Analysis of behavior of the respiratory system in sedated -
paralyzed morbidly obese patients: effects of flow, volume, and
time.
Pelosi, P., M. Croci, I. Ravagnan, M. Cerisara, P. Vicardi, A.
Lissoni, L. Gattinoni.
Istituto di Anestesia e Rianimazione - Universita' di Milano -
Ospedale Maggiore, IRCCS, via Francesco Sforza 35, 20122 Milano,
Italy
APStracts 3:0460A, 1996.
The effects of inspiratory flow (V) and inflation volume (DV) on the
mechanical properties of the respiratory system in eight sedated and
paralyzed postoperative morbidly obese patients ( age 37.6 11.8 yrs,
never smokers and with normal pre-operative seated spirometry) were
investigated using the technique of rapid airway occlusion during
constant flow inflation. In the supine position, we measured the
interrupter resistance (Rint,rs), which in humans probably reflects
airway resistance, the "additional" resistance (DRrs) due to
viscoelastic pressure dissipation and time constant inequalities, and
static respiratory elastance (Est,rs). Intra-abdominal pressure (IAP)
was measured using a bladder catheter and functional residual
capacity (FRC) by the helium dilution technique. The results were
compared with a previous study on 16 normal anesthetized-paralyzed
humans (D'Angelo et al., J. Appl. Physiol. 67:2556-2564,1989).
Compared to normal persons, we found that in obese subjects: 1) FRC
was markedly lower (0.645 0.208 L) and IAP 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 DRrs
were higher than normal (29.3 5.04 cmH2O.L-1 and 5.9 2.4 cmH2O.L-1.s
and 6.4 1.6 cmH2O.L-1.s, respectively); 5) Rint,rs increased with
increasing V, Est,rs did not change, and D Rrs decreased
progressively; 6) with increasing DV, Rint,rs and Est,rs decreased,
while D Rrs rose progressively. The above findings could be
interpreted in terms of the spring and dashpot model proposed by
Bates et al. (J. Appl. Physiol. 67: 2276-2285, 1989) to describe the
respiratory system. 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 intra-abdominal pressure.
Received 29 March 1995; accepted in final form 23 September 1996.
APS Manuscript Number A352-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996