Does efficacy of seal and fibreoptic view change during anaesthesia with the laryngeal mask airway: a comparison of oxygen and oxygen-nitrous oxide gas mixtures

Effect of diffusion of anaesthetic gases on fibre-optic view change of laryngeal mask airway and post-operative laryngo-pharyngeal morbidity in children - A randomised controlled trial

Background and Aims:

The diffusion of nitrous oxide (N₂O) into the air-filled cuff of the classic laryngeal mask airway (LMA) may lead to an increase in cuff pressure (CP) and displacement of LMA affecting its performance. This study was conducted to evaluate the change in optimal position of LMA by fibre-optic bronchoscope, the changes in cuff pressure and oropharyngeal leak pressure (OLP), and post-operative laryngo-pharyngeal morbidity during N₂O–oxygen (O₂) anaesthesia in children.

Methods:

After ethics committee approval and written informed consent, 84 children, aged 2 to 8 years undergoing lower abdominal surgery using LMA were included. Anaesthesia was induced with sevoflurane and maintained with either 33% O₂ in air (Group 1) or with 33% O₂ in 67% N₂O (Group 2) along with sevoflurane. The position of LMA using fibre-optic bronchoscope, CP and OLP were recorded at 30, 60 and 90 minutes and at the end of surgery. The incidence of post-operative sore throat, hoarseness of voice and dysphagia was assessed for 24 hours.

Results:

A mild (Grade 1) change in fibre-optic position of LMA was observed in 6 out of 42 children maintained with N₂O–O₂ anaesthesia. The cuff pressure was higher than baseline in group 2 at all three time points with the maximum at 90 minutes (93.23 ± 14.86 cm H₂O vs. 39.78 ± 7.75 cm H₂O; P < 0.05). The OLP was comparable between the groups during the initial 60 minutes and then increased in group 2. The incidence of post-operative sore throat was significantly higher in group 2 (P = 0.008).

Conclusion:

The diffusion of anaesthetic gases into the air-filled cuff does not change the fibre-optic position of the LMA significantly but increases the cuff pressure and incidence of post-operative laryngo-pharyngeal complications in children.

Time to consider supraglottic airway device oropharyngeal leak pressure measurement more objectively

Oropharyngeal leak pressure (OLP) is considered a measure of successful placement, adequate performance and is a useful comparator between supraglottic airway devices (SADs). OLP measurement is based on the premise that the SAD is sited properly in the hypopharynx after blind placements, but the evidence suggests otherwise. Several limitations and controversies surround OLP. This editorial addresses the uses and pitfalls of OLP, the rationale for and methods of ascertaining OLP, the pros and cons of OLP measurement and newer modalities to improve its accuracy.

Does anaesthesia with nitrous oxide affect mortality or cardiovascular morbidity? A systematic review with meta-analysis and trial sequential analysis

BACKGROUND

The role of nitrous oxide in modern anaesthetic practice is contentious. One concern is that exposure to nitrous oxide may increase the risk of cardiovascular complications. ENIGMA II is a large randomized clinical trial currently underway which is investigating nitrous oxide and cardiovascular complications. Before the completion of this trial, we performed a systematic review and meta-analysis, using Cochrane methodology, on the outcomes that make up the composite primary outcome.

METHODS

We used conventional meta-analysis and trial sequential analysis (TSA). We reviewed 8282 abstracts and selected 138 that fulfilled our criteria for study type, population, and intervention. We attempted to contact the authors of all the selected publications to check for unpublished outcome data.

RESULTS

Thirteen trials had outcome data eligible for our outcomes. We assessed three of these trials as having a low risk of bias. Using conventional meta-analysis, the relative risk of short-term mortality in the nitrous oxide group was 1.38 [95% confidence interval (CI) 0.22-8.71] and the relative risk of long-term mortality in the nitrous oxide group was 0.94 (95% CI 0.80-1.10). In both cases, TSA demonstrated that the data were far too sparse to make any conclusions. There were insufficient data to perform meta-analysis for stroke, myocardial infarct, pulmonary embolus, or cardiac arrest.

