• ¹²Spirometry: Definition--Spirometry measures the mechanical function of the lung, chest wall, and respiratory muscles. The method of analysis is based on an assessment of the total volume of air exhaled from a full lung, i.e. total lung capacity (TLC) to an empty lung (residual volume). For reliable assessment, this volume which represents the forced vital capacity (FVC) should be reproducible to within about 0.2 L. The process involves the patient inhaling as much as possible followed by rapid and forceful exhalation for as long as possible. The spirometry has been assigned a CPT code (94010) with a special code to cover cases in which spirometry is performed both before and after the use of bronchodilator (94060).

• ¹²To a first approximation a reduction in any amount is air exhaled forcefully within the first seconds of FEV, a.k.a. FEV₁ may indicate an elemental reduction in the maximum inflation capacity of the lung (TLC). The most common cause of FEV₁ reduction is airway obstruction and the use of inhalational bronchodilators determines the reversibility of airway obstruction. As noted earlier, determination this reversibility is important in development of a preanesthetic plan for patients with obstructive disease because the prophylactic use of bronchodilators may obviate interoperative pulmonary adverse events.

• ¹²The indication for use of spirometry includes many different endpoints in addition to preanesthetic assessment. 

  • Evaluation of dyspnea, determination of the presence of pulmonary disease as well as assessing the efficacy of drugs that might treat such disease, quantifying the extent of ventilatory impairment as well as monitoring for the presence or evolution of occupationally-related lung disease in addition to evaluation of operative risk all represent reasons to perform spirometric testing.

• ¹²In some patients there many relative contraindications for spirometry. 

  • Some examples include:

    1. unstable angina

    2. recent myocardial infarction

    3. abdominal or thoracic aneurysm

    4. cerebral aneurysms

    5. recent eye surgery in which increased intraocular pressure which occurs during forced expiration would be problematic

    6. patients with relatively recent abdominal or thoracic surgery 

    7. patients with a history of syncope associated with forced exhalation.

• ¹²Particularly for the perioperative or preoperative assessment, the efficacy of bronchodilators ( use of bronchodialator attenuate the likelihood of interoperative bronchoconstriction)  is often determined. 

  • To establish a baseline in those patients who routinely take bronchodilators, the medication may be withheld with the recognition that withholding medication may in fact itself worsened bronchospasm. 

  • Nevertheless in order to establish baseline lung function and determine the maximal theoretical effect of bronchodilator medication might be withheld.

• ¹²The extent to which interoperative planning will be based on spirometry is interdependent on the validity of the spirometric test. Accordingly the quality of the tests are important and unreliable test results must be considered accordingly. Guidelines from the American Thoracic Society defines an acceptable spirometric test in the following manner:

  •  (1) minimal hesitation associated with the start of the forced expiratory component, specifically extrapolated volume (EV) should be < 5% of the FVC or 0.15L, whichever is larger

  • (2) cough does not occur during the first seconds of forced exhalation

  • (3) at least 1 of 3 criteria which define a valid end-of-test has been met:

    • (a) smooth curvilinear rise of the line-time tracing to a plateau that lasts at least one second

    • (b) is a test fails to show a expiratory plateau but a forced expiratory time (FET) of 15 seconds obtains or 

    • (c) the patient should not to or could not continue forced exhalation for medical reasons.

• ¹²As suggested above, the two largest values for FVC and the two largest values for FEV₁ should vary by no more than 0.2L. 

  • Analysis of spirometric test problems indicate that start-of-test difficulties which effect FEV ₁assessment tend to be rare, maybe about 2%, but end-of-test difficulties which ultimately affect FVC quality are much more common, about 60%-80%. 

  • The quality of FVC is insured therefore if there is a 12 to 15 second expiratory time even if the expiratory plateau is not evident. 

  • Checking the beginning of the volume-time tracing for possible "hesitant" start is important since such hesitation can give an incorrect, underestimation of FEV₁. 

  • ¹²The most important 3 values for assessment of abnormal pulmonary function would be: (1) FVC, (2)  FEV₁, and (3)  FEV ₁/FVC.

• ¹²Fixed upper airway obstruction 

  • Some causes: 

    • postintubation stenosis

    • goiter

    • endotracheal neoplasms

    • bronchial stenosis

• ¹²Variable intrathoracic obstruction

  • Possible causes:

    • ¹³Tracheomalacia

      • "A congenital weakness and floppiness of the walls of the trachea (main airway).

