In the subsequent search for more cost beneficial methods for prophylactic bronchial hygiene, various expiratory maneuvers (from blow bottles to spontaneous coughing and carbon dioxide inhalation) were tried and found to be generally lacking. Then, in the 1970s, the incentive spirometer was developed and a new therapy called incentive spirometry came into vogue. Incentive spirometry (IS) is a technique that is both effective and appropriate for prophylactic bronchial hygiene.
Incentive spirometry is designed to mimic natural sighing by encouraging patients to take slow, deep breaths. Incentive spirometry is performed using devices which provide visual cues to the patients that the desired flow or volume has been achieved. The original type of incentive spirometor had a variable preset inspiratory volume with a light that turned on when that volume was reached by the patient's inspiratory effort. The light stayed on as long as the inspiratory flow rate was maintained, and the patient was encouraged to try keep the light on as long as possible.
The devices used today have various mechanisms whereby the flow through the tube lifts a colored ball up a column, and the sustained inspiratory flow is rewarded by the ball's reaching its goal and being sustained. Each device has a simple method of increasing the flow required to reach the goal, and the primary advantage of these newer devices is that they are less costly than the originals.
Advantages of Incentive Spirometry
Incentive spirometry (IS) has been the mainstay of lung expansion therapy since the development of the incentive spirometer, and its main advantages over IPPB as a prophylactic regimen are:
Incentive spirometry provides an effective means of restoring normal pre-operative pulmonary function in post surgical patients. Although such patients may be eager to improve, pain often makes it difficult for them to take deep, sustained breaths. The effect of this hypoventilation may be atelectasis, leading to increased shunting, hypoxemia or hypostatic pneumonia. Incentive spirometry enables the recuperating patient to take deep breaths while being able to "see" them and count them. The patient can monitor progress and is given incentive by seeing this progress.
Incentive spirometers emphasize sustained maximal inspiration (inspiration to total lung capacity for the longest possible time). This deep breathing expands the lungs and reduces postoperative micro-atelectasis. The practitioners, by observing the spirometer, are able to evaluate patient effort, volumes and durations of end-expiratory breath holds. The desired volume and number of repetitions to be performed is initially set by the RCP or other qualified caregiver. The inspired volume goal is set on the basis of predicted values, or observation of initial performance.
The basis of incentive spirometry (IS) involves having the patient take a sustained, maximal inspiration (SMI). An SMI is a slow, deep inhalation from the FRC up to the total lung capacity, followed by a 5 to 10 second breath hold. This is the functional equivalent of performing an inspiratory capacity maneuver, followed by a breath hold.
During the inspiratory phase of spontaneous breathing, the drop in pleural pressure caused by expansion of the thorax is transmitted to the alveoli. With alveolar pressure now negative, a pressure gradient is created between the airway opening and the alveoli. This transrespiratory pressure gradient (Prs) causes gas to flow from the airway into the alveoli.
Alveolar expansion during spontaneous inspiration (equivalent to the change in volume) is proportional to the difference between the alveolar and pleural pressures at end inspiration. The difference between the alveolar and pleural pressures at end inspiration is called the transpulmonary pressure gradient. You should think of the alveolar expansion occurring during spontaneous inspiration as based on an "outside-in" model of pressure changes. Pressure drops outside the lung (pleural space) are transmitted in to the alveoli.
During the patient's spontaneous expiration, the lungs and chest wall recoil, pleural pressure becomes less negative, and alveolar pressure rises above atmospheric. This reverses the transrespiratory pressure gradient. With alveolar pressure now greater than pressure at the airway opening, gas flows out from the alveoli to the atmosphere.
A sustained maximal inspiration causes the pleural pressure to drop well below normal. This increases the transpulmonary pressure gradient, which is sustained for a few seconds with a breath hold. Atelectasis can frequently be prevented or treated by increasing the transpulmonary pressure gradient and further expanding the alveoli.