Department of Anaesthesia and Intensive Care Therapy, Philipps University Marburg, 35033 Marburg, Germany
* Corresponding author. E-mail: kaigoldmann1{at}aol.com
Accepted for publication August 15, 2005.
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Abstract |
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Methods. Twenty anaesthetized, non-paralysed children aged 55 (range 2789) months, weighing 18 (SD 3) kg, were randomly allocated into two groups. Anaesthesia management and positive pressure ventilation were standardized. Size 2 and 2 PLMA were used. Artificial ventilation in Group I was with pressure controlled ventilation (PCV) and PEEP=5 cm H2O, in Group II with PCV without PEEP. A
was used for 20 min during induction of anaesthesia. Sixty minutes after induction of anaesthesia an arterial blood gas sample was taken under a
.
Results. Groups were comparable with respect to demographic data. in Group I [22.1 (1.6) kPa] was significantly (P=0.001) higher than in Group II [19.2 (1.7) kPa].
Conclusions. The PLMA can be used for PCV with PEEP in paediatric patients. Application of PEEP improves gas exchange.
Keywords: anaesthesia, paediatric ; equipment, laryngeal mask airway ; ventilation, mechanical ; ventilation, positive end-expiratory pressure
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Introduction |
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In the very young patient, closing volume tends to increase and functional residual capacity to decrease during general anaesthesia, resulting in atelectasis and subsequent decreased arterial oxygenation.6 8 Application of adequate tidal volumes and positive end-expiratory pressure (PEEP) play an important role in counteracting airway closure and atelectasis in adult9 and paediatric7 patients under general anaesthesia when the tracheal tube is used.
Because of its low-airway leak pressure (Pleak), application of large tidal volumes or PEEP may be impossible or result in gastric insufflation when the CLMA is used for positive pressure ventilation. As a consequence, the CLMA is usually used without PEEP and it has been recommended to limit tidal volumes to 68 ml kg1 using low inspiratory flow rates.10 The size 2 and 2 ProSealTM LMA (PLMA) (LMA North America, Inc., San Diego, CA) has been shown to form a more effective seal and to allow for a greater tidal volume than the CLMA in paediatric patients.11 12 This randomized study was designed to test the hypothesis that in anaesthetized paediatric patients the PLMA can be used effectively to apply PEEP during pressure-controlled ventilation (PCV) and that this leads to an improved arterial oxygenation.
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Methods |
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A standard anaesthesia protocol was followed. All patients were premedicated orally with midazolam 0.40.5 mg kg1 and EMLATM cream (Astra-Zeneca, Wilmington, DE) was applied to the back of both hands 30 min before induction of anaesthesia. Standard monitoring consisted of a precordial stethoscope, a rectal temperature probe, an automated arterial pressure monitor, ECG, pulse oximetry, and capnography. In all patients general anaesthesia was induced intravenously with alfentanil 0.02 mg kg1 followed by propofol 35 mg kg1. Anaesthesia maintenance was with propofol 0.10.15 mg kg1 min1 and remifentanil 0.20.3 µg kg1 min1. After cessation of spontaneous ventilation the lungs of the patients were ventilated manually via a facemask until a sufficient depth of anaesthesia was reached. The PLMA (a size 2 for children <20 kg, a size 2 for children >20 kg body weight) was then placed using the standard technique recommended by Brain.13 Manual ventilation was commenced after the breathing tube had been connected to the anaesthesia machine (Primus®, Draeger, Luebeck, Germany). Auscultation of the epigastrium and larynx took place before the device was taped.13 Thereafter a drain tube (DT) test (DT-test), as described in the PLMA instruction manual, was conducted in order to confirm correct position of the distal end of the DT at the proximal end of the oesophagus.14 The head of the child was then placed in a neutral position on a soft 3-cm high head-ring and the Pleak in the neutral head position was determined at an intra-cuff pressure (Pintracuff)=60 cm H2O (VBM Cuff Pressure Gauge, VBM Medizintechnik, Sulz a.N., Germany), as described previously.15 During Pleak measurement, auscultation of the epigastrium was performed again to detect any air entry into the stomach. Fibre-optic examination of the position of the LMA was performed thereafter (2.8 mm flexible endoscope, Karl Storz, Tuttlingen, Germany). The position of the LMA was graded in accordance with the fibre-optic scoring system described previously.16 Thereafter, a 12 French gauge gastric tube was placed through the DT. Gastric fluid was aspirated using a syringe and the amount of fluid noted. Once the Pleak measurement and the fibre-optic examination had been completed PCV was used to ventilate the lungs throughout the procedure. PEEP was set either to 0 or 5 cm H2O according to the group the patient had been randomized to. Randomization to two groups of equal size (n=10) had happened before commencement of the trial using the StatView (SAS Institute, Cary, NC, USA) computer program: Group I was PCV with PEEP=5 cm H2O and Group II PCV without PEEP. The information of the allocated group was contained in sealed envelopesnumbered from 1 to 20that were opened before induction of anaesthesia by a study nurse not participating in the investigation.
