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Searching for a Pain Indicator - Statistical Analysis of Variance in Anesthesia


E. Zanderigo

vol. AUT05-12

Nowadays, one important issue in providing adequate anesthesia in the surgical theater is the lack of a pain sensor for the unconscious patient. Goal of this study is to analyze vital signs of volunteers under anesthesia subject to painful stimulation to possibly identify a measurable reaction corresponding to the painful experiences. Twenty volunteers were enrolled in the study. Each volunteer was anesthetized and received one analgesic and one hypnotic drug in varying levels. Several painful stimulations were applied in randomized sequence and the volunteer's vital signs were continuously recorded. This work is dealing with the analysis of a subset of the acquired data: only one vital sign and one painful stimulation are considered in detail. According to the doctors experience and to recent literature [1], the amplitude of the pulse wave signal, referred to as PWA, seems to contain information about the body's response to painful stimulation. For the purposes of this investigation it is necessary to consider a standardized painful stimulation, to ensure that the stimulus intensity and duration are the same for all volunteers and all repetitions of the stimulation. Among the painful stimulation tested, the electrical stimulation of the ulnar nerve, referred to as ESN, fulfills requirements. Thus, this investigation aims at assessing wether the ESN induces a significant measurable change in the PWA and wether the extend of this change is influenced by the amount of the analgesic and the hypnotic drugs administered. The statistical analysis of variance was performed taking also into account inter-patient variability and fatigue as additional relevant factors. The results evidenced a significant decrease in the PWA in correspondence of each ESN stimulus, consistent with clinical experience. The extend of the pain-induced decrease was found to be dependent on the subject's sensitivity, the degree of fatigue and on the combined administered drug concentrations. As expected, higher drug concentrations in the body decrease the severity of the response to the stimulation. From the analysis, analgesic and hypnotic drugs are interacting in a synergistic manner in reducing the amount of the pain-induce PWA change. Further studies will be necessary to better assess the kind of this interesting and clinically relevant interaction. In addition, further research will have to investigate the other vital signs or a combination of them to identify the signal best related to the pain feeling of the patient.


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(04)Technical Report

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% Autogenerated BibTeX entry
@TechReport { Xxx:2005:IFA_2250,
    author={E. Zanderigo},
    title={{Searching for a Pain Indicator - Statistical Analysis of
	  Variance in Anesthesia}},
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