Anesthesia Challenges at High Altitude: Effects, Considerations, and Recommendations

1. Anesthesia at highaltitudeDr. S. ParthasarathyMD., DA., DNB, MD (Acu), Dip. Diab. Dip. Software statisticsPhD ( physiology), IDRA , FICA

2. The first use of general anaesthesia in Tibet was during the 1904 Anglo–Tibetan War, when British military doctors administered chloroform at altitudes of > 4000 m Greene was the expedition anesthetist

3. LobsangTsering, a Tibetan employed as the team’s messenger, fell from his pony and fractured his clavicle on 6th April 1933 • Greene administered chloroform • Surgery was over but the recovery was very delayed • coramine

4. So cases may be more ! • Transport and conditions are better • More number of people live • More number of tourists • Acclimatized and NonAcclimatized Emergency and accidents Illness

5. Two schools of thought !! 1500 meters !

6. 6650 • Darjeeling 2050 • Ooty - 2250 • Amarnath – 5100m • Everest – 8850 m Golden mount kailash

7. Respiration • Recall the alveolar gas equation: PAO2=FiO2(PB-PH2O)-PaCO2/RQ At 5000ft elevation, PB is 632 mmHg, PaO2 is 81 mmHg with SaO2 95%. At 10,000ft elevation, PB is 522 mmHg, PAO2 is 59 mmHg, SaO2 84%.

8. Hypoxic drive • Hyperventilation • PaCO2 decrease • But kidneys preserve acid pH not much change A new comer may show alkalosis !

9. That’s the safety !!

10. What happens ? • Decreased demands ! • 240 ml may come down to 210 ml ! • at 45000 sq feet , the pp is low that he needs 48 % to achieve sea level conditions

11. What does hypoxia do ? • Hyperventilation • May increase by 25-30 % • 2,3-DPG levels rise due to hypoxic stress, shifting O2-Hgb dissociation curve back toward the right. This facilitates O2 unloading into tissues • The normal diffusion capacity for oxygen through the pulmonary membrane is 21 ml / mmHg/ minute • May increase three times • Pulmonary blood flow increase • The drive ( pulmonary pressure} increase

12. Circulatory changes • Bone marrow stimulated • 15 grams Hb can become 22 gm • (Hypoxia and erythropoietin) • Muscle myoglobin appears to be increased at • altitude improving oxygen diffusion • Hypoxia of tissues induced • vasodilation can increase cardiac output ! May take three weeks

13. Hypothermia • marked irritability of AV Bundle leading to atrial and ventricular fibrillation • Can it bring down MAC of agents !

14. Circulatory system • On exposure to altitudes of 3,500 to 4,000 m, plasma volume is reduced by 3 to 5 mL/kg. • This occurs relatively rapidly after arrival at altitude, and the deficit would appear to persist for at least 3 or 4 months before starting to return toward normal

15. Miscellaneous changes ! • exercise and hypoxia stimulate rennin release • but aldosterone release is decreased at high altitude • Sodium potassium – no change • Capillary density in muscle is unchanged, although the average diameter of muscle fibers appears to be reduced – oxygen to travel less

16. The normal pulmonary arterial pressure at sea level is 12mm Hg • high altitude is 28 mm Hg. • Principal etiology is hypoxia • Is it like that

17. High Altitude Illness • High Altitude Illness can take several forms that often overlap • Pathophysiology may be the same ! • Acute Mountain Sickness (AMS) • High Altitude Pulmonary Oedema(HAPO) • High Altitude Cerebral Edema (HACO)

18. Acute Mountain Sickness • Anyone can be affected • Exertion, • poor hydration, • young age may contribute. • Fitness or gender ?? No use

19. Acute Mountain Sickness • Symptoms: • Early symptoms (12-24 hours): • Headache - standard analgesics may be useless • nausea, anorexia,, sleep disturbances. • Can progress to shortness of breath, g, vomiting, hallucinations, and impaired cognitive function, • Can go upto frank cyanosis

20. Acute Mountain Sickness • Rest, hydration, analgesics, oxygen can help. • Acetazolamide 250 mg q 8-12 hours may improve symptoms and SaO2 (especially during sleep) • Definitive treatment is only descent. • Come down by 500 to 1000m - we are fine !