PCV was commenced in the anaesthesia induction room immediately after fibre-optic inspection of the PLMA. Apart from the PEEP level, all other respirator settings were identical for both groups. Peak inspiratory airway pressure (PIP) was set to deliver a tidal volume of 810 ml kg1 and kept unchanged throughout the entire anaesthetic. The ventilatory frequency was adjusted to achieve an end-tidal carbon dioxide (E'CO2) of 5.1 (0.3) kPa. Peak inspiratory flow rate was set to 50 litre min1, fresh gas flow was set to 2 litre min1, and inspiratory:expiratory (I:E) ratio was set to 1:1. The fraction of inspired oxygen () was keep for a duration of 20 min at
. The child was then transferred into the operation room and the
reduced to
. After 60 min total anaesthesia time an arterial blood gas sample was obtained from the radial artery by a single sterile puncture and an arterial blood gas (ABG) measurement took place immediately (Radiometer ABL-System 625, Radiometer, Copenhagen, Denmark). The actual respiratory settings at the point of time of blood gas measurement were recorded. At the end of surgery anaesthesia was discontinued and the PLMA removed once the child was fully awake. Any adverse event, apparent oropharyngeal injury or problem with the devices was documented. A postoperative visit took place 68 h later.
Statistics
The primary variable tested was .
values for healthy anaesthetized paediatric patients under PCV and a
using the LMA have not been reported previously. Normal
values for healthy adolescents breathing room air are reported to be 12.7 (0.7) kPa.17 18 Based on the findings of Serafini and colleagues7 and pulmonary CT-scans of former paediatric patients of ours showing that atelectasis was present in most of the dependent lung regions shortly after induction of anaesthesia when a tracheal tube and no PEEP was used we hypothesized that atelectasis could possibly account for up to 15% of the lung tissue. We speculated that, as a consequence, there should be a difference in the
of a similar magnitude with and without PEEP. A 10% higher
for PCV with PEEP=5 cm H2O was considered to be clinically relevant, therefore a sample size of 12 patients was calculated to detect a projected difference of 10% between the groups with respect to
for a type I error of 0.025 (one-tailed testing) and a power of 0.9. Allowing for possible dropouts due to the inability to place the PLMA within two attempts or the inability to collect an arterial blood gas sample with a single puncture we chose to examine 20 patients. Results were analysed using the SPSS (SPSS Inc., Chicago, IL, USA) computer program. Unless otherwise stated data are expressed as mean values (SD) (95% CI) or mean values (range). The distribution of data was determined using KolmogorovSmirnov analysis. Statistical analysis was performed using t-test (one-tailed). Results were considered statistically significant for a P-value <0.025.
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Results |
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Discussion |
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As the under
was supranormal in both groups some clinicians would not consider the increased
in the PEEP group to be clinically relevant in healthy children. However, the technique of combining the PLMA with PCV and PEEP to improve gas exchange might be beneficial in children with lung disease; furthermore, as use of the PLMA is less likely to provide inadequate seal pressures this reduces the likelihood that it might need to be exchanged for a tracheal tube in children in whom positive pressure ventilation with PEEP is required to improve oxygenation. Therefore, the PLMA may be a better choice than the CLMA in paediatric patients with low lung compliance or a high airway resistance requiring high PIP, for instance, patients with bronchopulmonary dysplasia or reactive airway disease. It has been shown that supraglottic airway devices can be less irritating to the upper and lower airway than the tracheal tube so that particularly these patients can benefit from avoidance of tracheal intubation.19
So far, in most paediatric studies with the LMA a spontaneous mode of ventilation was used. Spontaneous ventilation under general anaesthesia can be associated with reduced functional residual capacity, hypoxia and hypercarbia.20 In the most recent study21 von Goedecke and colleagues were able to show that pressure support ventilation improved gas exchange compared with continuous positive airway pressure ventilation using the PLMA, but hypercarbia was present in both groups indicated by raised values of 6.1 (0.8) kPa and 6.9 (0.9) mmHg, respectively. In our study normal ventilation was possible in all children. In patients at risk, use of the PLMA with PCV should permit ventilation to a normal
. Application of PEEP could be used to potentially improve oxygenation in these patients, too.
Our results are in contrast to a study in adult patients suggesting that the use of a supraglottic airway device might not induce the same pulmonary responses, such as reflex bronchoconstriction, that can worsen gas exchange when the tracheal tube is used.22 We found that without use of a counter measure like application of PEEP arterial oxgenation was reduced. This suggests that in paediatric patients either similar pulmonary responses as with the use of the tracheal tube are activated or physiologic airway closure leads to an impairment of gas exchange during use of a supraglottic airway device and a controlled mode of ventilation without PEEP. This demonstrates, as for other areas of paediatric research, that the results of studies on the use of supraglottic airway devices in adults cannot automatically be translated into a paediatric population.
In conclusion, we found that PCV without PEEP leads to a decreased oxygenation compared with PCV with PEEP when a supraglottic airway device is used in paediatric patients. The PLMA can be used to apply PEEP=5 cm H2O during PCV and thereby improve gas exchange in healthy paediatric patients. Further studies are required to assess the value of our findings in paediatric patients with pulmonary disease.
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Acknowledgments |
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Footnotes |
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References |
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