Postgrad Med J: first published as 10.1136/pgmj.31.359.443 on 1 September 1955. Downloaded from September 1955 SCURR: Control of the Blood Pressure and Controlled 443 some other than that at the neuro-muscular GRIFFITH, H. R., and JOHNSON, G. E. (1942), Anaesthesiology action, 3, 4I8. junction, which is as yet unknown. BENNETT, A. E. (1940), J.A.M.A., 144, 322. GRAY, R. W., et al. (I941), Psych. Quart., 15, 159. BIBLIOGRAPHY WATERTON. C. (x812), 'Wanderings in S. America,' Everyman BERNARD, CLAUDE (1843), ' Note sur la Curarine et ses effects Series, Dent, London. physiologiques,' Paris. BEECHER, H. K., and TODD, D. P. (I954), Ann. Surg., I, 140.

>CONTROL OF THE BLOOD PRESSURE AND CONTROLLED HYPOTENSION By C. F. SCURR, M.V.O., M.B., B.S., D.A., R.C.S., F.F.A. Consultant Anaesthetist, Westminster Hospital; Honorary Anaesthetist, Hospital of Ss. John and Elizabeth

Control of the Blood Pressure during the vagus and sympathetic, it can be improved by Anaesthesia humoral agents (adrenaline) and inotropic drugs, Blood pressure is the lateral pressure exerted by and is readily depressed by certain anaesthetic the blood on the vessel walls; our considerations agents which produce dilatation. Protected by copyright. are especially directed to the arterial system. The (b) Cardiac Filling: This depends on the length difference between systolic and diastolic pressure of diastole and the effective venous pressure. is the pressure which depends on the stroke Venous pressure: The venous system accounts volume of the heart and the volume, elasticity and for 70 per cent. of the total volume of the vascular length of the arterial tree. In order to study bed; it is evident that considerable circulatory the various factors influencing the arterial pressure, adjustment can occur in this region. Surprisingly it is convenient to consider the mean pressure little is known of any venomotor mechanism :,3 which is proportional to the product of the cardiac it is usually stated that there is insufficient muscle output and the peripheral resistance.' in the walls of the to produce any important effect. In the case of the larger veins it is probable i. Cardiac Output that this thin layer of smooth muscle functions in This is the product of the stroke volume and the a manner characteristic of hollow organs having heart rate and depends on the force of the heart a relatively thin wall compared with the size of the and the cardiac the maintenance of tone in filling. lumen, purpose being http://pmj.bmj.com/ (a) The Force of Cardiac Contraction affects the order to allow considerable variation in capacity or efficiency with which the heart muscles produce filling with only slight changes in pressure.4 emptying. It depends on the initial length of the This tone is presumably regulated from the muscle fibres (Starling's law), so that an increased vasomotor centre: anaesthesia will diminish venous return leading to distension of the heart it, digitalis also can reduce venous pressure, enhances the force of the beat. In a failing heart, noradrenaline can produce constriction of the however, overdistension occurs and increasing veins and improve the venous return. A number of the venous pressure causes a further fall in output, factors influence filling of the venous system, on September 24, 2021 by guest. conversely in such cases venesection may improve notably the .6 This may be varied the circulation. in contrary directions by haemorrhage and The force of the heart is also dependent on its transfusion. Closely connected with this is the nutrition and oxygen supply, which are affected by state of the arterial bed, which accommodates a such factors as anoxaemia, the state of the proportion of the blood volume and provides a coronary vessels and the arterial blood pressure. through pressure to promote the venous return. Excessive potassium ions cause increasing relaxa- The state of the body cavities, respiration, tion of the heart, finally bringing about arrest in muscular activity and especially posture,9 mecha- diastole; for this reason stored blood is not nically influence the return of blood to the heart. advised for aortic transfusion during cardiac Apart from these effects on venous filling the .38 Cardiac contraction is also influenced venous pressure depends on the efficiency with by body temperature and by nervous effects from which the heart empties the great veins. For this Postgrad Med J: first published as 10.1136/pgmj.31.359.443 on 1 September 1955. Downloaded from 444 POSTGRADUATE MEDICAL JOURNAL September I955 reason attempts to correlate central venous if the circulation is already impaired (e.g. haemor- pressure with cardiac output can give inconsistent rhagic , constrictive pericarditis). 