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Istituto di Anestesia e Rianimazione, Istituto di Ricovero e Cura a Carattere Scientifico, Ospedale Maggiore, Universita' di Milano, 20122 Milan, Italy
Received 29 March 1995; accepted in final form 23 September 1996.
Pelosi, P., M. Croci, I. Ravagnan, M. Cerisara, P. Vicardi,
A. Lissoni, and L. Gattinoni. Respiratory system mechanics in
sedated, paralyzed, morbidly obese patients J. Appl.
Physiol. 82(3): 811-818, 1997.
The effects of
inspiratory flow and inflation volume on the mechanical properties of
the respiratory system in eight sedated and paralyzed postoperative
morbidly obese patients (aged 37.6 ± 11.8 yr who had never smoked
and had normal preoperative seated spirometry) were investigated by
using the technique of rapid airway occlusion during constant-flow
inflation. With the patients in the supine position, we measured the
interrupter resistance (Rint,rs), which in humans probably reflects
airway resistance, the "additional" resistance (
Rrs) due to
viscoelastic pressure dissipation and time-constant inequalities, and
static respiratory elastance (Est,rs). Intra-abdominal
pressure (IAP) was measured by using a bladder catheter, and functional
residual capacity was measured by the helium-dilution technique. The
results were compared with a previous study on 16 normal anesthetized
paralyzed humans. Compared with normal persons, we found that in obese
subjects: 1) functional residual
capacity was markedly lower (0.645 ± 0.208 liter) and IAP was
higher (24 ± 2.2 cmH2O);
2) alveolar-arterial oxygenation
gradient was increased (178 ± 59 mmHg);
3) the volume-pressure curve of the
respiratory system was curvilinear with an "inflection" point;
4) Est,rs, Rint,rs, and
Rrs were
higher than normal (29.3 ± 5.04 cmH2O/l, 5.9 ± 2.4 cmH2O · l
1 · s,
and 6.4 ± 1.6 cmH2O · l
1 · s,
respectively); 5) Rint,rs increased
with increasing inspiratory flow, Est,rs did not change, and
Rrs
decreased progressively; and 6) with
increasing inflation volume, Rint,rs and Est,rs decreased, whereas
Rrs rose progressively. Overall, our data suggest that obese
subjects during sedation and paralysis are characterized by hypoxemia
and marked alterations of the mechanical properties of the respiratory
system, largely explained by a reduction in lung volume due to the
excessive unopposed IAP.
morbid obesity; anesthesia and paralysis; functional residual capacity; intra-abdominal pressure
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