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

Distribution of morphine and methadone to the brain in a developmental chicken embryo model

The use and/or misuse of opioids by pregnant women would expose the fetuses to these drugs during critical stages of development with serious effects for the newborn, like the neonatal abstinence syndrome (NAS). We have revisited an established chicken model for NAS to describe the distribution of morphine and methadone to the brain and explore its validity as a valuable alternative to rodent models. For this purpose, chicken eggs were injected with a single dose of 10 mg/kg or 20 mg/kg morphine or 20 mg/kg methadone onto the chorioallantoic membrane (CAM) on embryonal day 13. Whole brains and lungs were harvested and the concentrations of morphine, methadone and their subsequent metabolites (morphine-3-glucuronide and EDDP, respectively) determined in the brain and lungs at different time points using LC-MS/MS. Morphine and methadone, as well as their metabolites, were detected both in the brain and lungs, with significantly higher concentrations in the lungs. Pharmacokinetic modelling showed that the distribution of morphine to the brain followed a first-order absorption with transit compartments and linear elimination, with concentrations linearly dependent on dose. Moreover, methadone, but not morphine, reduced μ receptor (the main morphine receptor) binding, which can be of relevance for opioid tolerance. The present study is the first to report the brain distribution of morphine, which can be described by standard pharmacokinetic processes, and methadone in the developing chicken embryo. The present findings supplement the already established model and support the use of this chicken model to study NAS.

Clinical and Economic Evaluation of the Impact of Midazolam on Morphine Therapy for Pain Relief in Critically Ill Ventilated Infants with Respiratory Distress Syndrome

BACKGROUND

The impact of midazolam on the overall performance of morphine therapy for pain in ventilated neonates with respiratory distress syndrome (RDS) has never been investigated.

OBJECTIVE

This study is a clinical and economic analysis of morphine monotherapy versus morphine plus midazolam in ventilated infants with RDS.

METHODS

A decision-analytic model from the hospital perspective was developed to follow the consequences of the use of the study drugs. Clinical and resource utilization data were extracted based on a retrospective cohort study of 104 neonates with RDS receiving morphine alone versus in combination with midazolam at the main neonatal intensive care unit (NICU) in Qatar, from 2014 to 2019. Primary outcome measures were the analgesia success rate, via the Premature Infant Pain Profile scale, and overall costs of therapies. Multivariate statistical analyses confirmed no significant variations in baseline characteristics between study groups.

RESULTS

With 0.05 significance and 80% power, morphine had a higher rate of successful analgesia (65.4 vs. 34.6%; risk ratio 1.91; 95% confidence interval 1.11-3.28; p = 0.019). Overall costs were also in favor of morphine compared with its combination with midazolam, with cost savings of 40,959 Qatari Riyal ($US11,222), year 2019/20 values. The Monte Carlo analyses confirmed the economic advantage of morphine alone in 100% of cases and demonstrated that it is not sensitive to uncertainties in study model inputs.

CONCLUSIONS

Morphine monotherapy enabled enhanced pain relief over its combination with midazolam in the NICU, at a reduced overall cost. Morphine alone, therefore, seems to be a dominant analgesia strategy.

New Nutritional and Therapeutical Strategies of NEC

Necrotizing enterocolitis (NEC) is an acquired severe disease of the digestive system affecting mostly premature babies, possibly fatal and frequently associated to systemic complications. Because of the severity of this condition and the possible long-term consequences on the child's development, many studies have aimed at preventing the occurrence of the primary events at the level of the bowel wall (ischemia and necrosis followed by sepsis) by modifying or manipulating the diet (breast milk versus formula) and/or the feeding pattern (time for initiation after birth, continuous versus bolus feeding, modulation of intake according clinical events). Feeding have been investigated so far in order to prevent NEC. However, currently well-established and shared clinical nutritional practices are not available in preventing NEC. Nutritional and surgical treatments of NEC are instead well defined. In selected cases surgery is a therapeutic option of NEC, requiring sometimes partial intestinal resection responsible for short bowel syndrome. In this paper we will investigate the available options for treating NEC according to the Walsh and Kliegman classification, focusing on feeding practices in managing short bowel syndrome that can complicate NEC. We will also analyze the proposed ways of preventing NEC.

