Introduction

Acute postoperative pain is a common complication. Nevertheless, this event often remains without adequate treatment. According to the US Institute of Medicine report, 80% of patients experience acute pain after surgery [1, 2]. Inadequate treatment of pain syndrome negatively affects the quality of life, functional recovery and risk of postoperative complications [3—5].

Modern methods of treating postoperative pain are based on multimodal analgesia. The last one involves a combination of drugs with different mechanisms of action on peripheral and central nervous systems [6].

Medicines have certain side effects and risk of further resistance. Non-drug pain therapy using virtual reality (VR) is a new technology immersing the patient in a synthetic 3D space created by a special headset. This technique provides immersive multi-sensory environment that mimics the feeling of presence [7].

There are several studies evaluating VR therapy for pain management [8—10]. The mechanism of this method is not fully understood. Efficiency is associated with reduced psycho-emotional and sensory perception of pain following active distraction. This hypothesis has no contradictions, as it corresponds to the modern idea of the International Association for the Study of Pain [11].

To date, there are 2 studies evaluating the effectiveness of VR therapy after abdominal surgery. Yesilot S. et al. [12] analyzed VR therapy with immersive environment in patients undergoing gastric resection. They revealed significant decrease in pain scores without changing anxiety. Haisley B. et al. [13] found no decrease of pain syndrome and changes in consumption of opioid analgesics following VR therapy after fundoplication, paraesophageal hernia repair and esophageal myotomy. A few studies and contradictory results inspired this study.

The purpose of the study was to study the effectiveness of VR therapy as additional treatment of postoperative pain after abdominal surgery.

Material and methods

A randomized single-center clinical trial included 70 patients between March 2021 and November 2022. The local ethics committee of the Kirov Military Medical Academy approved the study (protocol No. 262 dated February 22, 2021).

Inclusion criteria: elective laparoscopic abdominal surgery under general anesthesia with mechanical ventilation, informed consent, age 18—60 years. Non-inclusion criteria: anamnestic cognitive impairment, severe visual impairment with impossible VR therapy, anamnestic data on motion sickness. Exclusion criteria: visually induced motion sickness when using immersive environment (FMS score >10), the patient’s desire to terminate the study, cancers or severe systemic diseases.

We randomized patients into 2 groups: the main (n=36) and control (n=34) ones.

Both groups were comparable in anthropometric and demographic parameters, surgical interventions (insignificant between-group differences; Fisher’s exact test p>0.05) (Table 1).

Table 1. Patient characteristics

All patients underwent general anesthesia with tracheal intubation and mechanical ventilation. Induction of anesthesia included propofol 2.0—2.5 mg/kg, fentanyl 2 μg/kg, rocuronium bromide 0.6 mg/kg, maintenance of anesthesia — insufflation of sevoflurane (0.8—1.0 MAC), intravenous fentanyl 0.1 mg every 25—30 min. Patients were weaned from ventilator at the operating theatre. Surgeries included cholecystectomy, inguinal and umbilical hernia repair. All procedures were laparoscopic.

After surgery, all patients were transferred to surgical department, and postoperative analgesia was prescribed regardless of the group (Table 2).

Table 2. Drug therapy for pain syndrome

Note. Tramadol was administered for severe pain (NRS score >6).

Technique of VR-therapy. On the eve of surgery, patients of the main group were offered to read the instructions for VR therapy device (virtual reality glasses Oculus Quest 2, Fig. 1) and choose one of three programs of virtual environment: 1) Fruit Ninja, 2) Cubism, 3 ) Nature Treks VR. The Fruit Ninja (arcade) program immerses the patient in virtual reality where he is asked to cut various vegetables with a Japanese sword. In the Cubism (puzzle) program, the patient assembles complex figures from multi-colored blocks. Nature Treks VR (exploration of tropical beaches, oceans and space) introduces the patient to various animals (>60). In addition, this program gives the opportunity to control the weather, time of day, create and change your own world.

Fig. 1. Virtual reality glasses Oculus Quest 2.

VR therapy was repeated 3, 7, and 12 hours after surgery regardless of ongoing drug treatment of pain. In the main group, we assessed pain perception before and after each course of VR therapy using numerical rating scale (NRS), in the control group — after 3, 7, 12 hours within the first day after surgery. On the next day, we analyzed severity of pain syndrome after 12 hours in both groups. The need for opioid analgesics was assessed by comparing the morphine milligram equivalent (MME). The coefficient for analysis of tramadol was 0.1 [14]. Endocrine-metabolic response was analyzed considering serum cortisol and ACTH in the morning one day before surgery and the next morning after surgery. We also analyzed complications using a 20-point fast-motion sickness scale (FMS) after each course of VR therapy and the need for antiemetic drugs (metoclopramide) after surgery.

