Getting High

John P. Hunt

LSU New Orleans

Department of Surgery

Which person could have this blood gas?

7.65/14/35/15/71%1) Scuba diver on his third 100 ft dive of the

day

2) A marathon runner during a race

3) A mountain climber at 22,000 ft

4) A COPD patient in respiratory distress

American Board of Surgery, written exam, 1995

Oxygen Delivery –From Start to Finish: Changes at Altitude

as a Model

John P. Hunt

LSU New Orleans

Department of Surgery

Objectives• Historical Perspectives

• Environmental and physiological changes

• Symptoms

• Effects on DO2

• Prevention

• Therapy

Where it’s High

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

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

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

Incidence

• 67% of mountaineers ascending Mount Rainier (14,405 ft)

• 53 % of trekkers in the Himalayas (13,900 ft)

• 12% of Coloradoskiers (8,000 ft)

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

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

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

Temperature at Altitude

-60

-40

-20

0

20

40

60

80

0 10,000 20,000 30,000

Altitude (ft)

Tem

per

atu

re (F

)

Oxygen Availability at Altitude

50

70

90

110

130

150

170

0 3,000 6,000Par

tial

Pre

ssu

re o

f O

2 (m

m t

orr)

Altitude (meters)

Oxygen Delivery

DO2 = C.O. x 10 x

[(Hgb x SaO2 x 1.34) + (PO2 x 0.0031)]

Oxygen Delivery may be calculated as a function of?

1) C.O., O2 saturation, mvO2 saturation

2) C.O., mvO2 extraction, mvO2 saturation

3) C.O., mvO2 saturation, Hgb

4) C.O., Hgb, O2 saturation

5) Difference between mvO2 saturation O2 saturation and C.O.

Acute Hypoxia Produces?

1) Increased pulmonary vascular resistance

2) Increased pulmonary blood flow

3) Increased total blood volume

4) Decreased epinephrine

5) Increased splanchnic perfusion

0

50

100

150

Inspired Alveolar Arterial Venous Tissue

Sea Level

Altitude

Level

Comparative Oxygen TensionP

arti

al P

ress

ure

O2

Ventilation

How does Ventilation Improve Oxygenation?

• Classic Ventilator Management dictates

-M.V. – PCO2

-FiO2 – PO2

Alveolar Gas Equation

PAO2 = (PB – PH2O)FIO2

– PaCO2/RQ

0

50

100

150

Inspired Alveolar Arterial Venous Tissue

Sea Level

Altitude

Level

Comparative Oxygen TensionP

arti

al P

ress

ure

O2

V/Q Mismatch

V/Q Mismatch

• Dead space

• Shunt

• Diffusion

Calculation of Shunt

QS/QT = (CC02 – Ca02)/(CC02 – Cv02)

• Understand the concept

Lung Volumes

RVFRC

ERV

TVIC

IRV

Without PEEP

RV

FRCERV

TVIC

IRV

With PEEP

•Pursed-lips technique

0

10

20

30

40

50

60

70

80

90

0 5,000 6,000 7,500 9,000

Diffusion

V/Q Mismatch

Altitude (M)

V/Q Mismatch and Diffusion%

Tot

al A

-a P

O2

Wagner PD et al J Appl Physiol 1987;63:2348

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?

1) Increase minute ventilation

2) Decrease minute ventilation

3) Increase functional residual capacity

4) Increase compliance

5) Decrease the I:E ratio

The primary mechanism by which PEEP improves oxygenation is?

1) Decreased air-flow resistance2) Increased functional residual capacity3) Increased forced vital capacity4) Decreased interstitial lung water5) Decreased ratio of dead space to total

volume

0

50

100

150

Inspired Alveolar Arterial Venous Tissue

Sea Level

Altitude

Level

Comparative Oxygen TensionP

arti

al P

ress

ure

O2

Circulation & Extraction

Hemoglobin

• 33% Increase in Hgb

• Secondary to significant increases in erythropoetin

• Chronic exposure typically yields Hct in the 60 range

Cardiac Output

• Preload

• Contractility

• Afterload

Cardiac Output

• Increase in SV

• No changes in afterload

• Preload sensitive DO2

Starling Mechanism• Dehydration and

subsequent decrease in preload is the mountaineers worst enemy

• 80% of carried fuel is used to make water

0

5

10

15

Car

dia

c O

utp

ut

EDV

Starlings Law states that cardiac contractility increases when?

1) SVR Increases

2) SV Increases

3) LVSW Decreases

4) EDV Increases

5) SV Increases and SVR Increases

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

01020304050

60708090

100

0 40 60 80 100

PaO2

O2

Sat

A Shift in the Oxygen-Hemoglobin-Dissociation curve to

the right is characteristic of?1) Hyperventilation2) Increased carboxy-hemoglobin3) Decreased affinity of hemoglobin for

oxygen

4) Decreased A-V O2 difference5) May be caused by hypothermia

Extraction Ratio

• VO2/DO2

• VO2 = Q x (Ca02 – Cv02)

= Q x 1.34 x Hgb (Sa02 – MV02)

• Mountaineers have a maximized extraction ratio

At rest MvO2 Saturation?

1) Normally ranges between .48-.55

2) Increases as O2 consumption increases3) Increases as Hgb decreases4) Increases as Cardiac Output increases5) Decreases as Arterial oxygen saturation

increases

Therapy

• Descend

• Bedrest

• Supplemental oxygen

• Gamow Bag

Prevention

• Slow ascent

• Climb high, sleep low

• Acetazolamide

• Nifedipine

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

0

10

20

30

40

50

60

PAPressure

A-agradient

PlaceoNifedipine

Bartsch P. et al NEJM 1996;325:1284

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

0

5

10

15

20

25

MinuteVolume

Vitalcapacity

Placeo

Acetazolamide

Larson EB. et al JAMA 1982;248:329

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

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