Upper Airway Collapsibility in Anesthetized Children
Ronald S. Litman, DO, Joseph M. McDonough, MS, Carole L. Marcus, MBBCh,
Alan R. Schwartz, MD, and Denham S. Ward, MD, PhD
Department of Anesthesiology, University of Rochester, Rochester, New York; Department of Anesthesiology and Critical
Care, Division of Pulmonary Medicine, The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania; Johns
Hopkins Hospital, Johns Hopkins University School of Medicine, Baltimore, Maryland
We sought to establish the feasibility of measuring up-
per airway narrowing in spontaneously breathing,
anesthetized children using dynamic application of
negative airway pressure. A secondary aim was to com-
pare differences in upper airway collapsibility after the
administration of sevoflurane or halothane. Subjects
were randomized to either drug for inhaled anesthetic
induction. Each was adjusted to their 1 MAC value
(0.9% for halothane and 2.5% for sevoflurane) and a
blinded anesthesia provider held the facemask without
performing manual airway opening maneuvers but
with inclusion of an oral airway device. Inspiratory
flows were measured during partial upper airway ob-
struction created by an adjustable negative pressure-
generating vacuum motor inserted into the anesthesia
circuit. Critical closing pressure of the pharynx (Pcrit)
was obtained by plotting the peak inspiratory flow of
the obstructed breaths against the corresponding nega-
tive pressure in the facemask and extrapolating to zero
airflow using linear correlation. Fourteen children were
enrolled, seven in each anesthetic group. Two children
in the halothane group did not develop flow-limited
airway obstruction despite negative pressures as low as
-9 cm H
2
O. Pcrit for sevoflurane ranged from -6.7 to
–11.6 (mean sd, -9.8 1.9) cm H
2
O. Pcrit for halo-
thane ranged from -8.1 to -33 (mean sd, -19.4
9.3) cm H
2
O (sevoflurane versus halothane, P = 0.048).
We conclude that when using dynamic application of
negative airway pressure, halothane appears to cause
less upper airway obstruction than sevoflurane at equi-
potent concentrations.
(Anesth Analg 2006;102:750 –4)
A
nesthetic-induced upper airway obstruction is a
common and serious cause of hypoxemia. Al-
though the prevalence of this problem is widely
appreciated, little is known about the effects of inhaled
anesthetics on upper airway patency in adults (1,2),
and even less is known about the characteristics of
upper airway patency during anesthesia in children
(3–5).
The primary aim of this study was to establish the
feasibility of characterizing pharyngeal collapse in
children using a previously described method called
dynamic application of negative airway pressure
(DNAP) (6). A secondary aim was to compare differ-
ences in upper airway collapse after the administra-
tion of sevoflurane or halothane.
Methods
This study, which was performed at Strong Memorial
Hospital (Rochester, NY) and The Children’s Hospital
of Philadelphia, was approved by the respective insti-
tutions’ IRBs. Consent was obtained from parents of
all participating children, and assent was obtained
from children older than 7 yr, when appropriate.
Healthy children, 4 to 12 yr of age, who were sched-
uled for elective surgery, were eligible to participate.
Exclusion criteria included significant medical dis-
ease, history of obstructive sleep apnea syndrome,
obesity (90th percentile for weight), and cases in
which there were contraindications to inhaled anes-
thesia (e.g., malignant hyperthermia susceptibility) or
if the attending anesthesiologist did not feel that mask
induction of general anesthesia was appropriate. In
addition, in an effort to exclude children with possible
Accepted for publication October 25, 2005.
Supported by the individual departmental internal funding
mechanisms of the Department of Anesthesiology, University of
Rochester, and the Department of Anesthesiology and Critical Care,
The Children’s Hospital of Philadelphia.
Presented, in part, at the annual meeting of the Association of
University Anesthesiologists, Milwaukee, Wisconsin, May 2003.
Address correspondence and reprint requests to Ronald S. Lit-
man, DO, Department of Anesthesiology, The Children’s Hospital
of Philadelphia, 34th Street and Civic Center Boulevard, Philadel-
phia, PA 19104. Address e-mail to Litmanr@email.chop.edu.
DOI: 10.1213/01.ane.0000197695.24281.df
©2006 by the International Anesthesia Research Society
750 Anesth Analg 2006;102:750–4 0003-2999/06