The effect of dexmedetomidine on motor-evoked potentials during pediatric posterior spinal fusion surgery: a retrospective case-control study.

PURPOSE: Motor-evoked potentials (MEPs) are frequently used in pediatric posterior spinal fusion surgery (PSFS) to detect spinal cord ischemia. Dexmedetomidine is increasingly being used as an adjunct to total intravenous anesthesia, but its effect on MEP amplitude has been variably reported. The purpose of this study was to evaluate the effect of an infusion of dexmedetomidine on the amplitude of MEPs. METHODS: We performed a retrospective case-control study of 30 pediatric patients who received a 0.5 µg·kg-1·hr-1 infusion of dexmedetomidine, ten patients who received 0.3 µg·kg-1·hr-1 dexmedetomidine, and 30 control patients who did not receive dexmedetomidine during PSFS. Two neurophysiologists reviewed the MEP amplitudes in six muscle groups at three time points: when the patient was turned prone (baseline; T1), one hour after incision (T2), and after exposure of the spine but before insertion of the first screw (T3). RESULTS: In all muscles tested, the mean MEP amplitude was reduced by T3 when dexmedetomidine was infused at 0.5 µg·kg-1·hr-1. The greatest reduction from baseline MEP amplitude was 829 µV (95% confidence interval, 352 to 1230; P < 0.001) seen in first right dorsus interosseous. When dexmedetomidine was infused at 0.3 µg·kg-1·hr-1, there was a significant reduction in MEP amplitude in four of the six muscles tested at T3 compared with the control group. CONCLUSIONS: Dexmedetomidine at commonly used infusion rates of 0.3 µg·kg-1·hr-1 or 0.5 µg·kg-1·hr-1 causes a significant decrease in MEP amplitude during pediatric PSFS. We suggest that dexmedetomidine should be avoided in children undergoing PSFS so as not to confuse the interpretation of this important neurophysiological monitor.

RéSUMé: OBJECTIF: Les potentiels évoqués moteurs (PEM) sont fréquemment utilisés lors de chirurgies de fusion spinale postérieure chez l'enfant afin de détecter une ischémie de la moelle épinière. La dexmédétomidine est de plus en plus utilisée comme adjuvant à l'anesthésie intraveineuse totale, mais son effet sur l'amplitude des PEM n'a été rapporté que de façon variable. L'objectif de cette étude était d'évaluer l'effet d'une perfusion de dexmédétomidine sur l'amplitude des PEM. MéTHODE: Pendant une chirurgie de fusion spinale postérieure, nous avons réalisé une étude cas témoins rétrospective auprès de 30 patients pédiatriques ayant reçu une perfusion 0,5 µg·kg−1·h−1 de dexmédétomidine, 10 patients ayant reçu 0,3 µg·kg−1·h−1 de dexmédétomidine, et 30 patients témoins n'ayant pas reçu de dexmédétomidine. Deux neurophysiologistes ont passé en revue les amplitudes des PEM dans six groupes musculaires à trois moments de la chirurgie : lorsque le patient a été tourné sur le ventre (valeur de base; T1), une heure après l'incision (T2), et après l'exposition de la colonne mais avant l'insertion de la première vis (T3). RéSULTATS: Dans tous les muscles testés, l'amplitude moyenne des PEM était réduite à T3 lorsque la dexmédétomidine était perfusée à 0,5 µg·kg−1·h−1. La plus grande réduction par rapport à l'amplitude de base des PEM était de 829 µV (intervalle de confiance 95 %, 352 à 1230; P < 0,001) et a été observée au niveau du premier interosseux dorsal. Lorsque la dexmédétomidine était perfusée à 0,3 µg·kg−1·h−1, une réduction significative de l'amplitude des PEM a été observée dans quatre des six muscles testés à T3 par rapport au groupe témoin. CONCLUSION: La dexmédétomidine, administrée à des taux de perfusion fréquemment utilisés de 0,3 µg·kg−1·h−1 ou 0,5 µg·kg−1·h−1, a entraîné une réduction significative de l'amplitude des PEM pendant une chirurgie de fusion spinale postérieure chez l'enfant. Nous proposons d'éviter l'administration de dexmédétomidine chez les enfants devant subir une chirurgie de fusion spinale postérieure afin de ne pas brouiller l'interprétation de ce moniteur neurophysiologique important.

