Ventilator Self-Test Procedures

1. Importance of self-testing

Mechanical ventilators are among the most critical devices in acute clinical care and hold an important role in modern hospital equipment. Because ventilators are life-support devices with unique operational requirements, they are also prone to clinical issues and can be difficult to operate. Routine maintenance is therefore essential. When dedicated test equipment is not available, using the ventilator's built-in self-test functions helps determine whether the device is operating normally and enables early detection of faults to keep the ventilator at optimal performance.

2. Differences in self-test implementations

Common ventilator series in clinical use include Puritan-Bennett (PB), Newport, Siemens, and Drager. These models vary in their level of automation, configuration options, and allowable measurement tolerances, so their self-test behaviors differ. Some units perform very simple automatic checks where panel indicators light and the test completes without operator intervention after a few minutes (for example, Newport and Drager). Other models have more complex, time-consuming procedures that require a sequence of operator actions to complete (for example, PB and Siemens).

3. Self-test procedures

Self-test sequences vary by ventilator type and model. Some are straightforward, while others are comprehensive and take more time. The PB840 ventilator provides a representative example; its self-tests include POST (Power On Self Test), SST (Short Self Test), and EST (Extended Self Test).

3.1 POST (Power On Self Test)

POST checks the integrity of the ventilator's hardware and detects system faults not caused by operator actions. It runs automatically on power-up or restart. Under normal conditions, POST takes about 7.25 seconds.

3.2 SST (Short Self Test)

SST primarily checks patient circuit leak, calibrates the patient circuit, and measures resistance of the expiratory bacterial filter. SST should be executed before connecting the ventilator to a patient, after 15 days of use, whenever the patient circuit is changed, after maintenance, and when accessories that affect airway resistance or compliance (such as humidifiers or water traps) are replaced.

The SST procedure:

1. Connect mains power, gas sources, and the patient circuit. Power on the ventilator. When the selection menu appears on the screen, touch SST to choose the short self test. Within 5 seconds press the TEST key on the left side of the ventilator to enter SST mode.
2. After entering SST mode, a setup menu appears. Select the patient circuit and humidifier type.
3. After selecting circuit and humidifier type, press Accept to confirm. The ventilator begins the automated SST sequence:

Sequence of SST checks:

1. Flow Sensor Test: The screen prompts to connect the circuit without the humidifier and with the inspiratory filter in place. Confirm to proceed, then the screen prompts to block the Y-piece. After confirmation the ventilator performs the flow sensor check. When complete, if a humidifier is used the screen prompts to connect it; confirm to continue.
2. Circuit Pressure Test.
3. Circuit Leak Test.
4. Expiratory Filter Test: The screen prompts to disconnect at the FROM PATIENT port. Confirm to run the test; if it passes the system proceeds automatically.
5. Circuit Resistance Test: The screen prompts to unblock the Y-piece. Confirm to continue.
6. Compliance Calibration: The screen prompts to unblock the Y-piece, run the test, then prompts to block the Y-piece and run the test again. When complete, all SST items are finished. Finally choose EXIT SST to leave the short self test.

3.3 EST (Extended Self Test)

EST checks the full pneumatic pathway and many electrical subsystems (including pneumatics, compressor, sensors, and power). EST includes elements of POST and SST. Run EST after six months of operation, after maintenance, or after part replacement. EST helps identify faulty components that require repair.

EST procedure summary:

1. Allow the ventilator to warm up for at least 10 minutes.
2. Connect mains power and both air and oxygen supplies (an air compressor may serve as the air source). Remove the inspiratory filter and connect a gold-standard test circuit directly between the inspiratory and expiratory ports.
3. Power on the ventilator. When the gas delivery unit indicator lights, press the Test key on the left side within 1 second to enter service mode.
4. In service mode, touch EST and press Accept to start the EST sequence. The ventilator will step through the following automated tests:

EST test items:

1. Circuit Pressure Test: Prompts to connect air and oxygen, remove the inspiratory filter, and install the test circuit. Press Accept to run the automatic test; if PASSED, it proceeds.
2. Flow Sensors Cross-Check Test: Automatic; proceeds if PASSED.
3. Gas Supply / Safety Valve Test: Checks for wall air connection. If wall air is present, connect it and press Accept; if not present, press Clear and follow prompts to block the patient port and disconnect oxygen and air as instructed, then reconnect oxygen and wall air and the test circuit, pressing Accept at each prompt. If PASSED, it proceeds.
4. Leak Test: Automatic; proceeds if PASSED.
5. GUI Keyboard Test: Prompts to press the "*" key. Proceed if PASSED.
6. GUI Knob Test: Prompts to turn knobs counterclockwise and clockwise. Proceed if PASSED.
7. GUI Lamp Test: Prompts to acknowledge LED indicators; press Accept as prompted (11 Accept presses total). Proceed if PASSED.
8. BDU Lamp Test: Acknowledge LEDs are on; press Accept as prompted (3 Accept presses total). Proceed if PASSED.
9. GUI Audio Test: Prompts the user to verify audible GUI alarms; acknowledge when the alarm sounds (3 Accept presses total). Proceed if PASSED.
10. GUI Nurse Call Test: Prompts to acknowledge whether the nurse call system is installed. If installed press Accept; if not installed press Clear. Proceed if PASSED.
11. BDU Audio Test: Verify audible BDU alarm; press Accept if heard, Clear if not. Proceed if PASSED.
12. PSOL Loopback Test: Automatic; proceed if PASSED.
13. Safety System Test: Automatic; proceed if PASSED.
14. Expiratory Valve Loopback Test: Automatic; proceed if PASSED.
15. Expiratory Valve Seal Test: Automatic; proceed if PASSED.
16. Expiratory Valve Test: Automatic; proceed if PASSED.
17. Expiratory Valve Velocity Transducer Test: Automatic; proceed if PASSED.
18. Expiratory Heater Test: Automatic; proceed if PASSED.
19. Compressor Test: If an air compressor is installed, the ventilator runs this test and may prompt to disconnect or reconnect wall air as required. If no compressor is installed, this step is skipped. Proceed if PASSED.
20. Analog Data Display: Verifies analog outputs. Proceed if PASSED.
21. GUI Touch Test: Verifies touch screen functionality. Proceed if PASSED.
22. GUI Serial Port Test: Verifies serial communications. Proceed if PASSED.
23. Battery Test: The ventilator checks whether a backup battery is installed. If no battery is present, the EST completes. If a battery is installed, the test prompts to disconnect AC power, then runs the battery test. If PASSED, EST completes successfully.

Each self-test item can yield three possible results:

• PASSED: No action required.
• ALERT: An alarm condition. Check the ventilator peripheral tubing for leaks and other issues that might affect clinical use. If no significant problem is found, the test may be overridden by selecting OVERRIDDEN in the final menu. The ventilator can then be returned to normal operation.
• FAILURE: The ventilator cannot be used. If a FAILURE occurs, run SST from start to finish until all items return PASSED before placing the ventilator back into clinical service. If failures persist, notify a qualified engineer for repair.

The above summarizes the PB840 self-test sequence and key considerations. Different ventilator models and classes will have different self-test procedures and precautions. Biomedical engineering staff should be familiar with the self-test steps for each ventilator model in their facility.

4. Summary

Regular use of a ventilator's built-in self-test routines allows efficient, accurate identification of device faults and can save valuable time when treating critically ill patients. As self-test procedures in modern ventilators become more comprehensive, routinely performing these maintenance checks helps detect and mitigate potential faults before they affect clinical care.