Mask squeeze
Background
- The air in the mask decreases in volume during a dive, and that causes negative pressure on the covered area of the face.
- Occurs when air is not added to facemask during scuba diving descent to equalize the negative pressure.
Barotrauma Types
- Otic barotrauma
- Pulmonary barotrauma
- Sinus barotrauma
- Mask squeeze
- Barodentalgia (trapped dental air causing squeeze)
Diving Physiology
- Pascals Law applies to the diving body (without air filled areas such as lungs) states that the pressure applied to any part of the enclosed liquid will be transmitted equally in all directions through the liquid.
- Boyles Law applies to the diving body's air filled areas such as lungs, sinuses, middle ear, and states that the volume and pressure of a gas at a given temperature are inversely related.
- At 2 ATA (10m/33ft) a given gas would be 1/2 it's volume, at 3 ATA (20m/66ft) it would be 1/3 it's volume and so on.
- Dalton's Law applies to the total pressure of an ideal gas mixture being the sum of the partial pressures of each individual gas.
- Divers may used Enriched Air NITROX mixtures to proportionally increase partial pressures of oxygen and reduce partial pressures of nitrogen while diving.
- At extremes of depth, additional inert gasses such as helium in TRIMIX are used to further reduce partial pressures of both oxygen and nitrogen below toxic levels.
- Henry's Law applies to the dissolvability of gasses into fluids, including body tissues, being proportional to the partial pressure of the gas.
- The increased pressure at depth causes divers to breath their gas mix at increased pressure to defeat the external water pressure.
- Increased inhaled partial pressures of nitrogen increase risk of nitrogen narcosis, and dissolved nitrogen in tissues re-expanding in micro-bubbles on ascent is the essential cause of decompression sickness. This can affect divers at any depth, including commonly-seen recreational diving depths of 20m/60ft or less.
- Increased inhaled partial pressures of oxygen, generally beyond 1.4-1.6atm, increases risk of oxygen toxicity. This is typically not a substantial risk in common depths of recreational divers at 20m/60ft of depth or less, but can be for more advanced divers at deeper depths.
- The increased pressure at depth causes divers to breath their gas mix at increased pressure to defeat the external water pressure.
Clinical Features
- Facial bruising
- Conjunctival Injection/hemorrhage
- Retrobulbar hemorrhage if severe
Differential Diagnosis
Diving Emergencies
- Barotrauma of descent
- Otic barotrauma
- Pulmonary barotrauma
- Sinus barotrauma
- Mask squeeze
- Barodentalgia (trapped dental air causing squeeze)
- Barotrauma of ascent
- Pulmonary barotrauma (pulmonary overpressurization syndrome)
- Decompression sickness (DCS)
- Arterial gas embolism
- Alternobaric vertigo
- Facial baroparesis (Bells Palsy)
- At depth injuries
- Oxygen toxicity
- Nitrogen narcosis
- Hypothermia
- Contaminated gas mixture (e.g. CO toxicity)
- Caustic cocktail from rebreathing circuit
Evaluation
- Clinical diagnosis, most often benign, with subconjunctival hemorrhage common.
- Rule out rare complications such as hyphema, orbital hematoma, retrobulbar hematoma
- May warrant CT orbit if exam concerning for ocular compartment syndrome or retrobulbar hematoma
- Check IOP
Management
- If presentation concerning for ocular compartment syndrome with Retrobulbar hemorrhage, orbital hematoma, hyphema
- These patients should be treated in usual manner (ophtho, lateral Canthotomy if needed, CT evaluation) if clear signs of mask squeeze and related symptoms instead of jumping to hyperbaric treatments.
- If benign presentation
- Resolves over a few days to a week
- Cold compresses and analgesics may help
Disposition
- Outpatient