Clinical Otolaryngology 1979, 4, 241-246
Deliberate hypotension in ENT surgery H. A . CONDON Royal National Throat, Nose and Ear Hospital, 330 Gray’s Inn Road, London WCr
Accepted for publication 6 March 1978 CONDON H.A. (1979) Clinical Otolaryngology 4, 241-246 Deliberate hypotention in ENT surgery The development of deliberate hypotension for E N T surgery is described. A hitherto unrecorded case of paraplegia complicating hypotensive anaesthesia is reported. The use of sodium nitroprusside as a hypotensive agent is assessed. Indications and contraindications to deliberate hypotension are reviewed. Possible neurological damage is considered. Keywords hypotension-deliberate paraplegia sodium nitroprusside
Bleeding during surgery has always presented problems. T h e earliest anaesthetists for ear, nose and throat operations were rightly concerned exclusively with the prevention of aspiration of blood into the 1ungs.l There were, however, isolated reports of anaesthetic methods which resulted in diminished bleeding, e.g. the use, in 1903, of spinal analgesia for maxillectomy.2 Immediately after the Second World War, methods by which the anaesthetist could directly influence the amount of bleeding at the operation site were introduced. These techniques, which involved lowering the patient’s arterial blood pressure, became known as, ‘controlled hypotension’. It was the application of these methods to the fenestration operation for otosclerosis , ~ spinal analge~ia,~ which pioneered their use in E N T surgery : controlled a r t e r i ~ t o m y total and the methonium compounds, i.e. sympathetic ganglion blockade allied with posture. Subsequent developments were the introduction of the shorter acting trimetaphan (arfonad), the use of halothane with its hypotensive action, and more recently the introduction of sodium nitroprusside (SNP). Although first used as long ago as 1929 to control acute hypotensive crises,8 it was 1968 before SNP reached the British anaesthetic scene.9 It produces vasodilation by direct action on the smooth muscle of the vessel walls and is ultrashort acting, thus ensuring a rapid return to normality. In recent years the term ‘deliberate hypotension’ has come to be used instead of ‘controlled hypotension’. Many will regret this change of adjective, so placing less emphasis on the allimportant need for control. ‘s7
Case report Numerous complications of hypotensive anaesthesia have been reported. 0307-77740800-0241
$0~.00
0 1979 Blackwell Scientific Publications
242
H. A . CONDON
A man, aged 58, complained of nasal obstruction. Nasal polypi were diagnosed. RadioA right fronto-ethmoidectomy graphs showed a mucocele of the right frontalsinus. B.P. 135/90. and left transantral ethmoidectomy were performed. T h e anaesthetic consisted of 300 mg thiopentone, 75 mg suxamethonium, nitrous oxide, oxygen and halothane, with 75 mg pethidine and 25 nig trimetaphan, both in divided doses. No untoward episode was observed. On the first post-operative day, he complained of inability to move both legs and was diagnosed as paraplegia secondary to spinal cord ischaemia following anterior spinal artery thrombosis. Intensive rehabilitation led to some recovery but essentially the patient was confined to a wheelchair, dying of coronary disease some years later. This case is very similar to that recorded by Forrester,l0 of paraplegia following laryngectomy under hypotensive anaesthesia. Present study
A study of the use of sodium nitroprusside in ENT surgery has been carried out on 80 patients (Table
I).
Table I Sodium nitroprusside in ENT surgery Indications Rhinoplasty Microsurgery of ear Lateral rhinotomy Maxillectomy Patterson's ethmoidectomy Orbital decompression Parotidectomy Others Total
Number 21
'7
6 8 5
7 5 I1
80
Under halothane anaesthesia with spontaneous respiration and the patient in a head-up tilt, SNP has been administered by intravenous drip (25 mg SNP in 500 ml 5% dextrose), the maximum dose being I .5 mg/kg body weight. All patients have also received hydroxocobalamin I mg i.v. to aid detoxication of cyanate. In one case SNP was changed to trimetaphan when the maximum dose of SNP had been administered. There was no morbidity or mortality. It has, however, proved difficult to maintain a stable low level blood pressure, there has also been considerable individual variation in response, but the overwhelming advantage is the rapid restoration of normality at the conclusion of surgery. It is this rapid detoxication which makes SNP the hypotensive agent of choice. It is appreciated that this is a small series, e.g. in relation to that of MacRae," but it represents the cautious approach of one anaesthetist.
