Structural and functional linkages between subunit interfaces in mammalian pyruvate kinase.

Mammalian pyruvate kinase (PK) is a four-domain enzyme that is active as a homo-tetramer. Tissue-specific isozymes of PK exhibit distinct levels of allosteric regulation. PK expressed in muscle tissue (M1-PK) shows hyperbolic steady-state kinetics, whereas PK expressed in kidney tissue (M2-PK) displays sigmoidal kinetics. Rabbit M1 and M2-PK are isozymes whose sequences differ in only 22 out of 530 residues per subunit, and these changes are localized in an inter-subunit interface. Previous studies have shown that a single amino acid mutation to M1-PK at either the Y (S402P) or Z (T340 M) subunit interface can confer a level of allosteric regulation that is intermediate to M1-PK and M2-PK. In an effort to elucidate the roles of the inter-subunit interaction in signal transmission and the functional/structural connectivity between these interfaces, the S402P mutant of M1-PK was crystallized and its structure resolved to 2.8 A. Although the overall S402P M1-PK structure is nearly identical with the wild-type structure within experimental error, significant differences in the conformation of the backbone are found at the site of mutation along the Y interface. In addition, there is a significant change along the Z interface, namely, a loss of an inter-subunit salt-bridge between Asp177 of domain B and Arg341 of domain A of the opposing subunit. Concurrent with the loss of the salt-bridge is an increase in the degree of rotational flexibility of domain B that constitutes the active site. Comparison of previous PK structures shows a correlation between an increase in this domain movement with the loss of the Asp177: Arg341 salt-bridge. These results identify the structural linkages between the Y and Z interfaces in regulating the interconversion of conformational states of rabbit M1-PK.

Quaternary structure of the lactose transport protein of Streptococcus thermophilus in the detergent-solubilized and membrane-reconstituted state.

The quaternary structure of LacS, the lactose transporter of Streptococcus thermophilus, has been determined for the detergent-solubilized and the membrane-reconstituted state of the protein. The quaternary structure of the n-dodecyl-beta-d-maltoside-solubilized state was studied using a combination of sedimentation velocity and equilibrium centrifugation analysis. From these measurements it followed that the detergent-solubilized LacS undergoes reversible self-association with a monomer to dimer mode of association. The association constants were 5.4 +/- 3.6 and 4.4 +/- 1.0 ml mg(-1) as determined from the velocity and equilibrium sedimentation measurements, respectively. The experiments did not indicate significant changes in the shape of the protein-detergent complex or the amount of detergent bound in going from the monomeric to dimeric state of LacS. Importantly, a single Cys mutant of LacS is labeled by 2-(4'-maleimidylanilino)naphthalene-6-sulfonic acid in a substrate-dependent manner, indicating that the detergent-solubilized protein exhibits ligand binding activity. The quaternary structure of membrane-reconstituted LacS was determined by freeze-fracture electron microscopy analysis. Recent developments in the analysis of freeze-fracture images (Eskandari, S. P., Wright, E. M., Freman, M., Starace, D. M., and Zampighi, G. A. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 11235-11240) allowed us to directly correlate the cross-sectional area of the transmembrane segment to a dimeric state of the functionally membrane-reconstituted LacS protein. The cross-sectional area of the LacS protein was calibrated using the membrane-reconstituted transmembrane domain of the mannitol transporter enzyme II, an intramembrane particle for which the cross-sectional area was obtained from maps of two-dimensional crystals. The consequences of the determined quaternary structure for the transport function and regulation of LacS are discussed.

Rotational mobility and orientational stability of a transport protein in lipid membranes.

A single-cysteine mutant of the lactose transport protein LacS(C320A/W399C) from Streptococcus thermophilus was selectively labeled with a nitroxide spin label, and its mobility in lipid membranes was studied as a function of its concentration in the membrane by saturation-transfer electron spin resonance. Bovine rhodopsin was also selectively spin-labeled and studied to aid the interpretation of the measurements. Observations of spin-labeled proteins in macroscopically aligned bilayers indicated that the spin label tends to orient so as to reflect the transmembrane orientation of the protein. Rotational correlation times of 1-2 micros for purified spin-labeled bovine rhodopsin in lipid membranes led to viscosities of 2.2 poise for bilayers of dimyristoylphosphatidylcholine (28 degrees C) and 3.0 poise for the specific mixture of lipids used to reconstitute LacS (30 degrees C). The rotational correlation time for LacS did not vary significantly over the range of low concentrations in lipid bilayers, where optimal activity was seen to decrease sharply and was determined to be 9 +/- 1 micros (mean +/- SD) for these samples. This mobility was interpreted as being too low for a monomer but could correspond to a dimer if the protein self-associates into an elongated configuration within the membrane. Rather than changing its oligomeric state, LacS appeared to become less ordered at the concentrations in aligned membranes exceeding 1:100 (w/w) with respect to the lipid.

