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INTRATHECAL OR EXTRADURAL: WHICH APPROACH FOR SURGERY?
" / would have everie man write what he knowes and no more.'"—MONTAIGNE
BRITISH
JOURNAL
OF
ANAESTHESIA
VOLUME 59, No. 4
APRIL 1987 EDITORIAL
INTRATHECAL OR EXTRADURAL: WHICH APPROACH FOR SURGERY?
be more associated with the development of unilateral blockade than are single injections. What of the time course of the block? A rapid onset after extradural injection may be obtained by using 2% lignocaine with adrenaline, but its duration may be inadequate for a number of common surgical procedures. Bupivacaine 0.5 % will give a longer duration, but the use of this solution is probably responsible for the reputation that extradural block has for being slow and "patchy" in onset. The relatively recent availability of 0.75% bupivacaine overcomes this problem and can produce an extradural block that is almost as rapid in onset as intrathecal techniques. The injection of up to 15 ml at low lumbar level produces very reliable conditions for lower limb surgery in a short period of time— especially if the anaesthetist is prepared to supplement the block with light sedation. Analgesia persists for several hours, generally for longer than it does after intrathecal block. Many anaesthetists seem reluctant to use the concentrated solution of bupivacaine because of the reports of severe systemic reactions after its injection. A number of these cases were in obstetric patients and this led to the inclusion in the data sheet of a warning against the use of this concentration during labour. It would be a brave anaesthetist who used it in that situation at present, although the proscription is quite illogical and merits reconsideration. Used with full awareness that it is a very concentrated solution, 0.75 % bupivacaine is no more dangerous than any other local anaesthetic preparation. One of the great features of extradural blockade is that its distribution can be varied to suit the site of the operation, a point emphasized by Dogliotti in his original description. Intrathecal injection is always performed at low lumbar level, and the concentration of local anaesthetic is greatest in the nerves of the cauda equina. As the solution spreads cranially, so its concentration decreases. Thus, the duration of blockade is shorter in the upper dermatomes and this can produce the distressing
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2015
Traditional teaching presents the anaesthetist with some fairly standard attitudes to guide his choice between the intrathecal and extradural approaches to spinal anaesthesia. The intrathecal technique is usually described as easier to learn, quicker to perform, clearer in the endpoint of successful needle positioning, more rapid in onset and more controllable in its spread than extradural blockade. It requires a smaller dose of local anaesthetic, yet will produce a profound degree of blockade which is more consistent in its distribution—"missed" segments (as distinct from inadequate spread) being very rare after intrathecal injection. For these reasons, the intrathecal approach is usually preferred for a single injection technique, and the extradural when a catheter is needed to prolong blockade into the postoperative period. However, the intrathecal method has some disadvantages which the extradural does not. The most discussed is the headache that can occur after dural puncture, particularly in the young, pregnant female. Careful technique can minimize its incidence, but nobody should use intrathecal blockade if they cannot deal with this complication. Since extradural blood patch is now the definitive treatment, the modern anaesthetist must be skilled in both techniques. If this is the case, why is extradural blockade not preferred more often for a single injection technique? The standard arguments have been presented, but do they stand up to critical analysis? The actual process of extradural needle insertion should take no longer than lumbar puncture. Indeed, the delay while the free flow of cerebrospinal fluid through a fine-gauge needle is confirmed may make the latter technique slower. It is the subsequent insertion of a catheter, with appropriate verification of its position, that delays extradural block. If a catheter is not inserted, time is saved and the risks of the two dreaded complications of extradural blockade (i.v. and intrathecal injection of a large dose of local anaesthetic) are almost nil. Catheters also seem to
398
blockade. The only alternatives are the plain solutions of lignocaine and bupivacaine, which are not isobaric and cannot be relied upon to produce blockade to the level of the inguinal ligament yet, frequently, (bupivacaine in particular) cause very extensive blockade. Recent years have seen a great reawakening of interest in intrathecal blockade. In no other way can an anaesthetist obtain so much effect for the injection of so little drug, and for many patients and procedures it is the regional method of choice. The elderly patient in poor general condition who requires amputation of a leg is best served by the production of a profound block with the smallest possible dose of local anaesthetic. Transurethral resection of the prostate needs analgesia of the low thoracic segments to block the discomfort of bladder distension as well as profound blockade of the sacral segments. Again, a properly chosen intrathecal technique is the best way to achieve this. In many other surgical situations, an extradural technique, based on the» principles outlined above, can provide all the benefits of intrathecal blockade and also avoid some of its problems. Every time that a spinal anaesthetic is considered for a patient, careful thought should be given as to which is the more appropriate approach to its administration. J.A.W. Wildsmith
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2015
situation where a patient who has had an inguinal hernia repaired can have wound pain, but totally blocked legs. Such total paralysis is in fact fairly unusual during extradural blockade with the doses of 0.75% bupivacaine mentioned above. If an extradural injection is performed at the same dermatomal level as that at which the wound is to be made, the greatest concentration of drug will be in the most relevant nerves. The patient becomes aware of pain only when all other features of the block have regressed. If this "segmental" approach to extradural block is used, it can be very reliable. With intrathecal injection, spread from the lumbar region depends on the properties of the solution injected and the way in which they are manipulated. Ideally, any local anaesthetic prepared for intrathecal use should be available in a range of baricities, or in a form that allows its baricity to be adjusted before injection. In North America, the commercial preparations of amethocaine meet this requirement and its isobaric form will produce good blockade of the legs and perineum with minimal thoracic spread. Currently, this agent is unavailable in the U.K., where the only preparation specifically marketed for intrathecal use is hyperbaric bupivacaine. In the supine patient, this produces a block that is usually far more extensive than is needed for the sort of surgery commonly performed under intrathecal
BRITISH JOURNAL OF ANAESTHESIA
BRITISH
JOURNAL
OF
ANAESTHESIA
VOLUME 59, No. 4
APRIL 1987 EDITORIAL
INTRATHECAL OR EXTRADURAL: WHICH APPROACH FOR SURGERY?
