Study objective: To demonstrate a favorable effect of propofol on respiratory system resistance during anesthetic induction, and to determine if generic propofol causes adverse effects on respiratory resistance.
Design: Randomized pilot study.
Setting: Anesthetic induction for elective surgery.
Patients: 27 consenting ASA physical status II and III patients with reactive airways (positive smoking history or chronic obstructive pulmonary disease), but not receiving bronchodilator therapy.
Interventions: Patients were randomized equally to one of three anesthetic induction (and maintenance) drugs: sodium thiopental, 5 mg/kg (25 microg/kg/min), generic or nongeneric propofol, 1.25 mg/kg (50 microg/kg/min). They received preinduction midazolam and fentanyl (2 mg and 150 microg) and intravenous lidocaine (0.5 mg/kg). After anesthetic induction, tracheal intubation was established, and predetermined settings for mechanical ventilation were initiated.
Measurements: Immediately after intubation, a sensor was placed on the 8-mm endotracheal tube to detect baseline airway pressure and flow. During maintenance, repeat measurements of pressure and flow were obtained at 2.5-minute intervals for 10 minutes. Respiratory system resistance was derived off-line using the isovolumetric technique.
Main results: Patients were similar across groups. The respiratory resistance measured after anesthetic induction did not differ among groups. During the maintenance infusion of thiopental or propofol, respiratory resistance increased gradually across all groups. There was no difference in the response of respiratory resistance either at induction or during the 10-minute maintenance between the generic and the nongeneric propofol groups.
Conclusions: In contrast to earlier reports, this pilot study was unable to document a difference in the respiratory resistance in patients induced with thiopental or propofol. In addition, we were unable to demonstrate any different respiratory responses between generic propofol, containing sodium metabisulfite preservative, and nongeneric propofol.