Comparison of remifentanil versus regional anaesthesia in children anaesthetised with isoflurane/nitrous oxide. International Remifentanil Paediatric Anaesthesia Study group

Repeated complete atrioventricular block during remifentanil administration in a pediatric patient with brain tumor and acute hydrocephalus: a case report

BACKGROUND

Remifentanil, an ultra-short-acting µ-opioid receptor agonist, is commonly used for anesthetic management due to excellent adjustability. Remifentanil is known to cause sinus bradycardia, however, because it has a direct negative chronotropic effect on the cardiac conduction system and there is an indirect negative chronotropic effect via the parasympathetic nervous system.

CASE PRESENTATION

An 8-year-old Japanese boy was diagnosed with acute hydrocephalus due to a brain tumor in the fourth ventricle and underwent emergency surgery. Imaging examination showed brainstem compression. Endoscopic third ventriculostomy and ventriculoperitoneal shunt surgery were scheduled. Remifentanil was started during induction of general anesthesia, but electrocardiogram showed sinus bradycardia, then Wenckebach-type atrioventricular block, and then complete atrioventricular block. Remifentanil was immediately discontinued, and we administered atropine sulfate. Complete atrioventricular block was restored to sinus rhythm. When remifentanil was restarted, however, the electrocardiogram again showed sinus bradycardia, Wenckebach-type atrioventricular block, and then complete atrioventricular block. Remifentanil was again immediately discontinued, we administered adrenaline, and then complete atrioventricular block was restored to sinus rhythm. Fentanyl was used instead of remifentanil with continuous infusion of dopamine. There has since been no further occurrence of complete atrioventricular block.

CONCLUSIONS

This is the first known case of complete atrioventricular block in a pediatric patient with increased intracranial pressure seemingly caused by administration of remifentanil.

Remifentanil, a different opioid: potential clinical applications and safety aspects

IMPORTANCE OF THE FIELD

Opioids play an important role in every aspect of modern anesthetic practice. Remifentanil is an ultra-short-acting opioid featuring a unique pharmacokinetic profile allowing clinical versatility and improved control of its action. In this review, we assess the pharmacology of remifentanil, its clinical uses as well as safety issues on its action on the major organ systems and in particular clinical settings.

AREAS COVERED IN THIS REVIEW

A synthesis of evidence from a MEDLINE search for articles from 1993 to 2009 for available up-to-date information on remifentanil and its current applications and safety profile.

WHAT THE READER WILL GAIN

A synopsis of the unique pharmacokinetic properties of remifentanil and its action on major organ systems will provide insight on the safe and effective use of the drug in a variety of clinical settings.

TAKE HOME MESSAGE

Remifentanil is a valuable opioid in the armamentarium of the clinician, providing great clinical flexibility and safety but vigilance is required to avoid pitfalls.

Experience with remifentanil in neonates and infants

Remifentanil is a relatively new synthetic opioid, which is not licensed worldwide for neonates and infants. Because of its unique pharmacokinetic properties with a short recovery profile, it could be the ideal opioid for neonates and infants, who are especially sensitive to respiratory depression by opioids. Therefore, we conducted a MEDLINE search on all articles dealing with the use of remifentanil in this important subgroup of patients. Most experience with remifentanil in neonates and infants is as maintenance anaesthesia during surgery. In approximately 300 neonates and infants, remifentanil proved to be an effective and safely used opioid for this indication. However, very limited data exist on remifentanil for analgesia and sedation of mechanically ventilated paediatric intensive care patients. Further research with remifentanil in neonates and infants should focus on this group of patients because remifentanil, with its very short context-sensitive half-life, could result in shorter extubation times compared with commonly used opioids such as morphine or fentanyl.

