Abstract

Background

The LMA-Supreme™ (SLMA) is a single-use, latex-free, supraglottic airway device with a drain tube which allows immediate assessment of correct positioning of the device at insertion and throughout the procedure and provides access to gastric contents. The anatomically shaped airway tube facilitates easy insertion in anaesthetized patients in the supine, lateral, and prone positions. We present a prospective audit in 205 consecutive adult patients presenting for elective spine surgery in the prone position. Patients positioned themselves in the prone position, on a Montreal or Wilson mattress to optimize patient comfort in this position. Anaesthesia was then induced, and an appropriate-sized SLMA was inserted.

Methods

Prospective, descriptive audit of SLMA insertion in 205 consecutive adult patients, anaesthetized in the prone position for elective orthopaedic surgery with spontaneous (n=6) or positive pressure ventilation (PPV) (n=199).

Results

First-pass success was achieved in 184 insertions. Forty-two SLMA insertions were performed by anaesthesia trainees with first-pass success achieved in 38 insertions. All problems encountered during insertion were minor, and no patient had to be turned to the supine position for an airway problem. Problems during insertion were independent of patients' BMI. There were no failures of SLMA insertion or of maintenance of PPV during surgery.

Conclusions

The results suggest that the SLMA is a useful device for airway management in patients anaesthetized in the prone position and for subsequent airway management with PPV, with or without neuromuscular block.

Key points

  • SLMA can be used as an airway management device for patients undergoing orthopaedic surgery in the prone position.

  • Insertion of the SLMA in the anaesthetized, prone patient was successful in 184 of 205 patients at the first attempt.

  • Minor airway problems were rectified in prone position without turning patients supine.

  • Regurgitation of gastric contents through LMA drainage tube observed in four of 205 patients. There were no cases of clinically relevant aspiration.

The limitation of use of the laryngeal mask airway (LMA) for surgery in the prone position appears to be based on opinion rather than on available, published data.1 The use of the Laryngeal Mask Airway-Classic™ (CLMA) in fasted patients in the prone position, with the head turned to either side, using recommended insertion techniques (the index finger or the ‘thumb insertion’ technique) has been previously described.2,3 The CLMA has also been used for anaesthesia in the prone position for minor surgery.4

The introduction of the re-usable LMAs with gastric access, the LMA-Proseal™ (PLMA) in 20005 and the single-use LMA-Supreme™ (SLMA) in 2007,6 has provided additional features to ensure successful use in a wider range of applications than the CLMA. The SLMA has an anatomically shaped airway tube, a drain tube (DT), a modified inflatable cuff, an integral bite block, and a fixation tab (FT).6 The airway and DT project from a manifold at the proximal end of the device. The anatomically shaped firm airway tube, elliptical in cross-section, facilitates easy insertion and minimizes accidental rotation of the SLMA. The DT helps in immediate diagnosis of incorrect device placement and acts as a conduit for access to gastric contents. The DT runs along the posterior surface of the cuff and has an open end facing the oesophagus. The DT serves as a continuous clinical monitor during positive pressure ventilation (PPV), indicating whether the SLMA is correctly positioned. Malposition of the SLMA during PPV results in a poor airway seal and an audible and immediately detectable leak of delivered gases through the DT, hence minimizing the possibility of gastric insufflation.6 Two fin-shaped structures extend on either side of the DT and prevent the epiglottis from occluding the airway. An integral bite block and FT further aid easy insertion and fixation of the SLMA. A distance of 1.5–2 cm between the FT and the patient's upper lip indicates appropriate size of the SLMA, otherwise a different size may be chosen. A modified and enhanced inflatable cuff is designed to provide a superior anatomical fit into the pharynx. The cuff has a conventionally placed inflation line terminating in a pilot balloon and a one-way valve for inflation and deflation of the mask.6

Brimacombe and colleagues7 in a retrospective audit described their experience with the insertion and maintenance of anaesthesia with the PLMA in 245 healthy adults in the prone position. More recently, Lopez and colleagues8 reported that the SLMA is easy to insert and suitable to manage the patient's airway in the prone position. Insertion and removal of LMA devices causes less physiological consequences than those associated with a tracheal tube (TT), and thus offer an attractive alternative to the TT for airway management in fasted patients undergoing surgery with PPV in the supine and prone positions. The CLMA, PLMA, and SLMA, unlike the TT, also provide a minimally invasive airway during the recovery phase after general anaesthesia.9

This prospective audit describes airway management after induction of anaesthesia and prone insertion of the SLMA™ in 205 consecutive adult patients for elective orthopaedic surgery on the spine.

