Page 69 - JSOM Spring 2021

Red-Green Tactical Lighting Is Preferred for
Suturing Wounds in a Simulated Night Environment

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Brandon P. Noyes, DO, MC, USN *; Julie B. McLean, PhD ;
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Alexandra C. Walchak, MPH ; Gregory J. Zarow, PhD ; Micah J. Gaspary, MD, MC, USN ;
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Kevin J. Knoop, MD, MC, USN ; Paul J.D. Roszko, MD, MC, USN 7
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ABSTRACT
Background: Delivering medical care in nighttime conditions is Historically, red light has been used in nighttime operations
challenging, as 25% of Special Operations medical Operators because red light wavelengths mainly stimulate the rods of the
have reported that problems with lighting contributed to poor peripheral retina rather than the cones of the fovea, so the sco-
casualty outcomes. Red light is often used in nighttime opera- topic vision from monochromatic red light allows the rods to
tions but makes blood detection difficult and diminishes depth retain dark adaptation. The rod-based vision from red light,
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perception and visual acuity. Red-green combination lighting however, yields lower spatial acuity and contrast sensitivity
may be superior for differentiating blood from tissue and other than white light. This is important, because low spatial acuity
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fluids but had not been tested versus red-only or green-only and contrast sensitivity may interfere with the effective execu-
lighting for combat-related medical procedures, such as wound tion of fine motor skill tasks, such as suturing a wound.
suturing. Methods: Dark-adapted medical resident physicians
(N = 24) sutured 6cm long, 3cm deep, full- thickness lacerations Green light is increasingly used in nighttime operations. Green
in deceased swine under red-only, green-only, and red-green light has shorter wavelengths than red light and thus activates
lighting provided by a tactical flashlight using a randomized slightly more cones. As a result, green light fosters visual acu-
within-subjects design. Time to suture completion, suture ity somewhat better than monochromatic red light but still re-
quality, user ratings, and user preference data were contrasted sults in lower visual acuity and contrast sensitivity than white
at p < .05. This study was approved by Naval Medical Center light, and confers inferior depth perception compared to red
Portsmouth IRB. Results: Suture completion time and suture light. 2,3
quality were similar across all lighting conditions. Participants
rated red-green lighting as significantly easier for identifying Perhaps more importantly, the monochromatic wavelengths of
blood, identifying instruments, and performing suturing (p < red or green light can make blood detection difficult. Com-
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.01). Red-green lighting was preferred by 83% of participants bining red and green wavelengths activates both rods and
compared to 8% each for red-only and green-only (p < .001). cones, which results in mesopic vision with greater acuity, con-
Conclusions: Pending further study under tactical conditions, trast sensitivity, and depth perception. One recent study, for
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red-green lighting is tentatively recommended for treating bat- example, demonstrated that a red-green light combination has
tlefield wounds in low-light environments. similar contrast sensitivity and visual acuity to white light.
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Further, benchtop investigation has demonstrated that com-
Keywords: First-Light; combat medicine; light discipline; bining red and green light can make blood detection much
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combat lighting; tactical lighting easier. However, no published studies to date have explored
the differential efficacy of red-only, green-only, and red-green
combination light in conducting combat-related medical pro-
cedures, such as suturing a wound.
Introduction
Tactical lighting is fundamental for providing battlefield med- To fill this important gap in the literature, we conducted a
ical care in nighttime conditions, but little is known regarding randomized prospective experiment wherein dark-adapted
which tactical lighting wavelengths are optimal. Quickly de- participants performed a two-layered wound suture closure
tecting blood and providing quality care while simultaneously task under red, green, and red-green light conditions. This task
maintaining both dark adaptation (unaided “night vision”) was chosen because suturing requires spatial acuity, contrast
and a low-light profile for personal and mission safety has his- sensitivity, and depth perception towards both tissue differ-
torically been a difficult balance to achieve. Determining opti- entiation and the effective execution of fine motor skills. Our
mal tactical lighting is of prime importance, as 25% of Special objectives were to determine whether different tactical light-
Operations medical Operators have reported that problems ing conditions had differential effects on the time to complete
with lighting contributed to poor casualty outcomes. 1 wound suturing, suture quality, ease in identifying blood, ease

*Correspondence to Combat Trauma Research Group, Naval Medical Center Portsmouth, 620 John Paul Jones Circle, Portsmouth, VA 23708;
or noyes.b@yahoo.com
1 LT Noyes is a resident physician and CDR Gaspary, CAPT (Ret) Knoop, and LCDR Roszko are emergency medicine physicians affiliated with
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the Combat Trauma Research Group, Naval Medical Center Portsmouth in Portsmouth, VA. LCDR Roszko is also affiliated with the Depart-
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ment of Emergency Medicine, Walter Reed National Military Medical Center in Bethesda, MD. Dr McLean, Ms Walchak, and Dr Zarow are
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all affiliated with the Combat Trauma Research Group. Dr Zarow is also the founder of The Emergency Statistician in Idyllwild, CA.
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