be more associated with the development of unilateral blockade than are single injections. What of the time course of the block? A rapid onset after extradural injection may be obtained by using 2% lignocaine with adrenaline, but its duration may be inadequate for a number of common surgical procedures. Bupivacaine 0.5 % will give a longer duration, but the use of this solution is probably responsible for the reputation that extradural block has for being slow and "patchy" in onset. The relatively recent availability of 0.75% bupivacaine overcomes this problem and can produce an extradural block that is almost as rapid in onset as intrathecal techniques. The injection of up to 15 ml at low lumbar level produces very reliable conditions for lower limb surgery in a short period of time— especially if the anaesthetist is prepared to supplement the block with light sedation. Analgesia persists for several hours, generally for longer than it does after intrathecal block. Many anaesthetists seem reluctant to use the concentrated solution of bupivacaine because of the reports of severe systemic reactions after its injection. A number of these cases were in obstetric patients and this led to the inclusion in the data sheet of a warning against the use of this concentration during labour. It would be a brave anaesthetist who used it in that situation at present, although the proscription is quite illogical and merits reconsideration. Used with full awareness that it is a very concentrated solution, 0.75 % bupivacaine is no more dangerous than any other local anaesthetic preparation. One of the great features of extradural blockade is that its distribution can be varied to suit the site of the operation, a point emphasized by Dogliotti in his original description. Intrathecal injection is always performed at low lumbar level, and the concentration of local anaesthetic is greatest in the nerves of the cauda equina. As the solution spreads cranially, so its concentration decreases. Thus, the duration of blockade is shorter in the upper dermatomes and this can produce the distressing
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2015
Traditional teaching presents the anaesthetist with some fairly standard attitudes to guide his choice between the intrathecal and extradural approaches to spinal anaesthesia. The intrathecal technique is usually described as easier to learn, quicker to perform, clearer in the endpoint of successful needle positioning, more rapid in onset and more controllable in its spread than extradural blockade. It requires a smaller dose of local anaesthetic, yet will produce a profound degree of blockade which is more consistent in its distribution—"missed" segments (as distinct from inadequate spread) being very rare after intrathecal injection. For these reasons, the intrathecal approach is usually preferred for a single injection technique, and the extradural when a catheter is needed to prolong blockade into the postoperative period. However, the intrathecal method has some disadvantages which the extradural does not. The most discussed is the headache that can occur after dural puncture, particularly in the young, pregnant female. Careful technique can minimize its incidence, but nobody should use intrathecal blockade if they cannot deal with this complication. Since extradural blood patch is now the definitive treatment, the modern anaesthetist must be skilled in both techniques. If this is the case, why is extradural blockade not preferred more often for a single injection technique? The standard arguments have been presented, but do they stand up to critical analysis? The actual process of extradural needle insertion should take no longer than lumbar puncture. Indeed, the delay while the free flow of cerebrospinal fluid through a fine-gauge needle is confirmed may make the latter technique slower. It is the subsequent insertion of a catheter, with appropriate verification of its position, that delays extradural block. If a catheter is not inserted, time is saved and the risks of the two dreaded complications of extradural blockade (i.v. and intrathecal injection of a large dose of local anaesthetic) are almost nil. Catheters also seem to
398
blockade. The only alternatives are the plain solutions of lignocaine and bupivacaine, which are not isobaric and cannot be relied upon to produce blockade to the level of the inguinal ligament yet, frequently, (bupivacaine in particular) cause very extensive blockade. Recent years have seen a great reawakening of interest in intrathecal blockade. In no other way can an anaesthetist obtain so much effect for the injection of so little drug, and for many patients and procedures it is the regional method of choice. The elderly patient in poor general condition who requires amputation of a leg is best served by the production of a profound block with the smallest possible dose of local anaesthetic. Transurethral resection of the prostate needs analgesia of the low thoracic segments to block the discomfort of bladder distension as well as profound blockade of the sacral segments. Again, a properly chosen intrathecal technique is the best way to achieve this. In many other surgical situations, an extradural technique, based on the» principles outlined above, can provide all the benefits of intrathecal blockade and also avoid some of its problems. Every time that a spinal anaesthetic is considered for a patient, careful thought should be given as to which is the more appropriate approach to its administration. J.A.W. Wildsmith
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2015
situation where a patient who has had an inguinal hernia repaired can have wound pain, but totally blocked legs. Such total paralysis is in fact fairly unusual during extradural blockade with the doses of 0.75% bupivacaine mentioned above. If an extradural injection is performed at the same dermatomal level as that at which the wound is to be made, the greatest concentration of drug will be in the most relevant nerves. The patient becomes aware of pain only when all other features of the block have regressed. If this "segmental" approach to extradural block is used, it can be very reliable. With intrathecal injection, spread from the lumbar region depends on the properties of the solution injected and the way in which they are manipulated. Ideally, any local anaesthetic prepared for intrathecal use should be available in a range of baricities, or in a form that allows its baricity to be adjusted before injection. In North America, the commercial preparations of amethocaine meet this requirement and its isobaric form will produce good blockade of the legs and perineum with minimal thoracic spread. Currently, this agent is unavailable in the U.K., where the only preparation specifically marketed for intrathecal use is hyperbaric bupivacaine. In the supine patient, this produces a block that is usually far more extensive than is needed for the sort of surgery commonly performed under intrathecal
BRITISH JOURNAL OF ANAESTHESIA