Morphine infusion after pediatric cardiac surgery

An interview with Dr. Anne Marie Lynn, a pioneering woman in medicine

Dr. Anne Marie Lynn (1949-present), Professor Emeritus of Anesthesiology, Pain Medicine, and Pediatrics at the University of Washington, Seattle, was one of the most influential women in pediatric anesthesiology of her generation. Dr. Lynn embodies the spirit of discovery and advancement that have created the practice of pediatric anesthesiology as we know it today. A pioneer in pain medicine pharmacology, particularly morphine and ketorolac, her research transformed pediatric anesthesia, pediatric pain medicine, and pediatric intensive care medicine. Through her journal articles, book chapters, national and international lectures, mentoring of residents, fellows, and faculty, and leadership in the Society for Pediatric Anesthesia, she inspired a generation of women and men physicians by demonstrating that gender should not be a barrier to undertaking roles once only held only by men. In 2017, for her many contributions, she was awarded the Society for Pediatric Anesthesia's Myron Yaster lifetime achievement award.

Pharmacodynamic Analysis of Morphine Time-to-Remedication Events in Infants and Young Children After Congenital Heart Surgery

OBJECTIVE

The aim of this study was to characterize the relationship between morphine plasma concentration and repeated time to postoperative remedication events in children undergoing cardiac surgery.

METHODS

Data from our previously published study of morphine pharmacokinetics were utilized in this pharmacodynamic study. A population survival analysis based on hazard functions was undertaken in NONMEM(®).

RESULTS

Hazard was best described by a Gompertz function changing in steps over time. Concentration and age were the only predictors of the hazard function. Concentration producing 50 % reduction in hazard was 19.6 (bootstrap 95 % confidence interval 5.90-49.5 ng/ml). The hazard ratio for a 1-year-old child to a 1-month-old child was 1.91 (1.35-2.86). Sensitivity to morphine decreased with age and leveled off after 1-year of life. Morphine sulfate doses >0.1 mg/kg did not noticeably increase tolerable pain durations.

CONCLUSION

Time to remedication is a clinically useful endpoint for assessing opioid-induced analgesia. Sensitivity to morphine treatment is age-dependent. Morphine sulfate doses of 0.1-0.2 mg/kg are adequate for the management of postoperative pain in children. Our findings may help avoid unnecessary large morphine doses in children.

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.

Safety of the breast-feeding infant after maternal anesthesia

There has been an increase in breast-feeding supported by the recommendations of the American Academy of Pediatrics and the World Health Organization. An anesthesiologist may be presented with a well-motivated breast-feeding mother who wishes to breast-feed her infant in the perioperative period. Administration of anesthesia entails acute administration of drugs with potential for sedation and respiratory effects on the nursing infant. The short-term use of these drugs minimizes the possibility of these effects. The aim should be to minimize the use of narcotics and benzodiazepines, use shorter acting agents, use regional anesthesia where possible and avoid agents with active metabolites. Frequent clinical assessments of the nursing infant are important. Available literature does suggest that although the currently available anesthetic and analgesic drugs are transferred in the breast milk, the amounts transferred are almost always clinically insignificant and pose little or no risk to the nursing infant.

The relationship between age and morphine infusion rate in children

AIM

We performed a retrospective audit of intravenous morphine infusion administered to children in an effort to characterize the relationship between dose and age.

METHODS

A retrospective audit of morphine infusions was reviewed for a 24-months period and included all children who received continuous intravenous nurse-controlled morphine infusions and patient-controlled analgesia; a population undergoing acute and elective surgical procedures, as well as medical and oncological treatments. The relationship between age and infusion rate was investigated using nonlinear mixed effects models.

RESULTS

There were 886 children whose data were acceptable for review. Morphine dose increased with age from 9.97 (CV 28%) μg · kg(-1) per h in neonates. The Hill equation with an exponential of 1.5 best described these changes. Morphine rate reached 90% of its mean final rate of 22.5 (CV 167%) μg · kg(-1) per h, observed in teenagers, at approximately 5 years of age. There was considerable uncertainty of this age-morphine rate profile, and the maturation half-life of this profile was 20 months of age (CV 632%). An increase in dosing variability was observed with increasing age.

CONCLUSIONS

Morphine infusions at steady-state did not mirror clearance maturation in children nursed in our hospital. We suggest that initial infusion rates in children are started at 10 μg · kg(-1) per h in neonates, 15 μg · kg(-1) per h in toddlers and 25 μg · kg(-1) per h in children above the age of 5 years. The large variability associated with infusion rates means that subsequent infusion rates will depend on feedback from pain scores, adjuvant medications and adverse effects.

Prediction of morphine dose in humans

BACKGROUND

Morphine is widely used throughout the human life span. Several pharmacokinetic models have been proposed to predict how morphine clearance changes with weight and age. This study uses a large external data set to evaluate the ability of pharmacokinetic models to predict morphine doses.

METHODS

A data set of morphine clearance estimates was created from published reports in premature neonates, full-term neonates, infants, children, and adults. This external data set was used to evaluate published models for morphine clearance as well as other models proposed for use in neonates and infants. Morphine clearance predictions were used to predict morphine dose rates to achieve similar target concentrations in all age groups.

