Epidural sufentanil provides better analgesia from 24 h after surgery compared with epidural fentanyl in children

Mechanisms and treatment of opioid-induced pruritus: Peripheral and central pathways

BACKGROUND AND OBJECTIVE

Pruritus (also known as itch) is defined as an unpleasant and irritating sensation of the skin that provokes an urge to scratch or rub. It is well known that opioid administration can cause pruritus, which is paradoxical as itch and pain share overlapping sensory pathways. Because opioids inhibit pain but can cause itching. Significant progress has been made to improve our understanding of the fundamental neurobiology of itch; however, much remains unknown about the mechanisms of opioid-induced pruritus. The prevention and treatment of opioid-induced pruritus remains a challenge in the field of pain management. The objective of this narrative review is to present and discuss the current body of literature and summarize the current understanding of the mechanisms underlying opioid-induced pruritus, and its relationship to analgesia, and possible treatment options.

RESULTS

The incidence of opioid-induced pruritus differs with different opioids and routes of administration, and the various mechanisms can be broadly divided into peripheral and central. Especially central mechanisms are intricate, even at the level of the spinal dorsal horn. There is evidence that opioid receptor antagonists and mixed agonist and antagonists, especially μ-opioid antagonists and κ-opioid agonists, are effective in relieving opioid-induced pruritus. Various treatments have been used for opioid-induced pruritus; however, most of them are controversial and have conflicting results.

CONCLUSION

The use of a multimodal analgesic treatment regimen combined with a mixed antagonist and κ agonists, especially μ-opioid antagonists, and κ-opioid agonists, seems to be the current best treatment modality for the management of opioid-induced pruritus and pain.

SIGNIFICANCE

Opioids remain the gold standard for the treatment of moderate to severe acute pain as well as cancer pain. It is well known that opioid-induced pruritus often does not respond to regular antipruritic treatment, thereby posing a challenge to clinicians in the field of pain management. We believe that our review makes a significant contribution to the literature, as studies on the mechanisms of opioid-induced pruritus and effective management strategies are crucial for the management of these patients.

Flip-Flop Phenomenon in Epidural Sufentanil Pharmacokinetics: A Population Study in Children and Infants

The aims of this study were to develop a population pharmacokinetic model of sufentanil coadministered with 0.2% ropivacaine as an epidural infusion in infants and describe the sufentanil absorption profile from epidural space. Data from 2 previously published studies were merged for analysis-20 infants aged 3-36 months receiving sufentanil as an epidural infusion and 41 children 0-17 years old receiving sufentanil as a long-term intravenous infusion. A population nonlinear mixed-effects model was built in NONMEM. Sufentanil pharmacokinetics were described by a 2-compartment model with first-order absorption. The effect of body size on all volume and clearance parameters was included in the model according to allometric scaling with theoretical exponents. The maturation process of metabolic clearance was described by the Hill model. During the model-building process the population was divided into 2 fractions with different typical values of metabolic clearance (CL1 and CL2). The typical values of systemic clearance scaled to a 70-kg patient for the 2 subpopulations were CL1 = 52.6 L/h and CL2 = 158 L/h. The parameters of the Hill function were 54.9 weeks for the postmenstrual age of 50% clearance maturation and 0.802 for the Hill coefficient. The typical values of distribution clearance and volumes of the central and peripheral compartments for a patient with a weight of 70 kg were Q = 40.5 L/h, VC = 7.63 L, and VT = 473 L, respectively. The value of the absorption rate constant from the epidural space was 0.0459/h, which suggests flip-flop pharmacokinetics of sufentanil after epidural administration.

Estimation of the plasma effect site equilibration rate constant of sufentanil in children using the time to peak effect of heart rate and blood pressure

Objectives:

Although targeting the effect site concentration may offer advantages over the traditional forms of administering intravenous anesthetics, it is not applicable for sufentanil in children because its plasma effect site equilibration rate constant (k_e0) is not known yet. We estimated k_e0 of sufentanil in children using the time to peak effect (t_peak) method.

Materials and Methods:

Under general anesthesia, sufentanil t_peak was measured after administration of a submaximal bolus dose by means of the decrease in heart rate, blood pressure and calculated approximate entropy (ApEn) of electroencephalogram in 105 children (age range: 3–11 years). k_e0 was estimated using t_peak and known sufentanil pharmacokinetic parameters in normal children.

Results:

The mean t_peaks were measured as 44 ± 22 s and 227 ± 91 s by heart rate and by mean blood pressure respectively. The estimated k_e0 were 5.16/min and 0.49/min by heart rate and blood pressure respectively. t_peak could not be measured using the ApEn, thus k_e0 could not be calculated by ApEn in children.

