J. B. Dahl

The effect of 0.5% ropivacaine on epidural blood flow.

Twenty patients scheduled for elective abdominal surgery received epidural analgesia with 20 ml 0.5% ropivacaine or 0.5% bupivacaine. Epidural blood flow was measured by an epidural 133Xe clearance technique on the day before surgery (no local anaesthetic) and again 1 h before surgery, 30 min after injection of the local anaesthetic during continuous infusion (8 ml/h). Median initial blood flow was 5.0 ml/min and 6.0 ml/ min per 100 g tissue in patients receiving ropivacaine and bupivacaine, respectively. After epidural bupivacaine, blood flow increased in 8 of 10 patients to 6.9 ml/min per 100 g tissue (P<0.05) in contrast to a decrease in 9 of 10 patients to 3.3 ml/min per 100 g tissue after ropivacaine (P<0.05), (P<0.01 between groups). The median level of sensory analgesia was T3.5 and T4.5 in the ropivacaine and bupivacaine group, respectively (P>0.05). The demonstrated vasoconstrictor effect of epidural ropivacaine may influence the duration of its local anaesthetic effect.

Wound infiltration with ropivacaine and bupivacaine for pain after inguinal herniotomy.

In a double‐blind, randomized study, 32 patients scheduled for elective inguinal herniotomy under general anaesthesia received subcutaneous infiltration with 40 ml ropivacaine 2.5 mg/ml or bupivacaine. Postoperative pain intensity was assessed repeatedly for 24 hours at rest, during cough and movement on a visual analogue scale (VAS) and by means of pressure algometry. No differences between pain intensities or wound tenderness were found between the groups. The demand for analgesics was similar in the two groups. We conclude that incisional ropivacaine is as effective as bupivacaine in the management of post‐herniotomy pain.

Post‐operative analgesic effects of paracetamol, NSAIDs, glucocorticoids, gabapentinoids and their combinations: a topical review

In contemporary post‐operative pain management, patients are most often treated with combinations of non‐opioid analgesics, to enhance pain relief and to reduce opioid requirements and opioid‐related adverse effects. A diversity of combinations is currently employed in clinical practice, and no well‐documented ‘gold standards’ exist. The aim of the present topical, narrative review is to provide an update of the evidence for post‐operative analgesic efficacy with the most commonly used, systemic non‐opioid drugs, paracetamol, non‐steroidal anti‐inflammatory drugs (NSAIDs)/COX‐2 antagonists, glucocorticoids, gabapentinoids, and combinations of these. The review is based on data from previous systematic reviews with meta‐analyses, investigating effects of non‐opioid analgesics on pain, opioid‐requirements, and opioid‐related adverse effects. Paracetamol, NSAIDs, COX‐2 antagonists, and gabapentin reduced 24u2009h post‐operative morphine requirements with 6.3 (95% confidence interval: 3.7 to 9.0)u2009mg, 10.2 (8.7, 11.7)u2009mg, 10.9 (9.1, 12.8)u2009mg, andu2009≥u200913u2009mg, respectively, when administered as monotherapy. The opioid‐sparing effect of glucocorticoids was less convincing, 2.33 (0.26, 4.39)u2009mg morphine/24u2009h. Trials of pregabalinu2009>u2009300u2009mg/day indicated a morphine‐sparing effect of 13.4 (4, 22.8)u2009mg morphine/24u2009h. Notably, though, the available evidence for additive or synergistic effects of most combination regimens was sparse or lacking. Paracetamol, NSAIDs, selective COX‐2 antagonists, and gabapentin all seem to have well‐documented, clinically relevant analgesic properties. The analgesic effects of glucocorticoids and pregabalin await further clarification. Combination regimens are sparsely documented and should be further investigated in future studies.

Pregabalin and dexamethasone improves post‐operative pain treatment after tonsillectomy

Background: Post‐tonsillectomy pain can be severe. We investigated the analgesic effect from combinations of paracetamol, pregabalin and dexamethasone in adults undergoing tonsillectomy.

Pressure pain thresholds in volunteers and herniorrhaphy patients

Pressure algometry is a method to estimate pressure pain sensitivity in tissues. The aim of the present study was to evaluate the reproducibility of pressure pain thresholds (PPT) in the abdominal integument and to evaluate the use of pressure algometry as a measure of wound tenderness following surgery. PPT was determined in 20 healthy volunteers on two separate examinations, and in 14 patients at the incisional site before and following inguinal herniotomy. In volunteers, PPT was higher for men than for women, and no difference was observed between the first and second day of examination. In surgical patients a significant decrease in PPT was observed following operation. Morphine 0.07 mg/kg caused a slight but significant increase in PPT. Pressure algometry may be useful to study nociceptive mechanisms and the dynamics of wound pain in surgical patients.