Deliberute hypotewsion
243
Discussion
Following certain episodes of cardiac arrest in this hospital, further consideration was given as to the place of deliberate hypotension in the hospital's clinical practice. As a result, certain guidelines have been laid down (Tables 2-4). Table 2 Possible indications Rhinoplasty Lateral rhinotomy Transorbital ethmoidectomy Hypophysectomy Maxillectomy Vidian neurectomy These are relative indications, the closest to absolute being hypophysectomy .
Table 3 In normal circumstances not indicated Laryngectomy Block dissection Stapedectomy M yringoplasty Tympanoplasty Mastoidectomy Many patients in this group with malignant disease will also show medical contraindications.
There are in addition, 2 E N T contra-indications, i.e. i Cranio-facial ethmoidectomybecause of the danger of retractor anaemia of the frontal lobe of the brain and zi pharyngolaryngo-oesophagectomy with transfer of colon or stomach to the neck. The maintenance of an adequate blood supply to the bowel is essential. The most controversial question is the place of deliberate hypotension in anaesthesia for microsurgery of the ear. Morrison considered that hypotension during stapedectomy reduced the use of suction, minimized labyrinthine trauma and led to a lower incidence of post-operative vertigo and vomiting. In many centres deliberate hypotension is now the norm for middle ear ~ u r g e r y . ' ~ , ' ~ However, Deacock' has shown what can be achieved by meticulous conventional anaesthesia, i.e. endotracheal halothane anaesthesia with spontaneous respiration. Special attention
244
H . A . CONDON
Table 4 Relative medical contra-indications Chronic bronchitis and emphysema Asthma Cerebral vascual disease Coronary vascular disease Impaired renal function Impaired hepatic function Pregnancy Diabetes Previous steroid therapy Although these contra-indications may be relative, the risks are substantially increased if these are ignored.
is paid to i adequate local analgesia of the tracheo-bronchial tree, ii depression of laryngeal reflexes with pethidine to prevent straining, iii the infiltration of I in zoo ooo adrenaline and the topical application of I in 1000 adrenaline, iv the use of beta-blockers to control tachycardia. His indications for deliberate hypotension include: i a fit patient, ii an inexperienced surgeon, iii previous surgery to the same ear, iv troublesome bleeding, either on an earlier occasion, or actually occurring at the time. With these criteria, he found hypotension to be needed in 8% of stapedectomies, 10'3;of myringoplasties and 22% of tympanoplasties. In the light of this work, the need for the routine use of hypotensive anaesthesia in otology must be questioned. How safe is deliberate hypotension? If the normal B.P. is considered to be 120/75it is a big step if the systolic pressure is lowered to 60 mmHg. However, Richardson", using an automatic B.P. recorder over period of 24 hours in normal subjects, found falls in deep sleep, often to 80 mmHg. If light anaesthesia is considered as equivalent to deep sleep, the normal B.P. during anaesthesia is lower than has hitherto been accepted. T o lower the B.P. deliberately from 80 to 60 is therefore, not such a drastic step. Nevertheless, despite the best endeavours of anaesthetists, hypotensive anaesthesia has not proved to be free of complications. Some idea of the mortality may be obtained from a study of the literature. However, the incidence of neurological damage is much more difficult to assess. Some reported cases are shown in Table j. Deliberate hypotension is said by its advocates to be 'safe', in skilled hands. However, private conversation commonly reveals 'a case' which has done badly. Complications may be uncommon, but for the individual patient, these can be disastrous. A cautious approach by anaesthetists is therefore recommended. Anaesthetists should aim for diminished bleeding rather than no bleeding. T h e completely dry operative field should be looked on as a sign of excessive hypotension. Surgeons should neither request, nor expect such a result. The introduction of controlled hypotension was marred by a dispute between the leading
Deliberate hypotension
245
Table 5 Some reported cases of neurological damage after hypotensive anaesthesia Number Author Bodman’ LittleZo Forrester l o Way & Clarkez1 Rollason & HoughZ2 Grace23 Enderb~~~ Brierley & CooperZ5 Conleyz6 Prys Robertsz7 Condon
of
patients Case report 27930 Case report 50 40 40 9107 Case report I00 15
Case report
Year I952 I955 I959 I959 1960 1961 1961 1962 I965 I974 7979
Cerebral vascular accident
Dementia
Personality change
Paraplegia
I
47 I I
2
3 I
I I
2 2 I
surgical advocate of the new method and his long-standing anaesthetist colleague. ‘If you don’t use the new method, someone else will.’l* It is surely a matter for regret that, as in a recent paper, an otologist can still ‘demand’ a bloodless field.
