Morphine pharmacokinetics in children following cardiac surgery: effects of disease and inotropic support

Possible unusual presentation of opioid side effect in a child: a case report

Atypical presentations are commonly encountered in the Pediatric intensive care unit (PICU) but having a high index of suspicion is crucial to prevent or treat severe and life-threatening conditions. This case describes the clinical presentation and course of a 14-month-old girl with congenital heart disease who was admitted to the PICU after cardiac repair and remained agitated, irritable, in hysteria and delirium despite adequate sedation. Different measures to relieve her condition were attempted but to no avail. All the common causes of this atypical presentation including pain, ventilator induced agitation, low cardiac output syndrome (LCOS), opioid side effects, toxicity, opioid induced neurotoxicity (OIN) as well as withdrawal syndrome were ruled out. However, the use of naloxone as a last resort after exhausting all the other options has led to immediate and successful reversal of her symptoms.

Management of routine postoperative pain for children undergoing cardiac surgery: a Paediatric Acute Care Cardiology Collaborative Clinical Practice Guideline

BACKGROUND

Pain following surgery for cardiac disease is ubiquitous, and optimal management is important. Despite this, there is large practice variation. To address this, the Paediatric Acute Care Cardiology Collaborative undertook the effort to create this clinical practice guideline.

METHODS

A panel of experts consisting of paediatric cardiologists, advanced practice practitioners, pharmacists, a paediatric cardiothoracic surgeon, and a paediatric cardiac anaesthesiologist was convened. The literature was searched for relevant articles and Collaborative sites submitted centre-specific protocols for postoperative pain management. Using the modified Delphi technique, recommendations were generated and put through iterative Delphi rounds to achieve consensus.

RESULTS

60 recommendations achieved consensus and are included in this guideline. They address guideline use, pain assessment, general considerations, preoperative considerations, intraoperative considerations, regional anaesthesia, opioids, opioid-sparing, non-opioid medications, non-pharmaceutical pain management, and discharge considerations.

CONCLUSIONS

Postoperative pain among children following cardiac surgery is currently an area of significant practice variability despite a large body of literature and the presence of centre-specific protocols. Central to the recommendations included in this guideline is the concept that ideal pain management begins with preoperative counselling and continues through to patient discharge. Overall, the quality of evidence supporting recommendations is low. There is ongoing need for research in this area, particularly in paediatric populations.

Perioperative Opioid Consumption is Not Reduced in Cyanotic Patients Presenting for the Fontan Procedure

Adequate pain control is a critical component of the perioperative approach to children undergoing repair of congenital heart disease (CHD). The impact of specific anatomic and physiologic disturbances on the management of analgesia has been largely unexplored at the present time. Studies in other pediatric populations have found an association between chronic hypoxemia and an increased sensitivity to the effects of opioid medications. The purpose of this retrospective study was to examine perioperative opioid administration and opioid-associated adverse effects in children undergoing surgical repair of CHD, with a comparison between patients with and without chronic preoperative cyanosis. Patients between the ages of 2 and 5 years whose tracheas were extubated in the operating room were included and were classified in the cyanotic group if they presented for the Fontan completion. The primary outcomes of interest were intraoperative and postoperative opioid administration. Secondary outcomes included pain scores and opioid-related side effects. The study cohort included 156 patients. Seventy-one underwent the Fontan procedure, twelve of which were fenestrated. Fontan patients received fewer opioids intraoperatively (11.33 µg/kg fentanyl equivalents versus 12.56 µg/kg, p = 0.03). However, there were no differences with regards to opioid consumption postoperatively and no correlation between preoperative oxygen saturation and total opioid administration. There were no differences between groups with regards to the respiratory rate nadir, postoperative pain scores, or the incidence of opioid-related side effects. In contrast to other populations with chronic hypoxemia exposure, children with cyanotic CHD did not appear to have increased sensitivity to the effects of opioid medications.

Intravenous morphine versus intravenous paracetamol after cardiac surgery in neonates and infants: a study protocol for a randomized controlled trial

BACKGROUND

Morphine is worldwide the analgesic of first choice after cardiac surgery in children. Morphine has unwanted hemodynamic and respiratory side effects. Therefore, post-cardiac surgery patients may potentially benefit from a non-opioid drug for pain relief. A previous study has shown that intravenous (IV) paracetamol is effective and opioid-sparing in children after major non-cardiac surgery. The aim of the study is to test the hypothesis that intermittent IV paracetamol administration in children after cardiac surgery will result in a reduction of at least 30% of the cumulative morphine requirement.

METHODS

This is a prospective, multi-center, randomized controlled trial at four level-3 pediatric intensive care units (ICUs) in the Netherlands and Belgium. Children who are 0-36 months old will be randomly assigned to receive either intermittent IV paracetamol or continuous IV morphine up to 48 h post-operatively. Morphine will be available as rescue medication for both groups. Validated pain and sedation assessment tools will be used to monitor patients. The sample size (n = 208, 104 per arm) was calculated in order to detect a 30% reduction in morphine dose; two-sided significance level was 5% and power was 95%.

