Respiratory investigations

Question 1

Peak expiratory flow rate (PEFR or peakflow)

Answer 1

• Auseful test for COPD or asthma.
• Measured on the ward, using a peak flow meter (best of three attempts); technique is important. For normal values, see E p. 1223.
• the patient’s daily record gives a good indication of current fitness.
• Coughing is ineffective if the peak flow is <200L/min.

Question 2

Spirometry

Answer 2

• Useful to quantify the severity of ventilatory dysfunction and to differentiate between restrictive and obstructive defects.
• Measured in the respiratory function laboratory or at the bedside using a bellows device.
• normally, FVC, FEV1, and the ratio FEV1/FVC (as a percentage) are reported. the results of these tests are given with normal values calculated for that individual. Anormal FEV1/FVC ratio is 70% (see E p. 1223).
• In those with an obstructive picture (low FEV1/FVC ratio), reversibility with a bronchodilator should be tested. Spirometry after a course of steroids (prednisolone 20–40mg daily for 7d) should be repeated.
• Previously used to assess risk in patients with significant respiratory disease scheduled for major surgery. However, recent evidence suggests that spirometry does not predict pulmonary complications, even in patients with severeCOPD.
• Spirometry should not be used as the 1° factor to deny surgery. Despite poor preoperative spirometry, series of patients successfully undergoing thoracic and major non-thoracic surgery are being increasingly reported. An FEV1 <1000mL indicates that post-operative coughing and secretion clearance will be poor and increases the likelihood of needing respiratory support following major surgery.
• Spirometry should not be ordered routinely prior to abdominal or other high-risk surgery.

• Specific subgroups of patients who may benefit from spirometryare:
~those with dyspnoea or exercise intolerance that remains unexplained after clinical evaluation. In this case, the differential diagnosis may include cardiac disease. Spirometry results may change preoperative management

~In patients with COPD or asthma if the clinical evaluation cannot determine if the patient is at their best baseline and that airflow obstruction is optimally reduced. Spirometry may identify patients who will benefit from more aggressive preoperative management

~Patients in whom functional ability cannot be assessed because of lower extremity disability.

• Spirometry also forms part of the assessment of patients for lung parenchymal resection (see E p. 356).

Question 3

Flow–volumeloops

Answer 3

• Measured in the respiratory function department.
• Peak flows at different lung volumes are recorded. Although more complex to interpret, loops provide more accurate information regarding ventilatory function. they provide useful data about the severity of obstructive and restrictive respiratory disease.
• Used in the assessment of airway obstruction from both extrinsic (e.g. thyroid) and intrinsic causes (e.g. bronchospasm).

Question 4

Transfer factor, TLCO (diffusing capacity,DLCO)

Answer 4

• Measures the diffusion of carbon monoxide (CO) into the lung, using a single breath of gas containing 0.3% CO and 10% helium held for20s.
• With restrictive disease, DLCO helps to differentiate between intrinsic lung disease (DLCO usually reduced) and other causes of restriction (DLCO usually normal). With obstructive disease, the DLCO helps to differentiate between emphysema and other causes of chronic airway obstruction.
• normal value is 17–25mL/min/mmHg; however, most use the percentage value compared to the predicted.

Question 5

Arterial blood gas analysis

Answer 5

• Measure baseline blood gases in air for any patient breathless on minimal exertion. Compare with previous results if the patient has had previous arterial blood gas (ABg) measurements.
• Detects CO2 retention. Aresting PaCO2 >6.0kPa (45mmHg) is predictive of pulmonary complications and suggests ventilatory failure.
• Demonstrates the usual level of oxygenation, which indicates the severity of disease and is useful to set realistic parameters post-operatively

Question 6

ChestX-ray

Answer 6

• there is insufficient evidence to determine which patients will benefit from a preoperativeCXR.
• It is reasonable to obtain a CXR in patients with known cardiopulmonary disease and in those over the age of 50, undergoing high-risk surgical procedures, including upper abdominal, aortic, oesophageal, and thoracic surgery.
• An abnormality predicts the risk of pulmonary complications.
• Reveals lung pathology, cardiac size and outline, and provides a baseline should post-operative problems develop.

Question 7

CTthorax

Answer 7

• Chest Ct is required in a few patients with lung cysts/bullae to accurately assess the size and extent of their disease.
• Impingement of mass lesions on the major airways and the likely extent of lung resection can be assessed.
• May demonstrate anterior or posterior pneumothorax and interstitial disease, such as lung fibrosis, not seen onCXR.
• Spiral Ct chest investigations can detect PE and dissecting aortic lesions.

Question 8

Ventilation/perfusionscan

Answer 8

• Reports the likelihood of PE. Difficult to interpret in the presence of other pathology.
• Useful in the assessment of patients for lung parenchymal resection to predict the effect of resection on overall pulmonary performance (resecting a non-ventilated/perfused lung will reduce shunt and should improve oxygenation).

Question 9

Cardiopulmonary exercise testing

Answer 9

(See also E p. 15.) • Has been studied most extensively in preparation for lung resection.

• CPEt, with a calculation of the maximum O2 uptake and anaerobic threshold, may have a role in the evaluation of patients undergoing non-cardiopulmonary surgery with unexplained dyspnoea.
• Both measurements have been shown to predict survival and overall post-operative complications.
• Studies have not measured post-operative pulmonary complications as a separate outcome.