References DUNCUM B.M. (1947) The Development of Inhalation Anaesthesza, p. 597. Oxford University Press, London. MORTONA.W. (1903) Excision of the Superior Maxillary under medullary narcosis. American Medicine 5, 451. 3 LEIGHJ.M. (1975) The history of controlled hypotension. British Journal of Anaesthesia 47, 745. 4 HALE D.E. (1948) Controlled hypotension by arterial bleeding during operation and anaesthesia. Anesthesiology 9, 498. 5 HALLI.S. & MILLARA.A. (1950) Haemostasis in the fenestration operation. Journal of Laryngology and Otology 64, 233. 6 STIRLING J.B. (1955) Anaesthesia with hypotension for Fenestration British Journal o f Anaesthesia 27, 80. G.E.H. (1950) Controlled circulation with hypotensive drugs and posture to reduce bleeding in 7 ENDERBY surgery. Preliminary results with pentamethonium iodide. Lancet i, I 145. 8 JOHNSON C.C. (1929) The actions and toxicity of sodium nitroprusside. Archives internationales de pharmacodynamie et de the‘rapie 35,480. 9 JONES G.O.M. & COLEP. (1968) Sodium nitroprusside as a hypotensive agent. BritishJournal ofAnaesthesia I
2
40, 804.
FORRESTER A.C. (1959) Mishaps in anaesthesia. Anaesthesia 14, 388. MACRAE W.R. (1976) Nitroprusside induced metabolic acidosis. (Correspondence). Anesthesiology 45, 578. 1 2 CONDON H.A. (1976) Cardiac arrest in otorhinolaryngology. Clinical Otolaryngology I , 137. A.W. (1967) Treatment of otosclerosis by stapedectomy. British MedicalJournal i, 1804. 13 MORRISON 14 BARROND.W. (1976) Anaesthetic management of micro-surgical operations on the ear. Journal of Laryngology and Otology 90,401. 10 II
246
H. A . C O N D O N
15 KERKA.R. (1977) Anaesthesia with profound hypotension for middle ear surgery. British Journal of Anaesthesia 49, 447. 16 DEACOCK A.R. (1971) Aspects of anaesthesia for middle ear surgery and blood loss during stapedectomy. Proceedings of the Royal Society of Medicine 64, 1226. 17 RICHARDSON D.W., HONOUR A.J., FENTON G.W., STOTTF.H. & PICKERING G.W. (1964) Variation in arterial blood pressure throughout the day and night. Clinical Science 26, 445. 18 MCLEAVE H. (1961) In Mclndoe: Plastic Surgeon, p. 173. Muller, London. 19 BODMAN R.I. (1952) Death after anaesthesia with hypotension. Lancet ii, 1085. 20 LITTLE D.M. (1955) Induced hypotension during surgery and anesthesia. Anesthesiology 16, 323. 21 WAYG.L. & CLARKE H.L. (1959) An anesthetic technique for prostatectomy. Lancet ii, 888. 22 ROLLASON W.N. & HOUGH J.M. (1960) A study of hypotensive anaesthesia in the elderly. British Joburrral of Anaeslhesia 32, 276. A.H. (1961) Prostatectomy under hypotensive anaesthesia Prucezdings uf the Royal Society of’ 23 GRACE Medicine 54, I 130. 24 ENDERRY G.E.H. (1961) A report on mortality and morbidity following 9107 hypotensive anaesthetics. British Journal of Anaesthesia 33, 109. 25 BRIERLY J.B. & COOPER J.E. (1962) Cerebral complications of hypotensive aniesthesia in a healthy adult. Journal of Neurology, Neurosurgery and Psychiatry 25, 24. J., HICKSR.G. & JASAITIS J.D. (1965) Hypotensive anaesthesia in surgery of head and neck. 26 CONLEY Archives of Otolaryngology 81, 580. 27 PRVSROBERTS C., LLOYD J.W., FISHER A,, KERKJ.H. & PATTERSON T.J.S. (1974) Deliberate profound hypotension induced with halothane: Studies of haemodynamics and pulmonary gas exchange. British Journal o f Anaesthesia 46, 105.
