November 2, 2024

20-year-old woman in MVC with burning sensation in eyes

By Med-Challenger · 3 minute read

A 20-year-old woman is involved in a motor vehicle collision in which her frontal air bag deploys. Her only complaint is a burning sensation in her eyes (see Figure 1).

image (12)

Figure 1.

Emergency medical services personnel report that a fine black powder was present on the patient’s face.

Which of the following statements is correct regarding the care of this patient’s eyes?

Prolonged irrigation (> 20 minutes) is counterproductive in airbag-related ocular injuries.
As part of her overall treatment, ophthalmic antibiotics and a cycloplegic should be considered in consultation with an ophthalmologist.
Irrigation should continue until the pH of the conjunctival sac reaches = 7.3.
Airbag leakage can result in mild acid burns to the eyes that are irritating but not vision threatening.

The correct answer is:

As part of her overall treatment, ophthalmic antibiotics and a cycloplegic should be considered in consultation with an ophthalmologist.

Key Point:

A dilated pupil with injury to the cornea (whitish in Figure 1), stinging, and conjunctival injection should raise concern for a burn from an airbag. Fine black powder in a patient’s eye (barely visible in Figure 1) further supports this diagnosis.

Explanation:

The automobile air bag is a rubberized nylon bag that inflates on spark ignition of sodium azide, yielding nitrogen gas, ash (the black powder seen in the patient's eye in Figure 1), and a small amount of sodium hydroxide. If the airbag leaks or ruptures, then the alkaline (not acidic) contents of the bag are dispersed as a fine, black powder that usually causes no problems unless the eyes are exposed. Such a leak or rupture should be suspected when there is a fine black powder and the patient reports stinging eyes.

Figure 1 reveals a corneal injury, which, in the context of the deployed airbag, black dust on the face, and a burning ocular sensation, must be interpreted as a corneal alkali burn. Careful inspection of Figure 1 shows fine black particles on the inferior lid margin, in the fornix, the conjunctiva, and cornea of the patient’s eye, further substantiating the impression of an airbag-related alkaline burn of the eyes.

In consultation with an ophthalmologist, topical antibiotics (eg, ciprofloxacin, gentamycin, sulfacetamide) and cycloplegics should be considered for this patient after immediate copious flushing has been completed. These medications decrease the burn-related risk of corneal infection, pupillary spasm, rising intraocular pressure, and glaucoma.

In addition, an ophthalmologist is likely to encourage early mobility of the eyes to minimize the formation of adhesions called symblepharon (see Figure 2).

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Figure 2.

In some cases of an alkaline burn, an ophthalmologist may also add a carbonic anhydrase inhibitor for 2 weeks (or until the pain has subsided) to increase the patient’s protection against increased intraocular pressure and glaucoma.

Similar to cutaneous burns, ocular burns can be classified into four grades. Grade I (corneal injury, but no hazy cornea) and grade II ocular burns (hazy cornea) are associated with hyperemia, conjunctival ecchymosis, and defects in the corneal epithelium.

The more severe grades III and IV ocular burns (see Figure 3) are associated with deeper penetration and, as such, present with mydriasis, a gray discoloration of the iris, and rapid cataract formation. The difference between a grade III and grade IV burn is the degree to which the cornea appears opacified and the conjunctiva appears blanched.

imageeye

Figure 3.

Suspected ocular alkali burns can easily be verified by testing the pH of the inferior cul-de-sac with litmus paper (pH > 7.4). However, it is important to remember that the immediacy of flushing in any suspected ocular alkali burn is crucial; copious flushing should be initiated immediately with normal saline (or water if saline is unavailable), even before verification of the diagnosis. Ocular alkali burns can initially appear deceptively trivial, but a continued chain reaction with the lipids in the corneal epithelial cells promotes ongoing chemical burning through the corneal stroma. With some alkaline agents, this continued burning can progress very rapidly. For example, anhydrous ammonia (which is not present in airbags) can penetrate into the anterior chamber in less than 1 minute, resulting in complete, permanent blindness within 1 minute after exposure.

In alkali burns (in contrast to acid burns), prolonged flushing (ie, several hours) may be necessary. This can be facilitated by the use of handheld intravenous tubing, an irrigating eyelid speculum, or a special scleral contact lens connected to intravenous tubing. Severe ocular alkali burns may require continuous irrigation for 24 hours or more because of the potential duration of chemical penetration for hours to days.

Initial therapy can consist of continual irrigation of the eye with 2 L of normal saline over 30 minutes followed by a check of the pH level. The duration of continued flushing can then be guided by repeated pH checks, but flushing should be continued until a pH of 7.4 in the conjunctival sac has been achieved. The pH level should be checked immediately after irrigation and again 30 minutes later, because it may begin to rise again after flushing has been discontinued. In addition to flushing, the conjunctival fornices should be swabbed to ensure that no particulate matter remains that might continue to release alkaline chemicals.

Immediate ophthalmologic consultation and close follow-up care are indicated for all ocular alkali burns.

References:

Knoop KJ. Ophthalmic procedures (chapter 62). In: Roberts JR. Roberts and Hedges’ Clinical Procedures in Emergency Medicine. 7th ed., 2019:1295-1337.

Levine MD. Chemical injuries (chapter 57). In: Walls R, et al. Rosen's Emergency Medicine: Concepts and Clinical Practice. 9th ed., 2018:724-736.

White JE, McClafferty K, Orton RB, Tokarewicz AC, Nowak ES. Ocular alkali burn associated with automobile air-bag activation. CMAJ. 1995;153:933-934.

This question appears in Med-Challenger Emergency Medicine Exam Review with CME.

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