BRONCHIAL HYGIENE THERAPY
Hospitalized patients often have diminished respiratory effort
and impaired mucociliary clearance of pulmonary secretions. A number of factors
can contribute to these impairments, including decreased physical activity, pain,
altered mental status, and certain medications. These deficiencies can lead to atelectasis
and pulmonary infections which may prolong hospital stay and increase mortality.
The goal of bronchial hygiene therapy is to supplement airway mucociliary clearance
and optimize pulmonary function. The essential components of bronchial hygiene therapy
include (1) humidification of the airways, (2) deep breathing and incentive spirometry,
(3) chest physiotherapy, (4) noninvasive positive-pressure techniques, and (5) invasive
suctioning of the bronchotracheal tree. While many of these specific techniques
have been studied in clinical trials, most of these trials were small and inconclusive.
Therefore, although bronchial hygiene therapy is clearly important, the optimal
regimen remains controversial. In clinical practice, the choice of bronchial hygiene
regimen must be individualized.
Humidification
Humidity refers to the level of moisture or water vapor in air.
Absolute humidity can be defined as the mass of water vapor in a specific volume
of gas (typically expressed as mg/L). Air is fully saturated at its maximum absolute
humidity. The maximum absolute humidity is a function of temperature, as shown in
Table 75-5
.
Relative humidity is the content of water vapor expressed as a
percentage of the maximum absolute humidity at a given temperature. Alveolar air
is normally fully saturated. Thus, at body temperature (37°C) alveolar air has
an absolute humidity of 44 mg/L and a relative humidity of 100%, yielding a partial
pressure of water of 47 mm Hg. Conversely, standard room air at a temperature of
21°C has a 50% relative humidity, or an absolute humidity of 9 mg/L. Inspired
air must therefore be warmed and humidified by the airways. Inadequate humidification
of inspired gas can lead to dried secretions, poor mucociliary clearance, atelectasis,
and pulmonary infections. The administration of dry oxygen lowers the inspired water
content, increasing the risk of these complications. The water content of delivered
oxygen can be increased with humidifiers or nebulizers.