Use of Serratus Plane Block for Repair of Coarctation of Aorta: A Report of 3 Cases.

OBJECTIVES: The practice of regional anesthesia techniques (thoracic, epidural, paravertebral) in pediatric cardiac surgery enhances perioperative outcomes such as improved perioperative analgesia, decreased stress response, early extubation, and shortened hospital stay. However, these blocks can be technically challenging and can be associated with unacceptable failure rate and complications in infants. For these reasons, regional anesthesia is sometimes avoided in pediatric cardiac surgery. We describe the simple and effective serratus plane block for thoracotomy analgesia in 2 neonates and a child. CASE REPORT: We present 3 pediatric patients, each of whom was having coarctation repair and received an ultrasound-guided serratus plane block for thoracotomy analgesia. The patients were 3 days, 14 days, and 4 years old, weighing from 1.9 to 16 kg. The serratus plane block was performed prior to surgical incision. The block was technically simple compared with thoracic epidural or paravertebral block. All patients were extubated immediately after completion of surgery. Apart from the induction dose of fentanyl (2 µg/kg), no further opioids were required intraoperatively. Postoperative opioid requirements as well as duration of intensive care and hospital stay were lower than recent averages (for the same demographic and procedure) in our hospital. CONCLUSIONS: We propose that the serratus plane block is a simple procedure that provides good perioperative analgesia for infant thoracotomy, potentially facilitating early extubation and a shorter hospital stay.

Midline posterior glossectomy and lingual tonsillectomy in obese and nonobese children with down syndrome: Biomarkers for success.

OBJECTIVES/HYPOTHESIS: To examine outcomes following midline posterior glossectomy (MPG) plus lingual tonsillectomy (LT) for the treatment of significant obstructive sleep apnea (OSA) in children with Down syndrome (DS). METHODS: Patients with DS who had persistent OSA following tonsillectomy and adenoidectomy (TA) and were relatively intolerant of positive airway pressure (PAP) therapy were evaluated by physical examination and sleep/CINE magnetic resonance imaging to determine the etiology of upper airway obstruction. Patients with relative macroglossia underwent MPG plus LT if required. Successful surgical outcome was defined as the resolution of OSA or the ability to tolerate PAP. RESULTS: Thirteen children (8 male, 5 female), mean (standard deviation) age 14.2 (4.0) years underwent MPG plus LT. Fifty-four percent of patients were obese (Body mass index [BMI] > 95th centile) and 8% were overweight (BMI 85th-95th centile) preoperatively. All patients underwent pre- and postoperative polysomnography. Postoperatively, the obstructive apnea-hypopnea index fell significantly from 47.0/hour to 5.6/hour (P <.05) in normal weight individuals who did not become obese, but not in obese patients or those who became obese postoperatively. Successful surgical outcome was seen in all (N = 6) children who were normal weight or overweight preoperatively compared with none who were obese preoperatively (N = 7). CONCLUSION: Midline posterior glossectomy and LT are beneficial in normal weight and overweight children with DS who have persistent OSA following TA and are intolerant of PAP therapy. Obesity pre- or postoperatively portends a worse prognosis following MPG, suggesting that aggressive weight loss initiatives should be considered as an adjunct to surgery in this population. LEVEL OF EVIDENCE: 4. Laryngoscope, 127:757-763, 2017.

Intra-arterial nitroglycerin for intra-operative arterial vasospasm during pediatric renal transplantation.

Intra-operative arterial vasospasm during pediatric renal transplantation is an urgent clinical situation resulting in end-organ ischemia, associated changes in parenchymal turgor and color, diminished flow on ultrasound, and if left untreated, allograft loss. We hypothesized that intra-operative intra-arterial injection of nitroglycerin would reverse vasospasm and improve renal perfusion. A three-yr-old girl with end-stage renal disease due to autosomal recessive polycystic kidney disease on peritoneal dialysis underwent deceased donor renal transplantation. After optimal immediate reperfusion and hemodynamic parameters, the kidney lost turgor and became mottled in appearance despite adequate hilar arterial and venous Doppler waveforms. Two aliquots of 40 µg (0.4 mL of a 100 µg/mL) nitroglycerin solution were injected directly into the renal artery 10 min apart. Nitroglycerin resulted in dramatic change in the consistency and appearance of the allograft. An improvement in renal blood flow was demonstrated by ultrasound after the second intra-arterial nitroglycerin injection with only a transient decrease in systemic arterial blood pressure. The child experienced normal allograft perfusion on serial postoperative ultrasounds, with a prompt decrease in serum creatinine and excellent diuresis. Intra-arterial nitroglycerin is a promising option for intra-operative arterial vasospasm during pediatric renal transplantation with objective improvement in blood flow and perfusion.

