ACMT Toxicology Visual Pearls: Lye to the Eye

4. Sodium Hydroxide (Lye)

While automobile airbags are an important life-saving device, sodium hydroxide powder and aerosol released by their inflation can cause significant ocular injury for which prompt ocular irrigation is indicated [1,2].

Why in the world is lye used in airbags? [1,2]

• To create rapid airbag inflation, sodium azide is ignited producing hydrocarbon gas.
• This reaction releases powdered sodium hydroxide, sodium bicarbonate, and fine metallic oxides.
• Upon impact, sodium hydroxide may escape through the fabric resulting in ocular exposure.

What is caustic ocular exposure? [3-5]

• Both acid and alkali substances can cause corrosive ocular injury
• Alkali substances, such as lye, are more harmful than acidic substances partly due to rapid tissue penetration.
• Alkali solutions saponify the cell membranes and penetrate the corneal stroma causing tissue damage.
• The damaged tissue secretes proteolytic enzymes, further worsening the injury.
• Other caustic alkali agents include ammonia, potassium hydroxide, magnesium hydroxide, and calcium oxide.
• Caustic eye injury symptoms include irritation, pain, redness, and visual disturbance.

How do I treat caustic ocular exposure? [3-6]

• Whether acidic or alkaline, treatment is the same.
• Prompt irrigation is of paramount importance and should not be delayed to perform a thorough ophthalmologic examination
• Remove contaminated clothing.
• To facilitate irrigation, proparacaine HCL 0.5% or tetracaine HCl 0.5% solution may be used to anesthetize the eye.
• You can measure an initial pH a minimum of 5 minutes after initiation of irrigation.
• Consider anxiolytics or analgesics if systemic symptoms or other sites of injury are a barrier to prompt irrigation.

What is the best way to irrigate the eye? [5-7]

• Begin by anesthetizing the eye with proparacaine or tetracaine.
• While a sterile solution such as normal saline or lactated ringers is preferred, tap water can be used as well.
• Avoid neutralizing solutions as this can worsen damage.
• A Morgan™ lens, if available, or a nasal cannula can be used to irrigate the eye(s).
  • If you utilize the nasal cannula method, you may connect it directly to the IV tubing and the bag of irrigation fluid.
  • If a Morgan lens is used, start the flow of irrigation solution before the lens is placed on the eye to avoid a suction contact injury to the cornea.
• Irrigation should be continued for a minimum of 30 minutes using 1-3 L of fluid or continued until a physiological pH is reached at 7.0.

What should I do after irrigation is completed? [2,4,5,8]

• Assess visual acuity.
• Perform a detailed examination of the limbus, cornea, and iris. Chemical ocular injury is classified by ophthalmologists based on limbal ischemia via the Roper-Hall classification or the Dua classification [4,8].
• Evaluate intraocular pressure.
• If greater than mild injury is suspected, ophthalmologic consultation is warranted.
• In patients who are discharged, discuss treatment and follow up with ophthalmology.

Bedside Pearls

• Suspect caustic eye injury in patients with eye pain after airbag deployment
• Do not delay irrigation if caustic eye injury is suspected.
• Perform irrigation until pH is physiologic.
• Perform a thorough eye examination after the irrigation is complete.
• Consult with ophthalmology