The effect of microwave heating on the acidity of 0.9% saline in 1 litre and 100 mL polyvinyl chloride packaging

Microwave warming of intravenous crystalloid solutions is an accepted practice in operating suites and emergency departments. These intravenous solutions are stored in polyvinyl chloride (PVC) and are known to be acidic. Some of this acidity may be from PVC packaging. We asked if microwave heating affected the acidity of 0.9% saline solution in 1 litre and 100 mL PVC bags.

Seven 1 litre bags were heated in an 800 Watt microwave for 2 minutes each and seven 100 mL bags were heated for 30 seconds each. After overnight cooling to room temperature, pH and temperature were measured and compared with two control groups of 7 unheated bags.

There was no significant difference between the pH of heated and unheated solutions of saline. The median pH of the 1 litre bags were 5.01 (control) and 5.02 (heated). The median pH of the 100 mL bags were 4.58 (control) and 4.59 (heated). Post hoc, we found the 100 mL bags were more acidic than the 1 litre bags by a median difference of 0.43 pH units (P = 0.002).

Microwave heating does not change the acidity of 0.9% saline in 1 litre or 100 mL PVC packaging.