Pulmonary gas pressures

Pathophysiology sample values
BMP/ELECTROLYTES:
Na+ = 140 Cl = 100 BUN = 20 /
Glu = 150
K+ = 4 CO2 = 22 PCr = 1.0 \
ARTERIAL BLOOD GAS:
HCO3 = 24 paCO2 = 40 paO2 = 95 pH = 7.40
ALVEOLAR GAS:
pACO2 = 36 pAO2 = 105 A-a g = 10
OTHER:
Ca = 9.5 Mg2+ = 2.0 PO4 = 1
CK = 55 BE = −0.36 AG = 16
SERUM OSMOLARITY/RENAL:
PMO = 300 PCO = 295 POG = 5 BUN:Cr = 20
URINALYSIS:
UNa+ = 80 UCl = 100 UAG = 5 FENa = 0.95
UK+ = 25 USG = 1.01 UCr = 60 UO = 800
PROTEIN/GI/LIVER FUNCTION TESTS:
LDH = 100 TP = 7.6 AST = 25 TBIL = 0.7
ALP = 71 Alb = 4.0 ALT = 40 BC = 0.5
AST/ALT = 0.6 BU = 0.2
AF alb = 3.0 SAAG = 1.0 SOG = 60
CSF:
CSF alb = 30 CSF glu = 60 CSF/S alb = 7.5 CSF/S glu = 0.4

The factors that determine the values for alveolar pO2 and pCO2 are:

Following is a list of average partial pressures (in torr) for a human at rest:

Partial pressure of oxygen (at sea level)

Location pO2
(mmHg)
Ambient air 160
Alveoli 100 (PAO2)
Arterial blood 80-100 (PaO2)
Venous blood 40-50
Lung Capillaries 20-40

The alveolar oxygen partial pressure is lower than the atmospheric O2 partial pressure for two reasons.

The alveolar pO2 is not routinely measured but is calculated from blood gas measurements by the Alveolar gas equation.

Partial pressure of carbon dioxide

Location pCO2
(Torr)
Outside air - dry air at sea level 0.3
Alveolar air 35
Arteriole blood 40
Venous blood 50
Cells 50

The pCO2, along with the pH, can be used to distinguish among metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis.

Pathology

Hypoventilation exists when the ratio of carbon dioxide production to alveolar ventilation increases above normal values.

Hyperventilation exists when the same ratio decreases.

See also


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