A predictive pharmacokinetic/pharmacodynamic model of fentanyl for analgesia/sedation in neonates based on a semi-physiologic approach

BACKGROUND AND OBJECTIVES

Fentanyl is a synthetic opioid commonly used as an anesthetic and also increasingly popular as a sedative agent in neonates. Initial dosage regimens in this population are often empirically derived from adults on a body weight basis. However, ontogenic maturation processes related to drug disposition are not necessarily always body weight correlates. We developed a predictive pharmacokinetic/pharmacodynamic model that includes growth and maturation physiologic changes for fentanyl in neonatal care.

METHODS

Key pharmacokinetic variables and principles (protein binding, clearance, distribution) as related to fentanyl pharmacokinetic/pharmacodynamic behavior in adults (tricompartmental model) and to neonatal physiologic data (organ weights and blood flows, body composition, renal and hepatic function, etc.) were used to guide the building of a semi-physiologic ontogenic model. The model applies to a normal-term neonate without any other intervention. Then, extension to a pharmacokinetic/pharmacodynamic link model for fentanyl was made. The final model was evaluated by predicting the time course of plasma concentrations and the effect of a standard regimen of 10.5 μg/kg over a 1-h period followed by 1.5 μg/kg/h for 48 h.

RESULTS

Hepatic clearance was linked to ontogeny of unbound fraction and of α1-acid glycoprotein. All parameters were reduced in the neonate compared to adults but in a differing proportion due to qualitative changes in physiology that are analyzed and accounted for. Systemic clearance (CLS), volume of the central compartment (V1) and steady-state volume of distribution predicted by the model were 0.028 L/min, 1.26 L, and 22.04 L, respectively. Weight-corrected parameters generally decreased in adults compared with neonates, but differentially, e.g., CLS = 0.0093 versus 0.0088 L/min/kg, while V1 = 0.42 versus 0.18 L/kg (neonates vs. adults). Under such complexity a pharmacokinetic/pharmacodynamic model is the appropriate method for rational efficacy targeting. Fentanyl pharmacodynamics in neonates were considered to be similar to those in adults except for the equilibrium rate constant, which was also scaled on an ontogenic basis. The model adequately predicted the reported mean expected concentration-time profiles for the standard regimen.

CONCLUSIONS

Integrated pharmacokinetic/pharmacodynamic modeling showed that the usually prescribed dosage regimens of fentanyl in neonates may not always provide the optimum degree of sedation. The model could be used in optimal design of clinical trials for this vulnerable population. Prospective clinical testing is the reasonable next step.

Tolerance and withdrawal from prolonged opioid use in critically ill children

OBJECTIVE

After prolonged opioid exposure, children develop opioid-induced hyperalgesia, tolerance, and withdrawal. Strategies for prevention and management should be based on the mechanisms of opioid tolerance and withdrawal.

PATIENTS AND METHODS

Relevant manuscripts published in the English language were searched in Medline by using search terms "opioid," "opiate," "sedation," "analgesia," "child," "infant-newborn," "tolerance," "dependency," "withdrawal," "analgesic," "receptor," and "individual opioid drugs." Clinical and preclinical studies were reviewed for data synthesis.

RESULTS

Mechanisms of opioid-induced hyperalgesia and tolerance suggest important drug- and patient-related risk factors that lead to tolerance and withdrawal. Opioid tolerance occurs earlier in the younger age groups, develops commonly during critical illness, and results more frequently from prolonged intravenous infusions of short-acting opioids. Treatment options include slowly tapering opioid doses, switching to longer-acting opioids, or specifically treating the symptoms of opioid withdrawal. Novel therapies may also include blocking the mechanisms of opioid tolerance, which would enhance the safety and effectiveness of opioid analgesia.

CONCLUSIONS

Opioid tolerance and withdrawal occur frequently in critically ill children. Novel insights into opioid receptor physiology and cellular biochemical changes will inform scientific approaches for the use of opioid analgesia and the prevention of opioid tolerance and withdrawal.

