Gastric insufflation pressure, air leakage and respiratory mechanics in the use of the laryngeal mask airway (LMA) in children

BACKGROUND: The objective of the present study was to evaluate the prelaryngeal position of the laryngeal mask airway (LMA(TM)) in children, and to determine the influence of mask positioning on gastric insufflation and oropharyngeal air leakage. METHODS: A total of 100 children, 3-11 years old, scheduled for surgical procedures in the supine position under general anaesthesia were studied. After clinically satisfactory LMA placement, tidal volumes were increased stepwise until air entered the stomach, airway pressure exceeded 30 cmH(2)O, or air leakage from the mask seal prevented further increases in tidal volume. LMA position in relation to the laryngeal entrance was verified using a flexible bronchoscope. RESULTS: The insertion of the LMA with a clinically satisfactory position was achieved in all patients at the first attempt. Gastric air insufflation occurred in five of 49 patients with malpositioned LMA. No incident of gastric air insufflation was observed in 51 patients with correctly positioned LMA. The minimum inspiratory pressure leading to mask leakage was 17 cmH(2)O for incorrectly positioned LMA, and 25 cmH(2)O for correctly positioned LMA. Clinically unrecognized LMA malposition was associated with a significantly increased incidence of either oropharyngeal leakage (r = 0.59; P = 0.0001) or gastric insufflation (r = 0.25; P = 0.01). CONCLUSIONS: Clinically undetected LMA malpositioning is a significant risk factor for gastric air insufflation in children between 3 and 11 years, undergoing positive pressure ventilation, especially at inspiratory airway pressures above 17 cmH(2)O.     

Pressure versus volume-controlled ventilation with a laryngeal mask airway™ in paediatric patients

BACKGROUND: The utility of positive pressure ventilation with the laryngeal mask airway (LMA) in children was described previously, but the possibility of gastric insufflation, related to high peak airway pressure, continues to be a disadvantage. In this prospective study, inspiratory pressures, air leak and signs of gastric insufflation were compared between volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) using an LMA. METHODS: Thirty-two ASA I patients, aged 4.5 +/- 4 years, who were scheduled for elective procedures under combined general anaesthesia and caudal analgesia, were enrolled. After inhalation induction and LMA insertion, each patient was randomly assigned to receive successively PCV and VCV. Peak pressures (PCV) and tidal volumes (VCV) were changed in order to achieve adequate ventilation [endtidal CO2 5-5.4 kPa (38-42 mmHg)]. RESULTS: Peak airway pressures were significantly lower with PCV than VCV (14.1 +/- 1.6 cmH2O versus 16.7 +/- 2.3 cmH2O, P < 0.001). No patient ventilated with PCV required peak pressure higher than 20 cmH2O compared with six patients ventilated with VCV (P < 0.05). Haemodynamic parameters, expiratory tidal volume and percent of leak were similar in both ventilatory modes and no signs of gastric insufflation were detected. CONCLUSIONS: During general anaesthesia in children using an LMA, PCV offers lower peak inspiratory airway pressures while maintaining equal ventilation compared with VCV. Although no signs of gastric insufflation were detected in both groups, the lower pressures might be significant in patients with reduced chest wall or lung compliance.     

Differential lung ventilation in an infant using LMA and a long tracheal tube

This is a case report of differential lung ventilation in an infant using a conventional laryngeal mask airway (LMATM) and a commercially available longer paediatric tracheal tube. This 2-month-old infant had her left-sided congenital diaphragmatic hernia repaired on the sixth day of her life, and had been mechanically ventilated. The right middle lobe became grossly emphysematous and herniated into the left side of the chest, and the right lower lobe became totally atelectatic. A right middle lobe lobectomy was planned. To avoid hyperinflating the right middle lobe, and to expand the right lower lobe without providing a high airway pressure on the left lung, the dependent lung (i.e. left lung) was ventilated with an LMA, and the right lower lobe was expanded with a long tracheal tube inserted through the LMA via the swivel connector. This combination of a conventional LMA and a commercially available longer paediatric tracheal tube could be another way of providing differential ventilation in infants.     

