CPFT common mistakes
CPFT · Understand the traps and how to avoid them.
Asks the patient 'are you on any inhalers?' and writes only yes/no, then begins testing immediately.
Candidates treat medication review as a demographic formality because most practice patients are stable; the timing windows for short- versus long-acting bronchodilators are memorized as facts but never applied at the point of testing, so the resulting spirometry is filed without knowing whether it is pre- or post-bronchodilator.
What to do instead
Use a scripted medication script: drug name, dose, route, and clock time of last use for SABA/SAMA (hold ~4-6 h), LABA/LAMA (hold ~12 h or per protocol), and oral/theophylline agents if bronchodilator response is being measured. Write 'pre-bronchodilator' or 'post-bronchodilator' plus the interval on the report before leaving the room.
Accepts the patient's 'no, I'm fine' as clearance instead of running a structured contraindication screen before an forced expiratory maneuver.
Candidates are focused on obtaining a good curve and fear that screening will cost time or embarrass the patient; they also recall contraindications as a list for a written question rather than as a bedside gate.
What to do instead
Read a fixed checklist aloud to every patient: recent myocardial infarction, unstable angina, recent pneumothorax, recent thoracic or abdominal surgery, recent hemoptysis of unknown origin, thoracic or abdominal aneurysm, retinal detachment, and acute illness such as vomiting. Document each item as asked and answered, and record the supervising clinician's decision if a relative contraindication is present.
Performs a daily syringe check, sees that the values 'look close,' and initials the log without calculating whether the result is inside the tolerance band.
The 3-L calibration syringe delivers 3.000 L, and a reading of 2.93 L looks visually acceptable, so the candidate never converts the acceptance criterion into an actual number; the ±3.5% rule is recalled as a phrase, not an arithmetic step.
What to do instead
Compute the window before testing: 3.000 L ± 3.5% equals 2.895-3.105 L. Push the syringe at low, medium, and high flows (roughly 0.5, 3, and 8 L/s), confirm the volume is within the window and flows are linear, and record the actual measured values, not just a checkmark. Out-of-window results trigger correction or service, not a retry until the number looks better.
Skips the leak test, ambient-condition entry, or BTPS/sample-line checks because 'the machine auto-corrects,' and does not record temperature, barometric pressure, or humidity anywhere.
Modern spirometers hide the corrections, so candidates assume the device has eliminated the variables; they also do not connect an uncorrected or leaky system to a shift in FEV1 or to an unstable DLCO bag volume.
What to do instead
Treat the pre-test block as a fixed sequence every day: leak/occlusion test per manufacturer, zero the analyzers, verify the syringe calibration, and enter measured ambient temperature, barometric pressure, and humidity so BTPS correction is traceable. Document each step with the operator, time, and result; if the device applies automatic correction, state that on the QC log rather than leaving the fields blank.
Ends the forced expiratory effort at a fixed 6 seconds on every patient, and accepts a curve that stopped because the patient ran out of air rather than because flow plateaued.
Candidates memorize 'at least 6 seconds' and treat it as the stop rule; the second half of the rule, that an obstructed patient may need up to 15 seconds and that a plateau in the volume-time curve must exist, is remembered as text but not watched in real time.
What to do instead
Coach continuously and watch the volume-time trace: keep the patient going while flow is still visibly declining, up to 15 seconds, and stop only when the change in volume is 25 mL or less over 1 second. Confirm the end-of-test criteria on the screen before accepting the trial, and label trials that ended early rather than silently including them.
Selects the 'best-looking' curve and reports FEV1 and FVC from it, ignoring back-extrapolation volume and repeatability between the best two acceptable trials.
Candidates judge curves by smoothness and peak height, which are cosmetic; a sharp PEF can coexist with a poor or hesitating start, and a single impressive FEV1 makes the repeatability check feel unnecessary.
What to do instead
Apply the acceptance rules numerically: back-extrapolated volume no greater than 0.15 L or 5% of FVC (whichever is larger), no cough in the first second, no glottic closure or variable effort, and a satisfying end-of-test. Then verify that the largest FEV1 and second-largest FVC agree within 150 mL. Report the largest FVC and largest FEV1 across all acceptable trials, even when they come from different curves, and grade the session quality on the report.
Uses the same correction factor for every measurement, reporting plethysmographic thoracic gas volume and single-breath DLCO volumes under identical BTPS assumptions.
Candidates learn 'BTPS' and 'STPD' as vocabulary pairs without linking each to its compartment: lung volumes are gas at body conditions, while diffusing capacity relies on dry gas at standard conditions for the tracer concentrations. Applying one label everywhere produces plausible-looking but systematically shifted results.
What to do instead
State the convention aloud at each step: plethysmographic TLC, FRC, RV, and the alveolar volume used clinically are reported BTPS; DLCO and its component gas concentrations are handled STPD, and the VA inserted into the DLCO equation must match the convention the system expects. Check that the reported TLC from plethysmography and the VA from the single-breath maneuver are not identical by accident.
Performs a single-breath DLCO with a breath-hold that varies between patients, or accepts a maneuver in which the patient exhaled to RV slowly and then inhaled with a pause or Valsalva.
Candidates focus on getting the gas mixture inhaled and the breath held 'about ten seconds' and do not see that breath-hold time, inspired volume, and expiratory effort each change the calculated VA and the DLCO itself.
What to do instead
Standardize the maneuver: exhale to RV, inhale rapidly to near TLC, and hold for 10 seconds (±2 seconds), keeping the mouthpiece pressure near atmospheric and avoiding Valsalva or Müller maneuvers. Discard the dead-space washout volume (approximately 0.75-1.0 L, or the volume the system specifies) and collect the alveolar sample after it. Report the inspired volume and breath-hold time with the result so an outlier can be recognized.
Accepts a self-drawn arterial sample, lets air bubbles sit in the syringe, and delivers it to the analyzer when convenient, then reports the PaO2 without recording the FiO2 or the patient's temperature.
The analysis step feels like the technical work, so pre-analytic handling feels like someone else's job; bubbles and delay produce changes that look like real physiologic shifts, and without FiO2 or temperature on the requisition the result cannot be interpreted or corrected.
What to do instead
Run a pre-analytic checklist at the bedside: expel all air bubbles immediately, cap and mix by inversion, label with the draw time, FiO2 or supplemental flow device, mode of breathing, and patient temperature, then analyze within the protocol window (commonly about 15 minutes at room temperature, longer only if iced per policy). If temperature is not 37 °C, correct pH and PaCO2 before interpreting, and note the correction on the report.
Reads a pulse oximeter value as the saturation, accepting the first number displayed on a cool or poorly perfused finger, and uses it to judge oxygenation in a patient who may have carbon monoxide exposure or abnormal hemoglobin.
The SpO2 number is the most familiar value on the monitor and appears definitive; the candidate does not link poor signal quality, dyshemoglobins, or the shape of the oxyhemoglobin dissociation curve to the difference between SpO2 and a co-oximetry-measured SaO2.
What to do instead
Confirm a stable waveform and a rate that matches the ECG or counted pulse, warm and reposition a cool or poorly perfused digit, and remove nail polish or switch to an alternate site if the signal is poor. Document the probe site and signal quality. When carboxyhemoglobin, methemoglobin, or a discrepancy with the clinical picture is possible, obtain a co-oximetry SaO2 and report SpO2 and SaO2 separately.