1006
Correspondence
anaesthesia has to be recommended and none of the patients in the single space group in the study mentioned required conversion to general anaesthesia. Failure rates ranging from as low as 0.46% to as high as 35% have been quoted for subarachnoid anaesthesia [I]. We were disappointed to see a failure rate of 16% for subarachnoid anaesthesia in the single space group. This, we feel can be reduced to more acceptable levels by greater attention to technical detail, namely by using not only needles of appropriate size and resistance, but also by waiting for cerebrospinal fluid (CSF) to appear a t the hub of the needle prior to injecting. When using a single space technique, Randalls et al. [2] reported a failure rate of 4%, with a 26 gauge Quincke point needle, while Carrie and Donald, using a 26 gauge pencil point needle, reported no failures [3]. We have recently finished conducting a study which compared the resistance to fluid flow of the 26 gauge, 120 mm long Braiin spinal needle with that of the 27 gauge, 120 mm long Becton Dickinson (BD) needle. This was done by using a pressure infusion monitor pump (IVAC 560), a technique previously described by Morris et al. [4]. Surprisingly, we found that the mean resistance to fluid flow for the 26 gauge needle was twice the mean resistance for the 27 gauge needle. The findings of this experiment were confirmed by a controlled randomised study in 100 obstetric patients who required regional anaesthesia. We found that the time taken from dural puncture to appearance of CSF was on average about three times faster with the 27 gauge needle. The failure rate for subarachnoid anaesthesia with the 27 gauge needle was 4% and with the 26 gauge needle was 10%. These failure rates are lower than the 16% reported by Lyons and his colleagues. We feel that needles of low resistance can greatly increase the success rate of subarachnoid anaesthesia for a number of reasons. Firstly, the time taken for CSF to appear a t the hub of the needle is decreased and secondly, not only is aspiration of CSF during and after injection much easier, but also loss of local anaesthetic during injection is less likely. Finally, they are less likely to suffer from blockage and the ability to inject quickly and easily reduces the incidence of patchy blocks. In fact, some of the problems associated with needles of high resistance have already been highlighted by the authors in their evaluation of the 30 gauge needle for single space CSE technique (51. Since the completion of the above study we have used the 27 gauge needle in 190 patients with a failure rate of only 3%. The Middlesex Hospital. London WIN 8AA
M. PATEL A. SWAMI
References [ I ] MANCHIKANT~ L, HADLEY C, MARKWELLSJ, COLLIVER JA. A retrospective analysis of failed spinal anesthetic attempts in a community hospital. Anesthesia and Analgesia 1987; 66: 363-6. [2] RANDALLS B, BROADWAY JW, BROWNE DA, MORGAN B. Comparison of four subarachnoid solutions in a needle through needle technique for elective Caesarean section. British Journal of Anaesthesia 1991; 66: 314-8. [3] CARRIE LES, DONALD F. A 26 gauge pencil point needle for combined epidural anaesthesia for Caesarean section. Anaesthesia 1991; 46: 230-1. [4] MORRISR, ALLENP, VAN RENSBURG M, PHILIP JM. Report of a problem with a spinal needle. Anesthesia and Analgesia 1987; 66: 1 3 4 3 4 . [5] LESSER P, BEMBRIDGEM, LYONSG , MACDONALD R. An evaluation of a 30 gauge needle for spinal anaesthesia for Caesarean section. Anaesthesia 1990; 4 5 767-8.