Deliberate hypotension in ENT surgery H. A . CONDON Royal National Throat, Nose and Ear Hospital, 330 Gray’s Inn Road, London WCr
Accepted for publication 6 March 1978 CONDON H.A. (1979) Clinical Otolaryngology 4, 241-246 Deliberate hypotention in ENT surgery The development of deliberate hypotension for E N T surgery is described. A hitherto unrecorded case of paraplegia complicating hypotensive anaesthesia is reported. The use of sodium nitroprusside as a hypotensive agent is assessed. Indications and contraindications to deliberate hypotension are reviewed. Possible neurological damage is considered. Keywords hypotension-deliberate paraplegia sodium nitroprusside
Bleeding during surgery has always presented problems. T h e earliest anaesthetists for ear, nose and throat operations were rightly concerned exclusively with the prevention of aspiration of blood into the 1ungs.l There were, however, isolated reports of anaesthetic methods which resulted in diminished bleeding, e.g. the use, in 1903, of spinal analgesia for maxillectomy.2 Immediately after the Second World War, methods by which the anaesthetist could directly influence the amount of bleeding at the operation site were introduced. These techniques, which involved lowering the patient’s arterial blood pressure, became known as, ‘controlled hypotension’. It was the application of these methods to the fenestration operation for otosclerosis , ~ spinal analge~ia,~ which pioneered their use in E N T surgery : controlled a r t e r i ~ t o m y total and the methonium compounds, i.e. sympathetic ganglion blockade allied with posture. Subsequent developments were the introduction of the shorter acting trimetaphan (arfonad), the use of halothane with its hypotensive action, and more recently the introduction of sodium nitroprusside (SNP). Although first used as long ago as 1929 to control acute hypotensive crises,8 it was 1968 before SNP reached the British anaesthetic scene.9 It produces vasodilation by direct action on the smooth muscle of the vessel walls and is ultrashort acting, thus ensuring a rapid return to normality. In recent years the term ‘deliberate hypotension’ has come to be used instead of ‘controlled hypotension’. Many will regret this change of adjective, so placing less emphasis on the allimportant need for control. ‘s7
Case report Numerous complications of hypotensive anaesthesia have been reported. 0307-77740800-0241
$0~.00
0 1979 Blackwell Scientific Publications
242
H. A . CONDON
A man, aged 58, complained of nasal obstruction. Nasal polypi were diagnosed. RadioA right fronto-ethmoidectomy graphs showed a mucocele of the right frontalsinus. B.P. 135/90. and left transantral ethmoidectomy were performed. T h e anaesthetic consisted of 300 mg thiopentone, 75 mg suxamethonium, nitrous oxide, oxygen and halothane, with 75 mg pethidine and 25 nig trimetaphan, both in divided doses. No untoward episode was observed. On the first post-operative day, he complained of inability to move both legs and was diagnosed as paraplegia secondary to spinal cord ischaemia following anterior spinal artery thrombosis. Intensive rehabilitation led to some recovery but essentially the patient was confined to a wheelchair, dying of coronary disease some years later. This case is very similar to that recorded by Forrester,l0 of paraplegia following laryngectomy under hypotensive anaesthesia. Present study
A study of the use of sodium nitroprusside in ENT surgery has been carried out on 80 patients (Table
I).
Table I Sodium nitroprusside in ENT surgery Indications Rhinoplasty Microsurgery of ear Lateral rhinotomy Maxillectomy Patterson's ethmoidectomy Orbital decompression Parotidectomy Others Total
Number 21
'7
6 8 5
7 5 I1
80
Under halothane anaesthesia with spontaneous respiration and the patient in a head-up tilt, SNP has been administered by intravenous drip (25 mg SNP in 500 ml 5% dextrose), the maximum dose being I .5 mg/kg body weight. All patients have also received hydroxocobalamin I mg i.v. to aid detoxication of cyanate. In one case SNP was changed to trimetaphan when the maximum dose of SNP had been administered. There was no morbidity or mortality. It has, however, proved difficult to maintain a stable low level blood pressure, there has also been considerable individual variation in response, but the overwhelming advantage is the rapid restoration of normality at the conclusion of surgery. It is this rapid detoxication which makes SNP the hypotensive agent of choice. It is appreciated that this is a small series, e.g. in relation to that of MacRae," but it represents the cautious approach of one anaesthetist.
