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* From the Department of Anesthesiology, National Cancer Center, Koyang, Kyunggi-Do, Korea and the
Department of Anesthesiology and Clincal Research Institute, Seoul National University Hospital, Seoul, Korea.
Address correspondence to: Dr. Jae-Hyon Bahk, Department of Anesthesiology, Seoul National University College of Medicine, #28 Yongon-Dong, Chongno-Gu, Seoul 110-744, Korea. Phone: 82-2-760-2818; Fax: 82-2-747-5639; E-mail: bahkjh{at}plaza.snu.ac.kr
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Abstract |
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Methods: Pediatric patients (n=158), < 30 kg, ASA 1 or 2 were studied. After paralysis, an LMA of the recommended size was inserted and connected to a volume ventilator. Fibreoptic bronchoscopy (FOB) was performed and graded: 1, larynx only seen; 2, larynx and epiglottis posterior surface seen; 3, larynx, and epiglottis tip or anterior surface seen—visual obstruction of epiglottis to larynx: < 50%; 4, epiglottis down-folded, and its anterior surface seen—visual obstruction of epiglottis to larynx: > 50%; 5, epiglottis down-folded and larynx not seen directly. Inspiratory and expiratory tidal volumes (VT), and airway pressure were measured by a pneumo-tachometer, and the fraction of leakage (FL) was calculated. In 79 cases, LMA was used for airway maintenance throughout surgery.
Results: Successful LMA placement was achieved in 98% of cases: three failures were due to gastric insufflation. For LMA # 1, 1.5, 2, and 2.5, FOB grades [median (range)] were 3(1-5), 3(1-5), 1(1-5) and 1(1-3) respectively. In smaller LMAs, the cuff more frequently enclosed the epiglottis (P < .001). FL of LMA # 1 was higher than those of LMA # 1.5 and LMA # 2.5 (P < .05), and FL of LMA # 2 was higher than that of LMA # 2.5 (P < .05). In the 79 patients, the number of patients experiencing complications decreased as LMA size increased (P < .05).
Conclusion: Use of the LMA in smaller children results in more airway obstruction, higher ventilatory pressures, larger inspiratory leak, and more complications than in older children.
ALTHOUGH the laryngeal mask airway (LMA) has been recommended in situations, where positive pressure ventilation (PPV) is necessary, there are few investigations of its utility in this situation.1–8 We were unable to find any studies about LMA insertion, its positioning, and/or its effect on controlled ventilation in paralyzed pediatric patients. No LMA study has been performed with the recommended sizes in large numbers of infants and young children.
Several LMA studies of infants have been reported.7–12 In some,7,9,10 only a few infants weighing > 5 kg were included. Size # 1 LMA (LMA 1) was used for 33 infants, but the mean weight was 5.6 kg.11 In a study of 50 infants, whose weight range was 3.8-10.0 kg, only the LMA 1 was used.12 These previous studies were performed in spontaneously breathing patients. Since size # 1.5 LMA (LMA 1.5), the recommended body weight of which is 5 - 10 kg, became available recently, a study of LMA 1, 1.5 or size # 2 LMA (LMA 2) was warranted.
There were three objectives for this study: first, to assess the position of the LMA when it is inserted in paralyzed pediatric patients; second, to evaluate the competence of PPV when the LMA is used to maintain airway patency in paralyzed pediatric patients; third, to compare the efficacy of the various LMA sizes using the above measures.
