Applied respiratory physiology

Publication date: Available online 17 January 2015 Source:Anaesthesia & Intensive Care Medicine Author(s): Derek Randles , Stuart Dabner Anaesthesia has many effects on respiratory physiology, the knowledge of which is relevant to clinical practice. Anaesthesia causes decreased muscle tone in the upper airway, which can lead to airway obstruction. Pulmonary hypoventilation occurs in the spontaneously breathing patient. There is a progressive decrease in the ventilatory response to CO2 with increasing concentration of volatile agents, and even low doses of volatile have a profound effect on the ventilatory response to hypoxia. Functional residual capacity (FRC) is significantly reduced in the anaesthetized patient. Airway closure occurs when closing capacity exceeds FRC, with a reduced FRC this is more likely to happen especially in older patients or patients with coexisting lung pathology when closing capacity may be increased. The resulting atelectasis will affect oxygenation. Respiratory system compliance reduces very early during anaesthesia and there is little difference between the paralysed and spontaneously breathing patient. Alveolar dead space is decreased due to impairment of V/Q matching. During anaesthesia venous admixture accounts for 10% of cardiac output due to increased shunt and changes in V/Q scatter. During anaesthesia and surgery patient position, type of surgery, smoking and obesity all have specific effects on respiratory physiology. Exerci...

Source: Anaesthesia and intensive care medicine - January 17, 2015 Category: Anesthesiology Source Type: research