Deliberute hypotewsion
243
Discussion
Following certain episodes of cardiac arrest in this hospital, further consideration was given as to the place of deliberate hypotension in the hospital's clinical practice. As a result, certain guidelines have been laid down (Tables 2-4). Table 2 Possible indications Rhinoplasty Lateral rhinotomy Transorbital ethmoidectomy Hypophysectomy Maxillectomy Vidian neurectomy These are relative indications, the closest to absolute being hypophysectomy .
Table 3 In normal circumstances not indicated Laryngectomy Block dissection Stapedectomy M yringoplasty Tympanoplasty Mastoidectomy Many patients in this group with malignant disease will also show medical contraindications.
There are in addition, 2 E N T contra-indications, i.e. i Cranio-facial ethmoidectomybecause of the danger of retractor anaemia of the frontal lobe of the brain and zi pharyngolaryngo-oesophagectomy with transfer of colon or stomach to the neck. The maintenance of an adequate blood supply to the bowel is essential. The most controversial question is the place of deliberate hypotension in anaesthesia for microsurgery of the ear. Morrison considered that hypotension during stapedectomy reduced the use of suction, minimized labyrinthine trauma and led to a lower incidence of post-operative vertigo and vomiting. In many centres deliberate hypotension is now the norm for middle ear ~ u r g e r y . ' ~ , ' ~ However, Deacock' has shown what can be achieved by meticulous conventional anaesthesia, i.e. endotracheal halothane anaesthesia with spontaneous respiration. Special attention
244
H . A . CONDON
Table 4 Relative medical contra-indications Chronic bronchitis and emphysema Asthma Cerebral vascual disease Coronary vascular disease Impaired renal function Impaired hepatic function Pregnancy Diabetes Previous steroid therapy Although these contra-indications may be relative, the risks are substantially increased if these are ignored.
is paid to i adequate local analgesia of the tracheo-bronchial tree, ii depression of laryngeal reflexes with pethidine to prevent straining, iii the infiltration of I in zoo ooo adrenaline and the topical application of I in 1000 adrenaline, iv the use of beta-blockers to control tachycardia. His indications for deliberate hypotension include: i a fit patient, ii an inexperienced surgeon, iii previous surgery to the same ear, iv troublesome bleeding, either on an earlier occasion, or actually occurring at the time. With these criteria, he found hypotension to be needed in 8% of stapedectomies, 10'3;of myringoplasties and 22% of tympanoplasties. In the light of this work, the need for the routine use of hypotensive anaesthesia in otology must be questioned. How safe is deliberate hypotension? If the normal B.P. is considered to be 120/75it is a big step if the systolic pressure is lowered to 60 mmHg. However, Richardson", using an automatic B.P. recorder over period of 24 hours in normal subjects, found falls in deep sleep, often to 80 mmHg. If light anaesthesia is considered as equivalent to deep sleep, the normal B.P. during anaesthesia is lower than has hitherto been accepted. T o lower the B.P. deliberately from 80 to 60 is therefore, not such a drastic step. Nevertheless, despite the best endeavours of anaesthetists, hypotensive anaesthesia has not proved to be free of complications. Some idea of the mortality may be obtained from a study of the literature. However, the incidence of neurological damage is much more difficult to assess. Some reported cases are shown in Table j. Deliberate hypotension is said by its advocates to be 'safe', in skilled hands. However, private conversation commonly reveals 'a case' which has done badly. Complications may be uncommon, but for the individual patient, these can be disastrous. A cautious approach by anaesthetists is therefore recommended. Anaesthetists should aim for diminished bleeding rather than no bleeding. T h e completely dry operative field should be looked on as a sign of excessive hypotension. Surgeons should neither request, nor expect such a result. The introduction of controlled hypotension was marred by a dispute between the leading
Deliberate hypotension
245
Table 5 Some reported cases of neurological damage after hypotensive anaesthesia Number Author Bodman’ LittleZo Forrester l o Way & Clarkez1 Rollason & HoughZ2 Grace23 Enderb~~~ Brierley & CooperZ5 Conleyz6 Prys Robertsz7 Condon
of
patients Case report 27930 Case report 50 40 40 9107 Case report I00 15
Case report
Year I952 I955 I959 I959 1960 1961 1961 1962 I965 I974 7979
Cerebral vascular accident
Dementia
Personality change
Paraplegia
I
47 I I
2
3 I
I I
2 2 I
surgical advocate of the new method and his long-standing anaesthetist colleague. ‘If you don’t use the new method, someone else will.’l* It is surely a matter for regret that, as in a recent paper, an otologist can still ‘demand’ a bloodless field.
