ICU: Cause of abnormal oxygen saturations from cardiac lines

Gen. rule: Check catheter tip position before interpreting the value! (Always know where the tip of each catheter is!)

Elevated RA saturation:

1) Catheter tip at renal vein

2) L→R shunt (ASD, Anomalous PV return, LV-RA shunt)

3) Decreased oxygen extraction (sepsis, CO poisoning)

4) High FiO2 (Increased dissolved oxygen)

Decreased RA saturation:

1) Catheter tip in Coronary sinus

2) Low cardiac output

3) Fever

4) Anemia

Elevated PA saturation:

1) Catheter tip is wedged

2) Left to right shunting (VSD, PDA, Other shunts: A-P collaterals, AP window)

Decreased PA saturation: (Same causes as in “Decreased RA saturation”)

Decrased LA saturation:

1) R→L shunt (ASD/PFO)

2) Systemic vein – PV or LA shunt (Veno-venous collaterals)

3) Pulmonary vein desaturation (Lung disease, V-Q mismatch, Pulmonary AVM)