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Breathing Mechanics, Dead Space and Gas Exchange in the Extremely Obese, Breathing Spontaneously and During Anaesthesia with Intermittent Positive Pressure Ventilation
Author(s) -
Hedenstierna GöraN,
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.tb05036.x
Subject(s) - dead space , medicine , anesthesia , ventilation (architecture) , tidal volume , transpulmonary pressure , general anaesthesia , breathing , arterial blood , respiratory physiology , mechanical ventilation , lung volumes , lung , respiratory system , mechanical engineering , engineering
Breathing mechanics and gas exchange were studied in 10 extremely obese subjects (average weight 138 kg) prior to and during anaesthesia with mechanical ventilation. Breathing mechanics were analysed from measurements of transpulmonary pressure (during anaesthesia, trans‐chest wall pressure as well) inspiratory gas flow and tidal volume. Gas exchange was studied by analysing inspired and expired gas as well as arterial blood samples. The total dead space was deduced from the Bohr equation, and the division into anatomical and alveolar dead space was arrived at by capnography. The patients were anaesthetised with neurolept agents and ventilated with an air‐oxygen mixture. Lung compliance during spontaneous breathing was below normal and decreased further during artificial ventilation. Chest wall compliance measured during anaesthesia was within normal limits. Lung resistance was above normal during spontaneous breathing and increased further during mechanical ventilation. Total dead space was normal during spontaneous breathing and increased moderately during artificial ventilation, the increment coming mainly from alveolar dead space. A moderate hypoxaemia was recorded during spontaneous breathing, and the alveolar‐arterial oxygen tension difference was slightly elevated. During anaesthesia this difference was markedly greater. It is concluded that the most probable reason for the relative hypoxaemia is right‐to‐left shunting.