RESULTS

An allometric ¾ power model using weight combined with a sigmoid maturation model using postmenstrual age successfully predicted the morphine dose rate (within 25% of target) in all age groups except infants [predicted dose 30% under target (95% CI, 7-46%)]. Other published models based on empirical allometric scaling all made unacceptable predictions (>100% of target) in at least one age group.

CONCLUSIONS

Clearance based on empirical allometric scaling predicted unacceptable doses. Theory-based allometric scaling combined with a maturation function has been confirmed by external evaluation to provide a sound basis for describing clearance and predicting morphine doses in humans of all ages.

Perioperative care following complex laryngotracheal reconstruction in infants and children

Laryngotracheal reconstruction (LTR) involves surgical correction of a stenotic airway with cartilage interpositional grafting, followed by either placement of a tracheostomy and an intraluminal stent (two-stage LTR) or placement of an endotracheal tube with postoperative sedation and mechanical ventilation for an extended period of time (singlestage LTR). With single-stage repair, there may be several perioperative challenges including the provision of adequate sedation, avoidance of the development of tolerance to sedative and analgesia agents, the need to use neuromuscular blocking agents, the maintenance of adequate pulmonary toilet to avoid perioperative nosocomial infections, and optimization of postoperative respiratory function to facilitate successful tracheal extubation. We review the perioperative management of these patients, discuss the challenges during the postoperative period, and propose recommendations for the prevention of reversible causes of extubation failure in this article. Optimization to ensure a timely tracheal extubation and successful weaning of mechanical ventilator, remains the primary key to success in these surgeries as extubation failure or the need for prolonged postoperative mechanical ventilation can lead to failure of the graft site, the need for prolonged Pediatric Intensive Care Unit care, and in some cases, the need for a tracheostomy to maintain an adequate airway.

Disposition of morphine in plasma and cerebrospinal fluid varies during neonatal development in pigs

The pharmacological effects of morphine are mediated via the central nervous system (CNS) but its clearance from the CNS in neonates has not been investigated. We have proposed that neonatal development of the blood-brain barrier affected CNS clearance mechanisms and CNS exposure to morphine. Male piglets (n=5) aged one, three and six weeks were given morphine sulfate (0.5 mg kg−1, i.v.). Serial blood and cerebrospinal fluid (CSF) samples were withdrawn over 360 min after morphine administration. Morphine concentration was measured by radioimmunoassay. A three-compartment model was fitted to individual data. Estimated parameters were reported as median and range. The peak morphine concentrations in plasma were not significantly different in the one-, three- or six-week-old piglets. Plasma clearance at one week (4.5, 3.8-8.6 mL min−1 kg−1) was significantly lower than at three weeks (30.0, 19.1- 39.0 mL min−1 kg−1) and six weeks (37.0, 29.7–82.8 mL min−1 kg−1). The peak morphine concentration in CSF at one week (59.84, 31–67 ng mL−1) was higher than at three weeks (18.8, 17.7–25 ng mL−1) and six weeks (24.51, 16.5–84 ng mL−1), while CSF clearance was lower at one week (1.0, 0.18-9 mL min−1 kg−1) compared with three weeks (6.2, 2.3–9.3 mL min−1 kg−1) and six weeks (3.95, 1.3–85.7 mL min−1 kg−1). Apparent plasma: CSF transfer ratio at one week was greater than at three and six weeks. The reduced plasma and CSF morphine clearance in early infancy resulted in elevated systemic and central morphine exposure in neonatal pigs.

A survey of sedation assessment and management in Australian and New Zealand paediatric intensive care patients requiring prolonged mechanical ventilation

INTRODUCTION

A retrospective analysis of sedation management for children receiving prolonged ventilation in one Australian paediatric intensive care unit (PICU) revealed no identifiable pattern in sedation management and an inadequacy in the sedation scoring system. Therefore, the investigators sought to explore the current practice of sedation in critically ill children in PICUs across Australia and New Zealand.

METHOD

This study used a mail-out survey to audit sedation management within the eight dedicated Australian and New Zealand PICUs.

RESULTS

100% of the units surveyed replied (n=8). There were a total of 6,133 admissions to 8 Australian and New Zealand PICUs, where 3036 (49.5%) required ventilation. Of these children, 888 (29.2%) required ventilation > or =72 hours. Only 4 units had written guidelines for sedation management. A combined sedation regime of benzodiazepines and opioids was employed in six units. Administration and titration of sedation agents was managed by nursing staff alone in six units. All units indicated that they aimed to achieve a 'moderate level' of sedation. Two units used designated assessment tools for sedation and withdrawal assessment. One unit utilised Bispectral Index (BIS) monitoring.

CONCLUSION

There were similarities observed in the methods and types of sedation agents used within Australian and New Zealand PICUs. However, only half of the units had guidelines for sedation management, and most units did not use validated paediatric scales to assist staff in assessing patient sedation and pain levels. Therefore it is recommended that a standardised approach to sedation assessment and management of critically ill children requiring prolonged ventilation be developed and tested.

Anesthesia and analgesia during and after surgery in neonates

BACKGROUND

Historically, the use of anesthetics and analgesics in neonates and infants has been based on extrapolations from studies performed in adults and older children. Over the past 20 years, there has been a growing body of research on the clinical pharmacology and clinical outcomes of these agents in neonates and infants.

