2005 Annual Scientific Meeting - CLICK FOR PROGRAMME

Depth of Analgesia Monitoring

 Ilkka Korhonen

VTT Information Technology, Tampere, Finland

 Introduction

General anaesthesia has three partially independent components: hypnosis, paralysis, and analgesia. Analgesia means literally "no pain". However, pain is a descriptor of a conscious, emotional, private experience, generated by wide variety of events. During general anaesthesia, the conscious experience of pain disappears due to hypnosis, and surgical stimulus with its immediate consequences on system function is recognised as nociception. During surgery, the intensity of autonomic or motor output of nociception is dependent on the nociceptive-anti-nociceptive balance (NANB). The combination of autonomic, hormonal, and catabolic changes that accompany surgery has been called the surgical stress response. Severe surgical stress may lead to exhaustion of essential body reserves, which delays post-operative recovery and may be associated with increased morbidity. Physiological effects of nociception, and thereafter surgical stress, can be attenuated with analgesics. As contrast to depth of hypnosis (e.g. with BIS or spectral entropy) or level of paralysis (e.g. train-of-four) monitoring, which are monotonically dependent on the corresponding drug effects, the NANB (or depth of analgesia) monitoring is dependent on the balance between the input (noxious stimulus) and the output (the nociceptive response), and as such it is characteristically different from the two other components. Direct, clinically relevant specific indicators of the NANB during general anaesthesia do not exist. Therefore, estimation of this balance is commonly based on isolated, unspecific autonomic reactions, such as presence or absence of hypertension, tachycardia, or sweating and tearing. Heart rate variability, pulse plethysmographic (PPG) waveform, pulse transition time, skin vasomotor response, and frontal electromyography have been suggested as measures for adequacy of analgesia. Unfortunately, these measures are subjected to inter-individual variability, are rather non-specific, may lack sensitivity to actual nociception, and are generally without real predictive value. A multi-parameter approach may significantly improve the estimation of nociceptive-anti-nociceptive balance during general anaesthesia¹.

Methods

We have developed a Surgical Stress Index, SSI, which uses the heart rate and PPG wave amplitude to quantify the surgical stress responses in the cardiovascular system^2,3.

Results

In 58 females under propofol-remifentanil anaesthesia, SSI increased at skin incision (p<0.01 – p<0.05, depending on remifentanil concentration), correlated with stimulus intensity (r= 0.42, p<0.0001) and with the level of remifentanil concentration (r=-0.33, p<0.0001). In 30 females undergoing laparoscopy with propofol and remifentanil (N=15) or esmolol (N=15), SSI was similar before incision but was lower during surgery in patients receiving remifentanil⁴.

Discussion

Multiparameter approach, such as SSI, seems to offer potential for monitoring NANB and the adequacy of analgesia during surgery.

Acknowledgements

GE Healthcare Finland (Matti Huiku, Minna Kymäläinen, Panu Takala, Kimmo Uutela, Hanna Viertiö-Oja), VTT Information Technology (Mark van Gils, Heidi Yppärilä-Wolters), Tampere University Hospital (Markku Rantanen, Arvi Yli-Hankala), Helsinki University Central Hospital (Jouni Ahonen, Markku Paloheimo, Elina Seitsonen, Anne Vakkuri). 

References

1.       Seitsonen ERJ et al. Acta Anaesthesiol Scand 2005; 49: 284-92

2.       Yli-Hankala A et al. Eur J Anaesthesiol 2005;22 (suppl 34): A-111.

3.       Huiku M et al. Anesthesiology 2005; 103: A67.

4.   Ahonen J et al. Anesthesiology 2005; 103: A822.