Population pharmacokinetics of epsilon-aminocaproic acid in infants undergoing craniofacial reconstruction surgery

BACKGROUND

Understanding the clinical pharmacology of the antifibrinolytic epsilon-aminocaproic acid (EACA) is necessary for rational drug administration in children. The aim of this study is to determine the pharmacokinetics (PKs) of EACA in infants aged 6-24 months undergoing craniofacial reconstruction surgery.

METHODS

Cohorts of six infants were enrolled sequentially to one of the three escalating loading dose-continuous i.v. infusion (CIVI) regimens: 25 mg kg(-1), 10 mg kg(-1) h(-1); 50 mg kg(-1), 20 mg kg(-1) h(-1); 100 mg kg(-1), 40 mg kg(-1) h(-1). Plasma EACA concentrations were determined using a validated high-performance liquid chromatography-tandem mass spectrometry assay. A population non-linear mixed effects modelling approach was used to characterize EACA PKs.

RESULTS

Population PK parameters of EACA were estimated using a two-compartment disposition model with weight expressed as an allometric covariate and an age effect. The typical patient in this study had an age of 38.71 weeks and a weight of 8.82 kg. PK parameters for this typical patient were: pre-/postoperative plasma drug clearance of 32 ml min(-1) (3.6 ml kg(-1) min(-1)), inter-compartmental clearance of 42.4 ml min(-1) (4.8 ml min(-1) kg(-1)), central volume of distribution of 1.27 litre (0.14 litre kg(-1)), and peripheral volume of distribution of 2.53 litre (0.29 litre kg(-1)). Intra-operative clearance and central volume of distribution were 89% and 80% of the pre-/postoperative value, respectively.

CONCLUSIONS

EACA clearance increased with weight and age. The dependence of clearance on body weight supports weight-based dosing. Based on this study, a loading dose of 100 mg kg(-1) followed by a CIVI of 40 mg kg(-1) h(-1) is appropriate to maintain target plasma EACA concentrations in children aged 6-24 months undergoing these procedures.

Prospective randomized observer-blinded study comparing the analgesic efficacy of ultrasound-guided rectus sheath block and local anaesthetic infiltration for umbilical hernia repair

BACKGROUND

Umbilical hernia repair, a common day-surgery procedure in children, is associated with considerable postoperative discomfort. Possible modes of postoperative analgesia for umbilical hernia repair are rectus sheath block (RSB) and local anaesthetic infiltration of the surgical site (LAI).

METHODS

We undertook an observer-blinded, randomized, prospective, observational study to compare the efficacy of ultrasound-guided RSB and LAI in providing postoperative analgesia for umbilical hernia repair. Our primary objective was to compare the use of opioid medication between patients who receive RSB and those who receive LAI. Our secondary objectives were to compare the duration of analgesia based on time to first rescue analgesic, to compare the quality of analgesia based on revised FACES scale, and to determine the incidence of side-effects.

RESULTS

Fifty-two patients (26 in each group) completed the study. There was a statistically significant difference in the perioperative opioid medication consumption between the LAI group [mean: 0.13 mg kg(-1), confidence interval (0.09-0.17 mg kg⁻¹)] and the RSB group [mean: 0.07 mg kg⁻¹, confidence interval (0.05-0.09 mg kg⁻¹)] (P=0.008). When we compared the postoperative opioid consumption between the LAI group [mean: 0.1 mg kg⁻¹, 95% confidence interval (0.07-0.13 mg kg⁻¹)] and the RSB group [mean: 0.07 mg kg(-1), 95% confidence interval (0.05-0.09 mg kg⁻¹)] (P=0.09), there was a trend towards statistical significance between the two groups. The difference in time to rescue analgesic administration between the RSB group [49.7 (36.9) min] and the LAI group [32.4 (29.4) min] was not statistically significant (P=0.11).

CONCLUSIONS

This study demonstrates that ultrasound-guided RSB provides superior analgesia in the perioperative period compared with infiltration of the surgical site after umbilical hernia repair. In comparing only the postoperative period, analgesia provided by an ultrasound-guided RSB showed a trend towards statistically significant improvement compared with infiltration of the surgical site.