      • Tracheomalacia occurs when the cartilage in the trachea fails to develop or mature in a timely manner, resulting in the wall of the trachea being floppy rather than relatively rigid. Children with tracheomalacia have noisy breathing (high-pitched sounds when breathing, called stridor, and rattling noisy breaths) that becomes even worse if they develop upper respiratory infections."
        

    • ¹⁴Polychondritis

      • "Relapsing polychondritis is a disease characterized by autoimmune-like episodic or progressive inflammation of cartilage and other connective tissue, such as the nose, ears, throat, joints, kidneys, and heart.

      • As relapsing polychondritis advances, it causes more dangerous symptoms such as deterioration of the cartilage that holds the windpipe open. Progressive disease can destroy the integrity of the airway and compromise breathing. Destruction of the rib cartilage can collapse the chest, again hindering breathing. Joints everywhere are involved in episodes of arthritis, with pain and swelling. Other tissues besides cartilage are also involved, leading to a variety of problems with the skin and other tissues. Occasionally, the aorta or heart valves are damaged."

    • Tumors of the lower trachea or main bronchus

• ¹²Variable extrathoracic obstruction

  • Possible causes:

    • unilateral/bilateral vocal cord paralysis

    • vocal cord constriction

    • airway burns

    • reduced pharyngeal cross-sectional area

• ¹²Obstructive defects:

  • FEV ₁ reduction disproportionate compared to the FVC is a key to diagnosing obstructive lung dysfunction. 

    • This characteristic would be associated with a number of lung diseases including:

      • asthma

      • acute/chronic bronchitis

      • bronchiectasis

      • emphysema

      • cystic fibrosis

      • pneumonia

      • emphysema

      • -1-antitrypsin deficiency

      • bronchiolitis. 

    • For any given expiratory volume, expiratory flow be reduced. The reduction in airflow in the situation can be secondary to a number of factors including airway inflammation, increased intraluminal secretions, bronchial spasm, and/or decreased airway parenchymal support due to reduced lung elastic recoil.

  • Assessment of reversibility is important in terms of developing an anesthetic planning; therefore, spirometry-determined airway obstruction raises the question of whether or not inhaled bronchodilators might be useful. 

    • The American Thoracic Society has developed a minimal response that would be demonstrated in order to affirmatively decide that bronchodilator treatment is useful. 

    • This minimum response corresponds to at least a 12% and 0.2 L increase in either the FVC or FEV₁ as documented by spirometry performed between 15-20 minutes following inhalation of a normal therapeutic bronchodilator dosage. In this protocol is reasonable in predicting the likelihood of bronchodilator-mediated clinical benefits; however, negative result does not mean that no clinically beneficial response might be obtained. Positive responses to bronchodilators appears to be well correlated with positive responses to steroid treatment.

• ¹²Restrictive defects

  • Restrictive lung disease is characterized by a reduction in FVC with a normal or elevated FEV₁/FVC ratio.

• ¹²Spirometric quantification:

  • FVC, FEV₁, and FEV₁/FVC ratios will usually be above the lower limits of normal; however, the question is how are these lower limits of normal estimated. The general approach is to define the lower limit of normal as a result that a mean predicted value -1.64 times the standard error of the estimate from the population study on which the reference is based. The reference would take into account patient gender, age and height. Should the lower limit of normal value be unavailable than the FVC and FEV₁ should be greater than or equal to 80% of predicted and the FEV₁/FVC ratio should be no more than about 8-9% below the predicted ratio. Of these two approaches, the American Thoracic Society, has recommended the use of the lower limit of normal measure rather than the 80% of predicted for setting the line below which abnormality would be concluded from the test results.

  • Reduced FVC on spirometry without a reduced FEV₁/FVC ratio indicates restrictive ventilatory dysfunction. Shortened exhalation during spirometry can result in a reduced FVC. Shortened exhalation can be due to a number of factors including cardiomegaly, ascites, pregnancy, obesity, pleural effusion, kyphoscoliosis, pulmonary fibrosis, pleural tumors, neuromuscular disease, diaphragmatic weakness or paralysis, space-occupying (mass) lesions, congestive heart failure, lung resection, inadequate expiration due to pain, severe obstructive lung disease, and inadequate inspiration.

  • Reductions in FVC and/or FEV₁ Classification.

    • "Mild: 70%-79% of predicted

    • Moderate: 55%-69% of predicted

    • Severe: 45%-54% of predicted

    • Very Severe: < 45% of predicted"

• ¹²Obese Patients:

  • Special assessments include: sitting vs. supine vital capacity measurements. 

