A single-center, pilot, prospective, randomized clinical trial with a 1:1 allocation ratio. The aim of our trial is to determine whether cryoablation of intercostal nerves provides a clinically significant analgesic effect, which is reflected in a decrease in opioid analgesics consumption and in a decrease in pain according to VAS in patients undergoing minimally invasive mitral valve surgery. To obtain preliminary data for planning a subsequent larger prospective randomized trial.

Cardiovascular diseases are one of the main causes of death worldwide. According to pathological studies, heart defects occur in 4-7% of cases, and the most common defect among the defects is damage to the mitral valve. Significant advances in surgical practice, instrumentation, tissue manipulation, and perfusion technology have made it possible to perform mitral valve surgery using mini-approaches. Minimally invasive mitral valve surgery has become the standard of care in some specialized cardiac centers around the world due to its excellent results, even despite longer cardiopulmonary bypass times and aortic occlusion. In 2008 a meta-analysis has been published in which the authors come to the conclusion that a minimally invasive approach for correcting mitral valve pathology actually has significant advantages: early activation of patients, shorter duration of stay in the recovery room, shorter wound healing times, advantages in case of repeated interventions, less the number of bleedings and purulent-septic complications compared to classical sternotomy. But despite all the advantages of this approach, severe pain after minimally invasive cardiac surgery continues to remain a serious problem. Acute pain occurs after dissection of the chest, pleura and pericardium, compression of the intercostal nerve with a retractor, as well as dissection of the intercostal and pectoral muscles during surgical access. It limits breathing and cough in the postoperative period, which can subsequently lead to hypoxemia, sputum stagnation, atelectasis, pneumonia, myocardial ischemia, slow recovery, and also an increase in the length of hospitalization. Therefore, additional emphasis and attention is paid to protocols for early functional restoration and pain reduction for this group of patients. There are protocols for "accelerated recovery after surgery" (ERAS - Enhanced Recovery After Surgery), their use makes it possible to achieve shorter stays in the intensive care unit, reduce hospitalization, improve treatment outcomes and reduce financial costs. One of the components of ERAS is the use of additional pain management modalities. However, in cardiac surgery, traditional methods of regional anesthesia, such as thoracic epidural anesthesia or paravertebral block, are not usually used due to intraoperative heparinization and the associated higher risk of spinal or epidural hematoma. Finding an optimal and effective pain management strategy for this category of patients remains an unsolved problem today.

Intercostal nerve cryoablation is considered a relatively new treatment for postoperative pain in patients undergoing minimally invasive mitral valve surgery. One of the first studies of cryoneurolysis was conducted back in 1974 in thoracic surgery. In 76 patients, the use of intercostal cryoablation resulted in a significant reduction in postoperative opioid analgesic consumption. These results were subsequently confirmed in several other studies and the data were retrospective. In 2000, a prospective randomized controlled trial was published involving 30 patients who underwent minimally invasive mitral valve surgery or minimally invasive coronary artery bypass grafting and underwent intercostal cryoablation. According to the results, a decrease in postoperative pain syndrome was observed, and less painkillers were required.

In the study in patients undergoing surgical stabilization of the ribs, cryoablation of the intercostal nerves resulted in a 25% reduction in opioid analgesics consumption compared with patients who received an extrapleural catheter, and pain scores were reduced by 22% in the cryoablation group. Similar results (cryoablation made it possible to significantly reduce morphine consumption compared to the control group and reduce pain)were also described inrecent retrospective studies through 2023 in other patient groups: patients who have undergone pulmonary resectionusing single-port thoracic video-assisted access, where cryoablation was used as a method of postoperative pain relief and patients undergoing lung transplantation.

In the other study for 2021 the use of this method in patients with lateral thoracotomy showed significant improvement in spirography parameters (FEV1, FVC) after 48 hours, as well as 30 and 60 days after surgery. Studying the influence of pain was not the main objective of this work; pain was assessed using VAS and did not show a difference. However, improvement in breathing parameters in the early postoperative period may indirectly be associated with a lower level of pain and a more comfortable state of the patient; the consumption of opioid analgesics was not properly assessed in this study.

In 2021 published a systematic review of 23 studies on the effectiveness of intercostal cryoneurolysis in patients with pectus excavatum, lateral thoracotomy, post-thoracotomy pain syndrome, traumatic rib fracture and chest wall malignancy. Most studies have demonstrated a reduction in inpatient opioid analgesic use with intercostal nerve cryoablation compared with traditional pain management techniques. In patients requiring lateral thoracotomy, intercostal cryoablation results in decreased opioid analgesic dosage (grade 2A) and improved pain scores (grade 2C) postoperatively (PICO guidelines).

Finding an effective and at the same time simple strategy for pain relief in the early postoperative period in patients undergoing minimally invasive mitral valve surgery is an urgent task; it is advisable to conduct a prospective clinical study with a well-thought-out design in this direction.

Inclusion criteria:

• Written informed consent;
• Minimally invasive mitral valve surgery.

Non-inclusion criteria:

• patient refusal;
• pregnancy;
• treatment with antidepressants or epileptic drugs;
• depression, which can significantly affect the perception of pain;
• chronic use of analgesics;
• participation in competing randomized clinical trials.

Exclusion criteria:

- Extended mechanical ventilation, more than 12 hours.