OBJECTIVE

This article summarizes clinical pharmacology and clinical outcomes studies of opioids, opioid antagonists, sedative-hypnotics, nonsteroidal anti-inflammatory drugs and acetaminophen, and local anesthetics in neonates and infants to highlight gaps in the available knowledge, review some concerns about study design, and identify drugs that should receive high priority for future study.

METHODS

Relevant studies were identified through a search of MEDLINE and a review of textbooks, conference proceedings, and abstracts. The available literature was subjected to expert committee-based review.

CONCLUSIONS

There is a growing body of information on analgesic and anesthetic pharmacokinetics, pharmacodynamics, and clinical outcomes in neonates and infants, permitting safe and effective use in some clinical settings. Major gaps in knowledge persist, however. Future research may involve a combination of clinical trials and preclinical studies in suitable infant animal surrogate models.

Sedation and analgesia in the pediatric intensive care unit

Various clinical situations may arise in the PICU that necessitate the use of sedation, analgesia, or both. Although there is a large clinical experience with midazolam in the PICU population and it remains the most commonly used benzodiazepine in this setting, lorazepam may provide an effective alternative, with a longer half-life and more predictable pharmacokinetics without the concern of active metabolites. However, there are limited reports regarding its use in the PICU population, and concerns exist regarding the potential for toxicity related to its diluent, propylene glycol. Although the synthetic opioid fentanyl frequently is chosen for use in the PICU setting because of its hemodynamic stability, preliminary data suggest morphine may have a slower development of tolerance and may cause fewer withdrawal symptoms than fentanyl. Morphine's safety profile includes long-term follow-up studies that have demonstrated no adverse central nervous system developmental effects from its use in neonates and infants. In the critically ill infant at risk following surgery for congenital heart disease, clinical experience supports the use of the synthetic opioids, given their ability to modulate PVR and prevent pulmonary hypertensive crisis. Alternatives to the benzodiazepines and opioids include ketamine, pentobarbital, or dexmedetomidine. Ketamine may be useful for patients with hemodynamic instability or airway reactivity. There are limited reports regarding the use of pentobarbital in the PICU, with one study raising concerns of a high incidence of adverse effects associated with its use. Propofol has gained great favor in the adult population as a means of providing deep sedation while allowing for rapid awakening; however, its routine use is not recommended because of its potential association with "propofol infusion syndrome." As the pediatric experience increases, it appears that there will be a role for newer agents such as dexmedetomidine.

Pain management for pediatric thoracic surgery

PURPOSE OF REVIEW

Pain management after thoracic surgery in children presents the challenge of providing adequate analgesia without excessive sedation, and maintaining adequate respiratory function in the face of compromise resulting from existing pathology, surgical trauma, single-lung ventilation and postoperative ventilation-perfusion abnormalities. In the pediatric population, pain assessment and reporting present additional challenges. The number and complexity of surgical procedures, including video-assisted thoracoscopic procedures, is increasing in the pediatric population. There is a need to explore pain management for these types of patients.

RECENT FINDINGS

There are effective and safe strategies whereby analgesia can be provided to this pediatric population. This review will outline the progress that has been made in this field, including the use of regional techniques. The routine use of caudal catheters in neonates and infants for thoracic surgical procedures and the use of electrical guidance of epidural catheters, the 'Tsui' technique, are reviewed.

SUMMARY

These techniques, applied within a comprehensive pain management strategy, can be extremely beneficial in the care of the pediatric thoracic patient.

Dose minimization study of single-dose epidural morphine in patients undergoing hip surgery under regional anesthesia with bupivacaine

BACKGROUND

In order to decrease the rate of adverse effects, we aimed to identify the lowest analgesic dose of epidural morphine administered to patients undergoing hip surgery.

METHODS

Forty-five ASA I-II children undergoing surgical correction of hip dysplasia under caudal or epidural anesthesia with bupivacaine were randomized to receive epidural morphine 11.2, 15 or 20 microg.kg(-1) (groups 1, 2 and 3, respectively; 15 patients per group) immediately after completion of surgery. Postoperative pain control, sedation, motor block, urinary retention, pruritus and vomiting were evaluated.

RESULTS

In the recovery room, 46.7% of patients from group 1, 33.3% from group 2, and 93.3% from group 3 were sleeping but were easy to arouse (x(2) = 12.2; P < 0.005). The rest of the patients from each respective group were completely asleep. The cardiovascular and respiratory parameters were within normal limits. The ability to move the legs returned approximately 1 h after surgery in all three groups. Seven patients (46.7%) from group 1, nine (60%) from group 2, and 13 patients (86.7%) from group 3 vomited (x(2) = 5.4; P = 0.06). One patient receiving 20 microg.kg(-1) morphine experienced urinary retention. One patient receiving 15 microg.kg(-1) morphine suffered from pruritus. The duration of analgesia was similar, 12-14 h, in all three groups.

CONCLUSIONS

In patients undergoing hip surgery under regional anesthesia with bupivacaine, epidural morphine at a dose of 11.2 microg.kg(-1) administered immediately after completion of the procedure resulted in adequate pain relief for more than 12 h. Explanation of the high rate of patients vomiting (>45%) remains to be elucidated.

