Anesthesia and research procedure

The trial was conducted from January 10, 2019 to March 01, 2019 at The First Affiliated Hospital of Wenzhou Medical University (Wenzhou, China). None of the patients received any premedication. In brief, a 20-gauge cannula was inserted into the dorsum of the hand of each patient and connected to a T-connector for drug administration. Standard ASA monitors were attached, including non-invasive arterial pressure, electrocardiography, and pulse oxygen saturation (SPO₂). The 84 patients were randomly and equally divided into two groups: R group for remifentanil 0.3 μg/kg (diluted to 2 ml) intravenous infusion; C group for 2 ml of NS. All patients were given oxygen via a face mask (6 L/min) before the induction of anesthesia. Injections of both two groups (remifentanil or saline) were completed within 5 s. One minute after injection, each patient was given a sufentanil bolus of 0.5 μg/kg within 5 s.

The number of coughs that occurred within 1 min after sufentanil injection were recorded and the severity was graded depending on the cough times (mild, 1–2; moderate, 3–4; and severe, ≥5).

One minute after the injection of sufentanil, etomidate 0.3 mg/kg and cisatracurium 0.15 mg/kg were given for the induction of general anesthesia irrespective of the presence or absence of cough. MAP and HR immediately before remifentanil or NS administration (T0), 3 min after administration (T1), 1 min after intubation (T2), and 3 min after intubation (T3) were recorded.

Throughout the experiment, side effects of remifentanil, such as muscle rigidity or other unintended effects were also recorded.