Effect of remifentanil with and without atropine on heart rate variability and RR interval in children

Remifentanil can cause bradycardia either by parasympathetic activation or by other negative chronotropic effects. The high frequency (HF) component of heart rate variability (HRV) is a marker of parasympathetic activity. This study aimed to evaluate the effect of remifentanil on RR interval and on HRV in children. Forty children ASA I or II were studied after approval by the human studies committee and informed parental consent was obtained. After stabilisation at sevoflurane 1 MAC, they were randomly divided into two groups: one received a 20 microg.kg(-1) atropine injection (AT + REMI) and the other ringer lactate solution (REMI). Three minutes later, a 1 microg.kg(-1) bolus of remifentanil was administered over 1 min, followed by a continual infusion at 0.25 microg.kg(-1).min(-1) for 10 min increased to 0.5 microg.kg(-1).min(-1) for a further 10 min. A time varying, autoregressive analysis of RR sequences was used to estimate classical spectral parameters: low (0.04-0.15 Hz; LF) and high (0.15-0.45 Hz; HF) frequency, whereas the root mean square of successive differences of RR intervals (rmssd) was derived directly from the temporal sequence. Statistical analyses were conducted by means of the multiple correspondence analysis and with non parametrical tests. Remifentanil induced an RR interval lengthening, i.e. bradycardia, in both groups compared to pretreatment values and was associated with an increase of HF and rmssd only for the REMI group. The parasympathetic inhibition by atropine did not totally prevent remifentanil's negative chronotropic effect. A direct negative chronotropic effect of remifentanil is proposed.

[Anesthetic management of pediatric cleft lip and cleft palate repair]

We have developed a modern strategy for the anesthetic management of pediatric cleft lip and cleft palate repair using anesthetic drugs such as sevoflurane, desflurane, acetaminophen, remifentanil, and pirtitramide together with new techniques. It provides best conditions for the surgeon and maximum safety for the pediatric patient. A team of pediatricians, neonatologists, pediatric surgeons, and pediatric anesthetists have tackled the problem of management of children with craniofacial abnormalities such as cleft lip and cleft palate. The best and safest anesthetic techniques are outlined and the most frequent complications are discussed, e.g. management of the difficult airway, the airway in patients with complex craniofacial abnormalities, fiberoptic endotracheal intubation through a laryngeal mask, intraoperative dislocation of the endotracheal tube, postoperative airway obstruction and perioperative bleeding.

The pharmacological treatment of neonatal pain

Optimal analgesia remains a major challenge for all involved in the care of (critically) ill newborns. The rapid changes in liver metabolism involving maturation of liver enzymes and renal clearance of drugs render (extreme) very low birth weight infants different from newborns of later postconceptional age with regards to the use of opioids such as morphine and fentanyl. Acute and/or procedural pain has been investigated fairly recently in randomized controlled trials and there are now guidelines. The long-term effects of opioid use in this particular age group of vulnerable babies await further evaluation.

Remifentanil update: clinical science and utility

The anilidopiperidine opioid remifentanil has pharmacodynamic properties similar to all opioids; however, its pharmacokinetic characteristics are unique. Favourable pharmacokinetic properties, minimally altered by extremes of age or renal or hepatic dysfunction, enable easy titration and rapid dissipation of clinical effect of this agent, even after prolonged infusion. Remifentanil is metabolised by esterases that are widespread throughout the plasma, red blood cells, and interstitial tissues, whereas other anilidopiperidine opioids (e.g. fentanyl, alfentanil and sufentanil) depend upon hepatic biotransformation and renal excretion for elimination. Consequently, remifentanil is cleared considerably more rapidly than other anilidopiperidine opioids. In addition, its pKa (the pH at which the drug is 50% ionised) is less than physiological pH; thus, remifentanil circulates primarily in the non-ionised moiety, which quickly penetrates the lipid blood-brain barrier and rapidly equilibrates across the plasma/effect site interface. By virtue of these distinctive pharmacokinetic properties, the context-sensitive half-time (i.e. the time required for the drug's plasma concentration to decrease by 50% after cessation of an infusion) of remifentanil remains consistently short (3.2 minutes), even following an infusion of long duration (> or =8 hours). Remifentanil, a clinically versatile opioid, is useful for intravenous analgesia and sedation in spontaneously breathing patients undergoing painful procedures. Profound analgesia may be achieved with minimal effect on cognitive function. Remifentanil may also provide sedation and analgesia during placement of regional anaesthetic blocks, and in conjunction with topical anaesthesia and airway nerve blocks, it may be useful for blunting reflex responses and facilitating 'awake' fibreoptic intubation. Compared with fentanyl and alfentanil in a day-surgery setting, remifentanil supplementation of general anaesthesia may improve intraoperative haemodynamic control. Both emergence time and the incidence of respiratory depression during post-anaesthetic recovery may be reduced. However, outcomes such as home discharge time, post-emergence adverse effect profile, and patient and provider satisfaction are not significantly improved, and the incidence of intraoperative hypotension and bradycardia is greater. In addition, drug acquisition costs for remifentanil are higher and clinicians may need extra time to familiarise themselves with the drug's unique pharmacokinetics.Ironically, the quick dissipation of opioid analgesic effect following remifentanil discontinuation may be a significant clinical disadvantage. Unless little or no postoperative pain is anticipated, the clinician may wish to treat prospectively using local or regional anaesthesia, non-opioid analgesics, or longer-acting opioid analgesics.