Effects of systemic and epidural morphine on antidiuretic hormone levels in children

BACKGROUND

Although the use of opioids during general anaesthesia suppresses stress response to surgery and pain, the effects on antidiuretic hormone (ADH) are controversial. The aim of this study was to find the effects of morphine with either intravenous infusion or epidural route on ADH and other stress hormones.

METHODS

Fifty children aging (1-15 years) undergoing major genito-urinary or abdominal operations were included in this study. The patients were allocated randomly to two groups receiving either a single dose of epidural morphine 0.1 mg.kg-1 (EP group, n = 25) postinduction or morphine infusion (INF group; n = 25) at 0.02 mg.kg-1.h-1 following 0.05 mg.kg-1 bolus. Blood samples were withdrawn for plasma ADH, osmolality, glucose, cortisol, insulin and morphine level analysis following induction and 1, 5, 12 and 24 h after initial morphine administration.

RESULTS

The two groups were similar in demographic factors, pain scores, sedation scores, and incidence of nausea and vomiting. The amount of morphine received was different between groups and the changes in serum levels of morphine were statistically significant in EP group ( P < 0.05). The changes in cortisol, blood glucose and insulin levels were insignificant in both groups (P > 0.05). The changes of ADH levels were significant at time-points in both groups, reaching control levels at the 24th hour (P < 0.05).

CONCLUSION

Despite the effective pain therapy and suppression of cortisol and insulin response to surgical stimulus, the increase in ADH secretion is not effected by systemic or epidural morphine administration.

New concepts in acute and extended postoperative pain management in children

Increased knowledge of the pathophysiology of pain in children and an improved understanding of the pharmacology and pharmacodynamics of multiple agents have provided the clinician with a wide variety of tools to treat postoperative pain in children. The interest in a multimodal approach is kindled by the realization that the combination of a number of therapies can enhance analgesia with fewer untoward side effects. The expertise of other health care professionals should be tapped to open new avenues of treatment. Many therapies still require critical evidence-based evaluations to assess how well they work in larger patient populations. Dedication to research, compassionate patient care, and a willingness to teach the next generation of clinicians will bring us closer to the goal of safe and pain-free surgery.

Pediatric thoracic anesthesia

The anesthesiologist caring for infants and children undergoing thoracic surgery faces many challenges. An understanding of the primary underlying lesion as well as associated anomalies that may impact perioperative management is paramount. A working knowledge of respiratory physiology and anatomy in infants and children is required for the planning and execution of appropriate intraoperative care. Familiarity with a variety of techniques for SLV suited to the patient's size will allow maximal surgical exposure while minimizing trauma to the lungs and airways. Finally, use of regional anesthetic techniques, including epidural anesthesia and analgesia, facilitates optimal postoperative pain control and pulmonary function.

The analgesic efficacy and neuroendocrine response in paediatric patients treated with two analgesic techniques: using morphine-epidural and patient-controlled analgesia

BACKGROUND

Pain treatment is one of the main concerns of paediatric anaesthesiologists. The purpose of this study was to assess and compare the quality of analgesia and stress suppression by morphine when used [epidural (single shot) (EP) or with intravenous (i.v.) for patient-controlled analgesia (PCA) in children].

METHODS

Forty-four children, aged 5-15 years, and who were undergoing major genitourinary or lower abdominal surgery with a standardized general anaesthesia technique, were included in this study. In the EP group (n=24) 0.1 mg x kg(-1) morphine in 0.2 ml x kg(-1) saline were given epidurally at the L3-4 level and in the PCA group (n=20) 0.1 mg x kg-1 morphine was given i.v. immediately after intubation. Postoperative PCA bolus doses were 0.5 mg for patients weighing less than 20 kg, 1 mg for children weighing 20-30 kg and 1.5 mg for children weighing 30-40 kg. Blood samples were withdrawn following induction and at 1, 8, 12 and 24 h after morphine administration for measurement of blood glucose, insulin, cortisol and morphine levels. Patients were observed for 24 h postoperatively; heart rate, systolic blood pressure, respiratory rate, FACES pain scores, sedation scores and complications were recorded.

RESULTS

The PCA group received 0.56 +/- 0.33 mg x kg(-1) x day(-1) morphine. The FACES pain scores, sedation scores, cortisol, blood glucose and insulin levels were similar in both groups. Haemodynamic and respiratory evaluations and cortisol levels were stable but blood glucose and insulin changes at certain time periods were significant (P < 0.05). Serum morphine levels and incidence of vomiting were different between groups (P < 0.05). Serum morphine levels were similar at the first hour.

CONCLUSIONS

Both techniques provided sufficient pain relief and attenuated the hormonal response without life-threatening complications.

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.

