Spirometry

Anatomy and Physiology

Lungs provide life-sustaining gas exchange by way of introducing oxygen for metabolism and eliminating the by-product carbon dioxide. Air-inspired will pass through the oropharynx to the trachea, which is a membranous tube covered by cartilage bifurcating at the carina as two bronchi at the level of C6. After passing the trachea, the air enters the right and left bronchi, which divide to give several million terminal bronchioles that end in alveoli. The alveoli and surrounding vessels provide a surface where the gas exchange takes place.[3]

Indications

Apart from being a key diagnostic test for asthma and chronic obstructive pulmonary disease, spirometry is indicated in several other places, as listed below:

Diagnostic Indications

• Evaluation of the signs and symptoms of a patient or their abnormal investigations and lab tests
• Evaluation of the effect a certain disease has on pulmonary function
• Screening and early detection of individuals who are at risk of pulmonary disease
• Assessing surgical patients for preoperative risk
• Assessing the severity and the prognosis of a pulmonary disease[4]

Monitoring Indications

• Assessment of the efficiency of a therapeutic intervention such as bronchodilator therapy
• Describing the course and progression of a disease that is affecting pulmonary function, such as interstitial lung disease or obstructive lung disease
• Monitoring pulmonary function in individuals with high-risk jobs
• Sampling data that can be used for epidemiologic surveys[5]

Contraindications

Spirometry has proved itself as an accessible utility to assess lung function. However, it may not be for every patient, and care must be taken in some cases where it may be absolutely or relatively contraindicated.

Absolute Contraindications

• Hemodynamic instability
• Recent myocardial infarction or acute coronary syndrome
• Respiratory infection, a recent pneumothorax, or a pulmonary embolism
• A growing or large (>6 cm) aneurysm of the thoracic, abdominal aorta
• Hemoptysis of acute onset
• Intracranial hypertension
• Retinal detachment

Relative Contraindications

• Patients who cannot be instructed to use the device properly and are at risk of using the device inappropriately, such as children and patients with dementia
• Conditions that make it difficult to hold the mouthpiece, such as facial pain
• Recent abdominal, thoracic, brain, eye, ear, nose, or throat surgeries
• Hypertensive crisis[2][3][6]

Equipment

The first requirement for spirometry is physical space in order for the patient to be positioned comfortably. The minimum space recommended is a 2.5* 3m room with 120 cm side doors.

Spirometers are classified into closed-circuit and open-circuit spirometers. Closed-circuit spirometers are further sub-classified into wet and dry spirometers, which consist of a piston or a bellow acting as an air collecting system and a supported recording system that moves at the desired rate.

Open-circuit spirometers, which are more commonly used at present, do not have an air-collecting system and instead measure the airflow, integrate the results, and calculate the volume. The most commonly used open-circuit spirometer is the turbine flow meter, which records the rate at which turbines turn and derives the flow measurement based on proportionality. Pneumotachographs are another example, which measure the airflow by measuring the pressure difference generated as the laminar flow passes through a certain resistance. Hotwire spirometers, in which a hot metal wire is heated, and the air used to cool it is used to calculate the flow, are also an example of open-circuit spirometers. Ultrasound spirometers can be based on any of the aforementioned open-circuit spirometer principles.[7]

The minimum specifications for a spirometer are the ability to measure a volume of 8L with an accuracy of ±3% or ±50ml with a flow measurement range of ±141 and a sensitivity of 200ml/s. It is recommended that the spirometer record at 15 s of the expiration time for the forced maneuver.[8][9]

Personnel

The personnel performing the procedure must be familiar with respiratory symptoms and signs. They have to undergo training to understand the technical and physiological background of the tests in order to be competent in performing the techniques of the operation of the device, be able to apply the universal precautions, instruct the patients properly to avoid complications, and act accordingly if any of the complications arise. The personnel should be able to identify responses to therapy, the need for initiating therapy, or discontinuing an inefficient one. Continuity of training and periodic retraining is a must for staff in charge of spirometry.[10]

Preparation

All patients must be informed that they must abstain from smoking and physical exercise in the hours before the procedure. Any bronchodilator therapy must also be stopped beforehand.

The procedure must be carefully explained to the patient focusing on the importance of the patient’s cooperation to provide the most accurate results. The patient’s weight and height must be recorded with the patient barefoot and wearing only light clothing. In the case of chest deformities such as kyphoscoliosis, the span should be measured from the tip of one middle finger to the tip of the other middle finger with the hands crossed, and the height can be estimated from the formula: height = span/1.06. The patient’s age must be recorded. The procedure should be performed with the patient sitting upright, wearing light clothing, and without crossing their legs. Children can perform the test sitting or standing, but the same procedure should be done for the same individual every time.

During the procedure, the back must be supported by a backrest and not lead forward. Dentures have to be removed if they interfere with the procedure. Manual occlusion of the nares with the help of nose clips helps to prevent air leakage through the nasal passages, although it is not mandatory to occlude nasal passage. The calibration of the spirometer has to be confirmed on the day of the test.