DISCUSSION

This study will focus on the reduction, or replacement, of morphine by IV paracetamol in children (0-36 months old) after cardiac surgery. The results of this study will form the basis of a new pain management algorithm and will be implemented at the participating ICUs, resulting in an evidence-based guideline on post-operative pain after cardiac surgery in infants who are 0-36 months old.

TRIAL REGISTRATION

Dutch Trial Registry ( www.trialregister.nl ): NTR5448 on September 1, 2015. Institutional review board approval (MEC2015-646), current protocol version: July 3, 2017.

Pharmacokinetic considerations for pediatric patients receiving analgesia in the intensive care unit; targeting postoperative, ECMO and hypothermia patients

INTRODUCTION

Adequate postoperative analgesia in pediatric patients in the intensive care unit (ICU) matters, since untreated pain is associated with negative outcomes. Compared to routine postoperative patients, children undergoing hypothermia (HT) or extracorporeal membrane oxygenation (ECMO), or recovering after cardiac surgery likely display non-maturational differences in pharmacokinetics (PK) and pharmacodynamics (PD). These differences warrant additional dosing recommendations to optimize pain treatment. Areas covered: Specific populations within the ICU will be discussed with respect to expected variations in PK and PD for various analgesics. We hereby move beyond maturational changes and focus on why PK/PD may be different in children undergoing HT, ECMO or cardiac surgery. We provide a stepwise manner to develop PK-based dosing regimens using population PK approaches in these populations. Expert opinion: A one-dose to size-fits-all for analgesia is suboptimal, but for several commonly used analgesics the impact of HT, ECMO or cardiac surgery on average PK parameters in children is not yet sufficiently known. Parameters considering both maturational and non-maturational covariates are important to develop population PK-based dosing advices as part of a strategy to optimize pain treatment.

An international survey of management of pain and sedation after paediatric cardiac surgery

OBJECTIVE

The mainstay of pain treatment after paediatric cardiac surgery is the use of opioids. Current guidelines for its optimal use are based on small, non-randomised clinical trials, and data on the pharmacokinetics (PK) and pharmacodynamics (PD) of opioids are lacking. This study aims at providing an overview of international hospital practices on the treatment of pain and sedation after paediatric cardiac surgery.

DESIGN

A multicentre survey study assessed the management of pain and sedation in children aged 0-18 years after cardiac surgery.

SETTING

Pediatric intensive care units (PICU)of 19 tertiary children's hospitals worldwide were invited to participate. The focus of the survey was on type and dose of analgesic and sedative drugs and the tools used for their pharmacodynamic assessment.

RESULTS

Fifteen hospitals (response rate 79%) filled out the survey. Morphine was the primary analgesic in most hospitals, and its doses for continuous infusion ranged from 10 to 60 mcg kg^-1 h^-1 in children aged 0-36 months. Benzodiazepines were the first choice for sedation, with midazolam used in all study hospitals. Eight hospitals (53%) reported routine use of sedatives with pain treatment. Overall, type and dosing of analgesic and sedative drugs differed substantially between hospitals. All participating hospitals used validated pain and sedation assessment tools.

CONCLUSION

There was a large variation in the type and dosing of drugs employed in the treatment of pain and sedation after paediatric cardiac surgery. As a consequence, there is a need to rationalise pain and sedation management for this vulnerable patient group.

Pharmacodynamics and Pharmacokinetics of Morphine After Cardiac Surgery in Children With and Without Down Syndrome

OBJECTIVE

To compare the pharmacodynamics and pharmacokinetics of IV morphine after cardiac surgery in two groups of children-those with and without Down syndrome.

DESIGN

Prospective, single-center observational trial.

SETTING

PICU in a university-affiliated pediatric teaching hospital.

PATIENTS

Twenty-one children with Down syndrome and 17 without, 3-36 months old, scheduled for cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

A loading dose of morphine (100 μg/kg) was administered after coming off bypass; thereafter, morphine infusion was commenced at 40 μg/kg/hr. During intensive care, nurses regularly assessed pain and discomfort with validated observational instruments (COMFORT-Behavior scale and Numeric Rating Scale-for pain). These scores guided analgesic and sedative treatment. Plasma samples were obtained for pharmacokinetic analysis.

MEASUREMENTS AND MAIN RESULTS

Median COMFORT-Behavior and Numeric Rating Scale scores were not statistically significantly different between the two groups. The median morphine infusion rate during the first 24 hours after surgery was 31.3 μg/kg/hr (interquartile range, 23.4-36.4) in the Down syndrome group versus 31.7 μg/kg/hr (interquartile range, 25.1-36.1) in the control group (p = 1.00). Population pharmacokinetic analysis revealed no statistically significant differences in any of the pharmacokinetic variables of morphine between the children with and without Down syndrome.