The safety and efficacy of parent-/nurse-controlled analgesia in patients less than six years of age

Over the past 5 yr, we have treated nonsurgical and postoperative pain in children <6 yr of age by using a patient-controlled analgesia pump to deliver small-dose continuous IV opioid infusions supplemented by parent- and nurse-controlled opioid bolus dosing. We call this technique parent-/nurse-controlled analgesia (PNCA). Because the safety and efficacy of PNCA have not been previously evaluated, we have undertaken a prospective, 1-yr observational study to determine patient demographics, effectiveness of analgesia, and the incidence of complications (pruritus, vomiting, and respiratory depression) in patients receiving PNCA. Data were collected on 212 children (98 female) who were treated on 240 occasions with PNCA for episodes of pain. Patients averaged 2.3 +/- 1.7 yr of age and 11 +/- 5 kg, and received a median of 4 (range 2-54) days of PNCA therapy. Maximum daily pain scores were < or =3/10 (objective pain scale) or < or =2/5 (objective or self-report pain scale) in more than 80% of all occasions of PNCA use. PNCA usage was associated with an 8% incidence of pruritus and a 15% incidence of vomiting on the first day of treatment. Nine children studied received naloxone, four (1.7%) for treatment of PNCA-related apnea or desaturation. All had improvement in their symptoms after naloxone administration.

IMPLICATIONS

Parent-/nurse-controlled analgesia provided effective pain relief in most children <6 yr of age experiencing nonsurgical or postoperative pain. The observed incidence of vomiting and pruritus was similar to that seen in older patients treated with patient-controlled analgesia. However, significant respiratory depression, although uncommon, did occur, thus reinforcing the need for close patient monitoring.

Analgesics and breast-feeding: safety considerations

The issue of prescription of analgesics during lactation is clinically important but also complex. Most of the information available is based on single dose or short term studies, and for many drugs only a single or a few case reports have been published. As great methodological problems exist in the assessment of possible adverse drug reactions in neonates and infants, there is limited knowledge about the practical impact of the, often very low, concentrations found. Nevertheless, some recommendations can be made. Breast-feeding during maternal treatment with paracetamol (acetaminophen) should be regarded as being safe. Short term use of nonsteroidal anti-inflammatory drugs seems to be compatible with breast-feeding. For long term treatment, short-acting agents without active metabolites, such as ibuprofen, should possibly be preferred. The use of aspirin (acetylsalicylic acid) in single doses should not pose any significant risks to the suckling infant. Use of codeine is probably compatible with breast-feeding, although the effects of long term exposure have not been fully elucidated. For propoxyphene, it seems unlikely that the suckling infant will ingest amounts that will cause any detrimental effects during short term treatment. However, it cannot be excluded that significant amounts of the metabolite norpropoxyphene may arise in the suckling infant during long term exposure. Treatment of the mother with single doses of morphine or pethidine (meperidine) is not expected to cause any risk for the suckling infant. Repeated administration of pethidine, in contrast to morphine, affects the suckling infant negatively. Thus, morphine should be preferred in lactating mothers. However, during long term treatment with morphine, the importance of uninterrupted breast-feeding should be assessed on an individual basis against the potential risk of adverse drug effects in the infant. If it is decided to continue breast-feeding the infant should be observed for possible adverse effects. In general, if treatment of a lactating mother with an analgesic drug is considered necessary, the lowest effective maternal dose should be given. Moreover, infant exposure can be further reduced if breast-feeding is avoided at times of peak drug concentration in milk. As breast milk has considerable nutritional, immunological and other advantages over formula milk, the possible risks to the infant should always, and on an individual basis, be carefully weighed against the benefits of continuing breast-feeding.

Morphine pharmacokinetics and pain assessment in premature newborns

OBJECTIVES

To determine morphine pharmacokinetics in premature neonates varying in postconceptional age (PCA) and evaluate behavioral pain response in relationship to serum morphine concentrations.

METHODS

Premature neonates (n = 48), stratified by weeks of PCA (group 1 = 24-27 weeks, group 2 = 28-31 weeks, group 3 = 32-35 weeks, and group 4 = 36-39 weeks) received morphine infusions. Blood samples were drawn at 48, 60, and 72 hours and at discontinuation of morphine, followed by 3 samples obtained during the next 24 hours. Newborns were videotaped during heel lances and restful states, with morphine at steady-state concentrations and without morphine. Pain was assessed by using the Neonatal Facial Coding System (NFCS). Statistical analysis included regression between NFCS score changes from baseline to painful procedure with and without morphine.

RESULTS

Morphine clearance for groups 1, 2, 3, and 4 was calculated as 2.27 +/- 1.07, 3.21 +/- 1.57, 4.51 +/- 1.97, and 7.80 +/- 2.67 mL/kg/min, respectively, and correlated with PCA (r = 0.63, P <.001). Pain measured by facial expression was diminished; however, it did not correlate with morphine concentrations.

CONCLUSION

Morphine clearance in premature neonates is less than reported, increasing with PCA. Facial activity discloses morphine analgesia; however, it is unrelated to morphine concentrations.

Population pharmacokinetics of oral morphine and its glucuronides in children receiving morphine as immediate-release liquid or sustained-release tablets for cancer pain

OBJECTIVES

(1) To determine the pharmacokinetics of morphine, morphine-6-glucuronide (M6G), and morphine-3-glucuronide (M3G) in children with cancer receiving morphine as immediate-release morphine liquid or sustained-release tablets. (2) To determine differences with age within the group and from adults. (3) To explore relationships between plasma concentration and pain measurements.