Any contraindications or infectious diseases that require special measures will lead to a delay in the procedure.[8][9][10]

Technique or Treatment

The patient must place the mouthpiece in their mouth, and the technician must ensure that there are no leaks, and the patient is not obstructing the mouthpiece. The procedure is carried out as follows:

1. The patient must breathe in as much air as they can with a pause lasting for less than 1s at the total lung capacity.
2. The mouthpiece is placed just inside the mouth between the teeth soon after the deep inhalation. The lips should be sealed tightly around the mouthpiece to prevent air leakage. Exhalation should last at least 6 seconds or as long as advised by the instructor. If only the forced expiratory volume is to be measured, the patient must insert the mouthpiece after performing step 1 and must not breathe from the tube.
3. If any of the maneuvers are incorrectly performed, the technician must stop the patient in order to avoid fatigue and re-explain the procedure to the patient.
4. The procedure is repeated in intervals separated by 1 minute until two matching and acceptable results are acquired.[11][12]

Complications

The complications of spirometry are fairly limited and will render the procedure inaccurate or ineffective once they occur. They include:[10][11][12]

• Respiratory alkalosis as a result of hyperventilation
• Hypoxemia in a patient whose oxygen therapy has been interrupted
• Chest pain
• Fatigue
• Paroxysmal coughing
• Bronchospasm
• Dizziness
• Urinary incontinence
• Increased intracranial pressure
• Syncopal symptoms

Clinical Significance

Spirometry has proved crucial in diagnosing lung disease, monitoring patients' pulmonary function, and assessing their fitness for various procedures. With further research, solid evidence can arise for the role of spirometry in assisting patients in quitting smoking. The American College of Physicians guidelines do not recommend spirometry testing for patients undergoing nonthoracic surgery. There, of course, are exceptions if the patient has preoperative asthma or COPD.

Recent evidence also supports the use of spirometry in nonthoracic surgeries. A recent retrospective observational study found that lower preoperative spirometry FVC may predict postoperative pulmonary complications in high-risk patients undergoing abdominal surgery.[13] In another retrospective observational study, the authors found that %VC (FVC/predicted VC) may be a predictor for postoperative pneumonia in patients undergoing colorectal cancer surgery.[14] More studies are needed, but spirometry may be an important tool in identifying nonthoracic surgical patients who are at high risk of postoperative pulmonary complications. 

Lung volumes are essential to understand when evaluating a patient for surgery or evaluating a patient with preexisting lung disease. Tidal volume (TV) is the amount of air that can be exhaled or inhaled in one respiratory cycle. Normal tidal volume ranges from 6 to 8 ml/kg. Inspiratory reserve volume (IRV) is the forcible amount of air inhaled after normal TV. Expiratory reserve volume (ERV) is the amount of forcible air exhaled after exhalation of a normal TV. Residual Volume (RV) is the amount of air in the lungs after maximum exhalation. Both RV and functional residual volume (FRC) can not be measured directly by spirometry. RV can be indirectly calculated from the FRC and ERV.

Lung capacities are the summation of lung volumes. Total lung capacity (TLC) is the summation of TV, IRV, ERV, and RV. This represents the maximum volume the lungs can accommodate. Vital capacity (VC) is the summation of TV, IR, and ERV. It represents the total air exhaled after maximum inhalation. Functional residual capacity (FRC) is the residual volume plus expiratory reserve volume. It is the volume of air remaining in the lungs after normal exhalation.

These static lung volumes and capacities can diagnose obstructive and restrictive lung patterns. Restrictive lung disease results in reduced lung compliance and a reduction in lung volumes and capacities. TLC is reduced greater than 80% or below the 5th percentile of the predicted value. Both FEV1 and FVC are reduced, but FVC is reduced more than FEV1. Therefore, the FEV1/FVC ratio is greater than 80%.[15] 

One of the most common causes of restrictive lung disease is obesity. Obese patients have a reduction in FRC, which becomes worse when moving from upright to a supine position. The weight of the chest wall pushes down on the lungs. The weight of the abdominal contents pushes against the diaphragm and base of the lungs, worsening the restrictive pattern. Other restrictive lung processes are chest wall diseases(scoliosis, chest trauma) and neuromuscular disorders (Myasthenia Gravis, Guillain-Barré syndrome). Obstructive lung disease is a disproportionate reduction in the maximum airflow from the lungs compared to the maximum air that can be displaced from the lungs.[15] This can be confirmed by an FEV/VC ratio below the 5th percentile of the predicted value.[15] The RV/TLC ratio will increase irrespective of whether VC increases or decreases. The TLC will either increase or stay the same.

Complete spirometry exams will identify FEV1, forced vital capacity (FVC), vital capacity (VC), residual lung volume (RV), maximum voluntary minute ventilation (MMV), and total lung capacity (TLC). One parameter highly indicative of postoperative complications is predicted postoperative FEV 1 (PPO FEV 1).[16] FEV1 measures the volume of air forcefully exhaled in the first second during a forced expiration maneuver. Small airway disease often results in obstruction or narrowing of the small airways, leading to difficulty rapidly expelling air. Predicted postoperative FEV1 <30% are at a higher risk of postoperative pulmonary complications after thoracic surgery.

Enhancing Healthcare Team Outcomes

Spirometry is an apparatus used to assess pulmonary function for diagnostic or monitoring purposes. The procedure must be explained thoroughly to the subject patient by competent personnel who underwent training under supervision by a specialist mentor and will undergo periodic retraining in order to ensure that the results obtained are as accurate as possible and the complications are kept to a minimum. The results are interpreted by a pulmonologist, and the consultation of an interprofessional group of specialists is recommended.[11][12]