Technological Advancements in the Objective Assessment of Nociception

Background

General anesthesia is a drug induced state, usually described as a triad of hypnosis, analgesia and paralysis (see Figure 1).

Figure 1.

General anesthesia triad of hypnosis, analgesia and paralysis, and some of the correspondent physiological signals used in clinical practice to assess the patients’ state in each component

For each component, the anesthesiologist administers specific drugs, aiming at an optimum combined state, conditioned by patient's characteristics, clinical background, and individual response to the treatment (Enderle, Blanchard, & Bronzino, 2005).

Both for the hypnosis and paralysis, simple and easy to use indexes have been developed (Jameson & Sloan 2006), nonetheless, for the analgesia component, this is still an open research question. Currently, anesthesiologists rely on physiological signals related to the autonomous nervous system to indirectly assess adequacy of analgesia (see Figure 1). Analgesia and pain are very difficult to objectively assess, and a tool, similar to what clinicians have available for the paralysis and hypnosis components, would most certainly aid them in the adequate control of this component, translating the noxious activation (nociception) and attenuation provided by the analgesic (anti-nociception), and allow for the quantification of the optimum state in the nociception/anti-nociception (Noc/ANoc) continuum, to assure patient’s homeostasis.

Nociception activity is initiated by nociceptors, sensors capable of detecting mechanical, thermal or chemical changes that rise above a certain threshold, triggering the nociceptive responses (Gannong, 2005; Rhoades & Bell, 2009), such as tachycardia, blood pressure (BP) increase, vasoconstriction, sweating, among others.

Nociception Objective Monitoring

Most of the methods proposed in the literature are based on altered cardiovascular state, and electroencephalogram (brain electrical activity, EEG) derived indexes variability in response to noxious activation. In the following subsections, the different methods proposed will be reviewed and discussed.