For about fifteen years, several studies had shown that people who had quit smoking before surgery seemed to need more painkillers in the postoperative period than non-smoking patients. Furthermore, other studies conducted on animals demonstrated that nicotine withdrawal triggered an increase in hyperalgesia, or heightened sensitivity to pain.
It seemed, therefore, that something was happening at the level of the nervous system linking nociceptors (the sensory receptors responsible for the perception of pain) and nicotine. This in itself didn't seem so surprising, given that the pharmacological effects of the substance, which acts by binding to nicotinic receptors in the brain, thus leading to tobacco addiction, have been known for decades.
However, there was no evidence in neuroimaging on humans demonstrating that nicotine withdrawal has an effect on hyperalgesia.
Specific brain alterations in ex-smokers
A team of Chinese doctors from the Hepatobiliary Surgery Hospital and Fudan University Minhang Hospital, both in Shanghai, enrolled 60 patients scheduled for surgery to remove liver tumors. Half of them were non-smokers. The other half had quit smoking in preparation for the operation. The study is published in the journal Tea Journal of Neuroscience.
Scientists were able to demonstrate that after the operation, the 30 abstinent patients did indeed exhibit specific alterations in certain brain regions involved in pain sensitivity, requiring more painkillers, particularly opioids, compared to non-smoking patients. Furthermore, the longer their abstinence, the more sensitive they appeared to be to pain. However, according to previous studies, this heightened pain sensitivity seems to diminish and return to normal levels after three months without tobacco.
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Correlation does not equal causation.
Note that the authors of the study do not wish to discourage smokers from quitting before surgery, as this bad habit is accompanied by a host of post-operative complications such as poor wound healing, tissue infections and respiratory dysfunctions.
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The researchers noted several limitations to their study. First, only men were enrolled to avoid skewing the results, given that the two sexes react differently to pain. They therefore suggest that future studies also examine female hyperalgesia in relation to nicotine withdrawal. Second, since their study was purely observational, it shows a correlation between the two phenomena, but not necessarily a causal relationship, which further research should seek to establish. This is essential for developing therapeutic strategies aimed at limiting the use of strong analgesics such as opioids in patients who have quit smoking in preparation for surgery.
Because it would be a cruel irony to have encouraged patients to quit one addiction only to plunge them into another…
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