Alkalinization of intra-cuff lidocaine and use of gel lubrication protect against tube-induced emergence phenomena

Editor—I read Dr Estebe and colleagues' article with interest.1 They describe using lidocaine 2% 2 ml, alkalinized with sodium bicarbonate 8.4% to a total volume of 4.5 ml, to fill high-volume low-pressure tracheal tube cuffs. The aim was to increase lidocaine diffusion across the cuff, and to reduce sore throat and other intubation sequelae. It seemed to work well.

Because sodium bicarbonate 8.4% is strongly hypertonic2 and endotracheal tube cuffs occasionally rupture, I wondered if such large volumes of bicarbonate were necessary. Using a pH monitor and simple titration techniques, Tackley and Coe3 managed to increase the pH of 10 ml of bupivacaine 0.5% with 1 in 200 000 epinephrine from about 3 to 6, with only 0.15 ml of sodium bicarbonate. Of course, the local anaesthetic solutions we used were different, but Dr Estebe and colleagues effectively used 60 times the bicarbonate per unit volume of local anaesthetic that we did. Also, whilst bupivacaine with epinephrine is buffered to maintain a low pH, lidocaine is not! I wondered if Dr Estebe and colleagues had performed any titration studies to arrive at the volume of bicarbonate they needed to use. (I could find no details of this in supporting references.)

A. J. Coe

Hull, UK


 
Editor—I read with interest the study by Estebe and colleagues.1 I am surprised that the researchers used intra-cuff air and saline lubrication as a control group. I think the most widely used method in anaesthesia is intra-cuff air and water soluble gel lubrication. It could be predicted that the incidence of emergence phenomena in this study would be greater than those previously quoted in a study of intra-cuff air and gel lubrication. It is always be better for a new technology to be compared with the most widely used practice in the field.

R. K. Jain

Castlebar, Ireland


 
Editor—We thank Drs Coe and Jain for their interest in our study.1 Their remarks are very important for clinical practice (e.g. in the case of rupture of the endotracheal tube (ETT) cuff). However, before performing our clinical studies, we evaluated the pH of the solution injected into the ETT in a preliminary in vitro study.4 The pH increases from 6.7 with lidocaine (2 ml of 2%) to 8.3 when adding 9 ml of sodium bicarbonate 8.4%. Sodium bicarbonate is necessary to transform lidocaine hydrochloride into lidocaine base to potentiate diffusion across the ETT; 65% of diffusion occurs over 6 h with the hydrophobic neutral form but only 1% with ionized lidocaine hydrochloride.4 The problems with lidocaine are different from those observed with bupivacaine. Although with bupivacaine, precipitation has been reported when bicarbonate is added,5 6 this crystallization has not been observed in vitro with lidocaine despite use of a large amount of bicarbonate (15 ml).1 4 7 In unpublished studies, we did not observe rupture of a cuff despite prolonged exposure of the ETT to the solution (14 days) in vitro. Nor has it been reported in current practice in our institution. It is always possible (in the clinical and experimental situation) to remove the solution from the cuffs of the different kinds of ETTs if necessary.1 4 7 We are currently performing a new study (in vitro and in vivo), which is not yet complete, of the various amounts of bicarbonate of differing concentrations (1.4% and 8.4%).

Although water soluble gel has become more popular in French anaesthesia practice, lubrication of the ETT is usually performed with sterile water (or, unfortunately, lidocaine spray). This may be the reason why we reported a higher incidence of emergence phenomena in our control group. However, I would like to make it clear these adult patients were scheduled for lumbar spine surgery in the prone then supine position with a duration of surgery of 3 h and sufentanil 0.14 (SD 0.06) µg kg–1 h–1. All of these factors could be sufficient to produce emergence phenomena, even without air deflation of the ETT despite the cuff pressure measurement. We think that the adverse effects of tracheal tubation are underestimated, and in a prospective study we are now studying this in some detail.

J. P. Estebe

Rennes, France

References

1 Estebe JP, Delahaye S, Le Corre P, Dollo G, Chevanne F, Ecoffey C. Alkalinization of intra-cuff lidocaine and use of gel lubrication protect against tube-induced emergence phenomena. Br J Anaesth 2004; 92: 361–6[Abstract/Free Full Text]

2 British National Formulary, September 2002, p. 459

3 Tackley RM, Coe AJ. Alkalinised bupivicaine and adrenaline for epidural Caesarean section. Anaesthesia 1988; 43: 1019–21[ISI][Medline]

4 Dollo G, Estebe JP, Le Corre P, Chevanne F, Ecoffey C, Le Verge R. Endotracheal tube cuffs filled with lidocaine as a drug delivery system: in vivo and in vitro investigations. Eur J Pharm Sci 2001; 13: 319–23[CrossRef][ISI][Medline]

5 Bigeleisen PE, Wempe M. Identification of the precipitate in alkalinized solutions of mepivacaine and bupivacaine at 37°C. J Clin Pharm Ther 2001; 26: 171–3[CrossRef][ISI][Medline]

6 Bourget P, Bonhomme L, Benhamou D. Factors influencing precipitation of pH-adjusted bupivacaine solutions. J Clin Pharm Ther 1990; 15: 197–204[ISI][Medline]

7 Estebe JP, Dollo G, Le Corre P, Le Naoures A, Le Verge R, Ecoffey C. Alkalinization of intracuff lidocaine improves endotracheal-tube-induced emergence phenomena. Anesth Analg 2002; 94: 227–30[Abstract/Free Full Text]