Haemodynamic depression by halothane is age-related in paediatric patients.

The hypothesis that young infants are more sensitive to the haemodynamic depressant effects of halothane compared with older children was tested. One hundred and sixty unpremedicated, ASA physical status I or II paediatric patients without cardiac or pulmonary disease were divided into five age groups: term neonates, 1-6 months, 6-24 months, 2-6 years and 6-12 years. Anaesthetic induction was achieved with halothane in oxygen and air via mask. Vecuronium 0.1 mg.kg-1 was administered intravenously. During normocapnic manual ventilation by mask, endtidal halothane concentration was maintained at either 2xage-specific MAC (Method I) or 1.7% (Method II) in 20 patients in each age group for 10 min. In both Method I and Method II, systolic and mean blood pressure of term neonates and infants aged 1-6 months decreased significantly (P < 0.01) compared with other age groups. The results of this study demonstrate that neonates and young infants are more susceptible to haemodynamic depression during halothane anaesthesia than are older children, confirming clinical experience.

Zinc stabilizes the SecB binding site of SecA.

The molecular chaperone SecB targets preproteins to SecA at the translocation sites in the cytoplasmic membrane of Escherichia coli. SecA recognizes SecB via its carboxyl-terminal 22 aminoacyl residues, a highly conserved domain that contains 3 cysteines and 1 histidine residue that could potentially be involved in the coordination of a metal ion. Treatment of SecA with a zinc chelator resulted in a loss of the stimulatory effect of SecB on the SecA translocation ATPase activity, while the activity could be restored by the addition of ZnCl2. Interaction of SecB with the SecB binding domain of SecA is disrupted by chelators of divalent cations, and could be restored by the addition of Cu2+ or Zn2+. Atomic absorption and electrospray mass spectrometry revealed the presence of one zinc atom per monomeric carboxyl terminus of SecA. It is concluded that the SecB binding domain of SecA is stabilized by a zinc ion that promotes the functional binding of SecB to SecA.

Allostery in rabbit pyruvate kinase: development of a strategy to elucidate the mechanism.

Isozymes of pyruvate kinase (PK) expressed in rabbit muscle and kidney show different allosteric kinetics. The only amino acid changes in the two isozymes, originating from alternative RNA splicing, occur at a stretch of 55 amino acids in the C domain near the subunit interface. The self-correcting distance geometry (SECODG) program DIAMOD was used to calculate a homology model of these interfacial contacts in the four helix bundle of the kidney PK dimer, based on the X-ray structure of the tetrameric rabbit muscle PK [Larsen et al. (1994) Biochemistry 33, 6301-6309]. Energy refinement with the program FANTOM, using the ECEPP/2 force field to assess packing and electrostatic interactions between the two subunits, yielded two groups of energetically favorable conformations. The primary difference in the two groups is the loop conformation of residue Pro 402, which is serine in muscle PK. In one loop conformation, the conserved Lys 421 can form an intersubunit salt bridge as observed in the muscle PK crystal structure. The other loop conformation favors an alternative intrasubunit salt bridge, similar to that found in the Escherichia coli PK structure, which was not used for generating the model. The intersubunit salt bridge leads to an intersubunit hydrogen bonding between Lys 421 of one subunit and Tyr 443 of the other. To provide direct evidence on the roles of these residues, site-directed mutagenesis of the muscle PK gene was conducted. Converting Ser 402 to a proline and Tyr 443 to a phenylalanine changed neither the secondary nor the tetrameric structure, as measured by far UV-CD and sedimentation velocity, respectively. However, the S402P mutant exhibits steady-state kinetics, indicating that the mutant is more reponsive to regulation by effectors, while the mutant Y443F was essentially equivalent to wild-type muscle PK protein except for a lower affinity to phosphoenolpyruvate. These findings suggest a pivotal role for a few key residues in the allosteric regulation in PK.