Tracheal intubation of morbidly obese patients: LMA CTrach vs direct laryngoscopy

Background. LMA CTrach^TM (CT), a modified version of the intubatingLMA Fastrach^TM, allows continuous video-endoscopy of the trachealintubation procedure. We tested the hypothesis that the CT isefficient for tracheal intubation of morbidly obese patientswho are at risk of a difficult airway. Methods. After Ethics’ Committee approval, 104 morbidlyobese patients (BMI >35 kg m^–2) scheduled for bariatricsurgery were included in this prospective study. Patients wererandomly assigned in two groups: tracheal intubation using directlaryngoscopy (DL) or the CT. Induction of anaesthesia was standardizedusing sufentanil, propofol and succinylcholine. Characteristicsand consequences of airway management were evaluated. Results. Preoperative characteristics of patients and consequencesof anaesthesia induction on physiological variables were similarin both groups. Difficulty in facemask ventilation was similarin both groups. Tracheal intubation was successfully carriedout with DL and CT. Forty-nine per cent of the patients fromthe CT group required laryngeal mask manipulation (ventilationand view optimization) resulting in increased duration of trachealintubation by 57 s as compared with DL. Oxygenation was of betterquality in the patients managed with CT than with DL. Blindtracheal intubation was mandatory in eight (17%) patients ofthe DL group, while tracheal intubation was seen in all patientsof the CT group. Conclusion. We demonstrated that the CT was an efficient airwaydevice for ventilation and tracheal intubation in case of adifficult airway in morbidly obese patients.      

Airway management in two of newborns with Pierre Robin Sequence: the use of disposable vs multiple use LMA for fiberoptic intubation

In this article, we discuss the use of LMAs as a conduit to intubate the trachea of two Pierre Robin Sequence infants. Multiple use LMAs will admit larger diameter tracheal tubes (TT) than their disposable counterparts. Increased friction with the surface of the TT makes passing even small diameter tubes through the lumen of the disposable LMA difficult.     

Intermittent positive ventilation through a laryngeal mask in children: does it cause gastric dilatation?

After obtaining Ethics Committee approval and informed consent, sixty children, ASA Grade 1 or 2 and aged six months to ten years, were randomly allocated to receive intermittent positive pressure ventilation through either a laryngeal mask or a tracheal tube. Inflation pressures were maintained below 20 cm H₂O, and gas aspirated from the stomach via an orogastric tube over a one h period. No large volumes were aspirated and no differences were detected between the groups. We conclude that healthy children over the age of six months can be safely ventilated through the laryngeal mask airway without gastric distension.     

Evaluation of the CTrach--an intubating LMA with integrated fibreoptic system

Background. The laryngeal mask airway CTrach^TM (CTrach) is avariant of the intubating laryngeal mask airway. It providesvisualization of the larynx during intubation and is designedto increase the success rates of ventilation and tracheal intubation. Methods. Sixty healthy anaesthetized and paralysed patientswith normal airways were studied. The success rates of ventilationand intubation using CTrach^TM were determined. Laryngeal viewscoring ranged from grade I (full view of arytenoids and glottis),II (arytenoids and glottis partly visible), III (view of arytenoids,glottis or epiglottis blurred, or view clear with only epiglottisvisible) to IV (no part of larynx identifiable). Adjusting manoeuvreswere undertaken to improve the laryngeal view in grades II orworse. Results. CTrach insertion and ventilation was possible in allpatients. Initial views were scored as grade I in 22 (36.7%),grade II in 14 (23.3%), grade III in 7 (11.7%) and grade IVin 17 (28.3%) patients. Adjusting manoeuvres were undertakenin 38 patients with grade II and worse (63.3%), resulting inimproved views of grade I in 33 (55.0%), grade II in 18 (30.0%),grade III in 4 (6.7%) and grade IV in 5 (8.3%) patients. Trachealintubation was successful in 58 (96.6%) patients at first attemptand in one at second. Tracheal intubation failed once. Conclusions. In 60 patients with normal airways, the CTrachwas used successfully for ventilation, with successful trachealintubation in 59 patients. Tracheal intubation can be successfuldespite grade III or IV views.      

