Failed Daily Calibration Verification With a Cold Syringe
At 07:45, before the first patient, a certified spirometry technician performs the daily calibration verification on a flow-type spirometer using a 3-L calibration syringe. The syringe was stored overnight in a car and feels cool. Three injections at low, medium, and high flow give 2.86 L, 2.92 L, and 3.08 L. The spirometer's software displays 'calibration check failed' because the low-flow value is outside the acceptance limit, but the mean of the three values is 2.953 L. A colleague says the mean is within 3.5% so they can start testing; the clinic has 14 patients scheduled and one spirometer. The device passed a leak test. There is no spare flow sensor. The room temperature is 22°C. The manufacturer's manual says to use a 3-L syringe and to recalibrate if any injection is outside ±3.5%.
1. Is the calibration verification acceptable? Show the calculation and explain the decision.
Read the worked answer
Acceptable range is 3.00 L ± 3.5%, i.e., 2.895-3.105 L. The low-flow injection of 2.86 L is 0.14 L below 3.00 L, or -4.7%, so it fails. The medium (2.92 L, -2.7%) and high (3.08 L, +2.7%) injections pass, but a mean of 2.953 L does not make the low-flow failure acceptable; calibration verification is intended to detect flow-dependent error, and accepting a failing injection could hide a leak or sensor problem. The cool syringe may contribute because gas temperature affects volume, so let the syringe equilibrate to room temperature and repeat. The technician should not start patient testing on the basis of the mean or on the software's single 'failed' flag alone. The device remains out of service until all three flows pass after repeat verification or recalibration.
2. What steps should the technician take before testing the 14 scheduled patients?
Read the worked answer
First, allow the syringe to reach room temperature, check the syringe seal and spirometer connections, and repeat three injections at low, medium, and high flow. If any remains outside 2.895-3.105 L, perform the manufacturer's recalibration procedure, then repeat verification. If it still fails, remove the spirometer from service, label it, notify the supervisor, and arrange service or a loaner; do not test the 14 scheduled patients with a device that has failed verification. Contact patients to reschedule or redirect them to another validated device. Document the failed values, actions, and final status. A biological control or a different operator is not a substitute for calibration verification. The clinic should also review syringe storage and temperature control so this does not recur.