The Use of Ultra-Short-Acting Opioids in Paediatric Anaesthesia

Remifentanil is a synthetic opioid that was developed in the early 1990s and introduced into clinical use in 1996. It is a methyl ester and is metabolised by nonspecific tissue and plasma esterases. Consequently, it is a drug that undergoes rapid elimination and has a reported terminal elimination half-life of between 10 and 35 minutes. Because there is no drug accumulation, the context-sensitive half-time remains constant; thus the pharmacokinetics of the drug do not change regardless of the duration of infusion. The organ-independent elimination of remifentanil, coupled with the fact that its clearance is greater in infants and neonates compared with older age groups, make its pharmacokinetic profile different from any other opioid. In addition, its unique metabolism confers predictability in its clinical use. Like other opioid mu receptor agonists, remifentanil provides dose-dependent analgesia, while the adverse effects of this drug, e.g. respiratory depression, are also thought to be dose related. The incidence of nausea and vomiting appear similar to other opioids. Its rapid and consistent metabolism regardless of duration of infusion has made remifentanil an attractive analgesic/anaesthetic option for paediatric care providers.

Haemodynamic effects of remifentanil in children with and without intravenous atropine. An echocardiographic study

BACKGROUND

Remifentanil is known to cause bradycardia and hypotension. We aimed to characterize the haemodynamic profile of remifentanil during sevoflurane anaesthesia in children with or without atropine.

METHODS

Forty children who required elective surgery received inhalational induction of anaesthesia using 8% sevoflurane. They were allocated randomly to receive either atropine, 20 microg kg(-1) (atropine group) or Ringer's lactate (control group) after 10 min of steady-state 1 MAC sevoflurane anaesthesia (baseline). Three minutes later (T0), all children received remifentanil 1 microg kg(-1) injected over a 60 s period, followed by an infusion of 0.25 microg kg(-1) min(-1) for 10 min then 0.5 microg kg(-1) min(-1) for 10 min. Haemodynamic variables and echocardiographic data were determined at baseline, T0, T5, T10, T15 and T20 min.

RESULTS

Remifentanil caused a significant decrease in heart rate compared with the T0 value, which was greater at T20 than T10 in the two groups: however, the values at T10 and T20 were not significantly different from baseline in the atropine group. In comparison with T0, there was a significant fall in blood pressure in the two groups. Remifentanil caused a significant decrease in the cardiac index with or without atropine. Remifentanil did not cause variation in stroke volume (SV). In both groups, a significant increase in systemic vascular resistance occurred after administration of remifentanil. Contractility decreased significantly in the two groups, but this decrease remained moderate (between -2 and +2 sd).

CONCLUSION

Remifentanil produced a fall in blood pressure and cardiac index, mainly as a result of a fall in heart rate. Although atropine was able to reduce the fall in heart rate, it did not completely prevent the reduction in cardiac index.

Remifentanil vs fentanyl/morphine for pain and stress control during pediatric cardiac surgery

BACKGROUND

Remifentanil is a short acting, potent synthetic opioid that does not accumulate after infusion or repeated bolus doses. It may be rapidly titrated to the requirements of individual patients. Titrated infusion of remifentanil may be able to provide potent analgesia required for pediatric cardiac surgery and obtund the stress response in theater whilst not having the persistent respiratory depression and sedation seen with longer acting opioids.

