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Interpleural analgesia
British Journal of Anaesthesia 1994; 72: 250-252
CORRESPONDENCE
Interpleural analgesia
J. RICHARDSON
Department of Anaesthesia S. SABANATHAN
Department of Cardio- Thoracic Surgery Bradford Royal Infirmary Bradford P . A. LONNQUIST
St Gdrans Paediatric Hospital Stockholm 1. Murphy DF. Interpleural analgesia. British Journal of Anaesthesia 1993; 71: 426-434. 2. Broome IJ, Sherry KM, Reilly CS. A combined chest drain and intrapleural catheter for post-thoracotomy pain relief. Anaesthesia 1993; 48: 724-762. 3. Rosenberg PH, Scheinin BM-A, Lepantalo MJA, Lindfors O. Continuous intrapleural infusion of bupivacaine for analgesia after ihoracotomy. Anesthesiology 1987; 67:811-813. 4. Ferrante FM, Chan VWS, Arthur GR, Rocco AG. Intrapleural analgesia afteT thoracotomy. Anesthesia and Analgesia 1991; 72: 105-109. 5. Lonnqvist PA, Hildinsson U. The caudal boundary of the paravertebral space. A study in human cadavers. Anaesthesia 1992; 47: 1051-1052. 6. EngJ, Sabanathan S. Site of action of continuous extrapleural intercostal nerve block. Annals of Thoracic Surgery 1991; 51: 387-389. 7. Sabanathan S, Richardson J, Mearns AJ. Management of pain in thoracic surgery. British Journal of Hospital Medicine 1993; 50: 114-120.
Sir,—While it is fair to say that local anaesthetic injected into the pleural or paravertebral spaces induces analgesia by inhibiting the same group of nerves, possibly by the same mechanism, clearly these are not identical tissue planes and some differences might be found between them. For all other indications, it is likely that interpleural, intercostal and paravcrtebral blocks may be used interchangeably, but at thoracotomy the tissue planes which would otherwise allow spread of local anaesthetic to reach distant intercostal nerves are disrupted and much of the local anaesthetic is lost. By locating specifically the intact tissue planes in the paravertebral gutter and
inserting the extradural catheter into this space under direct vision, Sabanathan and colleagues [1] have shown this technique to be consistently effective. This is likely to be the reason why these authors have achieved considerable success using this block for post-thoracotomy pain relief while others have found it to be inconsistent. I agree that in this situation it is simplistic to include both paravertebral and interpleural analgesia together. In my review of interpleural analgesia, this difference was cited specifically in the summary and conclusion of the article. D. F. MURPHY
Sir Charles Gairdner Hospital Perth, Western Australia 1. Sabanathan S, Mearns AJ, Bickford-Smith PJ, Eng J, Berrisford RG, Bibby SR, Majid MR. Efficacy of continuous extrapleural intercostal nerve block on postthoracotomy pain and pulmonary mechanics. British Journal of Surgery 1990; 77: 221-225.
Effect of nitrous oxide on cerebral blood flow Sir,—We read with interest the article by Field and colleagues [1], addressing the important issue of the effect of nitrous oxide on cerebral blood flow. The authors have shown that there is an increase in cerebral blood flow (CBF) after inhalation of 30-60 % nitrous oxide in oxygen. However, in their study, "baseline measurements" of CBF were made using 100% oxygen and not air. This is rather unfortunate and makes the conclusions drawn questionable. Hyperoxia (FiOt 0.85-1.0) has been known to cause vasoconstriction of the cerebral vessels [2], resulting in a decrease in global CBF by 11-14% of control values [3]. In our laboratory, Eintrei, Odman and Lund have shown a reduction of 40 % in cortical blood flow in pigs after inhalation of 100 % oxygen compared with air [4]. We have also found a significant decrease in capillary blood flow in the brain cortex after inhalation of increasing concentrations of oxygen using the hydrogen clearance technique [5]. Assuming that the normal global CBF level is in the range 50 ml/100 g min"1, the increase in CBF seen by Field and colleagues (8.6-9.8 ml/100 g min"') was less than 20% when nitrous oxide was added (and consequently the Fl Oi was reduced). In other words, the increase in flow seen after the addition of nitrous oxide may be explained, at least in part, by the decrease in inspired oxygen concentration and, the baseline values of CBF obtained by Field and colleagues using 100% oxygen, may have been falsely low. Therefore, could the increase in CBF after inhalation of nitrous oxide be the result of vasodilatation following a decrease in the inspired fraction of oxygen? F. SJOBERG