Early awakening and extubation with remifentanil in ventilated premature neonates

BACKGROUND

Morphine is one of the most commonly used drugs for sedation and analgesia during mechanical ventilation, but its pharmacological profile has limitations, such as prolonged duration of action, especially in premature neonates. Because of its very short context-sensitive half-time, remifentanil has rapid onset and quickly decreases in plasma concentration after interrupting administration. The aim of the present study was to compare a continuous infusion of remifentanil and morphine during mechanical ventilation of premature neonates with respiratory distress syndrome (RDS).

METHODS

Twenty premature neonates (28-34 weeks) with RDS were randomized in a prospective double-blinded study to receive either a continuous infusion of morphine (n = 10) or remifentanil (n = 10) for mechanical ventilation. The length of time to awaken and extubate the neonate after interrupting opioid administration was recorded. We also recorded stress (COMFORT scale), pain response [Neonatal Infant Pain Scale (NIPS)], hemodynamic and ventilatory variables as well as adverse effects secondary to infusion of the specific opioid.

RESULTS

After terminating infusion, the length of time required to awaken and extubate the neonates was 18.9- and 12.1-fold longer, respectively, in the morphine group than in the remifentanil group. Both groups produced good quality sedation and analgesia as evaluated by the NIPS and COMFORT scores. No major side effects were observed.

CONCLUSIONS

Our results show an interesting potential for the use of remifentanil in premature neonates. Remifentanil allowed an adequate level of sedation and analgesia as well as rapid recovery after discontinuation. However, further properly designed clinical trials are needed before it can be generally recommended.

Opioids for neonates receiving mechanical ventilation

BACKGROUND

Mechanical ventilation is a potentially painful and discomforting intervention widely used in neonatal intensive care units. Newborn babies (neonates) demonstrate increased sensitivity to pain, which may affect clinical and neurodevelopmental outcomes. The use of drugs that reduce pain might be important in improving survival and neurodevelopmental outcomes.

OBJECTIVES

To determine the effect of opioid analgesics (pain-killing drugs derived from opium e.g. morphine), compared to placebo, no drug, or other non-opioid analgesics or sedatives, on pain, duration of mechanical ventilation, mortality, growth and neurodevelopmental outcomes in newborn infants on mechanical ventilation.

SEARCH STRATEGY

Electronic searches included: the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 2007); MEDLINE (1966 to June 2007); EMBASE (1974 to June 2007); and CINAHL (1982 to 2007). Previous reviews and lists of relevant articles were cross-referenced.

SELECTION CRITERIA

Randomised controlled trials or quasi-randomised controlled trials comparing opioids to a control, or to other analgesics or sedatives in newborn infants on mechanical ventilation.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two review authors. Categorical outcomes were analysed using relative risk and risk difference; and continuous outcomes with weighted mean difference or standardised mean difference. A fixed effect model was used for meta-analysis except where heterogeneity existed, in which case a random effects model was used.

MAIN RESULTS

Thirteen studies on 1505 infants were included. Infants given opioids showed reduced premature infant pain profile (PIPP) scores compared to the control group (weighted mean difference -1.71; 95% confidence interval -3.18 to -0.24). Differences in execution and reporting of trials mean that this meta-analysis should be interpreted with caution. Heterogeneity was significantly high in all analyses of pain, even when lower quality studies were excluded and analysis limited to very preterm newborns. Meta-analyses of mortality, duration of mechanical ventilation, and long and short-term neurodevelopmental outcomes showed no statistically significant differences. Very preterm infants given morphine took significantly longer to reach full enteral feeding than those in control groups (weighted mean difference 2.10 days; 95% confidence interval 0.35 to 3.85). One study compared morphine with a sedative: the treatments showed similar pain scores, but morphine had fewer adverse effects.

AUTHORS' CONCLUSIONS

There is insufficient evidence to recommend routine use of opioids in mechanically ventilated newborns. Opioids should be used selectively, when indicated by clinical judgment and evaluation of pain indicators. If sedation is required, morphine is safer than midazolam. Further research is needed.