METHODS

Twenty patients were randomized to receive a titrated infusion of remifentanil (0-1 microg x kg(-1) x min(-1)) or a standard dose of fentanyl (30 microg x kg(-1)) prebypass plus morphine (1 mg x kg(-1)) on rewarming. Blood samples for glucose and cortisol were taken at regular intervals from induction through bypass and into the first 24 h of postoperative intensive care. In addition to biochemical indicators of the stress response we recorded baseline hemodynamic parameters and any acute physiological events.

RESULTS

Ten patients received morphine, seven received remifentanil. There were no statistically significant differences between the two treatment groups in cortisol measurements, mean arterial pressure or heart rate recordings. In the last time period the remifentanil group had a larger rise in blood glucose concentration (baseline 3.9, rise 3 mmol x l(-1)) than the fentanyl/morphine group (baseline 4.2 rise 1.9 mmol x l(-1)), CI -4.3 to -0.2.

CONCLUSIONS

The only significant difference was in glucose in the postbypass time periods. Although statistically significant, this difference is insufficient evidence of increased stress in the remifentanil group. The results show that in the patients studied there was no clinically important difference between the two techniques.

Remifentanil infusion for cleft palate surgery in young infants

BACKGROUND

The residual depressant effect of opioid is a major concern in infants scheduled for cleft palate repair. Remifentanil is associated with a fast and predictable recovery, independent of age.

METHODS

About 40 infants in the 2-12 month age range were prospectively enrolled in this open study, to receive either remifentanil (infusion starting at 0.25 microg x kg(-1) x min(-1)) or sufentanil as part of a balanced anaesthesia regimen. Isoflurane was maintained at an endtidal concentration of 1.2% in oxygen and nitrous oxide and the opioid dosing was titrated to autonomic responses. Postoperative pain relief was provided by morphine infusion. Morphine administration started intraoperatively in the remifentanil group.

RESULTS

Consistent haemodynamic stability was achieved throughout surgery in both groups. Infants of the remifentanil group required, on average, lower concentrations of isoflurane than children of the sufentanil group (1.2 +/- 0.2% vs 1.7 +/- 0.3%, P < 0.001). The median time from last suture to tracheal extubation was 12.5 min (5-25 min) in the remifentanil group and 15.0 min (10-30 min) in the sufentanil group. There was no evidence of hyperalgesia or enhanced morphine consumption in the remifentanil group compared with the sufentanil group. Postoperative pain scores were even lower in the remifentanil group, compared with the sufentanil group, soon after arrival in the postanaesthesia care unit.

CONCLUSIONS

Remifentanil-based anaesthesia appeared well suited for primary cleft palate repair in young infants.

The caudal catheter in neonates: where are the restrictions?

PURPOSE OF REVIEW

In neonates, epidural catheters inserted at the sacral hiatus can easily be advanced to a lumbar or thoracic level. These 'caudal catheters' are popular because they allow the neonate to benefit from epidural analgesia without the concerns of spinal cord injury potentially associated with primary thoracic placement in an asleep neonate. This review looks at use and benefits, and risks and complications of caudal epidural catheters in neonates.

RECENT FINDINGS

Restrictions of neonatal caudal catheters are related to risks associated with placement and advancement of the catheters, infectious risks of caudal catheters, and toxicity risks related to the higher free fraction and lower clearance of bupivacaine in neonates. Caudal catheters in neonates are popular, but evidence that they improve outcome is lacking.

SUMMARY

Epidural anesthesia and analgesia for neonates should be performed and managed by pediatric anesthesiologists. Potential risks and complications must be appreciated and all steps to maximize safety of the technique must be taken. In particular, close postoperative observation and pain service management are indispensable. Future research should investigate the risks of caudal and segmentally placed catheters in neonates, study the role of epidural analgesia in outcome improvement for neonates, and guide us to safer use of local anesthetics suitable for neonates with their pharmacologic immaturity.