Methods

The aim of this audit was to evaluate the safety, efficacy, and complication rate associated with the use of SLMA™ in the prone position. The use of the PLMA™ and the SLMA™ for airway management after induction of anaesthesia in the prone position is an accepted practice at our institution. Our Local Research Ethics Committee advised us against the need for ethical approval and written informed consent since this was an audit of current practice against local standards (i.e. the use of supraglottic airway devices by experienced users in adequately fasted adult patients for elective surgery) set at our institution. All adult patients meeting preoperative fasting guidelines for elective surgery, ASA physical status I–III, presenting for elective orthopaedic surgery in the prone position were prospectively audited from December 2008 to November 2009, using the logbook of The Royal College of Anaesthetists (rca logbook v6 and v7). Patients with documented gastro-oesophageal reflux disease and BMI up to 55 kg m−2 were included, in accordance with the current practice. Non-fasted, pregnant, paediatric (<16 yr of age), and patients with BMI >55 kg m−2 were considered ineligible for this audit.

All patients received a detailed explanation of the positioning procedure before induction of general anaesthesia. Patients were offered the option of having general anaesthesia induced in the supine position and subsequent positioning to the prone position. After adopting the prone position, patients were requested to position their arms on either side, on a board, in a position that was most comfortable. Care was taken to minimize damage to the brachial plexus and ulnar nerves, and patients' arms were repositioned, as indicated, before induction of general anaesthesia. The patient was asked to indicate the most acceptable position of his/her face on the pillows (facing left, right, or central). Pillows were added or removed to maximize patient comfort in the prone position on the Montreal or Wilson mattress. In those who preferred to lie with the head in the neutral position, the forehead was supported on a donut head pad (Central Medical Supplies: Critical Care model number 40204, 40211) with care to prevent pressure on the orbit. Patients who agreed to induction of anaesthesia in the prone position but subsequently experienced difficulty in positioning themselves were anaesthetized in a position most comfortable to them (left or right lateral or supine position) and then turned to the prone position.

Patient monitoring was instituted before induction of general anaesthesia, in accordance with recommendations of the Association of Anaesthetists of Great Britain and Ireland (AAGBI): three-lead ECG, peripheral pulse oximetry (Spo2), and non-invasive arterial pressure monitoring. These were monitored in all patients, using the Datex-Ohmeda Aestiva/5 system (Datex Ohmeda, Helsinki, Finland). After appropriate positioning and establishment of monitoring, venous access was secured on the dorsum of the non-dominant hand. Additional venous access, as clinically indicated, was established after induction of anaesthesia. Patient's lungs were preoxygenated via a face mask. After preoxygenation, anaesthesia was induced using midazolam 2 mg (all patients), followed by fentanyl 1–3 µg kg−1 and propofol (2–3 mg kg−1). Jaw relaxation was assessed clinically, and additional doses of propofol were administered at the anaesthetist's discretion to optimize jaw relaxation. Once acceptable jaw relaxation was obtained, the selected SLMA (size 3–5) was inserted. This was achieved with the face facing to the left or right or by simply raising the head (central position), which caused the lower jaw to fall, allowing insertion of the tightly deflated SLMA™.9 The number of attempts for successful insertion was recorded (removal of the device from the mouth of the patient was recorded as an attempt), the manipulations required to achieve an acceptable airway, and reinsertions with either the initially chosen SLMA™ or one of a different size were recorded.

The need to exchange the initial airway device for one with a larger or smaller size was determined by the distance of the FT from the upper alveolar margin.6 The cuff was inflated to a volume required to allow PPV without a leak around it. Leaks through the DT confirmed that the SLMA had not been inserted to the correct depth, and were corrected. Following verification of the correct sizing of the SLMA (distance from the FT to the upper alveolar margin), PPV was established using volume-controlled ventilation (tidal volumes of 5–8 ml kg−1) via the ventilator. The pressure–volume curves generated on the monitor were displayed throughout the procedure. Discrepancies between inspired and expired tidal volumes (leak volume) and sudden increases in peak inspiratory pressures (PIP) were monitored, and manoeuvres required to correct these were recorded. Anaesthesia was maintained with oxygen/air and sevoflurane or desflurane (minimum alveolar concentration >1). Neuromuscular blockers were used if the pressure–volume curves revealed an obstructive pattern during PPV, despite adequate level of anaesthesia (minimum alveolar concentration >1). Patients undergoing minimally invasive surgery (facet joint injection, rhizolysis, etc.) lasting <20 min, in the prone position, were allowed to breathe spontaneously, at the discretion of the anaesthetist.

The duration of surgery (time of insertion of the SLMA to discharge to the recovery ward) was recorded. Complications of airway maintenance and methods used to resolve these were recorded in the appropriate spaces provided in the logbook. Postoperative complications such as sore throat and difficulty in speaking and swallowing were entered in the logbook as free text. Data were recorded using the Royal College of Anaesthetists logbook v6 and v7 and transferred to a spreadsheet program (Microsoft Office Excel © 2003; Microsoft Corporation, Redmond, WA, USA).

