78
Correspondence Closed pipe
Next to exhaust valve
-d +I00 Pa -w a 3
0
v)
C K
-100 Pa
a.
b 1 Hour
-
Theatre doors opened
Fig. 1. Recordings taken from a sealed exhaust pipe from an exhaust hose in use.
50 Pa and 100 Pa applied to the exhaust hose was simply that the exhaust valve had to be tightened slightly to keep the reservoir bag full. In summary, the system in use at Salisbury works well in six theatres. Others have had as satisfactory’ or less satisfactory3 results with passive systems. The reason for varying results is not clear, but may be related to the need for careful siting of the exhaust terminal, ours being at roof level to avoid the wind pressures that build up on side walls. However, should a passive system be unsatisfactory because of back pressures, it may be ‘activated’ very simply by using an air mover.3 The principal reminder that the systems as a whole are working perfectly is the soft movement from flat sides 1-2 cm apart of the reservoir bag mounted on the safety block4 on the anaesthetic machine. This proves that there are neither strong positive nor
strong negative pressures developing in the system. Odstock Hospital, Salisbury,
J.A. LACK
SP2 8BJ
References
1. DHSS (1976) Pollution of operating departments etc. by Anaesthetic gases. Circitlar HC (76) 3 8 , Appendix I I , 2.2. 2. MEHTA, S., BEHR,G . , CHARI, J . & KENYON, D. (1977)
A passive method of disposal of expired anaesthetic gases. Brifish Journal of Anaesfhesia, 49, 589. 3 . ASBURY, A.J. & HANCOX, A.J. (1977) The evaluation of improvement of an antipollution system. British Journal of Anaesthesia, 49, 439. 4. BETHUNE,D.W., COLLIS,J.M. & LATIMER, R.D. (1976) A safety block for scavenging systems. Anaesthesia, 31, 1254.
Accidental injection of ephedrine into the epidural space Ephedrine is the vasopressor of choice in obstetrics when it becomes necessary to counter an excessive fall in blood pressure due to an epidural block. The main reason for the popularity of ephedrine in this situation is that it is only a weak vasoconstrictor, and most of its pressor action is attributable to myocardial stimulation.’ In spite of this it possesses some vascoconstrictor action which results among others in a decrease in uterine blood flow.’ The usual dose of ephedrine is 20-50 mg intravenously, and it has become the practice of some anaesthetists to prepare in advance a 50-mg dose diluted to 5 ml in saline just in case it should be needed. This solution was injected by mistake epidurally into two obstetric patients. The first patient, a 20-year-old primigravida, received an epidural block at a cervical dilatation of
2 cm for analgesia and to allow a forceps delivery if necessary. Localization of the epidural space was easy and a test-dose of 2 ml 1% lignocaine was given followed by the first effective dose, a mixture of 5 ml each of 2% chloroprocaine and 0.5% bupivacaine. When the second dose was required the midwife, by mistake, injected a syringe of 50 mg ephedrine in 5 ml saline. There was no complaint from the patient but understandably no analgesia was obtained, and, as soon as the mistake was realized, the medical staff was alerted. It was decided to continue with the block, and this was done with a total of 5 injections of 0.25% bupivacaine (10 ml) and a perineal dose of the chloroprocaine-bupivacaine mixture. Analgesia was entirely satisfactory throughout. The patient’s blood pressure rose t o 160/100 over the next few hours, with a moderate
Correspondence tachycardia (around 100 bpm). The child was delivered (without forceps) with an Apgar score of 9/10/10. The patient was closely observed and made a n entirely normal recovery. The second patient was a 28-years-old para 3. Epidural analgesia was initiated at the request of the obstetricians, at a cervical dilatation of 3 cm. Localization of the epidural space was easy, and a Portex catheter was introduced without difficulty. After a test-dose of lignocaine 1% (3 ml), a first dose of a mixture of chloroprocaine 2% 5 ml and bupivacaineO,S:/, 5 ml was injected, which produced satisfactory analgesia to a cutaneous level at T9 on the right side, and higher than the costal margin on the left side. Labour progressed swiftly and 52 min after the initial dose cervical dilatation was complete and a ‘perineal’ dose was to be