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Materials and methods |
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An LMA 1 was used for infants < 5 kg; an LMA 1.5 for 5 - 10 kg; an LMA 2 for 10 - 20 kg; and a size # 2.5 LMA (LMA 2.5) for 20 - 30 kg. An experienced investigator inserted all the LMAs following the manufacturer's recommendations.13 The leak pressure was measured by auscultation after the cuff was inflated with air to 80% of the maximum recommended inflation volume, and again after injecting an additional 10%. If there was a decrease in leak pressure after injecting an additional 10%, 80% of the maximum inflation volume was used unless, another 10% more would achieve 100% of the maximum volume. If leak pressure at 100% was lower than that at 90%, 90% was selected. Otherwise, 100% of the maximum recommended inflation volume was used. Namely, the inflation volume at a higher leak pressure was selected. All parameters including tidal volume (VT) and peak inspiratory pressure (PIP) were measured after the end-tidal CO2 partial pressure (PETCO2) was stable. The LMA was connected to a volume ventilator (Dameca A/S, Copenhagen, Denmark) incorporated into the anesthesia machine, and PPV with inspiratory to expiratory ratio of 1:2 was instituted. The VT was set at about 10 ml•kg–1 and, depending on age, a respiratory rate of 20-40 •min–1 was chosen to maintain the PETCO2 at 30 - 35 mmHg. On a randomized basis, using odd or even hospital numbers, patients were assigned to LMA use throughout surgery or to endotracheal intubation. For infants < 10 kg, the LMA was connected to the ventilator via an infant circle system (Aika Medical Corp., Tokyo, Japan). A CP-100 neonatal pulmonary monitor (Bicore Monitoring Systems, Irvine, California, USA) with a disposable VarFlex® flow transducer was used to measure inspiratory and expiratory VT. For children > 10 kg, a CP-100 adult pulmonary monitor (Bicore Monitoring Systems, Irvine, Calif.) was used. The CP-100 pulmonary monitor is a pneumo-tachometer, the flow transducer of which is inserted between the patient's LMA adapter and Y-connector. Measurements were taken over 10 breaths. The PIP was recorded from the pulmonary monitor reading. The fraction of leakage (FL) (%) was defined as:
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The position and effectiveness of the LMA were assessed using the folllowing techniques and, once the position was clinically acceptable, no further adjustment to the LMA position was made. First, manual ventilation was possible with regular ETCO2 display without gastric distention; second, bilateral breath sounds as heard by auscultation over axillae. If not acceptable, the LMA was removed and re-inserted. It was regarded as a failure if the positioning of LMA was not clinically acceptable after three attempts. The larynx was inspected through the self-sealing diaphragm of an elbow connector, using a fibreoptic bronchoscope (FOB; Olympus LF-P, Olympus Optical Co., Tokyo, Japan) located just proximal to the aperture bars, while an assistant prevented the LMA from moving. The FOB findings were defined as Grade 1, larynx only seen; Grade 2, larynx and epiglottis posterior surface seen; Grade 3, larynx, and epiglottis tip or anterior surface seen—visual obstruction of epiglottis to larynx: < 50%; Grade 4, epiglottis down-folded, and its anterior surface seen—visual obstruction of epiglottis to larynx: > 50%; Grade 5, epiglottis down-folded and larynx cannot be seen directly.
By placing a stethoscope on the stomach, gastro-esophageal insufflation at 30 cmH2O airway pressure was qualitatively assessed by an independent observer. The observer measured the leak pressure by using a stethoscope placed on the neck, while the lungs were manually inflated at 5 cmH2O intervals until an air leak was audible.
If PETCO2 increased, but was still < 45 mmHg, head flexion,14 head extension or mandibular elevation was tried. If all procedures failed, the cuff volume was changed. When PETCO2 increased to > 45 mmHg, the LMA was removed and changed to an endotracheal tube. At the end of surgery, FOB was performed to recheck the position of the LMA.
Statistical analysis
The PIPs were compared with Kruskal-Wallis test. Analysis of variance (ANOVA) with Duncan's test for multiple comparisons was used to compare the FL of each LMA size. FOB findings of each LMA size were compared with ridit test. The duration of PPV was compared with ANOVA. While maintaining PPV through LMA, the number of patients with problems among the groups of each LMA size was compared using Fisher's exact test. A P-value < .05 was considered significant.
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Results |
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The PIP varied with the LMA size (P < .001) (Table I
): PIP of smaller LMAs was higher than that of larger LMAs. The FL of LMA #1, 1.5, 2, and 2.5 (mean ± SD) was respectively 12.0 ± 3.4, 7.8 ± 3.6, 11.4 ± 7.6, and 7.2 ± 2.4; FL of LMA 1 was higher than those of LMA 1.5 and LMA 2.5 (P < .05), and FL of LMA 2 was higher than that of LMA 2.5 (P < .05) (Table I). In smaller LMAs, the cuff more frequently enclosed the epiglottis than in larger LMAs (P < .001) (Table II).
