Lung function tests

Spirometry is a measure of airflow and lung volumes during a forced expiratory maneuver from full inspiration. It is the simplest of all respiratory functional tests. Indication for Lung function tests:

1. To evaluate for presence of lung disease

2. To assess severity and progression of known lung disease

3. To diagnose/differentiate obstructive vs. restrictive lung disease

4. To assess the effectiveness of therapy

5. To evaluate the amount of disability

6. To assess postoperative complications.

Correct interpretation of spirometry requires that it be performed correctly. To obtain an accurate recording the subject should be told to:

· Stand or sit up straight

· Inhale maximally ('breathe in all the way')

· Get a good seal around the mouthpiece of the spirometer

· Blow out as hard and as fast as possible ('blast out')

· Continue to exhale until he or she can blow no more. In practice this is when less than 50 mL has been exhaled over 2 seconds. Expiration should continue for at least 6 seconds and up to 15 seconds if necessary (some patients will find this exhausting, and prolonged maneuvers should be used with caution)

· Repeat until three technically acceptable maneuvers (no coughs, air leaks, false-starts) are completed

Two FEV1s and FVCs within 200 mL and within 5% of each other should be obtained.

Using spirometry tidal volume (VT), vital capacity (VC), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), forced vital capacity (FVC), forced expiratory volume in 1s (FEV1), forced expiratory flow between 25% and 75% of FVC (FEF25-75%), peak expiratory flow (PEF), maximum voluntary ventilation (MVV) can be measured.

All spirometry parameters depend on patient age, sex, height and weight. They are calculated by computer programs of spirometer and named predictor value. For patient normal values of lung function are 80% and more from predictor.

The FEV1/FVC ratio gives a good estimate of severity of airflow obstruction; normal ratio is 75-80%.

In case of obstructive defects (for example COPD or asthma) FEV1 is reduced more than the FVC and FEV1/FVC ratio is< 70%.

In case of restrictive defects (for example lung fibrosis, sarcoidosis, pneumoconiosis, interstitial pneumonias, connective tissue diseases, pleural effusion, obesity, kyphoscoliosis, neuromuscular problems) FVC is reduced and the FEV1/FVC ratio is normal or raised.

Peak expiratory flow (PEF) is measured by a maximal forced expiration through a peak flow meter. It correlates well with the forced expiratory volume in 1 second (FEV1) and is used as an estimate of airway caliber. Peak flow rates should be measured regularly in asthmatics to monitor response to therapy and disease control.

Pulse oximetry allows non-invasive assessment of peripheral O₂ saturation. It provides a useful tool for monitoring those who are acutely ill or at risk of deterioration. On most pulse oximeters, the alarm is set at 90%. An oxygen saturation of <80% is clearly abnormal and action is required (unless this is normal for the patient, e.g. in COPD. Here, check arterial blood gases (ABG) as P_aCO₂ may be rising despite a normal P_aO₂). Erroneous readings may be caused by: poor perfusion, motion, excess light, skin pigmentation, nail varnish, dyshaemoglobinaemias, and carbon monoxide poisoning.

Fibreoptic bronchoscopy is an essential tool in the investigation of many forms of respiratory diseases. Under local anesthesia, the flexible bronchoscope is passed through the nose, pharynx and larynx, down the trachea, and the bronchial tree is then inspected.

Diagnostic indications:

· Suspected lung cancer,

· Slowly resolving pneumonia,

· Pneumonia in the immunosuppressed,

· Interstitial lung disease.

Bronchial lavage fluid may be sent to the lab for microscopy, culture, and cytology. Mucosal abnormalities may be brushed (cytology) and biopsied (histopathology). Flexible biopsy forceps are passed down a channel inside the bronchoscope, and are used to obtain tissue samples for histological examination. In diffuse interstitial lung disease; such as sarcoidosis or pulmonary fibrosis, the technique of transbronchial biopsy can be used to obtain small specimens of lung parenchyma for histological examination and confirmation of the diagnosis.

