Safety and efficacy of semi-closed circle ventilation in small infants

The purpose of this clinical trial was to investigate the safety and efficacy of semi-closed circle ventilation of the Dräger anaesthesia ventilators (Cicero, Cato), using a fresh gas flow (FGF) of 600 ml·min^?1. Twenty infants, weighing less than 6000 g, without cardiorespiratory abnormalities who required general anaesthesia of at least 30 min were included. The FGF was reduced to 600 ml·min^?1 after 10 min of denitrogenation with a FGF of 4 to 6 l·min^?1. The composition of the FGF (600ml·min^?1) was calculated as follows: oxygen necessary for consumption (60 ml·min^?1) plus the remaining FGF in a 1:2 relationship for oxygen. The inspiratory nitrogen fraction was calculated to exclude accumulation. Inspiratory fractions of O₂ and N₂O plus inspiratory and endtidal CO₂ partial pressures and noninvasive oxygen saturation were the control parameters. The gas concentrations (O₂ and N₂O) remained within safe limits. Hypoxic gas concentrations were not observed. Neither nitrogen nor CO₂ accumulated in the circle system. In conclusion, low flow anaesthesia can be performed safely in infants under 6000 grams with the Dräger Cicero and Cato anaesthesia ventilators.     

Fresh gas flow changes during controlled mechanical ventilation with the circle breathing system have significantly greater effects on the ventilatory parameters of toddlers compared with children*

Fresh gas flow into a circle system can affect the delivered minute ventilation because fresh gas flow augments the flow delivered by the ventilator bellows during inspiration. After establishing a stable ventilatory pattern with 3.0 l·min^-1 fresh gas flow into a circle system, changes in peak inflation pressure, minute ventilation and end-tidal carbon dioxide were measured at 1.5 l·min^-1 and 6.0 l·min^-1 in 10 toddlers (10–20 kg) and 10 children (30–60 kg). Changes in all variables were observed but these changes were greater in toddlers compared with children (P < 0.001). Some toddlers were noted to have as much as a 37% change in ventilatory parameters when fresh gas flow was altered between 1.5 and 6.0 l·min^-1. Whenever changes are made in fresh gas flow, compensatory changes in minute ventilation should be considered to avoid unintended hyperventilation or hypoventilation. This is especially important during anaesthesia for toddlers.     

Clinical evaluation of low-flow sevoflurane anaesthesia for paediatric patients

Background: Sevoflurane expenditure, inspired gas humidity, temperature, soda lime temperature, and compounds A and B were measured during high and low fresh gas flow anaesthesia in paediatric patients. Methods: Sixty ASA 1 or 2 paediatric patients were randomly allocated to two groups: low-flow circle anaesthesia (LFA) patient group (n=30) and high-flow circle anaesthesia (HFA) patient group (n=30). Initial fresh gas flow (FGF) was 4 l · min^?1 of nitrous oxide and 2 l · min^?1 of oxygen in both groups. This FGF of 6 l · min^?1 was maintained in the HFA group. After 10 min of HFA, the FGF was reduced to 600 ml · min^?1 (nitrous oxide and oxygen 300 ml · min^?1 each) in the LFA group. Results: Sevoflurane expenditure during LFA was about 1/7 of that during HFA (3.3±0.2 ml · h^?1 · vol.%^?1 compared to 22.8±0.6 ml · h^?1 · vol.%^?1, mean±SEM, respectively). Absolute humidity in the LFA patients was 4 times higher than that in the HFA patients (22.8±2.4 g · m^?3, 5.6±3.4 g · m^?3 respectively). There was no significant difference in the inspiratory gas temperature between the LFA (28.5±0.6°C) and HFA (26.9±1.3°C) groups. There was significant difference in the mean highest soda lime temperature between the LFA (35.5±1.2°C) and HFA (28.7±1.2°C) groups. The mean highest concentration of compound A was 12.2±3.8 ppm in the LFA group. The mean highest concentration of compound B was less than 1 ppm. Compounds A and B were below detectable level in the HFA group. Conclusion: In conclusion, sevoflurane used for paediatric patients in a circle system with a fresh gas flow of 0.6 l · min^?1 resulted in a significantly reduced sevoflurane expenditure, higher inspired absolute humidity, but not temperature, compared to a fresh gas flow of 6 l · min^?1. Low levels of compounds A and B were detected.     

