Hot Button Topic – CAGE in Zoo and Aquarium Dive Operations

— October 12, 2023 in Featured Articles / Hot Button Topics
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Arterial Gas Embolism and Considerations for Zoo and Aquarium Dive Programs

Cole Drake1, Jake Emmert2, Gregory Barefoot3, Sean Eckley4, Pat McLaughlin5 

1St. Louis Aquarium at Union Station, St. Louis MO

2Moody Gardens, Galveston TX

3Applied Baromedical Solutions

4Aquarium of the Pacific, Long Beach CA5Adventure Aquarium, Camden NJ

The ADPA’s 2022 Symposium saw a number of presentations describing incidents occurring within zoo and aquarium dive programs. One such case involved a cerebral arterial gas embolism, or CAGE, case and outcome. The incident involved a 26 year old diver, with a dive profile of 14 feet for approximately 60 minutes, while conducting standard exhibit maintenance utilizing a hydraulic scrubber. Immediately after the dive, the diver presented with a worsening headache, dizziness, loss of coordination, and eventually nausea. The emergency action plan for the facility was activated, and the diver was transported to a local hospital by EMS. This article serves as a follow up to the 2022 ADPA Symposium presentation, and provides information for the dive program administrator on CAGE definition, pathophysiology, patient care, and risk management considerations.

Zoo and aquarium dive program administrators must be aware of arterial gas embolism, or AGE, risks because the majority of diving in these programs is conducted in shallow water, where the greatest change between atmospheric pressure, and the ambient pressure placed on a diver occurs. This is important because the mechanism of action for an AGE is a reduction of ambient pressure while the diver’s airway is closed, resulting in a lung over expansion injury, there are at least two documented cases in the literature where AGE was reported in less than 1.2 meters in depth (2, 3). The US Navy Dive Manual states “Arterial gas embolism, sometimes simply called gas embolism, is caused by entry of gas bubbles into the arterial circulation which then act as blood vessel obstructions, called “emboli,” and these “emboli” are frequently the result of a lung over expansion injury” (p. 20-3). Lung barotrauma caused by the expansion of gas in the lungs while breathing under pressure and held in the lungs during ascent can come about in a number of ways, such as voluntary breath holding, unknown blocked air passages, trapped gas in an obstructed portion of the lung previously damaged from disease or accident, or reaction in a panic situation resulting in an unintentional breath hold with ascent (7, p. 20-3.1). Additionally, heavy work loads and straining has been found to be a contributing factor to pulmonary barotrauma resulting in an AGE (6). Because of this, all cases of AGE should also include scrutiny of associated lung overexpansion injuries, most specifically pneumothorax.

A good tool for the dive program administrator is to suspect any diver taking a breath of compressed gas at depth who surfaces unconscious, or loses consciousness within 10 minutes of reaching the surface, must be assumed to be suffering from arterial gas embolism (7, p. 20-3). The US Navy Dive Manual describes onset as “usually sudden and dramatic, often occurring within seconds after arrival on the surface or even before reaching the surface,” Signs and symptoms include any obvious neurological symptoms such as numbness, weakness, dizziness, paralysis or weakness in the extremities, blurred vision, large areas of abnormal sensation, convulsions, and altered mental status. Additionally, the diver may lose consciousness without warning and may even stop breathing (p. 20-3.1).

AGE is a formidable opponent to the dive program administrator. Symptoms can develop within minutes after surfacing, and must be correctly identified and treated quickly. Further, because the supply of blood to the central nervous system is almost always involved, AGE is likely to result in death or permanent brain damage without swift intervention and recompression care (7, p 20-3). Although AGE, heart attack, and stroke may have similar presentations, it is prudent for the dive program administrator to treat any neurological signs and symptoms that present within 10 minutes post dive as an AGE until it can be ruled out with a proper neurological exam. Divers suspected of AGE must be placed on 100% oxygen via non-rebreather mask or demand regulator and transported via EMS immediately. Be prepared to maintain airway, breathing, and circulation when managing patient care for a suspected AGE because the diver may become unconscious without warning and may even stop breathing (7, p. 20-3.1). When emergency medical personnel arrive on scene, be sure to provide information of a suspected arterial gas embolism hyperbaric injury, that a pneumothorax may be present, and swift hyperbaric treatment is not only the definitive care but also critical to a positive patient outcome. If first responders call in a medevac transport (air transport), be sure to inform them hyperbaric injuries can worsen with a reduction of atmospheric pressure, and advise pilots to avoid flight paths in excess of 1000’ altitude. Institutional emergency action plans (EAPs) are a great tool to ensure efficient and effective emergency management when needing to move quickly from injury recognition to definitive care, and allow dive program administrators to be prepared for a wide range of emergencies, to include AGE. 

