed study was presented at the American Society of Pediatric Otolaryngology (ASPO) annual meeting; April 27, 2013; Arlington, Virginia.
Additional Contributions: All work was performed at the Children’s Hospital of The King’s Daughters and Eastern Virginia Medical School. Charles Sukenik, PhD, Chairman of the Department of Physics at Old Dominion University, assisted in designing the measurement apparatus.