Impact of various anesthetic regimens on motor-evoked potentials in infants undergoing spinal surgery: A case series

Motor-evoked potential (MEP) monitoring is commonly used in children. MEP monitoring in infants is difficult due to smaller signals requiring higher stimulation voltages. There is limited information on the effect of different anesthetics on MEP monitoring in this age group. This case series describes the effect of different anesthetic regimens on MEP monitoring in infants. Patients <1 year of age who underwent spinal surgery with MEP monitoring between February 2022 and July 2023 at a single tertiary care children hospital were reviewed. The motor-evoked potential amplitudes were classified into 4 levels based on the voltage in the upper and lower limbs (none, responded, acceptable, sufficient). "Acceptable" or "sufficient" levels were defined as successful monitoring. A total of 19 infants were identified, involving 3 anesthesia regimens: 4/19 (21.1%) cases were anesthetized with propofol/remifentanil total intravenous anesthesia (TIVA), 3/19 (15.8%) with propofol/remifentanil/low-dose sevoflurane and another 12/19 (63.2%) cases who initially received propofol/remifentanil/sevoflurane and were converted to propofol/remifentanil anesthesia intraoperatively. The 4 cases with propofol/remifentanil showed 20/32 (62.5%) successful monitoring points. In contrast, 6/24 (25%) successful points were achieved with propofol/remifentanil intravenous anesthesia/0.5 age-adjusted minimum alveolar concentration sevoflurane. In 12 cases converted from propofol/remifentanil/low-dose inhalational anesthetics to TIVA alone, successful MEP monitoring points increased from 46/96 (47.9%) to 81/96 (84.4%). Adding low-dose inhalation anesthetic to propofol-based TIVA suppresses MEP amplitudes in infants. The optimal anesthetic regimen for infants requires further investigation.

Postoperative pain management for pediatric urologic surgery

The issues relating to postoperative pain management for pediatric urologic surgery have been discussed. Child development and the behavioral responses to pain have been reviewed, with emphasis on their relation to pain assessment in the pediatric patient. The benefits and limitations of various modalities for the treatment of postoperative pain have been reviewed, and their appropriate use for different urologic surgical procedures has been presented.

Comparative effects of halothane, enflurane, and isoflurane on atrioventricular conductivity and subsidiary pacemaker function in dogs

This study compares effects of equipotent concentrations of halothane, enflurane, and isoflurane on atrioventricular (AV) function in dogs. Enflurane anesthesia was associated with more AV nodal depression, only at faster heart rates than either halothane or isoflurane. These rate-related effects are important in the genesis of supraventricular reentrant tachyarrhythmias. Subsidiary pacemaker function exhibited marked variability between and within animals with no demonstrable difference between anesthetic drugs. Enflurane has more depressant effects on AV nodal recovery properties than halothane or isoflurane; however, there were no differences demonstrated on slow AV nodal conduction. This suggests that enflurane would be the most effective volatile anesthetic in converting or slowing supraventricular tachyarrhythmias, while carrying no more risk of causing advanced heart block.

Comparison of the analgesic and emetic properties of ketorolac and morphine for paediatric outpatient strabismus surgery

In a prospective, double-blind, randomized study, we have compared i.v. ketorolac and morphine in paediatric outpatients undergoing strabismus surgery. Forty-two ASA I or II children, aged 2-12 yr, were allocated randomly to receive either ketorolac 0.75 mg kg-1 i.v. or morphine 0.1 mg kg-1 i.v. and metoclopramide 0.15 mg kg-1. Anaesthesia was induced with propofol and maintained with propofol and nitrous oxide. Pain was assessed at 15-min intervals until discharge, and the incidence of nausea and vomiting was recorded for the first 24 h. There was no difference in pain behaviour scores or recovery times. The incidence of nausea and vomiting during the first 24 h was 19% in the ketorolac group and 71% in the morphine group (P < 0.001). We concluded that ketorolac was an effective analgesic for this type of surgery and that it was associated with less postoperative emesis than morphine and metoclopramide.

Propofol infusion and the incidence of emesis in pediatric outpatient strabismus surgery

A prospective, randomized, double-blind study was conducted to examine the effect of a propofol infusion on the incidence of postoperative emesis in children undergoing outpatient strabismus surgery. Seventy-eight children, aged 3-12 yr, were allocated randomly to receive either nitrous oxide and halothane or nitrous oxide and a propofol infusion for the maintenance of anesthesia. The overall incidence of vomiting during the first 24 h was 64% in those receiving halothane and 41% in those receiving the propofol infusion; this difference was statistically significant (P < 0.05). In children who received no opioids postoperatively, the incidence of vomiting in the first 24 h was 71% in the halothane group and 24% in the propofol group; this difference was also significant (P = 0.001). We conclude that propofol was effective in reducing the incidence of postoperative emesis in pediatric outpatient strabismus surgery.