P. KjELLGREN A. GuTTA Department of Anaesthesiology and the Bums Unit University Hospital Linkoping, Sweden 1. Field LM, Dorrancc DE, Krzeminska EK, Barsoum LZ. Effect of nitrous oxide on blood flow in normal humans. British Journal of Anaesthesia 1993; 70: 154-159. 2. McDowall DG. Interrelationship between blood oxygen tension and cerebral blood flow. In: Payne JP, Hill DW, eds. Oxygen Measurements in Blood and Tissue. London: Churchill, 1966; 205-214. 3. Edvinsson L, MacKenzie ET, McCulloch J, eds. Changes in arterial gas tensions. In: Cerebral Blood Flow and Metabolism. New York: Raven Press, 1992: 524-552. 4. Eintrei C, Odman S, Lund N. Effects of increases in the inspired oxygen fraction on brain surface oxygen pressure fields and regional cerebral blood flow. Advances m Experimental and Medical Biology 1985; 191: 131-13*. 5. Eintrei C, Bergsten B, Gustafsson U, Malmqvist L-A, Sjoberg F. Selective reduction of high cerebral capillary
Downloaded from http://bja.oxfordjournals.org/ at Emory University on August 18, 2015
Sir,—We are concerned that the review by Murphy [1], which grouped together paravertebral analgesia and intrapleural analgesia and reviewed both subjects under the heading" interpleural analgesia" may worsen existing confusion between these different techniques. Instillation of local anaesthetic into the paravertebral or cxtrapleural space behaves differently from local anaesthetic injected between the parietal and visceral pleura and this is apparent in thoracic surgery. Post-thoracotomy intrapleural administration results in loss of up to 60% of anaesthetic solution dirough chest drains [2], mixing of the local anaesthetic with blood and fluid in the pleural space [3,4] and unimpeded gravitational pooling of solution in the dependent parts of the chest [3], all to the detriment of efficacy. We and others have demonstrated that solutions administered extrapleurally, on the other hand, remain confined but well distributed within the paravertebral space in close proximity to the intercostal nerve roots, their posterior primary rami and the sympathetic chain [5, 6]. Not only is post-thoracotomy pain relief reliably excellent, but blood concentrations of local anaesthetic are predictable and side effects are minimal [7], By combining research references from these two techniques, inconsistent results are explained adequately. These differences are much too important to be referred to as "variations on the technique of interpleural analgesia (with)... little to choose between them".
CORRESPONDENCE
Interpleural analgesia
J. RICHARDSON
Department of Anaesthesia S. SABANATHAN
Department of Cardio- Thoracic Surgery Bradford Royal Infirmary Bradford P . A. LONNQUIST
St Gdrans Paediatric Hospital Stockholm 1. Murphy DF. Interpleural analgesia. British Journal of Anaesthesia 1993; 71: 426-434. 2. Broome IJ, Sherry KM, Reilly CS. A combined chest drain and intrapleural catheter for post-thoracotomy pain relief. Anaesthesia 1993; 48: 724-762. 3. Rosenberg PH, Scheinin BM-A, Lepantalo MJA, Lindfors O. Continuous intrapleural infusion of bupivacaine for analgesia after ihoracotomy. Anesthesiology 1987; 67:811-813. 4. Ferrante FM, Chan VWS, Arthur GR, Rocco AG. Intrapleural analgesia afteT thoracotomy. Anesthesia and Analgesia 1991; 72: 105-109. 5. Lonnqvist PA, Hildinsson U. The caudal boundary of the paravertebral space. A study in human cadavers. Anaesthesia 1992; 47: 1051-1052. 6. EngJ, Sabanathan S. Site of action of continuous extrapleural intercostal nerve block. Annals of Thoracic Surgery 1991; 51: 387-389. 7. Sabanathan S, Richardson J, Mearns AJ. Management of pain in thoracic surgery. British Journal of Hospital Medicine 1993; 50: 114-120.
Sir,—While it is fair to say that local anaesthetic injected into the pleural or paravertebral spaces induces analgesia by inhibiting the same group of nerves, possibly by the same mechanism, clearly these are not identical tissue planes and some differences might be found between them. For all other indications, it is likely that interpleural, intercostal and paravcrtebral blocks may be used interchangeably, but at thoracotomy the tissue planes which would otherwise allow spread of local anaesthetic to reach distant intercostal nerves are disrupted and much of the local anaesthetic is lost. By locating specifically the intact tissue planes in the paravertebral gutter and
inserting the extradural catheter into this space under direct vision, Sabanathan and colleagues [1] have shown this technique to be consistently effective. This is likely to be the reason why these authors have achieved considerable success using this block for post-thoracotomy pain relief while others have found it to be inconsistent. I agree that in this situation it is simplistic to include both paravertebral and interpleural analgesia together. In my review of interpleural analgesia, this difference was cited specifically in the summary and conclusion of the article. D. F. MURPHY
Sir Charles Gairdner Hospital Perth, Western Australia 1. Sabanathan S, Mearns AJ, Bickford-Smith PJ, Eng J, Berrisford RG, Bibby SR, Majid MR. Efficacy of continuous extrapleural intercostal nerve block on postthoracotomy pain and pulmonary mechanics. British Journal of Surgery 1990; 77: 221-225.