Assessment of aspiration risk from dynamic modulation of endotracheal tube cuff pressure.

OBJECTIVES/HYPOTHESIS: To assess the risk of aspiration using a novel valve circuit that dynamically modulates endotracheal tube cuff pressure during the ventilatory cycle using bench and live animal models. STUDY DESIGN: Animal model. METHODS: The bench model consisted of a cuffed endotracheal tube inserted into an artificial trachea. Leakage of liquid around the cuff was measured after 4 hours of constant or dynamic modulation of cuff pressure at variable peak end expiratory pressures. In the porcine model, eight animals were ventilated with the modulating valve circuit and compared to eight controls ventilated with a constant cuff pressure (25 cm of water). Aspiration was monitored quantitatively using a pH probe (measured as voltage) and visually using fluoroscopy. RESULTS: There was no difference in the amount of fluid leakage around the endotracheal tube cuff in the constant or dynamically modulated pressure-cuff groups in the bench or animal models. CONCLUSION: Dynamically modulating endotracheal tube-cuff pressures to minimize tracheal mucosal damage does not increase the tendency to leak around the cuff compared to endotracheal tube cuffs inflated to a constant pressure. LEVEL OF EVIDENCE: N/A.

A simple mechanical device reduces subglottic injury in ventilated animals.

OBJECTIVES/HYPOTHESIS: To test whether a simple inexpensive device that dynamically minimizes endotracheal cuff pressure throughout the respiratory cycle reduces endotracheal cuff pressure-related subglottic injury. STUDY DESIGN: Hypoxic animal model with one control and one experimental group. METHODS: Twelve S. scrofa domesticus piglets (14-16 kg) were intubated with standard endotracheal tubes and maintained in a hypoxic state to accelerate airway injury. Animals in the control group (n = 6) were ventilated with a constant pressure of 20 cm H2O in the endotracheal tube cuff. Animals in the experimental group (n = 6) were ventilated using a custom-designed circuit that altered the pressure in the endotracheal tube cuff in synchrony with the ventilatory cycle. Larynges were harvested at the end of the experiment and examined histologically to determine the degree of airway injury induced by the endotracheal cuff. RESULTS: Animals in the experimental group suffered significantly less airway damage than those in the control group. The differences were seen primarily in the subglottis (aggregate damage score 6.5 vs. 12, P <0.05), where the experimental endotracheal tube cuff exerted the least pressure. There was no difference in damage to the glottic or supraglottic structures. CONCLUSIONS: A simple, reliable, and inexpensive means of modulating endotracheal tube cuff pressure with the ventilatory cycle led to a substantial decrease in airway injury in our animal model. Such reduction in cuff pressure may prove important for humans, particularly those in intensive care units who tend to have underlying conditions predisposing them to tracheal damage from the endotracheal tube cuff.

Effect of nitrous oxide exposure during surgery on the homocysteine concentrations of children.

BACKGROUND: Nitrous oxide converts vitamin B12 to its nonmetabolically active form, inhibits methionine synthase, and results in an elevation of plasma total homocysteine (tHcy). The authors investigated the effect of nitrous oxide anesthesia on the plasma tHcy concentrations in children the morning after surgery and whether blood concentrations of folate and vitamins B12 and B6 were associated with any potential increase. METHODS: The authors measured plasma tHcy concentrations in 32 children before and 24 h after initial exposure to nitrous oxide (≥ 2 h). Genotype for methylenetetrahydrofolate reductase C677T and blood concentrations of folate, vitamins B12 and B6, and methylmalonic acid were measured before surgery. RESULTS: The median age of participants was 11 months (3-126 months). The median (first, third quartile) postoperative plasma tHcy concentration was significantly higher than the preoperative concentration (6.4 [4.7, 8.9] vs. 5.1[4.1, 6.4] µM, P < 0.0001), a 25% (2%, 42%) relative increase. Six of 28 (21%) children with normal, age-appropriate, preexposure plasma tHcy concentrations had postoperative plasma tHcy concentrations greater than the cutoff values. The duration of nitrous oxide exposure was associated positively with the rise in plasma tHcy concentration (R2 = 0.696, P = < 0.001). CONCLUSION: Exposure to ≥ 2 h nitrous oxide is associated with a small, albeit statistically significant, increase in postoperative plasma tHcy concentrations the morning after surgery in young children. The clinical significance of this increase is unknown.

