BRITISH JOURNAL OF ANAESTHESIA
84 A SIMPLE RE-USABLE ELECTRODE SYSTEM
PETER M. H. PIKE
Liestal, Switzerland
alone. In my experience, alcuronium in combination with halothane 0.5-1.0% provides smooth operating conditions and residual neuromuscular block is antagonized easily after 15-20 min. M. E. DODSON
Manchester REFERENCE
Datta, S., Crocker, J. S., and Alper, M. H. (1977). Muscle pain following administration of suxamethonium to pregnant and non-pregnant patients undergoing laparoscopic tubal ligation. Br. J. Anaesth., 49, 625. Sir,—Thank you for the opportunity to reply to Dr Dodson's letter. We agree that a non-depolarizing relaxant like alcuronium might be a good substitute for suxamethonium in laparoscopic tubal ligation. We are also aware of the frequent occurrence after this surgical procedure of shoulder pain which is probably the result of diaphragmatic irritation by the intraperitoneal insufflation of carbon dioxide. We noticed a 50% incidence of shoulder pain in our study and, interestingly enough, it was more common in the right shoulder. However, there was no difference in the incidence of shoulder pain between the non-pregnant and pregnant groups. That is why we excluded shoulder pain from our definition of "suxamethonium pain". Any patient who complained only of shoulder pain was not included in our study. While we did not consider pain in the neck and the rib cage to be related to carbon dioxide irritation, we are interested in Dr Dodson's speculation that the reduced incidence of rib and neck pain in pregnant patients may be a result of more rapid absorption of carbon dioxide because of increased vascularity. This hypothesis would be difficult to test. S. DATTA J. S. CROCKER M. H. ALPER
Boston, Massachusetts LAPAROSCOPY AND SUXAMETHONIUM MUSCLE PAIN
Sir,—I was interested to read the article by Datta, Crocker and Alper (1977) on the incidence, following laparoscopy, of muscle pain in patients to whom suxamethonium had been administered. I am surprised that the authors have considered suxamethonium as the sole cause of postoperative pain in these patients. It is my practice to use alcuronium and not suxamethonium, and in 13 patients examined recently mild to moderate pain round the ribs, neck and shoulders was present following operation in 10. In three patients the pain was severe enough to require a narcotic analgesic. It must be assumed that this was caused by residual carbon dioxide irritating the diaphragm with referred pain to the neck and shoulders. The irritant nature of carbon dioxide is manifest by the pain experienced by the patient in whom the gas is insufflated into the abdominal wall and not into the abdominal cavity. It can be postulated that the decreased incidence of such pain in pregnant patients having laparoscopy may result from the greater vascularity of the pelvic peritonium with more rapid absorption of residual carbon dioxide. It is perhaps unfair to add suxamethonium-induced pain to that which these patients experience from the procedure
PROFOUND HYPOTENSION FOR MIDDLE EAR SURGERY
Sir,—There are a number of disturbing aspects to the recent article describing profound hypotension for middle ear surgery (Kerr, 1977). Those anaesthetists who have been practising induced hypotension for many years must feel uneasy at the low values of arterial pressure which were the object of the technique. Orthodox opinion regards the lowest level of systolic arterial pressure which may be induced with safety as approx. 60 mm Hg. Since normal intracranial pressure is considered usually to be 5-13 mm Hg, Dr Kerr's patient with a mean arterial pressure of 20 mm Hg had a cerebral perfusion pressure of 7-15 mm Hg. It is difficult to imagine that this pressure is adequate to perfuse a large, complex and highly vulnerable organ such as the brain. Current knowledge of the physiology of cerebral blood flow is too inadequate to employ these low perfusion pressures. In addition, Dr Kerr assumes that the relationship between blood loss and arterial pressure is linear, and that the lower the arterial pressure the better will be the operating conditions. This assumption has never been examined adequately, but a clinical impression exists, for which there is some evidence (Donald, 1969), that the
Downloaded from http://bja.oxfordjournals.org/ at New York University on May 28, 2015
Sir,—The quest for a simple, inexpensive e.c.g. electrode system has been fulfilled largely by the semi-disposable card electrodes which are placed under the patient's shoulder. Their ease of use has offset certain disadvantages including a restricted range, a small amplitude trace, and liability to electrode bridging when soiled by blood or sterilizing solutions. Unreadable traces may be produced when they are used on patients in the lateral or prone position. With a relatively short life, they are comparatively expensive. Owners of a clamp-electrode system can increase its versatility and achieve economies with a readily made elegant substitute. The principle remains the same, that of a conductive foil on a pliable base. The foil strips are cut from rolls of industrial aluminium conductive tape (3M Company, tape No. X-1170). As a base, templates from spent x-ray film are eminently suitable, for they do not tear, are washable and hug the contours of the patient's body. Experience has shown that the presently used alignment of foil on the electrode is best for use in the supine position. Good recordings may be obtained also from a precordial application. For this purpose a low profile pear-shape is more appropriate and it may be fixed in place with a 500-g sand sack. Electrode paste is unnecessary and the trace is not influenced by respiratory excursions. The pear-shaped electrode system is also suitable for prone patients. In the lateral position, the greater flexibility of celluloid film produces a greater area of contact than the cardboard-backed electrode system. The trace amplitude is equal to, or better than, that of commercial systems. A little experimentation with the splay of the foil strips on the film may reward the user with an e.c.g. tracing more appropriate to his needs than that obtained from the disposable card electrode.
