Opioids-associated Cough:
Opioids are known to have a central antitussive effect. However, some opioids, such as alfentanil, fentanyl, and sufentanil, can produce a brief tussive effect within a few seconds of rapid intravenous bolus injection in about 50% of patients (especially smokers). This is due to chemical stimulation of opioid receptors in the smooth muscle of the trachea, bronchi and bronchioles. It is unlikely that this pulmonary chemoreflex is mediated by the vagus nerve, as it is not affected by atropine pretreatment. Instead, pretreatment with an inhaled β-2-adrenergic agonist significantly reduces the rate of cough associated with intravenous opioid injection. This opioid-associated cough is usually self-limiting. It is also related to circulation time and could serve as a clinical cue for vein-to-brain time or cardiac output (63).