THE RESCUE: UNDERWATER ANESTHETICS EXPLAINED

3 Feb 20223 Feb 2022THE ANESTHESIA CONSULTANT 2 Comments

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Physician anesthesiologist at Stanford at Associated Anesthesiologists Medical Group

Richard Novak, MD is a Stanford physician board certified in anesthesiology and internal medicine.Dr. Novak is an Adjunct Clinical Professor in the Department of Anesthesiology, Perioperative and Pain Medicine at Stanford University, the Medical Director at Waverley Surgery Center in Palo Alto, California, and a member of the Associated Anesthesiologists Medical Group in Palo Alto, California.
emailrjnov@yahoo.com

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Underwater general anesthetics of 3 hours duration? See it in The Rescue, a new National Geographic Documentary Film directed by Jimmy Chin (winner of the 2018 Academy Award for Best Documentary Feature for Free Solo). The Rescue details the miraculous extraction of 12 boys and their coach from a flooded Thailand cave in June and July of 2018. The Rescue required 13 underwater general anesthetics delivered by an anesthesiologist and maintained by non-medical cave divers during their 3-hour swim to the mouth of the cave. How did this once-in-history anesthetic tour de force come about? You can watch the movie—a favorite for this year’s Oscar for Best Documentary—on Disney+ for their $7.99 monthly fee. This column explains the specifics as to how anesthesiology innovation saved thirteen lives in The Rescue.

The site of The Rescue was the Tham Luang Nang Non cave in Chiang Rai Province in northern Thailand. Twelve boys of ages 11 – 16 from the Wild Boar soccer team and their coach entered the cave for a birthday celebration. June monsoon rains hit and flooded the entrance of the cave, trapping all thirteen inside.

The boys were trapped at the left of this diagram. The entrance to the cave is at the right.

The synopsis of The Rescue follows this timeline:

Day 1 – Trials of gas-powered generators to pump the water out of the cave fail to lower the water level.

Day 2 – The Thai Navy Seals arrive on site. They attempt scuba diving into the cave but abort their efforts because of low visibility and difficult access. They were only able to advance 200 meters into the cave. None had experience diving into dark narrow caves. John Volanthen, an information technology consultant who does cave diving as a hobby, shows them a map of the long tortuous cave route, and surmises that the boys are trapped about 2 kilometers into the cave. Richard Stanton, a retired middle-aged British firefighter who is also an expert in cave diving, is alerted to the predicament, and flies to Thailand to help.

Day 5 – Stanton assembles a collection of his friends who are fellow cave divers. These men have real world jobs such as electricians, contractors, mechanics, and consultants, but are experienced in underwater cave exploration. At first, the Thai Navy Seals will not allow the cave divers to attempt a rescue because they deem it is too dangerous. Eventually the Thai Seals consent to let the cave divers proceed. Stanton describes their passage as scuba diving against a raging river of white water, with the added problem of poor visibility. They surface at the first air-filled chamber inside the cave, and instead of finding the boys they find four pump workers who were unknowingly trapped inside the cave. The cave divers swim the pump workers out, sharing their scuba regulators as they swim, but find the pump workers are easily panicked in the dark cold underwater conditions, and the passage out is very difficult. Their entire swim rescue of these men takes only 30 to 40 seconds, yet Stanton describes the ordeal as “an underwater wrestling match.”

Day 7 –Rain continues and the water levels rise. Hundreds of people surround the mouth of the cave, and worldwide media coverage is ongoing.

Day 10 – The cave divers continue their attempts to explore the length of the cave. They extend a rope behind them to trace their route back to the outside world. After several hours of traversing the narrow route, including passing through several air chambers above water, they reach a chamber where the atmosphere smells pungent. They fear they have located the rotting flesh of decomposing bodies. Instead they shine a light into the chamber and see 13 people—the Thai boys and their coach—sitting on the rocky floor. They are skinny and frightened, but alive. They’ve had no food for 10 days and have existed by drinking the water from the cave. The cave divers return to the mouth of the cave and announce that the boys are alive.