Ensuring safety of patients receiving sedation for procedures: evaluation of clinical practice guidelines

BACKGROUND

In 1995 The Johns Hopkins Hospital in Baltimore convened an interdisciplinary task force to evaluate sedation practices, create a comprehensive set of sedation guidelines, and evaluate patient safety outcomes following guideline implementation.

METHODOLOGY

Baseline data were collected on all procedures in which sedation was administered by a nonanesthesiologist for a 6-month period, using scanning technology to automate data entry. Sedation practices were reviewed, and four critical events were examined: unresponsiveness, obstructed airway, airway placement, and cardiopulmonary resuscitation (CPR). In 1998 data collection procedures were repeated to evaluate the impact of the guidelines on sedation practices and patient safety outcomes.

RESULTS

In 1995 sedation practices varied, and one or more critical events occurred in 45 (1.4%) of 3,255 procedures. Steps taken included development and dissemination of a clinical sedation guideline, including monitoring criteria to guide nonanesthesiologists, and evaluation planning. In 1998 sedation practices were more consistent. One or more critical events occurred in 50 (1.6%) of 3,134 procedures, representing a small increase in critical events from 1995. More events of unresponsiveness were identified, and no event required CPR. Although not statistically significant, this trend suggests that critical events were being identified earlier, preventing patients from progressing to a more serious event requiring CPR. Steps taken included further refinement of clinical practice guidelines and establishment of ongoing monitoring.

CONCLUSIONS

Standardization of sedation practices is a complex and resource-intensive activity, requiring ongoing oversight and monitoring. Commitment from medical staff, nursing staff, and administration is essential to successful implementation of sedation guidelines.

Perioperative management issues in pediatric patients

Recent developments in perioperative practice, emphasizing issues that are of greatest concern in pediatric patients, are reviewed in this article. Many areas bear further evaluation in the evolving field of perioperative medicine: Effective techniques of psychologic preparation for children and their parents in an era in which the family rarely encounters the hospital environment before the day of surgery Application of newer intraoperative anesthetics, such as new narcotics and muscle relaxants, to shorten PACU and pediatric ICU stay while maintaining safety and comfort Critical evaluation of current methods of pain management to optimize comfort, while minimizing cost of such management in an increasingly cost-conscious health care environment The recent advent of a process for credentialing pediatric anesthesia fellowship programs, which requires a research component, bodes well for the prospect of finding answers to some of these questions.

The management of pain in sickle cell disease

The pain of vaso-occlusive crisis in patients with sickle cell disease is excruciating, incapacitating, and sometimes refractory to even the most advanced analgesic treatments. A comprehensive, multimodal approach to therapy that includes education, cognitive therapies, anti-inflammatory drugs, opioids, and psychostimulant adjuvant drugs has been presented. Until a cure for the underlying disease is found, these are the best approaches available. The authors hope that future research will find even better modalities of analgesic care.

Polysomnography after adenotonsillectomy in mild pediatric obstructive sleep apnea

OBJECTIVES

a) To determine the need for intensive monitoring on the first operative night of surgery in children undergoing adenotonsillectomy for mild obstructive sleep apnea; b) to examine the effect of narcotics on postoperative obstructive sleep apnea.

DESIGN

Randomized, prospective study.

SETTING

University hospital.

PATIENTS

Children, ranging in age between 1 and 18 yrs, presented to the Pediatric Otolaryngology Clinic for adenotonsillectomy for mild obstructive sleep apnea defined as from one to 15 obstructive apnea events per hour on preoperative polysomnogram.

INTERVENTIONS

Patients were assigned to receive either a narcotic- or a halothane-based anesthetic for adenotonsillectomy. A postoperative polysomnogram was performed in the pediatric intensive care unit on the first operative night.

MEASUREMENTS AND MAIN RESULTS

Eighteen patients were recruited, 15 of whom met inclusion criteria: nine patients received a halothane-based anesthetic and six patients received a fentanyl-based anesthetic. When the data were analyzed by pooling both groups, the differences between pre- and postoperative sleep studies demonstrated a reduction in the number of obstructive events and less severe oxygen desaturations on the operative night. Total sleep time between the two sleep studies decreased from 371 +/- 13 to 304 +/- 14 mins. The number of obstructive apnea events/hr decreased as well. The lowest oxygen saturation measured during rapid eye movement sleep was 78 +/- 5% preoperatively and 92 +/- 1% postoperatively.