Preoxygenation before laryngoscopy in children: how long is enough?

The ideal preoxygenation period prior to laryngoscopy in children is unclear. This study was performed to determine an appropriate duration of preoxygenation for infants and children prior to laryngoscopy using endtidal oxygen (FE'O2) criteria. Healthy paediatric patients for elective day surgery procedures were studied. An inflatable mask connected to an oxygen-primed paediatric anaesthesia semiclosed circuit was placed on the face while patients breathed spontaneously during 6.min-1 oxygen flow. An FE'O2 of 0.9 was considered the endpoint, and if not achieved in two min the protocol was ended. Fifty-eight children were studied. Six patients never achieved an FE'O2 of 0.9 and were not considered in the analysis. The times (in seconds with mean +/- SD and range) to achieve a minimum endtidal (FE'O2) of 0.9 for under six months were 36 +/- 11.4(20-50), 7-12 months were 35.5 +/- 13.3(20-60), 13-36 months were 42.6 +/- 18.7(20-90), 37-60 months were 50.8 +/- 18.5(30-90), > 60 months were 68.4 +/- 24.1(30-100). Logistic regression curves were determined for each age group describing the probability of achieving an FE'O2 of 0.9 against time of preoxygenation. All children with satisfactory mask fit were able to preoxygenate to an FE'O2 of 0.9 within 100 s.

The negative dominant effects of T340M mutation on mammalian pyruvate kinase.

A fundamental issue in allosteric regulatory enzymes is the identification of pathways of signal transmission. Rabbit muscle and kidney pyruvate kinase isozymes are ideal to address this issue because these isozymes exhibit different enzymatic regulatory patterns, and the sequence differences between these isozymes have identified the amino acid residues that alter their kinetic behavior. In an earlier study, Cheng et al. (Cheng, X., Friesen, R. H. E., and Lee, J. C. (1996) J. Biol. Chem. 271, 6313-6321), reported the effects of a threonine to methionine mutation at residue 340 in the muscle isozyme. In this study, the same mutation was effected in the kidney isozyme. Qualitatively, the same negative effects are observed in both isozymes, namely a significant decrease in catalytic efficiency and decrease in apparent affinity for phosphoenolpyruvate but no change in affinity for ADP, and a decrease in responsiveness to the presence of effectors, be it activator or inhibitor. Because the diversity in the primary sequence between these two isozymes does not alter the negative impact of the T340M mutation, it can be concluded that this mutation exerts a dominant, negative effect. The negative effects of T340M mutation on the kinetic properties imply that there is communication between residue 340 and the active site. Residue 340 is located at the 1,4 subunit interface; however, a T340M mutation enhances the dimerization affinity along the 1,2 subunit interface. Thus, this study has identified a communication network among the active site, residue 340, and the 1,2 subunit interface.

Interfacial communications in recombinant rabbit kidney pyruvate kinase.

Tissue-specific isozymes of pyruvate kinase are particularly attractive systems to elucidate the molecular mechanism(s) of conferring allostery. The muscle- and kidney-type isozymes are coded by the same gene. As a consequence of alternative message RNA splicing, the two primary sequences differ by a small number of residues. However, they exhibit very different regulatory behavior. In an effort to identify the roles of specific residues in conferring allostery, the gene encoding rabbit kidney-type pyruvate kinase was cloned and expressed in Escherichia coli. The primary structure of recombinant rabbit kidney-type pyruvate kinase (rRKPK) and recombinant rabbit muscle-type pyruvate kinase (rRMPK) differ at 22 positions, which are located in a region that forms important intersubunit contacts in the RMPK structure. Velocity sedimentation and analytical gel chromatographic studies show that rRKPK undergoes reversible dimer left and right arrow tetramer assembly with an equilibrium constant of 28 +/- 3 mL/mg. This subunit assembly process provides the opportunity to elucidate the role of this dimer interface in transmission of signal upon binding of substrates and allosteric effectors. The assembly to tetrameric rRKPK is favored by the binding of phosphoenolpyruvate (PEP), one of the two substrates, or fructose 1,6-bisphosphate (FBP), an activator. In contrast, the equilibrium is shifted toward dimeric rRKPK upon binding of adenosine diphosphate (ADP), the other substrate, or l-phenylalanine (Phe), the inhibitor. These observations provide significant new insights to the molecular mechanism of allosteric regulation in the pyruvate kinase system. First, all substrates and effectors communicate through this particular dimer-dimer interface. Second, the thermodynamic signatures of these communications are qualitatively different for the two substrates and between the activator, FBP, and inhibitor, Phe.