Serial measurement of leak conductance around uncuffed endotracheal tubes in children after cardiopulmonary bypass

Introduction: Judging the correctness of the fit of an uncuffed tube in the trachea is an imprecise process that may rely on detecting a just‐audible leak (1). An optimal fit would allow adequate ventilation whilst minimising trauma to the subglottis. If ventilation is prolonged, the fit of the tube in the trachea might vary. We believe that the leak of gas around an uncuffed tube may be evaluated to give an indication of the ‘goodness’ of fit. Methods: In the laboratory we developed a technique for quantifying the leak around the tracheal (TT) tube in ventilated children from continuous measurements of airway pressure and inspiratory and expiratory flow acquired from a ventilator. We obtained ethical approval to study 20 children who were ventilated on our PICU after undergoing cardiac surgery on cardiopulmonary bypass. Recordings were made for sequences of 100 breaths at intervals of approximately 4 h during the time that the child was ventilated. Audible leak was graded as ‘none’, ‘minute’, ‘moderate’ or ‘large’ by the anaesthetist responsible for each patient. We calculated the leak conductance (in l.s.^–1 cmH2O^–1) for each recording and plotted it against time for each patient. We calculated the average leak conductance from the normalised area under this curve to account for irregular sampling, and used this quantity (2) to compare patients who were grouped according to grade of audible leak. Results: A total of 286 recordings were collected from 20 patients (age range 5–1356 days, mean age 193 days, weight range 3.0–12.4 kg, mean weight 5.5 kg). Eleven recordings were rejected due to failure or artefact, and two patients were excluded due to insufficient data (two or fewer recordings). Five patients were graded with moderate or large audible leak and the mean leak conductance for this group (mean 360 l.s ^–1 cmH₂O^–1) significantly exceeded the leak conductance for the remaining 13 patients with no leak or minute leak (mean 125 l.s ^–1 cmH₂O^–1)) with P < 0.05. Discussion: We have demonstrated that the physical characteristics of a leak around an uncuffed ET tube can be quantified (3) and that, in this small study, serial measurement of leak conductance is consistent with qualitative audible assessment of leak. Conclusion: Leak conductance may provide an objective method for analysing the leak around an uncuffed TT tube and thereby the fit of the tube in the subglottis. We believe that this technique, if adapted, may be useful in the clinical setting. References 1 Fine GF, Borland LM. The future of the cuffed endotracheal tube. Pediatr Anesth 2004; 14 : 38–42. 2 Matthews JNS et al. Analysis of serial measurements in medical research. BMJ 1990; 300 : 230–235. 3 Smith JH et al. Leak resistance around uncuffed endotracheal tubes. Pediatr Anesth 2005; 15 : 805–806.     

A comparison between low-flow leak test and oxygen flush leak test

Purpose. The clinical efficacy of two methods of preanesthetic leak test,namely the oxygen flush leak test (OFLT) and the low-flow leak test (LFLT), was compared regarding their ability to detect leakage in the anesthesia circuit and their accuracy. Methods. Examinees comprised 16 staff anesthesiologists and 7 physicians undergoing anesthesia training at our institution. They performed the two leak tests on anesthesia machines with some intentional leaks (0.1–1.0 l·min⁻¹). The leakage detection rates (LDR) were analyzed by the χ²-test. The ability to detect leaks was measured by recording how many leaks were detected by 50% (LDR₅₀) and 95% (LDR₉₅) of the examinees. Results. The LDRs in the two tests were significantly different (χ²- analysis, P < 0.0001). Both LDR₅₀ and LDR₉₅ for the LFLT (0.23 and 0.41 l·min⁻¹, respectively) were smaller than the values for the OFLT (0.37 and 0.82 l·min⁻¹, respectively). The sensitivity and specificity of the LFLT (0.97 and 0.84, respectively) were higher than those of the OFLT (0.78 and 0.80, respectively). Conclusion. The LFLT was found to be superior to the OFLT regarding leak detection and reliability. We therefore recommend the LFLT for preanesthetic leak testing. Received: June 23, 1999 / Accepted: July 5, 2000     

