Arterial blood gas analysis
- Measurement of acidity or alkalinity of solution . The normal range is 7.35 to 7.45
- pH > 7.45 = alkalosis
- pH< 7.35 = acidosis
- The partial pressure of oxygen that is dissolved in the arterial serum that is not carried by hemoglobin. The normal range is 80 to 100 mm Hg.
- Used to assess alveolar-arterial (A-a) gradient, or [[PaO2/FiO2 ratio]].
- The arterial oxygen saturation
- The normal range is 95% to 100%.
- The amount of carbon dioxide dissolved in arterial blood
- The normal range is 35 to 45 mm Hg.
- pCO2 >45 = primary respiratory acidosis
- pCO2 <35 = primary respiratory alkalosis
- The calculated value of the amount of bicarbonate in the bloodstream
- The normal range is 22 to 26 mEq/liter
- HCO3 > 26 = alkalosis
- HCO3 < 22 = acidosis
- The base excess indicates the amount of excess or insufficient level of bicarbonate in the system.
- The normal range is -2 to +2 mEq/liter.
- A negative base excess indicates a base deficit in the blood.
ABG in Hypothermia
- Blood gas analyzers typically warm blood to 37°C before making calculations however physicians should simply interpret the values as given by the lab
- At any temperature, a pH of 7.4 and a PCO2 of 40 mm Hg represent normal acid-base balance
The best (simplest) approach is to use uncorrected ABG values compared with the normal values at 37°C
TEMPERATURE CORRECTION OF PO2 and PCO2
Oxygen and carbon dioxide increase in solubility as water temperature lowers, so warmed ABGs from hypothermic patients with show a higher PaO2, higher PaCO2 and a lower pH than what is actually present in the patient’s blood although the clinical implications of this change is not significant.
- PO2 is 5 mmHg lower for each degree below 37C°
- PCO2 is 2mmHg lower for each degree below 37C°
ABG after Cardiac Arrest
pH of blood dependent on:
- cause of arrest
- duration of arrest when ABG is taken
- the quality of the CPR and ventilation the patient is receiving
- temperature of the patient when ABG taken
- drugs administered during arrest (ie. Adrenaline and NaHCO3)
- often due to inadequate ventilation during resuscitation
- insufficient oxygenation during resuscitation
- pulmonary edema
- primary respiratory pathology
- cell death
- loss of cell membrane integrity and acidosis
- other sources such as missed dialysis
- Burnett RW, Noonan DC. Calculations and correction factors used in determination of blood pH and blood gases. Clin Chem. 1974 Dec;20(12):1499-506. Review.
- Ashwood ER, Kost G, Kenny M. Temperature correction of blood-gas and pH measurements. Clin Chem. 1983 Nov;29(11):1877-85. Review. PubMed PMID: 6354511.