STUDY DESIGN

Blood samples were collected and plasma analyzed by high-performance liquid chromatography with electrochemical and fluorescence detection. Population pharmacokinetic parameters were derived with the program P-PHARM.

RESULTS

Forty children with a median age of 11.4 years (range 1.7 to 18.7 years) received a median dose of 1.4 mg/kg/d (range 0.4 to 24.6 mg/kg/d). A median of 4 blood samples per child was collected. Plasma clearance of morphine was 23.1 mL/min per kg body weight. The volume of distribution was 5.2 L/kg. Molar ratios of M3G/morphine, M6G/morphine, and M3G/M6G were 21.1, 4.7, and 4.2, respectively. Children <11 years had significantly higher clearance and larger volume of distribution for morphine and its glucuronides than older children and adults. Regression analysis indicated average plasma morphine concentration equal to dose (mg/kg/d) x 8.6 (95% confidence interval 7.4 to 9.9). Significant pain was present in 30% of the children. Higher pain scores were recorded in children with average morphine concentrations <12 ng/mL (P <.01 MW).

CONCLUSION

Age differences in morphine pharmacokinetics exist within children and compared with adults. The study supports a starting dose of 1.5 to 2. 0 mg/kg/d to provide plasma morphine concentrations >12 ng/mL in children with cancer pain unrelieved by mild to moderate strength analgesia.

Sedation and analgesia in paediatric intensive care units: a guide to drug selection and use

The indications for sedation in the paediatric intensive care unit (PICU) patient are varied ranging from short term use for various procedures to prolonged administration to provide comfort during mechanical ventilation. When faced with the decision to institute sedation, the healthcare provider must make three decisions: the agent to be used, the route of delivery, and the mode of administration (intermittent versus continuous). There are several agents that have been used to provide sedation in the PICU patient including the inhalational anaesthetic agents, benzodiazepines, opioids, ketamine, propofol, chloral hydrate, phenothiazines, and the barbiturates. This review describes the various agents for sedation and discusses their advantages and disadvantages as they pertain to the PICU. Consequences of and treatment strategies for long term problems with prolonged sedation including tolerance, physical dependency, and withdrawal are reviewed.

[Frequency, intensity, development and repercussions of postoperative pain as a function of the type of surgery]

Type of surgery is the most important factor conditioning intensity and duration of postoperative pain. Thoracic and spinal surgery are the most painful procedures. Abdominal, urologic and orthopedic surgery lead to severe postoperative pain. Duration of severe pain rarely exceeds 72 hours. Mobilization increases pain intensity after abdominal, thoracic and orthopaedic surgery. Pain could occur after daycase minor surgical procedures and is often underestimated. Postoperative complications related to pain are difficult to disclose because of the interposition of the direct effects of analgesic treatments. Respiratory and cardiovascular postoperative complications are unrelated to postoperative pain in healthy subjects. This could be different in high risk patients. The surgical procedure is the major determinant of metabolic and psychologic postoperative deterioration. Adequate pain relief allows postoperative rehabilitation and physiotherapy programmes after abdominal and orthopaedic surgery. This could be expected to reduce hospital stay and improve convalescence.

The use of intravenous opioids to provide analgesia in critically ill, premature neonates: a research critique

The intravenous (i.v.) administration of opioids to neonates is a common method of providing analgesia in the intensive care setting. This paper reviews and critiques the studies that have investigated this intervention. The studies are grouped into four major areas: pharmacokinetic studies; i.v. opioids for anesthesia; i.v. opioids for sedation or analgesia in mechanically ventilated neonates; and cardiorespiratory effects of i.v. opioids. An attempt is made to synthesize current knowledge about the analgesic effects and side effects associated with the use of i.v. opioids in neonates. The intent is to stimulate additional research on the management of neonatal pain using opioid analgesics.

Postoperative pain management

Recent evidence has documented the deleterious physiologic effects of pain and the beneficial results of effective postoperative analgesia. As outlined in this article, a three-step approach is recommended depending on the severity of pain. The three-step approach utilizes a combination of NSAIDs, oral or intravenous opioids. In addition to selecting a particular opioid to use, the practitioner must also consider the route of administration and the mode of administration. All three choices may significantly impact on the efficacy of analgesia. While we continue to use primarily intravenous opioids to treat moderate and severe pain in the hospital setting, future formulations and developments may allow for the increased use of non-parenteral routes.

Morphine pharmacokinetics during continuous infusion of morphine sulfate for infants receiving extracorporeal membrane oxygenation

OBJECTIVES

To determine a) if serum morphine concentration changes during the first 3 hrs of extracorporeal membrane oxygenation (ECMO); and b) if absorption of morphine onto the membrane oxygenator is responsible for these changes. Also, morphine clearance during the first 5 days of ECMO was studied.

DESIGN

Prospective, open-label study with consecutive patient enrollment.

SETTING

Neonatal intensive care unit at a university-affiliated, children's hospital.

SUBJECTS

Eleven neonates with severe persistent pulmonary hypertension of the newborn receiving continuous intravenous infusions of morphine sulfate and requiring ECMO.

INTERVENTIONS

Blood samples were obtained from the subjects and ECMO circuits at predetermined time intervals.

