Franz J. Frei

Effect of combined mouth closure and chin lift on upper airway dimensions during routine magnetic resonance imaging in pediatric patients sedated with propofol.

BACKGROUND In pediatric patients, obstruction of the upper airway is a common problem during general anesthesia. Chin lift is a commonly used technique to improve upper airway patency. However, little is known about the mechanism underlying this technique. METHODS The authors studied the effect of the chin lift maneuver on airway dimensions in 10 spontaneously breathing children (aged 2-11 yr) sedated with propofol during routine magnetic resonance imaging. The minimal anteroposterior and corresponding transverse diameters of the pharynx were determined at the levels of the soft palate, dorsum of the tongue, and tip of the epiglottis before and during the chin lift maneuver. Additionally, cross-sectional areas were calculated at these sites, including tracheal areas 2 cm below the glottic level. RESULTS Minimal anteroposterior diameter of the pharynx increased significantly during chin lift at all three levels in all patients. The diameters of the soft palate, tongue, and epiglottis increased from 6.7+/-2.8 mm (SD) to 9.9+/-3.6 mm, from 9.6+/-3.6 mm to 16.5+/-3.1 mm, and from 4.6+/-2.5 mm to 13.1+/-2.8 mm, respectively. The corresponding transverse diameter of the pharynx also increased significantly at all three levels in all patients but without significant predominance. The diameters at the levels of the soft palate, tongue, and epiglottis increased from 15.8+/-5.1 mm to 22.8+/-4.5 mm, from 13.5+/-4.9 mm to 18.7+/-5.3 mm, and from 17.2+/-3.9 mm to 21.2+/-3.7 mm, respectively. Cross-sectional pharyngeal areas increased significantly at all levels (soft palate, from 0.88+/-0.58 cm2 to 1.79+/-0.82 cm2; tongue, from 1.15+/-0.45 cm2 to 2.99+/-1.30 cm2; epiglottis, from 1.17+/-0.70 cm2 to 3.04+/-0.99 cm2), including the subglottic level (from 0.44+/-0.15 cm2 to 0.50+/-0.14 cm2). CONCLUSIONS This study shows that all children had a preserved upper airway at all measured sites during propofol sedation. Chin lift caused a widening of the entire pharyngeal airway that was most pronounced between the tip of the epiglottis and the posterior pharyngeal wall. In pediatric patients, chin lift may be used as a standard procedure during propofol sedation.

Respiratory Reflex Responses of the Larynx Differ between Sevoflurane and Propofol in Pediatric Patients

Background:The effects of anesthetics on airway protective reflexes have not been extensively characterized in children. The aim of this study was to compare the laryngeal reflex responses in children anesthetized with either sevoflurane or propofol under two levels of hypnosis using the Bispectral Index score (BIS). The authors hypothesized that the incidence of apnea with laryngospasm evoked by laryngeal stimulation would not differ between sevoflurane and propofol when used in equipotent doses and that laryngeal responsiveness would be diminished with increased levels of hypnosis. Methods:Seventy children, aged 2–6 yr, scheduled to undergo elective surgery were randomly allocated to undergo propofol or sevoflurane anesthesia while breathing spontaneously through a laryngeal mask airway. Anesthesia was titrated to achieve the assigned level of hypnosis (BIS 40 ± 5 or BIS 60 ± 5) in random order. Laryngeal and respiratory responses were elicited by spraying distilled water on the laryngeal mucosa, and a blinded reviewer assessed evoked responses. Results:Apnea with laryngospasm occurred more often during anesthesia with sevoflurane compared with propofol independent of the level of hypnosis: episodes lasting longer than 5 s, 34% versus 19% at BIS 40 and 34% versus 16% at BIS 60; episodes lasting longer than 10 s, 26% versus 10% at BIS 40 and 26% versus 6% at BIS 60 (group differences P < 0.04 and P < 0.01, respectively). In contrast, cough and expiration reflex occurred significantly more frequently in children anesthetized with propofol. Conclusion:Laryngeal and respiratory reflex responses in children aged 2–6 yr were different between sevoflurane and propofol independent of the levels of hypnosis examined in this study.

