Prospective study on the occurrence of withdrawal in critically ill children who receive fentanyl by continuous infusion

Opioid tolerance in neonates: mechanisms, diagnosis, assessment, and management

Opioid tolerance and withdrawal have been challenges for decades. The neurochemical mechanisms of tolerance and dependence are clinically important only because they can affect weaning schedules and the adjustment of doses for neonates. Analgesic effects are characterized by an increased depolarization threshold for the neuron, shorter duration of the action potential generated, and reduced release of neurotransmitters. Tolerance and withdrawal are associated with the reversal of these cellular effects. Adverse clinical effects associated with the use of opioids in neonates include respiratory depression, chest wall rigidity, urinary retention, and decreased gastrointestinal motility. The physiological systems most prominently affected by opioid withdrawal include the central nervous system, gastrointestinal system, and the autonomic nervous system. Opioid withdrawal symptoms in neonates can be assessed by using easily available scoring systems, although these need to be validated for different populations. Management of opioid withdrawal includes the use of other opioids, benzodiazepines and alpha-2 adrenergic receptor antagonist, clonidine. Careful titration of opioids with attention given to appropriate weaning schedules can reduce the incidence of withdrawal in neonates.

Variation among neonatal intensive care units in narcotic administration

OBJECTIVES

To compare rates of narcotic administration for medically treated neonates in different neonatal intensive care units (NICUs) and to compare treated and untreated neonates to assess whether narcotics provided advantages or disadvantages for short-term outcomes, such as cardiovascular stability (ie, blood pressure and heart rate), hyperbilirubinemia, duration of respiratory support, growth, and the incidence of intraventricular hemorrhage.

STUDY DESIGN

The medical charts of neonates weighing less than 1500 g, admitted to 6 NICUs (A-F), were abstracted. Neonates who had a chest tube or who had undergone surgery were excluded from the study, leaving the records of 1171 neonates. We modeled outcomes by linear or logistic regression, controlling for birth weight (<750, 750-999, and 1000-1499 g) and illness severity (low, 0-9; medium, 10-19; high, > or =20) using the Score for Neonatal Acute Physiology (SNAP), and adjusted for NICU.

RESULTS

Narcotic use varied by birth weight (<750 g, 21%; 750-999 g, 13%; and 1000-1499 g, 8%), illness severity (low, 9%; medium, 19%; and high, 37%), day (1, 11%; 3, 6%; and 14, 2%), and NICU. We restricted analyses to the 1018 neonates who received mechanical ventilation on day 1. Logistic regression, adjusting for birth weight and SNAP, confirmed a 28.6-fold variation in narcotic administration (odds ratios, 4.1-28.6 vs NICU A). Several short-term outcomes also were associated with narcotic use, including more than 33 g of fluid retention on day 3 and a higher direct bilirubin level (6.8 micromol/L higher [0.4 mg/dL higher], P = .03). There were no differences in weight gain at 14 and 28 days or mechanical ventilatory support on days 14 and 28. Narcotic use was not associated with differences in worst blood pressure or heart rate or with increased length of hospital stay.

CONCLUSIONS

Our study found a 28.6-fold variation among NICUs in narcotic administration in very low-birth-weight neonates. We were unable to detect any major advantages or disadvantages of narcotic use. We did not assess iatrogenic abstinence syndrome or long-term outcomes. These results indicate the need for randomized trials to rationalize these widely differing practices.

Acute withdrawal syndrome related to the administration of analgesic and sedative medications in adult intensive care unit patients

OBJECTIVES

To estimate the frequency of acute withdrawal syndrome related to the administration of analgesic and sedative medications in mechanically ventilated adult intensive care unit (ICU) patients; to identify associated clinical factors.

DESIGN

Retrospective review of medical records.

SETTING

An adult trauma/surgical ICU in an urban Level I trauma center.

PATIENTS

Twenty-eight mechanically ventilated adult trauma/ surgical ICU patients requiring >7 days of ICU care.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Daily doses of all opioid, sedative, hypnotic, and major tranquilizer drugs administered to each patient were measured, as was duration of ICU stay, duration of mechanical ventilation, and duration of the administration of analgesic, sedative, and neuromuscular blocking agents (NMBAs) for each patient. All opioids and benzodiazepines were converted to their respective fentanyl and lorazepam equivalent units based on potency and bioavailability. Calculation of the weaning rate for each patient during tapering from opioid and benzodiazepine medications was performed. The presence or absence of acute withdrawal syndrome was identified for each patient. Nine (32.1%) patients developed acute withdrawal syndrome potentially related to the administration of analgesic or sedative medications. Patients in the withdrawal group received significantly higher mean daily (p = .049) and peak (p = .032) doses of fentanyl equivalents, as well as higher mean daily lorazepam equivalents (p = .049) compared with patients not experiencing withdrawal. Patients in the withdrawal group were also significantly more likely to have received neuromuscular blocking agents (p = .004) or propofol (p =.026) for >1 day during ICU admission compared with patients not experiencing withdrawal. Duration of mechanical ventilation (p = .049), benzodiazepine therapy (p = .048), and propofol therapy (p = .049) was also significantly longer in the group experiencing withdrawal. Withdrawal patients received a significantly lower mean daily dose of haloperidol (p = .026). There was a significant association between the development of withdrawal syndrome and the presence of ARDS (p = .017). Finally, the slopes of the lines representing opioid and benzodiazepine drug weaning were more steep for the withdrawal group, although these results did not achieve statistical significance.