Cuffed endotracheal tubes in children reduce sevoflurane and medical gas consumption and related costs

Background: This study aims to evaluate sevoflurane and anaesthetic gas consumption using uncuffed vs. cuffed endotracheal tubes (ETT) in paediatric surgical patients. Methods: Uncuffed or cuffed ETT were used in paediatric patients (newborn to 5 years) undergoing elective surgery in a randomized order. Duration of assessment, lowest possible fresh gas flow (minimal allowed FGF: 0.5 l/min) and sevoflurane concentrations used were recorded. Consumption and costs for sevoflurane and medical gases were calculated. Results: Seventy children (35 uncuffed ETT/35 cuffed ETT), aged 1.73 (0.01–4.80) years, were enrolled. No significant differences in patient characteristics, study period and sevoflurane concentrations used were found between the two groups. Lowest possible FGF was significantly lower in the cuffed ETT group [1.0 (0.5–1.0) l/min] than in the uncuffed ETT group [2.0 (0.5–4.3) l/min], P<0.001. Sevoflurane consumption per patient was 16.1 (6.4–82.8) ml in the uncuffed ETT group and 6.2 (1.1–14.9) ml in the cuffed ETT group, P=0.003. Medical gas consumption was 129 (53–552) l in the uncuffed ETT group vs. 46 (9–149) l in the cuffed ETT group, P<0.001. The total costs for sevoflurane and medical gases were 13.4 (6.0–67.3)€/patient in the uncuffed ETT group and 5.2 (1.0–12.5)€/patient in the cuffed ETT group, P<0.001. Conclusions: The use of cuffed ETT in children significantly reduced the costs of sevoflurane and medical gas consumption during anaesthesia. Increased costs for cuffed compared with uncuffed ETT were completely compensated by a reduction in sevoflurane and medical gas consumption.     

Reduced air leakage by adjusting the cuff pressure in pediatric laryngeal mask airways during spontaneous ventilation

Background: Optimal inflation of the laryngeal mask airway (LMA) cuff should allow ventilation with low leakage volumes and minimal airway morbidity. Manufacturer’s recommendations vary, and clinical end‐points have been shown to be associated with cuff hyperinflation and increased leak around the LMA. However, measurement of the intra‐cuff pressure of the LMA is not routine in most pediatric institutions, and the optimal intra‐cuff pressure in the LMA has not been determined in clinical studies. Methods: This was a prospective audit in100 pediatric patients undergoing elective general anesthesia breathing spontaneously via LMA (size 1.5–3). Cuff pressure within the LMA was adjusted using a calibrated pressure gauge to three different values (60, 40, and 20 cmH₂O) within the manufacturers’ recommended LMA cuff pressure range (≤60 cmH₂O). Three corresponding inspiratory and expiratory tidal volumes were recorded, and the differences were calculated as the ‘leak volume’. Results: Compared with 20 and 60 cmH₂O intra‐cuff pressure, measured leakage volumes were the lowest at cuff inflation pressures of 40 cmH₂O [median (range) 0.42 (0.09–1.00) ml·kg^?1] in most patients (83%), while 17% of children demonstrated minimally smaller leakages at 20 cmH₂O [0.51 (0.11–1.79) ml·kg^?1]. Maximum leakage values occurred with cuff pressures of 60 cmH₂O in all groups [0.65 (0.18–1.27) ml·kg^?1] and were not associated with the smallest value of air leakage in any patient. Conclusion: Using cuff manometry, an intra‐cuff pressure of 40 cmH₂O was associated with reduced leak around the LMA while higher (60 cmH₂O) and lower (20 cmH₂O) cuff pressures resulted in higher leak volumes during spontaneous ventilation. In spontaneously breathing children, reducing the intra‐cuff pressure of pediatric‐sized LMAs even below the manufacturers’ recommendations allows ventilation with minimized leakage around the LMA cuff.     