11 As results, for increased cardiac output can operate to passive ventilation is now undertaken during produce a fall in venous pressure and.vice versa. many anaesthetics, these facts merit serious This is unfortunate, because the venous pressure consideration. is easily measured and would provide valuable information if it were a reliable index of cardiac 2. The Peripheral Resistance. output. As a guide to the onset of shock a falling Peripheral vascular resistance depends upon venous pressure is an earlier sign than arterial two factors: (i) the viscosity of the blood, and hypotension; the degree of its elevation by (2) the total cross-sectional area of the available transfusion provides a guide to replacement.5, 6, 7 exit vessels, which varies according to (a) the Changes in the thorax may have important anatomical state of the vessels, (b) nervous control effects on the blood pressure. The lungs during and (c) peripheral chemical and humoral effects full inspiration hold 120 cc. more blood than on the'vessels. during expiration; it follows that with the smaller Nervous Control: The most important part of vascular bed available during expiration there is this mechanism is the medullary vasomotor increased resistance to blood flow. The calibre centre, the function of which is to adapt the of the vessels may also vary reflexly, but little volume of the vascular bed to the volume of blood information is available on pulmonary vasomotor available; this it does by regulating the calibre of phenomena. Reflexes initiated by deep inspira- the vessels, notably the arterioles which constitute tion or inflation produce generalized cutaneous the most important part of the peripheral re- vasoconstriction. Apart from these vasomotor sistance. Nervous contrbl has also been demon- effects, inspiration by reducing intrathoracic strated in the larger and on the venous pressure and by the descent of the diaphragm side of the circulation. All these changes Protected by copyright. in improves the venous return-the respiratory calibre are mediated through constrictor and pump effect. In expiration the converse is true: dilator nerves of various types. Numerous expiration against resistance (Valsalva manoeuvre) factors act on the vasomotor centre to produce impedes the venous return and the cardiac output these effects, including the hypothalamus and and blood pressure (especially pulse pressure) higher centres. Raised carbon dioxide tension fall.8 During expiration some blood is expelled and oxygen lack exert a pressor effect. Afferent from the lung vessels and the outflow into the impulses from the lungs, muscles and abdominal arteries is thereby increased; there is also a direct organs produce varied results. Experimentally transmission of changes of thoracic pressure to the demonstrable reflexes involving the centre may be arterial system. In view of the lag of two or three pressor or depressor according to the strength and beats for venous return changes to be manifest as frequency of the stimulus and the type of nerve arterial pressure fluctuations, it is not surprising fibre excited; for example, ' C' fibre stimulation that mixed effects upon the blood pressure are characteristically produces a fall of blood pressure. of these effects are reported.10 These phasic variations can be Under anaesthesia many http://pmj.bmj.com/ detected by means of direct electromanometry, abolished, but presumably reflex changes in and during average respirations are minimal. pressure resulting from traumatic stimuli are often As most examples of protest to surgical stimuli observed during light anaesthesia. during inadequate anaesthesia take the form of an The most important impulses acting on the increase in expiratory tone with decrease in size of vasomotor centre emanate from baroceptors in the thorax, it is evident that relaxants by preventing the carotid sinus, aortic arch and certain other such voluntary muscular activity will obviate areas. The higher the arterial pressure the blood pressure fluctuations of this type. Passive greater is the rate of discharge of these special end on September 24, 2021 by guest. ventilation reverses the normal pressure phases organs. The resulting impulses have a depressor in the chest. During inflation the venous return is action on the vasomotor centre: by this impeded, especially if there is active muscular mechanism it has been said ' the blood pressure resistance due to inadequate anaesthesia, and so the regulates the blood pressure.' Pressure on the arterial pressure will tend to fall. With the chest carotid sinus may stimulate these nerve endings open such changes are less striking. Recent and lead to a depressor effect associated with investigation indicates that cardiac output is vasodilatation and cardiac inhibition.12 Anaes- greatest with a rapid build-up of inflation pressure thesia has been said to depress this sinoaortic followed by a total release of pressure in expiration, apparatus; this will not, however, serve as an the duration of the expiratory phase being longer explanation for hypotension because depression than inspiration. If these conditions are not of the carotid sinus will reduce inhibition of the fulfilled cardiac output may be reduced, especially vasomotor centre and so should lead to a rise in Postgrad Med J: first published as 10.1136/pgmj.31.359.443 on 1 September 1955. Downloaded from September 1955 SCURR: Control of the Blood Pressure and Controlled Hypotension 445 blood pressure. Creyssel has blocked the sinus effect of anoxia or hypercapnia,16 their administra- nerves with procaine in shocked patients and