Application of Photo-biomodulation as Part of Multimodal Analgesia to Improve Pain Relief and Wound Healing for Patients Having Elective Caesarean Section: a Randomized Controlled Trial

Background Caesarean section (CS) is the most common inpatient surgical procedure performed in Canada, with an average duration of stay of 2.7 days. Its rate continues to increase; from 28.2% in 2016-2017 to 31.0% in 2020-2021. CS is commonly performed under neuraxial anesthesia (spinal or epidural) with majority of elective CSs being carried out under spinal anesthesia. It is associated with moderate to severe pain in most women and is more severe within the first 2 days. In a large cohort study involving 1288 parturients including 391 women having caesarean delivery, the mean pain score (standard deviation) was 4.7 (2.0). In another prospective study of 195 women having elective CS under spinal anesthesia, the median (interquartile range) visual analogue score (0-100 scale) with movement was 53 (32-72). Avoidance of pain during and after CS was noted to be the topmost priority among women. Significant pain after CS not only causes maternal distress but interferes with neonatal bonding and furthermore predisposes a woman for persistent pain and postpartum depression.

Chronic or persistent pain after CS can be an important problem. As per the International Association for the Study of Pain (IASP), chronic post-surgical pain (CPSP) is defined as pain that develops on increases after a surgical procedure as identified at three months or more after surgery; localized to the area of surgery or projected to the innervation territory; and pain that is not explained by an infection, malignancy, a pre-existing pain condition or any other alternative cause.

A prospective study of 527 women noted an incidence of 18.3 %, 11.3 % and 6.8 %, respectively at 3, 6 and 12 months, and observed that more severe pain during movement within 24 h of surgery and preoperative depression were predictive of pain persistence at 6 months. A more recent prospective study of 462 women (among 621) notes an incidence of 25.5% (95% CI: 21.8-29.7) at 90 days. Presurgical anxiety (adjusted relative risk [RR] 1.03; 95%CI: 1.01-1.05), smoking (adjusted RR 2.22; 95%CI: 1.27-3.88) and severe pain in the early postoperative period (adjusted RR 2.79; 95%CI: 1.29-6.00) were predictive of CPSP. Overall, the incidence of CPSP after CS can vary between 4% to 41.8% and generally decreases over time. Although factors associated with its development are noted to be inconsistent in studies, presence of severe pain in the first 1-2 days after surgery can be noted as the most commonly identified factor. CPSP can lead to significant maternal distress, suffering, continued need and potential long-term exposure to opioids, and post-partum depression (PPD). PPD is one of the commonest maternal long-term complication after childbirth, with an incidence of around 13%, as noted in published studies and also in a large observational study. History of preoperative depression and post-surgical pain can influence the incidence of PPD. In a longitudinal study of 1288 women, there was a threefold increase in the odds of PPD (at 8 weeks) in women having severe acute postpartum pain. In studies, screening for PPD is commonly performed using the Edinburgh Postnatal Depression Scale consisting of 10 questions, and a threshold of >12 is considered as positive for PPD.

Photo-biomodulation therapy (PBMT) and pain relief Biological effects of low-level LASER therapy have been studied for various clinical indications. Over the years the differential effects of light emitting diodes (LEDs) in causing stimulatory effects including wound healing, epithelialization and angiogenesis, and deeper inhibitory doses of radiation by LASER in modulating pain signals have been recognized (19). As per the American Society for Laser Medicine and Surgery the term photo-biomodulation should be used, and PBMT is defined as a "form of light therapy that utilizes non-ionizing forms of light sources including LASERS, LEDs, and broadband light, in the visible and near infrared spectrum". PBMT has been used in many musculoskeletal conditions and in some acute pain conditions. Its proposed mechanism of action on pain and wound healing includes increased production of anti-inflammatory cytokines and local neo-angiogenesis apart from other actions.

Considering the existing limitations in multimodal analgesia and a concerted need to avoid opioids in this context, there is a greater need for non-pharmacological strategies. Photo-biomodulation therapy (PBMT) can improve pain control and wound healing. By using PBMT after surgery, the investigators have the potential to achieve better pain control and postoperative outcomes. The study aims to evaluate the effectiveness of PBMT as part of existing multimodal analgesia, so that it can be demonstrated as appropriate for clinical use. This will result in improved maternal satisfaction and wound healing; decrease the use of perioperative opioids; potentially influence a decrease in the incidence of postpartum depression and persistent pain; and overall lead to better postoperative outcomes thereby decreasing healthcare costs.