1 Department of Thoracic Anaesthesia, Freeman Hospitals Trust, Freeman Road, Newcastle upon Tyne NE7 7DN, UK. 2 University Cincinnati College of Medicine, Ohio, USA. 3 Westwood, Massachusetts, USA
Corresponding author. E-mail: i.d.conacher@btinternet.com
Accepted for publication: April 2, 2003
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Abstract |
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Methods. In order to distinguish the disaggregated nociception conducted along one of three possible pathways, the vagus, the phrenic and, in this study, the intercostal nerves, data from 143 patients undergoing thoracic surgery, and that from two previously conducted studies of multimodal analgesic regimens, were reviewed. The values of one subjective outcome measure (verbal rating score) at different stress levelsat rest, on raising the arm, and on coughing (dynamic pain scores)were used to construct individuals charts (pain profiles) of the progress of pain relief over time. These were batched, and analysed using statistics of summary measures.
Results. This was a crude exercise in the handling of redundant data, but there is a suggestion that it is possible to distinguish a disaggregated route by an effect of a treatment on a mass of nociception.
Conclusions. This information could underpin a paradigm of quantum nociception, and has potential to quantify aspects of analgesia practice and current and future neurophysiological theories of pain. Prospective studies are warranted.
Br J Anaesth 2003; 91: 27981
Keywords: pain, postoperative; statistics
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Introduction |
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In thoracic surgery, there is an example of significance because of the distress caused. The different pathways involved in nociception, and which contribute to the total post-thoracotomy pain experience, typically become broken up into constituents, or disaggregated, by analgesia regimens that interfere with nociception conducted by intercostal nerves. As a result, in the absence of intercostal nerve stimulation, patients complain of, and are discomforted by, shoulder-tip pain resulting from predominance of nociception via the phrenic nerve. This classic of referred pain affects 80% of patients after posterolateral thoracotomy treated with clinically effective analgesic regimens.3 4
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Methods and results |
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The pain analogue scores (five-point verbal rating score (VRS)) were taken from two previously conducted ethically approved, double-blind placebo-controlled studies involving 143 patients, all of whom had had a posterolateral thoracotomy.5 6 All patients, as part of the test regimen or as controls, had access to a patient-controlled-analgesia system containing morphine. For each patient, a 10-h pain profile was constructed from on-the-hour VRS data at each of the three levels of stress (rest, arm movement, coughing). The area under the curve (AUC) of the pain profile was calculated and tested by analysis of variance using the Minitab statistical package.7
Statistics were prepared for each of the different types of analgesic regimen from the batched data of those from each study who, in effect, received the same analgesia regimen. These were: paravertebral block regimen (intercostal nerve blockade, labelled PVB); intrathecal fentanyl regimen (no intercostal nerve block, neuraxial opioid, labelled ITF); and patient-controlled analgesia only (non-intercostal nerve block, systemic opioid, labelled PCA).
Table 1 shows the information derived from the AUC summary measures. The mean baseline (at rest) value for each analgesic regimen has been subtracted from that when the arm movement or cough stimulus is activated. In addition, a measure of the different nociception magnitude is achieved by subtracting the value for arm movement from that on coughing for the treatment regimens ITF, PVB and PCA. There are no statistical differences in the values that represent change from rest to movement, but a highly significant change (P<0.001) in those from rest to coughing, and between movement and coughing, as a result of intercostal nerve blockade (Table 1). Quality of pain control, in terms of reduced magnitude of pain in the ITF group, was superior overall to that experienced by the other groups. However, when analysed in this fashion, it was the ITF group in which the negative value represents pain appearing to have been worse on movement rather than on coughing (3.5 vs 2.13 or 1.14)the reverse of the situation in the other groups, and of that anticipated.
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Comment |
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The null hypothesis was that it would not be possible to distinguish intercostal nerve nociception from the mass of nociception (i.e. no detectable difference between those who had intercostal nerve deafferentation and those who did not). Implicit was that the responses of patients to the requests to grade pain would be the same irrespective of the regimen or the pain-provoking stimulus; that the sentient would be unable to detect a difference between two contrived painful stimuli; and that, even if they could, the methodology of pain analogue scoring is so suspect that it would not be quantifiable. In casting doubt on the proof of the null hypothesis, it can be argued that intercostal-conducted nociception can be abstracted from that conducted by the vagus and phrenic nerves, and may be quantifiable. Besides, other intriguing issues have been raised.
Quantifying nociception could clarify the sites of action of analgesics. For example, in the field of thoracic analgesia, there has been debate about interpleural local anaesthetics. Whether action is by diffusion to intercostal nerves or on pleural sites that also feed nociception along the phrenic and vagus nerves could be demonstrated with a disaggregation methodology.
And it is not only local anaesthetic pharmacodynamics to which pain disaggregation theory could be applied. The observation that the fentanyl group were discomforted more by arm movement than coughing, in comparison to those who had intercostal nerve block or systemic opioid, is probably a reflection of the small numbers in the former and not repeatable. But it may have other significance. That fentanyl suppresses the cough reflex can be discounted. The cough manoeuvre was contrived for the studies and is not a natural observation. A distant possibility is that the dynamic pain scoring technique has shown a marker for a segmental action of opioids such as fentanyl. Also, a new problem is emerging in clinical practice that of acute tolerance to opioids following the intraoperative use of remifentanil. The descriptions of the pain experiences of some of these patients are new and there is anecdotal evidence of disaggregation phenomena to such an extent that old operations are requiring the application of novel multimodal analgesic regimens.
Applying the logic that follows from a theory based on quantum nociception extends to clarification of the activity of a third component of multimodal regimens: the non-steroidal anti-inflammatory drugs. Current belief is that these drugs reduce a nocigenic soup of inflammatory mediators. This may be a quantifiable reduction measurable with double-blind, placebo-controlled methodology. The effect and influence of pre-emptive techniques on postoperative pain could similarly be measured. Therefore, it is to be hoped that, besides enlightening the science of clinical analgesia, a paradigm of quantum nociception ultimately will lead to improvements in patient care.
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References |
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