ABG interpretation
Contents
Basics
pH
- Measurement of acidity or alkalinity of solution . The normal range is 7.35 to 7.45
- pH > 7.45 = alkalosis
- pH< 7.35 = acidosis
PaO2
The partial pressure of oxygen that is dissolved in arterial blood. The normal range is 80 to 100 mm Hg. SaO2 The arterial oxygen saturation. The normal range is 95% to 100%.
pCO2
- The amount of carbon dioxide dissolved in arterial blood. The normal range is 35 to 45 mm Hg.
- pCO2 >45 = acidosis
- pCO2 <35 = alkalosis
HCO3
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
B.E.
- 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[1]
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.[2]
- 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)
Elevated pCO2
- often due to inadequate ventilation during resuscitation
Low PaO2
- insufficient oxygenation during resuscitation
- aspiration
- pulmonary edema
- PE
- primary respiratory pathology
Hyperkalemia Causes
- cell death
- loss of cell membrane integrity and acidosis
- other sources such as missed dialysis
References
- ↑ 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.