Effective options exist to mitigate risk for AGE in zoo and aquarium dive programs. A good place to start is with prevention. All divers are taught to not hold their breath when first learning to use SCUBA. This is a good rule to reinforce during orientation dives and exhibit specific training, and also gives an opportunity for the dive program administrator to share why risks are still present even in shallow, exhibit diving operations, and identify them. Another prevention strategy is coaching divers to stay aware of scenarios that can lead to uncontrolled ascents, the most practical being exhausting a diver’s gas supply while attempting to accomplish more tasks than a diver’s gas supply permits or losing a diver’s ballast (weight) at depth. Pragmatic dive planning, detailed pre dive equipment checks, and situational awareness during the dive are all tools a diver maintains to complete the day’s underwater tasks, safely. One option for mitigating risk post dive is to require all divers remain within visual sight of one another post dive for ten minutes. Many times, talking through a dive after surfacing and breaking down equipment can exceed ten minutes and maintain productive and efficient time management while also adding an effective mitigation strategy in the unlikely event an AGE presents. Lastly, because pulmonary barotrauma is a contributing factor to AGE, this is another opportunity to coach divers to avoid diving while ill, especially a respiratory illness such as a cold.

Zoo and aquarium dive programs continue to serve as strong examples of occupational diving with effective risk management (i.e., low to no incidence of diver injury). Though AGE cases are not particularly common, and causes can be confounding, they should not be overlooked when completing risk assessments and implementing mitigation measures. The diver referenced in this article was transported by EMS, evaluated, and provided recompression therapy for suspected CAGE. Though these injuries can be particularly challenging to treat, the diver’s symptoms are fully resolved. The diver has since been cleared to return to diving with direction to use air tables while breathing a nitrox mixture. This case serves as a reminder that risks for underwater operations remain present even in the shallow depths common among zoo and aquarium dive programs.

References

Folder of References: https://drive.google.com/drive/folders/1_45KV4fMYbMivUXb51UyzUmPuD0L8cwl?usp=sharing

  1. Walker, III, J. R., Hexdall, E. J., & Murphy-Lavoie, H. M. (2022). Diving Gas Embolism. In StatPearls. StatPearls Publishing.
  2. Lindblom, U., & Tosterud, C. (2021). Pulmonary barotrauma with cerebral arterial gas embolism from a depth of 0.75-1.2 metres of fresh water or less: A case report. Diving and hyperbaric medicine, 51(2), 224–226. https://doi.org/10.28920/dhm51.2.224-226
  3. Hampson, N. B., & Moon, R. E. (2020). Arterial gas embolism breathing compressed air in 1.2 metres of water. Diving and hyperbaric medicine, 50(3), 292–294. https://doi.org/10.28920/dhm50.3.292-294
  4. Eldridge, M. W., Dempsey, J. A., Haverkamp, H. C., Lovering, A. T., & Hokanson, J. S. (2004). Exercise-induced intrapulmonary arteriovenous shunting in healthy humans. Journal of Applied Physiology, 97(3), 797–805. https://doi.org/10.1152/japplphysiol.00137.2004
  5. Madden, D., Lozo, M., Dujic, Z., & Ljubkovic, M. (2013). Exercise after scuba diving increases the incidence of arterial gas embolism. Journal of Applied Physiology, 115(5), 716–722. https://doi.org/10.1152/japplphysiol.00029.2013
  6. Buzzacott, P., Grier, J. W., Walker, J., Bennett, C. M., & Denoble, P. J. (2019). Estimated workload intensity during Volunteer Aquarium dives. Occupational Medicine, 69(3), 177–181. https://doi.org/10.1093/occmed/kqz011

Naval Sea Systems Command. (2018). US Navy Diving Manual Rev. 7A.

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