Modified ultrafiltration attenuates dilutional coagulopathy in pediatric open heart operations.

BACKGROUND: Extreme hemodilution caused by relatively large prime volumes required for cardiopulmonary bypass in infants causes a dilutional coagulopathy, characterized by low concentrations of fibrinogen and other circulating coagulation factors. Modified ultrafiltration results in hemoconcentration and is associated with decreases in postoperative bleeding and transfusion requirements in children. This study was undertaken to quantify the effect of modified ultrafiltration on concentrations of fibrinogen, plasma proteins, and platelets in infants and small children. METHODS: Twenty patients less than 15 kg were studied. Cardiopulmonary bypass circuits were primed with crystalloid solutions. Red blood cells were added during cardiopulmonary bypass for hematocrits less than 15%. Colloid solutions were not administered. Concentrations of fibrinogen, plasma proteins, and platelets, and hematocrit were measured before cardiopulmonary bypass, before modified ultrafiltration, and after modified ultrafiltration. RESULTS: Modified ultrafiltration was associated with significant (p < 0.001) increases in hematocrit (19% +/- 6% to 31% +/- 9%), fibrinogen (65 +/- 29 to 101 +/- 45 mg/dL), and total plasma proteins (2.7 +/- 0.3 to 4.9 +/- 0.7 g/dL), but no change (p = 0.129) in platelet count. CONCLUSIONS: We conclude that modified ultrafiltration significantly attenuates the dilutional coagulopathy associated with cardiopulmonary bypass in infants.

Effects of conserved residues on the regulation of rabbit muscle pyruvate kinase.

A cDNA encoding the complete rabbit muscle pyruvate kinase isozyme (RMPK) was cloned using the method of rapid amplification of cDNA ends. The sequence encodes a polypeptide chain of 530 amino acids which differs in three amino acid residues from a sequence reported by Larsen et al. (Larsen, T.M., Laughlin, T., Holden, H.M., Rayment, L, and Reed, G.H. (1994) Biochemistry 33, 6301-6309). Glu233-Gln234 and Ala400 were identified instead of Asp233-Glu234 and Ser400, respectively. The recombinant RMPK was overexpressed in the Escherichia coli JM 105 cells. Purified recombinant pyruvate kinase displayed identical physical and enzymatic properties as the authentic enzyme. Three point mutants of RMPK were constructed using site-directed mutagenesis. Like the wild type RMPK, sedimentation, and CD spectroscopic studies show that purified RI 19C and T340M are tetrameric proteins with similar secondary and tertiary structures. Mutant R119C enzyme exhibits 0.6% of the value of k(cat) and an order of magnitude decrease in the apparent affinity for ADP as compared to the wild type PK. The overall response to inhibitor and activator, Phe and FBP, respectively, were not affected by the R119C mutation. The T340M mutant enzyme is only half as active as the wild type PK. T340M is more susceptible to inhibition by Phe but apparently is not responsive to the activator FBP. The kinetic behavior of the Q377K mutant enzyme is in between that of the R119C and T340M mutants exhibiting 5% of the wild type enzymatic activity and an enhanced sensitivity to the inhibitor, Phe, while maintaining the same responsiveness to FBP and apparent affinities for substrates. The significant decrease in activity in all three mutants mimics the exact consequences of the same mutations in human erythrocyte PK from hemolytic anemia patients. Thus, this study demonstrates not only the effects of these conserved residues in the regulatory properties of mammalian PK. but also that the observed effects are most likely applicable to all isozymic forms of PK.

End-tidal PCO2 monitoring via nasal cannulae in pediatric patients: accuracy and sources of error.