CONCLUSION

This systematic review demonstrated that we currently do not have robust evidence for how nitrous oxide used as part of general anaesthesia affects mortality and cardiovascular complications.

Fiberoptic intubation through a laryngeal mask airway as a management of difficult airwary due to the fusion of the entire cervical spine - A report of two cases -

Patients with cervical spine instability and limited range of motion are challenge to anesthesiologists. It is important to consider alternatetive methods for securing the airway while maintaining neutral position and minimizing neck motion, because these patients are at increased risk for tracheal intubation failure and neurologic injury during airway management or position change. We experienced two cases that patients had cervical spine instability and severe limited range of motion due to the fusion of the entire cervical spine. One patient was a 6-year-old girl weighing 12.7 kg and had Klippel-Feil syndrome with Arnold-Chiari malformation, the other was a 24-year-old female weighing 31 kg and had juvenile rheumatoid arthritis. We successfully performed the intubation by using the fiberoptic intubation though a laryngeal mask airway in these two cases.

Low flow anesthesia: Efficacy and outcome of laryngeal mask airway versus pressure-optimized cuffed-endotracheal tube

BACKGROUND

Low flow anesthesia can lead to reduction of anesthetic gas and vapor consumption. Laryngeal mask airway (LMA) has proved to be an effective and safe airway device. The aim of this study is to assess the feasibility of laryngeal mask airway during controlled ventilation using low fresh gas flow (1.0 L/min) as compared to endotracheal tube (ETT).

PATIENTS AND METHODS

Fifty nine non-smoking adult patients; ASA I or II, being scheduled for elective surgical procedures, with an expected duration of anesthesia 60 minutes or more, were randomly allocated into two groups - Group I (29 patients) had been ventilated using LMA size 4 for females and 5 for males respectively; and Group II (30 patients) were intubated using ETT. After 10 minutes of high fresh gas flow, the flow was reduced to 1 L/min. Patients were monitored for airway leakage, end-tidal CO(2)(ETCO(2)), inspiratory and expiratory isoflurane and nitrous oxide fraction concentrations, and postoperative airway-related complications.

RESULTS

Two patients in the LMA-group developed initial airway leakage (6.9%) versus no patient in ETT-group. Cough and sore throat were significantly higher in ETT patients. There were no evidences of differences between both groups regarding ETCO(2), uptake of gases, nor difficulty in swallowing.

CONCLUSION

The laryngeal mask airway proved to be effective and safe in establishing an airtight seal during controlled ventilation under low fresh gas flow of 1 L/min, inducing less coughing and sore throat during the immediate postoperative period than did the ETT, with continuous measurement and readjustment of the tube cuff pressure.

Lower intracuff pressure of laryngeal mask airway in the lateral and prone positions compared with that in the supine position

We compared the intracuff pressure (ICP) of a laryngeal mask airway (LMA) in the lateral and prone positions with that in the supine position. One hundred and eight patients, weighing 50-70 kg, scheduled for elective orthopedic and plastic surgery, were assigned to three groups, based on their body position during surgery. General anesthesia was induced and then a size 4 deflated LMA was inserted in each patient in the supine (group 1; n = 42), lateral (group 2; n = 45), or prone position (group 3; n = 21). The LMA cuff was inflated with 15 ml of air. Anesthesia was maintained without nitrous oxide, and the ICP was measured until LMA removal in the supine position. ICP in groups 2 and 3 was significantly lower than that in group 1 from immediately after insertion to the end of surgery. After surgery, turning from the lateral (group 2) or prone (group 3) position to the supine position significantly raised the ICP. Because the ICP is related to the seal pressure of the LMA and postoperative pharyngolaryngeal morbidity, we recommend evaluating and adjusting the ICP appropriately in each body position.