CONCLUSIONS

These results suggest that mechanically ventilated adult patients with extended ICU care (> or =7 days) who receive large doses of analgesic and sedative medications are at risk for acute withdrawal syndromes during drug weaning. The association between ARDS and withdrawal syndrome, combined with the observation that withdrawal syndromes were also associated with the use of neuromuscular blocking agents and prolonged mechanical ventilation, suggests that patients with ARDS may be more likely to receive high doses of analgesic and sedative medications, and are therefore at increased risk for withdrawal syndrome.

Characterization of neonatal rat morphine tolerance and dependence

The administration of morphine and fentanyl by continuous intravenous infusion has been shown to produce analgesic tolerance and physical dependence in human neonates. In animals, daily repeated morphine bolus injections is a common method of inducing neonatal rat tolerance and dependence. Yet this method differs from the intravenous route reported to affect human neonates. Alzet osmotic minipumps were implanted in postnatal day 14 rats to provide a continuous morphine infusion more closely mimicking the clinical picture. Rats remained naive or were infused with saline or morphine (0.7 mg/kg/h) for 72 h. Morphine's antinociceptive potency was similar between naive and saline-infused animals, while morphine-infused animals were tolerant. Gender did not contribute to the degree of tolerance observed. Naloxone precipitated withdrawal in the morphine pump-implanted rats was similar to that reported by others. Thus, minipumps provide a useful model for assessing the tolerance and dependence liability of different opioids.

Adverse reactions to the withdrawal of opioids and benzodiazepines in paediatric intensive care

The aim of this study was to examine adverse reactions to the withdrawal of opioids and benzodiazepines among critically ill children. Although withdrawal reactions have been well documented in relation to substance abusers and their newborn infants, there has been little study of this phenomenon as an iatrogenic problem. We developed a graphical case study method for examining patterns over time, and applied this to five cases referred to us by the nursing staff of a 10-bed paediatric intensive care unit. A striking pattern of behavioural distress was clearly associated with the diminution of opioids and benzodiazepines. These adverse reactions were characterized by various combinations of inconsolable crying, tremors, jitteriness, irritability, gagging, vomiting, and feeding problems. These signs appeared as early as 1 h and as late as 24 h following a significant reduction in opioid and benzodiazepine infusion rates, sometimes following very short-term therapy. We elaborate an interpretation of this distress, in light of the multiple disruptions undergone by critically ill children, and conclude by outlining our recommendations for preventing/minimizing these adverse reactions.

Opioid Withdrawal Presenting as Stridor

Following the prolonged administration of opioids for sedation in the PICU, tolerance and physical dependency may occur. In patients who have become tolerant, physical signs of withdrawal may occur when these agents are discontinued. The actual signs and symptoms of withdrawal vary from patient to patient, but the majority of the literature documents problems such as hyperactivity of the sympathetic nervous system included tachycardia, hypertension, diaphoresis, and tremulousness. The author presents two patients who developed symptoms of upper airway obstruction, including stridor, as the major manifestation of opioid withdrawal. Operative inspection of the airway with rigid bronchoscopy and direct laryngoscopy demonstrated no airway abnormalities. Reinstitution of opioid therapy resulted in a prompt resolution of symptoms and a more gradual tapering of the opioid dose prevented recurrence of the problem.

Neonatal abstinence syndrome due to codeine

The neonatal abstinence syndrome (NAS) is a potentially life threatening illness associated with significant morbidity especially in the neonatal period. A case of NAS due to codeine prescribed for pain relief during pregnancy is reported. Clinicians should be aware that narcotic derivatives prescribed in late pregnancy can give rise to this type of problem.

Out-patient Therapy of Iatrogenic Opioid Dependency following Prolonged Sedation in the Pediatric Intensive Care Unit

As a result of heightened awareness of the need for aggressive sedation and analgesia in the pediatric intensive care unit population, the risk for opioid withdrawal continues to increase. Although gradual tapering of the intravenous dose of opioid can be used to prevent such problems, this approach mandates maintenance of intravenous access and in-patient hospital admission. I present experience with the out-patient use of oral methadone to prevent opioid withdrawal following prolonged fentanyl sedation in the pediatric intensive care unit. A cohort of 18 patients is reviewed, and suggested guidelines for out-patient management of these patients using oral methadone are presented.

Possible involvement of the total amount of morphine infused in the development of acute morphine dependence in rats

The severity of naloxone-precipitated withdrawal in rats infused intravenously with morphine at the rates of 2.5, 5 and 10 mg/kg/hr over various time periods was investigated. Plasma morphine concentration reached a constant and rate-dependent level at 1 hr after the start of morphine infusion, and this level was maintained until the termination of infusion. Naloxone (2.0 mg/kg, s.c.) was challenged 18 hr after infusion was stopped, and the withdrawal was evaluated by plasma corticosterone (PCS) increase, diarrhea and body weight loss. The incidence of naloxone-precipitated withdrawal signs was related to both the infusion rate and duration of morphine infusion. The duration of morphine infusion (ET50) needed to elicit naloxone-precipitated PCS increase and diarrhea in 50% of the rats was inversely related to the morphine infusion rates, but the total amount of infused morphine (EA50) that elicited naloxone-precipitated withdrawals in 50% of rats was the same at all infusion rates. These results suggest that the total amount of morphine infused may play an important role in the development of acute physical dependence on morphine rendered by continuous intravenous morphine infusion for 1-8 hr.

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.