Effects of Inhaled Anesthetics on Mucociliary Function
Gamsu and coworkers[109]
compared
the rate of tantalum clearance from the lungs of postoperative patients who had received
general anesthesia for intra-abdominal or lower extremity operations. Patients who
underwent lower extremity surgery demonstrated no significant difference in tantalum
clearance when compared with a control group measured using tracheography. These
patients also did not develop atelectasis. In contrast, retention of tantalum was
demonstrated for as long as 6 days after intra-abdominal surgery, with an average
retention time three times greater than that observed in the control group. Retention
of tantalum was gravity dependent and correlated with the retention of mucus demonstrated
in areas of atelectasis. Disappearance of tantalum from these atelectatic areas
occurred only after reexpansion of collapsed lung segments. Teflon disks placed
on the tracheal mucosa and observed with fiberoptic bronchoscopy were used to study
tracheal mucus velocity in young women undergoing gynecologic surgery.[110]
The average velocity of mucus in the awake volunteers was 20 mm/min. Administration
of halothane (1% to 2%) and nitrous oxide (60%) rapidly decreased the rate of mucus
movement to 7.7 mm/min. Little or no mucus motion was observed after 90 minutes
of halothane-nitrous oxide exposure. Inspired gases were humidified, but the use
of high inspired concentrations of oxygen, a cuffed endotracheal tube, and positive-pressure
ventilation were confounding factors in this study. Bronchial mucosal transport
velocity was also determined using radiolabeled albumin microspheres deposited distally
in the mainstem bronchi using a
Figure 6-7
Effect of halothane on phosphatidylcholine (PC) synthesis
by alveolar type II cells. PC synthesis measured as the incorporation of [3
H-methyl]-choline
into PC and expressed as disintegrations per minute per microgram of intracellular
protein (*P < .05, **P
< .01 versus respective control.) A, Effect of
increasing halothane concentration with 4-hour exposure. B,
Effect of increasing exposure time to 2% halothane. (Adapted from Molliex
S, Crestani B, Dureuil B, et al: Effects of halothane on surfactant biosynthesis
by rat alveolar type II cells in primary culture. Anesthesiology 81:668, 1994.)
fiberoptic bronchoscope in healthy patients.[111]
In contrast to the findings of the study with halothane,[110]
mucus velocity was unchanged after administration of isoflurane (1.5 MAC). Whether
this relative lack of effect of isoflurane on the transport of mucus was specifically
related to the type of volatile agent was unclear. However, mucus pooling has been
observed during and after anesthesia. The data indicate that vigorous pulmonary
therapy directed at enhancing clearance of secretions from the airways should be
instituted in the immediate postoperative period, regardless of the type of inhaled
anesthetic chosen.
Konrad and coworkers[112]
have
shown that smokers have significantly slower bronchial mucus transport velocities
than nonsmokers in patients undergoing abdominal or thoracic surgery. The investigators
postulated that this observation may be related to an increased incidence of postoperative
pulmonary complications in smokers.[112]
Some evidence
exists to support the contention that patients with chronic obstructive pulmonary
disease (COPD) receiving regional anesthesia demonstrate a lower incidence of respiratory
failure than those having general anesthesia,[113]
but other studies have failed to confirm this hypothesis. The consequences of the
specific procedure with intrathoracic and intra-abdominal surgery appear to be of
greater importance in determining morbidity related to compromised respiratory function
compared with peripheral procedures performed under regional anesthesia.
Mucociliary function impairment also occurs after lung transplantation.
The mechanism for this dysfunction
may be related to alterations in the surface properties of mucus and marked impairment
of mucociliary transport distal to bronchial transection and reanastomosis.[114]
Many factors contribute to postoperative pulmonary complications.
The specific roles of depressed mucociliary function and alterations in type II
alveolar cells in such complications are unclear. Prolonged administration of inhaled
anesthetics may produce mucus pooling and adversely alter alveolar cell surfactant
metabolism. These actions may result in deleterious effects on pulmonary function
including atelectasis and infection. Those at greatest risk appear to include patients
with excessive or abnormal mucus or surfactant production (e.g., chronic bronchitis,
asthma, cystic fibrosis, chronic mechanical ventilation).
Controlled studies of the effects of inhaled anesthetics on mucociliary
function and surfactant metabolism in patients with compromised pulmonary performance
have yet to be undertaken, nor has the precise action of inhaled anesthetics on the
incidence of pulmonary complications been clearly defined. The specific actions
of the newer volatile anesthetics desflurane and sevoflurane on mucociliary function
have not been adequately studied, although there are no compelling reasons to suspect
a clinically significant difference should exist between these agents and other inhaled
anesthetics.