CONCLUSIONS

Our data suggest that children without underlying medical conditions, neuromotor diseases, or carniofacial abnormalities, 1 to 18 yrs of age, who suffer from mild obstructive sleep apnea, have improvements documented by polysomnography on the night of surgery following adenotonsillectomy and do not necessarily need to be monitored intensively. These findings were not significantly affected by the choice of intraoperative anesthetic.

Preanesthetic medication of children with midazolam using the Biojector jet injector

BACKGROUND

A rapid, dependable, and economical technique to atraumatically sedate children before anesthesia that does not prolong postanesthesia care unit time remains elusive. The Biojector jet injection system uses carbon dioxide rather than a needle to deliver an intramuscular injection. The dose-response relationship when midazolam is administered was studied using this jet injector.

METHODS

Forty children (2.3 +/- 1.3 yr old) undergoing elective myringotomy and tube placement were randomly assigned to receive 0.05, 0.1, 0.15, 0.2, or 0.3 mg.kg-1 midazolam injected intramuscularly using the Biojector disposable syringe (0.006-inch orifice). Assessment of each child before, during, and 10 min after injection, on application of the anesthesia face mask, and every 15 min for 1 h after arrival to the postanesthesia care unit was made by an observer blinded to drug dosage.

RESULTS

Face mask tolerance using doses > or = 0.1 mg.kg-1 midazolam was acceptable and statistically different from 0.05 mg/kg. Crying on injection tended to increase with increasing dose. All children were awake and arousable, meeting discharge criteria, after 30 min from arrival in the postanesthesia care unit.

CONCLUSIONS

Midazolam (0.1-0.15 mg.kg-1) administered using jet injection effectively and rapidly produces sedation, in a manner acceptable to parents, without delaying postanesthesia care unit discharge.

Preoperative evaluation of children

Preoperative evaluation and preparation are directed toward minimizing the intrinsic risks of anesthesia and surgery by having the child in the healthiest possible condition prior to surgery. The pediatrician can contribute to this goal by understanding the effects of general anesthesia on the physiology of children. This knowledge allows an appreciation of the anesthesiologists' concerns regarding underlying diseases, which may seem "stable" (and, therefore, of little present concern to the pediatrician) but which may have grave consequences during anesthesia. The preoperative evaluation is designed to ensure that the child's preoperative needs may be met by providing the anesthesiologist both qualitative and quantitative information regarding the child's state of health and disease. The relationship between the child, parents, and pediatrician places the pediatrician in an ideal position to prepare families for their children's surgical experience.

Disposition and respiratory effects of intrathecal morphine in children

BACKGROUND

The extent and duration of respiratory depression after opioid administration are poorly defined in infants and children.

METHODS

The disposition and respiratory effects of intrathecal morphine were studied in ten patients (ages 4 months-15 yr) after repair of craniofacial defects. Morphine, 0.02 mg/kg, was administered intrathecally before the end of surgery. Postoperatively, we determined the minute ventilation (VE) in response to increasing partial pressure of end-tidal carbon dioxide (PETCO2) during carbon dioxide rebreathing. The slope (VE/PETCO2) and intercept (VE at PETCO2 60 mmHg, VE 60) of the carbon dioxide response curve were calculated at 6, 12, and 18 h after morphine administration. Cerebrospinal fluid (CSF) and blood were analyzed for morphine concentration by radioimmunoassay.

RESULTS

Mean VE/PETCO2 decreased from a preoperative value of 35.1 +/- 3.7 to 16.3 +/- 2.8 ml.kg-1 x min-1 x mmHg-1 at 6 h after morphine, and remained depressed to 23.4 +/- 2.9 and 23.5 +/- 3.3 ml.kg-1 x min-1 x mmHg-1 at 12 h and 18 h, respectively, compared to preoperatively). The infants' (n = 3) VE/PETCO2 at 6 h were 21, 4, and 27 ml.kg-1 x min-1 x mmHg-1. Mean VE 60 decreased from 874 +/- 125 to 276 +/- 32 ml x kg-1 x min-1 at 6 h, but then recovered at 12 and 18 h to 491 +/- 68 and 567 +/- 82 ml.kg-1 x min-1, respectively. The infants' VE 60 at 6 h were 350, 142, and 245 ml.kg-1 x min-1. Mean CSF morphine concentration was 2,860 +/- 540 ng/ml at 6 h, and decreased to 640 +/- 220 and 220 +/- 150 ng/ml at 12 and 18 h, respectively.

