Background: To avoid negative effects of painful stimuli under general anesthesia, an adequate analgesia is needed. Since both overdosing and underdosing of analgesics may lead to negative consequences, an optimal dosing is crucial, requiring a continuous monitoring of the balance between the ongoing nociception and the level of analgesia.
Methods: This review describes current methods for the monitoring of nociception and analgesia as well as their inherent differences.
Results: Monitors of nociception register organic responses that are triggered through painful stimuli and therefore allow the detection of phases of excessive nociception during inadequate analgesia. In contrast, monitors of analgesia register nociception-specific organic responses that are triggered through test stimuli and allow a preemptive adaption of the level of analgesia, before a painful clinical stimulus is applied, but require the application of test stimuli. Preliminary proof-of-concept studies were able to demonstrate the potential of the here described methods; however, an effect on the clinical outcome of patients has not yet been shown for either of the two types of monitoring.
Conclusions: For the routine application of monitors of nociception and analgesia in daily clinical practice, large clinical studies are necessary, proving a positive outcome effect. Without reliable parameters for nociception and analgesia it was hitherto impossible to perform such studies. The progress made in recent years generates optimism that in the not too distant future the currently available methods to monitor nociception and analgesia might improve to a level of reliability to allow them to be used to investigate the clinical outcome relevance of nociception and analgesia.
Keywords: Analgesia; Depth of anesthesia; Monitoring; Nociception; Pain.