Direct spinal effect of intrathecal acetaminophen on visceral noxious stimulation in rabbits

The aim of this study was to investigate the effect of intrathecal acetaminophen on visceral and somatic noxious stimulation in the intact, non‐anesthetized rabbit. Sixteen rabbits had intrathecal catheters implanted surgically. Visceral noxious stimulation was induced by intestinal distension of the distal colon and somatic stimulation with increasing electrical current through skin electrodes placed in either the cervical or the lumbar area. The effect on visceral noxious stimulation was assessed following intrathecal injection of 0.5, 2.5 and 5 mg of acetaminophen and following 10 and 50 mg acetaminophen intravenously. Naloxone 0.2 mg and yohimbine 0.1 mg were administered intrathecally prior to intrathecal injection of acetaminophen 5 mg. A dose‐dependent effect of intrathecal acetaminophen against the visceromotor reflex produced by intestinal distension was shown. No effects on thresholds to lumbar or cervical electrical stimulation or intestinal distension were observed following i.v. administration. Thresholds to noxious electrical stimulation were only significantly elevated at the lumbar level following i.t. injection of 5 mg acetaminophen. Naloxone failed to antagonize the effect of intrathecal acetaminophen, whereas intrathecal yohimbine attenuated the effect of intrathecal acetaminophen in both tests. In conclusion, a spinal, dose‐dependent, naloxone‐irreversible, and yohimbine‐reversible effect of intrathecal acetaminophen on electrical and visceral noxious stimulation was demonstrated.

Effect of naloxone on primary and secondary hyperalgesia induced by the human burn injury model

Background: Opioid antagonists may change the responses in models of experimental hyperalgesia. This indicates a possible involvement of the endogenous opioid system in these models. The aim of the present study was to evaluate whether activation of the endogenous opioid system could be demonstrated in the human burn injury model of cutaneous hyperalgesia, using an intravenous challenge with the non‐selective opioid antagonist naloxone.

Wound catheters for post-operative pain management: overture or finale?

Sir, Williamson and colleagues’ description of their successful use of rocuronium for rapid sequence induction with subsequent reversal using sugammadex in an obstetric cohort is interesting for a number of reasons. Firstly, the paper states that the mean duration of action of rocuronium at a dose of 1.2 mg/kg is 60–73 min and that this ‘is significantly longer than most obstetric procedures’. However, the authors’ own results demonstrate a mean time from administration to reversal of rocuronium of 62 min, which although not supporting their assertion regarding duration of obstetric procedures, does seem to provide evidence for an extended duration of action of rocuronium in the obstetric patient. Secondly, in referring to a case series of seven obstetric patients who received rocuronium at a lower dose of 0.6 mg/kg, the authors state that a dose of sugammadex of 3 mg/kg is not supported by the literature. Profound (deep) block has been described as being present when there is a post-tetanic count (PTC) of two or less for which the recommended dose of sugammadex for reversal is 4 mg/kg. Moderate (shallow) block is described as being present when the train-of-four count is two or more responses and the recommended dose of sugammadex for reversal is 2 mg/kg. Very often the block is somewhere between these points, as in Williamson et al. ‘s series where 7/17 patients had a PTC of > 2 but a train-of-four response of < 2. Consideration of dose-response curves suggests a reversal dose of 3 mg/kg may be appropriate particularly when, as in the authors’ hospital, normal practice involves careful monitoring of neuromuscular function and also bearing in mind the current expense of sugammadex. Thirdly, in discussing the use of rocuronium and sugammadex in place of suxamethonium, the authors highlight the fact that with rocuronium, multiple intubation attempts can occur without deterioration of the intubating conditions. Recently published guidelines suggest that multiple attempts at intubation in the obstetric setting are to be avoided and that each attempt should be completed within 1 min. Some authors advise no more than two attempts in the obstetric patient. Our concern is that the use of rocuronium may lead the anaesthetist to lose situational awareness and become fixated upon trying to intubate rather than proceeding along a failed intubation pathway. One could argue that the fact that suxamethonium wears off spontaneously after 7–10 mins is advantageous as this allows plenty of time for two intubation attempts and also gives a visual reminder that it is time to abandon intubation. Finally, we congratulate the authors on their work in moving forward our understanding of the place of rocuronium/ sugammadex in obstetric anaesthesia and we also look forward to further studies in this area. We declare no conflict of interest.

Effects of lidocaine aerosol on postoperative pain and wound tenderness following minor gynaecological laparotomy

Twenty‐four female patients undergoing sterilization through a minor lower laparotomy received, in a double‐blind, randomized study, either lidocaine spray 200 mg or placebo in the surgical wound. Postoperative pain intensity was evaluated on a verbal and a visual analogue scale and wound tenderness with an algometer. During mobilisation from the supine to the sitting position, VAS‐score was lower (P<0.05) in the lidocaine group 2 h postoperatively, but not 4, 6 and 8 h postoperatively (P>0.05). No significant differences were found in VAS‐scores at rest or during cough, or in verbal scale ratings during rest, cough or mobilisation, and postoperative consumption of morphine was similar in the two groups. Pressure pain thresholds were higher (P<0.05) 2 h postoperatively in the lidocaine group, but not 4, 6 and 8 h postoperatively. In conclusion, topically applied lidocaine aerosol in the surgical wound leads to very short and clinically insignificant relief of postoperative pain.

Associations between psychological variables and pain in experimental pain models. A systematic review

The association between pain and psychological characteristics has been widely debated. Thus, it remains unclear whether an individuals psychological profile influences a particular pain experience, or if previous pain experience contributes to a certain psychological profile. Translational studies performed in healthy volunteers may provide knowledge concerning psychological factors in healthy individuals as well as basic pain physiology. The aim of this review was to investigate whether psychological vulnerability or specific psychological variables in healthy volunteers are predictive of the level of pain following experimental pain models.