ABEM UHM flashcards
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- Boyle's law
- At constant temperature, the volume of a gas is inversely proportional to its pressure. This explains barotrauma on descent and gas expansion on ascent in divers.
- Dalton's law
- The total pressure of a gas mixture equals the sum of the partial pressures of its components. This determines oxygen and nitrogen partial pressures at depth.
- Henry's law
- The amount of gas dissolved in a liquid is proportional to the partial pressure of that gas above the liquid. This underlies nitrogen loading and decompression sickness.
- Absolute pressure formula
- Absolute pressure in atmospheres equals 1 plus depth in meters divided by 10, or 1 plus depth in feet divided by 33, for seawater.
- Nitrogen narcosis
- A reversible impairment of judgment, coordination, and reaction time caused by dissolved nitrogen at depth. It typically appears below 30 meters and resolves with ascent.
- Oxygen toxicity threshold
- Central nervous system oxygen toxicity risk rises above a partial pressure of 1.4 ATA. A partial pressure of 1.6 ATA is generally the maximum for working dives.
- Gas density at depth
- Gas density increases with absolute pressure, raising the work of breathing. Dense gas at depth can cause CO2 retention and hypercapnia in divers.
- Water heat conductivity
- Water conducts heat about 25 times faster than air. This makes hypothermia a major risk during diving and increases gas uptake in cold conditions.
- Middle-ear barotrauma
- Failure to equalize middle-ear pressure on descent causes tympanic membrane and middle-ear hemorrhage. It is graded by otoscopy and can cause hearing loss.
- Inner-ear barotrauma
- A forceful Valsalva during descent can rupture the round or oval window, causing vertigo, tinnitus, and sensorineural hearing loss. It contraindicates further diving until evaluated.
- Alternobaric vertigo
- Unequal middle-ear pressures during ascent produce transient vertigo and disorientation underwater. It usually resolves with equalization or surfacing.
- Pulmonary barotrauma of ascent
- Expanding gas in the lungs during ascent causes alveolar rupture, leading to pneumothorax, pneumomediastinum, subcutaneous emphysema, or arterial gas embolism.
- Arterial gas embolism onset
- Symptoms of arterial gas embolism usually appear within 10 minutes of surfacing. Later onset suggests decompression sickness rather than gas embolism.
- Saltwater versus freshwater drowning
- Saltwater aspiration causes surfactant washout and pulmonary edema. Freshwater aspiration can cause hemodilution, hemolysis, and ventricular fibrillation.
- Stonefish sting treatment
- Stonefish and scorpionfish stings are treated with hot water immersion at about 45 degrees C for pain control, along with supportive care.
- Box jellyfish first aid
- Vinegar inactivates box jellyfish nematocysts and should be applied to the sting site. Avoid pressure immobilization for box jellyfish stings.
- Flying after diving
- A surface interval of at least 12-24 hours is recommended before flying after repetitive dives without symptoms. Longer intervals apply after decompression sickness treatment.
- Hyperbaric oxygen definition
- Breathing 100% oxygen at greater than 1 atmosphere absolute. Treatment pressures are typically 2.0-3.0 ATA in a monoplace or multiplace chamber.
- HBO mechanisms of action
- Hyperbaric oxygen hyperoxygenates tissues, causes vasoconstriction, enhances neutrophil killing, promotes angiogenesis, and reduces gas bubble size via Boyle's law.
- HBO absolute contraindication
- Untreated pneumothorax is the absolute contraindication to hyperbaric oxygen therapy because gas expansion during treatment can cause tension pneumothorax.
- CNS oxygen toxicity
- Presents with tinnitus, visual changes, nausea, twitching, and seizures. Risk rises above 2.8-3.0 ATA and is managed with air breaks.
- Pulmonary oxygen toxicity
- Prolonged oxygen exposure causes tracheobronchial irritation and decreased vital capacity. It is managed by limiting exposure and using air breaks.
- Air break schedule
- A common oxygen toxicity mitigation is 20 minutes of air breathing every 90-120 minutes of oxygen. Air breaks reduce both CNS and pulmonary toxicity risk.
- Carbon monoxide HBO
- Carbon monoxide poisoning is treated at 2.5-3.0 ATA. Indications for HBO include syncope, neurologic deficits, pregnancy, and severe metabolic acidosis.
- US Navy Treatment Table 6
- A hyperbaric treatment schedule at 2.8 ATA with oxygen and air breaks, used for decompression sickness and arterial gas embolism.
- Decompression illness initial care
- Place the patient supine, give 100% oxygen by nonrebreather mask, provide IV fluids, and transport urgently to a hyperbaric facility.
- Imaging in decompression illness
- Decompression sickness is a clinical diagnosis. Recompression should not be delayed to obtain imaging or laboratory studies.
- DCS Type I versus Type II
- Type I involves joints, skin, and lymphatics. Type II involves neurologic, pulmonary, or cardiac systems and is more severe.
- Arterial gas embolism treatment
- Arterial gas embolism and decompression sickness are often treated identically with US Navy Treatment Table 6 because the distinction is unreliable.
- Dive history elements
- Record depth, bottom time, ascent rate, repetitive dives, surface interval, and time of symptom onset when evaluating a diving emergency.
- Neurologic decompression sickness
- Presents with paresthesias, weakness, incontinence, or altered mental status. It is a neurologic emergency requiring urgent recompression.
- Adjunctive DCI therapy
- Severe decompression illness may be treated with lidocaine for neurologic symptoms and aggressive hydration. Avoid nitrous oxide and air travel until cleared.