Cuffed vs. uncuffed tracheal tubes in children: a randomised controlled trial comparing leak,tidal volume and complications

Cuffed tracheal tubes are increasingly used in paediatric anaesthetic practice. This study compared tidal volume and leakage around cuffed and uncuffed tracheal tubes in children who required standardised mechanical ventilation of their lungs in the operating theatre. Children (0–16 years) undergoing elective surgery requiring tracheal intubation were randomly assigned to receive either a cuffed or an uncuffed tracheal tube. Assessments were made at five different time‐points: during volume‐controlled ventilation 6 ml.kg^?1, PEEP 5 cmH₂O and during pressure‐controlled ventilation 10 cmH₂O / PEEP 5 cmH₂O. The pressure‐controlled ventilation measurement time‐points were: just before a standardised recruitment manoeuvre; just after recruitment manoeuvre; 10 min; and 30 min after the recruitment manoeuvre. Problems and complications were recorded. During volume‐controlled ventilation, leakage was significantly less with cuffed tracheal tubes than with uncuffed tracheal tubes; in ml.kg^?1, median (IQR [range]) 0.20 (0.13–0.39 [0.04–0.60]) vs. 0.82 (0.58–1.38 [0.24–4.85]), respectively, p < 0.001. With pressure‐controlled ventilation, leakage was less with cuffed tracheal tubes and stayed unchanged over a 30‐min period, whereas with uncuffed tracheal tubes, leakage was higher and increased further over the 30‐min period. Tidal volumes were higher in the cuffed group and increased over time, but in the uncuffed group were lower and decreased over time. Both groups showed an increase in tidal volumes following recruitment manoeuvres. There were more short‐term complications with uncuffed tracheal tubes, but no major complications were recorded in either group at long‐term follow‐up. With standardised ventilator settings, cuffed tracheal tubes produced better ventilation characteristics compared with uncuffed tracheal tubes during general anaesthesia for routine elective surgery.     

Efficacy of a heat and moisture exchanger in inhalation anesthesia at two different flow rates

In general anesthesia with endotracheal intubation, a circle system with a heat and moisture exchanger (HME) and a low total flow is often used to prevent hypothermia and to maintain inspired gas humidity. The purpose of the present study was to compare the inspired gas humidity and body temperature, in general anesthesia with or without an HME at two different total flow rates. Eighty patients (American Society of Anesthesiologists [ASA] I or II) scheduled to undergo either orthopedic or head and neck surgery were studied. They were divided into four groups, of 20 patients each: total flow of 2 l·min⁻¹ with (group HME2L) or without (group 2L) HME, and a total flow of 4 l·min⁻¹ with (group HME4L) or without (group 4L) HME. The relative and absolute humidity and pharyngeal and inspired gas temperatures were measured for 2 h after endotracheal intubation. The relative humidity was not significantly different among groups 2L, HME2L, and HME4L. Group 4L had significantly lower absolute humidity than group 2L. The pharyngeal temperature did not decrease significantly for 2 h in any of the groups. During general anesthesia with a total flow of 2 l·min⁻¹ in 2 h, HME might not be necessary, while with a total flow of 4 l·min⁻¹, HME could be useful to maintain inspired gas humidity.     

Humidification during low-flow anesthesia in children

Purpose The aim of this study was to compare the effect of low-flow anesthesia with or without a heat and moisture exchanger with high-flow anesthesia on airway gas humidification in children. Methods One hundred twenty children were randomly assigned to one of three groups: low-flow anesthesia with 0.5l·min⁻¹ of total gas flow (LFA,n=40), low-flow anesthesia with 0.5l·min⁻¹ using a heat and moisture exchanger (HME,n=40), and high-flow anesthesia with 6l·min⁻¹ (HFA,n=40). The temperature and relative humidity of the inspired gas were measured throughout anesthesia. Results The relative humidity of the inspired gas in the HME group was increased compared with that of the LFA and HFA groups 20 min after induction (p<0.05). The airway humidification in the LFA group was higher than that in the HFA group 10 min after induction (p<0.05). The temperature of the inspired gas in the HME group was increased compared with that in the LFA and HFA groups after 70 min (P<0.05). Conclusion Low-flow anesthesia is less effective in providing adequate humidification of inspired gas than low-flow anesthesia with a heat and moisture exchanger, but significantly better than high-flow anesthesia in children.     