Results

All patients provided verbal consent to being awake and conscious during positioning in the prone position before general anaesthesia, and there were no exclusions from this audit. One patient, who consented to prone positioning, was unable to comfortably position herself in the prone position, and in order to minimize discomfort, she accepted our suggestion that anaesthesia be induced in the left lateral position.

Patient characteristics are presented in Table 1. Seventy-nine patients were classified as obese (BMI ≥30 kg m−2). Within this group, 53 patients were obese class I (BMI 30–34.99 kg m−2), 20 patients were obese class II (BMI 35–39.99 kg m−2), and six patients had a BMI ≥40 kg m−2. Surgical procedures included microdiscectomy, multiple level spinal decompression, and spinal fusion procedures. One hundred and ninety-nine patients underwent PPV, and neuromuscular blocking drugs were used in 27 patients. The mean (range) duration of surgery was 102 (15–300) min. Some problems were encountered during insertion of the SLMA and maintenance of anaesthesia with the SLMA in the prone position (Table 2). Repositioning (manual adjustment without removal from the oral cavity) of SLMA™ required in 13 patients was achieved easily. Regurgitation of gastric contents (an infrequent but potentially serious complication), all via the DT (n=4), was observed and patients were followed up for clinical evidence of aspiration (auscultation of lungs, dyspnoea, and hypoxaemia). None of these patients had clinical evidence of aspiration, and there were no long-term complications documented during follow-up visits. Five patients required a change of the initial SLMA. In four of these patients, a different sized SLMA solved the problem, while one patient required a change to PLMA due to unavailability of an appropriate-sized replacement SLMA. Difficult insertion of SLMA (greater than two attempts at insertion) occurred in two patients. No patient required rotation back into the supine position due to a complication during airway management. We did not experience an increase in the incidence of problems with insertion of SLMA (repositioning of SLMA n=6, multiple attempts at insertion n=1, regurgitation of gastric contents n=1) in obese patients.

Table 1

Patient characteristics presented as median (inter-quartile range) or n

 Male (n=94) Female (n=111) 
Age (yr) 51 (41–65) 57 (47–64) 
ASA grade (I/II/III) 45/29/20 34/63/14 
Weight (kg) 85 (77–98) 75 (65–83) 
Height (cm) 177 (173–182) 160 (155–165) 
Body mass index (kg m−227 (25–32) 28 (25–31) 
 Male (n=94) Female (n=111) 
Age (yr) 51 (41–65) 57 (47–64) 
ASA grade (I/II/III) 45/29/20 34/63/14 
Weight (kg) 85 (77–98) 75 (65–83) 
Height (cm) 177 (173–182) 160 (155–165) 
Body mass index (kg m−227 (25–32) 28 (25–31) 
Table 2

Problems encountered during insertion of SLMA™ in the prone position

Problem Comment 
Repositioning of SLMA (n=13) Only one attempt at repositioning. SLMA repositioned easily 
Regurgitation of gastric contents through the DT (n=4) No clinical evidence of aspiration 
Laryngospasm (n=1) Neuromuscular blocking drug given. No further problems 
Change of SLMA (n=6) Change of size in five patients, change to PLMA in one patient 
More than two attempts at insertion (n=2) Success with careful head positioning 
Problem Comment 
Repositioning of SLMA (n=13) Only one attempt at repositioning. SLMA repositioned easily 
Regurgitation of gastric contents through the DT (n=4) No clinical evidence of aspiration 
Laryngospasm (n=1) Neuromuscular blocking drug given. No further problems 
Change of SLMA (n=6) Change of size in five patients, change to PLMA in one patient 
More than two attempts at insertion (n=2) Success with careful head positioning 

Forty-two prone insertions of SLMA were performed by anaesthesia trainees. First-pass success was achieved in 38 insertions (first-pass success rate 90.5%).

There was no incidence of failure to insert the SLMA and establish and maintain PPV with the SLMA in the prone position.

Discussion

In this prospective audit, we found that the SLMA™ provided an acceptable, alternative means of inducing anaesthesia and maintaining an unimpeded airway in the prone position. Complications encountered during insertion were minor and easily resolved.

Traditional airway management for patients undergoing surgical procedures with general anaesthesia in the prone position is to induce anaesthesia in the supine position and secure the airway with a cuffed TT. After correct TT placement and secure fixation of the TT, the anaesthetized patient is then turned into the prone position. Positioning of the anaesthetized patient from the supine to prone requires meticulous attention to airway maintenance during turning (to prevent accidental extubation of the TT). Additional care is taken to ensure unimpeded ventilation of the lungs, minimize obstruction of venous return, and to ensure that upper and lower limbs are suitably arranged to prevent injury to peripheral nerves. A variety of measures such as firm pillows placed below the chest and pelvis, the Montreal mattress, and the Wilson mattress are currently used to achieve these objectives. Despite meticulous attention to placing the patient in the prone position which is perceived acceptable, the chosen prone position may not be optimal for all patients initially anaesthetized in the supine position. Accidental displacement of the TT may occur during repositioning from the supine to prone position, during perioperative head and neck manipulation and lengthy surgical procedures. Replacement of an accidentally displaced TT in the prone position is very difficult and may require cessation of surgery and the turning of the patient into either the lateral or supine position to enable reinsertion of the TT.