tion may obviate hypotension following carbon described clinical improvement with a rise in the dioxide retention: such an action may be partly arterial pressure.13 responsible for the improved post-operative state A fall in blood pressure can result from block observed when these drugs have been given. of vasoconstrictor reflexes at any level: chlorpro- Reflex Hypertension: Reflex rises in blood mazine affects the hypothalamus, the vasomotor pressure due to stimuli from the field of operation centre may be depressed by anaesthetic agents, the are occasionally seen; the type of stimulus and sympathetic nerves may be blocked (e.g. by spinal depth of anaesthesia especially conducive to this or epidural anaesthesia) or the block may be at reaction are uncertain.17 Distension of the ganglionic level (T E A B, hexamethonium, etc.). bladder, and injection of solutions into the capsule Local Chemical Influences can act directly on of the prostate often lead to a transitory hyper- blood vessels: CO2, histamine and metabolites tension. In paraplegics the response to such generally produce vasodilatation, noradrenaline stimuli can be very dramatic: hypertensive crises and numerous pressor drugs are vasoconstrictors. result from the operation of a mass autonomic reflex; this complication can be controlled by the Hypertension During Anaesthesia administration of a ganglioplegic drug.18,19 Of The Effects of Carbon Dioxide especial interest to anaesthetists is the hypertension Anoxia and carbon dioxide retention may both reflexly produced by laryngoscopy and intubation produce hypertension. In so far as these factors during light anaesthesia.20, 21 are due to maladministration of the anaesthetic, Adrenaline and Pressor Drugs: Handling the such changes in pressure are avoidable. Increase adrenal gland during adrenalectomy (even when in carbon dioxide tension affects the blood the is produces a brief

pressure gland normal) commonly Protected by copyright. in two directions: acting on the vasomotor centre hypertension. This response can be prevented it causes vasoconstriction, peripherally dilatation by the anti-adrenaline drug, chlorpromazine is produced by a direct action on the vessels. In (I2.5 mg. to 25 mg. intravenously). When a the anaesthetized patient carbon dioxide accumu- phaeochromocytoma is present such hypertensive lation, due for instance to soda lime exhaustion, crises may be very severe, even fatal,22 and must frequently leads to a rise in pressure. In patients be controlled during extirpation of the tumour by under extensive spinal anaesthesia this pressor the intravenous injection of adrenolytic drugs,23 effect is annulled due to the sympathetic block, and e.g. Benzodioxane 15 mg., Regitine 3 mg., or in these patients the peripheral dilator effect pre- chlorpromazine 25 mg.; these doses may need dominates leading to hypotension. Similar con- to be repeated. Hypotension following removal siderations may apply after ganglioplegics or of the tumour may need to be counteracted by during deep anaesthesia. Under cyclopropane, 1 noradrenaline given in a drip (4 mg. 1 noradren- carbon dioxide retention, due to hypoventilation, aline to I litre of normal saline).24 may maintain the blood pressure at a relatively 1 noradrenaline is -the most powerful overall high level despite major surgical trauma. (Yandell vasoconstrictor available (being the physiological http://pmj.bmj.com/ Henderson's carbon dioxide therapy of shock will agent).25 Adrenaline produces a marked increase be recalled.) When the anaesthetic is discontinued in cardiac output while acting as an overall the carbon dioxide level falls with resulting vasodilator.26 Chlorpromazine reverses the pressor hypotension-' cyclopropane shock.'l4 It is effect of adrenaline and if this drug be given obvious that any anaesthetic technique which may beforehand infiltration of io cc. of I:Io,ooo cause hypoventilation (e.g. the relaxants) can adrenaline can be used during the fenestration produce a similar effect. When such methods are operation to produce local ischaemia combined employed assisted or passive ventilation must be with hypotension. on September 24, 2021 by guest. undertaken, ensuring an adequate minute volume, Many other drugs (with varying activity on to avoid carbon dioxide retention. There is an cardiac output and peripheral resistance) can be urgent need at present for the development of given to raise the blood pressure: most of these are some indicator to place ' controlled respiration' allied chemically to adrenaline and many produce on a basis other than empirical. Carbon dioxide dangerous types of during anaesthesia. balance is far more difficult to assure than adequate Evidently beneficial results from these agents can oxygenation. The post-operative hypotension be expected when hypotension is associated with following such hypercapnia may be of long vasodilatation (e.g. during spinal or hypotensive duration; its severity appears to be directly related anaesthesia): during oligaemic shock when the to the degree of hypercapnia but not to the duration blood pressure is falling despite intense vaso- of the hypercapnic state.15 In so far as