Venous congestion of the neck; its relation to laryngeal mask cuff pressures

Editor—During anaesthesia with a laryngeal mask airway (LMA{dagger}), I have observed venous congestion of the neck in some patients, and thought this might be caused by over-inflation of the cuff. A search of the literature did not show that this problem had been reported previously, but there were two studies relating the LMA to neck vessels, one showing reduction of carotid flow by an LMA,1 and another showing displacement of the internal jugular vein.2

A review by Asai and Brimacombe3 re-emphasized the fact that LMAs are often over-inflated by anaesthetists and operating department practitioners (ODPs), despite several papers advocating inflation of the cuff with volumes less than the manufacturer's recommended maximum. Reported cuff pressures have been as high as 250 mm Hg or more.4 In order to measure such high pressures, a pressure measuring device was constructed using a metal bourdon gauge from an old sphygmomanometer, which was connected to a three-way tap with an Abbot-T-connector and a short length of green oxygen tubing (Fig. 1). The gauge was calibrated by the medical physics department using a Timeter RT 200 pressure calibration device. The three-way tap was turned off between readings (Fig. 1), to prevent leakage through the gauge.



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Fig 1 Pressure measuring device.

 
Data were collected sequentially from 137 adult patients, who underwent anaesthesia in the supine, lithotomy, lateral or head-up positions. Anaesthesia was carried out with fentanyl, propofol, nitrous oxide (56%), oxygen and sevoflurane. In the first 63 patients, Group 1, the ODP was allowed to inflate the cuff according to their normal practice. This was often to the maximum recommended volumes, although some limited the pressure by feeling the pilot balloon. In the next 38 patients, Group 2, the cuff was fully deflated to a negative pressure, and then inflated with 10 ml less than the recommended maximum volume. Any air added before insertion of the LMA was included in the total volume. In the last 36 patients, Group 3, the LMA cuff was inflated to just above airway leak pressure. A standard of no venous congestion in any case was set.

Some patients in Groups 2 and 3 were given a neuromuscular blocking drug, and their lungs were artificially ventilated. The age, weight and sex of all the patients was recorded, as were LMA cuff pressures at the start and end of anaesthesia. Obvious venous congestion of the neck was also noted, specifically looking for purple discoloration of the skin of the neck and/or face, with or without mottling. If there was doubt about slight congestion, it was not counted. In some cases of severe congestion, the cuff pressure was lowered to just above airway leak pressure in an attempt to reduce it.

In Group 1, very high cuff pressures were recorded (mean 132, range 41–238 mm Hg) increasing to a mean of 153 (range 41–241) mm Hg after nitrous oxide, oxygen, sevoflurane anaesthesia. There were 14 patients with marked venous congestion of the neck. In three patients, congestion visibly improved over a few minutes after the cuff was partially deflated to reduce the pressure. In Group 2, a lower cuff pressure was noted (mean 62 (range 7–114) mm Hg, increasing to mean 88 (7–131) mm Hg) by the end of anaesthesia. Only four patients were noted to have venous congestion.

In Group 3, the cuff was inflated according to the recommendations of Asai and Brimacombe3 (10–15 ml initially and then another 5–10 ml as necessary to prevent a leak at 15 cm H2O airway pressure, or >15 cm H2O in patients at increased risk of aspiration from above the cuff). In this group, the LMA cuff pressure was lower (mean 20, range 0 to 66 mm Hg, increasing to mean 29, range 3–74 mm Hg) with the pressure in one LMA being atmospheric, yet still preventing an airway leak during artificial ventilation. No patient in this group became congested. In the 15 patients in Group 3 undergoing controlled ventilation, the mean cuff pressure was 21 (range 0–66) mm Hg, increasing to 32 (range 4–74) mm Hg (Table 1).


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Table 1 Characteristics of patients, laryngeal mask sizes and cuff pressures (mm Hg). Data are presented as mean, median (range)

 
This audit has demonstrated that much higher volumes of air are used to inflate LMAs than are necessary, and that after nitrous oxide diffusion, this can lead to very high cuff pressures, well above the standard of 60 cm water recommended.5 6 The incidence of venous congestion was also reduced in association with lower cuff volumes, and not observed at all in patients in whom the LMA cuff was inflated just above airway leak pressure. This would have particular relevance in patients undergoing general anaesthesia for eye or head and neck surgery, where raised venous pressure may lead to raised intra-ocular pressure or increased bleeding. In any circumstances, obstructed venous drainage of the head and neck cannot be beneficial.

I conclude that we should adopt the guidelines used in the patients in Group 3, inflating LMA cuffs to just above airway leak pressure. An audit of LMA cuff pressures could usefully be carried out in all anaesthetic departments. The second edition of the LMA instruction manual recommends monitoring the intra-cuff pressure to prevent postoperative throat discomfort, but this practice has not generally been adopted.7 I would suggest that every theatre should be equipped with a laryngeal mask cuff pressure gauge, but meanwhile anaesthetists could use the simple pressure gauge I have described (Fig. 1).

R. J. Lenoir

Portsmouth, UK

Footnotes

{dagger} LMA® is the property of Intavent Ltd. Back

References

1 Colbert SA, O'Hanlon DM, Flanagan F, Page R, Moriarty DC. The laryngeal mask airway reduces blood flow in the common carotid artery bulb. Can J Anaesth 1998; 45: 23–7[Abstract]

2 Nandwani N, Fairfield MC, Krarup K, Thompson J. The effect of laryngeal mask airway insertion on the position of the internal jugular vein. Anaesthesia 1997; 52: 77–83[CrossRef][ISI][Medline]

3 Asai T, Brimacombe J. Cuff volume and size selection with the laryngeal mask. Anaesthesia 2000; 55: 1179–84[CrossRef][ISI][Medline]

4 Margot R. Pressure exerted by the laryngeal mask airway cuff upon the pharyngeal mucosa. Br J Anaesth 1993; 70: 25–9[Abstract]

5 Brimacombe J, Keller C, Morris R, Mecklam D. A comparison of the disposable versus the reusable laryngeal mask airway in paralysed adult patients. Anaesth Analg 1998; 87: 921–4[Abstract]

6 Keller C, Brimacombe J, Benzer A. Calculated vs measured pharyngeal mucosal pressures with the laryngeal mask airway during cuff inflation: assessment of four locations. Br J Anaesth 1999; 82: 399–401[Abstract/Free Full Text]

7 Brimacombe J, Holyoake L, Keller C, et al. Emergence characteristics and post-operative laryngopharyngeal morbidity with the laryngeal mask airway: a comparison of high versus low initial cuff volume. Anaesthesia 2000; 55: 338–43[CrossRef][ISI][Medline]





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