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); the FOB grade was 3 in six patients, 4 in two and 5 in one. Their FOB findings at the end of surgery did not change when compared with the initial findings. When we attempted to solve the problem, the mandibular elevation worked well in two of the nine only while elevating the mandible with both hands. Because of high PETCO2, the LMA was removed in two of the nine (LMA 1.5 and 2 each). One of the nine vomited during emergence, while the LMA was still in place (Table III). There was no evidence of aspiration. The other LMAs were removed after reflexes had returned. There was no case of hypoxia, SpO2 < 95%. The number of patients experiencing complications decreased as LMA size increased (P < .05) (Table III).
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Discussion |
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TOPAbstractMaterials and methodsResultsDiscussionReferences |
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Because of individual variation in the size of the larynx, the LMA sometimes encloses the epiglottis, even when the tip of its cuff correctly occupies the hypopharynx.15 In the majority of correctly placed LMAs in children, the epiglottis lies within the confines of the mask.9,11,12 However, optimal position of the LMA (FOB grade 1) was achieved in a comparatively large proportion of infants (29%11 or 44%12), where smaller-size LMAs than recommended were used. In our study, the FOB grade was higher in neonates and infants, so that a satisfactory position was more difficult to achieve in those age groups as suggested by Wilson.16 In children who weighed > 10 kg, the FOB finding was improved. This was comparable to our clinical impression that LMA > 2 is easier to use than smaller LMAs. This may be partly because the LMA was designed after cadaveric examination of the adult larynx, and the small LMA is a scaled-down version of the adult LMA.17 Although the anatomy regarding the LMA is reported to be comparable in infants,18 the anatomy of the larynx of infants differs from that of children. Thus, it might be more difficult to achieve a good position with an infantile size LMA than with a pediatric size.
Even though the airway diameter of the LMA is larger than that of a comparable endotracheal tube and the LMA does not occupy the narrowest portion of the upper airway (the cricoid cartilage), PIP through the small LMA was not particularly low. Incorporation of the epiglottis into the LMA cuff and its deflection (higher FOB grades) caused higher PIP especially in the smaller LMA. By comparing PIP and leak pressure, we know that PIP of the smaller LMAs was sometimes higher than the leak pressure. Because the leak through the LMA may increase at airway pressure > 25 cmH2O,19 ventilation may be lost during inspiration.
In nine of 79 patients whose airways were maintained with a LMA throughout the surgery, the PETCO2 slowly increased. Although this sign occurs late, we could find no other earlier and reliable sign during the surgery. If surgery had continued longer, we may have had to abandon the LMA in more cases. Even if we could not hear an air leak with a stethoscope on the stomach, at the end of operation the abdomen appeared inflated or tympanic on percussion, so subclinical gastric insufflation might be a cause of the increased PETCO2.
Compared with other reports without paralysis,8,10 some problems related to insertion such as airway obstruction, coughing, laryngospasm, and difficulty with placement 8,10 were bypassed. Even though the complications during insertion were excluded, our overall complication rate was higher than in previous studies.8,10 Since this study group consisted of small children, the complication rate was high as was suggested by another study.8 Insertion of an LMA in paralyzed patients may affect the LMA position that cannot be detected by FOB. Thus it may have a higher complication rate than when paralyzed after LMA insertion.8 Slowly increasing PETCO2 might be a particular complication of LMA insertion and maintaining PPV in paralyzed pediatric patients.
The pharyngeal, laryngeal and genioglossus muscles are relaxed under general anesthesia,20 and upper airway anatomy therefore changes when muscle relaxation is achieved. However, there has been no well-controlled study of LMA position in pediatric patients without paralysis. Furthermore, large variations in LMA position have been reported even in adults. Latorre and colleagues6 stated that the ideal position (FOB grade 1) was achieved in 70% of cases, but Fullekrug and colleagues5 reported that this figure was only 13%. Thus it is difficult to say that, from the results of this study, whether muscle relaxation has some definite effect on LMA position.