    • Diaphragmatic strength assessments can be made by vital capacity measurements in patients who are either sitting or in the supine position. First measurements are made in the upright (sitting position) and then measurements made in the supine position 

    • Diaphragm weakness (or paralysis) would be reflected by reduction in the vital capacity of less than 90% of the upright vital capacity. 

    • Increased vital capacity reduction in the supine position may not mean diaphragmatic dysfunction if the patient is obese. In that case, resistance to obesity to diaphragm descent may explain the reduction.

• ¹²Interoperative and postoperative risk assessment

  • FEV ₁ is an important measurement for operative risk assessment associated with pulmonary impairment. The general rule is that when FEV ₁  is greater than 2L or greater than about 50% of normal (predicted), significant complications are unlikely. 

    • However, the surgical site is an important consideration in risk assessment. For example, chest surgery has the highest risk. Furthermore, the patient-related considerations can translate to higher operative risk due to pulmonary complications.

  • Increased operative risk for pulmonary related complications is associated also with pre-existing patient conditions. Some of these conditions include: cardiovascular disease, pulmonary hypertension, exertional dyspnea, pre-existing pulmonary dysfunction, a history of heavy smoking, respiratory infection, cough, advanced age (> 70 years), poor nutrition, obesity, general debilitation, as well as the expectation of a prolonged surgical procedure.

  • Lung surgery: assessment for this type of surgery requires an estimation of postoperative FEV₁ based on preoperative FEV ₁. Scintigraphy (perfusion scans) may be helpful in certain ambiguous cases to more quantitatively ascertain contributions from remaining pulmonary parenchyma. Relative perfusion percentage (Q) of remaining parenchyma is thought proportional to its ventilation contribution and may be helpful in estimating postoperative pulmonary function using the following relationship:

    • postoperative FEV ₁ = preoperative FEV ₁ x Q% of remaining lung parenchyma. An example calculations also presented in reference 12 as follows:

      • in this example the preoperative FEV ₁ is 1.6 L and lung to be resected indicates 40% perfusion. Therefore postoperative FEV ₁ would be estimated by 1.6 x 0.6 or 0.96 L (i.e. 1 L). Chronic respiratory failure could be associated with an estimated postoperative FEV ₁ < 0.8 L. so the 0.8 L might be used as a cut-off for acceptable operative risk. For patients with preoperative FEV ₁ < 2 L or 50% of predicted, arterial blood gas values and cardiopulmonary exercise evaluation may be helpful in further assessing operative risk. The equation above for assessing operative risk in lung resection procedures has been itself validated in clinical trial (17⁾. 

        • In that study patients were considered relatively safe for pneumonectomy if they exhibited a negative history for cardiovascular problems and a normal ECG and also demonstrated in FEV ₁ and a pulmonary diffusing capacity for carbon monoxide (DLCO) > 80% predicted. If FEV ₁ or CLVO was found less than 80% of predicted, patients would be subjected to cardiopulmonary exercise testing as part of a more complete preoperative assessment.

• ³"The interstitial lung diseases are a group of heterogeneous disorders characterized by diffuse and usually chronic involvement of the connective tissue of pulmonary interstitium. These disorders are grouped together because of common clinical, radiological and patho-physiological changes, but in establishing a diagnosis you must consider dozens of different disorders. These can be classified according to etiology."--University of Western Ontario, Department of Pathology; maintained by C.J. Gibson--http://www.uwo.ca/pathol/MedsII/NonNeolung/lung3.htm#Objectives

Interstitial Fibosis (Lung): left--low power; right--higher power:University of Western Ontario, Department of Pathology

• ³Several history and physical considerations and diagnostic test results support a diagnosis of idiopathic interstitial fibrosis

  • Clinical data

    • Male, age 50. (Onset of disease in the 4th or 5th decade with a ratio of 2:1 occurrence in males versus females)

    • progressive dyspnea, non-productive cough

    • no history of a predisposing condition

    • clubbing of fingernails, auscultatory crackles

  • "Radiologic data

    • bilateral reticulonodular infiltrates with basal prominence"

    • 

  • "A chest x-ray showed bilateral reticulonodular pulmonary infiltrates more prominent in the bases.
    There was no obvious lymphadenopathy."

• ³"At autopsy the lungs had the gross appearance of "honeycomb lung" - the gross manifestation of interstitial fibrosis."

