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Oxygen Transport and Venous Admixture in the Extremely Obese. Influence of Anaesthesia and Artificial Ventilation with and without Positive End‐Expiratory Pressure
Author(s) -
Santesson Joakim
Publication year - 1976
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1976.tb05055.x
Subject(s) - medicine , anesthesia , functional residual capacity , oxygenation , ventilation (architecture) , oxygen , positive end expiratory pressure , oxygen tension , artificial ventilation , fraction of inspired oxygen , mechanical ventilation , lung volumes , lung , respiratory disease , chemistry , mechanical engineering , organic chemistry , engineering
Eight extremely obese patients (mean weight 136 kg) were studied when awake and breathing air, and during anaesthesia with controlled ventilation (oxygen fraction in inspirate (F i o 2 ): 0.5). During anaesthesia, the patients were first studied with zero end‐expiratory pressure (ZEEP) ventilation. Then two different positive end‐expiratory pressures (PEEP) were applied, 10 cmH 2 O and 15 cmH 2 O 2 in order to study the effect of an increase in functional residual capacity (FRC). Arterial oxygenation and oxygen availability, as well as cardiac output (Q t ) and venous admixture (Q s /Q t ) were studied. With the institution of anaesthesia and ZEEP, the alveolar arterial oxygen tension difference (P(A‐a)o 2 ) rose from 3.5 ± 1.1 to 28.4 ± 2.6 kPa, and the oxygen availability fell from 1346 ± 222 to 1039 ± 239 ml/min, due to the additive effect of an increase in Q s /Q t from 10 ± 4 to 21 ± 5% and a fall in Q T , from 7.7 ± 1.2 to 5.5 ± 1.1 l/min. With increasing levels of PEEP, despite a fall in P(A‐a)o 2 , there was a reduction in oxygen availability. This was due to simultaneous reduction in Q s /Q t and Q T . At a PEEP of 15cmH 2 O, the P(A‐a)o 2 was 21.2 ± 7.1 kPa, oxygen availability 862 ± 170 ml/min, Q s /Q t 13 ± 4 and Q T 4.4 ± 0.6 I. It is concluded that PEEP ventilation significantly reduces Q s /Q t in extremely obese patients during anaesthesia and should be used in these patients if there is arterial hypoxemia despite a high F i o 2