Pulmonary Function Tests

O Tidal Volume (TV): volume of air inhaled or exhaled with each breath during quiet breathing (6-8 ml/kg)

O Inspiratory Reserve Volume (IRV): maximum volume of air inhaled from the end-inspiratory tidal position.(1900-3300ml)

O Expiratory Reserve Volume (ERV): maximum volume of air that can be exhaled from resting end-expiratory tidal position.( 700-1000ml).

O Residual Volume (RV): O Volume of air remaining in lungs after maximium

exhalation (20-25 ml/kg) (1700-2100ml)O Indirectly measured (FRC-ERV)O It can not be measured by spirometry

• Total Lung Capacity (TLC): Sum of all volume compartments or volume of air in lungs after maximum inspiration (4-6 L)

• Vital Capacity (VC): TLC minus RV or maximum volume of air exhaled from maximal inspiratory level. (60-70 ml/kg) (3100-4800ml)

• Inspiratory Capacity (IC): Sum of IRV and TV or the maximum volume of air that can be inhaled from the end-expiratory tidal position. (2400-3800ml).

• Expiratory Capacity (EC): TV+ ERV

Vital CapacityO Considered abnormal if <80% of

predicted value.O Physiological factors influencing VC: Height Sex Age Posture Strength of respiratory muscle

Factors decreasing Vital Capacity:

① Alteration in muscle power.

② Pulmonary diseases.

③ Space occupying lesions in chest.

④ Abdominal causes.

⑤ Depression of respiration.

⑥ Posture – by altering pulmonary Blood volume.

Different postures affecting VC

O POSITION

TRENDELENBERG LITHOTOMY PRONE RT. LATERAL LT. LATERAL

O DECREASE IN VC

14.5% 18% 10% 12% 10%

Vital Capacity pre and post op.

Before epidural

1hr after epidural

24hrs after epidural

1. Upper Abdominal

35.2% 69% 83.2%

2. Lower Abdominal

55.5% 84.8% 94.7%

Vital capacity readings expressed as a % of pre op values.

Functional residual capacity

O Functional Residual Capacity (FRC): O Sum of RV and ERV or the volume of air in the lungs

at end-expiratory tidal position.(30-35 ml/kg) (2300-3300ml).

O Measured with multiple-breath closed-circuit helium dilution, multiple-breath open-circuit nitrogen washout, or body plethysmography.

O It can not be measured by spirometry)

Functional Residual Capacity

• FRC INCREASES WITH• Increased height • Erect position (30% more than in supine) • Decreased lung recoil (e.g. emphysema)

• FRC DECREASES WITH• Obesity • Muscle paralysis (especially in supine) • Supine position • Restrictive lung disease (e.g. fibrosis, Pregnancy) • Anaesthesia

Functions of FRC:• Oxygen store • Buffer for maintaining a steady

arterial po2 • Partial inflation helps prevent

atelectasis • Minimise the work of breathing • Minimise pulmonary vascular

resistance • Minimised v/q mismatch

- only if closing capacity is less than FRC.

Maximum Voluntary Ventilation

O Also known as the Maximum Breathing Capacity (MBC)

O It is the largest volume of gas that can be moved into and out of the lungs in 1 minute by voluntary effort.

O Normal- 125-170L/min O Subject is asked to breathe as hard and fast as

possible for 10-15secs. The value obtained is converted to 60secs.

O Reflects the status of respiratory muscle, compliance of chest wall and airway resistance.

O Effort dependent test.O It can reveal diminished reserves of weak respiratory

muscles.

What are pulmonary function tests?

O A group of studies or maneuvers that may be performed using standardized equipment to measure lung function.

Bedside PFT’sO Sniders match blowing testO Forced expiratory timeO Saberazes single breath countO Saberazes breath holding testO Cough testO De bono’s whistle testO Wrights peak flowmeter

Saberazes breath holding test

Ask the patient to take a full but not too deep breath & hold it as long as possible.

>25 SEC.-NORMAL Cardiopulmonary Reserve (CPR)

15-25 SEC- LIMITED CPR <15 SEC- VERY POOR CPR (Contraindication for

elective surgery)

25- 30 SEC - 3500 ml VC 20 – 25 SEC - 3000 ml VC 15 - 20 SEC - 2500 ml VC 10 - 15 SEC - 2000 ml VC 5 - 10 SEC - 1500 ml VC

Saberazes single breath count

After deep breath, hold it and start counting till the next breath.

N- 30-40 COUNT Indicates vital capacity.