ganglio- constriction such drugs are not indicated, but in plegics (e.g. pentamethonium) prevent the pressor shock when massive blood replacement fails to Postgrad Med J: first published as 10.1136/pgmj.31.359.443 on 1 September 1955. Downloaded from POSTGRADUATE MEDICAL JOURNAL -September 1955 restore the pressure (vascular paralysis) these treatment consists in removing the precipitating agents have a place.27 It is important to note that cause and blocking the vagal efferents with restoration of arterial pressure by these agents, atropine gr. 1/100 to 1/50 intravenously. During e.g. after hexamethonium, is the result of genera- anaesthesia many variable factors are implicated,29 lized vasoconstriction. The capacity of the body so that it will not always be possible to determine for physiological redistribution of blood by the cause of any blood pressure change according vasomotor reflexes is not restored. Furthermore, to these simple rules; therefore, further discussion the effect of the pressor drug, especially when seems merited. given intravenously, may wane before the ganglio- Induction of Anaesthesia is usually accompanied plegic and hypotension will then recur. Prolonged by depression of the vasomotor apparatus both indiscriminate vasoconstriction maintained for centrally and peripherally. This is evidenced by days, e.g. by 1 noradrenaline drip, leads to tissue the usual signs of vasodilatation (loss of tempera- anoxia and liver necrosis has been described as a ture gradient in the limbs, dilatation of the super- result of such therapy. Examples of useful ficial veins and increase in limb blood flow).30 pressor drugs are: ephedrine (50 to Ido mg.), Some authorities hold that consciousness of itself Phenylephrine (5 to Io mg.) and methyl-amphe- has a pressor influence.31 Many agents, notably tamine or methedrine (IO to 30 mg.)-the last the barbiturates and chloroform also depress the agent has a marked analeptic effect, and may cause myocardium and lead to cardiac dilatation; these post-operative restlessness and insomnia. factors reduce the circulatory reserve, but hypo- tension does not invariably occur in young people. Arterial Hypotension In the elderly, compensation is less effective and From physiological considerations it follows one report suggests combining methylamphe- that a fall in arterial pressure may be due to a tamine with thiopentone to avoid hypotension in reduced cardiac output, to reduced peripheral such patients.32 Ability to compensate againstProtected by copyright. resistance or to a combination of these. These hypotension resulting from changes in posture disturbances may be classified: is lost at a very light level of anaesthesia: in one I. Reduction in vasomotor tone. investigation 60 per cent. of men over forty years 2. Reduction of cardiac output of age who had previously received morphine (a) Reduced venous return gr. i had hypotension and fainted when they were (b) Reduced force of contraction abruptly tilted into the head-up position. Burstein (c) Changes in heart rate. suggests that such falls in pressure can be avoided Under normal conditions a reduction in cardiac by inducing anaesthesia in the position desired for output or peripheral resistance will be compensated operation. Vasoconstriction is still possible during reflexly and so long as this is adequate no marked light anaesthesia and blood loss may be well change in blood pressure will be observed. The compensated thereby. Pallor of the ears which most important compensatory mechanisms against develops during major operations is evidence of hypotension are increasing the heart rate and this. On rubbing with the hand, the ear becomes vasoconstriction. has that the red to vasodilatation as as Inglis28 suggested due long any circulatoryhttp://pmj.bmj.com/ pulse rate is the key to the treatment of hypo- reserve remains and to this it provides a guide. tension occurring during anaesthesia. Hypotension Blood oxygenation can be assessed by this test and associated with tachycardia is usually due to the rapidity and intensity with which the pallor reduction of the cardiac output from a fall in the recurs is a guide to the state of the circulation. venous return: treatment is to increase the venous Blood and Fluid Loss associated with the return by posture or transfusion. Cardiac output operation lead to decreased venous return and a may also fall owing to reduced force of cardiac fall in cardiac output. Compensatory widespread contraction, which may be due to anaesthetic vasoconstriction may mask blood pressure changes on September 24, 2021 by guest. overdosage: treatment should be directed to but after brisk or severe haemorrhage there is maintaining perfect oxygenation and promoting usually marked hypotension, the systolic pressure elimination of the anaesthetic-it has been sug- falling by a greater degree than the diastolic. gested that cardiac and medullary stimulants may More gradual loss of an even larger volume may be given. often be effectively masked in respect of blood Hypotension with an unchanged pulse rate is pressure changes, but anaesthetics impair the probably due to reduction in peripheral resistance: homeostatic