  • 

• ³"An additional microscopic finding was thickening of the walls of muscular arteries which occurs secondary to pulmonary hypertension which is in turn a sequela of interstitial fibrosis."

  • 

• ⁵Pulmonary alveolar proteinosis is a rare disease of unknown etiology characterized pathologically by accumulation of  periodic acid-Schiff (PAS)-positive material consisting mostly of phospholipids and protein within the alveolar spaces.

• ⁵Pulmonary alveolar proteinosis  occurs mainly in previously healthy men and women within the 20 to 60 yr old age range.

  • Pathologic findings are limited to the lungs.

  • The pathologic process may be diffuse or local, affecting typically the basal and posterior lung segments although occationally affecting only anterior segments.

• ⁵Physical findings are limited to the lungs but may be absent despite diffuse parenchymal involvement noted on chest x-ray. "Fine inspiratory crackles are usually heard over the affected lung areas."

• ⁵Chest x-ray often reveals a butterfly pattern of opacities similar to that seen in pulmonary edema. "High-resolution CT scanning shows ground-glass opacification and thickened intralobular structures and interlobular septa in typical polygonal shapes, referred to as crazy-paving."

• ⁵"Vital capacity, residual volume, functional residual capacity, total lung capacity, and carbon monoxide single-breath diffusing capacity are usually slightly reduced."

• ⁵"Hypoxemia may be present at rest or, if disease is mild, only with mild to moderate exercise. The Pa_O2 while breathing 100% O₂ is usually low, indicating an intrapulmonary right-to-left shunt."

"Granular, pink, PAS+ alveolar exudate fills alveoli. Denser pink clumps, acicular clefts, and a few disintegrating macrophages are present in the exudate. Electron microscopy shows myelin figures. Lavage fluid appears milky. Alveolar walls are only slightly thickened."

• ⁸Causes for Bronchiolitis Obliterans include infections (such as mycoplasma, Legionella, or viral),  toxic fume exposure usually nitrogen dioxide, collagen vascular disease (rheumatoid arthritis, system lupus erythematosis), bone marrow and heart-lung transplanation and drug reaction (penicillamine). An idiopathic manifestation ha also been reported.  Bronchiolitis Obliterans is formally defined as "concentrically scarred or stenotic small airways in the lung periphery.

• ⁸Imaging.
  "The chest radiograph is often normal but may demonstrate mild hyperinflation and peripheral attenuation of vascular markings.  

  • Computed tomography usually shows a mosaic pattern of low attenuation areas representing either air trapping or hypoxic vasoconstriction in secondary pulmonary lobes from obstruction of small airways. Centrilobular nodular opacities can be seen in some cases as a result of the peribronchiolar distribution of granulation tissue." 

   

• ⁸Alveolar space dilation and destruction of the alveolar walls is characteristic of emphysema. These changes results in significant reduction of lung elastic recoil of the lung.

• ⁸Physiological Changes with Emphysema: Compliance

  • Compliance is significantly above normal causing increased lung distention with reduced emptying.  This Chronic lung overinflation results (high total lung capacity, functional residual capacity, and residual volume), resulting in reduced diaphragmatic curvature which makes the diaphragm less efficient in generating small pleural pressure changes required for breathing. 

  • Pulmonary function tests on a patient with emphysema will reveal reduced expiratory flow (due to their low lung recoil), including a low FEV₁, FVC, and FEV₁/FVC ratio.(see below):

• Airway hyperresponsiveness that is associated with increased bronchiolar smooth muscle tone and chronic inflammation are hallmarks of asthma.  Bronchospasm further constricts an already attenuated airway caliber and defines the acute asthma attack.  Bronchospasm also tends to cause airway closure which traps air and promotes lung hyperinflation.  In acute asthma, the patient will exhibit high lung volumes with increased FRC and will inspire an air volume that approximates total lung capacity. 

• Pulmonary function tests during acute asthma exhibit obstructive flow properties, including a reduction in rate of maximal expiratory flow (a reduction in FEV1 and the FEV1/FVC ratio) secondary to increased resistance, and a decrease in FVC which correlates with the extent of lung hyperinflation.

• "Because these patients breathe at such high lung volumes (near the top of the pressure-volume curve, where lung compliance greatly decreases), they must exert significant effort to create an extremely negative pleural pressure, and consequently fatigue easily. Overinflation also reduces the curvature of the diaphragm, making it less efficient in generating further negative pleural pressure."