MEASUREMENTS AND MAIN RESULTS

Serum morphine concentration was determined using high-performance liquid chromatography. Morphine concentrations were no different from baseline at 5 mins, 1 hr, or 3 hrs after beginning ECMO. There was no significant difference in morphine concentration from samples taken immediately proximal and distal to the membrane oxygenator at 5 mins, 1 hr, and 3 hrs after the start of ECMO. Morphine clearance was calculated on days 1, 3, and 5 of ECMO. The mean value for morphine clearance was 11.7 +/- 9.3 (SD) ml/min/kg (range 2.6 to 34.5).

CONCLUSIONS

The initiation of ECMO does not lead to a significant decrease in serum morphine concentration and there is no uptake of morphine onto the membrane oxygenator of the ECMO circuit. Morphine clearance for infants receiving ECMO is variable.

Recommended use of morphine in neonates, infants and children based on a literature review: Part 2--Clinical use

The indication for morphine use is primarily pain, but also a combined analgesic and sedative effect may be the rationale behind morphine administration. Paediatric morphine regimens have been reported for children with postoperative pain, pain related to cancer, sickle cell crisis pain, burns and AIDS. No dose response curve for morphine in neonates, infants or children has been established, and different levels for the minimum effective plasma concentration have been estimated. The side effects observed in neonates, infants, and children are similar to those observed in adults, and neonates do not seem to be more susceptible to respiratory depression than older children. Despite shortcomings in the knowledge of the pharmacodynamics of morphine, it can be considered safe to administer morphine to neonates, infants or children. Initial regimens has been calculated from the pharmacokinetic parameters of morphine, but treatment must be adjusted according to analgesic effect and incidence of side effects.

Epidural and intravenous bolus morphine for postoperative analgesia in infants

PURPOSE

To compare two doses of bolus epidural morphine with bolus iv morphine for postoperative pain after abdominal or genitourinary surgery in infants.

METHODS

Eighteen infants were randomly assigned to bolus epidural morphine (0.025 mg.kg-1 or 0.050 mg.kg-1) or bolus iv morphine (0.050-0.150 mg.kg-1). Postoperative pain was assessed and analgesia provided, using a modified infant pain scale. Monitoring included continuous ECG, pulse oximetry, impedance and nasal thermistor pneumography. The CO2 response curves and serum morphine concentrations were measured postoperatively.

RESULTS

Postoperative analgesia was provided within five minutes by all treatment methods. Epidural groups required fewer morphine doses (3.8 +/- 0.8 for low dose [LE], 3.5 +/- 0.8 for high dose epidural [HE] vs. 6.7 +/- 1.6 for iv, P < 0.05) and less total morphine (0.11 +/- 0.04 mg.kg-1 for LE, 0.16 +/- 0.04 for HE vs 0.67 +/- 0.34 for iv, P < 0.05) on POD1. Dose changes were necessary in all groups for satisfactory pain scores. Pruritus, apnoea, and haemoglobin desaturation occurred in all groups. CO2 response curve slopes, similar preoperatively (range 36-41 ml.min-1.mmHg ETCO2-1.kg-1) were generally depressed (range, 16-27 ml.min-1.mmHg ETCO2-1.kg-1) on POD1. Serum morphine concentrations, negligible in LE (< 2 ng.ml-1), were similar in the HE and iv groups (peak 8.5 +/- 12.5 and 8.6 +/- 2.4 ng.ml-1, respectively).

CONCLUSION

Epidural and iv morphine provide infants effective postoperative analgesia, although side effects are common. Epidural morphine gives satisfactory analgesia with fewer doses (less total morphine); epidural morphine 0.025 mg.kg-1 is appropriate initially. Infants receiving epidural or iv morphine analgesia postoperatively need close observation in hospital with continuous pulse oximetry.

[Analgesia controlled by the patient in pediatrics]

The development of patient controlled analgesia (PCA) in children is the result of a search for an analgesia being both maximally efficient and secure, in the management of severe pain. The technique is based on self infusions of an analgesic, mainly morphine, by the child, through a special pump. The quality of the pump is essential in order to exclude any risk of overdosage. In order to prevent potential secondary effects and complications, a careful supervision is mandatory (clinical, by pulse oximetry, regular checking of pump parameters). PCA is applicable to children older than 5 years. The main indications are post-operative and oncological pains.

CAUDAL ANALGESIA FOR POSTOPERATIVE PAIN RELIEF IN CHILDREN

Postoperative pain relief in 40 children undergoing elective infraumbilical surgery was assessed after caudal epidural adminstration of either lignocaine or bupivacaine in the doses of 0.5 mL/kg body weight of a 1 per cent solution and 0.5 mL/kg body weight of a 0.25 per cent solution respectively. Pain free period was assessed by subjective pain scales. The pain free period was significantly prolonged in children who were given bupivacaine (14.75 ± 2.75 hours) as compared to lignocaine (7.25 ± 3.25 hours).

Rectal administration of morphine in children. Pharmacokinetic evaluation after a single-dose

BACKGROUND

There is limited knowledge about the pharmacokinetics of morphine and its metabolites after rectal administration in children. In this study the pharmacokinetics of two different rectal formulations of morphine were examined and compared with intravenous morphine.