Physiological dead space/tidal volume ratio during face mask, laryngeal mask, and cuffed oropharyngeal airway spontaneous ventilation

Objective: To compare the physiological dead space/tidal volume ratio and arterial to end-tidal carbon dioxide tension (ETCO₂) difference during spontaneous ventilation through a face mask, a laryngeal mask (LMA), or a cuffed oropharyngeal airway.

Design: Prospective, randomized, cross-over study.

Setting: Inpatient anesthesia at a university department of orthopedic surgery.

Patients: 20 ASA physical status I and II patients, without respiratory disease, who underwent ankle and foot surgery.

Interventions: After a peripheral nerve block was performed, propofol anesthesia was induced and then maintained with a continuous intravenous (IV) infusion (4 to 6 mg/kg/h). A face mask, a cuffed oropharyngeal airway, or an LMA were placed in each patient in a random sequence. After 15 minutes of spontaneous breathing through each of the airways, ventilatory variables, as well as arterial, end-tidal, and mixed expired CO₂ partial pressure, were measured, and physiological dead space/tidal volume ratio was calculated.

Measurements and Main Results: Expired minute volume and respiratory rate (RR) were lower with LMA (5.6 ± 1.2 L/min and 18 ± 3 breaths/min) and the cuffed oropharyngeal airway (5.7 ± 1 L/minand 18 ± 3 breaths/min) than the face mask (7.1 ± 0.9 L/min and 21 ± 3 breaths/min) (p = 0.0002 and p = 0.013, respectively). Physiological dead space/tidal volume ratio and arterial to end tidal CO₂ tension difference were similar with the cuffed oropharyngeal airway (3 ± 0.4 mmHg and 4.4 ± 1.4 mmHg) and LMA (3 ± 0.6 mmHg and 3.7 ± 1 mmHg) and lower than with the face mask (4 ± 0.5 mmHg and 6.7 ± 2 mmHg) (p = 0.0001 and p = 0.001, respectively).

Conclusion: Because of the increased dead space/tidal volume ratio, breathing through a face mask required higher RR and expired minute volume than either the cuffed oropharyngeal airway or LMA, which, in contrast, showed similar effects on the quality of ventilation in spontaneously breathing anesthetized patients.     

Gas leakage and the laryngeal mask airway: A comparison with the tracheal tube and facemask during spontaneous ventilation using a circle breathing system

The ability of the laryngeal mask airway, tracheal tube and facemask to provide a leak free seal in a clinical setting was assessed by measuring the minimal fresh gas flows needed in a closed circle system during spontaneous ventilation on 60 subjects. The fresh gas flow was reduced until no spillage occurred from the pop-off valve. This fresh gas flow was taken to represent the sum of gas uptake by the subject and gas leakage from the circuit. The median fresh gas flow after 20 minutes was 350 ml. min⁻¹ in the laryngeal mask airway group, 350 ml. min⁻¹ in the tracheal tube group and 450 ml. min⁻¹ in the facemask group. The fresh gas flow required for the facemask group was significantly higher than that for the laryngeal mask airway or tracheal tube groups (p < 0.01). There was no significant difference between the fresh gas flows required for the tracheal tube and laryngeal mask airway groups. We conclude that the laryngeal mask airway provides as good a gas tight seal as a tracheal tube in this context and would be of benefit in reducing anaesthetic gas pollution.     