mechanisms in varying degrees.33 vasomotor tone may be increased by pressor drugs It is certain that modern balanced anaesthesia, given intravenously, e.g. noradrenaline 4 mg. per employing nitrous oxide-oxygen supplemented by litre given as a drip, methylamphetamine io to such as pethidine and relaxants as 30 mg., or phenylephrine io mg. Hypotension indicated, allows these circulatory mechanisms to with may be due to vagal reflex action: act to a greater extent than during ether anaes- Postgrad Med J: first published as 10.1136/pgmj.31.359.443 on 1 September 1955. Downloaded from September 1955 SCURR: Control of the Blood Pressure and Controlled Hypotension 447 thesia.35 It is not clear that these influences are coeliac region is maximal the pressure suddenly entirely beneficial, vasoconstriction by reducing becomes unassessable by . The pulse blood flow leads to tissue anoxia-a stage in remains palpable, however, and is not materially surgical shock. It is possible that ganglioplegics changed in rate. With careful auscultation, (and also chlorpromazine), by blocking these allowing the cuff pressure to fall slowly, a reading changes, may prevent shock during severe surgical can be obtained in the region of the previous operations, provided that any blood loss is diastolic level: the pulse pressure is greatly promptly replaced by transfusion. Observations diminished, e.g. the reading may be 90/85. Direct have been made of the amount of blood lost during manometry has confirmed that such bizarre various surgical procedures and it has been noted readings are not due to artefact associated with that the measured loss is the minimal amount that the Riva-Rocci method. Such fantastically low must be replaced because additional blood is lost pulse pressure can only be caused by a great into traumatized areas by post-operative oozing, reduction in cardiac output. It is not known how etc.34 When the arterial pressure has fallen due this is produced reflexly; one report suggests that to haemorrhage mere restoration of this pressure the phenomenon is due to vagal cardiac inhibition to normal by transfusion is not the index of ade- and advises treatment with intravenous atropine.39 quate therapy, for persisting vasoconstriction In confirmation of this view high right auricular plays a part in this rise. Transfusion cannot be and venous pressures have been observed during considered adequate until the tone of the vessels is the operation of this reflex.4' 7 This disturbance restored to normal and good peripheral circulation is unlikely to occur when adequate dosage of is re-established. Examples of increase in the relaxant has been given. An alternative explana- arterial pressure above normal due to excessive tion is a fall in the venous return due to pressure transfusion are rare, the usual sign being a rise in by the surgeon on the great veins (by packs or- the venous pressure as evidenced by distension retractors). Extension of the spine (e.g. by aProtected by copyright. of superficial veins. Recent investigation of the rest or bridge) or the lateral jack-knife posture arterial route for transfusing blood shows that in may produce similar effects to stimulation in the desperate cases (e.g. patients in moribund condi- coeliac region.10 Should such posturing lead to tion following profound blood loss) this method serious hypotension, a prompt return to a more may produce dramatic resuscitative effects. Lives normal position is indicated: elevation of the legs may be saved which would be beyond the reach of and head-down. tilt may further improve the intravenous transfusion.36 The aortic route may venous return. be the most rapid and effective in such emer- Spinal Anaesthesia: Arteriolar dilatation re- gencies;37 the coronary flow is improved sulting from vasoconstrictor paralysis in the immediately the transfusion into the arterial anaesthetized part of the body is the principal system is begun and improvement in the arterial cause of hypotension during spinal anaesthesia. pressure is more rapid than that produced by The ratio between the area of vasodilatation and intravenous transfusion. that of compensatory vasoconstriction in the rest It is of the determines the of blood Neurogenic Hypotension: widely accepted body degree http://pmj.bmj.com/ that hypotension can occur as the result of pressure fall. When sympathetic block is com- neurogenic or reflex activity. Conclusive proof plete such compensation cannot occur. It is ofthis mechanism is lacking. Presumably nervous probable that some reduction in cardiac output impulses due to trauma travel up afferent nerves to results from the increased circulatory bed during produce inhibition of the vasomotor centre. It widespread vasodilatation.41 The above con- was commonly believed that anaesthesia of ade- siderations apply equally to epidural block. quate depth could prevent this type of fall. It is Gillies40 has advocated total spinal block anaes- doubtful if this view can be sustained since reflex thesia leading to a hypotension of 40 mm. to on September 24, 2021 by guest. hypotension rarely occurs during light general 70 mm. systolic, to reduce haemorrhage and anaesthesia