CPFT cheat sheet

Absolute contraindications to spirometry include pneumothorax, active hemoptysis, unstable cardiovascular status, recent myocardial infarction (within 1 month), recent chest or abdominal surgery, and thoracic or abdominal aneurysm.

Bronchodilator withholding before testing: short-acting beta-2 agonist 4-6 hours, ipratropium 6-8 hours, long-acting beta-2 agonist 12-24 hours, long-acting antimuscarinic 24 hours or longer per laboratory protocol.

Pre-test behavioral restrictions: no smoking for at least 1 hour, no alcohol for 4 hours, no vigorous exercise for 30 minutes, and no heavy meal for 2 hours before testing.

Height is measured standing without shoes, heels together, head in the Frankfort plane, recorded in centimeters; age, sex, height, and ethnicity are required to generate predicted values.

Pack-years are calculated as packs smoked per day multiplied by years smoked; a pack is 20 cigarettes.

Document medications, recent respiratory infection, baseline oxygen saturation or oxygen flow, smoking status, and the indication for testing before the first maneuver.

Standard precautions require a new mouthpiece or in-line bacterial filter for each patient, hand hygiene, gloves when handling secretions, and disinfection of reusable surfaces between patients.

Post-bronchodilator testing is performed 10-15 minutes after 400 mcg of albuterol (or 2.5 mg nebulized), with the same technique and effort as the baseline maneuvers.

A leak test is performed daily before volume calibration by occluding the spirometer and applying slight positive pressure; a declining volume signal indicates a leak that must be corrected.

Daily volume calibration uses a calibrated 3-L syringe discharged at low, medium, and high flows; the spirometer must read within ±3% (2.91-3.09 L for a 3.00-L injection).

Spirometer performance standards: volume accuracy ±3% or ±0.05 L, whichever is greater, and flow accuracy ±5% over the measured range.

ATPS to BTPS conversion: V(BTPS) = V(ATPS) x [310/(273 + T)] x [(PB - 47)/(PB - ambient water vapor pressure)].

Biological control testing uses a healthy, asymptomatic, nonsmoking reference subject tested regularly on each device; values are plotted on a control chart and trends or points outside laboratory limits trigger investigation.

DLCO test gas typically contains 0.3% CO, 0.3% helium or methane as the tracer, 21% oxygen, and balance nitrogen; analyzers are zeroed and spanned with a reference gas before each test day.

Blood gas analyzers undergo two-point calibration and analysis of low, normal, and high control materials at least every 8 hours and after maintenance, with results charted on Levey-Jennings plots.

Calibration records must document date, time, equipment identifier, ambient temperature, barometric pressure, operator, and the results of leak, volume, and gas checks.

Airflow obstruction is defined by an FEV1/FVC ratio below the lower limit of normal (5th percentile) or, per GOLD, below 0.70.

Acceptability requires a rapid start with back-extrapolated volume no greater than 5% of FVC or 0.150 L (whichever is greater), no cough in the first second, no glottic closure, no leak, and no extra breaths.

Reproducibility requires the two largest acceptable FVC and the two largest acceptable FEV1 values to agree within 0.150 L; at least three acceptable maneuvers are performed and testing stops at eight.

End of forced expiration is declared when the volume change is less than 0.025 L over 1 second, or at 15 seconds of exhalation; a minimum of 6 seconds of effort is required.

Obstruction severity by FEV1 percent predicted: mild 70% or greater, moderate 60-69%, moderately severe 50-59%, severe 35-49%, very severe less than 35%.

A significant bronchodilator response is an increase in FEV1 or FVC of at least 12% and at least 200 mL above baseline.

Flattening of the inspiratory limb with a normal expiratory limb indicates variable extrathoracic obstruction; flattening of both limbs indicates fixed obstruction.

A concave or scooped expiratory limb with reduced flows at low lung volumes is characteristic of intrathoracic airflow obstruction, while a box-shaped or truncated loop suggests poor effort or early termination.

FEF25-75% is highly effort- and volume-dependent, shows wide normal variability, and is not used alone to diagnose obstruction.

Body plethysmography measures thoracic gas volume at FRC using Boyle's law while the patient pants at about 1 Hz against a closed shutter, relating mouth pressure swings to box volume changes.

Helium dilution (closed circuit) and nitrogen washout (open circuit) determine FRC by gas equilibration or washout and underestimate FRC when poorly ventilated regions or trapped gas fail to communicate.

Derived relationships: TLC = FRC + inspiratory capacity; RV = TLC - slow vital capacity; RV/TLC above the upper limit of normal indicates hyperinflation or gas trapping.

The single-breath DLCO maneuver inhales test gas from residual volume to total lung capacity, holds the breath 10 seconds (acceptable 9-11 seconds), then exhales while discarding 0.75-1.0 L of washout before the sample is collected.

DLCO is adjusted for hemoglobin concentration, carboxyhemoglobin, barometric pressure or altitude, and alveolar volume; the ratio DLCO/VA (KCO) is reported with the absolute value.

A reduced DLCO with a normal or high DLCO/VA suggests anemia, carboxyhemoglobin, or pulmonary vascular disease; reduced DLCO and reduced DLCO/VA suggest parenchymal lung disease such as emphysema or interstitial fibrosis.

DLCO may be elevated with asthma, obesity, polycythemia, pulmonary hemorrhage, and left-to-right intracardiac shunts.

The plethysmograph requires a stable, leak-free box, correct shutter function, and correction of mouth pressure for the pressure drop across the shutter and airway resistance.

Normal arterial blood gas values at sea level: pH 7.35-7.45, PaCO2 35-45 mmHg, PaO2 80-100 mmHg, HCO3- 22-26 mEq/L, and SaO2 95-98%.

Radial artery puncture is preferred; a modified Allen test confirming ulnar collateral flow, a 20-22 gauge needle, heparinized syringe, anaerobic handling, and analysis within 15-30 minutes (or on ice) are standard.

Alveolar oxygen tension: PAO2 = FiO2 x (PB - 47) - (PaCO2 / 0.8); the alveolar-arterial gradient equals PAO2 - PaO2, with a normal value of roughly (age/4) + 4 mmHg.

Winter's formula for metabolic acidosis: expected PaCO2 = (1.5 x HCO3-) + 8, plus or minus 2 mmHg; a measured value outside this range implies a second acid-base disorder.

Expected compensation: acute respiratory acidosis raises HCO3- about 1 mEq/L per 10 mmHg rise in PaCO2, chronic respiratory acidosis about 3-4 mEq/L per 10 mmHg, and metabolic alkalosis gives expected PaCO2 = (0.7 x HCO3-) + 21, plus or minus 2 mmHg.

Pulse oximetry is unreliable in the presence of carboxyhemoglobin, methemoglobin, poor perfusion, motion artifact, dark nail polish, or severe anemia, and readings below about 70% are inaccurate; SpO2 does not assess ventilation.

Co-oximetry distinguishes oxyhemoglobin, reduced hemoglobin, carboxyhemoglobin, and methemoglobin, which pulse oximetry cannot do.

Methacholine challenge: PC20 is the provoking concentration producing a 20% fall in FEV1; a value below 16 mg/mL is generally positive, and testing is not performed when FEV1 is below 50% predicted or below 1.0 L.