Influence of variations in arterial PCO2 on surgical conditions during laparoscopic retroperitoneal surgery

BACKGROUND

Although deep neuromuscular block (post-tetanic-count 1-2 twitches) improves surgical conditions during laparoscopic retroperitoneal surgery compared with standard block (train-of-four 1-2 twitches), the quality of surgical conditions varies widely, often related to diaphragmatic contractions. Hypocapnia may improve surgical conditions. Therefore we studied the effect of changes in arterial carbon dioxide concentrations on surgical conditions in patients undergoing laparoscopic surgery under general anaesthesia and deep neuromuscular block.

METHODS

Forty patients undergoing elective laparoscopic surgery for prostatectomy or nephrectomy received propofol/remifentanil anaesthesia and deep neuromuscular block with rocuronium. Patients were randomized to surgery under hypocapnic or hypercapnic conditions. During surgery, the surgical conditions were evaluated using the 5-point Leiden-Surgical Rating Scale (L-SRS) ranging from 1 (extremely poor conditions) to 5 (optimal conditions) by the surgeon, who was blinded to group.

RESULTS

Mean (sd) arterial carbon dioxide concentrations were 4.5 (0.6) [range: 3.8-5.6] kPa under hypocapnic and 6.9 (0.6) [6.1-8.1] kPa under hypercapnic conditions. The L-SRS did not differ between groups: 4.84 (0.4) [4-5] in hypocapnia and 4.77 (0.4) [3.9-5] in hypercapnia. Ninety-nine percent of ratings were good or excellent irrespective of treatment.

CONCLUSIONS

Deep neuromuscular block provides good to optimal surgical conditions in laparoscopic retroperitoneal urological surgery, independent of the level of arterial [Formula: see text].

CLINICAL TRIAL REGISTRATION

NCT01968447.

A randomized controlled trial and novel mathematical analysis of the analgesic effect of oxycodone versus paracetamol orodispersible tablets

BACKGROUND

For effective treatment of acute pain, a rapid onset of action is important. Here we quantify the antinociceptive profile of an orodispersible oxycodone tablet (OOT) in a randomized, double-blind, active comparator (paracetamol orodispersible tablet, POT), crossover study design in a population of healthy volunteers.

METHODS

Twelve female volunteers were randomized to receive 20 mg OOT and 500 mg POT sublingually on two occasions. The electrical pain threshold (EPTh), electrical pain tolerance (EPTol) and pressure pain threshold (PPT) were obtained at regular intervals for 5 h. Time-response data were analysed with a longitudinal pharmacodynamic model characterized by rate constants for analgesia onset (kON ), offset (kOFF ), potency parameter (EFF) and validated with a bootstrap analysis. Values are the median (95% CI) as derived from the bootstrap analysis.

RESULTS

OOT produced a rapid increase in response values. For electrical pain analgesia onset, t½kON , 44 (25-67) versus analgesia offset, t½kOFF , 156 (63-552) min, p < 0.01. For pressure pain, t½kON equalled t½kOFF : 30 (16-48) min. OOT was most potent on EPTol: EFF 0.95 (0.39-1.71), p < 0.01, with similar potencies on EPTh, 0.43 (0.19-0.87) and PPT, 0.40 (0.21-0.67). Paracetamol displayed 14% of the analgesic efficacy of oxycodone.

CONCLUSIONS

The analgesic effect of orodispersible oxycodone was successfully quantified using a mathematical model of analgesia evolution. This method allows quantification of a variety of responses times from sparse data sets. Response times as defined by a 30% increase in response thresholds varied significantly among end points: EPTol 15 min, PPTh 18 min and EPTh 41 min.