CONCLUSIONS

This prospective trial showed that there are no differences in pharmacokinetics or pharmacodynamics between children with and without Down syndrome if pain and distress management is titrated to effect based on outcomes of validated assessment instruments. We have no evidence to adjust morphine dosing after cardiac surgery in children with Down syndrome.

Sedation and Analgesia in Pediatric Cardiac Critical Care

OBJECTIVES

This review will focus on the pharmacokinetics (with an emphasis on the context-sensitive half-time), pharmacodynamics, and hemodynamic characteristics of the most commonly used sedative/hypnotic, analgesic, and IV anesthetics used in cardiac intensive care. In addition, the assessment of pain and agitation and withdrawal will be reviewed.

DATA SOURCE

MEDLINE, PubMed.

CONCLUSIONS

Children in the cardiac ICU often require one or more components of general anesthesia: analgesia, amnesia (sedation and hypnosis), and muscle relaxation to facilitate mechanical ventilation, to manage postoperative pain, to perform necessary procedures, and to alleviate fear and anxiety. Furthermore, these same children are often vulnerable to hemodynamic instability due to unique underlying physiologic vulnerabilities. An assessment of hemodynamic goals, postoperative procedures to be performed, physiologic vulnerabilities, and the intended duration of mechanical ventilation should be made. Based on this assessment, the optimal selection of sedatives, analgesics, and if necessary, muscle relaxants can then be made.

Pediatric Cardiac Intensive Care Society 2014 Consensus Statement: Pharmacotherapies in Cardiac Critical Care: Sedation, Analgesia and Muscle Relaxant

OBJECTIVE

This article reviews pharmacotherapies currently available to manage sedation, analgesia, and neuromuscular blockade for pediatric cardiac critical patients.

DATA SOURCES

The knowledge base of an expert panel of pharmacists, cardiac anesthesiologists, and a cardiac critical care physician involved in the care of pediatric cardiac critical patients was combined with a comprehensive search of the medical literature to generate the data source.

STUDY SELECTION

The panel examined all studies relevant to management of sedation, analgesia, and neuromuscular blockade in pediatric cardiac critical patients.

DATA EXTRACTION

Each member of the panel was assigned a specific subset of the studies relevant to their particular area of expertise (pharmacokinetics, pharmacodynamics, and clinical care) to review and analyze.

DATA SYNTHESIS

The panel members each crafted a comprehensive summary of the literature relevant to their area of expertise. The panel, as a whole, then collaborated to cohesively summarize all the available, relevant literature.

CONCLUSIONS

In the cardiac ICU, management of the cardiac patient requires an individualized sedative and analgesic strategy that maintains hemodynamic stability. Multiple pharmacological therapies exist to achieve these goals and should be selected based on the patient's underlying physiology, hemodynamic vulnerabilities, desired level of sedation and analgesia, and the projected short- or long-term recovery trajectory.

Theophylline Population Pharmacokinetics and Dosing in Children Following Congenital Heart Surgery With Cardiopulmonary Bypass

Children undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) frequently develop acute kidney injury due to renal ischemia. Theophylline, which improves renal perfusion via adenosine receptor inhibition, is a potential targeted therapy. However, children undergoing cardiac surgery and CPB commonly have alterations in drug pharmacokinetics. To help understand optimal aminophylline (salt formulation of theophylline) dosing strategies in this population, a population-based pharmacokinetic model was developed using nonlinear mixed-effects modeling (NONMEM) from 71 children (median age 5 months; 90% range 1 week to 10 years) who underwent cardiac surgery requiring CPB and received aminophylline as part of a previous randomized controlled trial. A 1-compartment model with linear elimination adequately described the pharmacokinetics of theophylline. Weight scaled via allometry was a significant predictor of clearance and volume. In addition, allometric scaled clearance increased with age implemented as a power maturation function. Compared to prior reports in noncardiac children, theophylline clearance was markedly reduced across age. In the final population pharmacokinetic model, optimized empiric dosing regimens were developed via Monte Carlo simulations. Doses 50% to 75% lower than those recommended in noncardiac children were needed to achieve target serum concentrations of 5 to 10 mg/L.

