Spirometry & Post-Bronchodilator Studies

Objectives — Perform spirometry; evaluate flow-volume loops; follow user maintenance and quality-control procedures; interpret spirometry values and peak flow; and perform post-bronchodilator testing when indicated.

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Pulmonary Function Test Overview

Pulmonary diagnostic testing includes:

• Pulmonary Function Tests (PFTs)
• Spirometry
• Lung volumes
• DLCO
• Bronchoprovocation
• CPX
• Bronchoscopies
• Sleep studies

This lesson focuses on spirometry and post-bronchodilator studies.

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Spirometry

Definition

Spirometry is the measurement of air entering and leaving the lungs.

It includes measurements of several values of forced airflow and volume during inspiration and expiration.

Pattern Memory Aids

In general:

• Reduced volume suggests a possible restrictive pattern.
• Reduced flow suggests a possible obstructive pattern.

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Indications, Contraindications & Hazards

Indications

• Establish baseline pulmonary function
• Detect disease
• Follow the course of a disease or monitor treatment
• Evaluate impairment
• Test patients with dyspnea to see if symptoms are cardiac or pulmonary related
• Pre-operative evaluation
• Identify the high-risk smoker

Contraindications

• Hemoptysis of unknown origin
• Pneumothorax
• Unstable cardiovascular status, including recent MI or PE
• Thoracic, abdominal, or cerebral aneurysms
• Recent eye, chest, or abdominal surgery

Hazards

• Syncope or dizziness
• Paroxysmal coughing
• Nosocomial infections
• Bronchospasm
• Desaturation due to interruption of oxygen

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Equipment

Spirometer Types

Additional Equipment

• Filter and mouthpiece assembly
• Nose clips
• Appropriate gas sources

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Predicted Reference Values

Spirometry measurements are compared to predicted values according to:

• Race
• Age
• Sex
• Height

Predicted values are expected or reference values for lung function tests, usually derived from a large population of healthy individuals.

Predicted percent values compare the patient's actual measurements to predicted values:

Predicted % = (actual value / predicted value) x 100

LLN and Z Scores

LLN means Lower Limit of Normal.

PFT values are considered normal if they are greater than or equal to LLN.

The 5th percentile is the value below which 5% of normal reference-set results may be found. If a value falls below the LLN, there is only a 5% chance the result is normal and a 95% chance the result is abnormal.

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Pre-Procedure Assessment

Medication Preparation

Withhold bronchodilators before testing when ordered by protocol.

Patient Information

Collect:

• Age
• Height, or arm span if the patient cannot stand
• Sex
• Race
• Smoking history

Smoking History

Ask about:

• Cigarettes
• Pipe
• Cigar
• Marijuana
• Cocaine
• How long the patient smoked or did smoke
• How long ago the patient quit
• Whether the patient lives with a smoker

Calculate pack years:

Pack years = packs per day x years smoked

Symptom and Exposure History

Document:

• Description of cough and sputum production
• Description of dyspnea: at rest, on exertion, or at night
• Occupational exposure history, including work in or around mines, quarries, foundries, gases, fumes, or asbestos

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Forced Vital Capacity Procedure

The FVC maneuver is performed seated.

1. Have the patient place a tight seal around the mouthpiece.
2. Instruct the patient not to obstruct the mouthpiece with the tongue.
3. Place nose clips.
4. Record a few tidal breaths.
5. At end exhalation, coach the patient to inhale maximally to TLC.
6. Coach the patient to forcefully exhale until completely empty at RV.
7. Once the patient has completely exhaled, coach the patient to inhale as rapidly as possible back to TLC.
8. Repeat until 3 efforts have been obtained that meet ATS criteria for acceptability and reproducibility.

Coaching Instructions

Actively coach the subject:

• "Lips around the mouthpiece and good tight seal."
• "Normal breathing."
• "Fill your lungs completely / big deep breath in."
• "Blast the air out."
• "Keep going, push, push, push."
• Continue until a plateau is reached, a minimum of 6 seconds is met, or expiratory time reaches 15 seconds.
• "Big deep breath in."

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ATS Criteria for Acceptability

Each effort must be free from artifact.

Start-of-Test Errors

Back Extrapolation

Back extrapolation is used to determine and compensate for hesitation at the start of the test. The software determines time zero when the patient starts exhalation.

Extrapolated volume must be less than:

Middle-of-Test Errors

• Variable or inconsistent effort
• Partially blocked mouthpiece
• Glottic closure or breath hold
• Early termination or no plateau
• FIVC - FVC greater than 0.100 L or 5% of FVC, whichever is greater

Minimum exhalation time:

Patients who are older or obstructed commonly need more than 6 seconds.

End-of-Test Errors

• Extra breath
• Positive zero-flow error
• Negative zero-flow error
• Leak

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Core Spirometry Values

Forced Vital Capacity (FVC)

FVC is the volume that can be expired as forcefully as possible after maximum inhalation.