References DUNCUM B.M. (1947) The Development of Inhalation Anaesthesza, p. 597. Oxford University Press, London. MORTONA.W. (1903) Excision of the Superior Maxillary under medullary narcosis. American Medicine 5, 451. 3 LEIGHJ.M. (1975) The history of controlled hypotension. British Journal of Anaesthesia 47, 745. 4 HALE D.E. (1948) Controlled hypotension by arterial bleeding during operation and anaesthesia. Anesthesiology 9, 498. 5 HALLI.S. & MILLARA.A. (1950) Haemostasis in the fenestration operation. Journal of Laryngology and Otology 64, 233. 6 STIRLING J.B. (1955) Anaesthesia with hypotension for Fenestration British Journal o f Anaesthesia 27, 80. G.E.H. (1950) Controlled circulation with hypotensive drugs and posture to reduce bleeding in 7 ENDERBY surgery. Preliminary results with pentamethonium iodide. Lancet i, I 145. 8 JOHNSON C.C. (1929) The actions and toxicity of sodium nitroprusside. Archives internationales de pharmacodynamie et de the‘rapie 35,480. 9 JONES G.O.M. & COLEP. (1968) Sodium nitroprusside as a hypotensive agent. BritishJournal ofAnaesthesia I
2
40, 804.
FORRESTER A.C. (1959) Mishaps in anaesthesia. Anaesthesia 14, 388. MACRAE W.R. (1976) Nitroprusside induced metabolic acidosis. (Correspondence). Anesthesiology 45, 578. 1 2 CONDON H.A. (1976) Cardiac arrest in otorhinolaryngology. Clinical Otolaryngology I , 137. A.W. (1967) Treatment of otosclerosis by stapedectomy. British MedicalJournal i, 1804. 13 MORRISON 14 BARROND.W. (1976) Anaesthetic management of micro-surgical operations on the ear. Journal of Laryngology and Otology 90,401. 10 II
246
H. A . C O N D O N
15 KERKA.R. (1977) Anaesthesia with profound hypotension for middle ear surgery. British Journal of Anaesthesia 49, 447. 16 DEACOCK A.R. (1971) Aspects of anaesthesia for middle ear surgery and blood loss during stapedectomy. Proceedings of the Royal Society of Medicine 64, 1226. 17 RICHARDSON D.W., HONOUR A.J., FENTON G.W., STOTTF.H. & PICKERING G.W. (1964) Variation in arterial blood pressure throughout the day and night. Clinical Science 26, 445. 18 MCLEAVE H. (1961) In Mclndoe: Plastic Surgeon, p. 173. Muller, London. 19 BODMAN R.I. (1952) Death after anaesthesia with hypotension. Lancet ii, 1085. 20 LITTLE D.M. (1955) Induced hypotension during surgery and anesthesia. Anesthesiology 16, 323. 21 WAYG.L. & CLARKE H.L. (1959) An anesthetic technique for prostatectomy. Lancet ii, 888. 22 ROLLASON W.N. & HOUGH J.M. (1960) A study of hypotensive anaesthesia in the elderly. British Joburrral of Anaeslhesia 32, 276. A.H. (1961) Prostatectomy under hypotensive anaesthesia Prucezdings uf the Royal Society of’ 23 GRACE Medicine 54, I 130. 24 ENDERRY G.E.H. (1961) A report on mortality and morbidity following 9107 hypotensive anaesthetics. British Journal of Anaesthesia 33, 109. 25 BRIERLY J.B. & COOPER J.E. (1962) Cerebral complications of hypotensive aniesthesia in a healthy adult. Journal of Neurology, Neurosurgery and Psychiatry 25, 24. J., HICKSR.G. & JASAITIS J.D. (1965) Hypotensive anaesthesia in surgery of head and neck. 26 CONLEY Archives of Otolaryngology 81, 580. 27 PRVSROBERTS C., LLOYD J.W., FISHER A,, KERKJ.H. & PATTERSON T.J.S. (1974) Deliberate profound hypotension induced with halothane: Studies of haemodynamics and pulmonary gas exchange. British Journal o f Anaesthesia 46, 105.
