Blood Gases

BLOOD GASES Normal Values

Arterial (Sea Level) pH 7.35-7.45 PaO2* 80-100 mm Hg PaCO2 32-48 mm Hg HCO3 22-26 mEq/

L O2 saturation > 95%

*In a patient > 60 years old, PaO2 is equal to 80 mm Hg minus 1 mm Hg for every year over 60.

Expected PaO2 = FIO2 × 5.

Interpreting Arterial Blood Gases (ABGs)

1 Check pH ↑ = Alkalosis; ↓ = acidosis

2 Check PaCO2 ↑ = CO2 retention (hypoventilation); respiratory acidosis or compensating for metabolic

alkalosis ↓ = CO2 blown off (hyperventilation); respiratory alkalosis or compensating for metabolic

acidosis

3 Check HCO3 ↑ = Nonvolatile acid is lost; HCO3 gained (metabolic alkalosis or compensating for

respiratory acidosis) ↓ = Nonvolatile acid is added; HCO3 is lost (metabolic acidosis or compensating for

respiratory alkalosis)

4 Determine imbalances

Definition and Sources of Variation in ECG Waveforms and Intervals* Description Normal Duration

(sec) Source of Possible Variation

Definition and Sources of Variation in ECG Waveforms and Intervals* Description Normal Duration (sec)

Source of Possible Variation

P wave Represents time for the passage of the electrical impulse through the atrium causing atrial

depolarization (contraction); should be upright 0.06-0.12 Disturbance in conduction within atria

PR interval Measured from beginning of P wave to beginning of QRS complex; represents time taken for

impulse to spread through the atria, AV node and bundle of His, the bundle branches, and Purkinje

fibers, to a point immediately preceding ventricular contraction 0.12-0.20 Disturbance in conduction

usually in AV node, bundle of His, or bundle branches but can be in atria as well

QRS interval Measured from beginning to end of QRS complex; represents time taken for depolarization

(contraction) of both ventricles (systole) < 0.12 Disturbance in conduction in bundle branches or in

ventricles

ST segment Measured from the S wave of the QRS complex to the beginning of the T wave; represents

the time between ventricular depolarization and repolarization (diastole); should be isoelectric (flat)

0.12 Disturbances usually caused by ischemia or infarction

T wave Represents time for ventricular repolarization; should be upright 0.16 Disturbances usually

caused by electrolyte imbalances, ischemia, or infarction

QT interval Measured from beginning of QRS complex to end of T wave; represents time taken for entire

electrical depolarization and repolarization of the ventricles 0.34-0.43 Disturbances usually affecting

repolarization more than depolarization and caused by drugs, electrolyte imbalances, and changes in

heart rate