Automatic Patient Controlled Analgesia Injector

Patient-Controlled Analgesia (PCA) has become accepted as an important means of self-regulated relief from post-surgical pain. In commonly used PCA systems, patients use a hand-held push-button to indicate the presence of pain and initiate a predetermined bolus of drug infusion. A disadvantage of this system is that no means is provided to accommodate variations in the intensity of pain or the sensitivity of the patient to the analgesic in use apart from the frequency of button pushing. A fixed rate background infusion is usually an option. A new adaptive PCA system is proposed to provide improved PCA through the use a variable background infusion, the provision for an extended high range of analgesic dosages and a novel handset which allows patients to rate their pain. The total system is under the control of an expert algorithm and is proposed to overcome some of the shortcomings of current systems. The specially designed handset allows patients to indicate a range of pain intensities and so vary the level of drug administration. Data derived from the handset signals provide a basis for the expert system to adapt the drug dosage to patient sensitivity as well as pain intensity. The variable background infusion is used to supplement analgesic requested by patients and is periodically adjusted by the expert algorithm. In addition an Oximeter provides direct monitoring of the patient and this safety measure allows for a wider range of adaptation under expert system control. Although clear superior pain relief from the adaptive system could not be statistically established for the small trial population, clinical trials on 20 patients at the Royal Melbourne Hospital have indicated that the system provides effective pain control and is well accepted by both patients and clinical staff.