Use of the ProSeal laryngeal mask airway for pressure-controlled ventilation with and without positive end-expiratory pressure in paediatric patients: a randomized, controlled study

Background. Tracheal intubation and positive end-expiratorypressure (PEEP) are frequently used in children to avoid airwayclosure and atelectasis during general anaesthesia. Also, thelaryngeal mask airway (LMA     

Prediction of difficult mask ventilation using a systematic assessment of risk factors vs. existing practice – a cluster randomised clinical trial in 94,006 patients

We compared implementation of systematic airway assessment with existing practice of airway assessment on prediction of difficult mask ventilation. Twenty‐six departments were cluster‐randomised to assess eleven risk factors for difficult airway management (intervention) or to continue with their existing airway assessment (control). In both groups, patients predicted as a difficult mask ventilation and/or difficult intubation were registered in the Danish Anaesthesia Database, with a notational summary of airway management. The trial's primary outcome was the respective incidence of unpredicted difficult and easy mask ventilation in the two groups. Among 94,006 patients undergoing mask ventilation, the incidence of unpredicted difficult mask ventilation in the intervention group was 0.91% and 0.88% in the control group; (OR) 0.98 (95% CI 0.66–1.44), p = 0.90. The incidence of patients predicted difficult to mask ventilate, but in fact found to be easy (‘falsely predicted difficult’) was 0.64% vs. 0.35% (intervention vs. control); OR 1.56 (1.01–2.42), p = 0.045. In the intervention group, 86.3% of all difficult mask ventilations were not predicted, compared with a higher proportion 91.2% in the control group, OR 0.61 (0.41–0.91), p = 0.016. The systematic intervention did not alter the overall incidence of unpredicted difficult mask ventilations, but of the patients who were found to be difficult to mask ventilate, the proportion predicted was higher in the intervention group than in the control group. However, this was at a ‘cost’ of increasing the number of mask ventilations falsely predicted to be difficult.     

喉罩联合支气管封堵器单肺通气对学龄患儿呼吸功能的影响

目的探讨喉罩联合支气管封堵器对单肺通气学龄患儿呼吸功能的影响。方法选择择期行胸腔镜手术患儿60例,男37例,女23例,年龄6～10岁,BMI 20～25 kg/m~2,ASAⅡ级,将患儿随机分为两组:喉罩组和气管插管组,每组30例。全麻诱导后采用压力控制模式机械通气,压力(P) 16 cmH_2O,RR 16次/分,PEEP 0 cmH_2O,I∶E 1∶2。记录麻醉前(T_0)、单肺通气开始(T_1)和单肺通气45 min(T_2)时的SBP、DBP及HR及T_2时的V_T、P_(ET)CO_2和肺顺应性(C_L),并采集T_2时桡动脉血进行血气分析。记录高碳酸血症、低氧血症、咽喉痛、喉痉挛和误吸等术后并发症的发生情况。结果T_1时喉罩组SBP、DBP明显低于气管插管组(P0.05)。T_2时两组SBP、DBP和HR差异无统计学意义。T_2时喉罩组PaO_2明显高于气管插管组,PaCO_2明显低于气管插管组(P0.05)。喉罩组V_(T )、C_L明显高于气管插管组,P_(ET)CO_2明显低于气管插管组(P0.05)。喉罩组高碳酸血症发生率明显低于气管插管组(P0.05)。结论在患儿胸腔镜术中,喉罩联合支气管封堵器单肺通气较气管插管加封堵器可获得更大的V_T,改善通气,促进CO_2排出,降低高碳酸血症发生率,更有利于气体交换。     

不同充气量的食管引流型喉罩对于全麻患者机械通气的影响

目的研究不同充气量的食管引流型喉罩(PLMA)用于全麻患者机械通气时的囊内压及对患者通气功能的影响。方法40例ASAⅠ或Ⅱ级妇科及乳腺手术患者全麻下置入4号PLMA,在最大充气量30ml(MAX)、25ml(5/6MAX)、20ml(2/3MAX)、15ml(1/2MAX)、10ml(1/3MAX)、5ml(1/6MAX)和0充气量时监测囊内压并用旁气流通气监测法(SSS)监测患者的通气功能的变化,同时记录气道漏气情况。结果所有患者MAX的套囊内压都大于60cmH2O;气道密闭压(Pleak)随通气罩充气量减小而逐渐降低,而气道阻力(Raw)逐渐增大。在1/3MAX充气量以下的气道漏气发生率、动态胸肺顺应性(Compl)、1/6MAX以下的呼出潮气量(TVex)和呼出分钟通气量(MVex)与MAX时相比差异有统计学意义(P<0.05或P<0.01)。结论最适宜的充气方法为开始充气1/2MAX,如果气道压<15cmHO,喉罩周围有漏气,再增加5～10ml充气量。     

