Arterial blood gas interpretation in four steps
Four stacked stations: an acid-to-alkaline axis with one marker, two paired-arrow diagrams showing opposed and aligned movement, and three small axis strips showing the marker returning toward center.
The four values
Potential of hydrogen 7.35 to 7.45. Carbon dioxide partial pressure 35 to 45 millimeters of mercury. Bicarbonate 22 to 26 milliequivalents per liter. Oxygen partial pressure 80 to 100 millimeters of mercury. Printed once, here, inside the method.
Step 1 · Which side
Read the potential of hydrogen by itself. Below range is acidosis. Above range is alkalosis. Inside range still has a side, and you will find it in step 4.
Step 2 · Is it the lungs
Read the carbon dioxide. If it moved opposite the potential of hydrogen, the disorder is respiratory.
Step 3 · Is it the kidneys
Read the bicarbonate. If it moved the same direction as the potential of hydrogen, the disorder is metabolic.
Step 4 · How far has compensation got
The other system has not moved at all: uncompensated. It has moved but the potential of hydrogen is still outside range: partially compensated. It has moved and the potential of hydrogen is back inside range: fully compensated. In full compensation, the side of 7.40 the value sits on tells you which disorder was primary.
Oxygenation is a separate question
Oxygen partial pressure and saturation are read after the acid-base classification is finished, never mixed into it. A gas can be perfectly classified and the patient still hypoxemic.
Memory hookROME — Respiratory Opposite, Metabolic Equal.
Margin notepH first, always. Then ask who moved.
Watch outa normal potential of hydrogen sitting between two abnormal values is full compensation, not a normal gas.
Takeawayfour values, four steps, same order every time.
Timed drill → BOOK 07 · P10.