An animal model for endotracheal tube-related laryngeal injury using hypoxic ventilation.

OBJECTIVES: To explore whether hypoxic ventilation could allow a practical animal model of laryngotracheal injury secondary to endotracheal intubation. STUDY DESIGN: Randomized controlled animal study. SETTING: Animal laboratory in a tertiary pediatric hospital. SUBJECTS AND METHODS: Eight Sus scrofa piglets (15-18 kg) were anesthetized and intubated for 4 hours, with a 6-mm cuffed endotracheal tube. They were randomly assigned to either constant hypoxic ventilation (oxygen saturation under 70%) or nonhypoxic ventilation. Endotracheal tube cuff pressure was manually controlled and maintained at a constant level. After 4 hours, fluorescein dye was administered intravenously to highlight areas of hypoperfusion within the larynx. The animals were euthanized at the end of the procedure, and the larynx and trachea were harvested for gross and histological examination. The pathologist was blinded to the ventilation group. The severity of laryngeal injury was graded between 0 and 4 by a senior pathologist. RESULTS: The experiment protocol was successfully completed in all animal subjects. The animals undergoing hypoxic ventilation showed a significantly higher median injury grade than the nonhypoxic animals (2 vs 1, respectively; P = .003). Damage was significantly worse in the hypoxic group at all anatomical sublevels. CONCLUSIONS: Endotracheal tube-related laryngeal injury was demonstrated after only 4 hours of intubation using this animal model, and hypoxic ventilation increased the severity of injury. This study therefore provides an animal model that may be suitable for future investigation and prevention of intubation injury.

Automated cuff pressure modulation: a novel device to reduce endotracheal tube injury.

OBJECTIVE: To assess whether dynamically modulating endotracheal tube (ETT) cuff pressure, by decreasing it during each ventilatory cycle instead of maintaining a constant level, would reduce the extent of intubation-related laryngotracheal injury. DESIGN: Single-blind, randomized controlled animal study using a previously validated live porcine model of accelerated intubation-related tracheal injury. SETTING: Animal research facility. PATIENTS: Ten piglets (weight, 16-20 kg each) were anesthetized and underwent intubation using a cuffed ETT. INTERVENTIONS: The animals were randomized into the following 2 groups: 5 pigs had a novel device to modulate their cuff pressure from 25 cm H2O during inspiration to 7 cm H2O during expiration, and 5 pigs had a constant cuff pressure of 25 cm H2O. Both groups underwent ventilation under hypoxic conditions for 4 hours. MAIN OUTCOME MEASURE: Laryngotracheal mucosal injury after blinded histopathological assessment. RESULTS: The modulated-pressure group showed significantly less overall laryngotracheal damage than the constant-pressure group (mean grades, 1.2 vs 2.1; P < .001). Subglottic damage and tracheal damage were significantly less severe in the modulated-pressure group (mean grades, 1.0 vs 2.2; P < .001, and 1.9 vs 3.2; P < .001, respectively). There was no significant difference in glottic or supraglottic damage between the groups (P = .06 and .27, respectively). CONCLUSIONS: This novel device reduces the risk of subglottic and tracheal injury by modulating ETT cuff pressure in synchronization with the ventilatory cycle. This finding could have far-reaching implications for reducing the risk of airway injury in patients undergoing long-term intubation. Further clinical study of this device is warranted.

Effect of a novel anatomically shaped endotracheal tube on intubation-related injury.

