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Environmental Emergencies

Environmental Emergencies

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Environmental Emergencies

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  1. Environmental Emergencies National Resident Review Course Ian Rigby

  2. Outline • What’s New in Environmental Emergencies? • Diving Emergencies • High Altitude Illness • Snakes • Spiders • On the downloadable presentation is presentation notes for Heat Illnesses and Cold Illnesses • www.ianrigby.net - under Presentations

  3. What’s New? • Not much! • These topics are admirably covered in standard text books and very little is groundbreaking since they’ve been written. • Great reference is EMCNA May 2004

  4. What’s New? • Cochrane Protocol for “Recompression and adjunctive therapy for decompression illness”. 2007 • Recompression therapy is standard for the treatment of DCI, but there is no randomized controlled trial evidence. Both the addition • of an NSAID or the use of heliox may reduce the number of recompressions required, but neither improves the odds of recovery. The • application of either of these strategies may be justified. The modest number of patients studied demands a cautious interpretation. • Benefits may be largely economic and an economic analysis should be undertaken. There is a case for large randomized trials of high • methodological rigour in order to define any benefit from the use of different breathing gases and pressure profiles during recompression • therapy.

  5. Diving Injuries

  6. Diving Injuries

  7. Gas Laws • Boyle’s Law • Dalton’s Law • Henry’s Law

  8. Gas Laws – Boyle’s Law • PV=k @ constant temp • For every 10m of depth you increase pressure by 1 atm • So the size of bubbles in solution increases as pressure decreases • That’s why bubbles are small at the bottom of the glass and get bigger at the top

  9. Dalton’s Law • What is (Daltin) in the beer bubbles. • The pressure of a gas is the sum of the partial pressures of all it’s gasses • Pair = PPO2 + PPN2 + PPCO2 …etc • Let’s assume 20% 02 and 80%N2 in air • At 1 atm of air (i.e. sea level) you are inspiring 0.2 atm pressure of O2 and 0.8 atm of N2

  10. Dalton’s Law • At 30m depth (underwater) you are being subjected to 4 atm of pressure • Now breathing compressed air at 4 atm • (20% O2 and 80% N2) • Pair = PO2 + PN2 • At 4atm you are getting 0.8atm O2 and 3.2 atm of N2 • So, at depth you are breathing in more molecules of the gasses

  11. Henry’s Law • The number of beer bubbles • The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of that gas in contact with the liquid • The higher the pressure, the more gas is dissolved in the solution

  12. So…. • If Dalton’s Law means we are inhaling more of a gas with increasing pressure and…. • Henry’s law says with increased pressure, more gas dissolves into a liquid and… • Our tissues (muscle, nerves, blood) are mostly liquid then…. • As pressure increases more gas is dissolved into our tissues • We’ll see how this works out in a bit

  13. Diving Emergencies Key Question in Hx

  14. Descent – Facial Barotrauma • Failure to equalize pressure in mask • Leads to traction on face, eyes due to relative negative pressure • See edema and petechial hemorrhages of skin, sclera

  15. Middle Ear Barotrauma • Failure to equalize pressures of eustasian tube and the outer ear canal • Leads to squeeze on the TM • Most common disorder of diving

  16. Middle Ear Barotrauma • Various grades of injury of TM • 1 – Capilary dilation • 2 – Mucosal edema • 3 – Hemorrhage into TM • 4 – Hemorrhage or serrous exudate • 5 – TM rupture • Treat conservatively

  17. External Ear Barotrauma • Due to plug of the external canal with a patent eustachian tube • Develops a relative negative external pressure and bowing of the TM outwards

  18. Inner Ear Barotrauma • Rare • Occurs with rapid pressurization of the inner ear leads to a pressure wave that disrupts the cochlear round window • Presents with sensorineural hearing loss and severe vertigo • Usually requires ENT f/u