Effect of nitrous oxide on cerebral blood flow Sir,—We read with interest the article by Field and colleagues [1], addressing the important issue of the effect of nitrous oxide on cerebral blood flow. The authors have shown that there is an increase in cerebral blood flow (CBF) after inhalation of 30-60 % nitrous oxide in oxygen. However, in their study, "baseline measurements" of CBF were made using 100% oxygen and not air. This is rather unfortunate and makes the conclusions drawn questionable. Hyperoxia (FiOt 0.85-1.0) has been known to cause vasoconstriction of the cerebral vessels [2], resulting in a decrease in global CBF by 11-14% of control values [3]. In our laboratory, Eintrei, Odman and Lund have shown a reduction of 40 % in cortical blood flow in pigs after inhalation of 100 % oxygen compared with air [4]. We have also found a significant decrease in capillary blood flow in the brain cortex after inhalation of increasing concentrations of oxygen using the hydrogen clearance technique [5]. Assuming that the normal global CBF level is in the range 50 ml/100 g min"1, the increase in CBF seen by Field and colleagues (8.6-9.8 ml/100 g min"') was less than 20% when nitrous oxide was added (and consequently the Fl Oi was reduced). In other words, the increase in flow seen after the addition of nitrous oxide may be explained, at least in part, by the decrease in inspired oxygen concentration and, the baseline values of CBF obtained by Field and colleagues using 100% oxygen, may have been falsely low. Therefore, could the increase in CBF after inhalation of nitrous oxide be the result of vasodilatation following a decrease in the inspired fraction of oxygen? F. SJOBERG
P. KjELLGREN A. GuTTA Department of Anaesthesiology and the Bums Unit University Hospital Linkoping, Sweden 1. Field LM, Dorrancc DE, Krzeminska EK, Barsoum LZ. Effect of nitrous oxide on blood flow in normal humans. British Journal of Anaesthesia 1993; 70: 154-159. 2. McDowall DG. Interrelationship between blood oxygen tension and cerebral blood flow. In: Payne JP, Hill DW, eds. Oxygen Measurements in Blood and Tissue. London: Churchill, 1966; 205-214. 3. Edvinsson L, MacKenzie ET, McCulloch J, eds. Changes in arterial gas tensions. In: Cerebral Blood Flow and Metabolism. New York: Raven Press, 1992: 524-552. 4. Eintrei C, Odman S, Lund N. Effects of increases in the inspired oxygen fraction on brain surface oxygen pressure fields and regional cerebral blood flow. Advances m Experimental and Medical Biology 1985; 191: 131-13*. 5. Eintrei C, Bergsten B, Gustafsson U, Malmqvist L-A, Sjoberg F. Selective reduction of high cerebral capillary
Downloaded from http://bja.oxfordjournals.org/ at Emory University on August 18, 2015
Sir,—We are concerned that the review by Murphy [1], which grouped together paravertebral analgesia and intrapleural analgesia and reviewed both subjects under the heading" interpleural analgesia" may worsen existing confusion between these different techniques. Instillation of local anaesthetic into the paravertebral or cxtrapleural space behaves differently from local anaesthetic injected between the parietal and visceral pleura and this is apparent in thoracic surgery. Post-thoracotomy intrapleural administration results in loss of up to 60% of anaesthetic solution dirough chest drains [2], mixing of the local anaesthetic with blood and fluid in the pleural space [3,4] and unimpeded gravitational pooling of solution in the dependent parts of the chest [3], all to the detriment of efficacy. We and others have demonstrated that solutions administered extrapleurally, on the other hand, remain confined but well distributed within the paravertebral space in close proximity to the intercostal nerve roots, their posterior primary rami and the sympathetic chain [5, 6]. Not only is post-thoracotomy pain relief reliably excellent, but blood concentrations of local anaesthetic are predictable and side effects are minimal [7], By combining research references from these two techniques, inconsistent results are explained adequately. These differences are much too important to be referred to as "variations on the technique of interpleural analgesia (with)... little to choose between them".