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Lung function tests

LUNG FUNCTION TESTS FOR ANAESTHETICS

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Lung function tests

  1. 1. Lung function Tests Dr. PARTHA PRATIM DEKA
  2. 2. Pulmonary function tests (PFTs) • Pulmonary function testing is a valuable tool for evaluating the respiratory system • comparing the measured values for pulmonary function tests obtained on a patient at any particular point with normal values derived from population studies. • The percentage of predicted normal is used to grade the severity of the abnormality.
  3. 3. Pulmonary Function Tests •Evaluates 1 or more major aspects of the respiratory system
  4. 4. PFTs •Four lung components include : The airways (large and small), Lung parenchyma (alveoli, interstitium), Pulmonary vasculature, and The bellows-pump mechanism
  5. 5. PFTs• PFTs can include: simple screening spirometry, Flow Volume Loop Formal lung volume measurement, Bronchoprovocation testing Diffusing capacity for carbon monoxide, and Arterial blood gases. Measurement of maximal respiratory pressures • These studies may collectively be referred to as a complete pulmonary function survey.
  6. 6. Spirometry •Measurement of the pattern of air movement into and out of the lungs during controlled ventilatory maneuvers. •Often done as a maximal expiratory maneuver
  7. 7. Importance • Patients and physicians have inaccurate perceptions of severity of airflow obstruction and/or severity of lung disease by physical exam • Provides objective evidence in identifying patterns of disease
  8. 8. Spirometry  Simple, office-based  Measures flow, volumes  Volume vs. Time  Can determine: - Forced expiratory volume in one second (FEV1) - Forced vital capacity (FVC) - FEV1/FVC - Forced expiratory flow 25%-75% (FEF25-75)
  9. 9. Spirometry The most readily available most useful pulmonary function test It takes ten to 15 minutes carries no risk
  10. 10. Spirometry • Spirometry is the most commonly used lung function screening study. • should be the clinician's first option • other studies being reserved for specific indications • easily performed • in the ambulatory setting, physician's office, emergency department, or inpatient setting.
  11. 11. Patient care/preparations • Two choices are available with respect to bronchodilator and medication use prior to testing. Patients may withhold oral and inhaled bronchodilators to establish baseline lung function and evaluate maximum bronchodilator response, or they may continue taking medication as prescribed. If medications are withheld, a risk of exacerbation of bronchial spasm exists.
  12. 12. Spirometry • The slow vital capacity (SVC) can also be measured with spirometers collect data for at least 30 seconds when airways obstruction is present, the forced vital capacity (FVC) is reduced and slow vital capacity (SVC) may be normal
  13. 13. Spirometry • When the slow or forced vital capacity is within the normal range: No significant restrictive disorder . No need to measure static lung volumes (residual volume and total lung capacity).
  14. 14. Indications — Diagnosis  Evaluation of signs and symptoms - SOB, exertional dyspnea, chronic cough  Screening at-risk populations  Monitoring pulmonary drug toxicity  Abnormal study - CXR, EKG, ABG, hemoglobin  Preoperative assessment
  15. 15. Indications — Diagnosis  Evaluation of signs and symptoms - SOB, exertional dyspnea, chronic cough  Screening at-risk populations  Monitoring pulmonary drug toxicity  Abnormal study - CXR, EKG, ABG, hemoglobin  Preoperative assessment Smokers > 45yo (former & current)
  16. 16. Indications — Diagnosis  Evaluation of signs and symptoms - SOB, exertional dyspnea, chronic cough  Screening at-risk populations  Evaluation of occupational symptoms  Monitoring pulmonary drug toxicity  Abnormal study - CXR, EKG, ABG, hemoglobin  Preoperative assessment
  17. 17. Indications — Prognostic ■ Assess severity ■ Follow response to therapy ■ Determine further treatment goals ■ Referral for surgery ■ Disability
  18. 18. Contraindications for spirometry • Relative contraindications for spirometry include hemoptysis of unknown origin, pneumothorax, unstable angina pectoris, recent myocardial infarction, thoracic aneurysms, abdominal aneurysms, cerebral aneurysms, recent eye surgery (increased intraocular pressure during forced expiration), recent abdominal or thoracic surgical procedures, and patients with a history of syncope associated with forced exhalation
  19. 19. Spirometry • Spirometry requires a voluntary maneuver in which a seated patient inhales maximally from tidal respiration to total lung capacity and then rapidly exhales to the fullest extent until no further volume is exhaled at residual volume
  20. 20. Spirometry • The maneuver may be performed in a forceful manner to generate a forced vital capacity (FVC) or in a more relaxed manner to generate a slow vital capacity (SVC).
  21. 21. • In normal persons, the inspiratory vital capacity, the expiratory SVC, and expiratory FVC are essentially equal. However, in patients with obstructive airways disease, the expiratory SVC is generally higher than the FVC.
