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Getting High

Getting High. John P. Hunt LSU New Orleans Department of Surgery. Which person could have this blood gas? 7.65/14/35/15/71%. Scuba diver on his third 100 ft dive of the day A marathon runner during a race A mountain climber at 22,000 ft A COPD patient in respiratory distress .

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Getting High

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  1. Getting High John P. Hunt LSU New Orleans Department of Surgery

  2. Which person could have this blood gas?7.65/14/35/15/71% • Scuba diver on his third 100 ft dive of the day • A marathon runner during a race • A mountain climber at 22,000 ft • A COPD patient in respiratory distress American Board of Surgery, written exam, 1995

  3. Oxygen Delivery –From Start to Finish: Changes at Altitude as a Model John P. Hunt LSU New Orleans Department of Surgery

  4. Objectives • Historical Perspectives • Environmental and physiological changes • Symptoms • Effects on DO2 • Prevention • Therapy

  5. Where it’s High

  6. Historical Perspectives • “Men’s bodies become feverish, they lose color and are attacked with headache and vomiting; the asses and cattle being in the same condition” Qian Han Shu, 30 BC

  7. Historical Perspectives • “I was quite out of breathe from the rarity of the air” DeSaussure 1787 • “I feel funny and I don’t know why, excuse me while I kiss the sky” Hendrix 1969

  8. Historical Perspectives • “After we huddle over our ice axes, mouths agape, struggling for sufficient breath… I feel I no longer belong to myself and my eyesight. I am nothing more then a single narrow gasping lung” Messner 1978

  9. Incidence • 67% of mountaineers ascending Mount Rainier (14,405 ft) • 53 % of trekkers in the Himalayas (13,900 ft) • 12% of Colorado skiers (8,000 ft)

  10. High Altitude Cerebral Edema (HACE) • Less than 1% of all Mountain sickness • Always above 12,000 Ft • Symptoms: Severe headache, Ataxia, Loss of co-ordination, Diplopia, Confusion, Hallucinations, Death

  11. Acute Mountain Sickness (AMS) • Usually above 10,000 Ft • Onset is 4-6 hours after exposure & Duration 3 Days • Symptoms: Headache, Insomnia, Irritability, Fatique, Nausea/vomiting

  12. High Altitude Pulmonary Edema (HAPE) • Rarely below 8,000 Ft • Onset is 1-3 days after exposure • Symptoms: Dyspnea at rest, Pink frothy sputum, Rales, Cyanosis, mild temperature

  13. Temperature at Altitude Temperature (F) Altitude (ft)

  14. Oxygen Availability at Altitude Partial Pressure of O2 (mm torr) Altitude (meters)

  15. Oxygen Delivery DO2= C.O. x 10 x [(Hgb x SaO2 x 1.34) + (PO2 x 0.0031)]

  16. Oxygen Delivery may be calculated as a function of? • C.O., O2 saturation, mvO2 saturation • C.O., mvO2 extraction, mvO2 saturation • C.O., mvO2 saturation, Hgb • C.O., Hgb, O2 saturation • Difference between mvO2 saturation O2 saturation and C.O.

  17. Acute Hypoxia Produces? • Increased pulmonary vascular resistance • Increased pulmonary blood flow • Increased total blood volume • Decreased epinephrine • Increased splanchnic perfusion

  18. Comparative Oxygen Tension Ventilation Sea Level Partial Pressure O2 Altitude Level

  19. How does Ventilation Improve Oxygenation? • Classic Ventilator Management dictates -M.V. – PCO2 -FiO2 – PO2

  20. Alveolar Gas Equation PAO2= (PB – PH2O)FIO2– PaCO2/RQ

  21. Comparative Oxygen Tension V/Q Mismatch Sea Level Partial Pressure O2 Altitude Level

  22. V/Q Mismatch • Dead space • Shunt • Diffusion

  23. Calculation of Shunt QS/QT= (CC02 – Ca02)/(CC02 – Cv02) • Understand the concept

  24. Lung Volumes • Pursed-lips technique

  25. V/Q Mismatch and Diffusion Diffusion % Total A-a P O2 V/Q Mismatch Altitude (M) Wagner PD et al J Appl Physiol 1987;63:2348

  26. 3 days following operation for a perforated ulcer a 68 y.o man requires intubation. Initial ABG on 100% shows 7.32/72/36. To improve oxygenation the ventilator should be adjusted to? • Increase minute ventilation • Decrease minute ventilation • Increase functional residual capacity • Increase compliance • Decrease the I:E ratio

  27. The primary mechanism by which PEEP improves oxygenation is? • Decreased air-flow resistance • Increased functional residual capacity • Increased forced vital capacity • Decreased interstitial lung water • Decreased ratio of dead space to total volume

  28. Comparative Oxygen Tension Circulation & Extraction Sea Level Partial Pressure O2 Altitude Level

  29. Hemoglobin • 33% Increase in Hgb • Secondary to significant increases in erythropoetin • Chronic exposure typically yields Hct in the 60 range

  30. Cardiac Output • Preload • Contractility • Afterload

  31. Cardiac Output • Increase in SV • No changes in afterload • Preload sensitive DO2

  32. Starling Mechanism • Dehydration and subsequent decrease in preload is the mountaineers worst enemy • 80% of carried fuel is used to make water Cardiac Output EDV

  33. Starlings Law states that cardiac contractility increases when? • SVR Increases • SV Increases • LVSW Decreases • EDV Increases • SV Increases and SVR Increases

  34. Hemoglobin-Oxygen Dissociation • Shifting the curve to the right decreases the affinity of hemoglobin for oxygen inducing off-loading -Increased temp -Decreased pH -Increased CO2 -Increased 2-3 DPG O2 Sat PaO2

  35. A Shift in the Oxygen-Hemoglobin-Dissociation curve to the right is characteristic of? • Hyperventilation • Increased carboxy-hemoglobin • Decreased affinity of hemoglobin for oxygen • Decreased A-V O2 difference • May be caused by hypothermia

  36. Extraction Ratio • VO2/DO2 • VO2 = Q x (Ca02 – Cv02) = Q x 1.34 x Hgb (Sa02 – MV02) • Mountaineers have a maximized extraction ratio

  37. At rest MvO2 Saturation? • Normally ranges between .48-.55 • Increases as O2 consumption increases • Increases as Hgb decreases • Increases as Cardiac Output increases • Decreases as Arterial oxygen saturation increases

  38. Therapy • Descend • Bedrest • Supplemental oxygen • Gamow Bag

  39. Prevention • Slow ascent • Climb high, sleep low • Acetazolamide • Nifedipine

  40. Nifedipine For HAPE • 21 volunteers with previous history of HAPE • Ascended to 4559 M • Nifedipine vs Placebo • Pulmonary edema in 1 in 10 of treated group vs 7 of 11 in control group • Reproduced by Oelz O. et al Bartsch P. et al NEJM 1996;325:1284

  41. Acetazolamide For AMS • 64 healthy volunteers ascending Mount Rainier • 93.6% of treatment group and 75.8% of controls reached the summit • 66.7% of controls and 17.2% of the treatment group developed AMS • Reproduced by Grissom et al on Denali Larson EB. et al JAMA 1982;248:329

  42. Summary • Mountain Climbers optimize O2 delivery by -A four-fold increase in ventilation -Optimizing V/Q matching -Increasing Hgb via erythropoesis -Optimizing the O2 Extraction Ratio

  43. Summary • HACE, HAPE, AMS are different forms of Altitude sickness • Judicious climbing practices and medical prophylaxis are warranted • Descent is the best therapy for altitude sickness

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