CORRESPONDENCE
85
J. R. DONALD Glasgow REFERENCES
Donald, J. R. (1969). The effect of anaesthesia, hypotension and epidural analgesia on blood loss in surgery for pelvic floor repair. Br. J. Anaesth., 41, 155. Kerr, A. R. (1977). Anaesthesia with profound hypotension for middle ear surgery. Br. J. Anaesth., 49, 447. Sir,—Dr Donald's remarks and criticisms of my paper on profound hypotension are entirely predictable in the light of existing knowledge and opinions. I must emphasize that these arterial pressures were applied only in micro-surgery, where blood loss is so small that it can be discounted. I fully agree that to a large extent there is a relationship between blood loss and arterial pressure, but this applies only to "open" surgery, and Dr Donald's paper and remarks are applied to this type of operation. Unfortunately, these circumstances do not apply to micro-aural surgery, since microscopic "bleeding" appears to continue with little abatement at arterial pressures as low as 50 mm Hg. We have observed various techniques in a few other centres and we are convinced that the haemostasis produced by our method is superior to any other. Although only 700 patients were described in my publication (Kerr, 1977), over the past 12 years I have used the
technique on nearly double this number, with similar results and no complications. Physiological studies were carried out on several of the patients by Professor D. G. McDowall (personal communication). E.e.g. monitoring, arterial and jugular bulb blood samples for measurement of oxygen content and lactate/pyruvate ratios showed that brain oxygenation was being maintained adequately even at systolic arterial pressures as low as 20 mm Hg. Peripheral blood flow is always observed carefully and it is evident that this continues normally in spite of the supposedly tiny venous capillary pressures. That all these patients have survived this technique unscathed, together with the physiological measurements described above, suggests that so-called orthodox opinion was changed regarding induced hypotension, and that our previous assumptions may be erroneous. It is my belief that complications, reported elsewhere, have occurred as a result of hypotension in conjunction with controlled ventilation. This would seem to constitute a dangerous combination even at the expert hands of Barron (1976). Dr Donald is correct when he points out that the failure rate is high in some age groups. I make no claim that my technique is perfect and I am constantly modifying it to try to obtain more consistent results, and to render it as safe as possible. However, when it works well it produces the driest field we have seen with apparent absolute safety. A. R. KERR Huddersfield REFERENCES
Barron, D. W. (1976). Anaesthetic management of microsurgical operations on the ear. J. Laryngol. Otol., 4, 401. Kerr, A. R. (1977). Anaesthesia with profound hypotension for middle ear surgery. Br. J. Anaesth., 49, 447. AN UNUSUAL CAUSE OF RESPIRATORY OBSTRUCTION
Sir,—Anaesthesia is requested frequently for patients with a foreign body in the respiratory tract. However, in the following case report, I was confronted by a foreign body complicating anaesthesia. A 24-yr-old Indian woman presented with bilateral breast abscesses. Examination before anaesthesia revealed no other abnormalities. Premedication comprised atropine 0.6 mg i.v. and this was followed immediately by 250 mg of thiopentone 2.5%. When loss of consciousness occurred, the respiratory tract became obstructed despite attempts to turn the head to one side and protrude the mandible. An oropharyngeal airway was inserted, with no improvement. Laryngoscopy was performed, which showed the oropharynx was full of pieces of betel-nut (or pan-supari, as it is termed in India), which were removed laboriously with a Magill forceps. After the oropharynx was cleared of foreign bodies, the lungs were inflated with oxygen and subsequently anaesthesia was uneventful. In India it is a common practice to chew continually a betel-leaf with tobacco and nuts. Therefore it is desirable to inspect the oral cavity before administering anaesthesia. It is hoped that this case may illustrate the potential dangers of addiction to betel-nut chewing in the Indian population. C. V. SINGH