accompanied by relaxants. Direct facilitate surgery during lumbodorsal sympathec- recordings of arterial pressure show that traction tomy. He pointed out that the pressure at the on mesentery can produce an immediate fall in arterial end of the capillaries is normally 40 mm. pressure with instant recovery on the release of and stated that in cases thus anaesthetized the traction:10 these reactions are prevented by nerve major site of resistance is removed by dilatation block. The conclusion that such changes are due of the arterioles so that the arteriolar capillary to a reflex seems inescapable. One disturbance of pressure approximates the existing arterial pressure this type is of great interest and has been referred of 40 mm. to 70 mm. With the patient in the to as the coeliac plexus reflex;12 it may be en- head-down posture and breathing plentiful oxygen, countered during various upper abdominal tissue blood flow and oxygenation in important procedures.71 When operative stimulation in the organs is adequate. Coronary blood flow being Postgrad Med J: first published as 10.1136/pgmj.31.359.443 on 1 September 1955. Downloaded from POSTGRADUATE MEDICAL JOURNAL September 1955 dependent on the diastolic pressure may suffer, question obviously arises as to whether such but this effect is mitigated by the reduced cardiac hypotension can be tolerated or whether it en- work lowering oxygen need. Other methods of dangers the life of the patient. The work of producing controlled hypotension include the use Gillies40 appears to show that adequate tissue of ganglioplegics such as pentamethonium and oxygenation can be maintained provided the blood arterial . The ganglioplegics act in a is well oxygenated and that vasodilatation is similar fashion to spinal anaesthesia, producing, ensured. The low blood pressure associated with however, not only a sympathetic block but also a vasodilatation is not, of course, of the same serious block of parasympathetic ganglia. When arterial significance as a similar fall in pressure due to bleeding is used to produce hypotension, vaso- haemorrhage with which is associated extreme constriction occurs which is likely to produce vasoconstriction, low tissue circulation, anoxia and harmful tissue anoxia (haemorrhagic shock). capillary damage. In a 30 to 35° head-up tilt the On the other hand, a dry field is likely to be cerebral blood pressure has been calculated to be obtained at a relatively higher blood pressure level, 35 to 40 mm. when the heart pressure is 60 mm. furthermore the patient's own blood can be Hg. but other vital organs are at a pressure higher reinfused promptly to produce restoration of than heart level. Studies during hexamethonium- pressure immediately if it is indicated. This induced hypotension have shown an increase in technique and the apparatus required are fairly the cerebral arteriovenous oxygen difference complicated and reference should be made to the which implied a decrease in cerebral blood original articles.42'43 44 The excellence of the flow.16' 50 There is, however, a decrease in results obtainable with ganglioplegics even in cerebral oxygen need during anaesthesia and the neurosurgery have caused arteriotomy to fall into increased oxygen utilization which the above desuetude. researches demonstrated appeared to be adequate; other reports have suggested that cerebral bloodProtected by copyright. Controlled Hypotension flow may not, in fact, be reduced because there is The aim of this technique is to provide the a fall in cerebrovascular resistance.51 (Cerebral surgeon with an ischaemic operating field and to oxygen needs may be further reduced by hypo- protect the patient against shock. Indications for thermia, which has been proposed as an adjunct controlled hypotension have not been rigidly to increase the margin of safety.) Electroence- defined and differ in various centres. Justification phalograms have shown that virtually all cortical must be a product of the risk, the pathology and activity ceased when the pressure was reduced to the possible advantage to be gained.45 55 mm. systolic.6' 52,53 Some alteration in Three main methods are available as indicated: cerebral function has also been shown by the i. Arteriotomy. flicker fusion test of Berg.54 2. Spinal or epidural block. These methods Renal blood flow may not be greatly de- carry the advantage that not only the bloodless creased;55,56,57 naked eye changes in the liver field but analgesia and muscular relaxation are have been observed during laparotomy but their provided by the same manoeuvre. For further significance may have been misinterpreted.58 details reference should be made to published Technique:47, 59, 60 A well-adjusted blood pres- http://pmj.bmj.com/ work on these applications of spinal block.31, 46 sure apparatus (auscultatory or oscillometric) \ 3. Ganglionic blockade in which the hypo- must be fitted from the start and the blood tension is produced by intravenous agents, e.g. pressure must be checked frequently. Access to pentamethonium iodide.47' 48 Reduction in peri- a must be ensured by means of a diaphragm pheral vascular resistance, gravitational pooling of needle or an