Transmural redistribution of myocardial blood flow during isoflurane anesthesia and its effects on regional myocardial function in a canine model of fixed coronary stenosis

BACKGROUND

The effects of isoflurane on the transmural distribution of myocardial blood flow distal to an acute critical coronary stenosis and the relationship between the changes in regional blood flow and function were studied to determine whether isoflurane can produce a transmural "steal" phenomenon and to assess the role of this phenomenon in producing changes in regional myocardial function.

METHODS

After production of acute critical coronary stenosis under baseline chloralose and fentanyl anesthesia, the animals were exposed to increasing end-tidal concentrations of isoflurane (0.7%, 1.4%, and 2.1%) without control of the hemodynamic parameters. At 2.1% isoflurane, the blood pressure then was restored to the baseline level by administration of phenylephrine. Changes in the following parameters were assessed: global contractility (measured by changes in pressure with time), regional myocardial function (assessed by systolic wall thickening and measured by sonomicrometers), transmural distribution of myocardial perfusion (measured by the radioactive microsphere method), and regional oxygen consumption and extraction.

RESULTS

Distal to the critical stenosis, a transmural redistribution of myocardial blood flow (endocardial-epicardial ratio < 1) occurred with all concentrations of isoflurane. With higher concentrations (1.4% and 2.1%), a significant decrease in subendocardial blood flow occurred only in the presence of hemodynamic changes and was restored by phenylephrine. In this area, changes in regional myocardial function correlated most strongly with changes in subendocardial perfusion (y = -0.17 + 1.70x -0.58x2, r2 = 0.90). In the stenotic region, oxygen extraction remained stable, but oxygen consumption decreased in parallel with reductions in regional myocardial function. In the normal region, oxygen consumption did not change, but oxygen extraction decreased with increasing isoflurane concentrations.

CONCLUSIONS

These results show that isoflurane is a coronary vasodilator able to induce a transmural redistribution of myocardial blood flow distal to an acute critical coronary stenosis. A true transmural steal, however, was not produced reliably in the absence of hemodynamic changes, suggesting that isoflurane either is only a moderate vasodilator, or that the decrease in subendocardial blood flow is offset by the negative inotropic action of the drug. When regional myocardial dysfunction distal to a severe coronary stenosis occurs, this correlates with decreasing subendocardial blood flow during isoflurane anesthesia, suggesting ischemia as the cause.

High-frequency jet ventilation improves cardiac function after the Fontan procedure

Pulmonary vascular resistance is an important determinant of cardiac output after the Fontan procedure and is adversely affected by elevated mean airway pressure. High-frequency jet ventilation (HFJV) is an alternate form of mechanical ventilation which supports gas exchange at lower mean airway pressure. This study was performed to determine if HFJV could lower mean airway pressure and pulmonary vascular resistance and result in an increase in cardiac output after the Fontan procedure. We prospectively evaluated 13 patients ranging in age from 0.9 to 8.5 years (mean, 3.9 years) and in weight from 6.2 to 20.1 kg (mean, 13.9 kg). Right atrial, left atrial and pulmonary artery catheters were used to measure hemodynamic parameters. Cardiac index was measured by dye dilution technique, and pulmonary vascular resistance was calculated. The patients were stabilized on mechanical ventilation to achieve a PaCO2 = 30 +/- 5 mm Hg, and baseline hemodynamic and respiratory measurements were made. HFJV was begun at settings adjusted to achieve similar gas exchange. Respiratory and hemodynamic measurements were repeated after 30-60 minutes of HFJV. Mechanical ventilation was then resumed at baseline settings, and measurements were repeated 0.5-1 hour later. There was no significant change in gas exchange. HFJV resulted in a 50% reduction in mean airway pressure (9.2 +/- 0.2 cm H2O to 4.6 +/- 0.1 cm H2O, p less than 0.001), a 59% reduction in pulmonary vascular resistance (3.82 +/- 0.36 to 1.52 +/- 0.16 Woods units, p less than 0.001), and a 25% increase in cardiac index (2.32 +/- 0.12 l/min/m2 to 2.91 +/- 0.12 l/min/m2, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of P6 acupressure on postoperative vomiting in children undergoing outpatient strabismus correction

A prospective, double-blind study was conducted to compare the effect of pressure at the P6 (Neikuan) point with placebo as an antiemetic in children. Sixty-six patients, ages 3-12 yr, undergoing outpatient surgery for correction of strabismus, were allocated randomly to receive either bilateral P6 acupressure or placebo during the perioperative period. The study was designed to detect a 50% difference in the incidence of postoperative vomiting between the two groups, with a 90% power of achieving a statistically significant result at the 5% level (two-tailed). The incidence of postoperative vomiting for the placebo group was 58% before discharge from hospital, 73% at home and 82% in the first 24 h after surgery. The corresponding results for the acupressure group were 58% before discharge, 71% at home and 94% in the first 24 h. These differences were not significant; P6 acupressure did not reduce the incidence of postoperative vomiting in children undergoing strabismus surgery.

