British Journal of Anaesthesia, 2004, Vol. 92, No. 5 777-778
© 2004 The Board of Management and Trustees of the British Journal of Anaesthesia
Correspondence |
The CobraPLATM in 110 anaesthetized and paralysed patients: what size to choose?
Rome, Italy
LMA® is the property of Intavent Limited.
Editor—The Cobra Perilaryngeal Airway (PLA)TM is a new supraglottic device,1 which consists of a tube with an inflatable cuff and a 15 mm standard adaptor. The softened distal end (CobraPLATM head) of the breathing channel is designed to be positioned in the hypopharynx, opposite the laryngeal inlet, to divert the inspiratory gas into the trachea through the slotted openings (Fig. 1).
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Ethics committee approval and written informed consent was obtained from the patients before starting this study. Under supervision of a consultant anaesthetist, four residents inserted the CobraPLATM in 110 ASA I/II patients aged 20–78 yr, undergoing general anaesthesia. The residents had already inserted the CobraPLATM in a manikin 100 times and in 10 patients. Patients with gastro-oesophageal reflux, hiatus hernia, or other risk factors for pulmonary aspiration were excluded. After preoxygenation for 3 min, anaesthesia was induced with fentanyl 2–3 µg kg–1, followed by propofol 2–3 mg kg–1 and vecuronium 0.1 mg kg–1, and maintained with oxygen/air and sevoflurane. Routine monitoring was applied. The CobraPLATM size was chosen according to patient weight in the range suggested by the manufacturer: size 3 (between 35–70 kg), size 4 (70–100 kg), and size 5 (100–130 kg). The device was inserted when the eyelash reflex was lost, the jaw had relaxed, and the patient was apnoeic. Patient position for placement was extension of the head with flexion of the neck (sniffing position), and the mouth was opened using the non-dominant hand. After deflating the cuff and folding it back against the breathing tube, the front and the back of the tube were lubricated together with the cuff itself. The CobraPLATM was held in the dominant hand and inserted blindly straight back through the mouth until moderate resistance was felt. Ventilation was controlled with a tidal volume of 8 ml kg–1 and a ventilatory frequency of 10 bpm. Variables such as SpO2, E'CO2, blood pressure and heart rate were monitored and remained stable during insertion and the surgical procedure. Two attempts at insertion of the CobraPLATM were permitted. If an effective airway was not achieved, the CobraPLATM was removed and a tracheal tube inserted.
CobraPLATM insertion was possible in 100% of patients. It was considered easy (no tactile resistance or minimum tactile resistance) in 85/110 (77.3%), difficult (necessary to perform jaw trust or neck hyperextension) in 25/110 (22.7%) patients, and impossible in none. In 48/110 patients, a size 3 CobraPLATM was inserted, in 62/110 a size 4. After insertion, adequate ventilation and a satisfactory seal were verified. We documented airway sealing pressures by closing the expiratory valve of the circular breathing system and noting the airway pressure at which a leak was heard, using a stethoscope placed on the neck. All patients were artificially ventilated through the CobraPLATM. In 56/110 (51%) patients there was a leak, although the cuff was inflated with the maximum volume indicated by the manufacturers: size 3 <65 ml, size 4 <70 ml, and 5 < 85 ml. In these patients, the device was removed and a larger size of CobraPLATM was inserted. In 23 of the 48 patients in whom a size 3 CobraPLATM was inserted (mean (SD) weight: 65.1 (3.6) kg, 95% CI 62.3–67.8), a size 4 was used successfully. In 33 of the 62 patients in whom a size 4 CobraPLATM was inserted (weight 82.3 (3.4) kg, 95% CI 81.0–83.5), a size 5 was used successfully.
As a result, a good seal (leak pressure 34.2 (2.8) cm H2O) was obtained using a size 3 CobraPLATM in 25/110 patients (22.7%) who weighed 55.5 (3.6) kg (95% CI 53.9–56.9), a size 4 CobraPLATM in 52/110 (47.3%) with a weight of 70.2 (7.2) kg (95% CI 68.2–72.2), and a size 5 in 33 /110 (30%) with a weight of 82.3 (3.5) kg (95% CI 81.0–83.5). Cuff inflation volumes were 26.5 (2.1) ml for size 3; 31.9 (4.0) ml for size 4; and 40.0 (4.1) ml for size 5.
The mean time of insertion was 6.8 (2.0) s, which is shorter than that required to insert the laryngeal tube and LMA ProSeal.2 No adverse airway events occurred and gastric inflation was not detected by auscultation over the epigastrium, in any patient. The mean time of artificial ventilation through the CobraPLATM was 75 (12) min.
These preliminary results suggest that the CobraPLATM is easy to place blindly, allowing a rapid achievement of adequate oxygenation. In contrast to the recommendations of the manufacturers, we suggest the following range for choosing the size of CobraPLATM: size 3 for patients <60 kg; size 4 between 60–80 kg; and size 5 >80 kg. When using this range, the cuff inflation volume is much reduced from the maximum recommended by the manufacturer.
F. Agrò
G. Barzoi
B. Gallì
Rome, Italy
References
1 Agrò F, Barzoi G, Carassiti M, Gallì B. Getting the tube in the oesophagus and oxygen in the trachea: preliminary results with the new supraglottic device (CobraPLATM) in 28 anaesthetised patients. Anaesthesia 2003; 58: 920–1[Web of Science][Medline]
2 Cook TM, McKinstry C, Hardy R, Twigg S. Randomized crossover comparison of the ProSealTM laryngeal mask airway with the Laryngeal Tube® during anaesthesia with controlled ventilation. Br J Anaesth 2003; 91: 678–83
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