Difficult intubation in paediatrics

Optimal oxygenation and ventilation in anaesthetized or critically ill patients are crucial and because of the increased oxygen consumption and decreased oxygen reserve, hypoxaemia occurs more rapidly in infants and children than in adults. Several pathological conditions may lead to problems in airway management and in tracheal intubation, some of which are comparable while others differ markedly from those in adults. In nonobstetric adult surgical patients, the incidence of failed intubation is 12303 (l), whereas in obstetric patients it is as high as 1:300 (2). Difficult intubation occurs at a rate between 1.5 and 13% (3). The incidence of difficult or failed intubation in otherwise healthy children is not known but it is suggested that it is less than the above figures. In patients with rare diseases and syndromes, difficult intubation may occur more frequently.

Decrease of functional residual capacity and ventilation homogeneity after neuromuscular blockade in anesthetized young infants and preschool children

Background: Based on age-dependent differences in pulmonary mechanics, the effect of neuromuscular blockade may differ in infants compared with older children. The aim of this study was to determine the impact of neuromuscular blockade and its reversal by positive end-expiratory pressure (PEEP) on functional residual capacity (FRC) and ventilation distribution in young infants and preschool children. Methods: The authors studied 14 infants (aged 0–6 months) and 25 preschool children (aged 2–6 yr). FRC and lung clearance index were calculated. Measurements were taken (1) after intubation, (2) during neuromuscular blockade, and (3) during neuromuscular blockade plus application of PEEP (3 cm H2O). Results: Functional residual capacity (mean ± SD) decreased from 21.3 ± 4.7 ml/kg to 12.2 ± 4.8 ml/kg (P < 0.001) during neuromuscular blockade in infants and from 25.6 ± 5.9 ml/kg to 23.0 ± 5.3 ml/kg (P < 0.001) in preschool children. With the application of PEEP, FRC increased to 22.3 ± 5.9 ml/kg (P = 0.4829, compared with baseline) in infants and 28.2 ± 5.8 ml/kg (P < 0.001) in children. The lung clearance index increased after neuromuscular blockade, whereas baseline values were regained after the application of PEEP. The changes induced by neuromuscular blockade were significantly greater in infants compared with preschool children (P < 0.001). Conclusions: Although the use of neuromuscular blockade decreased FRC and ventilation distribution substantially in both groups, the changes were more pronounced in young infants. With PEEP, FRC increased and ventilation homogeneity was restored. These results provide a rationale to use PEEP in anesthetized, paralyzed infants and children.

Effects of Ondansetron in the Prevention of Postoperative Nausea and Vomiting in Children

BackgroundPostoperative nausea and vomiting (PONV) is a commonly observed adverse effect of general anesthesia. Recently, ondansetron, a new serotonin3 (5-hydroxytryptamine3) receptor antagonist was shown to be effective in the prophylaxis and prevention of chemotherapy-induced nausea and vomiting in children and adults as well as of PONV in adults. The aim of the current study was to evaluate the capacity of ondansetron to prevent PONV in pediatric patients. MethodsTwo hundred children (132 boys and 68 girls) 2–10 yr of age received general inhalational anesthesia for surgical procedures (the extremities; ear, nose, and throat; inguinal hernia and phimosis; and dentistry) of an expected duration of less than 90 min. This study was divided into two phases: prophylaxis and rescue treatment. For prophylaxis, patients were randomly assigned to two groups: one group received an intravenous injection of 0.1 mg/kg ondansetron, and the other group received a placebo before surgical incision under double-blind conditions. For rescue treatment, only placebo patients were included; as a rescue medication they received an intravenous injection of 0.1 mg/kg ondansetron or 0.02 mg/kg droperidol according to a prestudy randomization under double-blind conditions. Incidence and severity of PONV (PONV score 0 = no nausea and no retching; 1 = complaining of sickness and retching; 2 = vomiting one or two times in 30 min; 3 = vomiting more than two times in 30 min) was recorded over a 4-h period in the postanesthesia care unit. Within 72 h of the procedure, a follow-up nurse interviewed the parents for late-onset nausea in the children. ResultsWith regard to prophylaxis, 10% of patients receiving ondansetron had PONV during the 4-h observation period versus 40% of those receiving placebo (P < 0.001). The incidence of vomiting alone (PONV score ≤ 2) was 5% and 25%, respectively (P < 0.001). There were no significant differences between ondansetron and droperidol in the treatment of PONV. However, at the end of the 4-h period, ondansetron patients were less sedated than were patients who had received droperidol (P < 0.01). Interviews with parents could be performed for 143 of 200 children (76 ondansetron and 67 placebo). Twenty-four children (15 ondansetron and 9 placebo) showed late-onset PONV after the 4-h observation period but within 24 h of the procedure (19.7% vs. 13.4%; P not significant). ConclusionsOndansetron is effective in the prevention of PONV in pediatric patients for the first 4 h after general anesthesia. Lower sedation scores with ondansetron compared with droperidol may be an advantage, especially in ambulatory surgery. However, the incidence of late-onset PONV (>4–24 h) was not influenced by prophylactic treatment with one dose of ondansetron preoperatively.