intravenous drip. Respiratory blood in the veins of dependent parts and some obstruction must be avoided and a high level of a reduction in cardiac output may all play part.41 oxygenation must be maintained; therefore some on September 24, 2021 by guest. When the subject has been deprived of the nervous authorities suggest that endotracheal intubation control of his circulation, changes in posture have should be the rule. It does not greatly matter a profound effect. When the body is tilted which agents are used, but since most general gravity induces a gradient of arterial pressure anaesthetics produce a tendency to postural (30 mm. Hg. for every 15 in. vertical height from hypotension very deep planes of anaesthesia heart level).49 This fact, combined with the should be avoided. The combination usually hypotension, enables the anaesthetist to provide employed has been thiopentone, nitrous oxide a remarkably dry operative field. For adequate with abundant oxygen and a relaxant or supple- control of surgical haemorrhage it may be necessary ment as necessary. Apnoea, though not to be to reduce the blood pressure at the site of operation feared provided oxygenation is maintained, is to 35 to 45 mm. A pressure of at least 60 mm. perhaps better avoided, firstly because spontaneous must always be maintained at heart level. The respiration provides a valuable continuous indica- Postgrad Med J: first published as 10.1136/pgmj.31.359.443 on 1 September 1955. Downloaded from September 1955 SCURR: Control of the Blood Pressure and Controlled Hypotension 449 tion of the patient's condition, and secondly exceeded. In some patients such blockade pro- because controlled respiration may cause a further duces excessive hypotension, in others a' pressure lowering of the pressure. It must be noted, floor' at a level higher than 60 mm. Hg. may be however, that controlled respiration is at all times observed. Increased and additional doses of mandatory in preference to inadequate spontaneous ganglioplegic produce no further fall in these ventilation. resistant patients and only serve to prolong The patient is placed in the appropriate posture excessively such hypotension as is attained. The as soon as possible after the induction of anaes- phenomenon of tachyphylaxis is frequently thesia, in order to assess the lability of the blood observed with these drugs, being least marked pressure and to give as long a time as possible for with Arfonad.60, 61 In resistant patients deepen- blood to drain away from the operation site. The ing the anaesthetic, increasing the adverse tilt, first dose of ganglioplegic is then given intra- and administration of procaine amide62 may all venously; the aim is to obtain a systolic pressure help to secure satisfactory hypotension. In one of 60 mm. Hg. because the best results are obtained centre a negative pressure is applied to the legs as at this level. A lower pressure is physiologically part of the hypotensive technique.51, 63 undesirable and renders observation of the level Surgical Technique: Infiltration with adrenaline difficult. Should excessive hypotension occur solutions is unnecessary and (unless preceded by minute doses of a pressor agent are given to raise chlorpromazine) will produce a pressor effect the pressure to 60 mm. Hg. or, in the case of leading to failure of the method. Haemostasis Arfonad, the drip is temporarily stopped and the must be meticulous, even the smallest points adverse tilt reduced. being secured. Severe haemorrhage (e.g. damage Several factors are available as guides in to a major vessel) promptly leads to a further fall assessing the dosage of hypotensive agent: in blood pressure, the patient having been de- I. The body weight. prived of his compensatory mechanism. It is Protected by copyright. 2. The metabolic rate. When this is high, as essential if much blood is lost, that prompt in thyrotoxicosis, very large doses may be needed equivalent replacement be made; the blood for successful results. pressure then returns rapidly to its former level.59 3. The initial blood pressure. As buffering reflexes are not active, such restora- 4. The lability of the circulation as assessed by tion of pressure is an accurate guide to transfusion. the hypotension resulting from induction of At the end of the operation the pressure should be anaesthesia plus posturing. When this fall is rising and preferably should be in the 80 to profound (as is commonly observed in hyper- o00 mm. region. Any acute rise is undesirable tensive subjects) small doses of ganglioplegic and may provoke haemorrhage. Frequent post- suffice. operative checks on the pressure should be made 5. Age. This is the most valuable guide. for the first 24 hours. Should the hypotension Young patients require much larger doses than the persist unduly long cautious antagonism with aged. The young commonly develop tachycardia is indicated. which tends to the fall in blood pressor drugs prevent pressure. Operative Shock: The method has been used in http://pmj.bmj.com/ Bearing these factors in mind one may use the certain operations usually regarded as liable to following initial doses. lead to operative shock, e.g. abdominoperineal Average robust young adults: resection, pelvic evisceration, etc., but provided Pentamethonium Iodide .. 