III_B. DECREASED CHEST WALL COMPLIANCE
Pathophysiology:
The impaired expansibility of the chest wall
caused by deep burns is improved but certainly
not eliminated by escharotomy. A significant
impairment in compliance will persist as a
result of the loss of elasticity in burn
tissue. In addition, chest wall tissue edema
itself, which will remain for many days,
impairs expansion and, in turn, decreases
functional residual capacity and vital
capacity. Work of breathing and energy
requirements will remain increased. This
process is particularly relevant for operative
procedures requiring general anesthesia. The
effect of impaired chest wall compliance on
hemodynamic function will be accentuated with
the use of a general anesthetic that results
in any element of myocardial depression, since
the increased positive mean airway pressure is
already impairing cardiac output.60
In addition, general anesthesia invariably
impairs diaphragmatic activity, thereby
further increasing the amount of positive
pressure required to maintain a constant tidal
volume. 61 The process resolves as
edema is reabsorbed from a partial thickness
burn or as full-thickness burn is removed.
Treatment:
Maintenance of a semi-erect position will
assist in movement of edema away from the
chest wall to more dependent tissues.
Continued careful volume replacement will
minimize further edema formation. Mechanical
ventilator assistance with positive pressure
may be needed to help maintain functional
residual capacity and minimize atelectasis as
well as diminish oxygen demands during this
period of impaired energy stores. Early
excision of the full-thickness wound should
improve chest wall motion by removing both
edema and noncompliant tissue.
|