Conclusions:

Shorter measured sufentanil t_peak by heart rate compared to blood pressure indicate that the heart rate decrease faster than decreasing of blood pressure. Moreover, the calculated sufentanil k_e0 in children depends on the pharmacodynamics parameters.

Pharmacokinetics of sufentanil administered with 0.2% ropivacaine as a continuous epidural infusion for postoperative pain relief in infants

BACKGROUND AND OBJECTIVES

Our objective was to assess plasma sufentanil concentrations and postinfusion pharmacokinetics in infants receiving 0.2% ropivacaine with sufentanil as a continuous epidural infusion for postoperative pain relief.

METHODS

With consent of local ethics committee and informed parental consent, 20 infants 3-36 months old (m.o.) (median 9.3 m.o., 9.0 [3.5-15] kg, ASA PS I/II) were enrolled. Epidural catheter was placed under general anesthesia in L3-L4, L4-L5, or L2-L3 interspace and threaded not farther than 4 cm into epidural space. After initial bolus of 0.2% ropivacaine, 0.5 ml·kg(-1) and sufentanil 200 ng·kg(-1) , continuous infusion of 0.2% ropivacaine, 0.3 mg·kg(-1) ·h(-1) with sufentanil 112 ng·kg(-1) ·h(-1) was started. For the postoperative period, sufentanil dose was reduced to 37 ng·kg(-1) ·h(-1) . Blood samples were drawn at the end of surgery, 24 h later, by the end of 2nd day of infusion and after 3, 6, and 18 h from the end of infusion. Sufentanil was measured using liquid-liquid extraction (LLE) procedure and HPLC-MS/MS method with LOQ = 5 pg·ml(-1) .

RESULTS AND CONCLUSIONS

Elimination of sufentanil following epidural administration was very slow, with MRT = 28.25 [18.36-44.75] h and t1/2 MRT  = 19.57 [12.72-31.01] h. In infants, during a long-term infusion of sufentanil with ropivacaine, the opioid concentration in plasma increases during the postoperative infusion itself, then increases even further after discontinuation of the infusion, in some cases reaching the values consistent with a potential risk of respiratory depression. Meticulous monitoring of the infants' vital signs is therefore mandatory not only during the infusion, but also for several hours after its discontinuation.

Adjuvants in pediatric regional anesthesia

SUMMARY Local anesthetics have a limited duration of action. Adjuvants are used to prolong the duration of action and to augment analgesia allowing lower concentrations of local anesthetic to be used. Adjuvants have been used more extensively with neuraxial blocks, particularly caudal epidural blocks, but more recently to supplement peripheral nerve blocks. Intrathecal adjuvants are not covered in this review since spinal anesthesia is not widely used in children except in ex-premature infants. Morphine is the historical gold-standard with which other adjuvants are compared. Clonidine is most useful and is becoming increasingly popular, while the side-effect profile of other agents reduces their utility. Concerns with regard to the neurotoxicity of ketamine in animal models has led to its withdrawal in some countries.

Drug therapy for preventing post-dural puncture headache

BACKGROUND

Post-dural (post-lumbar or post-spinal) puncture headache (PDPH) is one of the most common complications of diagnostic, therapeutic or inadvertent lumbar punctures. Many drug options have been used to prevent headache in clinical practice and have also been tested in some clinical studies, but there are still some uncertainties about their clinical effectiveness.

OBJECTIVES

To assess the effectiveness and safety of drugs for preventing PDPH in adults and children.

SEARCH METHODS

The search strategy included the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library 2012, Issue 5), MEDLINE (from 1950 to May 2012), EMBASE (from 1980 to May 2012) and CINAHL (from 1982 to June 2012). There was no language restriction.

SELECTION CRITERIA

We considered randomised controlled trials (RCTs) that assessed the effectiveness of any drug used for preventing PDPH.

DATA COLLECTION AND ANALYSIS

Review authors independently selected studies, assessed risks of bias and extracted data. We estimated risk ratios (RR) for dichotomous data and mean differences (MD) for continuous outcomes. We calculated a 95% confidence interval (CI) for each RR and MD. We did not undertake meta-analysis because participants' characteristics or assessed doses of drugs were too different in the included studies. We performed an intention-to-treat (ITT) analysis.

MAIN RESULTS

We included 10 RCTs (1611 participants) in this review with a majority of women (72%), mostly parturients (women in labour) (913), after a lumbar puncture for regional anaesthesia. Drugs assessed were epidural and spinal morphine, spinal fentanyl, oral caffeine, rectal indomethacin, intravenous cosyntropin, intravenous aminophylline and intravenous dexamethasone.All the included RCTs reported data on the primary outcome, i.e. the number of participants affected by PDPH of any severity after a lumbar puncture. Epidural morphine and intravenous cosyntropin reduced the number of participants affected by PDPH of any severity after a lumbar puncture when compared to placebo. Also, intravenous aminophylline reduced the number of participants affected by PDPH of any severity after a lumbar puncture when compared to no intervention, while intravenous dexamethasone increased it. Spinal morphine increased the number of participants affected by pruritus when compared to placebo, and epidural morphine increased the number of participants affected by nausea and vomiting when compared to placebo. Oral caffeine increased the number of participants affected by insomnia when compared to placebo.The remainder of the interventions analysed did not show any relevant effect for any of the outcomes.None of the included RCTs reported the number of days that patients stayed in hospital.