Anaesthetic management for caesarean section in a patient with uncorrected truncus arteriosus

We describe the successful management of a 25-yr-old primigravida with uncorrected truncus arteriosus, requiring an urgent Caesarean section for delivery of a live infant and we discuss the rationale of using the chosen drug combination and the importance of adequate monitoring in selecting an anaesthetic technique based on the pathophysiology of the congenital cardiac lesion.

Recovery after single-breath halothane induction of anaesthesia in daycase patients. A comparison with thiopentone

A single-breath technique of inhalational induction of anaesthesia allows intravenous induction agents to be avoided. We have investigated recovery from anaesthesia in 40 daycase patients, using tests of psychomotor function. Patients anaesthetised with inhalational induction awaken earlier than those who receive thiopentone, but not significantly earlier. There were no significant differences in postoperative psychomotor function between patients who received thiopentone and those who had inhalational inductions. Single-breath halothane, nitrous-oxide, oxygen induction is an alternative to intravenous induction in cooperative adults, but does not confer significant benefits in terms of recovery.

The effect of trimethaphan-induced hypotension on canine spinal cord blood flow. Measurement at different cord levels using radiolabelled microspheres

Controlled hypotension which is used during scoliosis surgery to improve operating conditions and minimize transfusion requirements may decrease spinal cord blood flow (SCBF). Previous studies using hydrogen washout, an invasive technique, have shown that trimethaphan-induced hypotension is associated with a decrease in SCBF, whereas hypotension induced with sodium nitroprusside or nitroglycerin is not. To determine whether the decrease seen with trimethaphan represented a generalized rather than regional spinal cord phenomenon, SCBF was measured at three separate cord levels (T2-3, 7-8, L2-3) using a noninvasive radionuclide-labelled microsphere technique. When the mean arterial pressure was reduced by 50%, SCBF decreased 35 to 45% at all levels of the cord examined, and remained at this reduced level during the period of hypotension. The results confirm that trimethaphan-induced hypotension is associated with a significant reduction in SCBF and that this occurs throughout the spinal cord during the period of hypotension.

Effects of the volatile anesthetic agents on sinus node function and atrioventricular conduction in dogs: A comparison with chloralose anesthesia

The effects of equipotent concentrations (1.5 times minimum alveolar concentration) of the inhalational agents halothane, enflurane, and isoflurane on sinus node function, and atrioventricular (A-V) conduction and refractoriness were compared with chloralose anesthesia in 49 mongrel dogs. Sinus node function was assessed using corrected sinus node recovery time. Atrial-His and His-ventricular conduction times were measured at paced heart rates of 150, 180, and 200 beats/min, and A-V refractoriness was assessed by Wenckebach periodicity. There was no evidence that sinus node function was impaired by any of the inhalational agents. Enflurane anesthesia was associated with a significant prolongation of atrial-His conduction at paced heart rates of 180 and 200 beats/min when compared to chloralose anesthesia and the other two inhalational agents (P < .001). Atrioventricular refractoriness was impaired by enflurane (P < .001) and halothane (P < .05), but not isoflurane, when compared with chloralose anesthesia. Ventricular-His conduction was not altered by any of the agents. The authors conclude that enflurane is associated with a greater impairment of A-V conduction and refractoriness than halothane or isoflurane, and that these changes are related to the anesthetic agent and not the anesthetic state.

Delayed vomiting after papavaretum in paediatric outpatient surgery

The contribution of papavaretum to the incidence of vomiting observed in the 24 hours after paediatric outpatient anaesthesia was assessed in 129 children undergoing circumcision. Postoperative analgesia in all patients was achieved using caudal extradural blockade. The incidence of vomiting in the 24 hours after discharge from hospital was 56 per cent in those receiving papavaretum, compared with 15 per cent in those who did not (p less than 0.0001). The significance of this finding and the use of opiates in paediatric outpatient anaesthesia are discussed.

Single breath induction of anaesthesia, using a vital capacity breath of halothane, nitrous oxide and oxygen

Inhalational induction of anaesthesia, using a single vital capacity breath of 4% halothane in 66% nitrous oxide and 33% oxygen was evaluated in 100 unpremedicated outpatients. The technique was found to be acceptable to most (91%) of the patients studied, with a mean (SD) induction time (measured from beginning of inspiration to loss of 'eyelash reflex') of 83(21) seconds. Relative cardiovascular stability was a notable finding of the technique, with a slight decrease in the mean arterial pressure of only 10%. Anaesthetic induction time was unaffected by age, weight or smoking habits. The technique of single breath induction is therefore proposed as a safe and acceptable alternative to intravenous induction in co-operative adult patients.