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.)
Hull, UK
Castlebar, Ireland
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 kg1 h1. 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.
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: 3616
2 British National Formulary, September 2002, p. 459
3 Tackley RM, Coe AJ. Alkalinised bupivicaine and adrenaline for epidural Caesarean section. Anaesthesia 1988; 43: 101921[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: 31923[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: 1713[CrossRef][ISI][Medline]
6 Bourget P, Bonhomme L, Benhamou D. Factors influencing precipitation of pH-adjusted bupivacaine solutions. J Clin Pharm Ther 1990; 15: 197204[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: 22730