Final answer:
Before using a pressure injector, it is vital to ensure the solution is isotonic and that there are no air bubbles in the syringe to prevent harm to the patient.
Step-by-step explanation:
Before injecting a patient, a pressure injector should always be checked to ensure that the solution to be injected is isotonic and that there are no air bubbles in the syringe. Isotonic solutions, like saline, have the same solute concentration as the blood, preventing any adverse reactions like the destruction of red blood cells.
The presence of air bubbles can lead to air embolisms, which can be fatal. Therefore, it is crucial to check for these factors to ensure patient safety during an injection.