AUTHORS' CONCLUSIONS

Morphine and cosyntropin have shown effectiveness for reducing the number of participants affected by PDPH of any severity after a lumbar puncture, when compared to placebo, especially in patients with high risk of PDPH, such as obstetric patients who have had an inadvertent dural puncture. Aminophylline also reduced the number of participants affected by PDPH of any severity after a lumbar puncture when compared to no intervention in patients undergoing elective caesarean section. Dexamethasone increased the risk of PDPH, after spinal anaesthesia for caesarean section, when compared to placebo. Morphine also increased the number of participants affected by adverse events (pruritus and nausea and vomiting)There is a lack of conclusive evidence for the other drugs assessed (fentanyl, caffeine, indomethacin and dexamethasone).These conclusions should be interpreted with caution, owing to the lack of information, to allow correct appraisal of risk of bias and the small sample sizes of studies.

A systematic review of faces scales for the self-report of pain intensity in children

CONTEXT

Numerous faces scales have been developed for the measurement of pain intensity in children. It remains unclear whether any one of the faces scales is better for a particular purpose with regard to validity, reliability, feasibility, and preference.

OBJECTIVES

To summarize and systematically review faces pain scales most commonly used to obtain self-report of pain intensity in children for evaluation of reliability and validity and to compare the scales for preference and utility.

METHODS

Five major electronic databases were systematically searched for studies that used a faces scale for the self-report measurement of pain intensity in children. Fourteen faces pain scales were identified, of which 4 have undergone extensive psychometric testing: Faces Pain Scale (FPS) (scored 0-6); Faces Pain Scale-Revised (FPS-R) (0-10); Oucher pain scale (0-10); and Wong-Baker Faces Pain Rating Scale (WBFPRS) (0-10). These 4 scales were included in the review. Studies were classified by using psychometric criteria, including construct validity, reliability, and responsiveness, that were established a priori.

RESULTS

From a total of 276 articles retrieved, 182 were screened for psychometric evaluation, and 127 were included. All 4 faces pain scales were found to be adequately supported by psychometric data. When given a choice between faces scales, children preferred the WBFPRS. Confounding of pain intensity with affect caused by use of smiling and crying anchor faces is a disadvantage of the WBFPRS.

CONCLUSIONS

For clinical use, we found no grounds to switch from 1 faces scale to another when 1 of the scales is in use. For research use, the FPS-R has been recommended on the basis of utility and psychometric features. Data are sparse for children below the age of 5 years, and future research should focus on simplified measures, instructions, and anchors for these younger children.

On the ropivacaine-reducing effect of low-dose sufentanil in intrathecal labor analgesia

BACKGROUND

Combining ropivacaine with sufentanil for intrathecal (i.t.) analgesia in labor is well recognized, but information on dosing is limited. This study aimed to determine the ED 50 of i.t. ropivacaine and to assess the effect of adding defined low doses of sufentanil.

METHODS

This was a two-phase, double-blind, randomized and prospective study. One hundred and fifteen parturients receiving combined spinal epidural analgesia were allocated to one of four groups to receive ropivacaine or sufentanil alone or in combination. In phase one, sufentanil dose-response was calculated using logistic regression. In phase two, ED 50 of ropivacaine and of the combination with a fixed dosage of sufentanil at ED 20 and ED 40 was evaluated using the technique of up-down sequential allocation. Analgesic effectiveness was assessed 15 min after injection using a 100 mm visual analog scale, with <10 mm lasting for 45 min defined as effective. Furthermore, side effects and duration were recorded.

RESULTS

The ED 50 of i.t. ropivacaine was 4.6 mg [95% confidence intervals (95% CI) 4.28, 5.31]. Adding sufentanil at ED 20 significantly decreased the ED 50 of i.t. ropivacaine to 2.1 mg (95%CI 1.75, 2.5) (P<0.005); at ED 40, the reduction was similar (P<0.005). Combining sufentanil with ropivacaine resulted in a dose-independent prolongation of analgesia. Besides pruritus, which was well tolerated, there were no differences in side effects.

CONCLUSION

Adding sufentanil at ED 20 results in a more than 50% dose-sparing effect of ropivacaine and considerably prolongs analgesia. Increasing dosage implicates no clinical benefit.