Gregory B. Hammer

The effects of dexmedetomidine on cardiac electrophysiology in children.

BACKGROUND:Dexmedetomidine (DEX) is an &agr;2-adrenergic agonist that is approved by the Food and Drug Administration for short-term (<24 h) sedation in adults. It is not approved for use in children. Nevertheless, the use of DEX for sedation and anesthesia in infants and children appears to be increasing. There are some concerns regarding the hemodynamic effects of the drug, including bradycardia, hypertension, and hypotension. No data regarding the effects of DEX on the cardiac conduction system are available. We therefore aimed to characterize the effects of DEX on cardiac conduction in pediatric patients. METHODS:Twelve children between the ages of 5 and 17 yr undergoing electrophysiology study and ablation of supraventricular accessory pathways had hemodynamic and cardiac electrophysiologic variables measured before and during administration of DEX (1 &mgr;g/kg IV over 10 min followed by a 10-min continuous infusion of 0.7 &mgr;g · kg−1 · h−1). RESULTS:Heart rate decreased while arterial blood pressure increased significantly after DEX administration. Sinus node function was significantly affected, as evidenced by an increase in sinus cycle length and sinus node recovery time. Atrioventricular nodal function was also depressed, as evidenced by Wenckeback cycle length prolongation and prolongation of PR interval. CONCLUSION:DEX significantly depressed sinus and atrioventricular nodal function in pediatric patients. Heart rate decreased and arterial blood pressure increased during administration of DEX. The use of DEX may not be desirable during electrophysiology study and may be associated with adverse effects in patients at risk for bradycardia or atrioventricular nodal block.

Factors affecting survival after orthotopic liver transplantation in infants.

The technical and medical management of small infants requiring orthotopic liver transplantation remains a challenge. The present study examined 117 orthotopic liver transplantations performed in 101 infants from <1 to 23 months of age between March 1988 and February 1995 to determine factors that influence patient and graft outcome. Factors analyzed included etiology of liver disease, recipient and donor age and weight, United Network for Organ Sharing (UNOS) status, retransplantation, ABO-compatibility, full-size (FS) versus reduced-size grafts, vascular thrombosis (VT), including hepatic artery and portal vein (PVT), and the presence of lymphoproliferative disease (LPD). UNOS status 1, fulminant hepatic failure, and the development of Epstein-Barr virus-associated LPD were each associated with 10-20% lower patient and graft survival rates. Of 101 infants, 11 (11%) developed LPD with an associated 36% mortality. VT occurred in 10 (9 hepatic artery and 1 portal vein) of 117 orthotopic liver transplantations (9%), all less than 1 year of age, and was associated with significantly poorer 1-year (50% vs. 85% no VT, P<0.01) and 5-year patient survival rates (50% vs. 83% no VT, P<0.01). One-year graft survival rates for FS grafts in recipients <12 months versus 12-23 months were 67% vs. 94% (P<0.01); the patient survival rate was also significantly lower in FS graft recipients <12 months (76% vs. 100%, P<0.05). Recipients <5 months of age had the worst survival rates: 1-year and 5-year patient survival rates were 65% and 46% for recipients 0-4 months (n=17) versus 82% and 82% for recipients 5-11 months (n=56), and 93% and 93% for recipients age 12-23 months (n=28; P<0.05). In summary, factors associated with reduced survival rates include recipient age <5 months, recipient age <12 months who received FS grafts, development of VT and donor weight <6 kg. There was a trend for UNOS status 1, fulminant hepatic failure, and presence of LPD to be associated with reduced survival rates.

Methods for Single-Lung Ventilation in Pediatric Patients

We reviewed published values for airway measurements in children (Table 1) (1,2). Data from the first study was derived by analyzing fresh autopsy specimens of intact tracheo-bronchial trees from 160 children between the ages of 6 mo and 16 yr (1). Thin cross-sections of the airways were made at various levels and photographed on color slides. By using a metric rule photographed with the specimen, measurements were read from the projected slides. The second set of data was obtained from chest computed tomographic examinations of 130 children from 1–21 yr of age (2). The trachea is elliptical in shape, with the frontal diameter exceeding the sagittal diameter. Because the sagittal dimension is the “limiting” diameter and determines the largest tube that will fit, the sagittal measurement was used as our value for tracheal diameter. Data for bronchial dimensions were calculated using measured tracheal-to-bronchial ratios in children (3). Tube dimensions were obtained from each manufacturer and by direct measurement by a biomedical engineer using calipers accurate to within 0.025 mm.

A retrospective examination of regional plus general anesthesia in children undergoing open heart surgery.

The use of regional anesthesia in combination with general anesthesia for children undergoing cardiac surgery is receiving increasing attention from clinicians. The addition of regional anesthesia may improve clinical outcomes and decrease costs as a result of the reduced need for postoperative mechanical ventilation. The goal of this retrospective chart review was to evaluate whether spinal anesthesia (SAB) or epidural anesthesia (EPID) in combination with general anesthesia was associated with circulatory stability, satisfactory postoperative sedation/analgesia, and a low incidence of adverse effects. The medical records of 50 consecutive children having open heart surgery with SAB or EPID and general anesthesia between September 1996 and December 1997 were reviewed. We found no significant differences in the incidence of clinically significant changes in vital signs, oxygen desaturation, hypercarbia, or vomiting. Patients in the SAB group received significantly more sedative/analgesic interventions than those in the EPID group. Implications Techniques for combining regional and general anesthesia in children undergoing open heart surgery are described. Patients having spinal anesthesia may require more sedative/analgesic interventions postoperatively compared with those having epidural anesthesia. A prospective study with a larger sample size is required to determine other differences, including the incidence of postoperative vomiting.