We were interested to read the account of combined epidural/spinal anaesthesia for Caesarean section from Drs Lyons, Macdonald and Mikl (Anaesthesia 1992; 47: 199-201). We wish to make two observations. When discussing the ‘double space technique’ employing separate epidural and spinal punctures, the authors d o not make clear which procedure is performed first. A recent experience in this unit has led us to advise performing the epidural puncture before dural puncture. A large woman was scheduled for elective Caesarean section, and had requested regional anaesthesia. A combined technique using separate punctures had been explained and agreed. Dural puncture was achieved uneventfully at the L,, interspace by a n experienced senior registrar, with the woman sitting up. After injection of heavy bupivacaine, several attempts were made to site the epidural at L2-3.This proved extremely difficult, and after achieving a bloody tap with the epidural catheter, assistance was sought from the consultant obstetric anaesthetist. The epidural space was cannulated via the L3-4 interspace. Despite appropriate positioning, the level of spinal anaesthesia remained at T,, and it proved impossible to extend it above T, with the epidural. The woman was offered a second spinal but declined, and was given a general anaesthetic. Although siting the epidural catheter before performing spinal block carries a theoretical risk of transfixing the epidural catheter with the spinal needle, we have been unable to do this in vitro when using 24 gauge Sprotte or 25 gauge Whitacre tipped spinal needles. Once the epidural catheter has been successfully inserted dural puncture can proceed in an unhurried manner, rendering the technique suitable for teaching juniors. We are surprised at the failure rate of the ‘through needle’ technique reported. Since this technique was introduced into our maternity unit 4 months ago we have performed 78 Caesarean sections (emergency and elective) using Tuohy guided spinalanaesthesia with a I19 mm 25 g Whiteacre needle. In only one case was dural puncture impossible, and in three women the epidural was used to extend the level of spinal anaesthesia before starting surgery. This represents a failure rate of 5 % using Dr Lyons’ criteria. None of the junior anaesthetists had previous experience of the technique, but it has been accepted enthusiastically. Neither we nor our patients would choose to return to the technique of separate spinal and epidural punctures. Southampton General Hospital, Tremona Road Southampton SO9 4 X Y
E. ROBERTS D. BRIGHOUSE
A reply
Thank you for the opportunity to reply to Drs Roberts and Brighouse. We agree with their comments on order of procedure. At the time of writing we have performed 956 Caesarean sections using combined spinal/epidural anaesthesia and twice have attempted to introduce the ‘through the Tuohy’ technique. In our hands separate punctures work best. The point t o emphasise is, that whichever of these techniques is used, failure of regional anaesthesia, and recourse t o general anaesthesia, is a very rare event. St James University Hospital, Leeds LS9 7TF
G . LYONS R. MACDONALD B. MIKL
Correspondence
anaesthesia has to be recommended and none of the patients in the single space group in the study mentioned required conversion to general anaesthesia. Failure rates ranging from as low as 0.46% to as high as 35% have been quoted for subarachnoid anaesthesia [I]. We were disappointed to see a failure rate of 16% for subarachnoid anaesthesia in the single space group. This, we feel can be reduced to more acceptable levels by greater attention to technical detail, namely by using not only needles of appropriate size and resistance, but also by waiting for cerebrospinal fluid (CSF) to appear a t the hub of the needle prior to injecting. When using a single space technique, Randalls et al. [2] reported a failure rate of 4%, with a 26 gauge Quincke point needle, while Carrie and Donald, using a 26 gauge pencil point needle, reported no failures [3]. We have recently finished conducting a study which compared the resistance to fluid flow of the 26 gauge, 120 mm long Braiin spinal needle with that of the 27 gauge, 120 mm long Becton Dickinson (BD) needle. This was done by using a pressure infusion monitor pump (IVAC 560), a technique previously described by Morris et al. [4]. Surprisingly, we found that the mean resistance to fluid flow for the 26 gauge needle was twice the mean resistance for the 27 gauge needle. The findings of this experiment were confirmed by a controlled randomised study in 100 obstetric patients who required regional anaesthesia. We found that the time taken from dural puncture to appearance of CSF was on average about three times faster with the 27 gauge needle. The failure rate for subarachnoid anaesthesia with the 27 gauge needle was 4% and with the 26 gauge needle was 10%. These failure rates are lower