Day 12 – The divers follow the rope back to the boys and bring them power gel food and foil blankets. Their plan going forward is unclear. There appears to be no way to swim the boys out for the 3-hour underwater journey to the mouth of the cave. One option is to wait until October (four months) until the monsoon season is over, and the cave is no longer flooded. A second option is to somehow drill down to where the boys are trapped. A third option is to pump out millions of gallons of water out of the cave, but this is also deemed impossible. Another cave diver friend of Stanton’s is Dr. Richard Harris, who lives and works in Australia. Dr. Harris is an anesthesiologist. The team of cave divers telephone him and ask if the boys can be anesthetized for 3 hours to be extracted underwater. His initial answer is no, that this would be impossible.

At the same time, the divers bring an oxygen analyzer into the cave and discover that there is only 15% oxygen left in the atmosphere where the boys are trapped. Normal room air contains 21% oxygen, and 15% oxygen is considered an eminent threat to life for the boys. Immediate action is necessary.

Day 14 – Dr. Harris arrives at the cave. He and his cave diver colleagues come up with a plan to anesthetize and extract the boys, but there is a new problem: The Thai government does not want them to attempt the rescue. The government fears the boys will all die in the futile attempt. Enter Josh Morris, a cave diver who speaks Thai. He explains the facts and the threat of the low oxygen atmosphere to the government authorities, and convinces them there is no time to waste and that there is no other workable plan. The government agrees to let the cave divers proceed.

Day 15 – The rescue plan is as follows: Divers will swim into the cave to the chamber where the boys are located. The divers will transport an extra oxygen cylinder, a full-face dive mask and regulator, and a dive suit for each boy. They will also carry three medications: 1) Xanax, an oral anti-anxiety pill in the Valium family of benzodiazepines; 2) ketamine, an injectable general anesthetic drug, carried in a syringe-and-needle setup; and 3) atropine, an injectable drug which dries up oral secretions (necessary because ketamine can cause excessive salivation significant enough to choke off breathing). When the cave divers arrive at the chamber where the boys are situated, they dress the first boy in a dive suit complete with a rubber head-covering. Dr. Harris then administers the Xanax pill and the intramuscular injections of ketamine and atropine. After the boy loses consciousness, they tie the boy’s hands behind the boy’s back and apply the full-face oxygen dive mask to keep the water out. The boy is placed in the water atop a full oxygen cylinder, and a diver guides the boy and the cylinder under the water. This diver clings to the rope as he begins the 3-hour journey back toward the cave entrance. There are multiple air chambers on the route back to the entrance. At each air chamber, the diver surfaces and assesses if the boy is still alive and breathing, and whether the boy is anesthetized deeply enough. If the boy is twitching, the diver injects more ketamine. Keep in mind this diver is not a doctor—he has been taught by Dr. Harris to inject more drug if the boy seems to need more sedation. This process is repeated for four boys the first day and is successful. All four reach the surface, alive and anesthetized, and are transported to a nearby hospital.

Day 17 – The process is repeated and four more boys are successfully extracted.

Day 18 – A heavy monsoon rainstorm is expected, so all five remaining individuals are extracted before the cave is totally flooded. The cave divers are hailed as civilian heroes as the last of the boys is rescued. The rescue effort involved more than 10,000 people, including divers, rescue workers, 900 police officers, 2,000 soldiers representatives from 100 governmental agencies, 10 police helicopters, more than 700 diving cylinders, and the pumping of more than a billion liters of water from the caves.

In the aftermath, Richard Stanton returns to England and receives a George Medal, the second highest award for civilian gallantry, in a regal ceremony at Buckingham Palace.

The Rescue is riveting and suspenseful, and ultimately worth the one hour 45 minutes and the $7.99 you’ll invest in it.

Here’s the Anesthesia Consultant analysis of the medical circumstances in The Rescue:

In an operating room, anesthesia is typically delivered as a gas (e.g. sevoflurane), or intravenously. Neither gas anesthesia nor intravenous anesthesia is possible in an underwater cave rescue. Ketamine is the only general anesthetic drug which can be injected. Ketamine can be injected either into an IV (e.g. in an operating room by an anesthesiologist) or into a muscle (e.g. in a cave in Thailand). Ketamine has the advantages of quick onset and a lack of respiratory depression—that is, ketamine will not stop a patient’s breathing. But if a patient becomes over-sedated it’s possible they will have upper airway obstruction which can lead to inadequate ventilation, so ketamine administration typically needs to be administered by an anesthesia professional who monitors the patient’s breathing—unless you’re rescuing kids in a cave. Ketamine also has theses disadvantages: It results in a relatively slow wake up (compared to propofol and/or sevoflurane gas); it causes markedly increased saliva production (which is why we need to administer atropine, a secretion-blocking anticholinergic drug—along with ketamine); and ketamine can cause vivid bad dreams—for this reason we routinely give an IV benzodiazepine such as Versed along with ketamine. Re-dosing of ketamine was required because the drug’s half-life (the time it takes for the total amount of ketamine in the body to be reduced by 50%) is about 2.5 hours in adults. Dr. Harris couldn’t be with every boy en route, which is why he had to train the other cave divers how to inject ketamine for redosing.

Dr. Harris could have chosen to use an injection of intramuscular Versed instead of Xanax (the oral benzodiazepine used in The Rescue). A disadvantage with oral Xanax is its slow onset time. It’s unlikely the Xanax began to work until it was absorbed from the stomach and carried by the bloodstream to the brain, which likely took thirty minutes or more.

The choice of full-face dive masks (FFMs), capable of maintaining constant positive airway pressure (CPAP) during the anesthetics, was brilliant. All acute medical care, be it in an operating room, an intensive care unit, an emergency room, a battlefield, or a cave, follows the priority order of A-B-C, or Airway- Breathing-Circulation. The problems of keeping the airway open, as well as keeping oxygenation and ventilation intact, were daunting challenges underwater. There were no research articles and no textbooks to tell the cave divers how to deal with this situation. They used their best strategy and made their best guess, and it was successful. If excessive water had leaked into the mask, a boy could drown.

Fortunately all the boys and their coach were slender (per the video footage) and had low body-mass-indexes (BMIs). A patient with a low BMI typically has an easy airway, and would have a lower chance of obstructing their upper airway during a 3-hour underwater general anesthetic. An overweight patient would probably not have survived a 3-hour underwater general anesthetic. As well, all the boys and their coach were young and healthy with normal hearts and lungs. If they had been older, with any abnormal cardiac or respiratory function, they may not have survived the 3-hour underwater general anesthetic.

It’s striking that the boys could survive for two weeks with only water and no food. Hydration is critical—no one can survive two weeks without water—but food was not imperative for this length of time. They survived without calories for two weeks, but humans can only survive for about three days without water.

Hypothermia, or low body temperature, was a risk during the underwater rescue. Anesthetized patients have no muscle movement and are unable to generate any body heat in the cold water. The scuba suits and hoods were aimed at minimizing the temperature drop while the boys were anesthetized.

No one monitored the vital signs of the boys during their 3-hour underwater general anesthetics. General anesthetics always require monitoring of these parameters: heart rate, oxygen saturation, blood pressure, ECG, respiratory rate, temperature, and end-tidal carbon dioxide expiration. In an underwater cave anesthetic, none of this was possible. Luckily the ketamine anesthesia as administered must have kept all the vital signs within acceptable limits.

The oxygen concentration in the atmosphere of the cave was only 15%, far lower than the normal room air concentration of 21% we’re all breathing right now. This oxygen concentration of 15% is roughly equivalent to the oxygen concentration atop a mountain at 10,000 feet of altitude. The boys tolerated the gradual decrease of the oxygen level within the cave from 21% to 15% over 12 days without any brain damage or any damage to a vital organ system. An acute decrease from 21% to 15% may have caused low blood oxygen—hypoxia—and organ damage. During anesthetics in an operating room, anesthesiologists commonly administer at least 40-50% oxygen—a higher concentration than in room air—as an extra margin of safety.

Will this sort of underwater anesthetic cave rescue ever happen again? Perhaps. The blueprint for a successful result is here in this movie. The science of the full dive face masks in this rescue was published in the medical journal Diving and Hyperbaric Medicine in the article Deep anaesthesia: The Thailand cave rescue and its implications for management of the unconscious diver underwater.

The film The Rescue documents a remarkable feat of emergency medicine and emergency anesthesia care. I recommend you see the movie, and I hope you’ll understand the medical care better because of the discussion presented above.