Pharmacokinetics of Morphine and Its Metabolites in Infants and Young Children After Congenital Heart Surgery

The objective of this study was to characterize morphine glucuronidation in infants and children following cardiac surgery for possible treatment individualization in this population. Twenty children aged 3 days to 6 years, admitted to the cardiovascular intensive care unit after congenital heart surgery, received an intravenous (IV) loading dose of morphine (0.15 mg/kg) followed by subsequent intermittent IV bolus doses based on a validated pain scale. Plasma samples were collected over 6 h after the loading dose and randomly after follow-up doses to measure morphine and its major metabolite concentrations. A population pharmacokinetic model was developed with the non-linear mixed effects software NONMEM. Parent disposition was adequately described by a linear two-compartment model. Effect of growth (size and maturation) on morphine parameters was accounted for by allometric body weight-based models. An intermediate compartment with Emax model best characterized glucuronide concentrations. Glomerular filtration rate was identified as a significant predictor of glucuronide formation time delay and maximum concentrations. Clearance of morphine in children with congenital heart disease is comparable to that reported in children without cardiac abnormalities of similar age. Children 1-6 months of age need higher morphine doses per kilogram to achieve an area under concentration-time curve comparable to that in older children. Pediatric patients with renal failure receiving morphine therapy are at increased risk of developing opioid toxicity due to accumulation of morphine metabolites.

Inter-individual variation in morphine clearance in children

Objectives

The aim of the study was to determine the extent of inter-individual variation in clearance of intravenous morphine in children and to establish which factors are responsible for this variation.

Methods

A systematic literature review was performed to identify papers describing the clearance of morphine in children. The following databases were searched: Medline, Embase, International Pharmaceutical Abstracts, CINAHL, and Cochrane library. From the papers, the range in plasma clearance and the coefficient of variation (CV) in plasma clearance were determined.

Results

Twenty-eight studies were identified. After quality assessment, 20 studies were included. Only 10 studies gave clearance values for individual patients. The majority of the studies were in critically ill patients. Inter-individual variability of morphine clearance was observed in all age groups, but greatest in critically ill neonates (both preterm and term) and infants. In critically ill patients, the CV was 16–9 7 % in preterm neonates, 24–87 % in term neonates, 35 and 134 % in infants, 39 and 55 % in children, and 74 % in adolescents. The CV was 37 and 44 % respectively in non-critically ill neonates and infants. The mean clearance was higher in children (32 and 52 ml min^-1 kg^-1) than in neonates (2 to 16 ml min^-1 kg^-1).

Conclusions

Large inter-individual variation was seen in morphine clearance values in critically ill neonates and infants.

Electronic supplementary material

The online version of this article (doi:10.1007/s00228-015-1843-x) contains supplementary material, which is available to authorized users.

The challenges of multiple organ dysfunction syndrome and extra-corporeal circuits for drug delivery in critically ill patients

The multiple organ dysfunction syndrome (MODS) is characterized by more than one organ system failing, especially during critical illness. MODS is the leading cause of morbidity and mortality in current ICU practice; moreover, multiple organ dysfunction, especially liver and kidneys, may significantly affect the pharmacokinetics (PKs) of different drugs that are currently administered in critically ill patients. These PK alterations may either result in insufficient drug concentrations to achieve the desired effects or in blood and tissue accumulation, with the development of serious adverse events. The use of extra-corporeal circuits, such as extracorporeal membrane oxygenation (ECMO) and continuous renal replacement therapy (CRRT), may further contribute to PKs changes in this patients' population. In this review, we have described the main PK changes occurring in all these conditions and how drug concentrations may potentially be affected. The lack of prospective studies on large cohorts of patients makes impossible any specific recommendation on drug regimen adjustment in ICU patients. Nevertheless, the clinicians should be aware of these abnormalities in order to better understand some unexpected therapeutic issues occurring in such patients.

Pediatric palliative care: use of opioids for the management of pain

Pediatric palliative care (PPC) is provided to children experiencing life-limiting diseases (LLD) or life-threatening diseases (LTD). Sixty to 90% of children with LLD/LTD undergoing PPC receive opioids at the end of life. Analgesia is often insufficient. Reasons include a lack of knowledge concerning opioid prescribing and adjustment of opioid dose to changing requirements. The choice of first-line opioid is based on scientific evidence, pain pathophysiology, and available administration modes. Doses are calculated on a bodyweight basis up to a maximum absolute starting dose. Morphine remains the gold standard starting opioid in PPC. Long-term opioid choice and dose administration is determined by the pathology, analgesic effectiveness, and adverse effect profile. Slow-release oral morphine remains the dominant formulation for long-term use in PPC with hydromorphone slow-release preparations being the first rotation opioid when morphine shows severe adverse effects. The recently introduced fentanyl transdermal therapeutic system with a drug-release rate of 12.5 microg/hour matches the lower dose requirements of pediatric cancer pain control. Its use may be associated with less constipation compared with morphine use. Though oral transmucosal fentanyl citrate has reduced bioavailability (25%), it inherits potential for breakthrough pain management. However, the gold standard breakthrough opioid remains immediate-release morphine. Buprenorphine is of special clinical interest as a result of its different administration routes, long duration of action, and metabolism largely independent of renal function. Antihyperalgesic effects, induced through antagonism at the kappa-receptor, may contribute to its effectiveness in neuropathic pain. Methadone also has a long elimination half-life (19 [SD 14] hours) and NMDA receptor activity although dose administration is complicated by highly variable morphine equianalgesic equivalence (1 : 2.5-20). Opioid rotation to methadone requires special protocols that take this into account. Strategies to minimize adverse effects of long-term opioid treatment include dose reduction, symptomatic therapy, opioid rotation, and administration route change. Patient- or nurse-controlled analgesia devices are useful when pain is rapidly changing, or in terminal care where analgesic requirements may escalate. In this article, we present detailed pediatric pharmacokinetic and pharmacodynamic data for opioids, their indications and contraindications, as well as dose-administration regimens that include practical strategies for opioid switching and dose reduction. Additionally, we discuss the problem of hyperalgesia and the use of adjuvant drugs to support opioid therapy.