Rohtak (Haryana), India
Downloaded from http://bja.oxfordjournals.org/ at New York University on May 28, 2015
lowest arterial pressure necessary to produce maximal effects on blood loss is about 90-110 mm Hg. Any decrease in arterial pressure to less than this value increases anaesthetic morbidity and mortality without improving operating conditions. The literature on blood loss and arterial pressure contains many assumptions and deductions based on inadequate data. The most misleading assumption is that arterial pressure is a major factor in producing surgical bleeding. However, any critical reading of the literature on blood loss reveals two factors which are common to all carefully conducted series. The first is that the blood loss varies widely and the second is that hypotension to a systolic pressure of 60 mm Hg reduces blood loss on average by 50%. This suggests that some patients bleed extensively during surgery, while others bleed to a small extent, and the reasons for this phenomenon are largely unknown. Orthodox hypotension reduces bleeding by only 50%, which is small when the influence of the other unknown factors are considered. In my own series (Donald, 1969) the range of blood loss at pelvic floor repair was 32-1200 ml, which is fairly representative of all studies. Dr Kerr's study also suggests that arterial pressure is not a major factor in reducing bleeding, as there was a failure rate of up to 39.3% depending on the patient's age, despite very low arterial pressures. Dr Kerr would make a significant contribution to the literature on this subject if he would measure blood loss and relate it to different arterial pressures, and include a control group whose arterial pressure is unchanged. I suspect that he would find that many patients exhibit good operating conditions with normal or near normal arterial pressures. The real challenge in this field lies in defining these other unknown factors, with a view to reproducing the relatively bloodless field which occurs so commonly without any interference from the anaesthetist.
84 A SIMPLE RE-USABLE ELECTRODE SYSTEM
PETER M. H. PIKE
Liestal, Switzerland
alone. In my experience, alcuronium in combination with halothane 0.5-1.0% provides smooth operating conditions and residual neuromuscular block is antagonized easily after 15-20 min. M. E. DODSON
Manchester REFERENCE
Datta, S., Crocker, J. S., and Alper, M. H. (1977). Muscle pain following administration of suxamethonium to pregnant and non-pregnant patients undergoing laparoscopic tubal ligation. Br. J. Anaesth., 49, 625. Sir,—Thank you for the opportunity to reply to Dr Dodson's letter. We agree that a non-depolarizing relaxant like alcuronium might be a good substitute for suxamethonium in laparoscopic tubal ligation. We are also aware of the frequent occurrence after this surgical procedure of shoulder pain which is probably the result of diaphragmatic irritation by the intraperitoneal insufflation of carbon dioxide. We noticed a 50% incidence of shoulder pain in our study and, interestingly enough, it was more common in the right shoulder. However, there was no difference in the incidence of shoulder pain between the non-pregnant and pregnant groups. That is why we excluded shoulder pain from our definition of "suxamethonium pain". Any patient who complained only of shoulder pain was not included in our study. While we did not consider pain in the neck and the rib cage to be related to carbon dioxide irritation, we are interested in Dr Dodson's speculation that the reduced incidence of rib and neck pain in pregnant patients may be a result of more rapid absorption of carbon dioxide because of increased vascularity. This hypothesis would be difficult to test. S. DATTA J. S. CROCKER M. H. ALPER
Boston, Massachusetts LAPAROSCOPY AND SUXAMETHONIUM MUSCLE PAIN