  22. 22. Interpretation of spirometry results(1) •should begin with an assessment of test quality. to inspect the graphic data (the volume-time curve and the flow-volume loop)
  23. 23. Interpretation of spirometry results(2) •to ascertain whether the study meets certain well-defined acceptability and reproducibility standards
  24. 24. acceptable spirometry (ATS) • 1) minimal hesitation at the start of the forced expiration (extrapolated volume (EV) <5% of the FVC or 0.15 L, whichever is larger • Time to PEF is <120 ms (optional until further information is available) (2) no cough in the first second of forced exhalation, • 3) meets 1 of 3 criteria that define a valid end-of-test
  25. 25. Valid end-of-test • (a) smooth curvilinear rise of the volume-time tracing to a plateau of at least 1-second duration; (b) if a test fails to exhibit an expiratory plateau, a forced expiratory time (FET) of 15 seconds; or (c) when the patient cannot or should not continue forced exhalation for valid medical reasons.
  26. 26. • If both of these criteria are not met, continue testing until: Both of the criteria are met with analysis of additional acceptable spirograms or • A total of eight tests have been performed or • Save a minimum of three best maneuvers
  27. 27. Acceptability Criteria • Good start of test • No coughing • No variable flow • No early termination • Reproducibility
  28. 28. The volume-time tracing • The volume-time tracing is most useful in assessing whether the end-of-test criteria have been met
  29. 29. Spirometry
  30. 30. Flow-volume loop •the flow-volume loop is most valuable in evaluating the start-of-test criteria.
  31. 31. Flow-Volume Loop • Ruppel GL. Manual of Pulmonary Function Testing, 8th ed., Mosby 2003
  32. 32. Repeatability Criteria • After three acceptable spirograms have been obtained, apply the following tests. Are the two largest FVCs within 0.2 L of each other? • Are the two largest FEV1s within 0.2 L of each other? • If both of these criteria are met, the test session may be concluded
  33. 33. Lung Volumes
  34. 34. Lung Volumes • 4 Volumes • 4 Capacities • Sum of 2 or more lung volumes IRV TV ERV RV IC FRC VC TLC RV
  35. 35. Spirometry
  36. 36. Lung Factors Affecting Spirometry • Mechanical properties • Resistive elements
  37. 37. Mechanical Properties • Compliance • Describes the stiffness of the lungs • Change in volume over the change in pressure • Elastic recoil • The tendency of the lung to return to it’s resting state • A lung that is fully stretched has more elastic recoil and thus larger maximal flows
  38. 38. Resistive Properties • Determined by airway caliber • Affected by • Lung volume • Bronchial smooth muscles • Airway collapsibility
  39. 39. Factors That Affect Lung Volumes • Age • Sex • Height • Weight • Race • Disease
  40. 40. Technique • Have patient seated comfortably • Closed-circuit technique • Place nose clip on • Have patient breathe on mouthpiece • Have patient take a deep breath as fast as possible • Blow out as hard as they can until you tell them to stop
  41. 41. Terminology • Forced vital capacity (FVC): • Total volume of air that can be exhaled forcefully from TLC • The majority of FVC can be exhaled in <3 seconds in normal people, but often is much more prolonged in obstructive diseases • Measured in liters (L)
  42. 42. FVC • Interpretation of % predicted: • 80-120% Normal • 70-79% Mild reduction • 50%-69%Moderate reduction • <50% Severe reduction FV
  43. 43. Terminology • Forced expiratory volume in 1 second: (FEV1) • Volume of air forcefully expired from full inflation (TLC) in the first second • Measured in liters (L) • Normal people can exhale more than 75-80% of their FVC in the first second; thus the FEV1/FVC can be utilized to characterize lung disease
  44. 44. FEV1 • Interpretation of % predicted: • >75% Normal • 60%-75%Mild obstruction • 50-59% Moderate obstruction • <49% Severe obstruction FE F
  45. 45. Terminology • Forced expiratory flow 25- 75% (FEF25-75) • Mean forced expiratory flow during middle half of FVC • Measured in L/sec • May reflect effort independent expiration and the status of the small airways • Highly variable • Depends heavily on FVC
  46. 46. FEF25-75 • Interpretation of % predicted: • >60% Normal • 40-60% Mild obstruction • 20-40% Moderate obstruction • <10% Severe obstruction
  47. 47. Flow-Volume Loop • Illustrates maximum expiratory and inspiratory flow-volume curves • Useful to help characterize disease states (e.g. obstructive vs. restrictive) Ruppel GL. Manual of Pulmonary Function Testing, 8th ed., Mosby 2003