  19. Sinus Barotrauma • Same theory with the ear can lead to sinus pain either in descent or ascent if the sinuses fail to equalize pressure • Treat with pseudophed or other OTC decongestants

  20. Injuries at Depth • Nitrogen Narcosis • Hypothermia • Oxygen Toxicity

  21. Nitrogen Narcosis • Rapture of the Deep • Dalton’s law says…. • At depth inspiring more N2 • Henry’s law says…. • More N2 diffusing into tissues

  22. Nitrogen Narcosis • Nitrogen has a special affinity for fatty tissue • Diffuses into neural membranes and acts like an anesthetic gas • Causes euphoria, poor judgment and impaired motor skills • Injury occurs due to lack of judgment • Treatment is ascent

  23. DCS – Decompression Sickness

  24. DCS I – ‘the bends’ • Occurs with ascent from depth • Especially with long times at depth • Presents with periarticular joint pain • Can also see skin itching and marbling in DCS I • Occurs when N2 forms bubbles in tissues • Leads to obstructive and inflammatory changes • DCS is more than just bubbles • Is DCS I if symptoms limited to MSK system only • Relief when joint compressed with BP cuff at 200mmHg

  25. DCS I – Treatment • Treat by recompression therapy (hyperbaric O2) • Can utilize 100% O2 • Search for DCS II symptoms….

  26. DCS II • Decompression sickness involving anything more than the MSK system • Treatment for all is supportive care and recompression therapy (hyperbaric)

  27. DCS II - CNS • CNS – nitrogen dissolves easily into the fatty myelinated tissues of the nervous system • So has predilection for formation of bubbles with decompression • Spinal cord findings common especially in the thoracolumbar area • Presents as paresthesias, weakness, etc. • Can present as CVA • Inner Ear DCS gives vertigo – ‘the staggers’ • LOC is uncommon (as opposed to AGE)

  28. DCS II – ‘the chokes’ • Pulmonary circulation is a low pressure system • Large volume/size bubbles can cause venous gas emboli • Get progressive cough, chest pain, dyspnea in the 1st 24hr of surfacing • What gas laws? • Tx with supportive care, 100% O2 & recompression

  29. Rapid Ascent–Acute Gas Embolism • 2nd leading cause of death in diving • Rapid ascent causes bubble formation in pulmonary circulation • These can traverse the L atrium and ventricle and are sent to the systemic circulation • 60% of those who suffer AGE have demonstrated right to left shunts (i.e. patent foramen ovale, etc.) • Bubbles cause mechanical obstruction and then inflammatory rxn • Onset of symptoms occurs within 10min of surfacing (90% of the time)

  30. Predilection for cerebral and cardiovascular circulation Altered LOC Seizures Visual changes CN deficits Focal weakness Predilection for cerebral and cardiovascular circulation Ischemia MI Dysrhythmias AGE – CNS/CVS

  31. AGE - Treatment • Supportive care • 100% O2 • Recompression therapy (only definitive tx)

  32. Pneumothorax • Occurs with alveolar damage and gas crossing the visceral pleura • Treat as standard pneumo • Needs chest tube (not just aspiration) if patient undergoing recompression tx

  33. Pneumomediastinum • Air bubbles dissecting into pulmonary interstitium • Goes into neck, pericardium, mediastinum • Unless hemodynamically unstable, treat conservatively and gas will absorb on own

  34. Alternobaric Vertigo • Rare • Failure to equalize pressure of the inner ear on ascent. • Occurs with blockage of unilateral eustacian tube • Develops pressure difference from middle ear and cochlear organ • Get profound vertigo, nausea • Once pressures equalize symptoms disappear

  35. Diving Comes Down to Beer Bubbles Boyle’s Law describes size of bubbles Dalton’s Law describes what’s in the bubbles Henry’s Law describes the gas dissolved in the liquid and the number of bubbles