OBJECTIVES: To develop an anatomically shaped endotracheal tube (ETT) and to compare the degree of induced laryngeal injury of this ETT with that of a standard ETT using an animal model. DESIGN: Randomized controlled animal study. SUBJECTS: Eight Sus scrofa piglets (15-20 kg) randomly intubated with either a standard or a modified uncuffed ETT. INTERVENTIONS: The modified ETT was handcrafted by gluing and then trimming dry polyvinyl acetate foam circumferentially to the distal end of a standard uncuffed ETT. After intubation, the foam quickly self-expanded as it absorbed the secretions of the laryngopharynx and adopted the shape of the intraluminal airway. This conforming shape also sealed the larynx to allow for positive pressure ventilation. Both groups were intubated for 4 hours under constant hypoxic conditions (mean oxygen saturation <70%) to enhance and accelerate intubation damage. They were then humanely killed, and the larynx and trachea were harvested for histologic examination. MAIN OUTCOME MEASURES: The severity of laryngeal injury graded on a scale from 0 to 4 (0 indicates normal; 1, epithelial compression; 2, epithelial loss; 3, subepithelial and glandular necrosis; and 4, perichondrium involvement). RESULTS: All of the specimens histologically demonstrated areas of inflammation and epithelial loss. The standard ETT caused substantial deep damage, with a mean (SD) severity score of 2.79 (0.74). The modified ETT caused mainly superficial damage, with a mean (SD) severity score of 1.65 (0.56) (P < .001). CONCLUSION: The modified ETT objectively caused less laryngotracheal damage compared with the standard ETT and may be of potential clinical benefit.

Impact of anesthetic agents on cerebrovascular physiology in children.

The role of the pediatric neuroanesthetist is to provide comprehensive care to children with neurologic pathologies. The cerebral physiology is influenced by the developmental stage of the child. The understanding of the effects of anesthetic agents on the physiology of cerebral vasculature in the pediatric population has significantly increased in the past decade allowing a more rationale decision making in anesthesia management. Although no single anesthetic technique can be recommended, sound knowledge of the principles of cerebral physiology and anesthetic neuropharmacology will facilitate the care of pediatric neurosurgical patients.

Clinical adaptation of a pharmacokinetic model of Propofol plasma concentrations in children.

BACKGROUND: A previously published pharmacokinetic simulation suggested a simple manual infusion regimen to achieve propofol plasma concentrations of 3 microg.ml(-1). This study investigated if a simple variation in propofol infusion rates is able to achieve distinct propofol plasma concentrations and whether these are close to the propofol plasma concentrations predicted by the Kataria model. METHODS: With Research Ethics Board approval and written parental consent, a total of 17 healthy children requiring general anaesthesia were enrolled. Following inhalational induction of anaesthesia, a propofol bolus of 5 mg.kg(-1) was given and anaesthesia maintained using an adaptation of the McFarlan continuous propofol infusion regimen to achieve three distinct depths of propofol anaesthesia. Weight and propofol infusion data were used to calculate simulated propofol concentrations using the Kataria dataset and the TIVA simulation program. The performance of the infusion regimen was assessed by calculating the median performance error, median absolute performance error, wobble, and divergence. RESULTS: Measured propofol concentrations were (mean +/- sd) 7.15 +/- 1.4, 4.3 +/- 0.85, and 2.85 +/- 0.53 microg.ml(-1) against simulation values of 6.6, 4.1, and 2.8 microg.ml(-1), respectively, at 30, 50, and 70 min using the Kataria dataset. These differences were not significant. Formal assessment of the infusion regimen's performance was acceptable. CONCLUSION: The manual propofol infusion regimen achieved three distinct depths of propofol anaesthesia. The manual infusion regimen produced higher plasma propofol concentrations than predicted during the early part of the infusion period but was more accurate for later time points.

The effect of varying continuous propofol infusions on plasma cyclic guanosine 3',5'-monophosphate concentrations in anesthetized children.

