In order to detect spinal cord ischemia during scoliosis surgery, many surgeons request monitoring of intraoperative sensory and motor evoked potentials. Inhaled anesthetics suppress these potentials. For that reason total intravenous anesthesia using propofol is preferred. Outside of the United States, target-controlled infusion (TCI) pumps can be used to titrate propofol infusions to achieve a target blood level. The model used for the pump’s calculations may not be as accurate for children versus adults in general, and specifically for these operations due to the amount of blood loss and large volumes of intravenous fluid use.
In “Measured Versus Predicted Blood Propofol Concentrations in Children During Scoliosis Surgery,” published in this month’s issue of Anesthesia & Analgesia, Dr. Michael R J Sury, Portex Department of Anesthesia, Great Ormand Street Hospital for Children NHS Foundation Trust, London, United Kingdom, and Institute of Child Health, University College London, London, United Kingdom, and coauthors compared measured arterial blood propofol concentrations (Cm), using a point-of-care blood propofol analyzer (the Pelorus 1500 [Sphere Medical, UK]) to predicted concentrations (Cp) in 20 children, 9 through 17 years of age, who were undergoing scoliosis surgery.
The measured propofol concentrations were usually higher than the predicted concentrations. The mean performance error was 45%, which is considered high. This error decreased over time.
The study was small and many of the children had syndromes for which the pharmacokinetic models used to predict propofol concentration might not apply. If time to wake up is the desired endpoint, perhaps electroencephalography monitors, e.g., BIS or entropy, could be just as useful, and likely less expensive than blood propofol analysis. Neither target controlled drug delivery nor point-of-care propofol analysis is available in the United States. For now all we can do in the US is watch with envy.