given in the sitting position. In view of the higher than necessary cutaneous levels achieved with the first dose the volume was reduced to 8 ml. Unfortunately a prepared syringe of ephedrine, diluted to 10 ml, was injected instead. Again no untoward phenomena occurred during or immediately after the injection, but no analgesia was produced. Delivery was spontaneous 23 min after the injection of ephedrine. About 30 min later the blood pressure started to rise, from its value of 130/80 at the time of delivery to 180/90, and I & hr after the injection of ephedrine to 210/110; the patient complained of severe occipital headache. The pulse rate was slow, about 70/min. In view of the continuous rise of the blood pressure and headache, diazoxide 300 mg was given intravenously, which resulted in a fall of pressure to 140190. Simultaneously the pulse rate fose to 110, and, although the headache disappeared as soon as the blood pressure was reduced, the patient complained of the tachycardia. Propranolol 0.2 mg was given, which reduced the heart rate to 80-90/min. Both blood pressure and heart rate remained stable, at around 140/70 and 80-85 respectively, over the next 8 hr. The patient required no further treatment, and was discharged without sequelae. By comparison with the first patient, this second case necessitated the administration of an antihypertensive agent. Diazoxide is a valuable agent
79
which is unlikely to produce an excessive fall in blood pressure; its duration of action is not known precisely but is probably several hours or more. It is equally difficult to estimate the duration of action of ephedrine, but this may be of the order of 8-10 hours. The need for a second injection of diazoxide should therefore be kept in mind, even though i t was not necessary in our patient. Two conclusions can be drawn from these cases. Firstly, mistakes do and will occur and it is everyone’s duty to reduce the possibility of errors a s far as possible. The practice of having a syringe filled with ephedrine ready with other syringes containing local anaesthetics is, from that point of view, unsafe, even though, in this instance, the size of the syringes was different and they were properly labelled. A vasopressor is seldom needed-anyway hardly ever required so urgently-as to justify this potentially dangerous practice. Secondly, this unfortunate, though finally inconsequential, mistake is further support for the use of ephedrine as vasopressor in epidural blocks. It is likely that a pressor agent with a mainly vasoconstrictor action would not have proved so relatively harmless in the epidural space, especially since it was given a t a much higher concentration than that needed t o piolong the duration of action of a local anaesthetic. The association of vasoconstriction with hypotension can lead to ischaemic damage to nerve roots. Maternity Hospital, Lausanne, Switzerland
J. LODERER P.SUPPAN
References
1 . CRAWFORD, J.S. (1972) Principles and Practice of Obstetric Anaesthesia, 3rd edn, p. 185. Blackwell
Scientific Publications, Oxford. 2. JAMES, F.M., GHEISS,F.C. & KEMP,R.A. (1970)
Evaluation of pressor therapy for maternal hypotension during spinal anaesthesia. Anaesthesiology, 33, 25. 3 . HARRISON, P.D. (1975) Paraplegia following epidural analgesia. Anaesthesia, 30, 778.
Fenfluramine and halothane Some criticisms
As a clinician and researcher, I am disturbed by the article by Bennett & Eltringham (Anaesthesia, 1977, 32, 8) concerning a possible interaction between fenfluramine and halothane. I think the misconceptions generated by this article are significant and merit discussion. The case report and the ‘research’ almost defy
comment. Insufficient information is presented in the case report to allow any definitive conclusions to be made concerning the mechanisms of the cardiac arrest and the ‘research’ seems to be so illogically conceived and carried out that one again has difficulty in reaching any definitive conclusions in view of the fact that the species selected for their research is an inappropriate one in which to study the cardiovascular effects of
Correspondence Closed pipe
Next to exhaust valve
-d +I00 Pa -w a 3
0
v)
C K
-100 Pa
a.
b 1 Hour
-
Theatre doors opened
Fig. 1. Recordings taken from a sealed exhaust pipe from an exhaust hose in use.