The effects of common airway maneuvers on airway pressure and flow in children undergoing adenoidectomies.

Obstruction of the upper airway occurs frequently in anesthetized, spontaneously breathing children, especially in those with adenoidal hyperplasia. To improve airway patency, maneuvers such as chin lift (CL), jaw thrust (JT), and continuous positive airway pressure (CPAP) are often used. In this study, we examined the comparative efficacy of these maneuvers in children scheduled to undergo adenoidectomy. Sixteen children aged 2–9 yr were anesthetized with sevoflurane. During spontaneous breathing, the flows and pressures in the mask (ma), oropharynx (op), and esophagus (es) were measured simultaneously, and maximal pressure differences during inspiration (&Dgr;P) were calculated. After baseline recording, CL and JT maneuvers were performed in random order without and with CPAP (5 cm H2O). The observed &Dgr;Pma − Pes of 12.3 ± 3.4 cm H2O at baseline decreased with all airway maneuvers (P < 0.05). This resulted from decreases of &Dgr;Pma − Pop (P < 0.05) and &Dgr;Pop − Pes (P < 0.05) in all interventions except CL, in which &Dgr;Pma − Pop remained similar. In contrast, significant improvements of minute ventilation and maximal inspiratory peak flow (P > 0.05) were observed only with JT (with and without CPAP). We conclude that CL may improve airway patency and ventilation, whereas JT with or without CPAP was the most effective maneuver to overcome airway obstruction in children with adenoidal hyperplasia.

The airway endoscopy mask: useful device for fibreoptic evaluation and intubation of the paediatric airway

A mask is presented which allows the administration of 100% oxygen, inhalational anaesthetics, continuous positive airway pressure and intermittent positive pressure ventilation during diagnostic airway endoscopy and difficult intubation with a fibreoptic bronchoscope in paediatric patients. The mask is particularly useful in small or critically ill patients. It may also have its place in teaching situations.

The impact of positive end-expiratory pressure on functional residual capacity and ventilation homogeneity impairment in anesthetized children exposed to high levels of inspired oxygen

