What should the respiratory therapist suspect if a helicopter patient's ventilator frequency and delivered tidal volume are gradually decreasing?

When a respiratory therapist observes that the ventilator frequency and delivered tidal volume are gradually decreasing in a helicopter patient, it is important to consider the performance of the ventilator system. A depleted compressed gas source is the most likely cause of these observed changes.

In mechanical ventilation, gas is required to deliver breaths to the patient. If the compressed gas source, such as an oxygen or air tank, is running low or empty, the ventilator will not be able to achieve the necessary pressures to deliver the prescribed tidal volume effectively. This would result in a drop in the delivered tidal volume and may also affect the ventilatory frequency, as the system struggles to maintain normal function due to insufficient gas supply.

The other factors, such as changes in barometric pressure and altitude, could influence respiratory parameters, but they are less directly linked to an immediate operational issue with the ventilator itself regarding gas delivery. Depleted batteries could potentially impact the functionality of electronic ventilators but are less likely than a lack of compressed gas to cause a consistent drop in ventilatory parameters. Thus, the depletion of the compressed gas source is the most direct and significant reason for the changes observed in the ventilator’s output under these circumstances.