50 Pa and 100 Pa applied to the exhaust hose was simply that the exhaust valve had to be tightened slightly to keep the reservoir bag full. In summary, the system in use at Salisbury works well in six theatres. Others have had as satisfactory’ or less satisfactory3 results with passive systems. The reason for varying results is not clear, but may be related to the need for careful siting of the exhaust terminal, ours being at roof level to avoid the wind pressures that build up on side walls. However, should a passive system be unsatisfactory because of back pressures, it may be ‘activated’ very simply by using an air mover.3 The principal reminder that the systems as a whole are working perfectly is the soft movement from flat sides 1-2 cm apart of the reservoir bag mounted on the safety block4 on the anaesthetic machine. This proves that there are neither strong positive nor
strong negative pressures developing in the system. Odstock Hospital, Salisbury,
J.A. LACK
SP2 8BJ
References
1. DHSS (1976) Pollution of operating departments etc. by Anaesthetic gases. Circitlar HC (76) 3 8 , Appendix I I , 2.2. 2. MEHTA, S., BEHR,G . , CHARI, J . & KENYON, D. (1977)
A passive method of disposal of expired anaesthetic gases. Brifish Journal of Anaesfhesia, 49, 589. 3 . ASBURY, A.J. & HANCOX, A.J. (1977) The evaluation of improvement of an antipollution system. British Journal of Anaesthesia, 49, 439. 4. BETHUNE,D.W., COLLIS,J.M. & LATIMER, R.D. (1976) A safety block for scavenging systems. Anaesthesia, 31, 1254.
Accidental injection of ephedrine into the epidural space Ephedrine is the vasopressor of choice in obstetrics when it becomes necessary to counter an excessive fall in blood pressure due to an epidural block. The main reason for the popularity of ephedrine in this situation is that it is only a weak vasoconstrictor, and most of its pressor action is attributable to myocardial stimulation.’ In spite of this it possesses some vascoconstrictor action which results among others in a decrease in uterine blood flow.’ The usual dose of ephedrine is 20-50 mg intravenously, and it has become the practice of some anaesthetists to prepare in advance a 50-mg dose diluted to 5 ml in saline just in case it should be needed. This solution was injected by mistake epidurally into two obstetric patients. The first patient, a 20-year-old primigravida, received an epidural block at a cervical dilatation of
2 cm for analgesia and to allow a forceps delivery if necessary. Localization of the epidural space was easy and a test-dose of 2 ml 1% lignocaine was given followed by the first effective dose, a mixture of 5 ml each of 2% chloroprocaine and 0.5% bupivacaine. When the second dose was required the midwife, by mistake, injected a syringe of 50 mg ephedrine in 5 ml saline. There was no complaint from the patient but understandably no analgesia was obtained, and, as soon as the mistake was realized, the medical staff was alerted. It was decided to continue with the block, and this was done with a total of 5 injections of 0.25% bupivacaine (10 ml) and a perineal dose of the chloroprocaine-bupivacaine mixture. Analgesia was entirely satisfactory throughout. The patient’s blood pressure rose t o 160/100 over the next few hours, with a moderate
Correspondence tachycardia (around 100 bpm). The child was delivered (without forceps) with an Apgar score of 9/10/10. The patient was closely observed and made a n entirely normal recovery. The second patient was a 28-years-old para 3. Epidural analgesia was initiated at the request of the obstetricians, at a cervical dilatation of 3 cm. Localization of the epidural space was easy, and a Portex catheter was introduced without difficulty. After a test-dose of lignocaine 1% (3 ml), a first dose of a mixture of chloroprocaine 2% 5 ml and bupivacaineO,S:/, 5 ml was injected, which produced satisfactory analgesia to a cutaneous level at T9 on the right side, and higher than the costal margin on the left side. Labour progressed swiftly and 52 min after the initial dose cervical dilatation was complete and a ‘perineal’ dose was to be