The effect of circuit compliance on delivered ventilation with use of an adult circle system for time cycled volume controlled ventilation using an infant lung model

This in vitro study examined the effect of circuit compliance on delivered ventilation (V_E) using a time-cycled, volume controlled circle system in an infant lung model. A Bio-Tek ventilator tester set to simulate normal and abnormal lung compliance measured V_E delivered by the Narkomed 2B system. Circle circuits of varied compliance (2.75, 1.22 and 0.73 μl·cm H₂O^?1) were tested. Tidal volume was adjusted to peak inflation pressures (PIP) of 20, 30, 40, and 50 cm H₂O with three circuits, two lung compliances, and four different size tracheal tubes (TT) (2.5, 3.5, 4, 4.5 mm ID). Data were analysed using the multiple regression technique. Delivered V_E was directly related to PIP and lung compliance. Delivered V_E was not affected by the choice of circuit. TT size had minimal effects on V_E when lung compliance was low; TT size was a more important factor when test lung compliance was normal. Extrapolating this data to the clinical setting, adequate ventilation of infants can be achieved with an adult circle system if an appropriate PIP is chosen, regardless of the compliance of the circuit used. Infants with poor lung compliance may require very high PIP for adequate ventilation.     

Single-lung ventilation with carbon dioxide hemipneumothorax: hemodynamic and respiratory effects in piglets

Objectives: Video‐assisted thoracoscopic surgery (VATS) has become a standard procedure in pediatric surgery. To facilitate surgical access, the dependent lung has to collapse using intrathoracic carbon dioxide insufflation and/or single‐lung ventilation. These procedures can induce hemodynamic deteriorations in adults. The potential impacts of single‐lung ventilation in combination with capnothorax on hemodynamics in infants have never been studied before. Aim: We conducted a randomized experimental study focusing on hemodynamic and respiratory changes during single‐lung ventilation with or without capnothorax in a pediatric animal model. Methods: Twelve piglets were randomly assigned to receive single‐lung ventilation with (SLV‐CO₂) or without (SLV) capnothorax with an insufflation pressure of 5 mmHg for a period of two hours. Before, during, and after single‐lung ventilation, hemodynamic and respiratory parameters were measured. Results: Although mean arterial pressure remained stable during the course of the study and no critical incidents were monitored, cardiac index (CI) decreased significantly with SLV‐CO₂ (baseline 3.6 ± 1.6 l·min^?1·m^?2 vs 2.9 ± 1.1 l·min^?1·m^?2 at 120 min, P < 0.05). Furthermore, global end‐diastolic volume and intrathoracic blood volume (ITBV) decreased as well significantly with SLV‐CO₂, causing a significant between‐group difference in ITBV (P < 0.05). Conclusions: Despite a decrease in CI and preload parameters, the combination of single‐lung ventilation and low‐pressure capnothorax was well tolerated in piglets and could justify further clinical studies to be performed in infants and children focusing on hemodynamic and respiratory changes during VATS.     