BACKGROUND: The glutamate-nitric oxide-cyclic guanosine 3',5'-monophosphate (cGMP) pathway is potentially an effective target for general anesthetics. Plasma cGMP concentrations are reduced after an increase in predicted plasma propofol concentrations during sedation in healthy adult volunteers. We hypothesized that an increase in measured plasma propofol concentration leads to a reduction in plasma cGMP in anesthetized children. METHODS: Eighteen healthy children aged 46.8 (+/-19.6) mo, requiring general anesthesia for lower body surgical procedures were enrolled. After inhaled induction, tracheal intubation and initiation of intermittent positive pressure ventilation, caudal epidural analgesia was performed. Anesthesia was maintained using a continuous propofol infusion adapted from a previously published regimen to achieve predicted propofol plasma concentration of 6, 3, and 1.5 microg/mL after 30, 50, and 70 min, respectively. Samples for propofol and cGMP plasma concentrations were collected and analyzed using high-performance liquid chromatography and an enzyme immunoassay system. RESULTS: The plasma cGMP concentrations varied significantly (median [range]) 19.2 [11.8-23.5], 21.3 [14.6-30.8], and 24.9 [15.7-37.8] nmol/L among each predicted plasma propofol concentration, P < 0.0001. The correlation coefficient (r) was -0.62. CONCLUSIONS: This study demonstrates that an increase in plasma propofol concentration leads to a decrease in plasma cGMP in healthy children, and could serve as a biochemical marker for depth of propofol anesthesia in children.

Hemodynamic and respiratory effects of pediatric urological retroperitoneal laparoscopic surgery: a prospective study.

PURPOSE: Our understanding of the effects of retroperitoneal CO(2) insufflation on cardiopulmonary variables in children remains limited. This study was designed to investigate prospectively the effect of CO(2) insufflation in a pediatric population undergoing retroperitoneal laparoscopic surgery. MATERIALS AND METHODS: We prospectively evaluated a consecutive series of patients enrolled between July 2003 and August 2004. Anesthesia was administered following a standardized protocol. Data collection included respiratory rate, PAP, O(2) saturation, ETCO(2), HR, MAP, electrocardiogram and insufflation pressure. All variables were recorded before, during and after CO(2) insufflation at regular intervals of 1 to 2 minutes, with up to 23 measurements recorded for each period. RESULTS: A total of 18 participants were recruited. Mean +/- SD for age and weight were 79.4 +/- 53.2 months and 26.7 +/- 15.5 kg, respectively. Mean retroperitoneal CO(2) insufflation pressure was kept at 12 mm Hg. Significant differences (p <0.05) in average ETCO(2), PAP and MAP were noted after CO(2) insufflation compared to baseline (pre-pneumoretroperitoneum) values. HR and temperature did not change. At completion of the laparoscopic intervention physiological variables exhibited a trend to return to baseline values. CONCLUSIONS: This prospective study documents significant changes in systemic hemodynamic variables that seem to be directly associated with the insufflation of CO(2) during pediatric retroperitoneal laparoscopic surgery. This ongoing evaluation confirms the effect of laparoscopic urological surgery and CO(2) insufflation on cardiopulmonary function in children.

The effect of sevoflurane on cerebral autoregulation in young children as assessed by the transient hyperemic response.

The transient hyperemic response (THR) test is a simple, noninvasive technique to evaluate cerebral autoregulation using transcranial Doppler. It has not yet been used in studies involving children. In this study we evaluated this response in children undergoing general anesthesia using sevoflurane. Twenty ASA physical status I children undergoing elective urological surgery sequentially received sevoflurane at 0.5, 1.0, and 1.5 MAC in a randomized order. Analgesia was solely provided by caudal anesthesia. The right middle cerebral artery flow velocities before (F1), during (F2), and after (F3) a 10-s ipsilateral carotid artery compression were recorded. The THR ratios (THRR) (+/- sd) for 0.5 MAC, 1.0 MAC, and 1.5 MAC were 1.24 +/- 0.11, 1.16 +/- 0.09, and 1.13 +/- 0.07, respectively. The THRR was significantly different between 0.5 MAC versus 1.0 and 1.5 MAC, respectively (P < 0.05). However, no difference was detected between 1.0 and 1.5 MAC. A THRR of more than 1.09 has previously been accepted as the lower limit of a positive response. The results in this study suggest that THR is affected by sevoflurane in a dose-dependent fashion but is maintained at up to 1.5 MAC. This suggests cerebral autoregulation is preserved in children anesthetized with up to 1.5 MAC sevoflurane.

Desflurane increases cerebral blood flow velocity when used for rapid emergence from propofol anesthesia in children.

