*Department of Anesthesia and Critical Care, Martin Luther University, Halle, Germany; †Department of Anesthesia and Critical Care, University of Chicago, Chicago, Illinois; and ‡Department of Anesthesia, Ludwig Maximilians University, Munich, Germany
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Propofol is formulated as a 1% solution in a fat emulsion (Intralipid®; KabiVitrum, Stockholm, Sweden) containing 10% soybean oil (long-chain triglycerides). On injection with propofol, 32% to 67% of patients experience moderate to severe pain (1). In previous studies, larger concentrations of free propofol in the aqueous phase of an emulsion were associated with more pain on injection (2,3). A mixture of long-chain and medium-chain triglycerides in the carrier emulsion was associated with an infrequent incidence of moderate or severe pain on bolus injection, without change in the pharmacokinetics and pharmacodynamics in volunteers (4). This prospective, randomized, double-blinded study was designed to compare the incidence and intensity of pain on injection of Lipofundin® MCT 10% (B. Braun, Melsungen, Germany) or Diprivan® 1% (AstraZeneca, Germany) in patients undergoing elective surgical procedures.MethodsAfter approval by our IRB, 152 ASA physical status I-III patients provided written informed consent and were enrolled in this study. Patients were older than 18 yr and were scheduled for elective surgical procedures. Excluded from the study were breast-feeding mothers and patients with a history of neurologic disease, preexisting renal or hepatic insufficiency or a positive pregnancy test. The patients were randomly assigned to receive Diprivan® 1% or Lipofundin® MCT 10%. The investigators and patients were blinded to the preparations. The vials and the color of the formulations were identical.Premedication was with 1–2 mg lorazepam orally 1–2 h before induction of anesthesia. Standard monitoring devices were applied in the operating room. The pain caused by insertion of an 18-gauge venous cannula into a dorsal vein of the hand was measured with a 100-mm visual analog scale (VAS) 5 min after insertion was completed.Anesthesia was induced with propofol 20 mL/min until loss of eyelash reflex. During the injection, patients were asked to describe their sensations. After loss of consciousness, fentanyl and atracurium were administered IV at the discretion of the anesthesiologist before tracheal intubation. The lungs were ventilated with oxygen and air; propofol was used for maintenance continuously at the discretion of the anesthesiologist. One hour after tracheal extubation, patients were again asked to describe on the VAS their sensation during the initial injection of propofol. These data were analyzed by χ2 and Fisher’s exact test or by the Wilcoxon’s Mann-Whitney U-test.ResultsPatient characteristics, surgical duration, and pain 5 min after cannula insertion did not differ between groups. Mean induction dose, time until loss of eyelash reflex, and dose of propofol for maintenance of anesthesia were similar in both groups. All three variables were statistically equivalent between groups. The overall frequency of side effects (breath holding, excitement, cough) did not vary between groups. With Lipofundin® MCT 10%, 2 patients (2.7%) and with Diprivan® 1%, 11 patients (14.7%) complained spontaneously of discomfort during injection (P ≤ 0.005). The intensity of discomfort was less severe in the Lipofundin® MCT 10% group than in the Diprivan® group (Table 1). According to subjective ratings of pain on the VAS, Lipofundin® MCT 10% was associated with significantly less pain (P = 0.0007) than was Diprivan® 1%. Fewer patients (10.8% vs 26%) complained during induction about episodes of pain on injection of Lipofundin® MCT 10%. The pain intensity ratings given on the VAS 1 h after tracheal extubation were significantly lower with the new formulation (median, 2 mm vs 11.5 mm). The results of the VAS ratings are summarized in Table 2.