21. Acute Mountain Sickness • Can we prevent ! • Ascend slowly, but in army operations possible ! • Daily altitude gain of no more than 300m above 3000m. • Rest for two nights • Hydration and less exercise ! • Acetazolamide250mg 8 hourly prophylaxis and treatment !! .CA inhibitors – unknown benefits

22. High Altitude Pulmonary Oedema(HAPO) • A Life threatening form of AMS with similar early symptoms. • May occur in any healthy individual after rapid ascent above 2500 m (8200 ft) • Dyspnea, chest pain,crepitations , tachycardia, dry cough, pink frothy sputum • Respiratory failure and death can ensue. • Protein rich exudates in hyaline membranes • Form of ARDS !

23. High Altitude Pulmonary Oedema(HAPO) • CXR - patchy infiltrates, • Bases may not be affected ! • Elevated pulmonary artery pressure secondary to hypoxia. • ECG shows right heart strain • But with normal LV function

24. High Altitude Pulmonary Oedema(HAPO) • Treatment

25. High Altitude Cerebral Oedema(HACO) • One more danger ! • Increased BBB permeability and increased cerebral vascular blood flow ! • Hypoxia is the cause !

26. Early symptoms Headache Anorexia Nausea, Emesis Photophobia Fatigue Irritability Late symptoms Ataxia Hallucinations Visual disturbances ( retinal dots can also be there ! ) Focal neurological deficits Abnormal reflexes High Altitude Cerebral Oedema(HACO) Cerebral edema in CT

27. HACO and HAPO may co exist ! Dexa and oxygen may help but diuretics may worsen dehydration !

28. The Gamow Bag

29. The Gamow Bag • Portable, lightweight, • fabric hyperbaric chamber. • Can generate 103 mm Hg of pressure above ambient pressure. • Artificial descent of 4000 to 9000 ft at moderate altitudes.

30. ANAESTHESIA AT HIGH ALTITUDE General Principles • Prone for perioperative hypoxemia • Non acclimatized person more important • Hb may not be high ! • Volume Resuscitation • Bleeding : high venous pressure, increased blood volume, venous dilatation increased capillary density

31. Infection • pollution • Fire • ? Kerosene lamp operations !

32. Vaporizer !! • VO= (CGxSVP) / (Pb-SVP) • Where VO=vapor output (ml), • CG= carrier gas flow(mL.min), • SVP=saturated vapor pressure (mm Hg) at room temp, and • Pb- barometric pressure

33. Vaporizer ! • At a higher altitude where the barometric pressure is ½ that at sea level, the amount of isoflurane vapor output increases due to the lower barometric pressure. • Therefore, the settings that delivered 2% isoflurane now deliver 4% isoflurane.

34. What we need is partial pressure !! • partial pressure of isoflurane delivered would be approximately the same at both altitudes since 2% isoflurane at 760mm Hg (15.2 mm Hg) is the same as 4% isoflurane at 380mm Hg (15.2 mm Hg).

35. Shafer says ! • our vaporizer, set for 1.1%, • We need 1.5 % • is actually producing 1.7%, • Some overcompensation

36. But !! • Desflurane vaporizer is electrically heated to 39 degrees centigrade, which creates a vapor pressure of 2 atmospheres inside the vaporizer, regardless of ambient pressure. • The number on the dial reflects the percentage that will be delivered. • So at any altitude, when you dial 5%, it will give us 5%

38. Flow meters • At a simulated altitude of 10,000 ft (3048 m), both nitrous oxide and O2 flow meters under-read the actual flow rate. • May be upto 20 % • O2 analyser !! Actual Reading

39. TIVA

40. Venturi-type gas-mixing devices tend to deliver higher concentrations of O2 at altitude than they do at sea level • at an altitude of 10,000 ft (3048 m), • mask designed to deliver 35% O2 at sea level actually delivered 41% O2 41 % May be with less total flow

41. GA - considerations • Titrated premedication • Good preoxygenation • Increased FiO2 • Sedatives and opioids – titrated • Nitrous may dilute oxygen – may be avoided • 70% may actually be 50% nitrous ! • agents same percentage • Muscle relaxation OK - ? Hypothermia ! • Postoperative oxygen

42. Miscellaneous • Wait till acclimatization • Temperature of OT and the patient • Postoperative oxygen for atleast one hour • Pain killers – less narcotics • Watch for respiratory depression in the post op

43. Nepal in 1940s

44. Regional OK • But spinal headache is more common • Bladder bowel distension is more ! • Local anesthetic duration may be shortened • Cause ?

45. Summary • Definition • Changes • AMS, HAPO , HACO • Anesthesia – RA • GA – narcotics • FiO2, agents , • Temperature , • TIVA Himalayan task

46. Thank you all