Cessation of smoking should allow for gradual improvement in lung function. Nicotine with a half-life of approximately 30-60 minutes would fall precipitously with cessation of smoking for four hours prior to administration of the anesthesia. Although of some benefit, the stimulation of the sympathoadrenal system would take longer to normalize. Carboxyhemoglobin levels should approach that of a non-smoker after a smoke free period of approximately 48 hours. This should allow for increased availability of hemoglobin for oxygen transport. The hypersecretion of mucous requires a period of approximately six weeks to decline to normal levels after cessation of smoking. Alveolar macrophage, antimicrobial function has been shown to take six months or more to improve to that of a non-smoker. Narrowing of the bronchial airways and air trapping is another problem seen with smoking. Improvement in pulmonary function test generally requires a minimum period of six weeks of abstinence.