Sniders match blowing test

Ask to blow a match stick from a distance of 6” (15 cms) with-

Mouth wide open Chin rested/supported No purse lipping No head movement No air movement in the room Mouth and match at the same level

O Can not blow out a matchO MBC < 60 L/minO FEV1 < 1.6L

O Able to blow out a matchO MBC > 60 L/minO FEV1 > 1.6L

O MODIFIED MATCH TEST: DISTANCE MBC 9” >150 L/MIN. 6” >60 L/MIN. 3” > 40 L/MIN.

Cough test

Deep breath followed by cough ABILITY TO COUGH STRENGTH EFFECTIVENESSINADEQUATE COUGH IF: FVC<20 ML/KG FEV1 < 15 ML/KG PEFR < 200 L/MIN.

VC should be 3 TIMES TV FOR EFFECTIVE COUGH.

A wet productive cough / self propagated paraoxysms of coughing :patient susceptible for pulmonary complication.

Forced expiratory time

After deep breath, exhale maximally and forcefully & keep stethoscope over trachea & listen.

Normal FET – 3-5 SECS. OBS.LUNG DIS. - > 6 SEC RES. LUNG DIS.- < 3 SEC

Wrights Peak FLowmeter

• Measures tidal volume, mv (15 secs times 4)

• Simple and rapid• Instrument- compact, light and portable.• Disadvantage: It under- reads at low

flow rates and over- reads at high flow rates.

• Can be connected to endotracheal tube or face mask

• Prior explanation to patients needed.• Ideally done in sitting positoin.

Wrights peak flowmeter

• MV- instrument record for 1 min. And read directly

• Accurate measurement in the range of 3.7-20l/min.(±10%)

• USES: 1)BED SIDE PFT 2) ICU – Weaning patients from Ventilation.

Measures PEFR (Peak Expiratory Flow Rate) Normal – MALES- 450-700 L/MIN. FEMALES- 350-500 L/MIN. <200 L/ MIN. – INADEQUATE COUGH EFFICIENCY.

De bono’s whistle test

MEASURES PEFR.Patient blows down a wide bore tube at the end of which is a whistle, on the side is a hole with adjustable knob.

As subject blows → whistle blows, leak hole is gradually increased till the intensity of whistle disappears.

At the last position at which the whistle can be blown , the PEFR can be read off the scale.

Components of PFT

1.Tests of mechanical function: Spirometry Static lung

volumes Respiratory

Mechanics Respiratory

muscle strength

2.Tests of gas exchange: ABG, DLCO.3.Cardiopulmonary interaction:• Qualitative- stair

climbing• Quantitative-

6min walking test

Indications for spirometry:

O Diagnostic: • evaluate symptoms and signs• Effect of disease on PFT• Screen individuals• Pre-op riskO Monitoring- to assess therapeutic

interventionsO Public health

Contraindications• Hemoptysis• Pneumothorax• Recent MI, unstable angina pectoris• Thoracic, abdominal and cerebral

aneurysm• Recent abdominal or thoracic

surgical procedure.• H/o Syncope with forced exhalation• Recent eye surgery

Pre-requisitesO Prior explanation to the patientO Not to smoke /inhale bronchodilators 6 hrs prior or oral

bronchodilators 12hrs prior.O Remove any tight clothings/ waist belt/ denturesO Pt. Seated comfortablyO Nose clip to close nostrils.O Minimum exhalation time of 6 seconds, but up to

15 secondsO Number of maneuvers: Minimum of 3 and

maximum of 8O Should not be interfered by coughing, glottic closure,

mechanical obstruction.

Requirements of a good PFT.

O Lack of artifactO Satisfactory startO Satisfactory exhalation with six seconds of

smooth continuous exhalation.

O ATS Criteria for reproducibility after obtaining 3 acceptable spirograms:

1) Largest FVC within 0.15L of next largest FVC

2) Largest FEV1 within 0.15L of next largest FEV1

Measurements obtained from the FVC curve:

O FEV1---the volume exhaled during the first second of the FVC maneuver

O FEF 25-75%---the mean expiratory flow during the middle half of the FVC maneuver; reflects flow through the small (<2 mm in diameter) airways

O FEV1/FVC---the ratio of FEV1 to FVC X 100 (expressed as a percent); an important value because a reduction of this ratio from expected values is specific for obstructive rather than restrictive diseases

Causes of restrictive PFT

O Lung parenchymal pathology

O Inter pleural pathology

O Neuromuscular problems

Grading of severity of abnormality

O Based on TLC: Mild: predicted TLC is less than lower limit of normal

but >70% Moderate: predicted TLC is <70% and >60% Moderately severe: predicted TLC <60%

O Based on spirometry: Mild: Predicted VC is less than lower limit of normal but

>70% Moderate: Predicted VC <70% and >60% Moderately severe: Predicted VC <60% and >50% Severe: Predicted VC <50% and >34% Very Severe: Predicted VC <34%

Causes of obstructive PFT

O Narrowing of airways due to bronchial smooth muscle contraction.

