Hyperoxyc test in man

MUDr. Dobroslav Hájek, CSc.

MUDr. Michal Jurajda

The atmosphere

• N2 78,1%

• OO2 2 20,9%20,9%

• CO2 0,03%

• noble gases 1%

Concentration of gases

• Partial pressure- pressure of the given gas in the mixuture of gases.

ipP

• atmospheric pressure ????

Ventilation under extrem pressure conditions

• High altitudes – low pressure

• Diving – high pressure

• Remember: optimal pO2 cca 21 kPa

Hyperbaric oxygenation

• - increases physically dissolved oxygen in blood and tissues

Hyperbaric therapy is used in:

• CO intoxication.

• Air embolism.

• Decompression.

• Anaerobic infections.

• Non healing wounds

Hemoglobinu saturation

Oxygen measurements

• saturometer – saturation of Hb (%)• oxymeter - paO2 (Pa)

lung function Fi O2

paO2

Right to left shunt

• Hypothetical fraction of blood flow (right ventricle output) passing the lungs without beeing oxygenated.

Right to left shunt

• Anatomical

• Functional

Functional

Dead space

The dead space (alveoli with low ventilation/perfusion ratio) incrase the right-to left shunt.

• paO2 = S.pvO2+(1-S).piO2

• paO2 = S.pvO2-S.piO2+ piO2

• S.pvO2-S.piO2 = paO2-piO2

• S.(pvO2-piO2) = paO2-piO2

• S = (paO2-piO2)/(pvO2-piO2)

• S = (piO2-paO2)/(piO2-pvO2)

Remember

• When the increased right-to left shunt is caused by vascular bed involvement (typically: lung embolism) the response of partial oxygen pressure in arterial blood (paO2) to oxygen administration is very poor. (The paO2 increase is very low when oxygen is administered)

Clinical cases

• Poisoning by hyptotic or sedative drugs (e.g. barbiturates, benzodiazepins, morphin)

• Foreign body (corpus alienum) in bronchus with its obstruction

• Ventilation/perfusion unbalance.

The objective

• Estimate rght to left shunt

Material

• Transcutaneous oxymetr

• Medicinal oxygen in gas bottle with pressure reduction valve and flow regulation valve.

• Mask with gas blender and delivery hose

Leland C. Clark

The method

• Increasing FiO2 increases paO2

• paO2 can be measured in arterial blood or in arterialised capillary blood by transcutaneous oxymeter (heated electrode).

• The incerease of paO2 is dependent on FiO2

and right to left shunt.