The Laryngeal Mask Airway ProSeal(TM) as a temporary ventilatory device in grossly and morbidly obese patients before laryngoscope-guided tracheal intubation

We determined the efficacy of the laryngeal mask airway ProSeal(TM) (PLMA) as a temporary ventilatory device in morbidly obese patients before laryngoscope-guided tracheal intubation. Sixty patients (body mass index 35--60 kg/m(2)) scheduled for elective surgery, who preferred airway management under general anesthesia, were studied. The induction of anesthesia was with midazolam/fentanyl/propofol and maintenance was with sevoflurane 1%--3% in oxygen 100%. The PLMA was inserted and an effective airway established. Rocuronium was given IV for paralysis. Oropharyngeal leak pressure, ease of gastric tube placement, residual gastric volume, fiberoptic position of the airway/drainage tube, and ease of ventilation at a tidal volume of 8 mL/kg was determined. The PLMA was then removed and laryngoscope-guided tracheal intubation attempted. The number of insertion/intubation attempts (maximum two each) and time taken to establish an effective airway with each device were recorded. An effective airway was obtained at the first insertion attempt in 90% of patients (54/60) and at the second attempt in 10% (6/60). The time taken to provide an effective airway was 15 plus minus 7 s (7--42 s). Oropharyngeal leak pressure was 32 plus minus 8 cm H(2)O (12--40 cm H(2)O). The residual gastric volume was 36 plus minus 46 mL (0--240 mL). Positive pressure ventilation without air leaks was possible in 95% of patients (57/60). The vocal cords were seen from the airway tube in 75% of patients (45/60), but the esophagus was not seen. The fiberoptic view from the drainage tube revealed mucosa in 93% of patients (56/60) and an open upper esophageal sphincter in 7% (4/60). Tracheal intubation was successful at the first attempt in 90% of patients (54/60), at the second attempt in 7% (4/60), and failed in 3% (2/60). In these latter two patients, the PLMA was reinserted and surgery performed uneventfully with the PLMA. The time taken to tracheally intubate the patient was 13 plus minus 10 s (8--51 s). There were no episodes of hypoxia (SpO(2) <90%) or other adverse events. There were no differences in insertion success rate, or the time to successful insertion between the PLMA and laryngoscope-guided intubation. We conclude that the PLMA is an effective temporary ventilatory device in grossly or morbidly obese patients before laryngoscope-guided tracheal intubation.

IMPLICATIONS

The laryngeal mask airway ProSeal(TM) is an effective temporary ventilatory device in grossly and morbidly obese patients before laryngoscope-guided tracheal intubation.

The laryngeal mask airway is effective (and probably safe) in selected healthy parturients for elective Cesarean section: a prospective study of 1067 cases

PURPOSE

To report on the use of the laryngeal mask airway (LMA) for elective Cesarean section in 1067 consecutive ASA I-II patients preferring general anesthesia.

METHODS

Patients were excluded if they had pharyngeal reflux, a pre-pregnancy body mass index >30, or had a known/predicted difficult airway. Patients were fasted for six hours and given ranitidine/sodium citrate. A rapid sequence induction was performed with thiopentone and suxamethonium. The LMA was inserted by experienced users. Anesthesia was maintained with N(2)O and 50% O(2) and a volatile agent. Cricoid pressure was maintained until delivery, but was relaxed if insertion/ventilation was difficult. Patients were intubated if an effective airway was not obtained within 90 sec, or SpO(2) <94%, or end-tidal CO(2) >45 mmHg. Postdelivery, vecuronium and fentanyl were administered.

RESULTS

An effective airway was obtained in 1060 (99%) patients, 1051 (98%) at the first attempt and nine (1%) at the second or third attempt. Air leakage or partial airway obstruction occurred in 22 (21%) patients, and seven (0.7%) patients required intubation. There were no episodes of hypoxia (SpO(2) <90%), aspiration, regurgitation, laryngospasm, bronchospasm or gastric insufflation. Surgical conditions were satisfactory and all APGAR scores were >/=7 after five minutes.

CONCLUSION

We conclude that the LMA is effective and probably safe for elective Cesarean section in healthy, selected patients when managed by experienced LMA users.