O Narrowing of airways due to inflammation and swelling of bronchial mucosa.

O Material inside the bronchial passage.

O Destruction of lung tissue with loss of elasticity.

Severity of obstructive lung disease:

Obstructive vs Restrictive diseases on spirometry

Obstructive disorders

Restrictive disorders

O FVC N or↓O FEV1 ↓O FEF25-75% ↓ O FEV1/FVC ↓O TLC N or ↑

O FVC ↓O FEV1 ↓ O FEF 25-75% N to ↓O FEV1/FVC N to ↑O TLC ↓

Criteria for reversibility of small airway obstruction on PFT:

O 2 PFTs should be done one before and one after administration of bronchodilator.

O Drug used is usually beta-2 sympathomimetic.

O If 2 out of 3 measurements improve then patient has reversible airway obstruction.

1) FVC of 10% or more 2) FEV1 an increase of 200ml or 15% of baseline FEV1

3) FEF25-75% an increase of 25% or more

Flow volume loopsO Helpful in evaluation of air flow limitation on

inspiration and expiration

O In addition to obstructive and restrictive patterns, flow-volume loops can provide information on upper airway obstruction:O Fixed obstruction: such as in tumor, tracheal stenosisO Variable extrathoracic obstruction: such as in vocal

cord dysfunction O Variable intrathoracic obstruction:as in malignancy or

tracheomalacia

Measurement of other lung volumes

O Nitrogen washout technique

O Helium dilution technique

O Body plethysmography

DLCO (diffusion lung CO)

O The diffusing capacity is a measure of the ability of the lungs to transfer gas.

O Measure of interaction of alveolar surface area, alveolar capillary perfusion and physical properties of the alveolar capillary interface.

O CO is rapidly taken up by haemoglobin, its transfer is therefore limited mainly by diffusion

Causes of decreased DLCO:

Causes of increased DLCO:

O AnemiaO EmphysemaO ILDO Pulmonary edemaO Pulmonary

vascular disease

O ObesityO AsthmaO L to R shuntO Alveolar

hemorrhage

DLCO- capacity of the lungs to transfer CO (ml/min/mmHg)DLCOc- DLCO corrected for Hb (ml/min/mmHg)DLVA- DLCO corected for volume (ml/min/mmHg/L)DLVC- DLCO corrected for both volume and Hb (ml/min/mmHg/L)

Respiratory muscle function

O A number of diseases such as motor neuron disease can result in respiratory muscle weakness, which can ultimately lead to respiratory failure

O Inspiratory mouth pressure A measure of inspiratory muscle function in which subjects generate as much inspiratory pressure as possible against a blocked mouth piece .Values of 80 cm of water or more exclude any significant inspiratory muscle weakness O Expiratory mouth pressure A measure of expiratory muscle function in which subjects generate as much expiratory pressure as possible against a blocked mouth piece. Values of 80 cm of water or more exclude any significant expiratory muscle weakness

Tests for cardiopulmonary reserve:

O Number of flights of stairs patient can climb: inability to climb 2 flights of stairs indicates increased risk of post-op cardiopulmonary complications.

O Six minute walking test (6 MWT)

Anesthetic Implications

COPD classification by GOLD

ATS classification of severity of COPD

Evaluation of patient for lung resection

GOALS:1) to identify patients at risk of increased post-

op morbidity & mortality2) to identify patients who need short-term or

long term post-op ventilator support.Lung resection may be followed by – inadequate

gas exchange, pulm HTN & incapacitating dyspnoea.

EXAMPLE:Assuming pre op FEV1 to be 70%

ppoFEV1= 70 X (1-29/100)

ppoFEV1= 50%

ReferencesO A practice of anesthesia by Wylie 5th editionO Millers 7th editionO Clinical Anesthesiology- Morgan 5th editionO Interpreting pulmonary function tests: Recognize

the pattern, and the diagnosis will follow. CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 70 • NUMBER 10

O SERIES ‘‘ATS/ERS TASK FORCE: STANDARDISATION OF LUNG

FUNCTION TESTING’’ 2005

Thank YouTHE END