Dräger Evita: delivered tidal volume lower than set
What happened
As reported in the case: with a tidal volume set to 450 mL, the ventilator delivered only about 380 mL, confirmed by an external volumeter. The deviation was formally within the manufacturer's accuracy tolerance, but it was consistent and noticeable across settings.
What was checked
- Measure delivered volume with an independent calibrated volumeter instead of trusting the ventilator's own display.
- Repeat the measurement with BTPS and leak compensation switched off, to rule out compensation effects distorting the picture.
- Test at different tidal volumes and oxygen concentrations — an error that tracks oxygen concentration points to the oxygen-side flow sensor.
- During the calibration procedure from the manufacturer's service documentation (performed by authorised personnel), read the first calibration point: a value of roughly 11–13 L/min or higher, as cited in the case, is the engineers' practical sign of a worn sensor due for replacement.
Cause
Probable: worn input flow sensors, most likely on the oxygen side. The engineers judged this from the test pattern and from their own experience of similar symptoms on this model being resolved by flow sensor replacement — one case, not a rule.
The cause is probable and was not fully confirmed.
What was done
Replace the flow sensors and recalibrate the unit; the calibration is a procedure from the manufacturer's service documentation, done by authorised personnel. After replacement, re-verify set versus delivered volume with the external volumeter, and use the first calibration point as an early indicator of sensor wear.
Safety
Before returning the ventilator to clinical use, verify set versus delivered volume with an independent calibrated volumeter and complete the manufacturer's full verification and electrical safety testing; if the unit under-delivers, keep it out of service.
Lesson: A volume error that still sits inside tolerance can be the first sign of ageing flow sensors — cross-check with an external volumeter and assess the sensors early instead of waiting for a hard failure.
Covered in the course: Ventilator Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.