BACKGROUND:High fractions of inspired oxygen (Fio2) result in resorption atelectasis shortly after their application. However, the impact of different levels of Fio2 and their interaction with positive end-expiratory pressure (PEEP) on functional residual capacity (FRC) and ventilation distribution is unknown in anesthetized children. We hypothesized that the use of a Fio2 of 1.0 results in a decrease of FRC and ventilation homogeneity compared with that of a Fio2 of 0.3, and that this decrease is prevented by PEEP of 6-cm H2O compared to a PEEP of 3-cm H2O. METHODS:Forty-six children (3–6 yr) without cardiopulmonary disease were randomly allocated to receive PEEP of 6-cm H2O (PEEP 6 group) during the entire study period or PEEP of 3-cm H2O (PEEP 3 group). The order of the Fio2 (0.3 or 1.0) was also randomized. A defined recruitment maneuver was performed after tracheal intubation and 5 min later the first measurement. This procedure was then repeated with the second Fio2 level. FRC and lung clearance index (LCI) were calculated by a blinded observer. RESULTS:While FRC (mean ± sd) was similar at both levels of Fio2 (0.3: 25.6 ± 2.9 mL/kg vs 1.0: 25.6 ± 2.8 mL/kg, P = 0.189) in the PEEP 6 group, FRC decreased in the PEEP 3 group (0.3: 24.9 ± 3.8 vs 1.0: 21.7 ± 4.1, P < 0.0001). Furthermore, with continuous PEEP of 6-cm H2O a similar LCI was observed at both levels of Fio2 (0.3: 6.45 ± 0.4 vs 6.43 ± 0.4, P = 0.668) while LCI increased at the higher Fio2 in the PEEP 3 group (0.3: 6.5 ± 0.5 vs 1.0: 7.7 ± 1.2, P < 0.0001). CONCLUSIONS:During the application of a very low PEEP of 3–cm H2O, FRC and ventilation distribution decreased significantly at an Fio2 of 1.0 compared with that at an Fio2 of 0.3. This decrease could be counterbalanced by the administration of PEEP of 6-cm H2O, indicating that a low level of PEEP is sufficient to maintain FRC and ventilation distribution regardless of the oxygen concentration.

Intraoperative monitoring of motor-evoked potentials in children undergoing spinal surgery.

Study Design. Clinical case series. Objective. To study the combined use of modifications of stimulation methods and adjustments of anesthetic regimens on the reliability of motor-evoked potential (MEP) monitoring in a large group of children undergoing spinal surgery. Summary of Background Data. Monitoring of MEPs is advocated during spinal surgery, but systematic data from children are sparse. Methods. A total of 134 consecutive procedures in 108 children <18 years of age were analyzed. MEPs were elicited by transcranial electrical stimulation (TES) and supplemented by temporal and spatial facilitation. The standard anesthesia regimen consisted of propofol, nitrous oxide, and remifentanil. Propofol was replaced with ketamine if no reliable MEPs could be recorded. In children <6 years of age, a ketamine-based anesthesia was used. Results. With temporal facilitation alone, reliable MEPs were obtained in 78% (105 of 134) of the procedures and, if combined with spatial facilitation, in 96% (129 of 134) of the procedures. Reliable MEPs were documented in 98% (111 of 113) of children >6 years and in 86% (18 of 21) in children <6 years of age. Conclusions. Combining spatial facilitation with a TES protocol improved monitoring of corticospinal motor pathways during spinal surgery in children. A ketamine-based anesthetic technique was preferred in children <6 years of age.

Opening the upper airway: airway maneuvers in pediatric anesthesia

Maintenance of a patent airway is the most important aspect of the safe administration of anesthesia in children. However, in spontaneously breathing, anesthetized children, upper airway obstruction is a frequent problem (1) and failure to maintain a patent airway can rapidly result in hypoxemia, bradycardia or even cardiac arrest. Upper airway narrowing is most likely to appear in pharyngeal structures (2–4). Since the entire airway is composed of soft tissue and is kept patent during inspiration by the dilating action of the pharyngeal airway muscles, any drug that leads to a reduction of muscle activity can reduce airway patency and thus increase upper airway resistance (5). Children are particularly susceptible to upper airway obstruction because of the smaller dimensions of their airways and the high incidence of tonsillar and/or adenoidal hypertrophy which causes increased resistance to flow (6). During anesthesia and basic life support, positioning of body, head and neck as well as airway maneuvers such as jaw thrust and chin lift are commonly used to improve the patency of an obstructed or partially obstructed upper airway (7, 8). The importance of these maneuvers has been known for a long time; Jacob Heiberg wrote in 1874 that during chloroform anesthesia, noisy, obstructed breathing, particularly during inspiration, can be prevented by pulling the jaw forward (9), while other authors have even earlier advocated opening obstructed airways by pulling the tongue forward (10–12). This review focuses on the mechanisms and efficacy of different, simple methods to open and maintain a patent airway in spontaneously breathing children undergoing anesthesia, which include body, head and neck positioning and airway maneuvers such as mouth opening, chin lift, jaw thrust or the use of continuous positive airway pressure (CPAP).