Adequacy of preoperative safety checks of the Bain breathing system.

Effects of posture and baricity on spinal anaesthesia with 0.5% bupivacaine 5 ml. Spinal anaesthesia with 0.5 % bupivacaine 3 ml: comparison of plain and hyperbaric solutions administered to seated patients. POSTDURAL PUNCTURE HEADACHE Sir,—We read with interest the article by Lynch and colleagues [1] comparing the incidence of postdural puncture headaches (PDPH) associated with 22-gauge and 25-gauge Whitacre needles. As mentioned in the accompanying editorial, a significant factor affecting the incidence of PDPH is age. Lynch's group examined patients over a wide age range (15—81 yr). We feel that to include within die same group patients with such a well recognized difference in the incidence of PDPH, is inappropriate. Lynch and colleagues attempted to subdivide their patient groups further, but considering the previously demonstrated incidence of PDPH of less than 4 % (as stated by the authors) in younger patients [2,3], the number of patients needed to demonstrate a significant difference (P < 0.05) in PDPH, even in this susceptible group, would have to be much greater. We feel that it is important to stress that the stated result that there was "no significant difference between groups" does not mean that the 22-gaugc and 25-gauge Whitacre needles have clinically equivalent incidences of PDPH. Knowing the number of patients studied and the expected incidence of PDPH, there is a greater than 50% chance of finding no difference, between the two needles if, in fact, this is not the true situation. On examination of the published data, we were unable to reconcile the stated incidence of 0.9 % for PDPH in females older than 45 yr with the detailed patient characteristics shown in table III. Clarification would be helpful. It is important and clinically relevant to discover if a 25-gauge Whitacre needle has significant advantages over a 22-gauge and we hope that Dr Lynch and his colleagues are continuing their study so that this question may be answered. Use of a 25-gauge Whitacre needle to reduce the incidence of postdural puncture headache. Sir,—Thank you for the opportunity to respond to the letter from Drs Cooney and Tarpey. As the authors stated, the age factor in the aetiology of postdural puncture headache (PDPH) is indeed important, but as our study was designed also to look at the handling characteristics of the 25-gauge Whitacre needle, we feel that the inclusion of all age groups in the study was justified. Younger patients were still …