Effect of peak inspiratory flow on gas exchange, pulmonary mechanics, and lung histology in rabbits with injured lungs

Purpose The aim of this study was to evaluate, using a rabbit model, the little-known effect of different levels of peak inspiratory flow on acutely injured lungs. Methods Fourteen male rabbits (body weight, 2711 ± 146 g) were anesthetized and their lungs were injured by alveolar overstretch with mechanical ventilation until Pa_O2 was reduced below 300 mmHg. Injured animals were randomly assigned to: the P group—to receive pressure-regulated volume-control ventilation (PRVCV; n = 7); and the V group—to receive volume-control ventilation (VCV; n = 7). Other ventilator settings were: fraction of inspired oxygen (FI_O2), 1.0; tidal volume, 20 ml·kg⁻¹; positive end-expiratory pressure (PEEP) 5 cmH₂O; and respiratory rate, 20 min⁻¹. The animals were thus ventilated for 4 h. Throughout the protocol, ventilatory parameters and blood gas were measured every 30 min. After the protocol, the lung wet-to-dry ratio and histological lung injury score were evaluated in the excised lungs. Results Throughout the protocol, peak inspiratory flow and mean inspiratory flow values in the P group were significantly higher than those in the V group (26.7 ± 5.0 l·min⁻¹ vs 1.2 ± 0.2 l·min⁻¹, and 4.3 ± 0.3 l·min⁻¹ vs 1.1 ± 0.1 l·min⁻¹; P < 0.05). The wet-to-dry ratio in the P group was also significantly higher than that in the V group (7.7 ± 0.9 vs 6.3 ± 0.5; P < 0.05). More animals in the P group than in the V group had end-of-protocol Pa_O2/FI_O2 ratios below 200 mmHg (43% vs 0%; P = 0.06). Conclusion In rabbits with injured lungs, high peak inspiratory flow with high tidal volume (V_T) reduces the Pa_O2/FI_O2 ratio and increases the lung wet-to-dry ratio.     

Low and minimal flow inhalational anaesthesia

Purpose

To descnbe the pharmacokinetic behaviour and practical aspects of low (0.5–1l· min^?1) and minimal (0.25–0.5 l · min^?1) flow anaesthesia.

Methods

A Medline search located articles on low flow anaesthesia, and computer simulated anaesthetic uptake models are used.

Principal findings

Most, 85–90%, of anaesthetists use high fresh gas flow rates during inhalational anaesthesia. Low/minimal flow anaesthesia with a circle circuit may avoid the need for in-circuit humidifiers, raise the temperature of inspired gases by up to 6°C, reduce cost by about 25% by reduction of fresh gas flows to 1.51· mm^?1, and reduce environmental pollution with scavenged gas. Knowledge of volatile anaesthetic pharmacokinetic behaviour facilitates the use of minimal/low flow rates. Small amounts of nitrogen or minute amounts of methane, acetone, carbon monoxide, and inert gases in the circuit are of no concern, but the degradation of desflurane (to carbon monoxide by dry absorbent) and sevoflurane (to compound A by using a fresh gas flow of >2 l · min^?1) must be avoided. With modem gas monitoring technology, safety should be no more of a concern than with high flow techniques.

Conclusion

The use of fresh gas flow rates of < 1l · min^?1 for maintenance of anaesthesia has many advantages, and should be encouraged for inhalational anaesthesia with most modem volatile anaesthetics.     

Temporal variation of the leak pressure of uncuffed endotracheal tubes following pediatric intubation: an observational study

Purpose

Uncuffed endotracheal tubes are still preferred over cuffed tubes in certain situations in pediatric anesthesia. Inaccurately sized uncuffed endotracheal tubes may lead to inadequate ventilation or tracheal mucosal damage during anesthesia. Endotracheal tube size in children is usually assessed by measuring the audible leak pressure; if the fit of the tube and the leak pressure decrease significantly with time, reintubation during surgery as a result of inability to ventilate effectively may be challenging, and could lead to patient morbidity. There is no evidence to indicate whether leak pressure increases or decreases with time following endotracheal intubation with uncuffed tubes in children.

Methods

We measured leak pressure for 30 min following tracheal intubation in 46 ASA I children age 0–7 years after excluding factors known to modify leak pressure.

Results

The largest mean change in leak pressure occurred between time points 0 and 15 min, an increase of 3.5 cmH₂O. Endotracheal tube size and type of procedure were associated with the leak pressure. In the final linear mixed model, there were no statistically significant variations in leak pressure over time (P = 0.129) in this group of children.

Conclusions

We did not identify a consistent change in leak pressure within 30 min following tracheal intubation with uncuffed endotracheal tubes in this group of children.     

