Future

Anaesthesia will surely not be left untouched by the technological revolution already reshaping it in conjunction with the medical profession. Advances in our understanding of the mechanisms of anaesthesia, during the last decades, infer far reaching implications. Both the computer-assisted pharmacokinetic modelling of intravenous anaesthesia, and the quantification of the depth of induced sleep will play an important role in remodelling anaesthesia, as we now it today.

Pharmacokinetics is the science exploring what the human body does to drugs entering it. This includes absorption, distribution, redistribution, metabolism, and excretion of the drugs in the body.¹

As a result of long years of basic and clinical research, an infusion pump incorporating a new concept called ''target controlled infusion'' (TCI) appeared on the market in 1996. Based upon the patient's age, weight, and the time requested for the onset of the drug's effect, it allows the anaesthetist to set the requested target blood concentration of the medication infused. Based on the pharmacokinetic model, it calculates the blood concentration, compares it with the requested concentration, and adjusts it to the latter by giving either more or less of the given drug, at a faster or slower rate. In addition to this, the pump monitors the amount of drug infused, as well as calculating the effect-site concentration (i.e., the concentration of the medication in the tissue or organ where the medication exerts its effect, e.g. brain tissue). It also displays the predicted time necessary for the patient to wake up, if the pump were to be switched off (i.e. when the drug's effect is over).² Despite the precision of the pharmacokinetic models around which the whole TCI concepts revolves, no two humans are identical. Therefore it is up to the anaesthetist to adjust for individual variations in pharmacokinetics, thresholds of pain and consciousness, as well as the type and length of intervention/operation. This is done by raising or lowering the target blood concentration. At present only the pharmacokinetic models for a handful of intravenous drugs are available. But surely in the future this palette will expand, to include inhalational anaesthetic drugs too.

Another field of intense clinical research, which will undoubtedly shape the future of how anaesthesia is performed, is electroencephalographic (EEG) bispectral index (BIS) analysis. This is based on the electroencephalograph which records the electric activity of the brain (so-called brain waves) through electrodes placed on the head. The bispectral index is the result of a mode of analysis of these ''brain waves''. During years of research, BIS has been shown to be greatly valuable in reflecting the level of consciousness, hypnosis (sleep) and predicting movement during anaesthesia.^3,4

Surely these two innovations both alone and in combination with each other will contribute greatly not only to our understanding of how anaesthetic drug's work, but also to the efficacy, and safety for all those undergoing a general anaesthetic in the future. Unfortunately, it will also undoubtedly make this profession less personal to some extent, but in an age of call centres with automated voice messages, online customer services this is unavoidable. All in all, with all the new solutions (including new drugs, better equipment, and more knowledge) this young specialty continues developing and thriving. The future will enable more and more people with increasingly severe combination of illnesses to undergo anaesthesia in a safer environment, with an even better outcome. This in turn will enable advances in all those specialities of medical science that work together with anaesthesia, in order to provide society with better solutions to retain and restore humanities greatest asset: health.

References:

1. Makoid M, Vuchetich P, Banakar U. Basic Pharmacokinetics, 2000.
2. Target Controlled Infusion (TCI) in anaesthetic practice. Södertälje: stra Zeneca Neuroscience, 2004.
3. Schmidlin D, Hager P, Schmid ER. Monitoring level of sedation with bispectral EEG analysis: comparison between hypothermic and normothermic cardiopulmonary bypass. British Journal of Anaesthesia 2001; 86:769-776.
4. Degoute CS, Macabeo C, Dubreuil C, Duclaux R, Banssillon V. EEG bispectral index and hypnotic component of anaesthesia induced by sevoflurane: comparison between children and adults. British Journal of Anaesthesia 2001; 86:209-212.