Ontogeny of respiratory sensitivity and tolerance to the mu-opioid agonist fentanyl in rat

Whereas developmental changes in analgesic sensitivity and tolerance to the mu-opioid agonist fentanyl have been reported, knowledge of respiratory responses to that drug is lacking. Using 7- and 14-day-old (P7, P14) and adult conscious rats, we first established, using whole body plethysmography, the fentanyl dose that decreased minute ventilation by 50% (ED50) at each age. ED50 increased with postnatal age (40, 60 and 120 microg/kg sc, respectively), indicating a high sensitivity to fentanyl in the youngest rats that decreased with maturation. In separate rat groups of the 3 ages, we injected each ED50 dose, once a day, for several consecutive days, until tolerance was established. Tolerance was defined as a reduction in respiratory depression from 50% to 75% of baseline. All age groups reached tolerance in minute ventilation, respiratory frequency, tidal volume and instantaneous flow (equivalent to respiratory drive). The P14 rat pups attained tolerance more rapidly (at 2.6 days) than did either the younger (5.1 days) or the adult rats (4.4 days). These results indicate that respiratory sensitivity and tolerance to fentanyl in rat vary in a distinct manner during maturation.

Opioids for neonates receiving mechanical ventilation

BACKGROUND

Mechanical ventilation is a potentially painful intervention widely used in neonatal intensive care units. Since newborn babies (neonates) demonstrate increased sensitivity to pain, which may affect clinical and neurodevelopmental outcomes, the use of drugs which reduce pain might be very important.

OBJECTIVES

To determine the effect of opioid analgesics (pain-killing drugs derived from opium e.g. morphine), compared to placebo, no drug, or other non-opioid analgesics or sedatives, on pain, duration of mechanical ventilation, mortality, growth and neurodevelopmental outcomes in newborn infants on mechanical ventilation.

SEARCH STRATEGY

Electronic searches included: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 3, 2004); MEDLINE (1966 to June 2004); EMBASE (1974 to June 2004); and CINAHL (1982 to 2003). Previous reviews and lists of relevant articles were cross-referenced.

SELECTION CRITERIA

Randomised controlled trials or quasi-randomised controlled trials comparing opioids to a control, or to other analgesics or sedatives in newborn infants on mechanical ventilation.

DATA COLLECTION AND ANALYSIS

Data were extracted by two reviewers independently. Categorical outcomes were analysed using relative risk and risk difference; and continuous outcomes with weighted mean difference or standardised mean difference. A fixed effect model was used for meta-analysis except where heterogeneity existed, when a random effects model was used.

MAIN RESULTS

Thirteen studies on 1505 infants were included. Infants given opioids showed reduced premature infant pain profile (PIPP) scores compared to the control group (weighted mean difference -1.71; 95% confidence interval -3.18 to -0.24). Differences in execution and reporting of trials mean that this meta-analysis should be interpreted with caution. Heterogeneity was significantly high in all analyses of pain, even when lower quality studies were excluded and analysis limited to very preterm newborns. Meta-analyses of mortality, duration of mechanical ventilation, and long and short term neurodevelopmental outcomes showed no statistically significant differences. Very preterm infants given morphine took significantly longer to reach full enteral feeding than those in control groups (weighted mean difference 2.10 days; 95% confidence interval 0.35 to 3.85). One study compared morphine with a sedative: the treatments showed similar pain scores, but morphine had fewer adverse effects.

AUTHORS' CONCLUSIONS

There is insufficient evidence to recommend routine use of opioids in mechanically ventilated newborns. Opioids should be used selectively, when indicated by clinical judgment and evaluation of pain indicators. If sedation is required, morphine is safer than midazolam. Further research is needed.

