Prediction and Characterization of Acute and Chronic Postoperative Pain - a Longitudinal Observational Study of the Relationship Between Experimental Pain Modulation and Clinical Postoperative Pain in Patients Undergoing Minimally Invasive Repair of Pectus Excavatum

Despite enormous progress insufficient postoperative pain management remains a frequent problem in the early postoperative phase after surgery. Furthermore, the pain that persists after healing of the surgical wound is a large, but often unrecognized, clinical problem and it is estimated that 5-10% of those undergoing surgery will develop severe persistent pain leading to chronic disability and psychosocial distress.

Conditioned Pain Modulation (CPM), also known as the phenomenon "pain-inhibits-pain", is a reduction in pain somewhere on the body in response to the application of a second painful stimulus outside the painful area. In recent years, the CPM has been identified as a psycho-physical measure with clinical relevance in characterizing the individual's ability to modulate pain and consequently the individual's disposition to acquire painful conditions.

The purpose of this study is primarily to assess the relationship between CPM efficacy and clinical postoperative pain (postoperative pain intensity, use of analgesics, the intensity of secondary hyperalgesia and allodynia, and the incidence of persistent postoperative pain) associated with minimally invasive repair of pectus excavatum. In addition, the study aims at identifying other patient- and/or surgery-related factors affecting the course of postoperative pain.

Hypothesis:

• The greater the positive difference between the experimental pressure pain threshold (kPa) measured before and after application of a second painful stimulus (Cold Pressor Test), the lower the risk of developing persistent postoperative pain.

Secondary hypotheses

• The greater the positive difference between the experimental pressure pain threshold (kPa) measured before and after application of a different experimental painful stimulus (Cold Pressor Test) lower the pain intensity in the early postoperative period.
• The greater the positive difference between the experimental pressure pain threshold (kPa) measured before and after application of a different experimental painful stimulus (Cold Pressor Test), the shorter duration of early postoperative pain.
• The greater the positive difference between the experimental pressure pain threshold (kPa) measured before and after application of a different experimental painful stimulus (Cold Pressor Test), the lower the usage of epidural analgesia (mg / ml).
• The larger the positive difference between the experimental pressure pain threshold (kPa) measured before and after application of a different experimental painful stimulus (Cold Pressor Test) the lower consumption of oral analgesics (mg / day).
• Severe acute pain in the early postoperative period (postoperative days 0-3) is positively associated with the development of persistent postoperative pain (6 months postoperatively).
• Presence of preoperative pain and / or high postoperative use of analgesics and / or high pain intensity during the first 6-8 weeks postoperatively predicts pain 6 months postoperatively.
• The higher pain intensity and discomfort associated with brush-evoked allodynia and / or pinprick (Von Frey) secondary hyperalgesia the greater the risk for developing persistent postoperative pain (6 months postoperatively).
• High levels of preoperative catastrophizing (assessed on the day of admission) is related to the severity of acute pain (rated third postoperative day) and chronic pain (assessed 6 months postoperatively), even if controlled for depression and anxiety.
• The degree of preoperative positive and negative emotions (as assessed on the day of admission) is related to the degree of acute pain (rated third postoperative day) and chronic pain (assessed 6 months postoperatively) so that negative emotions are associated with high levels of pain, while positive feelings are related to low levels of pain.
• The study population does not differ significantly from the normal population in terms of personality traits (emotional reactions, extraversion, openness to experience, friendliness, conscientiousness).
• The study population does not experience a significant change in personality traits during the first 6 months after surgery.
• The quality of life and self-esteem is lower among patients who develop persistent postoperative pain compared with pain patients.
• Quality of life and self-esteem improve as a result of minimally invasive repair of pectus excavatum.