METHODS

Children undergoing elective surgery received rectal morphine 0.2 mg/kg before start of surgery. Ten children (mean age 14 months) received morphine rectally in a hydrogel formulation and another 10 children (mean age 16 months) received morphine rectally in a parenteral formulation. For comparison, 6 children (mean age 21 months) were given the same dose intravenously. The plasma concentrations of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) were measured by HPLC over 6 h after drug administration.

RESULTS

The mean rectal bioavailability of morphine was 35% (range 18-59) after hydrogel administration and 27% (range 6-93) after the solution. Mean values of Cmax were 76 nmol/l (25-129) and 56 nmol/1 (15-140), respectively. The results showed that morphine gel had a significantly higher bioavailability (P < 0.02) than the solution. The ratios of plasma (M3G + M6G) to morphine were higher after rectal administration (mean 7.5-8.7) than after i.v. injection (mean 5.3), indicating the presence of first-pass metabolism using the rectal route.

CONCLUSIONS

The rectal morphine hydrogel has pharmacokinetic properties which makes it a useful formulation for premedication and pain alleviation in paediatric patients.

Fatal morphine poisoning in a child due to accidental oral ingestion

A case of fatal intoxication of an 8 year old child due to accidental oral ingestion of morphine is presented. Following a tonsillectomy and release from the hospital the decedent was prescribed meperidine syrup 50 mg per teaspoon (tsp) to be taken 2 tsps every 4 h. A pharmacist when filling her prescription mistakenly dispensed Roxanol which contained 20 mg/ml morphine sulfate. She took 1 or 2 tsp of the prescription prior to bed and was found dead the next morning. Autopsy findings were unremarkable. Quantitation by gas chromatography/mass spectrometry (GC/MS) yielded the following morphine results: blood, 0.128 mg/l; bile, 135 mg/l and stomach contents, 16 mg/l (2.3 mg total). Based upon the clinical history, autopsy and toxicology finding the cause of death was determined to be poisoning by morphine and the manner of death accidental.

Sedation and Analgesia for Children in the Pediatric Intensive Care Unit

Several situations arise in the Pediatric Intensive Care Unit (PICU) patient which may require the pharmacologic control of pain and anxiety. The author discusses the various pharmacologic agents available for sedation and analgesia including the inhalational anesthetic agents, nitrous oxide, benzodiasepines, opioids, ketamine, propofol, and the barbiturates. While intravenous administration is generally chosen for the PICU patient, certain situations may arise which preclude this route. The available information concerning alternative routes of delivery for the various agents including subcutaneous and transmucosal administration is presented. The role of various regional anesthetic techniques to control pain in the PICU patient are reviewed.

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.

Pain management and sedation in the pediatric intensive care unit

Several situations arise in the PICU patient that require the administration of drugs for sedation and analgesia. A "cookbook" approach is impossible because of the diversity of patient and clinical scenarios. When amnesia is required, these authors prefer a continuous infusion of a benzodiazepine such as midazolam or lorazepam. Although the majority of clinical experience has been with midazolam, lorazepam either by bolus dose or continuous infusion offers a cost-effective alternative. When analgesia is required, the addition of a continuous infusion of narcotic or the use of a PCA device in the older patient should prove effective. Although fentanyl is frequently chosen, morphine is an effective and cost-effective alternative for patients with stable cardiovascular function. The synthetic narcotics are recommended for neonates, especially following cardiac surgical procedures and those at risk for pulmonary vasospasm. Narcotics may also be used for the treatment of agitation in those situations that do not necessarily require analgesia. Our clinical experience suggests that narcotics may be more effective for sedation than benzodiazepines in children less than 1 year of age. When the above agents fail to be effective or are associated with cardiovascular depression, alternatives may include ketamine or pentobarbital. Ketamine may be useful for the unstable patient or those with a bronchospastic component to their disease process. We have found pentobarbital to be effective when the combination of benzodiazepines and narcotics fails to provide the desired level of sedation. Aside from these techniques, regional anesthesia may offer a more effective means of controlling pain in the PICU patient. These techniques may be effective when parenteral narcotics are inadequate or lead to undesired effects. Although most commonly used for postoperative analgesia, their use in patients with pain from other causes (e.g., multiple trauma) may be indicated, especially when parenteral narcotics may interfere with respiratory function or the ongoing assessment of the patient's mental status.

Morphine pharmacokinetics in premature and mature newborn infants

The pharmacokinetics of a single dose of morphine was investigated in five term infants (gestational age 37-40 weeks) and eight preterm infants (gestational age 25-32 weeks). In the five term infants, median (range) volume of distribution at steady state (Vd beta) was 1758 (634-2700) ml/kg, plasma clearance (Cl) was 4.73 (1.75-6.61) ml/kg/min and terminal half-life (T1/2) was 224 (107-394) min. In the eight preterm infants, Vd beta was 2366 (1662-2876) ml/kg, Cl was 2.82 (1.88-6.60) ml/kg/min and T1/2 was 556 (248-834) min. No correlation was found between clearance and gestational age, but we found a significant negative correlation between T1/2 and gestational age. We conclude that there is considerable variation in the pharmacokinetic properties of morphine in both term and preterm newborn infants. Because of this variation, careful individual assessment of the clinical effect of therapy with morphine in newborn infants should be exercised.