given in the sitting position. In view of the higher than necessary cutaneous levels achieved with the first dose the volume was reduced to 8 ml. Unfortunately a prepared syringe of ephedrine, diluted to 10 ml, was injected instead. Again no untoward phenomena occurred during or immediately after the injection, but no analgesia was produced. Delivery was spontaneous 23 min after the injection of ephedrine. About 30 min later the blood pressure started to rise, from its value of 130/80 at the time of delivery to 180/90, and I & hr after the injection of ephedrine to 210/110; the patient complained of severe occipital headache. The pulse rate was slow, about 70/min. In view of the continuous rise of the blood pressure and headache, diazoxide 300 mg was given intravenously, which resulted in a fall of pressure to 140190. Simultaneously the pulse rate fose to 110, and, although the headache disappeared as soon as the blood pressure was reduced, the patient complained of the tachycardia. Propranolol 0.2 mg was given, which reduced the heart rate to 80-90/min. Both blood pressure and heart rate remained stable, at around 140/70 and 80-85 respectively, over the next 8 hr. The patient required no further treatment, and was discharged without sequelae. By comparison with the first patient, this second case necessitated the administration of an antihypertensive agent. Diazoxide is a valuable agent
79
which is unlikely to produce an excessive fall in blood pressure; its duration of action is not known precisely but is probably several hours or more. It is equally difficult to estimate the duration of action of ephedrine, but this may be of the order of 8-10 hours. The need for a second injection of diazoxide should therefore be kept in mind, even though i t was not necessary in our patient. Two conclusions can be drawn from these cases. Firstly, mistakes do and will occur and it is everyone’s duty to reduce the possibility of errors a s far as possible. The practice of having a syringe filled with ephedrine ready with other syringes containing local anaesthetics is, from that point of view, unsafe, even though, in this instance, the size of the syringes was different and they were properly labelled. A vasopressor is seldom needed-anyway hardly ever required so urgently-as to justify this potentially dangerous practice. Secondly, this unfortunate, though finally inconsequential, mistake is further support for the use of ephedrine as vasopressor in epidural blocks. It is likely that a pressor agent with a mainly vasoconstrictor action would not have proved so relatively harmless in the epidural space, especially since it was given a t a much higher concentration than that needed t o piolong the duration of action of a local anaesthetic. The association of vasoconstriction with hypotension can lead to ischaemic damage to nerve roots. Maternity Hospital, Lausanne, Switzerland
J. LODERER P.SUPPAN
References
1 . CRAWFORD, J.S. (1972) Principles and Practice of Obstetric Anaesthesia, 3rd edn, p. 185. Blackwell
Scientific Publications, Oxford. 2. JAMES, F.M., GHEISS,F.C. & KEMP,R.A. (1970)
Evaluation of pressor therapy for maternal hypotension during spinal anaesthesia. Anaesthesiology, 33, 25. 3 . HARRISON, P.D. (1975) Paraplegia following epidural analgesia. Anaesthesia, 30, 778.
Fenfluramine and halothane Some criticisms
As a clinician and researcher, I am disturbed by the article by Bennett & Eltringham (Anaesthesia, 1977, 32, 8) concerning a possible interaction between fenfluramine and halothane. I think the misconceptions generated by this article are significant and merit discussion. The case report and the ‘research’ almost defy
comment. Insufficient information is presented in the case report to allow any definitive conclusions to be made concerning the mechanisms of the cardiac arrest and the ‘research’ seems to be so illogically conceived and carried out that one again has difficulty in reaching any definitive conclusions in view of the fact that the species selected for their research is an inappropriate one in which to study the cardiovascular effects of