Opioid analgesia in neonates following cardiac surgery

Pain in the newborn is complex, involving a variety of receptors and mechanisms within the developing nervous system. When pain is generated, a series of sequential neurobiologic changes occur within the central nervous system. If pain is prolonged or repetitive, the developing nervous system could be permanently modified, with altered processing at spinal and supraspinal levels. In addition, pain is associated with a number of adverse physiologic responses that include alterations in circulatory (tachycardia, hypertension, vasoconstriction), metabolic (increased catabolism), immunologic (impaired immune response), and hemostatic (platelet activation) systems. This "stress response" associated with cardiac surgery in neonates could be profound and is associated with increased morbidity and mortality. Neonates undergoing cardiac operations are exposed to extensive tissue damage related to surgery and additional painful stimulation related to endotracheal and thoracostomy tubes that may remain in place for variable periods of time following surgery. In addition, postoperatively neonates endure repeated procedural pain from suctioning of endotracheal tubes, placement of vascular catheters, and manipulation of wounds (eg, sternal closure) and dressings. The treatment and/or prevention of pain are widely considered necessary for humanitarian and physiologic reasons. Improved clinical and developmental outcomes underscore the importance of providing adequate analgesia for newborns who undergo major surgery, mechanical ventilation, and related procedures in the intensive care unit. This article reviews published information regarding opioid administration and associated issues of tolerance and abstinence syndromes (withdrawal) in neonates with an emphasis on those having undergone cardiac surgery.

Morphine metabolite pharmacokinetics during venoarterial extra corporeal membrane oxygenation in neonates

OBJECTIVE

To examine morphine metabolite serum concentrations in neonates undergoing venoarterial extra corporeal membrane oxygenation (ECMO) and to quantify clearance differences between these neonates and those subjected to noncardiac major surgery.

PATIENTS AND METHODS

This was an observational study in level III referral centre. Fourteen neonates (< 7 days old) undergoing ECMO were included. Morphine and concomitant medications were given by protocol, adapted to the clinical conditions of the neonates. Pharmacokinetic findings were compared with those from a previous study in infants after noncardiac major surgery. Nonlinear mixed-effect modelling was used. Parameter estimates were standardised to a 70 kg person using allometric modeling

RESULTS

Morphine-3-glucuronide (M3G) was the predominant metabolite. Formation clearance to M3G at the start of ECMO on day 1 was lower than those in postoperative children, but matured more rapidly. After 10 days formation clearances of M3G in neonates on ECMO equalled those of postoperative children. Higher ECMO flows were associated with reduced formation clearances. Elimination clearances of M3G, but not morphine-6-glucuronide (M6G), were lower in the ECMO neonates; this was attributable to reduced renal clearance. These elimination clearances were correlated positively with ECMO flow and negatively with dopamine dose. Haemofiltration cleared M3G and M6G, but not morphine.

CONCLUSION

Formation clearance to M3G, the predominant metabolite, is reduced during the first 10 days of ECMO. Elimination clearance of M3G and M6G is related to creatinine clearance. ECMO flow had a small effect on metabolite clearance. Higher flows were associated with decreased formation clearances, possibly reflecting illness severity. Dopamine dose reflected decreased renal clearance.

Bilateral diaphragm paralysis following cardiac surgery in children: 10-years' experience

OBJECTIVE

To review the incidence and complications of conservative management of bilateral diaphragm paralysis following pediatric cardiac surgery.

DESIGN AND SETTING

Retrospective clinical review based on computerized database with daily follow-up in a pediatric cardiac intensive care unit in a tertiary care center. PATIENT AND PARTICIPANTS: Were reviewed the data on nine patients with bilateral diaphragm paralysis from the 3,214 consecutive children (0.28%) after operations performed between 1995 and 2004.

MEASUREMENTS AND RESULTS

A fluoroscopy-confirmed diagnosis of bilateral diaphragm paralysis was made in all nine patients. Mechanical ventilation was required for 14-62 days; maximum time to recovery was 7 weeks. Three patients underwent unilateral plication. Patients with a complicated postoperative course required longer mechanical ventilation. All patients were managed with a nasotracheal tube. One patient had minor subglottic stenosis. All patients survived.

