Exploring the Depths: Integrating Medicine and Diving
Published 08/14/2024 in Scholar Travel Stipend
Written
by Nhi Ho |
08/14/2024
In June 2018, twelve boys and their coach were trapped in a flooded cave system in Tham Luang, Northern Thailand, and an unprecedented international rescue effort ensued. There were many factors that increased the difficulty of this rescue mission: the size and complexity of the cave network, the lack of food and water, lowering oxygen levels in the air pockets where the boys took shelter, and heavy rainfall in the region which exacerbated the flooding. Due to the flooding, only highly-trained and specialized divers could perform the rescue.
To reach the boys, rescuers had to dive through 1.5 miles of the flooded cave system to an air pocket over half a mile below the surface. There were some parts of the dive that involved steep slopes while other parts were too narrow to wear SCUBA tanks on their backs. Navigating these obstacles prolonged the journey to the air pocket to a minimum of 1-2 hours. How did the rescuers extract the boys, inexperienced in diving, through a 1.5 mile long cave system completely submerged, navigating all of these obstacles and managing their air reserves?
In March 2024, I flew to the Philippines to pursue additional diving experience and gain perspective on these questions. Holding a PADI Advanced Open Water diver certification, I opted to pursue additional training in Nitrox. Nitrox, or “enriched air”, is a special blend of oxygen and nitrogen with an oxygen concentration between 32-36% as opposed to a concentration of 21% in the air we normally breathe. The main benefit of the higher oxygen content is the resulting lower amount of nitrogen in the tank. The lower concentration of nitrogen inhaled during the dive lowers the amount of oxygen dissolved in the blood from the water pressure at depth. This prolongs a diver’s “bottom time”, which is a measured time limit where divers must make incremental stops at shallower depths upon ascent to prevent rapid decompression of dissolved nitrogen in the blood, a potentially fatal condition known as the “bends”. A danger associated with higher oxygen content are the flammable hazards when handling and filling the tank, and oxygen narcosis, the overabsorption of oxygen in the blood, if a diver strays too far below depth limits. Given the dangers of higher oxygen content, enriched air divers are required to test their tanks for oxygen content and are responsible for monitoring their depth and bottom times using a dive computer. The added attention I was required to give my tank and depth through enriched air diving gave me perspective on the special care and attention the rescue divers needed to have on their equipment, which was compounded by the need to share equipment with the boys undergoing rescue, as even the slightest miscalculation or equipment malfunction could have led to disastrous outcomes.
I took my course in Moalboal, a beach front town known world-wide for its corrals and sea life. I started by re-learning the details of SCUBA diving via a refresher course to re-familiarize myself with SCUBA equipment. Diving equipment includes a Buoyancy Control Device (BCD), a weighted jacket worn with connections to your tank to allow control of your buoyancy by taking in and expelling air. The BCD carries the oxygen tank, and holds a diver’s mouthpiece, or regulators in place. The regulator has a first stage which is attached to the cylinder valve that reduces the high-pressure gas from the tank, approximately 3000 psi, to a breathable pressure. The regulator’s second stage is the mouthpiece that a diver puts in their mouth to breathe in and out. All standard SCUBA diving equipment includes an alternate second stage, which is a backup in case obstacles in the water cause one to lose their primary mouthpiece, or if one needs to share air with another diver during an emergency. An intimate understanding of one’s own capabilities underwater and their equipment is crucial for the first certification level. During the PADI advanced certification, I had to further hone these basic skills and also learn to be aware of the environment around me and better navigate, manage air consumption, and buoyancy. These skills can take a lifetime to master and refreshing them put into perspective the amount of skill displayed by the rescue divers during the Thai cave rescue.
Scuba diving is a particularly dangerous activity. The open ocean water places divers at risk of hypothermia and dehydration. Inexperience with rapid descent or ascent can cause barotrauma (injury of increased air pressure) leading to lung, ear, and sinus injury. If a diver ascends too quickly, the air in their lungs expands as the ambient water pressure decreases, much like air expanding in a balloon. Expanding air pockets in the lungs (alveoli) can damage the bronchial passages and alveoli. This can cause a collapsed lung (pneumothorax), air trapped in the sinuses, and also, tragically, an expanding air pocket in the brain that can cause a blockage and lead to a stroke or if in the coronary arteries, the blood vessels supplying your heart, can cause a heart attack. All of these are a form of decompression illness. The very oxygen that we all care for, can also cause oxygen toxicity, which the most feared complication is seizure. A seizure episode under water can cause the diver to lose track of the regulator, vomit and involuntarily aspirate, and therefore drown underwater. Such episodes are likely to be fatal.
With all these potential emergencies and complications in mind, and the fact that I had not dived in two years, it was incredibly nerve wracking when I jumped in the water and deflated my BCD. I slowly watched the water line pass above my goggles, and one moment I saw the boat, and the next, I was looking up at the “sky” that is the water surface above me. Around me was an endless wilderness of blue. A sense of claustrophobia spread over me, and I had to fight the instinctual urge to kick with my legs upward, pull away the regulator that is delivering down-regulated oxygen in my mouth, and gasp for fresh air above the water surface, but this would be the exact maneuver that causes decompression illness. I descended 5 meters, and then laid down on my stomach, inflated my BCD with a puff of air to add buoyancy, and my training kicked in as I started kicking my legs. Once again, I looked up and saw rays of sunshine fighting through the water ripples. My mind now only focused on one thing: “Breath in, breath out Nhi” I told myself to stop from hyperventilating and having an anxiety attack. I thought about the boys in the cave system, and the overwhelming anxiety they would have had donning this equipment and squeezing their way to safety having not gone through formal training.
