NCC Pediatrics Continuity Clinic Curriculum Hyperbaric & Dive Medicine (temporary place holder – in progress) Goals & Objectives: Know the basic gas laws and equations Know sea level atmospheric pressure and how it changes with depth Identify contraindications to diving through history & physical exam Know the basics of decompression sickness (the bends) Know the basics of a hyperbaric chamber and its common applications Pre-Meeting Preparation: Watch a Youtube video to refresh yourself on the Gas Laws Read a review of the Basics of Diving Medicine Read a review of Carbon Monoxide poisoning Conference Agenda: Visit the Undersea Medicine Research Lab in Silver Spring, MD Review basics of dive medicine Observe hyperbaric chamber demonstration Review dive medicine cases Extra Credit: Diving Medicine: A Review of Current Evidence (JABFM 2009) Decompression Illness (The Lancet 2011) The US Navy’s Submarine Force (Navy.mil) Deep Submergence Rescue Vehicle (military.com) Hyperbaric Programs in the United States (Undersea & Hyperbaric Medical Society) NCC Pediatrics Continuity Clinic Curriculum Hyperbaric & Dive Medicine (temporary place holder – in progress) Case 1 Part 1 – Pre-work SGT Rambo, a 22-year-old male Special Forces Soldier, wants to attend the U.S. Army Special Forces Combat Dive Qualification Course (CDQC) and asks for a physical. What would be potentially disqualifying conditions that you could detect by history and physical exam? Loose teeth fillings, history of pneumothorax or lung blebs, sinus disease, inability to clear Eustachian tube with Valsalva maneuver After being cleared, SGT Rambo is two weeks into the overall course and two days into the open circuit self-contained underwater breathing apparatus (SCUBA) training in which he had been breathing compressed gas from tanks through a regulator. On the second day of SCUBA, he conducted a shallow-water (shallower than 10 feet) open- circuit dive in the Special Forces Underwater Operations (SFUWO) pool and had practiced 10- foot free-surface ascents (FSA) multiple times with no issue. He then moved onto the 50-foot FSA, taking breaths of compressed air prior to ascending to the surface with no air. 1) Match the gas law with the appropriate equation and summary: Boyles’ The total pressure exerted by a mixture of gases is Law equal to the sum of the pressures of the different gases making up the mixture, with each gas acting as if it alone occupied the total volume. Charles’ At a constant volume, the pressure of a gas directly Law proportional to the temperature. Henry’s At constant temperature, the absolute pressure and the Law volume of gas are inversely proportional. NCC Pediatrics Continuity Clinic Curriculum Hyperbaric & Dive Medicine (temporary place holder – in progress) Dalton’s At a constant pressure, the volume of a gas is directly Law proportional to the change in the absolute temperature. Gay- The amount of any given gas that will dissolve in a Lussac’s liquid at a given temperature is directly proportional to Law the partial pressure of that gas. 2) Based on the gas laws above, if SGT Rambo holds his breath from 50 feet deep to the surface, what do you expect to happen to his lungs? Which gas law(s) did you apply? He will have the same quantity of gas in his lungs and as he ascends the pressure surrounding his lungs (i.e. atmospheric pressure) will decrease, allowing the gas in his lungs to expand. His lungs will therefore expand, placing him at risk for barotrauma. This is an example of Boyles’ law at a constant temperature, the absolute pressure decreases so the volume of the gas increases. There may also be a small component of temperature change that leads to increase in volume (though pressure isn’t held constant). So, there is part of Charles’ Law. 3) An inert gas is any gas that is unknown to affect metabolism, such as nitrogen and helium. These gases are expected to dissolve into the blood stream and tissues, moving toward equilibrium with the partial pressure of the inhaled gas. Some tissues achieve this equilibrium very rapidly, such as muscle, while others (nerves and adipose tissue) take much longer (hours) to achieve equilibrium with the inspired gas. Based on the information above, answer the following questions: a. What inert gas is SGT Rambo breathing on SCUBA? What percentage of this gas is he breathing? Nitrogen. Approximately 79% (Could use 80% too for easy math). Air is approximately 21% oxygen. There is less than 1% of all the other gases, so we just omit them for convenience. b. What is the partial pressure of this gas at sea level (1 ATA)? What is the partial pressure of this gas at 33 feet of sea water (fsw)? ATA * % = pp 1 * 0.79 = 0.79 ATA ppN2 (sea level) NCC Pediatrics Continuity Clinic Curriculum Hyperbaric & Dive Medicine (temporary place holder – in progress) fsw * ATA/33 fsw 33 fsw * ATA/33 fsw = 1 ATA MUST add 1 ATA for the atmosphere above the ocean, so total 2 ATA. ATA * % = pp 2 * 0.79 = 1.58 ATA ppN2 (at 33 fsw) c. Do you expect SGT Rambo to have more or less inert gas dissolved in his tissues at 50 fsw compared to sea level? Why? What gas law(s) are you applying? He will have more. At depth, the pressure increases, which increases the partial pressure of nitrogen. This will drive the nitrogen toward equilibrium in the tissues, so more nitrogen will move into the tissues. This is really a combination of Dalton’s and Henry’s gas laws. Dalton’s explains how the increase in total pressure leads to the increase in partial pressure. Henry’s explains how the increase in pressure increases amount dissolved. d. What may happen to the inert gas in his blood or tissues if he ascends too quickly? What gas law(s) are you applying? It will form expanding bubbles. These can contribute to decompression sickness. This applies Boyles’ Law and Henry’s Law – bubble expansion is from Boyles’ Law (expansion of bubbles with reducing pressure) and the quantity of gas in the blood stream and tissues is related to Henry’s law (highest inert gas load a the deepest pressures; with rapid ascent there is not sufficient time to have a redistribution of inert gas to reach a new equilibrium (i.e. Le Chatelier’s Principle) so there is an excessive bubble load). SGT Rambo breathed compressed air from the diving bell (essentially SCUBA equivalent, but without any equipment) for 3 minutes, exited the diving bell, and began his escape swim to the surface. He ascended at a rate of 40 – 50 fsw/min, faster than recommended, and exhaled throughout his ascent at a slower rate than recommended. Upon reaching the surface he signaled to the dive supervisor (Dive Sup) that he felt “ok” and he swam over to the ladder. He grabbed onto the ladder started to ascend and then stopped. He was asked to exit the pool by the Diving Medical Officer (DMO) and responded, “I can’t feel my arms.” He had been on the surface for less than 2 minutes. A neurologic exam revealed deficits that were worsening over time. These deficits included only light appreciation in the left eye, blurred vision/decreased visual acuity in the right eye, decreased/impaired extraocular movements in both eyes, dysarthria, inability to perform simple math, worsening truncal ataxia (initially could hold himself upright in seated position but quickly progressed to inability to sustain a seated position. The diver was not tested standing or walking since his condition worsened so quickly. He had 0/5 strength in both upper extremities, intact NCC Pediatrics Continuity Clinic Curriculum Hyperbaric & Dive Medicine (temporary place holder – in progress) sensation in all dermatomes, normal pain, and temperature and light touch sensation. The remainder of his physical exam was normal. He was taken for definitive treatment. 4) What is your differential diagnosis (at least 5 items)? Arterial Gas Embolism Decompression Sickness, type II Intracranial Hemorrhage (hemorrhagic stroke) – For young, mainly consider this if there is history of trauma. Ischemic Stroke – Less like in a young, healthy population. Cerebral Aneurysm – Typically affects vision due to impingement of CN III (posterior communicating artery) and can rupture leading to subarachnoid hemorrhage. Incidence increases with age. Compression fracture with cervical nerve root impingement – Could explain initial symptoms (arms) with impingement of any of the following roots C6 – T1; however, this does not explain cranial nerve symptoms. Bilateral mononeuropathy – Impingement of a wet suit or tank strap could cause temporary mononeuropathy (akin to a peritoneal neuropathy post surgery), however, bilateral and other symptoms make this unlikely. Conversion Disorder (Functional Neurologic Symptom Disorder) – Often incited by a scary or stressful experience. Mental or emotional stress converts to a physical problem. Typically, the neurologic exam is not consistent with the complaints. Hypothermia – Temperature not given here. But, hypothermia could give a sense of numbness (not usually isolated) and could make it difficult to speak due to muscle temperature. Only the most severe (i.e. coma) would the physical exam demonstrate 0/5 strength potentially. PCP or Special K Drug Use – something with dissociative properties 5) What is the most likely diagnosis? What historical clues support this diagnosis? The most likely diagnosis is Arterial Gas Embolism/Emboli. His symptoms started within 10 minutes of surfacing. He ascended at a rate slightly faster than recommend, increasing the risk for bubble expansion/formation. This typically presents with neurologic symptoms with preference for the cerebrum. Difficult localize the lesion, given that he likely had multiple emboli; however, dysarthria would be in middle cerebral artery territory, (Broca’s or Wernicke’s area) as would his arm symptoms (though with a large MCA infarct, you might expect involvement of additional limbs based on the homunculus).