International anesthesiology clinics
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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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Int Anesthesiol Clin · Jan 1981
ReviewRespiratory and cardiovascular responses to hypoxemia and the effects of anesthesia.
The normoxic ventilatory drive contributes to the normal level of ventilation, and the hypoxic ventilatory drive contributes to the maintenance of adequate gas exchange in the presence of ventilation/blood flow maldistribution and increased mechanical load to breathing. This respiratory drive arises principally from stimuli at the carotid chemoreceptors. The reflex cardiovascular responses to hypoxia also contribute to the delivery of O2 to vital organs, and their efficacy depends on the integrity of the respiratory response and the autonomic nervous system as well as the function of the vascular system. ⋯ Hence the patient in the perioperative period continues to have impaired respiratory response to hypoxemia. As anesthetic and surgical care extends to older patients, patients with systemic disease, and recipients of cardiovascular peripheral and central drugs, the clinical implications of the impairment of ventilatory and cardiovascular responses to hypoxia, and the maintenance of organ and system function, escalate. Only a few hesitant steps have been taken into this vast arena of clinical and experimental research.