Therapeutic indications:

· Aspiration of mucus plugs causing lobar collapse,

· Removal of foreign bodies,

· Stopping lung bleeding.

Complications: respiratory depression, bleeding, and pneumothorax

Roentgenography or X-ray examination is commonly and widely used for diagnostics of the different respiratory diseases. It is obviously for confirming pneumonia, tuberculosis, pleural effusion, pneumothorax and revealing some form of lung cancer and other. For diagnostics of the respiratory diseases it should be performed in two positions: posterioranterior and lateral. If patient is bedridden anteriorposterior position is used but films of this position are inferior to posterioranterior view. Assessing X-ray film of the chest includes position, shadow of soft tissue (breast at women or subcutaneous layer at obesity patients, muscle and other), bones, diaphragm position, clear, opacity, different types of nodular shadows, mediastinum, heart and roots (hilum).

Computed tomography is cross-sectional scanning of the chest. This technique is more sensitive than plain radiography in detecting respiratory abnormalities. Computed tomography makes possible to distinguish more accurate tumors, small indurations, cavities and caverns in the lungs. This method is far better than radiographic studies at characterizing tissue density, distinguishing subtle differences in density between adjacent structures, and providing accurate size assessment of lesions. Indications for computed tomography:

· Evaluation of suspected interstitial lung diseases, pulmonary nodules and subpleural lesions when X-ray is normal or nonspecific

· Characterization of interstitial lung diseases or solitary pulmonary nodules

· Diagnosis of bronchiectasis (it replaced bronchography)

· Detecting or confirming presence of mediastinal mass and its size

· Differentiating pleural from parenchymal masses/ abnormalities

Magnetic resonance imaging provides a less detailed view of the pulmonary parenchyma as well as poor spatial resolution. However, magnetic resonance imaging offers several advantages over computed tomography in certain clinical settings: for imaging abnormalities near the lung apex, the spine, and the thoracoabdominal junction. Vascular structures can be distinguished from nonvascular without the need of contrast.

Bronchography is an integral part of the diagnosis evaluation of diseases of bronchi. The standard technique requires the injection of contrast medium, usually iodolipol, into the bronchi lumen. This may be done through a catheter passed via the nose or mouth through the anaesthetized larynx. Then radiographs are taken, that give a distinct patterns of the bronchial tree. This procedure is of particular importance to the evaluation of bronchiectasis, abscesses, caverns in the lungs, and compression of the bronchi by tumor.

Sputum examination Collect a good sample; if necessary ask a physiotherapist to help. Note the appearance: clear and colorless (chronic bronchitis), yellow/green (pulmonary infection), red (hemoptysis), black (smoke, coal), or frothy white/pink (pulmonary edema). Send the sample to the laboratory for microscopy (Gram stain and auramine/ZN stain, if indicated), culture, and cytology.

Thoracentesis is performed to aspirate pleural fluid for diagnostic purposes and in case of a large effusion to remove fluid from pleural cavity.

Laboratory assessment of pleural fluid:

1. Common – visual assessment, comparative density, Rivalt test.

2. Biochemistry for measurement of protein, LDH, glucose, cholesterol, triglycerides, amylase, depending on the clinical circumstances.

3. Cytology for examination for malignant cells and differential cell count.

4. Microbiology for Gram stain and microscopy, culture, MBT examination.

Is the pleural effusion a transudates or exudates?

Sign	Transudates	Exudates
Comparative density	< 1,015-1,018	>1,018
Rivalt test	Negative	Positive
Protein	<30 g/l	>30 g/l
Pleural fluid protein/serum protein ratio	<0,5	>0,5
LDH	<1,6 mMol/l	>1,6 mMol/l
Pleural fluid LDG/serum LDG ratio	<0,6	>0,6
Erythrocytes	<10*10^9/l	>100*10^9/l
Leucocytes	<1*10^9/l	>1*10^9/l
PH	>7,3	<7,3
Glucose	3,3-5,5 mMol/l	<3,3 mMol/l

Materials for self-control (added)

Дата добавления: 2015-10-30