Sir,—I was interested to read the article by Datta, Crocker and Alper (1977) on the incidence, following laparoscopy, of muscle pain in patients to whom suxamethonium had been administered. I am surprised that the authors have considered suxamethonium as the sole cause of postoperative pain in these patients. It is my practice to use alcuronium and not suxamethonium, and in 13 patients examined recently mild to moderate pain round the ribs, neck and shoulders was present following operation in 10. In three patients the pain was severe enough to require a narcotic analgesic. It must be assumed that this was caused by residual carbon dioxide irritating the diaphragm with referred pain to the neck and shoulders. The irritant nature of carbon dioxide is manifest by the pain experienced by the patient in whom the gas is insufflated into the abdominal wall and not into the abdominal cavity. It can be postulated that the decreased incidence of such pain in pregnant patients having laparoscopy may result from the greater vascularity of the pelvic peritonium with more rapid absorption of residual carbon dioxide. It is perhaps unfair to add suxamethonium-induced pain to that which these patients experience from the procedure
PROFOUND HYPOTENSION FOR MIDDLE EAR SURGERY
Sir,—There are a number of disturbing aspects to the recent article describing profound hypotension for middle ear surgery (Kerr, 1977). Those anaesthetists who have been practising induced hypotension for many years must feel uneasy at the low values of arterial pressure which were the object of the technique. Orthodox opinion regards the lowest level of systolic arterial pressure which may be induced with safety as approx. 60 mm Hg. Since normal intracranial pressure is considered usually to be 5-13 mm Hg, Dr Kerr's patient with a mean arterial pressure of 20 mm Hg had a cerebral perfusion pressure of 7-15 mm Hg. It is difficult to imagine that this pressure is adequate to perfuse a large, complex and highly vulnerable organ such as the brain. Current knowledge of the physiology of cerebral blood flow is too inadequate to employ these low perfusion pressures. In addition, Dr Kerr assumes that the relationship between blood loss and arterial pressure is linear, and that the lower the arterial pressure the better will be the operating conditions. This assumption has never been examined adequately, but a clinical impression exists, for which there is some evidence (Donald, 1969), that the
Downloaded from http://bja.oxfordjournals.org/ at New York University on May 28, 2015
Sir,—The quest for a simple, inexpensive e.c.g. electrode system has been fulfilled largely by the semi-disposable card electrodes which are placed under the patient's shoulder. Their ease of use has offset certain disadvantages including a restricted range, a small amplitude trace, and liability to electrode bridging when soiled by blood or sterilizing solutions. Unreadable traces may be produced when they are used on patients in the lateral or prone position. With a relatively short life, they are comparatively expensive. Owners of a clamp-electrode system can increase its versatility and achieve economies with a readily made elegant substitute. The principle remains the same, that of a conductive foil on a pliable base. The foil strips are cut from rolls of industrial aluminium conductive tape (3M Company, tape No. X-1170). As a base, templates from spent x-ray film are eminently suitable, for they do not tear, are washable and hug the contours of the patient's body. Experience has shown that the presently used alignment of foil on the electrode is best for use in the supine position. Good recordings may be obtained also from a precordial application. For this purpose a low profile pear-shape is more appropriate and it may be fixed in place with a 500-g sand sack. Electrode paste is unnecessary and the trace is not influenced by respiratory excursions. The pear-shaped electrode system is also suitable for prone patients. In the lateral position, the greater flexibility of celluloid film produces a greater area of contact than the cardboard-backed electrode system. The trace amplitude is equal to, or better than, that of commercial systems. A little experimentation with the splay of the foil strips on the film may reward the user with an e.c.g. tracing more appropriate to his needs than that obtained from the disposable card electrode.