Statistical analysis

Statistical analysis was performed using the StatPlus:mac program and the Psychometrica website (https://www.psychometrica.de/effect_size.html). We assessed distribution of quantitative variables using Shapiro-Wilk test. Considering abnormal distribution, we applied Mann-Whitney U-test and Fisher’s exact test. Differences were significant at p-value<0.05. Effect size was analyzed using the Cohen’s d coefficient (Cohen’s d — 0.2 small effect size; Cohen’s d — 0.5 medium effect size; Cohen’s d — 0.7 large effect size). Data are presented as median, 25^th and 75^th percentiles (Me (Q1; Q3)).

Results

At baseline, we analyzed serum cortisol and adrenocorticotropic hormone in the morning before surgery (Table 3). There were no significant between-group differences.

Table 3. Clinical and laboratory parameters before surgery

After VR therapy, median decrease of pain scores was 1.8 points (p=0.03; main group — 1.6 [1; 2]) (Fig. 2).

Fig. 2. NRS scores of postoperative pain after VR therapy.

The next day after surgery, NRS score of pain was 1 point less than in the control group (p=0.02; dCohen — 0.5; main group — 3 (2; 3.75); control group — 4 (3; 4)) (Fig. 3).

Fig. 3. NRS scores of postoperative pain the next day after surgery in both groups.

The need for opioid analgesics was similar (p=0.3; dCohen — 0.3; mean MME 3.05 [0; 10] and 4.06 [0; 10], respectively).

Postoperative serum cortisol significantly differed between groups (p=0.003; dCohen — 0.5). This value was higher by 70.1 nmol/l in the control group compared to the main group (∆Mecortisol=282.5 nmol/l; [208; 307] and 211.4 nmol/l [125; 300], respectively) (Fig. 4).

Fig. 4. Serum cortisol.

Serum ACTH in postoperative period was significantly lower in the main group (12 [10; 19] vs. 19 pg/ml [13; 29], p=0.004, dCohen — 0.4, ∆MeACTH).

Visually induced motion sickness developed in 8% of cases (the 1^st course — 11% [n=4]; the 2^nd course — 8% [n=3]; the 3^rd course — 6 % [n — 2]; MeFMS — 0 points; maximum 10 points). In 3 (8.3%) patients, visually induced motion sickness persisted more than after the first course. There were no differences in the incidence of visually induced motion sickness between courses of VR therapy (p=0.3). The need for antiemetics was similar (p=0.6).

Discussion

Pain management is a complex and time-consuming process. The etiology of pain syndrome after laparoscopic surgery accompanied by carboxyperitoneum is multicomponent, and postoperative pain is not always less than in open surgery [15]. Additional non-drug methods of treatment are perspective. One such approach is VR therapy. Virtual reality created by a reusable portable device has been actively studied as a component of multimodal analgesia. Its effectiveness was confirmed in various clinical studies, but there is no unambiguous interpretation of effectiveness of this method [16—18].

Analgesic effect of VR therapy is explained by modification of pain perception. VR therapy immersing the patient in artificial reality diverts attention from negative emotions that ultimately reduces emotional component of pain.

VR-therapy significantly decreased postoperative pain. Indeed, mean NRS scores decreased by 45%.

Milder pain in the main group persisted the next day after surgery. Pain index was 25% less compared to the control group (3 scores).

We found no available studies evaluating the effect of postoperative VR therapy on the need for opioid analgesics in patients undergoing abdominal surgery. Pandrangi et al. [17] revealed less need for narcotic drugs after surgical interventions on the head and neck if immersive environment was applied. According to our data, the need for opioid analgesics was 24% less in the main group, but this difference was insignificant.

Visually induced fast-motion sickness is the main undesirable effect of VR technology. In most cases, these symptoms do not require medical correction [12]. In our study, mean incidence of this complication was 8%. There are similar literature data for postoperative VR therapy [19, 20]. VR therapy did not increase the need for antiemetic drugs. Symptoms of visually induced fast-motion sickness regressed without therapy.

Elevated serum cortisol and adrenocorticotropic hormone indirectly indicate emotional stress and pain [21]. We observed significant between-group difference in serum cortisol and ACTH that confirmed positive analgesic effect of VR therapy (∆Mecortisol and ∆MeACTH were lower by 25% and 36% in the main group, respectively).

Conclusion

We found different effectiveness of postoperative pain relief with and without VR therapy. The FMS score was lower by 25% in the main group. Serum cortisol (∆Mecortisol) and ACTH (∆MeACTH) in the main group also indicated effectiveness of this approach. VR-therapy reduces postoperative pain and endocrine-metabolic response.

The authors declare no conflicts of interest.