Articles: general-anesthesia.
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Int Anesthesiol Clin · Jan 1981
ReviewHypoxemia and general anesthesia: an analysis of distribution of ventilation and perfusion.
There is now overwhelming evidence that anesthesia with and without muscle paralysis is associated with an increased inefficiency of gas exchange, with abnormal oxygenation and CO2 elimination. There is great variation in the degree of this change from individual to individual; it results from increased right-to-left intrapulmonary shunting, increased alveolar dead space, increased dispersion of VA/Q ratios, altered cardiac output, and changes of the ODC. In normal subjects the abnormality can be largely explained by mismatch of ventilation and perfusion. ⋯ They can persist, however, well into the postoperative period. Alterations of pulmonary function during anesthesia and surgery are rarely life threatening in the operating room. Awareness of the problems of hypoxemia during general anesthesia and an appropriate response by the anesthesiologist, however, is a prerequisite of good medical practice.
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It may be presumed that in 1979, 150 maternal deaths will occur in obstetrics (0.27 per 1000) in the Fed. Rep. of Germany, 40% of which will be due to caesarean sections. From 30% to 50% of this maternal death rate, must be related in one or another aspect to general or local anaesthesia. ⋯ Anaesthesists as well as obstetricians should be aware of the increased maternal risk from general or local anaesthesia. The maternal risk should be minimized. This can either be achieved if experienced anaesthesists only are responsible for obstetric anaesthesia (general as well as epidural, spinal etc.) if anaesthesia (general as well as local) is not considered as a comfortable service only but a strictly indicated medical procedure, and if new methods are developed to overcome the particular maternal risk in some regard.
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Pulmonary gas exchange is disturbed during general anaesthesia; both oxygenation and elimination of carbon dioxide are impaired. The shape of the chest wall alters after induction of anaesthesia-paralysis in recumbent subjects, and its motion during inspiration is also altered. The mechanical properties of lung and chest wall are also affected and FRC may be reduced. ⋯ These regions may progress into right-to-left shung during 100 per cent oxygen breathing. The low ventilation-to-perfusion regions and the shunt may both impair oxygenation. The development of lung regions with high ventilation-to-perfusion ratios after induction of anaesthesia-paralysis contributes to the inefficient elimination of carbon dioxide.