The Size 1 ProSeal™ laryngeal mask airway in infants: a randomized,noncrossover study with the Classic™ laryngeal mask airway

Background: In recent years, numerous scientific publications have endorsed the superiority of the ProSeal? laryngeal mask airway (PLMA) over the Classic? laryngeal mask airway (cLMA) in adults, children, and infants. The PLMA forms a better seal for both the respiratory and gastrointestinal tracts, provides easier access to the gastrointestinal tract, and exerts lower mucosal pressures for a given seal pressure. This study aims to determine whether this superiority can also be observed for the size 1 PLMA used in anesthetized neonates and infants with positive pressure ventilation. Methods: Sixty consecutive neonates and infants undergoing elective surgical procedures were randomized to airway management with the size 1 PLMA or cLMA. For all patients, we recorded ease of insertion, effective airway time, number of placement attempts, oropharyngeal leak pressure, fiberoptic position, audible leaks, mask displacement, number of reinsertions during maintenance, gastric insufflation, and frequency of blood stain. Results: Ease of insertion, successful insertion in <3 attempts, fiberoptic position of the airway tube, and frequency of blood stain were similar in both groups. Effective airway time was lower for the PLMA group (30.5 vs 35.6 s). Oropharyngeal leak pressure was higher with the PLMA (32.9 vs 22.2 cm H₂O, P < 0.001) and gastric insufflation less common (0% vs 6%, P = 0.492). There were fewer mask displacements during maintenance of anesthesia with the PLMA (0% vs 26.7%, P < 0.001). Mask reinsertion was not necessary during maintenance of anesthesia with the PLMA, although it was necessary in 14 cases in the cLMA group (0% vs 46%, P < 0.001). Audible leaks were less common with the PLMA (0% vs 46%, P < 0.001). Conclusions: We conclude that the size 1 PLMA is a stable, safe, and efficacious airway control device during neonatal and infant anesthesia, allowing higher peak airway pressure during positive pressure ventilation, with fewer mask displacements and gastric insufflations than the cLMA.     

Gastro-oesophageal reflux during day case gynaecological laparoscopy under positive pressure ventilation: laryngeal mask vs. tracheal intubation

This study aimed to evaluate whether or not the use of intermittent positive pressure ventilation via the laryngeal mask airway is associated with a higher risk of gastro-oesophageal reflux when compared with intermittent positive pressure ventilation via a tracheal tube in patients undergoing day case gynaecological laparoscopy in the head down position. Sixty healthy women were randomly allocated to receive either the laryngeal mask or cuffed tracheal tube for intra-operative airway maintenance. Using continuous oesophageal pH monitoring, four patients in the tracheal tube group and none in the laryngeal mask group had evidence of gastro-oesophageal reflux (as indicated by a decrease in oesophageal pH to below 4). The difference in the incidence of reflux did not achieve statistical significance (p = 0.11). In conclusion, we found no evidence to suggest that the use of intermittent positive pressure ventilation via the laryngeal mask increases the risk of gastro-oesophageal reflux in patients undergoing elective day case gynaecological laparoscopy.     