The effects of analgesia in the vulnerable infant during the perinatal period

Although our knowledge of pain and its management in the perinatal period has increased, little is known about the first hours and days of life when major physiologic transition events occur. Prematurity and critical illnesses further complicate analgesic use during this time. Increased morbidity and mortality have been shown in infants receiving placebo infusions after surgery compared with infants with analgesia, highlighting the negative consequences of pain in infants. Opioids can help promote hemodynamic stability, promote respirator synchrony, and decrease the incidence of grade III & IV intraventricular hemorrhage in ventilated preterm neonates. Long-term follow-up studies suggest improved behavioral and cognitive outcomes in children given morphine infusions during NICU confinement. The necessity of fetal analgesia is dictated by the ability of the fetus to feel pain and by the adverse effects of noxious stimuli on future sensory development. Effects of drugs given to the pregnant woman on the (preterm) newborn might be influenced by decreased or absent transplacental transport, compression of the umbilical cord during delivery, or diminished blood flow in the placenta in pre-eclamptic women, resulting in higher serum concentrations. Pharmacokinetics and drug metabolism change in the last trimester, and pain sensitivity may be altered after 32 weeks of gestation. Consequently, dose and dose interval may vary considerably between neonates and within an individual during the first days of life. This subpopulation is not homogenous, and drug doses in a term neonate with a postnatal age of 2 weeks may be quite different from those at birth and are certainly different from those in a premature neonate. Size must be disentangled from age-related factors when examining developmental pharmacokinetic parameters. There are no longitudinal studies published investigating the pharmacokinetic properties of any analgesic more than once per infant. Polymorphisms of the genes encoding for the enzymes involved in the metabolism of analgesics or in genes involved in receptor expression may contribute to the large interindividual pharmacokinetic parameter variability. Polymorphism of the human mu opioid receptor has not yet satisfactorily explained pharmacodynamic variability.

Treatment of pain in the neonatal intensive care unit

Pain is a disruptive influence on infants in the NICU. The most obvious and effective strategy to decrease infant pain in the NICU is to stringently limit the frequency of painful procedures, especially those that are most commonly reported (i.e., heel lances and endotracheal suctioning), and have these performed on infants that are most unstable or critically ill by the most experienced person available. Organizational concerns over the cost of NICU care have forced a re-evaluation of the necessity of certain diagnostic and care procedures and a limiting of procedures to those that can be documented to positively affect clinical outcome. Pharmacologic and nonpharmacologic strategies are essential to the prevention and management of neonatal pain, and these should be considered for complementary use for every infant. Research has shown the safety and effectiveness of some of the strategies in reducing mild pain caused by brief invasive procedures; however, many of the studies had methodologic limitations. Therefore, more research is required to determine the comparative efficacy of the various strategies and to document additive or synergistic effects when combined.

Plasma norepinephrine levels, vagal tone index, and flexor reflex threshold in premature neonates receiving intravenous morphine during the postoperative period: a pilot study

OBJECTIVE

The goal of this study was to evaluate the effects of a single dose of intravenous morphine on postoperative pain in extremely premature neonates after thoracotomy.

DESIGN

Descriptive correlational study.

PATIENTS

Twenty-four critically ill mechanically ventilated premature neonates with a mean gestational age of 26.1 +/- 2.1 (SD) weeks and a postnatal age of 13.8 +/- 8.1 (SD) days.

OUTCOME MEASURES

Plasma norepinephrine (NE) levels, vagal tone index (VTI), and flexor reflex threshold were measured preoperatively, immediately before, and 20 and 60 minutes after the administration of the first postoperative dose of morphine (0.1 mg/kg).

RESULTS

One-way repeated-measures ANOVA revealed no significant change in plasma NE levels from baseline levels (df[2,32] = 2.40, p = 0.11). Pre- and postmorphine VTI values were significantly lower than preoperative values (df[3,60] = 6.04, p = 0.0012), but no significant differences were found between pre- and postmorphine VTI values. Neonates (n = 10) who had a flexor reflex response during the postoperative period demonstrated no significant differences in the force required to elicit a flexor reflex across the four measurements (df[3,27] = 0.76, p = 0.53); however, the flexor reflex responses were significantly less vigorous during the postoperative period than at baseline.

CONCLUSIONS

Findings from this pilot study suggest that the dose of morphine commonly used to treat postoperative pain in premature neonates does not affect NE, VTI, and flexor reflex threshold values within 1 hour of administration.

Infant handling in the NICU: does developmental care make a difference? An evaluative review of the literature

Infant handling and disruptions in the neonatal intensive care unit are environmental stressors over which nurses have the most control. Two of the major goals of developmental care are individualizing care by decreasing infant disruptions and handling by caregivers, and modulating or attenuating infant responses to the care they receive. However, it has yet to be established to what extent these goals have been achieved. This article will provide a comparative review of selected literature to ascertain what effect, if any, the introduction of developmental care has had on infant handling or disruption in the neonatal intensive care unit.