Heart rate variability is not suitable as a surrogate marker for pain intensity in patients with chronic pain.

ABSTRACT: The search towards more objective outcome measurements and consequently surrogate markers for pain started decades ago; however, no generally accepted biomarker for pain has qualified yet. The goal is to explore the value of heart rate variability (HRV) as surrogate marker for pain intensity chronic pain setting. Pain intensity scores and HRV were collected in 366 patients with chronic pain, through a cross-sectional multicenter study. Pain intensity was measured with both the visual analogue scale and numeric rating scale, whereas 16 statistical HRV parameters were derived. Canonical correlation analysis was performed to evaluate the correlation between the dependent pain variables and the HRV parameters. Surrogacy was determined for each HRV parameter with point estimates between 0 and 1 whereby values close to 1 indicate a strong association between the surrogate and the true endpoint at the patient level. Weak correlations were revealed between HRV parameters and pain intensity scores. The highest surrogacy point estimate was found for mean heart rate as marker for average pain intensity on the numeric rating scale with point estimates of 0.0961 (95% confidence interval [CI] 0.0384-0.1537) and 0.0209 (95% CI 0-0.05) for patients without medication use and with medication, respectively. This study indicated that HRV parameters as separate entities are no suitable surrogacy candidates for pain intensity, in a population of chronic pain patients. Further potential surrogate candidates and clinical robust true endpoints should be explored, to find a surrogate measure for the highly individual pain experience.

High-frequency (10 kHz) spinal cord stimulation for the treatment of focal, chronic postsurgical neuropathic pain: results from a prospective study in Belgium.

Aim: Chronic postsurgical pain (CPSP) is a common complication of surgery. This study was conducted to evaluate the efficacy and safety of paresthesia-free, 10-kHz spinal cord stimulation (SCS) as a treatment for CPSP. Patients & methods: Subjects in this prospective, single-arm study had an average pain intensity of ≥5 cm on a 10-cm visual analog scale. The subjects who had pain relief of ≥50% (response) with temporary trial stimulation were permanently implanted with 10-kHz SCS and assessed for 1 year. Results: At 12 months, 94% of subjects were responders to 10-kHz SCS, and 88% had pain remission (visual analog scale ≤2.5 cm). Conclusion: The pain relief was durable in CPSP subjects and the safety profile of 10-kHz SCS was as expected. Clinical Trial registration number: VT005076953 (Privacy Commission of Belgium).

Conscious Sedation Using Dexmedetomidine During Surgical Paddle Lead Placement Improves Outcome in Spinal Cord Stimulation: A Case Series of 25 Consecutive Patients.

OBJECTIVES: Different anesthesia techniques are used for surgical implantation of paddle lead electrodes for neurostimulation through a laminectomy. We wanted to evaluate the use of dexmedetomidine as sedative for this procedure in a series of patients. Second, we wanted to verify whether the stimulation pattern and position of the electrode had to be changed during the procedure guided by the patient's feedback. MATERIAL AND METHODS: Twenty-five consecutive patients received surgical implantation of a spinal cord stimulation electrode under conscious sedation using dexmedetomidine and local anesthesia. We evaluated the effects of the administered drug, the patient comfort, and the adequacy of the stimulation pattern. RESULTS: Twenty-four patients completed the procedure with only dexmedetomidine and local anesthetic. Infusion was started on average 55 minutes (sd 29) prior to incision. The mean dose of lidocaine was 430 mg (sd 95). There were no significant hemodynamic changes. Median time to reach Modified Aldrete's score postoperative was 67 minutes (sd 38). In 46% of the patients, the position of the electrode was changed guided by the feedback of the patient. More than half of the patients remember most details of the procedure. Only four patients mentioned substantial discomfort and only three would definitely not want to undergo this procedure again. CONCLUSIONS: Implantation of spinal cord stimulation electrodes through a surgical laminectomy using dexmedetomidine is a safe and feasible procedure with adequate comfort for patient and surgeon. This way of working increases the optimal position of the electrode resulting in the most convenient stimulation pattern and avoiding revisions.