"/ would have everie man write what he knowes and no more"—MONTAIGNE
BRITISH JOURNAL OF ANAESTHESIA VOLUME 47, No. 7
JULY 1975
GUEST EDITORIAL SOME OBSERVATIONS ON THE PRACTICE OF DELIBERATE HYPOTENSION
the mandible or the tissues of the neck. Such differences can be observed clinically both by observation of skin colour, and of the amount of bleeding at operation. No fixed pressure value can be regarded as optimal for all tissues; skin and mucous membrane, being more vascular than most, require a lower pressure for an equivalent effect on bleeding. Although obviously suitable for the extremities, the tipped position cannot be so easily or successfully employed for operations on the body wall or witnin the pelvis. In these cases the effect of postural ischaemia is minimal, for arterial pressure at heart level must be maintained at a safe figure, usually within the range 55-65 mm Hg. Nevertheless, a lowered systolic pressure often contributes materially to reduced bleeding in these cases. Present day drugs and techniques ensure that it is possible and technically not too difficult to obtain satisfactory hypotension in a very high percentage of patients. The practical advantages of deliberate hypotension, although at times debatable and often misunderstood, become obvious when attempting an extensive and haemorrhagic surgical dissection. The ability to reduce bleeding to insignificant proportions is an outstanding achievement and one of the most important and obvious indications. However, serious and extensive operations of this nature are infrequent, and the need to achieve such dramatic results is rare in comparison with the large number of more However, to reduce bleeding to an insignificant ordinary operations where deliberate hypotension degree, arterial pressure at heart level must usually contributes a clearer operation field for more be within the range 60-90 mm Hg and the site of definitive surgery. By its aid, small intricate operaoperation raised. This means that, for head and neck tions within nasal and sinus cavities, and the middle surgery when using 20°-30° of foot-down tilt, the ear, can be made easier, more exact, and thereby pressure in the operation area will be 10-20 mm Hg more successful, and a wide range of skin surgery lower, the exact figure depending on the vertical is often facilitated and improved. These advantages elevation above heart level. Thus, the scalp at the are of genuine benefit to the patient. vertex of the cranium will be more ischaemic than Thus, many surgeons now request hypotension
Deliberate hypotension remains today an ill-defined and often poorly understood technique, and its practice can still arouse heated discussion among anaesthetists, some ardent in their support, others condemning its use as unjustifiable. The first critical question concerns the nature of the contribution which hypotension makes to a surgical operation. The obvious answer, "reduced bleeding", is unsatisfactory for it offers no explanation as to how it is achieved. On the other hand, "postural ischaemia" is an excellent and precise description, which was given in 1949 (in this writer's presence) by Sir Henry Dale, to explain what he was witnessing. It is now accepted that gravity leads to a gradient of arterial pressure throughout the erect human body, the pressure above heart level being reduced and that below the heart increased by 2 mm Hg for each 2.5 cm of vertical height. If to this reduction of local arterial pressure is added systemic hypotension and free venous drainage, as for example in the head and neck of a tipped patient, then bleeding is minimal. The assumption is that blood vessels should not be dilated at the site of operation, for this might counteract some of the benefits of low pressure and improved drainage. Many of these advantages can be attained quite easily and simply by careful attention on the part of the anaesthetist to the patient's posture, and to the intelligent use of drugs and techniques.
Downloaded from http://bja.oxfordjournals.org/ at Simon Fraser University on May 30, 2015
G. E. H. Enderby
744
"to make the impossible possible". In my opinion, this approach is fundamentally wrong and very misleading for it assumes that all anaesthetists are equally skilled and well practised in the technique, and are able on demand to ensure safe and satisfactory hypotension. The experience of the last 25 years has shown very clearly that skilled anaesthesia and technical excellence are essential for the safe practice of deliberate hypotension. Such skills can only be obtained and maintained by constant practice, and therefore any attempt at a "one off' performance will always be fraught with danger. The fact that deliberate hypotension is not widely practised derives almost certainly from the bad reputation surrounding the early work (and the associated technical difficulties), and there is no doubt that it would be used more often today were it possible to guarantee greater safety than attended its introduction in 1950. The work which has been done since, and the increased knowledge and skills of those who practise it regularly, now ensure a level of safety as high as that for normotensive anaesthesia. To maintain this record, any anaesthetist attempting a hypotensive technique must have received training and instruction in the drugs and techniques involved, and be able to apply such knowledge usefully to the surgical team. This can be a formidable undertaking, and one which rightly deters many from the occasional foray or the misguided request. In reaching out for these benefits, every anaesthetist would be wise to ask critically what are the real advantages, and weigh them against the certain need for better than average medical and nursing skills which are essential for safety. More refined surgical technique and a diminished blood loss, although important, are not often absolute requisites for success, while the relative advantage of more definitive surgery cannot be quantified readily. It is obvious that no claim can be made that hypotension is indispensable, and it is foolish to think that modern surgery cannot be successful without it. Rather, apart from the occasional case where it may be of dramatic value, it achieves in the majority a finesse which cannot be obtained by any other means, and which can materially assist the skilled surgeon. It would be mistaken to imagine that these advantages are great enough for any anaesthetist to substitute enthusiasm for prudence, or to risk the serious complications which have so often accompanied mismanagement.