Lower cuff pressures improve the seal of pediatric laryngeal mask airways

Background: Hyperinflation of laryngeal mask airway (LMA) cuffs may be harmful because of the exertion of high pressures on pharyngeal and laryngeal structures. Although cuff manometers may be used to monitor cuff pressure, their use is not routine in many institutions and clinical endpoints are used instead. Furthermore, it is common clinical practice to add air to the cuff in the presence of an air leak to obtain a better seal. Methods: In a prospective audit, the authors assessed air leakage around pediatric sized LMAs (n = 200) following inflation guided by common clinical endpoints (slight outward movement of the LMA) and then following adjustment of the cuff pressure to the recommended pressure range (<60 cmH₂O) according to institutional guidelines with the use of a calibrated cuff manometer, directly after induction of anesthesia. Following induction, all children were gently ventilated with pressure control ventilation with 10 cmH₂O and a positive end‐expiratory pressure of 5 cmH₂O. Results: Following inflation of the cuff guided by clinical endpoints, the median initial cuff pressure (LMA size 1–3) was 92 (size 3) to >120 cmH₂O (size 1) and the median leakage around the cuff ranged from 0.66 to 1.07 ml·kg^?1. Following cuff pressure adjustment according to the recommended pressure range (<60 cmH₂O), the leakage decreased significantly to 0.51–0.79 ml·kg^?1 (P = 0.002 for size 1, P < 0.001 for size 1.5–3). Conclusion: The use of clinical endpoints to inflate LMA cuffs is not only associated with significant hyperinflation in the majority of patients but also with an increased leakage around the LMA cuff when compared with adjusted LMA cuff pressures. Therefore, cuff manometers should routinely be used not only to avoid unnecessary hyperinflation but also to improve cuff sealing of LMA in children.     

Comparison of Cuffed and Uncuffed Endotracheal Tubes in Young Children during General Anesthesia

Background: Uncuffed endotracheal tubes are routinely used in young children. This study tests a formula for selecting appropriately sized cuffed endotracheal tubes and compares the use of cuffed versus uncuffed endotracheal tubes for patients whose lungs are mechanically ventilated during anesthesia.

Methods: Full-term newborns and children (n = 488) through 8 yr of age who required general anesthesia and tracheal intubation were assigned randomly to receive either a cuffed tube sized by a new formula [size(mm internal diameter) = (age/4) + 3], or an uncuffed tube sized by the modified Cole's formula [size(mm internal diameter) = (age/4) + 4]. The number of intubations required to achieve an appropriately sized tube, the need to use more than 21 [center dot] min sup -1 fresh gas flow, the concentration of nitrous oxide in the operating room, and the incidence of croup were compared.

Results: Cuffed tubes selected by our formula were appropriate for 99% of patients. Uncuffed tubes selected by Cole's formula were appropriate for 77% of patients (P < 0.001). The lungs of patients with cuffed tubes were adequately ventilated with 2 1 [center dot] min sup -1 fresh gas flow, whereas 11% of those with uncuffed tubes needed greater fresh gas flow (P < 0.001). Ambient nitrous oxide concentration exceeded 25 parts per million in 37% of cases with uncuffed tubes and in 0% of cases with cuffed tubes (P < 0.001). Three patients in each group were treated for croup symptoms (1.2% cuffed; 1.3% uncuffed).     

Initial experience of complete switchover to sevoflurane in 1550 children*

A report of our experience with a complete switchover from halothane (HAL) to sevoflurane (SF) in 1550 paediatric cases over a period of 17 months is presented. SF became the sole inhalational anaesthetic in our institution in July 1990. Induction of anaesthesia with SF was performed with the overpressure technique by administering rapid increases of concentration and assisted pulmonary ventilation with a large fresh gas flow (6 l·min^?1 of nitrous oxide and 3 l·min^?1 of oxygen). SF concentration was increased rapidly up to 5 or 7% in increments of 2% in every 2–3 breaths. Induction time as measured in 60 cases (3–6 years) was 50 ± 5 (mean ± SD) sec for loss of eyelash reflex and 119 ± 10 (mean ± SD) sec for loss of movement to venepuncture at 7% SF concentration. No serious complications were observed. Peak serum levels of inorganic fluoride were within a safe range (less than 30 μmol·l^?1) in all 7 cases in which this was studied. The results suggest that SF is a useful anaesthetic agent in paediatric anaesthesia, particularly because of its smooth and rapid inhalation induction.     