OBJECTIVE: To assess the correlation and accuracy of end-tidal PCO2 (PetCO2) sampled via nasal cannulae in pediatric patients by comparison to the criterion standard PaCO2, and to identify sources of error during PetCO2 monitoring via nasal cannulae. METHODS: PetCO2 was monitored continuously by sampling end-tidal gas through nasal cannulae that had been designed and manufactured for this purpose in spontaneously breathing children undergoing conscious or deep sedation during either cardiac catheterization (n = 43) or critical care (n = 54). When both the capnographic wave form and the PetCO2 value had been stable for at least 10 minutes, the PetCO2 value was recorded while blood was drawn from an indwelling arterial line for PaCO2 measurement. The effects of age, weight, respiratory rate, oxygen delivery system, airway obstruction, mouth breathing, and cyanotic heart disease were evaluated by linear regression analysis and calculation of absolute bias (PaCO2-PetCO2). RESULTS: Mouth breathing, airway obstruction, oxygen delivery through the ipsilateral nasal cannula, and cyanotic heart disease adversely affected accuracy. In patients without those factors, PetCO2 correlated well with PaCO2 (R2 = 0.994), and absolute bias was 3.0 +/- 1.8 mmHg. CONCLUSIONS: Several factors-some controllable and all recognizable-affect the accuracy of PetCO2 monitored via nasal cannulae in pediatric patients. When these factors are not present, PetCO2 correlates well with PaCO2 and appears to be a useful monitor of ventilatory status during conscious or deep sedation.

Changes in carbon dioxide tension and oxygen saturation during deep sedation for paediatric cardiac catheterization.

The purpose of this observational study was to determine whether hypercarbia or oxygen desaturation occurred during our current regimens of deep sedation or general anaesthesia of infants and children undergoing cardiac catheterization. Data were gathered prospectively from 50 consecutive infants and children aged 4 months to 12 years undergoing cardiac catheterization. Several anaesthetists used the following regimens, which were not randomized: 1) propofol. 1.5-2.0 mg.kg-1 and fentanyl 1 microgram.kg-1 IV over 2 min for induction, followed by propofol infusion of 100-150 micrograms.kg-1.min-1; 2) fentanyl 2-3 micrograms.kg-1 and midazolam 0.1-0.2 mg.kg-1 IV over 10-15 min; 3) ketamine 8 mg.kg-1 IM, or 4) same as regimens 1 or 2, plus pancuronium, intubation and controlled ventilation. Regimens 1, 2, and 3 were associated with spontaneous ventilation through the natural airway. End-tidal carbon dioxide tension (PetCO2), SpO2, and respiratory rate were monitored for 60 min. The three regimens employing spontaneous ventilation through the natural airway were associated with both statistically and clinically significant increases in PetCO2 and decreases in SpO2. This raises the possibility that acute exacerbation of PAP and PVR may occur in pulmonary hypertensive patients. In contrast, PetCO2 and SpO2 did not change significantly from baseline in the controlled ventilation group.

Oral transmucosal fentanyl citrate for preanaesthetic medication of paediatric cardiac surgery patients.

The safety and efficacy of oral transmucosal fentanyl citrate (OTFC) as a preanaesthetic medication were evaluated in 42 children aged two to twelve years scheduled to undergo general anaesthesia for open cardiac surgery. Patients were randomly assigned to receive either a placebo lozenge or a lozenge of 15-20 micrograms.kg-1) OTFC 45 min preoperatively and were managed in a double-blinded manner. Heart rate, respiratory rate (RR), blood pressure, and digital pulse oximetry (SpO2) were monitored throughout the study. Scoring systems were utilized to evaluate sedation, anxiety, cooperation, and ease and quality of parental separation and anaesthetic induction. Adverse effects were noted. Preoperatively, sedation was observed in both groups, but children receiving OTFC had significantly less distress at time of separation from parents. Clinically significant less distress at and SpO2 were observed more frequently in children in the OTFC group than in the placebo group. The authors conclude that, in paediatric cardiac surgical patients, OTFC induces preoperative sedation and facilitates separation of the patients from their parents, but is associated with decreases in respiratory rate and SpO2 that may be of clinical importance.

Effect of preanesthetic medication on carbon dioxide tension in children with congenital heart disease.