From our clinical impression, higher PIP and more frequent occurrence of PETCO2 increase with small LMAs, we think that the larger the LMA, the less the leakage was around the LMA. However, in our study, the FL of LMA 2 was not different from that of LMA 1 or 1.5. In patients weighing < 10 kg, we used the infantile breathing circuit and ventilator bellows, and neonatal pulmonary monitor, which has a lower dead space volume. As stated earlier, more ventilation was lost during inspiration through small LMAs. For the small LMAs such as # 1 and # 1.5, FL was calculated to be relatively lower than it should be.
Because of the common occurrence of partial airway obstruction by the epiglottis while using the LMA in young children, the risk/benefit ratio should be carefully evaluated before using an LMA with paralysis and PPV in this age group.
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Footnotes |
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Accepted for publication December 20, 2000.
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References |
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2 Devitt JH, Wenstone R, Noel AG, O'Donnell MP. The laryngeal mask airway and positive-pressure ventilation. Anesthesiology 1994; 80: 550–5.[Medline]
3 Dich-Nielsen JO, Nagel P. Flexible fibreoptic bronchoscopy via the laryngeal mask. Acta Anaesthesiol Scand 1993; 37: 17–9.[Medline]
4 Graziotti PJ. Intermittent positive pressure ventilation through a laryngeal mask airway. Is a nasogastric tube useful? Anaesthesia 1992; 47: 1088–9.[Medline]
5 Füllekrug B, Pothmann W, Werner C, Schulte am Esch J. The laryngeal mask airway: anesthetic gas leakage and fiberoptic control of positioning. J Clin Anesth 1993; 5: 357–63.[Medline]
6 Latorre F, Eberle B, Weiler N, et al. Laryngeal mask airway position and the risk of gastric insufflation. Anesth Analg 1998; 86: 867–71.[Abstract]
7 Epstein RH, Ferouz F, Jenkins MA. Airway sealing pressures of the laryngeal mask airway in pediatric patients. J Clin Anesth 1996; 8: 93–8.[Medline]
8 Lopez-Gil M, Brimacombe J, Alvarez M. Safety and efficacy of the laryngeal mask airway. A prospective survey of 1400 children. Anaesthesia 1996; 51: 969–72.[Medline]
9 Rowbottom SJ, Simpson DL, Grubb D. The laryngeal mask in children. A fibreoptic assessment of positioning. Anaesthesia 1991; 46: 489–91.[Medline]
10 Mason DG, Bingham RM. The laryngeal mask airway in children. Anaesthesia 1990; 45: 760–3.[Medline]
11
Dubreuil M, Laffon M, Plaud B, Penon C, Ecoffey C. Complications and fiberoptic assessment of size 1 laryngeal mask airway. Anesth Analg 1993; 76: 527–9.
12 Mizushima A, Wardall GJ, Simpson DL. The laryngeal mask airway in infants. Anaesthesia 1992; 47: 849–51.[Medline]
13 Brain AIJ. The Intravent Laryngeal Mask Instruction Manual, 2nd ed. Henley-on-Thames, England: Intravent International, 1993.
14
Isserles SA, Rozenberg B. LMA - reduction of gas leak (Letter). Can J Anaesth 1995; 42: 449.
15
Asai T. Difficulty in assessing the correct position of the laryngeal mask airway (Letter). Br J Anaesth 1994; 72: 366.
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Wilson IG. The laryngeal mask airway in paediatric practice (Editorial). Br J Anaesth 1993; 70: 124–5.
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Brain AIJ. The laryngeal mask - a new concept in airway management. Br J Anaesth 1983; 55: 801–5.
18 Brain AIJ. The development of the laryngeal mask—a brief history of the invention, early clinical studies and experimental work from which the laryngeal mask evolved. Eur J Anaesthesiol 1991; 4(Suppl): 5–17.
19
Ho-Tai LM, Devitt JH, Noel AG, O'Donnell MP. Gas leak and gastric insufflation during controlled ventilation: face mask versus laryngeal mask airway. Can J Anaesth 1998; 45: 206–11.
20 Ochiai R, Guthrie RD, Motoyama EK. Effect of varying concentrations of halothane on the activity of the genioglossus, intercostals, and diaphragm in cats: an electromyographic study. Anesthesiology 1989; 70: 812–6.[Medline]
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