Robotic surgery elicited a lower increase in salivary amylase compared to laparoscopic surgery when adjusted to individual surgeon stress response, indicating that robotic surgery may be less physiologically stressful than laparoscopic surgery. Comfort with complex laparoscopic cases was also associated with decreased amylase during robotic surgery, indicating that previous experience with laparoscopic surgery may be helpful prior to using the robotic platform. Changes in salivary cortisol were not significantly different between laparoscopic and robotic surgical cases, which may be due to underlying differences in what cortisol truly measures or a decreased reactivity to stress compared to amylase.
Robotic surgery has increased in use across surgical specialties, despite many studies concluding that there is no significant difference in postoperative outcomes between laparoscopic and robotic surgery.[3, 14, 15] In fact, some studies have concluded that robotic surgery leads to increased operative length and increased operative cost, with the funds required to set up robotic surgery being as high as $2 million.[16] Despite this, there are benefits to the surgeon that could ultimately positively impact patient care. It is estimated that by 2030, surgeon shortages could increase clinical workload for practicing surgeons by an additional 10–50% wRVUs.[17] In the United States, nearly one third of practicing surgeons are over 55 years old, and the trend of the aging surgeon is expected to continue.[18] As expectations to continue operating to meet the demands of an aging population grow, robotic surgery and other modalities that reduce physical stress and promote superior ergonomics may help to safely extend surgical career longevity.
Although previous studies have compared the differences in ergonomic and musculoskeletal strain between laparoscopic and robotic surgery, little data exists on the differences in physiological stress levels between each surgical modality.[5] Most comparative studies completed have utilized electromyography (EMG) data as a proxy for physical demand and the NASA Task Load Index (NASA TLX) as a proxy for mental demand.[4] One recent study by Krämer et al. aimed to compare surgeon stress in conventional vs robot assisted laparoscopic hysterectomy by collecting EMG data in combination with heart rate and found mixed results, as musculoskeletal stress during robotic hysterectomy was decreased in arm and neck muscles but increased in finger muscles. Additionally, heart rate was significantly lower during robotic hysterectomy, while mental workload was found to be significantly lower during laparoscopic hysterectomy.[19] Additionally, Mazella et al. compared surgeon stress during open or robot-assisted lung resections and utilized heart rate, respiratory rate, body temperature, and oxygen saturation as proxies for autonomic nervous system response in conjunction with psychological stress questionnaires. Mazella et al. found that robot-assisted lung resection had decreased autonomic responses in comparison to open approaches, supporting the idea that robotic surgery may be less stressful for surgeons.[20]
Given the equipment necessary to examine physical demand, such as EMG, we chose to use saliva to measure physiological stress in the operating room. Salivary amylase has been utilized in other fields to measure physiologic stress as a proxy for autonomic nervous system response but has not been used to measure stress during surgical cases.[12, 21] Notably, the use of salivary amylase as a biomarker for stress has been analyzed in various studies that noted a significant decrease in salivary amylase levels following stress-reductive activities such as meditation, mindfulness-based interventions, relaxation training, and yoga.[21] Studies have also noted that salivary amylase levels are increased in both laboratory-induced stressful situations and in groups experiencing stress such as pediatric burn patients subject to burn wound care procedures and wound dressing changes.[22, 23] Finally, a study by Vente et al also suggests that those subject to chronic stress, such as those diagnosed with burnout, experience blunted salivary amylase reactivity in response to stress and therefore lower basal levels of salivary amylase.[24] Our study found a significant difference in change in salivary amylase levels between robotic and laparoscopic surgery, indicating that robotic surgery may be less stressful for the surgeon in comparison to laparoscopic surgery. Reduced stress during surgery could potentially help reduce intraoperative mistakes and increase surgical career longevity, ultimately improving quality and access to surgical care for patients. However, it is important to note that salivary amylase levels are also impacted by factors other than stress response, including daily diurnal rhythm, exercise, radiation, and the ingestion of certain foods and beverages, such as caffeine.[23, 25–27] Salivary amylase also exhibits a diurnal rhythm with decreased levels during the first 60 minutes of the day followed by a steady rise thereafter.[23]
Cortisol has been utilized primarily as a measure of psychosocial stress hypothalamic-pituitary-adrenal-axis activity, although it has not yet been utilized to measure stress during surgical cases.[13] Salivary cortisol levels have also been used in recent years as a marker for loneliness and social isolation during COVID-19, indicating it may not solely indicate stress response. In a study by Hopf et al., higher cortisol levels were seen in single and divorced/widowed persons compared to those in relationships, indicating its use as a marker for loneliness.[28] We did not find a difference in salivary cortisol during our study. This may represent a positive for surgeons. With new research suggesting that salivary cortisol is a better measure of loneliness and social isolation, a finding of no difference means that robotic surgery is not significantly more isolating than laparoscopic surgery. Less physiologic stress and loneliness theoretically could lead to less intraoperative mistakes. In addition, studies have demonstrated that salivary cortisol level has a higher latency time to reach peak levels compared to amylase; soothing or relaxing stimuli were also found to decrease salivary amylase, but this effect did not extend to cortisol.[12] These differences in reactivity combined with individual mood such as loneliness and isolation could confound cortisol levels and contribute to why cortisol levels did not reach significance in our study. Additionally, without outside input such as stress, cortisol follows a circadian rhythm pattern and peaks early in the morning with minimal levels closer to evening.[29] This diurnal pattern may have impacted the amount by which cortisol increased during cases in the morning compared to cases completed later in the day. Given the constraints of surgery, we were unable to control for the timing of operations performed. It is also important to note that many additional factors can impact cortisol levels, including daily rhythm, caffeine ingestion, food intake, recent infection, and antibiotic and other medication use.[30, 31] In addition, the established ergonomic improvements may be beneficial to long term surgeon health. Therefore, the value of robotic surgery is not only related to patient outcomes, but long-term surgeon ability as well.
Our study has several limitations. The first is that this is an initial application of salivary amylase in the operating room. Therefore, while precedent has been made for studying physiologic stress with salivary amylase, it is possible that its application here has pitfalls unforeseen at this time. Of note, de Vente et al’s study reported a blunted salivary amylase response in individuals undergoing chronic stress.[24] Many surgeons may fit into this category depending on individual stress tolerance levels, variance in practice environments, and what point in their career a surgeon may be at. It is also difficult to control for the effect that residents and trainees may have on surgeon stress levels. Although years in practice and comfort levels with each technology were assessed to help control for stress level variation, it may be important to further analyze and control for differences in salivary amylase responses that surgeons may experience in comparison to less chronically stressed populations. Additionally, this study was not blinded, and the choice of time to collect saliva during the case was left up to the surgeon. Therefore, there is natural variability between cases. In addition to case variability, time of day can also affect both cortisol and amylase levels and was not controlled for in this experiment.[23, 29] Finally, this is only a small series of surgeons and does not represent the entire surgeon population.