Hypercarbia during the postoperative period following repair of congenital heart defects in children has been associated with acute pulmonary hypertension. Because decreases in respiratory rate (RR) and digital pulse oximetry (SpO2) have been observed after preanesthetic medication of similar children, it is possible that hypercarbia and pulmonary hypertension may be unappreciated risks in premedicated children during the preoperative period. As the first step in addressing this question, changes in transcutaneous and end-tidal PCO2 (PtcCO2 and PetCO2) were examined after preanesthetic medication of children prior to cardiac surgery. Forty-four children were randomly assigned to receive either intramuscular morphine, 0.2 mg/kg, and scopolamine, 0.01 mg/kg, or oral midazolam, 0.75 mg/kg, 1 hour before anesthetic induction. PtcCO2, PetCO2, SpO2, RR, and sedation score were monitored. Significant sedation occurred after both premedication regimens. Following morphine/scopolamine, PtcCO2 increased from 36 +/- 4 (mean +/- SD) to 43 +/- 6 mmHg (P < 0.01), PetCO2 increased from 35 +/- 3 to 40 +/- 5 mmHg (P < 0.01), SpO2 decreased from 93 +/- 2 to 91 +/- 4% (P < 0.01), and RR decreased from 30 +/- 10 to 24 +/- 7 breaths/minute (P < 0.01). After midazolam, PtcCO2 increased from 35 +/- 4 to 40 +/- 6 mmHg (P < 0.01), PetCO2 increased from 34 +/- 5 to 39 +/- 3 mmHg (P < 0.01), SpO2 decreased from 93 +/- 6 to 90 +/- 7% (P < 0.01), and RR decreased from 33 +/- 13 to 30 +/- 13 breaths/minute (P < 0.01). Clinically significant increases in PtcCO2 (> 45 mmHg) occurred in nine patients, including five with pulmonary hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood conservation during pediatric cardiac surgery: ultrafiltration of the extracorporeal circuit volume after cardiopulmonary bypass.

After separation of pediatric patients from cardiopulmonary bypass (CPB), the authors salvaged red blood cells (RBCs) from the extracorporeal circuit by ultrafiltration and reinfused them to the patients. The purposes of this study were to determine 1) the effects of infusion of hemoconcentrated RBCs on hemoglobin, plasma free hemoglobin, and activated clotting time, and 2) the incidence of perioperative homologous RBC transfusion. Data were collected prospectively from 200 consecutive infants and children undergoing CPB during correction of congenital heart defects. The patients' hemoglobin, plasma free hemoglobin, and activated clotting time were measured both before and after infusion of 10 mL/kg of hemoconcentrate. Guidelines for intraoperative and postoperative transfusion of homologous RBCs were followed, and such transfusions were recorded. Significant increases in hemoglobin concentrations occurred when the hemoconcentrate was infused, as did statistically significant, but clinically manageable, increases in plasma free hemoglobin and activated clotting time. Perioperative homologous RBC transfusion was performed in 67% of patients (56% received intraoperative transfusion). Intraoperative transfusion was more frequent in small infants who were more hemodiluted by the clear CPB priming solution. Postoperative transfusion was more frequent in patients who had operation for cyanotic heart disease. Hemoconcentration by ultrafiltration after CPB is an effective and safe means of salvaging RBCs and reducing homologous RBC transfusion.

Oral transmucosal fentanyl citrate for preanesthetic medication of pediatric day surgery patients with and without droperidol as a prophylactic anti-emetic.

he safety and efficacy of oral transmucosal fentanyl citrate (OTFC) as a preanesthetic medication and the efficacy of droperidol as a prophylactic anti-emetic were evaluated in 100 children aged 2-8 yr undergoing general anesthesia for outpatient surgery. Patients were randomly assigned to one of four groups and managed in a double-blinded manner: 1) placebo lozenge 45 min preoperatively and placebo (normal saline) injected intravenously after induction of anesthesia; 2) placebo lozenge 45 min preoperatively and 50 micrograms/kg droperidol intravenously after induction; 3) 15-20 micrograms/kg OTFC lozenge 45 min preoperatively and placebo intravenously after induction; and 4) 15-20 micrograms/kg OTFC lozenge 45 min preoperatively and droperidol 50 micrograms/kg intravenously after induction. Anesthesia was induced and maintained with halothane and nitrous oxide in oxygen. Heart rate, respiratory rate, blood pressure, and hemoglobin oxygen saturation (SpO2) were monitored throughout the study. Scoring systems were used to evaluate sedation, anxiety, cooperation, and ease and quality of anesthetic induction. Emergence, recovery, and discharge times were recorded. Nausea, vomiting, and adverse effects were noted. Preoperatively, children receiving OTFC had significantly greater sedation, slower respiratory rates, lower SpO2, and less excitement during induction. Postoperative nausea and vomiting occurred significantly more frequently after OTFC than after placebo. Prophylactic droperidol did not significantly reduce the incidence of nausea and vomiting. The authors conclude that, in pediatric surgical outpatients, OTFC reliably induces preoperative sedation and facilitates inhalation induction of anesthesia, but it is associated with significant decreases in respiratory rate and SpO2 and a high incidence of postoperative nausea and vomiting that is not significantly reduced by prophylactic droperidol.