Downloaded from http://bja.oxfordjournals.org/ at Simon Fraser University on May 30, 2015
for the very real assistance it gives to their surgical technique, but it is pertinent to observe that it is they and they alone who can make any use of it. It is obvious that no anaesthetist, however skilled, should try to persuade an unwilling and unversed surgeon to use hypotension, for it brings little advantage to the patient unless the surgeon is able to use the improved operating conditions which it provides. Conversely, it is equally unwise (and certainly more dangerous) for an enthusiastic surgeon to persuade an unwilling and unpractised anaesthetist into using it against his wishes. Of the many techniques which are presently available for inducing hypotension, each receives its quota of support from those who are most experienced in a particular method. Whichever is chosen, the practice of deliberate hypotension is necessarily a highly specialized technique involving close co-operation between surgeon and anaesthetist. It is essential for the anaesthetist to learn how to control the patient's arterial pressure to an exact value, and to maintain it there for the required time. In some cases, this may be easily and simply achieved, and in others it may be extremely difficult. Always, however, exact beat-by-beat control is sought, and is essential when pressure lies within the range 60-80 mm Hg systolic. Constant vigilance and a strict attention to technique is needed to maintain pressure on this "knife-edge", and to do so safely for any period of time requires the use of an accurate and reliable pressure monitoring device. The intra-arterial technique, although the only scientifically acceptable method for measuring arterial pressure, is unsuitable for the routine monitoring of all surgical operations. The instrument which best fills the clinical requirement is the oscillometer, a remarkably reliable mechanical pulse-wave monitor, which has proved its worth in anaesthesia over the past 22 years. In my view, this instrument is the focal point of safety in any hypotensive technique, and no attempt should be made to induce hypotension unless the anaesthetist has such an instrument and is familiar with its use. There are institutions, today, where deliberate hypotension is practised routinely for a wide selection of patients, and sometimes for relatively minor operations. In such cases it is important to question its safety, and to ask whether it should not be reserved for those serious life-threatening procedures where any additional risk to the patient is offset by the advantages it brings or, as once recommended,
BRITISH JOURNAL OF ANAESTHESIA
BRITISH JOURNAL OF ANAESTHESIA VOLUME 47, No. 7
JULY 1975
GUEST EDITORIAL SOME OBSERVATIONS ON THE PRACTICE OF DELIBERATE HYPOTENSION
the mandible or the tissues of the neck. Such differences can be observed clinically both by observation of skin colour, and of the amount of bleeding at operation. No fixed pressure value can be regarded as optimal for all tissues; skin and mucous membrane, being more vascular than most, require a lower pressure for an equivalent effect on bleeding. Although obviously suitable for the extremities, the tipped position cannot be so easily or successfully employed for operations on the body wall or witnin the pelvis. In these cases the effect of postural ischaemia is minimal, for arterial pressure at heart level must be maintained at a safe figure, usually within the range 55-65 mm Hg. Nevertheless, a lowered systolic pressure often contributes materially to reduced bleeding in these cases. Present day drugs and techniques ensure that it is possible and technically not too difficult to obtain satisfactory hypotension in a very high percentage of patients. The practical advantages of deliberate hypotension, although at times debatable and often misunderstood, become obvious when attempting an extensive and haemorrhagic surgical dissection. The ability to reduce bleeding to insignificant proportions is an outstanding achievement and one of the most important and obvious indications. However, serious and extensive operations of this nature are infrequent, and the need to achieve such dramatic results is rare in comparison with the large number of more However, to reduce bleeding to an insignificant ordinary operations where deliberate hypotension degree, arterial pressure at heart level must usually contributes a clearer operation field for more be within the range 60-90 mm Hg and the site of definitive surgery. By its aid, small intricate operaoperation raised. This means that, for head and neck tions within nasal and sinus cavities, and the middle surgery when using 20°-30° of foot-down tilt, the ear, can be made easier, more exact, and thereby pressure in the operation area will be 10-20 mm Hg more successful, and a wide range of skin surgery lower, the exact figure depending on the vertical is often facilitated and improved. These advantages elevation above heart level. Thus, the scalp at the are of genuine benefit to the patient. vertex of the cranium will be more ischaemic than Thus, many surgeons now request hypotension
Deliberate hypotension remains today an ill-defined and often poorly understood technique, and its practice can still arouse heated discussion among anaesthetists, some ardent in their support, others condemning its use as unjustifiable. The first critical question concerns the nature of the contribution which hypotension makes to a surgical operation. The obvious answer, "reduced bleeding", is unsatisfactory for it offers no explanation as to how it is achieved. On the other hand, "postural ischaemia" is an excellent and precise description, which was given in 1949 (in this writer's presence) by Sir Henry Dale, to explain what he was witnessing. It is now accepted that gravity leads to a gradient of arterial pressure throughout the erect human body, the pressure above heart level being reduced and that below the heart increased by 2 mm Hg for each 2.5 cm of vertical height. If to this reduction of local arterial pressure is added systemic hypotension and free venous drainage, as for example in the head and neck of a tipped patient, then bleeding is minimal. The assumption is that blood vessels should not be dilated at the site of operation, for this might counteract some of the benefits of low pressure and improved drainage. Many of these advantages can be attained quite easily and simply by careful attention on the part of the anaesthetist to the patient's posture, and to the intelligent use of drugs and techniques.
