Propofol in Obese Children

Overview

Obesity in children,as in adults,has rapidly become a public health concern. Studies in adults have shown that obesity, now considered to be a disease state, is a modifier of the effect of drugs on the body as well as how the body handles the drug.The anesthetic management of obese children poses a variety of significant challenges which include determination of the appropriate dose of anesthetic intravenous agents. Dosing of most drugs is calculated based on the effective dose in 50% of patients but the more practical and required information is the effective dose in 95%(ED95%)of patients. The aim of this study is to determine the effective dose in 95% of patients(children). The hypothesis is the ED95 of propofol in obese children will be higher than that of non-obese children.

All subjects were fasted in keeping with our institutional NPO guidelines and had IV access established in the upper extremity in the pre-anesthesia area. No pre-induction sedative drugs were administered. Routine ASA monitors were applied and in cooperative children, a bispectral index (BIS) monitor pad (Aspect Medical Systems, Inc., Shattuck, MA) was applied over the forehead. Each child was given a water-filled syringe to hold tightly in the hand contralateral to the IV site. Lidocaine 1 mg/kg IV (maximum of 60 mg) was administered to decrease pain with propofol injection. A predetermined sequential dose of propofol (Diprivan, APP Pharmaceuticals, LLC, Schaumburg, IL) was administered IV rapidly over 10 seconds, followed by a normal saline flush. Biased Coin Design An independent observer blinded to the propofol dose tested for lash reflex at 20 seconds, and also recorded the vital signs; level of sedation, using the University of Michigan sedation scale (UMSS)10; and the BIS values at 20, 60, and 120 seconds after propofol administration, along with the time the patient dropped the handheld syringe. The study was terminated after 120 seconds and additional propofol administered if needed. Both nonobese and obese patients were studied in parallel using the biased coin design (BCD), in which a certain number of dose levels (k levels) are chosen with a fixed constant interval. In the absence of dose-ranging data in obese children, we chose a low starting dose of 1.0 mg/kg for the first patient in both groups to avoid missing a desired response in this patient population. If the desired effect (loss of lash reflex at 20 seconds) was not observed, the next patient in the assigned group received the next higher dose of propofol in predetermined increments (0.25 mg/kg) from the previous dose. If the desired effect was observed, the next patient in the same assigned group was randomized with a 0.95 probability to receive the same dose or a 0.05 probability to receive the next lower dose (also in 0.25 mg/kg decrements).