CONCLUSIONS

Intrathecal morphine, 0.02 mg/kg, depressed the ventilatory response to carbon dioxide for up to 18 h concomitant with increased CSF morphine concentrations. Infants (4-12 months of age) did not exhibit greater ventilatory depression than did children (2-15 yr of age).

Preinduction of anesthesia in children with rectally administered midazolam

The authors evaluated the efficacy of rectally administered midazolam for preinduction (i.e., premedication/induction) of anesthesia in 67 pediatric patients, ASA physical status 1 or 2, undergoing a variety of elective surgical procedures. In phase 1, 41 children weighing 12 +/- 3 kg (range 7-20 kg) and 31 +/- 16 months (range 8-67 months) of age (mean +/- SD) received midazolam, 0.4-5.0 mg.kg-1, in an attempt to produce unconsciousness. Only one child lost consciousness (4.5 mg.kg-1). However, at all doses, inhalational induction of anesthesia was facilitated because children were tranquil and calmly separated from their parent(s). There were no clinically significant changes in arterial blood pressure, heart rate, oxyhemoglobin saturation, and end-tidal carbon dioxide concentration, 10 min after drug administration. In phase 2, 26 children weighing 17 +/- 4 kg (range 10-26 kg) and 44 +/- 19 months (range 17-84 months) months of age undergoing tonsil and/or adenoid surgery were studied to determine the optimal sedative dose of rectally administered midazolam. Patients received 0.3, 1.0, 2.0, or 3.0 mg.kg-1 of midazolam in a randomized, double-blind fashion. One third (3 of 9) of patients receiving 0.3 mg.kg-1 struggled during mask induction. All patients receiving greater than or equal to 1.0 mg.kg-1 were adequately sedated (P less than 0.008). Discharge from the postanesthesia care unit (PACU), however, was delayed (greater than 60 min) in children receiving greater than or equal to 2.0 mg.kg-1 (P less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Postoperative analgesia. Use of intrathecal morphine in children

The identification of opiate receptors in the spinal cord gave rise to the suggestion that the use of intrathecal and epidural narcotics may provide effective and safe postoperative analgesia. The authors retrospectively reviewed the records of ten children who received intrathecal morphine as part of their anesthetic care over the last 2 years. Preservative-free morphine (Duramorph) in a dose of 0.02 mg/kg was administered to all patients in the lumbar intrathecal space before the start of the surgical procedure. Adequate postoperative analgesia was achieved in the ten children. No patient required supplemental analgesic agents for the initial 15-hour postoperative period. Surgical procedures included exploratory laparotomy, laryngotracheoplasty, and craniofacial reconstruction. As with narcotics administered by any route, intrathecal morphine can cause respiratory depression, and such depression may be delayed for up to 24 hours after the dose. Therefore, the postoperative respiratory status of these children should be monitored for 24 hours after the dose, preferably in an intensive care unit. With this caveat, the use of intrathecal morphine provides safe and effective postoperative analgesia in children undergoing major surgery.

Prediction of successful primary closure of congenital abdominal wall defects using intraoperative measurements

To determine whether intragastric pressure (IGP) and central venous pressure (CVP) would reliably predict successful primary closure of congenital abdominal wall defects (omphalocele/gastroschisis) in newborn infants, we developed the following prospective intraoperative management protocol. Following a temporary trial of fascial closure, infants who had an IGP less than 20 mm Hg or an increase in CVP of less than 4 mm Hg were primarily closed. If IGP was greater than 20 mm Hg or if CVP increased by more than 4 mm Hg, the temporary closure of the abdomen was reopened and a prosthetic silo was placed. Ten infants who were less than 24 hours old and averaged 2.7 kg (range, 1.4 to 4.2 kg) and 37-weeks gestation (range, 32 to 41 weeks) were studied. Eight infants met criteria for primary closure. Their IGP averaged 14 +/- 4 mm Hg (+/- SD) (range, 8 to 19 mm Hg), and their increase in CVP averaged 1 +/- 2 mm Hg (range, -2 to 3 mm Hg). In the two infants who required staged repair, IGP averaged 25 +/- 1 mm Hg (+/- SD) (range, 24 to 25 mm Hg), and the increase in CVP averaged 7 +/- 1 mm Hg (range, 6 to 8 mm Hg). All patients were anesthetized with fentanyl (12.5 micrograms/kg) and paralyzed with metocurine (0.3 mg/kg) intraoperatively. There were no postoperative complications in either group of patients related to increased intraabdominal pressure, and all patients were extubated within 48 hours of the initial surgery. We conclude that the intraoperative measurement of changes in IGP and CVP can serve as a guide to the operative management of congenital abdominal wall defects and can reliably predict successful outcome following repair.

