Analysis of Autonomic Function During Anesthesia Using Response Surface Model
Condition: Anesthesia; Reaction; Autonomic Imbalance
Study type: Observational

Summary: 
      Anesthesia in the modern age is at least a two-drug process consisting of an opioid and a
      sedative hypnotic (e.g., fentanyl and propofol in combination, among others). Therefore, it
      is important to understand the interaction pharmacodynamics of these agents as they are used
      clinically. A good method for visualizing the pharmacodynamic interaction behavior of drug
      combinations is through response surface models. Unlike traditional isobolograms that
      represent the concentrations of two agents that combine to produce a single degree of drug
      effect, response surface models characterize the complete spectrum of interaction between two
      or more agents for all possible levels of concentration and effect. The investigators try to
      use the response surface model to evaluate the effect of anesthetic combination of autonomic
      system.
    

Detailed description: 
      Spectral analysis of heart rate variability (HRV) is a widely used, noninvasive technique to
      assess autonomic indexes of neural cardiac control. The presence of low-frequency (LF) and
      high-frequency (HF) oscillatory rhythms in the variability of the R-R interval (RRI) is well
      established. To date, it is believed that LF is mediated by the parasympathetic and
      sympathetic systems, whereas HF is mediated primarily by the parasympathetic system. The
      current study used HRV in order to characterize autonomic nerve system (ANS) activity in
      patients before and during stable hypnosis, nociceptive surgical stimulation and (adequate)
      or light (inadequate) analgesia. These effects may vary with the anesthetic technique used.
      Despite these previous studies, attempts to derive the relation between anesthetic
      concentrations and HRV have so far remained inconclusive. Such characterization would provide
      additional information on the behavior of the ANS during different anesthesic drug level and
      may lay the basis for the development of new clinical application.

      Propofol is now widely used in clinical practice because of its favorable recovery profile
      and low incidence of side effects. However, induction of anesthesia with propofol is often
      associated with a significant decrease in arterial blood pressure and heart rate (HR). The
      hypotensive effect of propofol has been attributed to a decrease in systemic vascular
      resistance or in cardiac output caused by a combination of venous and arterial vasodilation,
      impaired baroreflex mechanisms and depression of myocardial contractility. Besides, there are
      some conflicting data regarding the effects of propofol on cardiac sympathetic or
      parasympathetic tone.

      The investigators hypothesis was that at different propofol anesthetic drug level would have
      reproducible effects on HRV. In addition, these results should be reliably characterized in
      anesthetized patients provided that HRV uses analysis that can assess transient and rapid
      changes in ANS activity. Therefore, the first goal of this study was to test the hypothesis
      that propofol anesthesia would affect HRV depending on the concentrations, and so do opioid
      and midazolam. Second, the investigators will evaluate the effect of anesthetic combination
      of autonomic system.
    

Observational model: Case-Only
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        A prospective, observational, non-randomized study was conducted in 30 patients with
        American Society of Anaesthesiologists (ASA) physical status I who underwent elective
        surgery. Participants ages ranged from 20 to 60 years. Exclusion criteria were recent
        administration of sedative or opioid drugs, emergency surgery and impairment of renal,
        hepatic, cardiac or respiratory function. No sedative or opioid drugs were administered
        before induction of anaesthesia.