I also took a trip to Coron, Palawan. The Palawan region is famous for picture-perfect white sandy beaches and turquoise blue water. Beneath the waters of Coron bay lay a plethora of sunken naval ships – the result of an attack on the Imperial Japanese Navy by US Navy aircraft during the Second World War. I still do not hold a certification to conduct cave diving, therefore, a close parallel to diving in caves was to dive in wrecks of Coron Bay. Coron Bay is unique because its wreck sites are between 10 and 30 meters below sea level—which is to say that they are relatively shallow, making them easier to access than most wreck diving sites. Nonetheless, it was incredibly challenging to dive here—maintaining control over my buoyancy and depth, while navigating tight spaces filled with sharp, tetanus-prone metal pieces from the hull of the ship and avoiding sharp corrals that grew on these surfaces.
I have dived over 20 times in my life, having obtained Open water PADI and Advanced Open water PADI certification, yet I still struggled to dive for the first time in two years. How did the Thailand rescuers rescue the soccer team boys from the mile and a half long underwear passageway—none of whom has ever dived before? How did the rescuers maximize safety for the boys and for the rescuers, while avoiding anxiety, and inopportune movements that can cause catastrophic complications in a mile deep and mile long cave?
The answer is a remarkable feat in the field of anesthesia. With the inherent stress diving can induce on someone, expecting the boys to be able to operate this equipment under duress would be nearly impossible. With anesthesia, the boys would be able to tolerate the long stressful journey through the cave system. The four components of anesthesia are: amnesia, unconsciousness, analgesia, and immobility. Anesthesia can also be described in depths, or levels, which range from light sedation to general anesthesia. A patient under light sedation is still alert and able to hold a simple conversation. On the other hand, a patient under deep sedation is asleep and will only respond to loud verbal or strong physical stimulation. A person under general anesthesia will not move at all—and a trained anesthesia provider is necessary to control the person’s vital signs, airway, and depth of anesthesia continuously. Because of the need for constant monitoring, typically one anesthesia provider takes care of only one patient at a time.
To understand how the Thai rescue mission was able to do this rescue, I did a deep dive and read the research paper written by the Australian anesthetist cave diver involved in designing and implement this unprecedented rescue mission. The author and his dive partner were flown into Thailand on July 6, 2028, 12 days after the Thai soccer team entered the cave and three days after they were found.
Although the team had arrived at the conclusion that administering anesthesia to the trapped boys was necessary to safely extract them from the cave system, the rescue effort was further complicated by the fact that the other cave divers were not trained anesthetists.
After extensive discussions with other consultants and review of anesthetic agents, ketamine was chosen. Ketamine has a favorable side effect profile as it has less respiratory depressant side effects and less negative effects on blood pressure. It can be administered via injection directly into the muscle without the need for an IV. The plan was for the anesthesiologist to induce anesthesia with an initial loading dose of ketamine to a child. Once the child is rendered unconscious, by testing for his responsiveness to voice and touch, a positive pressure regulated mask is placed over the child’s face which forces air into the child’s airway. A rescue diver assists the anesthesiologist in placing the mask on and testing it with child face down under the water level and assesses their vital signs and depth of anesthesia. The positive pressure mask also acts as a “stent” to help keep the child’s airway patent during the excursion. A SCUBA tank is tethered to the child via two bungee cords. The child’s hands are clipped together with cable ties and ankles bound by bungee cord to prevent entanglement of their limbs on cave projections and also to stop the child from pulling at the mask or endangering the rescue diver should the anesthesia wear off unexpectedly. The scuba dive rescuers are trained to give “top-up” doses of ketamine upon any signs of spontaneous patient movement. Other agents were given intramuscularly, such as atropine to maintain the child’s heart rate and cardiac output, and a benzodiazepine for anxiolysis. On occasion, if a child appears to be holding their breath or becomes apneic, rescue divers were trained to give a positive pressure breath by pressing on the second stage regulator purge valve. Medical providers were also stationed at various dry chambers within the cave to aid the rescue diver in addition to providing additional top-up doses.
Miraculously, all twelve of the soccer teammates and their coach were rescued. The team required no airway management beyond supplemental oxygen. One boy needed additional support for closed vocal cords. No rescuers suffered aspiration or drowning. Regrettably, one diver did die during one of the initial dive search and rescue trips due to running out of air.
As an anesthesiologist and a recreational SCUBA diver, I understand the dangers of administering anesthesia to children—and to add to that – administering general anesthesia to children, while they are underwater. The heroic efforts and leadership displayed by the anesthesiologist in this case, able to adequately train the other divers to administer the doses and monitor for vitals, serve as inspiration to continue honing my craft.
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