CONCLUSIONS

Bilateral diaphragm paralysis can be managed conservatively with good prognosis and minor complications. The recovery time is relatively short, less than 7 weeks.

Relationship between changes in thyroid hormone level and severity of the postoperative course in neonates undergoing open-heart surgery

BACKGROUND

Our aim was to determine whether the changes in thyroid function after open-heart surgery in neonates depend on the postoperative course.

METHODS

Twenty neonates undergoing open-heart surgery for congenital heart disease were prospectively studied in the cardiac intensive care unit of a university-affiliated children's hospital. The patients were divided into two groups by level of inotropic support (high or mild).

RESULTS

The groups were similar in age, bypass time and ultrafiltration volume. In both groups, there was a significant reduction in levels of thyroid-stimulating hormone and FT4 at 24 h postoperatively. However, in the high inotropic support group, FT4 was lower for a longer time. This group also had a significantly higher score on The Pediatric Risk of Mortality (PRISM; P < 0.042) and a longer duration of ventilation (P < 0.014).

CONCLUSIONS

Neonates after open-heart surgery undergo changes in thyroid function characteristic of euthyroid sick syndrome. The degree of hypothyroxinemia may be related to the severity of illness and the postoperative course.

Pharmacokinetics of piritramide in newborns, infants and young children in intensive care units

Piritramide is indicated for treatment of postoperative pain and analgosedation in the intensive care unit (ICU) setting. In an open prospective study the pharmacokinetics of piritramide were investigated in four groups: newborns (NB, age: 1-28 days) (n=8), infants 1 (IF1, age: 2-4 months) (n=7), infants 2 (IF2, age: 5-12 months) (n=14) and young children (YC, age: 2-4 years) (n=10). The recommended paediatric dose range for therapy of postoperative pain is 50-200 microg/kg. Piritramide was administered intravenously as a single dose by bolus injection of 50 microg/kg. Blood samples were collected at 0, 15, 45, 90 min and 3, 6, 9, 12 h after application, and urine samples were collected before application and during the following intervals: 1-2, 2-6, 6-12 h. Piritramide was measured in blood and urine by HPLC-ESI-MS. The following pharmacokinetic parameters: maximum plasma concentration (C(max)), distribution half-life (t 1/2 alpha), elimination half-life (t 1/2 beta), total clearance (Cl(t)) and median volume of distribution at equilibrium (Vd(ss)) were calculated using a non-compartment and a two-compartment model for the disposition of piritramide (TOPFIT and NONMEM-pharmacokinetic analysis). Newborns (NB) showed the highest maximum plasma concentrations (median+/-SD) C(max) (79+/-240 microg/l) compared to the other three groups (IF1 36+/-367, IF2 12+/-81 and YC 16+/-9 microg/l) without statistical significance. The median elimination half-lives (t 1/2 beta) were 702+/-720 min in NB, 157+/-102 min in IF1, 160+/-68 min in IF2 and 166+/-143 min in YC. For t 1/2 beta the difference between NB and the other three groups (IF1, IF2 and YC) was statistically significant (Mann-Whitney-U, P<0.05). Cl(t) was 15.9+/-16.7, 46.6+/-76.9, 235.5+/-454.1 and 338+/-168.1 ml/min in NB, IF1, IF2 and YC respectively. The total clearance increased exponentially with an elimination half-life of 702 min from 15.9 ml/min in NB to 46.6 ml/min in IF2. Differences between the NB/IF1 groups and IF2/YC groups were significantly significant (NB vs. IF2, NB vs. YC, IF1 vs. IF2 and IF1 vs. YC). Vd(ss) was 2.0+/-4.93, 1.7+/-2.5, 7.0+/-5.2 and 6.7+/-2.2 l/kg in NB, IF1, IF2 and YC respectively. In comparison to group IF1 the Vd(ss) was significantly larger in groups IF2 and YC (Mann-Whitney U, P<0.05). Newborns showed a high initial concentration and a distinct prolongation of the elimination half-life of piritramide compared to infants, young children and adults. Therefore, dosage needed to treat postoperative pain should be reduced, and the repetitive doses should be geared to the analgesic effects. In infants and young children the elimination of piritramide is increased compared to adults; therefore the duration of the effects of piritramide will be shortened, and dose intervals ought to be reduced. Subsequent clinical trials for detailed dose adjustment of piritramide in paediatric patients comparing pharmacokinetics and effectiveness are needed.

Morphine pharmacokinetics during venoarterial extracorporeal membrane oxygenation in neonates

OBJECTIVE

To study morphine pharmacokinetics in neonates undergoing venoarterial ECMO and to quantify differences between these neonates and neonates subjected to noncardiac major surgery.

DESIGN AND SETTING

Observational study in a level III referral center.

PATIENTS AND METHODS

Pharmacokinetic estimates from 14 neonates undergoing ECMO were compared with findings from a previous study in 0- to 3-year-olds after noncardiac major surgery using a nonlinear mixed effect model. A one-compartment linear disposition model with zero-order input (infusion) and first-order elimination was used to describe all data.