The CLMA, PLMA, and the SLMA are easily inserted in the prone position, unlike the TT, and offer an easily replaceable and secure airway device in the prone position.4,7,10 The PLMA and SLMA offer the additional advantages of higher glottic seal pressures than the CLMA and provide a separate conduit for passive passage of gastric contents and allow the passage of a lubricated gastric tube via the DT to access liquid and gaseous gastric contents. The advantages of a higher glottic seal pressure, easy access to liquid gastric contents,6 ease of insertion in the supine lateral and prone positions, its efficacy for PPV and as a reliable and non-invasive airway during the recovery phase from general anaesthesia support its use in this form of surgery.

The relatively firm, anatomically shaped airway tube of the SLMA makes it a more suitable choice of device to insert in the prone position.

The major advantages, apart from those mentioned above, are easy reinsertion in the prone position, a clear airway provided during the recovery phase from anaesthesia, and minimizing the sequelae commonly accompanying tracheal intubation and accidental tracheal extubation.

This audit has distinct features. It is the largest audit of SLMA insertion in adult patients undergoing elective orthopaedic surgery in the prone position. Previous studies in the prone position have featured the use of CLMA or PLMA.4,7,10–12 This audit included obese patients and our results show that the SLMA™ can be inserted in this cohort of patients without an increase in the incidence of complications of airway management. Our results highlight that duration of surgery, use of PPV, and neuromuscular blocking drugs are not contraindications for the use of SLMA for surgical procedures in the prone position. Problems encountered during insertion of SLMA in the prone position were minor and were not influenced by the BMI of patients and the experience of the anaesthetist.

This audit has some limitations. We used pillows as our head and neck support system in patients who indicated that the head and neck turned either to the left or right was their preferred choice, in the prone position. There have been case reports of serious consequences following occlusion of carotid or vertebral arteries with excessive head rotation for prolonged periods.13 Newer head support systems such as Prone View® (unavailable at our hospital at the time of the audit) may prevent the occurrence of complications associated with excessive head rotation. The longest duration of surgery in our audit was 5 h. Complex spinal surgeries may involve considerably longer periods of anaesthesia in the prone position, but prolonged duration of surgery is not a contraindication for the use of SLMA, provided adequate measures have been taken to maintain the neck in a neutral position. This audit has been undertaken by very experienced users of the LMA in all its forms. One of the authors has experience of inducing anaesthesia and inserting PLMA and SLMA in the prone position in more than 500 patients. The safety of this technique, especially for long duration surgery, will need further evaluation in a large cohort of patients. There are instances when intense surgical stimulation may lead to laryngospasm; however, these can be addressed by increasing the depth of anaesthesia, administration of neuromuscular blocking agents, or both. Despite the low incidence of complications with the use of SLMA, we do not advocate that the use of TT for surgery in the prone position should be abandoned.

We note that the incidence of problems encountered did not increase when insertion of SLMA was performed by trainee anaesthetists under adequate supervision. Ng and colleagues4 postulated that insertion of PLMA™ in the prone position can be learned and practiced within ∼10 supervised cases. Lopez and colleagues8 in their study of prone insertion of SLMA in 40 adult patients achieved success rates of 92.5% (37/40) and 7.5% (3/40) at the first and second attempts, respectively, and concluded that the use of SLMA in the prone position by experienced users is feasible. Our results reinforce their findings which may encourage experienced users and trainee anaesthetists that with appropriate supervision and experience; this technique can be safely used for elective surgical procedures in the prone position. We do not encourage anaesthesia trainees to practice this technique without adequate supervision and experience.

In conclusion, our findings suggest that the SLMA is a useful alternative to tracheal intubation for surgery in fasted patient in the prone position, as it is easily inserted in the anaesthetized patient in the prone position and could be easily re-inserted in the prone position. In addition, it is a useful airway management technique to acquire for airway management experts, to rescue the ‘lost airway’, in patients undergoing surgery in the prone position, including those requiring PPV. Further studies in a large cohort of patients and comparison of SLMA with similar airway devices such as CLMA and PLMA for use in surgical procedures in the prone position will be required to establish the relative safety of SLMA in this clinical situation.

Conflict of interest

C.V. receives an annual honorarium from The LMA Company, Jersey, Channel Islands.

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