CORRESPONDENCE
85
J. R. DONALD Glasgow REFERENCES
Donald, J. R. (1969). The effect of anaesthesia, hypotension and epidural analgesia on blood loss in surgery for pelvic floor repair. Br. J. Anaesth., 41, 155. Kerr, A. R. (1977). Anaesthesia with profound hypotension for middle ear surgery. Br. J. Anaesth., 49, 447. Sir,—Dr Donald's remarks and criticisms of my paper on profound hypotension are entirely predictable in the light of existing knowledge and opinions. I must emphasize that these arterial pressures were applied only in micro-surgery, where blood loss is so small that it can be discounted. I fully agree that to a large extent there is a relationship between blood loss and arterial pressure, but this applies only to "open" surgery, and Dr Donald's paper and remarks are applied to this type of operation. Unfortunately, these circumstances do not apply to micro-aural surgery, since microscopic "bleeding" appears to continue with little abatement at arterial pressures as low as 50 mm Hg. We have observed various techniques in a few other centres and we are convinced that the haemostasis produced by our method is superior to any other. Although only 700 patients were described in my publication (Kerr, 1977), over the past 12 years I have used the
technique on nearly double this number, with similar results and no complications. Physiological studies were carried out on several of the patients by Professor D. G. McDowall (personal communication). E.e.g. monitoring, arterial and jugular bulb blood samples for measurement of oxygen content and lactate/pyruvate ratios showed that brain oxygenation was being maintained adequately even at systolic arterial pressures as low as 20 mm Hg. Peripheral blood flow is always observed carefully and it is evident that this continues normally in spite of the supposedly tiny venous capillary pressures. That all these patients have survived this technique unscathed, together with the physiological measurements described above, suggests that so-called orthodox opinion was changed regarding induced hypotension, and that our previous assumptions may be erroneous. It is my belief that complications, reported elsewhere, have occurred as a result of hypotension in conjunction with controlled ventilation. This would seem to constitute a dangerous combination even at the expert hands of Barron (1976). Dr Donald is correct when he points out that the failure rate is high in some age groups. I make no claim that my technique is perfect and I am constantly modifying it to try to obtain more consistent results, and to render it as safe as possible. However, when it works well it produces the driest field we have seen with apparent absolute safety. A. R. KERR Huddersfield REFERENCES
Barron, D. W. (1976). Anaesthetic management of microsurgical operations on the ear. J. Laryngol. Otol., 4, 401. Kerr, A. R. (1977). Anaesthesia with profound hypotension for middle ear surgery. Br. J. Anaesth., 49, 447. AN UNUSUAL CAUSE OF RESPIRATORY OBSTRUCTION
Sir,—Anaesthesia is requested frequently for patients with a foreign body in the respiratory tract. However, in the following case report, I was confronted by a foreign body complicating anaesthesia. A 24-yr-old Indian woman presented with bilateral breast abscesses. Examination before anaesthesia revealed no other abnormalities. Premedication comprised atropine 0.6 mg i.v. and this was followed immediately by 250 mg of thiopentone 2.5%. When loss of consciousness occurred, the respiratory tract became obstructed despite attempts to turn the head to one side and protrude the mandible. An oropharyngeal airway was inserted, with no improvement. Laryngoscopy was performed, which showed the oropharynx was full of pieces of betel-nut (or pan-supari, as it is termed in India), which were removed laboriously with a Magill forceps. After the oropharynx was cleared of foreign bodies, the lungs were inflated with oxygen and subsequently anaesthesia was uneventful. In India it is a common practice to chew continually a betel-leaf with tobacco and nuts. Therefore it is desirable to inspect the oral cavity before administering anaesthesia. It is hoped that this case may illustrate the potential dangers of addiction to betel-nut chewing in the Indian population. C. V. SINGH
Rohtak (Haryana), India
Downloaded from http://bja.oxfordjournals.org/ at New York University on May 28, 2015
lowest arterial pressure necessary to produce maximal effects on blood loss is about 90-110 mm Hg. Any decrease in arterial pressure to less than this value increases anaesthetic morbidity and mortality without improving operating conditions. The literature on blood loss and arterial pressure contains many assumptions and deductions based on inadequate data. The most misleading assumption is that arterial pressure is a major factor in producing surgical bleeding. However, any critical reading of the literature on blood loss reveals two factors which are common to all carefully conducted series. The first is that the blood loss varies widely and the second is that hypotension to a systolic pressure of 60 mm Hg reduces blood loss on average by 50%. This suggests that some patients bleed extensively during surgery, while others bleed to a small extent, and the reasons for this phenomenon are largely unknown. Orthodox hypotension reduces bleeding by only 50%, which is small when the influence of the other unknown factors are considered. In my own series (Donald, 1969) the range of blood loss at pelvic floor repair was 32-1200 ml, which is fairly representative of all studies. Dr Kerr's study also suggests that arterial pressure is not a major factor in reducing bleeding, as there was a failure rate of up to 39.3% depending on the patient's age, despite very low arterial pressures. Dr Kerr would make a significant contribution to the literature on this subject if he would measure blood loss and relate it to different arterial pressures, and include a control group whose arterial pressure is unchanged. I suspect that he would find that many patients exhibit good operating conditions with normal or near normal arterial pressures. The real challenge in this field lies in defining these other unknown factors, with a view to reproducing the relatively bloodless field which occurs so commonly without any interference from the anaesthetist.