PURPOSE: Desflurane may be used to replace propofol at the end of anesthesia to facilitate rapid emergence. This study determined the effect of administering desflurane during emergence of anesthesia on middle cerebral artery blood flow velocity (Vmca) in children anesthetized with propofol. METHODS: Thirty healthy children aged one to six years scheduled for orchidopexy or hypospadias repair under general anesthesia were enrolled. Anesthesia was maintained with a propofol infusion targeting an estimated serum level of 3 microg x mL(-1), remifentanil 0.2 microg x kg(-1) x min(-1) and a caudal epidural block. Transcranial Doppler sonography was used to measure Vmca at five-minute intervals. In half the patients, propofol was substituted with desflurane 1 MAC, 30 min prior to the end of the surgical procedure. Once steady-state had been achieved recordings of Vmca, heart rate, and mean arterial pressure were resumed. Upon termination of the surgical procedure, the maintenance agent was discontinued and recordings continued at one-minute intervals during emergence of anesthesia. RESULTS: There were no demographic differences between the two groups. Vmca increased from 37.2 +/- 3.1 cm x sec(-1) to 57.7 +/- 4.1 cm x sec(-1) when propofol was changed to desflurane (P < 0.01). Upon emergence of anesthesia, Vmca decreased from 57.8 +/- 4.2 cm x sec(-1) to 37.8 +/- 3.2 cm x sec(-1) in the desflurane group (P < 0.01) but remained unchanged in the propofol group. CONCLUSION: Desflurane is associated with an increase in cerebral blood flow velocity when used to facilitate rapid emergence following a propofol infusion in children. This may be of clinical significance in patients with intracranial pathology.

The effect of remifentanil on cerebral blood flow velocity in children anesthetized with propofol.

BACKGROUND: Cerebrovascular stability and rapid anesthetic emergence are desirable features of a neuroanesthetic regimen. In this randomized crossover study the effect of a low-dose remifentanil infusion on cerebral blood flow velocity (CBFV) in children anesthetized with propofol was evaluated. METHODS: Twenty healthy children aged 1-6 years undergoing urological surgery were enrolled. Following face mask induction with sevoflurane, anesthesia was maintained with a standardized propofol infusion. Rocuronium was used to facilitate tracheal intubation and normothermia, and normocapnia were maintained. All children received a caudal epidural block, and a transcranial Doppler probe was placed to measure middle cerebral artery blood flow velocity (Vmca). Each patient received a remifentanil regimen of 0.5 microg x kg(-1) followed by 0.2 microg x kg(-1) x min(-1) in a predetermined order of remifentanil + propofol or propofol alone. Vmca, mean arterial pressure (MAP) and heart rate (HR) were recorded simultaneously at equilibrium with and without remifentanil. RESULTS: The combination of remifentanil and propofol caused an 8.1% decrease in MAP (P = 0.0005) and an 11.8% decrease in HR (P < 0.0001) compared with propofol alone. Vmca was not different between the two groups (P = 0.4041). CONCLUSION: The addition of remifentanil to propofol anesthesia in children causes a reduction in MAP and HR without affecting CBFV. This may imply that cerebral blood pressure autoregulation is preserved in children under propofol and remifentanil anesthesia.

The cerebrovascular response to hypocapnia in children receiving propofol.

Hypocapnia is used to treat acute increases in intracranial pressure during neurosurgery. Cerebrovascular reactivity to carbon dioxide (CCO(2)R) is preserved above 35 mm Hg ETco(2) in children during propofol anesthesia; however, a plateau effect has been suggested below 35 mm Hg. To further delineate this phenomenon, we measured CCO(2)R by transcranial Doppler (TCD) sonography over small increments in ETco(2) in 27 healthy children. Anesthesia comprised a standardized propofol infusion and a caudal epidural block. A TCD probe was placed to measure middle cerebral artery blood flow velocity (V(mca)). ETco(2) was adjusted between 24 and 40 mm Hg at 1-2 mm Hg increments using an exogenous source of CO(2). There was an exponential relationship between ETco(2) and V(mca) above an ETco(2) value of 30 mm Hg (r = 0.82). However, V(mca) did not change with ETco(2) less than 30 mm Hg (r = 0.06). There were no significant changes in heart rate or arterial blood pressure. We conclude that when contemplating methods to decrease brain volume and intracranial pressure, hyperventilation to ETco(2) values less than 30 mm Hg may not be necessary in children receiving propofol, as no further reduction in cerebral blood flow velocity will be achieved.