Ketamine does not increase pulmonary vascular resistance in children with pulmonary hypertension undergoing sevoflurane anesthesia and spontaneous ventilation.

BACKGROUND:The use of ketamine in children with increased pulmonary vascular resistance is controversial. In this prospective, open label study, we evaluated the hemodynamic responses to ketamine in children with pulmonary hypertension (mean pulmonary artery pressure >25 mm Hg). METHODS:Children aged 3 mo to 18 yr with pulmonary hypertension, who were scheduled for cardiac catheterization with general anesthesia, were studied. Patients were anesthetized with sevoflurane (1 minimum alveolar anesthetic concentration [MAC]) in air while breathing spontaneously via a facemask. After baseline catheterization measurements, sevoflurane was reduced (0.5 MAC) and ketamine (2 mg/kg IV over 5 min) was administered, followed by a ketamine infusion (10 &mgr;g · kg−1 · min−1). Catheterization measurements were repeated at 5, 10, and 15 min after completion of ketamine load. Data at various time points were compared (ANOVA, P < 0.05). RESULTS:Fifteen patients (age 147, 108 mo; median, interquartile range) were studied. Diagnoses included idiopathic pulmonary arterial hypertension (5), congenital heart disease (9), and diaphragmatic hernia (1). At baseline, median (interquartile range) baseline pulmonary vascular resistance index was 11.3 (8.2) Wood units; 33% of patients had suprasystemic mean pulmonary artery pressures. Heart rate (99, 94 bpm; P = 0.016) and Pao2 (95, 104 mm Hg; P = 007) changed after ketamine administration (baseline, 15 min after ketamine; P value). There were no significant differences in mean systemic arterial blood pressure, mean pulmonary artery pressure, systemic or pulmonary vascular resistance index, cardiac index, arterial pH, or Paco2. CONCLUSIONS:In the presence of sevoflurane, ketamine did not increase pulmonary vascular resistance in spontaneously breathing children with severe pulmonary hypertension.

Anaesthetic management for the child with a mediastinal mass.

Administering anaesthesia to a child with an anterior mediastinal mass may lead to respiratory or circulatory collapse, even in those without symptoms. Institutions should have algorithms to manage children with mediastinal masses. Preoperative evaluations should include computed tomography, echocardiography and flow‐volume studies. Anaesthesia may be induced with inhalation agents and maintained with spontaneous respiration via facemask or laryngeal mask airway. Alternatively, positive‐pressure ventilation may be used, including tracheal intubation without muscle relaxants. Rigid bronchoscopy may be life‐saving in the event of tracheal or bronchial collapse under anaesthesia.

Prolonged infusion of dexmedetomidine for sedation following tracheal resection

Dexmedetomidine is a centrally acting alpha‐2 adrenergic agonist that is currently approved by the US Food and Drug Administration for short‐term use (≤24 h) to provide sedation in adults in the ICU. This drug has been shown to be efficacious in adult medical and surgical patients in providing sedation, anxiolysis, and analgesia. Dexmedetomidine has been associated with rapid onset and offset, hemodynamic stability, and a natural, sleep‐like state in mechanically ventilated adults. To date, there are few publications of the use of this drug in children, and prolonged infusion has not been described. We report our use of dexmedetomidine in a child during a 4‐day period of mechanical ventilation following tracheal reconstruction for subglottic stenosis.

Determination of the Pharmacodynamic Interaction of Propofol and Remifentanil during Esophagogastroduodenoscopy in Children

Background: Propofol is commonly used to anesthetize children undergoing esophagogastroduodenoscopy. Opioids are often used in combination with propofol to provide total intravenous anesthesia. Because both propofol and remifentanil are associated with rapid onset and offset, the combination of these two drugs may be particularly useful for procedures of short duration, including esophagogastroduodenoscopy. The authors previously demonstrated that the median effective concentration (C50) of propofol during esophagogastroduodenoscopy in children is 3.55 μg/ml. The purpose of this study was to describe the pharmacodynamic interaction of remifentanil and propofol when used in combination for esophagogastroduodenoscopy in pediatric patients. Methods: The authors studied 32 children aged between 3 and 10 yr who were scheduled to undergo esophagogastroduodenoscopy. Propofol was administered via a target-controlled infusion system using the STANPUMP software based on a pediatric pharmacokinetic model. Remifentanil was administered as a constant rate infusion of 25, 50, and 100 ng · kg−1 · min−1 to each of three study groups, respectively. A sigmoid Emax model was developed to describe the interaction of remifentanil and propofol. Results: There was a positive interaction between remifentanil and propofol when used in combination. The concentration of propofol alone associated with 50% probability of no response was 3.7 μg/ml (SE, 0.4 μg/ml), and this was decreased to 2.8 μg/ml (SE, 0.1 μg/ml) when used in combination with remifentanil. Conclusion: A remifentanil infusion of 25 ng · kg−1 · min−1 reduces the concentration of propofol required for adequate anesthesia for esophagogastroduodenoscopy from 3.7 to 2.8 μg/ml. Increasing the remifentanil infusion yields minimal additional decrease in propofol concentration and may increase the risk of side effects.

Single-lung Ventilation in Pediatric Patients

Single-lung Ventilation in Pediatric Patients Gregory Hammer;Steven Manos;Baird Smith;Erik Skarsgard;Jay Brodsky; Anesthesiology

Perioperative complications in children with pulmonary hypertension undergoing general anesthesia with ketamine

Background:  Pulmonary arterial hypertension (PAH) is associated with significant perioperative risk for major complications in children, including pulmonary hypertensive crisis and cardiac arrest. Uncertainty remains about the safety of ketamine anesthesia in this patient population.