RESULTS

Clearance in neonates (age <7 days) at the start of ECMO (2.2 l per hour per 70 kg) was lower than that in postoperative neonates (10.5 l per hour per 70 kg) but increased rapidly (maturation half-life 30 and 70 days, respectively) and equaled that of the postoperative group after 14 days. Clearance was affected by size and age only. Exchange transfusion, when used, contributed only 1.1% (CV 46%) of total clearance. Distribution volume increased with age and was 2.5 times (CV 102%) greater in ECMO children than in postoperative children. The between-subject variability values for volume of distribution and clearance were 49.4% and 38.7%. Weight and age information explained 83% of the overall clearance variability and 60% of overall distribution volume variability.

CONCLUSIONS

Morphine clearance is reduced in infants requiring ECMO, possibly reflecting severity of illness. Clearance maturation on ECMO is rapid and normalizes within 2 weeks. Initial morphine dosing may be guided by age and weight, but clearance and distribution volume changes (and their variability) during prolonged ECMO suggests that morphine therapy should be subsequently guided by clinical monitoring.

Efficacy and safety of continuous intravenous infusion of remifentanil in preterm infants undergoing laser therapy in retinopathy of prematurity: clinical experience

BACKGROUND

Preterm infants often require surgery. As experimental evidence suggests that premature infants may experience pain and this could even result in fatal complications, the anaesthesiologist must face problems related to lowbirth weight, high risk of hypothermia, concomitant pulmonary disease and metabolic and receptor immaturity. Recently remifentanil has been considered an optimal analgesic drug in a preterm infant undergoing mechanical ventilation and frequent surgical manoeuvres, but no clinical studies have been reported in the literature. The aim of our study was to evaluate the efficacy of a continuous intravenous infusion of remifentanil in premature infants undergoing laser therapy for retinopathy of prematurity (ROP).

METHODS

Six premature infants with ROP were scheduled for laser therapy. The procedure was performed in the neonatal intensive care unit. Transcutaneous carbon dioxide, pulse oximetry, respiratory rate, ECG and noninvasive blood pressure were continuously monitored. Infusion of remifentanil started with a dose of 0.75-1 microg x kg-1x min-1, 1 h before surgery. A midazolam bolus dose (0.20 mg x kg-1) was administered and the remifentanil infusion was increased to 3-5 microg x kg-1x min-1 taking into account haemodynamic and respiratory changes or spontaneous movements.

RESULTS

Increased dosage was necessary only for 10 min during the procedure. No changes in temperature and ventilatory settings were observed and after 2 h from the surgical procedure the preterm infants were back to their preoperative status.

CONCLUSIONS

A continuous infusion of remifentanil allowed optimal control of surgical stress and a return to preoperative status and ventilatory settings without side-effects.

Age- and therapy-related effects on morphine requirements and plasma concentrations of morphine and its metabolites in postoperative infants

BACKGROUND

To investigate clinical variables such as gestational age, sex, weight, the therapeutic regimens used and mechanical ventilation that might affect morphine requirements and plasma concentrations of morphine and its metabolites.

METHODS

In a double-blind study, neonates and infants stratified for age [group I 0-4 weeks (neonates), group II > or =4-26 weeks, group III > or =26-52 weeks, group IV > or =1-3 yr] admitted to the paediatric intensive care unit after abdominal or thoracic surgery received morphine 100 micro g kg(-1) after surgery, and were randomly assigned to either continuous morphine 10 micro g kg(-1) h(-1) or intermittent morphine boluses 30 micro g kg(-1) every 3 h. Pain was measured using the COMFORT behavioural scale and a visual analogue scale. Additional morphine was administered on guidance of the pain scores. Morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) plasma concentrations were measured before, directly after, and at 6, 12 and 24 h after surgery.

RESULTS

Multiple regression analysis of different variables revealed that age was the most important factor affecting morphine requirements and plasma morphine concentrations. Significantly fewer neonates required additional morphine doses compared with all other age groups (P<0.001). Method of morphine administration (intermittent vs continuous) had no significant influence on morphine requirements. Neonates had significantly higher plasma concentrations of morphine, M3G and M6G (all P<0.001), and significantly lower M6G/morphine ratio (P<0.03) than the older children. The M6G/M3G ratio was similar in all age groups.

CONCLUSIONS

Neonates have a narrower therapeutic window for postoperative morphine analgesia than older age groups, with no difference in the safety or effectiveness of intermittent doses compared with continuous infusions in any of these age groups. In infants >1 month of age, analgesia is achieved after morphine infusions ranging from 10.9 to 12.3 micro g kg(-1) h(-1) at plasma concentrations of <15 ng ml(-1).