Separation of craniopagus Siamese twins using cardiopulmonary bypass and hypothermic circulatory arrest

Occipitally joined craniopagus Siamese twins were separated with the use of cardiopulmonary bypass and hypothermic circulatory arrest. The 7-month-old infants shared a large sagittal venous sinus that precluded conventional neurosurgical approach because of risk of exsanguination and air embolism. After craniotomy and preliminary exposure of the sinus, each twin underwent sternotomy and total cardiopulmonary bypass with deep hypothermia. Hypothermic circulatory arrest allowed safe division and subsequent reconstruction of the sinus remnants. Several unusual problems were encountered, including transfusion of a large blood volume from one extracorporeal circuit to the other through the common venous sinus, deleterious warming of the exposed brain during circulatory arrest, and thrombosis of both pump oxygenators. Both infants survived, although recovery was complicated in each by neurologic injury, cranial wound infection, and hydrocephalus. This case demonstrates the valuable supportive role of cardiopulmonary bypass and hypothermic circulatory arrest in the management of complex surgical problems of otherwise inoperable patients.

The pharmacologic management of pain in children

We have attempted to dispel many of the myths and misconceptions surrounding the use of narcotic analgesics in the treatment of childhood pain. Our hope is that an improved understanding and application of effective and safe therapies will minimize the suffering of the child with acute or chronic pain.

Penile nerve block for newborn circumcision

Circumcision in neonates is performed, almost universally, without anesthesia or analgesia. It is associated with pain, crying, agitation, and physiologic stress. Twenty infants receiving penile nerve block for circumcision were compared with ten infants having circumcision without anesthesia. Heart rate and blood pressure rose 34 and 15%, respectively, in unblocked infants, and were unchanged in infants receiving local anesthesia. Oxygen saturation declined 16% in unanesthetized infants compared with 6% in blocked infants (P less than .03). Anesthetized infants were less agitated and cried less. Peak plasma concentrations of the local anesthetic lidocaine averaged 0.51 +/- 0.17 microgram/mL (range 0.1-1.6), well below accepted toxic levels. There were no local or systemic complications.

Monitoring the resuscitation of preterm infants in the delivery room using pulse oximetry

The first few minutes after birth are a critical time of adaptation of the newborn infant to extrauterine life. The adequacy of that adaptation has been evaluated by means of the summed Apgar score. In preterm infants, Apgar score may correlate less with adequacy of cardiopulmonary function because of developmental immaturity. Measurement of arterial oxygen saturation by means of pulse oximetry offers a physiologic, real time method of monitoring the progress of cardiopulmonary adaptation by which the clinician can evaluate the need for and success of resuscitative efforts. Four preterm infants are reported in whom pulse oximetry was useful in assessing the changes in oxygen saturation during resuscitation.

Primary cutaneous phaeohyphomycosis caused by Drechslera spicifera

A primary cutaneous lesion in a 5-year-old boy who had recently received chemotherapy for acute lymphocytic leukemia was found to be caused by a dematiaceous fungus, Drechslera spicifera. The lesion was an erythematous macule that rapidly developed necrotic ulcerations. The fungus, which is commonly found in soil and as a plant pathogen, was isolated from cultures of the lesion and from an excisional biopsy specimen. Hyphae and swollen hyphal cells resembling chlamydospores were observed in the biopsy specimen. Septate pigmented hyphae were found in the tissue, which is consistent with phaeohyphomycosis. Resolution of the infection occurred following excisional biopsy and systemic amphotericin B therapy. There was a concomitant recovery from neutropenia.