食管引流型喉罩间歇正压通气时头前屈位对气道密封压的影响

Objective To evaluate the influence of head anteflexion on airway sealing pressure during intermittent positive pressure ventilation(IPPV) with ProSeal laryngeal mask airway (PLMA) with an esophageal vent.Methods Fifty ASA Ⅰ or Ⅱ patients (20 males and 30 females), aged 18-51 ye are, weighing 50-70 kg and scheduled for elective plastic surgery under general anesthesia, were enrolled in this study. Anesthesia was induced with fentanyl 2 μg/kg, propofol 2 μg/kg and vecuromium 0.1 mg/kg. PLMA with an esophageal vent was inserted at 2 min after intravenous vecuronium injection.The airway sealing pressure, the anatomic position of the cuff and the efficacy of positive pressure ventilation were checked in the neutral and anteflexed head positions with the cuff deflated and inflated to an intracuff pressure of 60 cm H2 O, respectively.Results The lungs were better ventilated in the head anteflexion position than in the head neutral position whether the cuff was deflated or inflated. There was no significant difference in the volume of air required to achieve an intracuff pressure of 60 cm H2O between the two head positions ( P＞ 0.05). The airway seating pressure increased from (27 ± 6) cm H2O in the head neutral position to (33 ± 6) cm H2O in the head anteflexion position, with no significant difference between them ( P＞ 0.05). The expired tidal volume and the peak inspiratory pressure during IPPV were (496 ± 81 ) ml and (14.3 ± 1.9) cm H2O respectively in the head neutral position and (496 ± 81 ) ml and ( 14.5 ± 2.1 )cm H2O respectively in the head anteflexion position.Conclusion Head anteflexion can significantly improve airway sealing but does not affect the anatomic position of the cuff.Appropriate head anteflexion is a simple and effective way to improve IPPV when the airway sealing pressure is inadequate in the head neutral position.     

Comparison of incidence of gastroesophageal reflux and regurgitation associated with timing of removal of the laryngeal mask airway: on appearance of signs of rejection versus after recovery of consciousness

Study Objectives: To compare the incidence of gastroesophageal reflux and regurgitation associated with laryngeal mask airway (LMA) removal when signs of rejecting the LMA, such as swallowing, struggling, and restlessness, were observed and when the patient could open his or her mouth on command.

Design: Randomized clinical trial.

Setting: Operating room and recovery room of a tertiary care referral hospital.

Patients: 63 ASA physical status I and II adult patients scheduled for elective orthopedic surgery.

Interventions: Using a standardized general anesthetic technique, patients were allocated randomly to Group A (n = 34; LMA removed when signs of rejection, such as swallowing, struggling, and restlessness, were observed) or Group B (n = 29; LMA removed when the patient could open his or her mouth on command).

Measurements and Main Results: To detect gastroesophageal reflux throughout anesthesia, a pH monitoring probe was positioned in the lower esophagus on the day before surgery. To assess regurgitation during emergence, a gelatin capsule of methylene blue (50 mg) was swallowed prior to induction. At the end of anesthesia, episodes of reflux and regurgitation of gastric contents were analyzed/determined by pH below 4 and bluish staining of the pharynx and/or LMA, respectively. Physical events such as bucking, straining, and coughing during the arousal phase were recorded in both groups by an independent observer. The incidence of reflux (pH < 4) from the time of the appearance of rejection signs to LMA removal and the total incidence of reflux in Group B were significantly higher than in Group A (p < 0.05). Staining of the LMA and the pharynx by methylene blue was not observed in patients from either experimental group. The number of physical events in Group B during the arousal phase was significantly increased compared to Group A (p < 0.05). Considering all patients in Group A and Group B, physical events were associated with the occurrence of reflux (p < 0.05). Desaturation (SpO₂ < 95%) and clinical evidence of aspiration of gastric contents did not occur in either group.

Conclusion: Maintenance of the LMA until the patient can open his or her mouth on command increases the incidence of gastroesophageal reflux.     

Prevention of aspiration under general anesthesia by use of the size 2 1/2 ProSeal laryngeal mask airway in a 6-year-old boy: a case report

We report a case where use of the size 2 1/2 ProSeal laryngeal mask airway helped to prevent pulmonary aspiration of regurgitated gastric fluid. We describe the management of this case and discuss the potential advantages of this modified laryngeal mask airway for supraglottic airway management in pediatric patients.