  36. High Altitude Illnesses

  37. Am I High Yet? • No absolute definition for high altitude • The most accepted is altitudes greater than 2500 m • Very high is 3500-5500 m • Extreme is >5500 m

  38. Where Can I Go To Get High? • High altitude (>2500 m) is found only in western Alberta, British Columbia and the Yukon • Banff 1372 m • Lake Louise 1646/2637m • Sunshine 1658/2729m • Whistler 652/2182m • Mt.Columbia 3747m • Mt. Logan 5959m

  39. At sea level we are underneath an ocean of air %O2 is always 21% But as you climb higher, the Patm drops and thus your PO2 drops PiO2 = 0.21(PB-47) PB=barometric pressure At sea level PiO2= 160 mm Hg  At 2500m PiO2 = 119 mm Hg  Aconquilcha,Chile 5340m PiO2 = 82 mm Hg On top of Everest (8848m) PiO2 = 43 mm Hg  More About Gas!

  40. Respiratory Adaptations • Hypoxia sensed by carotid body (PaO2<60) and signals the brain for an increased respiratory rate (hypoxic ventilatory response - HVR) • After 30 minutes, the resulting respiratory alkalosis is sensed in the brain stem and the medullary respiratory centre limits HVR • The respiratory alkalosis is sensed by the kidney, which begins to excrete HCO3-, allowing the HVR to increase over the next week.

  41. Circulatory Adaptations • Hypoxia stimulates increased catecholamines • Thus a transient increase in cardiac output, heart rate, venous tone, and blood pressure • Hypoxia signals an increased cerebral blood flow (CBF) • Hypoxia causes pulmonary vasoconstriction • Cardiac function returns to baseline quickly but shows a decreasing ability to generate higher cardiac output with exercise

  42. Hematologic Changes • Within 2 days of ascent plasma volume falls due to diuresis and fluid shifts causing hemoconcentration • Erythropoetin is released rapidly on ascent and a few days later RBC mass increases

  43. Some Definitions • AMS • - Acute Mountain Sickness • HAPE • - High Altitude Pulmonary Edema • HACE • - High Altitude Cerebral Edema • HAFE • - High Altitude Flatus Expulsion

  44. Acute Mountain Sickness (AMS) • Onset 12-24 hours after arrival at altitude (can be 2-96 hr) • Very Common • 66% of Climbers on Mt. Rainier • 50% of visitors to Khumbu region of Nepal • 20% of visitors to Colorado ski resort

  45. AMS Diagnosis1991/93 Lake Louise Consensus • Recent gain in altitude • Headache • 2 of the following: • Fatigue or weakness • GI symptoms (nausea/vomiting/anorexia) • Dizziness or lightheadedness • Difficulty sleeping

  46. AMS Risk Factors • Higher risk populations include: • Rapid altitude gain • Previous AMS • Children and teenagers • People taking alcohol or other respiratory depressants

  47. What Causes AMS? • Bottom line is we don’t truly know • AMS is likely due to mild cerebral edema and a generalized high sympathetic tone • It is very likely that AMS/HAPE/HACE are a continuum of the same pathophysiological process

  48. Prevention of AMS • Gradual ascent beginning below 2500m • Rest on the first day above 2500m • Gain no more than 300-600m per day (sleeping altitude) • Two nights at same altitude every three days • Avoid ETOH, sedatives, etc as they depress HVR especially at night

  49. Prevention of AMS • Acetazolamide 125 – 500 mg BID beginning 24h prior to departure and continued for 3-4d • Causes a metabolic acidosis that allows for greater HVR • Diuresis helps with fluid shifts • Well designed trials demonstrating acetazolamide as effective in prevention

  50. Prevention of AMS • Dexamethasone 4 mg q6h • Will prevent AMS • Unknown physiology but likely relieves minor cerebral edema and produces euphoria • Has side effects (hyperglycemia/psychosis) • Rebound common when drug stopped • Generally not used in prophylaxis