Saturday, October 12, 2013

Pulmonary Function Test in children- PFT

PFT- The term encompasses a wide variety of objective methods to assess lung function.

1. Ventilatory Lung Function Tests
  • Spirometry
  • Peak Expiratory Flow Rate
  • Helium Dilution technique
  • Body Plethysmography
2.Assessment of Pulmonary Gas Exchange or Diffusion
  • Blood gas analysis
  • Pulse oximetry
  • Measurement of diffusing capacity
3.Assessment of Pulmonary perfusion
  • Methods of measurement of pulmonary circulation
  • Ventilation-Perfusion by Lung Scan


Pulmonary function testing in infants and young children
  • Plethysmography and nasal pneumotachography
  • Blood gas analysis provides the most sensitive index
  • Paediatric pneumogram

Uses of Pulmonary Function Testing in Children
  • Diagnose lung and chest wall disorders
  • Evaluate unexplained dyspnea
  • Identify airway reactivity
  • Evaluate bronchodilator response
  • Assess preoperative lung function
  • Determine course of respiratory failure
  • Assess prognosis
  • Evaluate exercise-related symptoms

Spirometry
Spirometry is a medical test that measures the volume of air an individual inhales or exhales as a function of time. (ATS, 1994)” .John Hutchinson (1811-1861)—inventor of the spirometer and originator of the term vital capacity (VC).
Measurement devices
  • Volume displacement spirometers
  • Flow sensing spirometers
  • Portable devices
Age:
Age : 6 years and above (Spirometry can be reproducibly done from the age of 5 years but these values should be interpreted with individual considering age, sex, height and nutritional status )
Faridi MMA, Gupta P and Prakash A. Lung functions in malnourished children aged five to eleven years. Indian Pedtiatr 1995; 32(1): 35-42

Reference Values
  • Lung volumes and flow rates vary with age, sex and ethnic group. Ideally Every Lab should develop its own Normal values or use data generated from same population.

A spirometer can be used to measure the following:
  • FVC and its derivatives (such as FEV1, FEF 25-75%)
  • Forced inspiratory vital capacity (FIVC)
  • Peak expiratory flow rate
  • Maximum voluntary ventilation (MVV)
  • Slow VC
  • IC, IRV, and ERV
  • Pre and post bronchodilator studies

Read Lung Volumes and Capacities
Procedure
1. Check spirometer calibration.
2. Explain test.
3. Prepare patient-Ask about recent illness, medication use, etc.
4. Give instructions and demonstrate:
  • Show nose clip and mouthpiece.
  • Demonstrate position of head with chin slightly elevated and neck somewhat extended.
  • Inhale as much as possible, put mouthpiece in mouth (open circuit), exhale as hard and fast as possible.
  • Give simple instructions.
5. Patient performs the maneuver
  • Patient assumes the position
  • Puts nose clip on
  • Inhales maximally
  • Puts mouthpiece on mouth and closes lips around mouthpiece (open circuit)
  • Exhales as hard and fast and long as possible
  • Repeat instructions if necessary –be an effective coach
  • Repeat minimum of three times (check for reproducibility)

Special Consideration in children
  • Ability to perform spirometry dependent on developmental age of child, personality, and interest of the child.
  • Patients need a calm, relaxed environment and good coaching. Patience is key.
  • Even with the best of environments and coaching, a child may not be able to perform spirometry

When is the Test Acceptable?
  • A clear start to the test with an apparently maximum effort
  • A smooth, continuous exhalation maintained for at least
  • 6 seconds, without coughing or Valsalva’s maneuver
  • An obvious end to the test (no change in volume for at least 2 seconds)
  • Subject should perform a minimum of three and a maximum of eight FVC maneuvers until at least two acceptable curves are obtained
  • The reproducibility of the two largest curves should be within 5% or 0.1 L, whichever is greater
  • The recorded FVC should be the maximum value from the acceptable curves
Flow is plotted against volume.
Maximum forced expiratory flow (FEF max) is generated in the early part of exhalation, and it is a commonly used indicator of airway obstruction in asthma and other obstructive lesions.
Provided maximum pressure is generated consistently during exhalation, a decrease in flow is a reflection of increased airway resistance.
The total volume exhaled during this maneuver is forced vital capacity (FVC). Volume exhaled in one second is referred to as FEV1. FEV1/FVC is expressed as a percentage of FVC.
FEV 25%-75% is the mean flow between 25% and 75% of FVC and is considered relatively effort independent.
Individual values and shapes of flow-volume curves show characteristic changes in obstructive and restrictive respiratory disorders
  • In intrapulmonary airway obstruction such as asthma or cystic fibrosis, there is a reduction of FEFmax, FEF25%-75%, FVC, and FEV1/FVC. Also, there is a characteristic concavity in the middle part of the expiratory curve.
  • In restrictive lung disease such as interstitial pneumonia, FVC is decreased with relative preservation of airflow and FEV1/FVC. The flow volume curve assumes a vertically oblong shape compared to normal.

Changes in shape of the flow volume loop and individual values depend on the type of disease and the extent of severity.




Approach to Diagnosis:


Click to enlarge
References
  1. Nelson Textbook of Pediatrics, 19 th edition
  2. PEDIATRIC ASTHMA, ALLERGY & IMMUNOLOGY Volume 16, Number 4, 2003 © Mary Ann Liebert, Inc.Basic Pulmonary Function Testing in Children LAURA S. INSELMAN, M.D.
  3. Interpreting pulmonary function tests:Recognize the pattern, and the diagnosis will follow CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 70 • NUMBER 10 OCTOBER 2003
  4. Interpretative strategies for lung function tests Eur Respir J 2005; 26: 948–968 DOI: 10.1183/09031936.05.00035205 CopyrightERS Journals Ltd 2005- ATS/ERS Task Force
  5. American Thoracic Society Documents- An Official American Thoracic Society/European Respiratory Society Statement: Pulmonary Function Testing in Preschool Children
  6. PAEDIATRIC PULMONARY FUNCTION TESTS (PFT) - A Review.- Dhaka
  7. Pulmonary Function Testing in Office Practice Soumya Swaminathan Tuberculosis Research Centre, Indian Council of Medical Research Chetput, Chennai
Submitted by - Dr Sujit Shrestha

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