than the 16% reported by Lyons and his colleagues. We feel that needles of low resistance can greatly increase the success rate of subarachnoid anaesthesia for a number of reasons. Firstly, the time taken for CSF to appear a t the hub of the needle is decreased and secondly, not only is aspiration of CSF during and after injection much easier, but also loss of local anaesthetic during injection is less likely. Finally, they are less likely to suffer from blockage and the ability to inject quickly and easily reduces the incidence of patchy blocks. In fact, some of the problems associated with needles of high resistance have already been highlighted by the authors in their evaluation of the 30 gauge needle for single space CSE technique (51. Since the completion of the above study we have used the 27 gauge needle in 190 patients with a failure rate of only 3%. The Middlesex Hospital. London WIN 8AA
M. PATEL A. SWAMI
References [ I ] MANCHIKANT~ L, HADLEY C, MARKWELLSJ, COLLIVER JA. A retrospective analysis of failed spinal anesthetic attempts in a community hospital. Anesthesia and Analgesia 1987; 66: 363-6. [2] RANDALLS B, BROADWAY JW, BROWNE DA, MORGAN B. Comparison of four subarachnoid solutions in a needle through needle technique for elective Caesarean section. British Journal of Anaesthesia 1991; 66: 314-8. [3] CARRIE LES, DONALD F. A 26 gauge pencil point needle for combined epidural anaesthesia for Caesarean section. Anaesthesia 1991; 46: 230-1. [4] MORRISR, ALLENP, VAN RENSBURG M, PHILIP JM. Report of a problem with a spinal needle. Anesthesia and Analgesia 1987; 66: 1 3 4 3 4 . [5] LESSER P, BEMBRIDGEM, LYONSG , MACDONALD R. An evaluation of a 30 gauge needle for spinal anaesthesia for Caesarean section. Anaesthesia 1990; 4 5 767-8.
We were interested to read the account of combined epidural/spinal anaesthesia for Caesarean section from Drs Lyons, Macdonald and Mikl (Anaesthesia 1992; 47: 199-201). We wish to make two observations. When discussing the ‘double space technique’ employing separate epidural and spinal punctures, the authors d o not make clear which procedure is performed first. A recent experience in this unit has led us to advise performing the epidural puncture before dural puncture. A large woman was scheduled for elective Caesarean section, and had requested regional anaesthesia. A combined technique using separate punctures had been explained and agreed. Dural puncture was achieved uneventfully at the L,, interspace by a n experienced senior registrar, with the woman sitting up. After injection of heavy bupivacaine, several attempts were made to site the epidural at L2-3.This proved extremely difficult, and after achieving a bloody tap with the epidural catheter, assistance was sought from the consultant obstetric anaesthetist. The epidural space was cannulated via the L3-4 interspace. Despite appropriate positioning, the level of spinal anaesthesia remained at T,, and it proved impossible to extend it above T, with the epidural. The woman was offered a second spinal but declined, and was given a general anaesthetic. Although siting the epidural catheter before performing spinal block carries a theoretical risk of transfixing the epidural catheter with the spinal needle, we have been unable to do this in vitro when using 24 gauge Sprotte or 25 gauge Whitacre tipped spinal needles. Once the epidural catheter has been successfully inserted dural puncture can proceed in an unhurried manner, rendering the technique suitable for teaching juniors. We are surprised at the failure rate of the ‘through needle’ technique reported. Since this technique was introduced into our maternity unit 4 months ago we have performed 78 Caesarean sections (emergency and elective) using Tuohy guided spinalanaesthesia with a I19 mm 25 g Whiteacre needle. In only one case was dural puncture impossible, and in three women the epidural was used to extend the level of spinal anaesthesia before starting surgery. This represents a failure rate of 5 % using Dr Lyons’ criteria. None of the junior anaesthetists had previous experience of the technique, but it has been accepted enthusiastically. Neither we nor our patients would choose to return to the technique of separate spinal and epidural punctures. Southampton General Hospital, Tremona Road Southampton SO9 4 X Y
E. ROBERTS D. BRIGHOUSE
A reply
Thank you for the opportunity to reply to Drs Roberts and Brighouse. We agree with their comments on order of procedure. At the time of writing we have performed 956 Caesarean sections using combined spinal/epidural anaesthesia and twice have attempted to introduce the ‘through the Tuohy’ technique. In our hands separate punctures work best. The point t o emphasise is, that whichever of these techniques is used, failure of regional anaesthesia, and recourse t o general anaesthesia, is a very rare event. St James University Hospital, Leeds LS9 7TF
G . LYONS R. MACDONALD B. MIKL