  48. 48. Categories of Disease • Obstructive • Restrictive • Mixed
  49. 49. Obstructive Disorders • Characterized by a limitation of expiratory airflow • Examples: asthma, COPD • Decreased: FEV1, FEF25-75, FEV1/FVC ratio (<0.8) • Increased or Normal: TLC
  50. 50. Spirometry in Obstructive Disease • Slow rise in upstroke • May not reach plateau
  51. 51. Restrictive Lung Disease • Characterized by diminished lung volume due to: • change in alteration in lung parenchyma (interstitial lung disease) • disease of pleura, chest wall (e.g. scoliosis), or neuromuscular apparatus (e.g. muscular dystrophy) • Decreased TLC, FVC • Normal or increased: FEV1/FVC ratio
  52. 52. Restrictive Disease • Rapid upstroke as in normal spirometry • Plateau volume is low
  53. 53. Large Airway Obstruction • Characterized by a truncated inspiratory or expiratory loop
  54. 54. Normal Spirometry
  55. 55. Obstructive Pattern ■ Decreased FEV1 ■ Decreased FVC ■ Decreased FEV1/FVC - <70% predicted ■ FEV1 used to follow severity in COPD
  56. 56. Obstructive Lung Disease — Differential Diagnosis  Asthma  COPD - chronic bronchitis - emphysema  Bronchiectasis  Bronchiolitis  Upper airway obstruction
  57. 57. Restrictive Pattern  Decreased FEV1  Decreased FVC  FEV1/FVC normal or increased
  58. 58. Restrictive Lung Disease — Differential Diagnosis  Pleural  Parenchymal  Chest wall  Neuromuscular
  59. 59. Spirometry Patterns
  60. 60. Bronchodilator Response  Degree to which FEV1 improves with inhaled bronchodilator  Documents reversible airflow obstruction  Significant response if: - FEV1 increases by 12% and >200ml  Request if obstructive pattern on spirometry
  61. 61. Flow Volume Loop  “Spirogram”  Measures forced inspiratory and expiratory flow rate  Augments spirometry results  Indications: evaluation of upper airway obstruction (stridor, unexplained dyspnea)
  62. 62. Flow Volume Loop
  63. 63. Upper Airway Obstruction  Variable intrathoracic obstruction  Variable extrathoracic obstruction  Fixed obstruction
  64. 64. Upper Airway Obstruction
  65. 65. Lung Volumes  Measurement: - helium - nitrogen washout - body plethsmography  Indications: - Diagnose restrictive component - Differentiate chronic bronchitis from emphysema
  66. 66. Pulmonary Function Testing The Basics of Interpretation
  67. 67. Lung Volumes – Patterns  Obstructive - TLC > 120% predicted - RV > 120% predicted  Restrictive - TLC < 80% predicted - RV < 80% predicted
  68. 68. Diffusing Capacity  Diffusing capacity of lungs for CO  Measures ability of lungs to transport inhaled gas from alveoli to pulmonary capillaries  Depends on: - alveolar—capillary membrane - hemoglobin concentration - cardiac output
  69. 69. Diffusing Capacity  Decreased DLCO (<80% predicted)  Obstructive lung disease  Parenchymal disease  Pulmonary vascular disease  Anemia  Increased DLCO (>120-140% predicted)  Asthma (or normal)  Pulmonary hemorrhage  Polycythemia  Left to right shunt
  70. 70. DLCO — Indications  Differentiate asthma from emphysema  Evaluation and severity of restrictive lung disease  Early stages of pulmonary hypertension  Expensive!
  71. 71. Bronchoprovocation  Useful for diagnosis of asthma in the setting of normal pulmonary function tests  Common agents: - Methacholine, Histamine, others  Diagnostic if: ≥20% decrease in FEV1
  72. 72. Continued… ↓ SYMPTOMS PFTs OBSTRUCTION? YES NO TREAT BRONCHOPROVOCATION Obstruction? TREAT No Obstruction? Other Diagnosis ↓ ↓ ↓ ↓ ↓ ↓ ↓
  73. 73. PFT Interpretation Strategy  What is the clinical question?  What is “normal”?  Did the test meet American Thoracic Society (ATS) criteria?  Don’t forget (or ignore) the flow volume loop!
  74. 74. Obstructive Pattern — Evaluation  Spirometry  FEV1, FVC: decreased  FEV1/FVC: decreased (<70% predicted)  FV Loop “scooped”  Lung Volumes  TLC, RV: increased  Bronchodilator responsiveness
  75. 75. Restrictive Pattern – Evaluation  Spirometry  FVC, FEV1: decreased  FEV1/FVC: normal or increased  FV Loop “witch’s hat”  DLCO decreased  Lung Volumes  TLC, RV: decreased  Muscle pressures may be important
  76. 76. PFT Patterns  Emphysema  FEV1/FVC <70%  “Scooped” FV curve  TLC increased  Increased compliance  DLCO decreased  Chronic Bronchitis  FEV1/FVC <70%  “Scooped” FV curve  TLC normal  Normal compliance  DLCO usually normal
  77. 77. PFT Patterns  Asthma  FEV1/FVC normal or decreased  DLCO normal or increased But PFTs may be normal  bronchoprovocation
  78. 78. Thank you

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