[Critical aspects of an outside evaluation of postoperative pain in infants. A placebo-controlled double-blind study of the question of the reliability and validity of the measurement system].

Postoperative analgesia in infants and young children is a topic of growing interest in pediatric anesthesia. Two systems measuring postoperative pain in this group of patients have been offered recently: CHEOPS (Childrens Hospital of Eastern Ontario Pain Scale) by McGrath et al. and OPS (Objective Pain Scale) by Hannallah et al. and Broadman et al. [3, 7, 8]. Both systems are economical and not reactive, but their validity is not satisfying. The validity of CHEOPS is based on the statements of experienced nurses, using the method of convergent validation by an expert's assertion. Hannallah and Broadman et al. judged the validity of their objective pain scale for infants and young children by statements of juveniles between 13 and 18 years of age. McGrath et al. accepted the item of spontaneous verbal communication as useful in the CHEOPS, although no such verbal comment occurred in their study on interrater and inter-item correlations. The aim of the present study was to evaluate the statistical qualification of items for measurements of the intensity of postoperative pain in young children and to investigate some aspects of their validity. MATERIAL AND METHODS. The study was performed in 54 children of ASA groups I and II aged 29.2 +/- 10.7 months. They were included in the study if they were pain-free before the operation and had no signs and symptoms of neurologic disease. The following operations were accepted: herniorrhapy, orchidopexy, circumcision, and umbilical herniorrhaphy. Premedication and general anesthesia were standardized. The patients were premedicated with midazolam 0.5 mg/kg rectally and subsequent intramuscular injections of ketamine 2.0 mg/kg with atropine 0.01 mg/kg. Anesthesia was induced and maintained by inhalation of oxygen/nitrous oxide and halothane (FiO2 0.3). All children were intubated and ventilation was controlled during the operation. After the operation and under steady-state anesthesia with 0.5 vol.% halothane and spontaneous respiration, the children received either nalbuphine 0.1 mg/kg, piritramide 0.1 mg/kg, or placebo in a randomized and double-blind manner. Respiratory and circulatory parameters were recorded for 15 min before anesthesia was discontinued. Five minutes after halothane had been discontinued the first measurement of the childrens' behavior was started with four subsequent measurements at fixed time intervals of 15 min. The measuring system was based on the six items of CHEOPS complemented by five items related to the waking state because it was assumed that the waking state generally modulates the child's ability to demonstrate pain. The design of the study was accepted by the ethic committee with the provision that neither a sedative nor an analgesic drug should be withheld from any child if indicated. Therefore, all children who seemed to feel discomfort according to the subjective impression of the anesthetist received midazolam intraveneously to a maximal dose of 2 mg. All the behavioral data were included in a factor analysis (principal components)...