Downloaded from http://bja.oxfordjournals.org/ at Simon Fraser University on May 30, 2015
G. E. H. Enderby
744
"to make the impossible possible". In my opinion, this approach is fundamentally wrong and very misleading for it assumes that all anaesthetists are equally skilled and well practised in the technique, and are able on demand to ensure safe and satisfactory hypotension. The experience of the last 25 years has shown very clearly that skilled anaesthesia and technical excellence are essential for the safe practice of deliberate hypotension. Such skills can only be obtained and maintained by constant practice, and therefore any attempt at a "one off' performance will always be fraught with danger. The fact that deliberate hypotension is not widely practised derives almost certainly from the bad reputation surrounding the early work (and the associated technical difficulties), and there is no doubt that it would be used more often today were it possible to guarantee greater safety than attended its introduction in 1950. The work which has been done since, and the increased knowledge and skills of those who practise it regularly, now ensure a level of safety as high as that for normotensive anaesthesia. To maintain this record, any anaesthetist attempting a hypotensive technique must have received training and instruction in the drugs and techniques involved, and be able to apply such knowledge usefully to the surgical team. This can be a formidable undertaking, and one which rightly deters many from the occasional foray or the misguided request. In reaching out for these benefits, every anaesthetist would be wise to ask critically what are the real advantages, and weigh them against the certain need for better than average medical and nursing skills which are essential for safety. More refined surgical technique and a diminished blood loss, although important, are not often absolute requisites for success, while the relative advantage of more definitive surgery cannot be quantified readily. It is obvious that no claim can be made that hypotension is indispensable, and it is foolish to think that modern surgery cannot be successful without it. Rather, apart from the occasional case where it may be of dramatic value, it achieves in the majority a finesse which cannot be obtained by any other means, and which can materially assist the skilled surgeon. It would be mistaken to imagine that these advantages are great enough for any anaesthetist to substitute enthusiasm for prudence, or to risk the serious complications which have so often accompanied mismanagement.
Downloaded from http://bja.oxfordjournals.org/ at Simon Fraser University on May 30, 2015
for the very real assistance it gives to their surgical technique, but it is pertinent to observe that it is they and they alone who can make any use of it. It is obvious that no anaesthetist, however skilled, should try to persuade an unwilling and unversed surgeon to use hypotension, for it brings little advantage to the patient unless the surgeon is able to use the improved operating conditions which it provides. Conversely, it is equally unwise (and certainly more dangerous) for an enthusiastic surgeon to persuade an unwilling and unpractised anaesthetist into using it against his wishes. Of the many techniques which are presently available for inducing hypotension, each receives its quota of support from those who are most experienced in a particular method. Whichever is chosen, the practice of deliberate hypotension is necessarily a highly specialized technique involving close co-operation between surgeon and anaesthetist. It is essential for the anaesthetist to learn how to control the patient's arterial pressure to an exact value, and to maintain it there for the required time. In some cases, this may be easily and simply achieved, and in others it may be extremely difficult. Always, however, exact beat-by-beat control is sought, and is essential when pressure lies within the range 60-80 mm Hg systolic. Constant vigilance and a strict attention to technique is needed to maintain pressure on this "knife-edge", and to do so safely for any period of time requires the use of an accurate and reliable pressure monitoring device. The intra-arterial technique, although the only scientifically acceptable method for measuring arterial pressure, is unsuitable for the routine monitoring of all surgical operations. The instrument which best fills the clinical requirement is the oscillometer, a remarkably reliable mechanical pulse-wave monitor, which has proved its worth in anaesthesia over the past 22 years. In my view, this instrument is the focal point of safety in any hypotensive technique, and no attempt should be made to induce hypotension unless the anaesthetist has such an instrument and is familiar with its use. There are institutions, today, where deliberate hypotension is practised routinely for a wide selection of patients, and sometimes for relatively minor operations. In such cases it is important to question its safety, and to ask whether it should not be reserved for those serious life-threatening procedures where any additional risk to the patient is offset by the advantages it brings or, as once recommended,
BRITISH JOURNAL OF ANAESTHESIA