Tapentadol potentiates descending pain inhibition in chronic pain patients with diabetic polyneuropathy

BACKGROUND

Tapentadol is an analgesic agent for treatment of acute and chronic pain that activates the µ-opioid receptor combined with inhibition of neuronal norepinephrine reuptake. Both mechanisms are implicated in activation of descending inhibitory pain pathways. In this study, we investigated the influence of tapentadol on conditioned pain modulation (CPM, an experimental measure of endogenous pain inhibition that gates incoming pain signals as a consequence of a preceding tonic painful stimulus) and offset analgesia (OA, a test in which a disproportionally large amount of analgesia becomes apparent upon a slight decrease in noxious heat stimulation).

METHODS

Twenty-four patients with diabetic polyneuropathy (DPN) were randomized to receive daily treatment with tapentadol sustained-release (SR) [average daily dose 433 (31) mg] or placebo for 4 weeks. CPM and OA were measured before and on the last day of treatment.

RESULTS

Before treatment, none of the patients had significant CPM or OA responses. At week 4 of treatment, CPM was significantly activated by tapentadol SR and coincided with significant analgesic responses. CPM increased from 9.1 (5.4)% (baseline) to 14.3 (7.2)% (placebo) and 24.2 (7.7)% (tapentadol SR, P<0.001 vs placebo); relief of DPN pain was also greater in patients treated with tapentadol than placebo (P=0.028). Neither placebo nor tapentadol SR treatment had an effect on the magnitude of the OA responses (P=0.78).

CONCLUSIONS

Tapentadol's analgesic effect in chronic pain patients with DPN is dependent on activation of descending inhibitory pain pathways as observed by CPM responses.

CLINICAL TRIAL REGISTRATION

The study was registered at trialregister.nl under number NTR2716.

Influence of ketamine and morphine on descending pain modulation in chronic pain patients: a randomized placebo-controlled cross-over proof-of-concept study

BACKGROUND

Descending inhibition of pain, part of the endogenous pain modulation system, is important for normal pain processing. Dysfunction is associated with various chronic pain states. Here, the effect of ketamine and morphine on descending inhibition is examined using the conditioned pain modulation (CPM) paradigm in chronic neuropathic pain patients.

METHODS

CPM responses were obtained in 10 adult neuropathic pain subjects (two men/eight women). All subjects had peripheral neuropathy as defined by abnormal quantitative sensory testing. The effects of S(+)-ketamine (0.57 mg kg(-1) h(-1) for 1 h) and morphine (0.065 mg kg(-1) h(-1) for 1 h) were tested in a randomized, placebo-controlled double-blind study. CPM was measured at baseline and 100 min after the start of treatment and was induced by immersion of the leg into a cold-water bath. The test stimulus was a 30 s static thermal stimulus to the skin of the forearm.

RESULTS

Without treatment, no CPM was detectable. Treatment with ketamine, morphine, and placebo produced CPM responses of 40.2 (10.9)%, 28.5 (7.0)%, and 22.1 (12.0)%, respectively (for all treatments, CPM effect P<0.05), with no statistical difference in the magnitude of CPM among treatments. The magnitude of CPM correlated positively with the magnitude and duration of spontaneous pain relief.

CONCLUSIONS

The observed treatment effects in chronic pain patients suggest a role for CPM engagement in analgesic efficacy of ketamine, morphine, and placebo treatment.

The widely used anesthetic agent propofol can replace alpha-tocopherol as an antioxidant

The cell membrane is protected against lipid peroxidation through endogenous antioxidants such as the lipid soluble alpha-tocopherol. The anesthetic agent propofol (2,6-diisopropylphenol) has a chemical structure which is similar to alpha-tocopherol, since it also contains a phenolic OH-group. The transient protection of GSH against lipid peroxidation in control liver microsomes is not observed in microsomes deficient in alpha-tocopherol. Introducing propofol (2 and 5 microM) restored the protective effect of GSH. Similar to the control microsomes the GSH-protective effect did not occur in previously heated microsomes. These results suggest that propofol acts similarly to alpha-tocopherol as a chain breaking antioxidant in liver microsomal membranes.