Cardiac surgical pain: complexities of researching a complex outcome

Dear Editor,

Given the cardiac surgery associated mortality has considerably declined owing to the major refinements over the last decades, the focus is increasingly shifting towards quality improvement in the perioperative care. Appropriate to the context, an effective perioperative pain management resonates well with the growing emphasis on the patient-centered outcomes in cardiac surgical practice. Meanwhile, the cardiac surgical analgesic literature gains impetus with the advent of novel safer fascial-plane blocks [1–3], we feel motivated to elaborate on the complexities of cardiac surgical pain.

Cardiac surgical pain can be peculiarly multifactorial emanating from a wide range of factors such as the surgical incision, chest wall retraction, rib trauma, muscle layer splitting, tissue dissection, vascular cannulation puncture cutdown sites, chest tube insertion sites, and the pleural irritation. Therefore, cardiac surgical pain is far more complicated than a sternotomy or a thoracotomy pain. In this context, the results of the Korsik et al. study highlighting a non-significant difference between the sternotomy and thoracotomy subset with regard to the incidence of moderate-to-severe acute postoperative pain are indeed thought provoking [4].

Alongside a complex pattern of genesis, equally complicated can be the assessment of cardiac surgical pain as a research outcome. Talking of the intraoperative phase first, cardiac surgical analgesic research faces peculiar challenges. While the sensitivity-specificity of hemodynamic fluctuations as surrogates for intraoperative pain is generally up for a debate, the Barry et al. review remarkably delineates the challenges particular to cardiac surgery [5]. They notably caution the reliance on the hemodynamic signs of pain pre- and post-cardiopulmonary bypass (CPB) (owing to hemodynamic lability, conduction blocks, pacemakers, vasopressors-inotropes, etc.) in cardiac surgery. More importantly, there is a discernible lack of even the hemodynamic surrogates on an extracorporeal support of CPB, complicating the matter furthermore [5].

In the postoperative phase, pain is often assigned discrete scores subsequent to a rating scale in analgesia randomized controlled trials (RCTs). Ahead of the plausible subjectivities in rating, problems are only compounded amidst a post-extubation evaluation of the pain scores, given the high-risk cardiac surgical patients tend to demonstrate readiness-to-extubation at varying times in the postoperative course. This readiness-to-extubation potentially translates as the readiness to pain evaluation, as was the case in a number of existing RCTs evaluating post-extubation pain scores in adult and pediatric cardiac surgical settings [1–3]. Needless to say, extubation serves as a poor reference point for comparing postoperative pain scores between groups, particularly when a significantly lower time-to-extubation has been observed in the intervention group in the RCTs when compared to the control group [1–3]. This interdependency of outcomes can be mitigated by referencing the postoperative pain scores (albeit evaluated post-extubation) to a more predictable event in the postoperative course like the intensive care unit admission.

Pain, the fifth vital sign, is essentially a patient-centered outcome and an equally important research outcome. As the concepts of opioid-sparing transcend into the cardiac surgical arena, it only becomes imperative to reflect upon the intricate complexities of cardiac surgical pain while we ardently march ahead with researching alternative analgesic modalities.

Funding

Support was provided solely from institutional and/or departmental sources.

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Conflict of interest

The authors declare no competing interests.