Pain management in the critically ill child

Children frequently received no treatment, or inadequate treatment, for pain and for painful procedures. The newborn and critically ill children are especially vulnerable to no treatment or under-treatment. Nerve pathways essential for the transmission and perception of pain are present and functioning by 24 weeks of gestation. The failure to provide analgesia for pain results in rewiring the nerve pathways responsible for pain transmission in the dorsal horn of the spinal cord and results in increased pain perception for future painful results. Many children would withdraw or deny their pain in an attempt to avoid yet another terrifying and painful experiences, such as the intramuscular injections. Societal fears of opioid addiction and lack of advocacy are also causal factors in the under-treatment of pediatric pain. False beliefs about addictions and proper use of acetaminophen and other analgesics resulted in the failure to provide analgesia to children. All children even the newborn and critically ill require analgesia for pain and painful procedures. Unbelieved pain interferes with sleep, leads to fatigue and a sense of helplessness, and may result in increased morbidity or mortality.

Modern concepts of paediatric analgesia

Laboratory data, economic pressures, and the wish for humane treatment have been some of the driving forces behind improvements in paediatric pain management. Within the space of 10 years, there have been dramatic changes in the quality of treatment received by children undergoing surgical operations. Moreover, those receiving medical treatment, for example, sickle cell disease, have also benefited from increased experience in pain management. Children receiving care in specialised centres can now expect to benefit from up-to-date techniques of pain management, such as patient-controlled analgesia, nurse-controlled analgesia, and epidural infusions. They will be managed by ward nurses experienced and trained in paediatric pain relief, they will be attended by nurses whose special interest and training is the management of children's pain, and they will be provided with the techniques of analgesia by competent, trained anaesthetic staff. Improved care, with close attention to pain relief, is not only humane, but improves the patient turnaround by enhancing rapid discharge. Further education is required to spread these benefits to children being managed outside highly specialised centres. Not only education, but investment, is needed also to ensure that all children receive a standard of care second to none.

Clearance of morphine in postoperative infants during intravenous infusion: the influence of age and surgery

We analyzed morphine clearance values in infants receiving the drug by continuous i.v. infusion for analgesia after surgery, because we found lower steady-state morphine concentrations than we expected from our previous studies. Infants received morphine after a loading dose of 0.05 mg/kg and continuous infusion calculated to reach a steady-state concentration of 20 ng/mL. Blood was sampled twice on Postoperative Day 1 at times separated by at least 2 h, and morphine and morphine-6-glucuronide (M-6-G) concentrations were determined by high-performance liquid chromatography. Clearance of morphine was calculated as infusion rate divided by the steady-state morphine concentration. Morphine given to 26 infants by continuous i.v. infusion after major noncardiac surgery has rapidly increasing clearance values, from a median value of 9.2 mL x min(-1) x kg(-1) in infants 1-7 days old, 25.3 in infants 31-90 days old, and 31.0 in infants 91-180 days old to 48.9 in infants 180-380 days old. Adult clearance values are reached by 1 mo of age, more quickly than in infants of the same age previously studied who received morphine after cardiac surgeries. M-6-G was measured in all infants. The ratio of M-6-G to morphine concentrations was 1.9-2.1 in these infants, which is lower than ratios reported in older infants or adults by others, but higher than those reported in newborns. Infants with normal cardiovascular systems undergoing surgery clear morphine more efficiently than infants of the same age undergoing cardiac surgery.

IMPLICATIONS

Morphine removal from the body is slow in newborns but increases to reach adult values in the first months of life. Calculating the clearance of morphine from blood samples drawn during continuous i.v. infusions after surgery shows that this maturation occurs more quickly in infants undergoing noncardiac surgery (by 1-3 mo of age) than in those receiving morphine after cardiac surgery (by 6-12 mo of age).

Clinical pharmacokinetics and pharmacodynamics of opioid analgesics in infants and children

Pain in childhood has not always been managed as actively as that in adults because of the limited amount of research available to provide guidelines for the management of paediatric pain. However, for many years now the pharmacokinetics and pharmacodynamics of opioid analgesics in infants and children have been studied intensively. Morphine is the standard for opioid analgesics and its pharmacology is the best studied in paediatric patients. During the neonatal period, the volume of distribution (Vd) appears to be smaller in neonates than in adults, but adult values are reached soon after the neonatal period. Although morphine is absorbed both orally and rectally, there is little information on the pharmacokinetics of morphine administered by these routes. The bioavailability of morphine after rectal administration appears to be highly variable. For all the opioid analgesics studied, the elimination of the opioids is slower in neonates than in adults. However, the rate of elimination usually reaches and even exceeds adult values within the first year of life. The high rate of drug metabolism means higher dosage requirements. In regard to the pharmacodynamics of opioid analgesics, infants and children do not appear to be more sensitive to the effects of opioids than adults. Thus, except for the neonatal period, the pharmacokinetics and pharmacodynamics of opioid analgesics are not markedly different from those of adults, and the risk of using opioids in infants and children is not higher.