Elevated serum bromide concentrations following repeated halothane anaesthesia in a child.

A 20-month-old child received 25 brief halothane general anaesthetics over a five-week period to allow cranial irradiation treatments for a posterior fossa ependymoma. Personality change during the last week of the treatment protocol raised the question of possible bromide intoxication. Serum bromide concentrations, using a gold chloride assay technique, were monitored at that time, and at four- and six-week intervals thereafter. Serum bromide concentrations demonstrated a four-fold change during this period ranging from peak levels of 2.2 mEq.L-1 (176 micrograms.kg-1) during the fifth week of treatment decreasing to less than 0.5 mEq.L-1 (less than 40 micrograms.ml-1) six weeks following the end of treatments. This demonstrates the possibility for repetitive, short halothane exposures to result in elevations of serum bromide and the potential of bromide intoxication in paediatric neuro-oncology patients.

Low-dose sufentanil as a supplement to halothane/N2O anaesthesia in infants and children.

Sufentanil as a supplement to halothane/N2O anaesthesia was evaluated in 32 unpremedicated infants and children age 6 months to 9 yr undergoing elective orthopaedic surgery. Patients were randomly assigned in a double-blind manner to receive one of four intravenous supplements: placebo, sufentanil 0.5, 1.0 or 1.5 micrograms.kg-1. Systolic arterial pressure (SAP), heart rate (HR) and end-tidal halothane concentration were recorded before and after induction, supplement administration, tracheal intubation, incision and every 15 min during the procedure. Venous catecholamine samples were obtained before and after incision. A pain score was assigned to the patients in the postanaesthesia care unit (PACU). Sufentanil at all three doses prevented increases in SAP and HR with intubation and incision, provided superior pain relief in the PACU and did not prolong wake-up time. Sufentanil 1.0 and 1.5 micrograms.kg-1 allowed for a reduction in the halothane requirements. Sufentanil 1.5 micrograms.kg-1 was associated with lower catecholamine levels than in the placebo group following incision. Sufentanil supplementation at 1.0 and 1.5 micrograms.kg-1 was associated with bradycardia and/or hypotension during induction and an increased incidence of vomiting during the first 24 hours postoperatively. One patient in the sufentanil 1.0 micrograms.kg-1 group whose surgical time was less than 45 min exhibited respiratory depression in the PACU requiring narcotic reversal. In conclusion, sufentanil 0.5 micrograms.kg-1 improved immediate postoperative pain relief and is acceptable as a supplement during halothane anasethesia in infants and children. The associated side effects of larger doses of sufentanil (1.0 and 1.5 micrograms.kg-1) make their use as a supplement to halothane anaesthesia unacceptable.

Comparison of the hemodynamic and echocardiographic effects of sufentanil, fentanyl, isoflurane, and halothane for pediatric cardiovascular surgery.

Sufentanil, fentanyl, halothane, and isoflurane were compared as sole anesthetic agents in 48 infants and children aged 6 months to 9 years, undergoing repair of congenital heart defects. Patients were randomly assigned to receive sufentanil, 20 microg/kg, fentanyl, 100 microg/kg, isoflurane, 1.6%, or halothane, 0.9%, along with pancuronium, 0.08 mg/kg, for induction and maintenance of anesthesia. Cardiovascular function was measured by echocardiography prior to induction, postinduction, and postintubation. Systemic arterial pressure and heart rate were also recorded. Left ventricular ejection fraction (LVEF) decreased following induction with each agent: sufentanil 9%, fentanyl 9%, isoflurane 4%, and halothane 8%. Following intubation LVEF increased in the sufentanil, fentanyl, and isoflurane groups, but LVEF remained 13% below baseline values in the halothane group. Five of the 12 patients in the halothane group had a LVEF less than 55%. Arterial pressure immediately prior to bypass was significantly less than baseline in each group; however, arterial pressure was higher in the narcotic groups during isolation and cannulation of the great vessels. It is concluded that halothane, 0.9%, used as an induction agent in infants and children undergoing cardiac surgery causes a clinically significant decrease in LVEF. Based on the echocardiographic data, sufentanil, fentanyl, and isoflurane as used in the present study do not have a clinically significant effect on cardiac function and may offer an advantage to infants and children with marginal cardiovascular reserve.