Hemodynamic effects of dobutamine and dopexamine after cardiopulmonary bypass in pediatric cardiac surgery*

Background: After surgical repair of congenital heart disease, inotropic support is sometimes necessary to wean from cardiopulmonary bypass. In pediatric cardiac surgery, dobutamine and dopamine are often used as inotropic support. Dopexamine is a synthetic catecholamine, which has positive inotropic and vasodilating properties. Because the hemodynamic effects of catecholamines are modified after cardiopulmonary bypass, the aim of this study was to investigate the effects of dobutamine and dopexamine on cardiac index and systemic vascular resistance index after cardiopulmonary bypass in pediatric cardiac surgery. Methods: The study was performed in a prospective, randomized, and double‐blinded cross‐over design. The investigation included 11 children for elective, noncomplex congenital heart surgery. After weaning from cardiopulmonary bypass and a 20‐min period of steady state, children received either 2.5 μg·kg^?1·min^?1 dobutamine or 1 μg·kg^?1·min^?1 dopexamine for 20 min. Cardiac index (transpulmonary thermodilution), mean arterial pressure, central venous pressure, stroke volume, systemic vascular resistance, and central venous oxygen saturation were determined. The primary outcome variable was cardiac index. Results: No difference in cardiac index was observed between the two groups (P = 0.594). Both drugs increased cardiac index, dopexamine from 3.9 ± 0.6 to 4.7 ± 0.8 l·min^?1·m^?2 (P = 0.003) and dobutamine from 4.1 ± 0.7 to 4.8 ± 0.7 l·min^?1·m^?2 (P = 0.004). During treatment with dobutamine, children presented with significantly higher mean arterial pressure (P = 0.003) and systemic vascular resistance index (P = 0.026). Conclusions: This trial demonstrates that low‐dose dobutamine and dopexamine both increase cardiac index during pediatric cardiac surgery but with different hemodynamic effects.     

Intra- and inter-observer reliability using a noninvasive ultrasound cardiac output monitor in healthy anesthetized children

Background: Accurate and reliable evaluation of cardiac index (CI) in critically ill pediatric patients can optimize their management. Although validated, noninvasive ultrasound measurement techniques have been previously shown to be unreliable because of observer variability. Objective: To confirm intra‐ and inter‐observer reliability when using the noninvasive USCOM^® in healthy anesthetized children. Methods: Prospective observational study at the Children’s Hospital of Eastern Ontario, Ottawa, included newborns to 12 years of age undergoing elective surgery or magnetic resonance imaging. The USCOM^® was used to assess CI via aortic flow with a trans‐sternal approach. Two trained observers were responsible for taking two measurements of CI each at steady state in randomized succession after stable depth of anesthesia was achieved. Results: Fifty‐nine patients were included. Forty‐seven (80%) were between 3 and 7 years old, with 57% male. The mean difference ± sd for repeat CI measurements by each of two observers was 0.11 ± 0.47 and 0.05 ± 0.65 l·min^?1·m^?2, respectively. Intra‐observer reliability for these repeat measurements by each observer determined by Lin’s concordance correlation coefficient was 0.92 and 0.85, respectively. The mean difference ± sd between observers was 0.16 ± 0.59 l·min^?1·m^?2, and Lin’s concordance correlation coefficient was 0.87. The two observers subjectively rated measurements as ‘Difficult’ or ‘Very difficult’ only 14% (16/118) and 3% (4/118) of the time, respectively. No adverse events were reported. Conclusion: This study confirms that the USCOM^® is relatively easy to use and reliable in healthy children when operated by trained users.