• Recorded in liters, BTPS
• Healthy patients: FVC equals SVC
• Obstructive disease: FVC may be less than SVC due to airway collapse and air trapping
• Restrictive disease: FVC is reduced due to loss of lung volume

FVC Percent Predicted

Forced Expiratory Volume-Time (FEVt)

FEVt is the volume of gas expired during a given interval from the beginning of the FVC maneuver.

Examples include 0.5, 1.0, and 3.0 seconds.

• Recorded in liters, BTPS
• FEV1 is the most commonly used timed interval
• FEV1 is the best value to grade the severity of airway obstruction

FEV1 Percent Predicted

FEVt/FVC Ratio

The FEVt/FVC ratio is the ratio of FEVt to FVC, expressed as a percentage. It is commonly called the ratio.

FEV1/FVC Interpretation

Actual Timed Values

Forced Expiratory Flow 25%-75%

FEF25%-75% is the average flow rate during the middle half of an FVC maneuver.

• Recorded in L/sec, BTPS
• Good indicator of flow characteristics in the medium and small airways
• Normal: 4-5 L/sec
• Values as low as 50% predicted may be considered normal
• Decreased values are common in early obstructive disease and are seen in asthma and bronchitis

Peak Expiratory Flow Rate (PEFR)

PEFR is the maximum flow rate attained during the FVC maneuver: the peak of the flow-volume loop.

• Recorded in L/sec or L/min, BTPS
• Sometimes displayed as forced expiratory flow max, or FEF Max
• Effort dependent
• Decreased values should be evaluated for reproducibility before diagnostic interpretation
• Good indicator for patient effort during spirometry

Patients with small-airway obstructive disease may show a relatively normal PEFR. A uniform decrease in PEFR is commonly associated with non-specific upper or large-airway obstruction.

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Spirometry Graphic Displays

Flow-Volume Loop

A flow-volume loop displays the flow generated during an FVC maneuver plotted against volume, usually followed by an FIV maneuver.

Values from the flow-volume loop:

• FVC
• PIFR, or forced inspiratory flow max
• PEFR, or forced expiratory flow max
• FEF25%-75%

Evaluate the flow-volume loop for:

• Shape of disease patterns
• The best loop
• PEFR
• TET, or total expired time

Volume-Time Curve

A volume-time curve displays volume over time.

Values from the volume-time curve:

• VT
• FVC/SVC
• FEVt

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Spirometry Interpretation

Before interpreting, check:

• Patient demographics
• Acceptability criteria
• Reproducibility criteria

Then evaluate:

1. FEV1/FVC measured value
2. FEV1
3. FVC percent predicted
4. FEF25%-75% percent predicted
5. Flow-volume loop

Not meeting LLN can determine if the patient has possible signs of restriction, obstruction, or both.

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Post-Bronchodilator Study

Objectives

Perform a lung post-bronchodilator study.

Indications

• Determine reversibility of airway obstruction
• Assess need for additional medication
• Diagnose asthma

Contraindications and Spirometry Hazards

Contraindications and hazards are the same as spirometry:

• Hemoptysis of unknown origin
• Pneumothorax
• Unstable cardiovascular status, including recent MI or PE
• Thoracic, abdominal, or cerebral aneurysms
• Recent eye, chest, or abdominal surgery
• Syncope, dizziness, paroxysmal coughing, nosocomial infection, bronchospasm, and desaturation due to interruption of oxygen

Bronchodilator Hazards

• Tachycardia
• HTN
• Tremors
• Nausea

Equipment

• Bronchodilator
• Beta-adrenergic medication, most commonly used
• Anticholinergic medication

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Medication Withholding Times

Inhaled Bronchodilators

Mediator Modifiers

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Post-Bronchodilator Procedure

1. Perform baseline spirometry according to ATS criteria.
2. Administer medication per local policy.
3. Use 4 puffs by MDI per ATS when following the listed protocol.
4. Wait 15 minutes.
5. Repeat spirometry according to ATS guidelines.
6. Calculate percent change using measured FEV1 or FVC.

% change = ((post - pre) / pre) x 100

Interpretation

Significant airway reversibility is:

• FEV1 or FVC increase of greater than 12%
• And an increase of 200 mL

FEV1 and FEF25%-75% usually show the greatest change, although lung volumes and DLCO may also respond to bronchodilator therapy.

Failure to show a significant response does not exclude a response. Reasons include:

• Moderate to severe COPD with patient fatigue
• Inadequate disposition of medication

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Review

Be able to:

• Define spirometry
• List indications and contraindications
• Identify required equipment
• Apply ATS criteria
• Interpret FVC, FEV1, FEV1/FVC, FEF25%-75%, and PEFR
• Evaluate flow-volume loops and volume-time curves
• Perform and interpret post-bronchodilator studies