50 to 200 mg. adequate blood transfusion was undertaken shock Hexamethonium Bromide .. 20 to 60 mg. did not occur. To what extent this phenomenon Pentapyrrolidinium Bistartrate I0 to 20 mg. is due to prevention ofblood loss or to the obtunda- Arfonad: drip solution I mg. per I mil- tion of circulatory reflexes is uncertain.64 This 60 drops per minute.60 observation has been corroborated65 and is in on September 24, 2021 by guest. Older patients: accordance with physiological studies. Wiggers66 Pentamethonium Iodide .. Io to 50 mg. states that recent studies favour the concept that Hexamethonium Bromide .. 10 to 30 mg. the net effect of compensatory vasoconstriction is Pentapyrrolidinium Bistartrate 5 to 20 mg. harmful and that the transition from impending Arfonad: I mg. per I mil--o to 30 drops to irreversible shock can be retarded or prevented per minute. of Subsequent doses are given as indicated by the by abrogation sympathogenic vasoconstriction. blood pressure readings, aiming to keep the Contraindications to Hypotensive Technique systolic pressure in the 60 to 70 mm. Hg. range. are: It seems probable that the danger of overdosage i. Inexperienced anaesthetist. is not great, the theoretical aim being complete 2. Unsettled anaesthetic conditions. When sympathetic block such limit is unlikely to be smooth anaesthesia cannot be secured or when an Postgrad Med J: first published as 10.1136/pgmj.31.359.443 on 1 September 1955. Downloaded from 450 POSTGRADUATE MEDICAL JOURNAL September 1955 anoxic has marred the induction and SHARPEY-SCHAFER, E. P. (1951), Brit. med. .7., episode hypo- 2, 382. tensive methods are contraindicated. 9. GORDH, T. (I945), Acta Chir. Scand., 92, Supp. 102. 3. Established shock. I0. EATHER, K. F., PETERSON, L. H., and DRIPPS, R. D. (1949), , Io, 125. 4. Recent coronary infarction or other severe II. HUBAY, C. A., et al. (1954), Ibid., 15, 445. cardiac disease. 12. BURSTEIN, C. L. (1949), Fundamental Considerations in Severe renal elimination of the Anaesthesia, New York. 5. damage: 13. CREYSSEL, J., et al. (1947), Lyon. Chir., 42, 23. drugs may be retarded. 14. DRIPPS, R. D. (1947), Anesthesiology, 8, 15. 6. Respiratory inefficiency, severe anaemia or 15. BUCKLEY, J. J., et al. (1953), Ibid., 14, 226. anoxia from cause. 16. VAN BERGEN, et al. (1954), Ibid., 15, 507. any 17. HOWLAND, W. S., and PAPPER, E. M. (1952), Ibid., 13, 343. 7. Severe diabetes.67 18. RISKIN, A. M., et al. (1954), Ibid., IS, 262. Dangers of the Method: Obvious dangers 19. CILIBERTI, B. J., et al. (1954), Ibid., 15, 273. include acute failure the 20. KING, B. D., et al. (1951), Ibid., 12, 556. circulatory during 21. KING, B. D., et al. (1954), Ibid., Is, 231. the induction of hypotension; this has been 22. HARRISON, B. L., and SEWARD, E. H. (1954), Brit. med.. ., but to be rare in the I, 1077. reported fortunately appears 23. COBB, C. C., HALL, J., and HALL, R. A. (1953), Lancet, absence of cardiac disease or anoxic incident 1, 973. anaesthesia. In deaths of this the 24. THOMPSON, J. E., and ARROWOOD, J. G. (1954), Anes- during type thesiology, 5I, 658. hypotensive technique seems directly implicated. 25. CHURCHILL-DAVIDSON, H. C. (1951), Brit. med. J., Deaths due to thrombosis, reactionary haemor- 2, 1551. renal were no means un- 26. SWANN, H. J. C. (1952), Ibid.,'3, 1003. rhage, failure, etc., by 27. ECKENHOFF, J. E., and DRIPPS, R. D. (1954), Anes- known prior to the introduction of hypotensive thesiology, 15, 681. methods: in one series the incidence of such 28. INGLIS, J. M. (1952), Lancet, 2, 362. 29. STEPHEN, C. R., NOWILL, W. K., and MARTIN, R. complications was approximately equal in similar (1953), Anesthesiology, 14, x8o. cases anaesthetised with or without 30. LYNN, R. B., and SHACKMAN, R. (195I), Brit. med. J., hypotension.68 2, 333. Deaths due to anoxia of vital organs due to the 31. BROMAGE, P. R. (1954), Spinal Epidural Analgesia, London.Protected by copyright. hypotension have not been proven as a compli- 32. LOCKETT, J. (1951), Anaesthesia, 6, 83. cation of the method. of this 33. HERSHEY, S. G., ZWEIFACH, B. W., and ROVENSTINE, Opponents technique E. A. (I953), Ibid., 14, 245. have suggested various complications, arguing 34. BONICA, J. J., and LYTER, C. S. (1951), Ibid., 12, 90. from and but unsubstantiated 35. STEPHEN, C. R. (1952), Ibid., 13, 540. hypothesis hearsay 36. BROWN, A. S. (1953), Lancet, 2, 745. by case reports. 37. HAXTON, H. A. (1953), Ibid., x, 622. In one report69 based on questionable evidence 38. MELROSE D. G., and WILSON, A. D. (1953), Ibid., a death rate of i in is but examina- 1, 1266. 450 suggested, 39. SMITH, B. H. (1953), Ibid., 2, 223. tion of the various causes of death reveals that 40. GILLIES, J., and GRIFFITHS, H. W. C. (1948), Anaesthesia, were not due to the 3, I34. many directly hypotension, 4I. SHACKMAN, R., et al. (1952), Ibid., 7, 2I7. other complications were well known before 42. BILSLAND, W. L. (1951), Ibid., 6, 20. hypotensive methods were introduced and the 43. MORTIMER, P. L. F. (1951), Ibid., 6, 25. of others is doubtful. Another 44. JACKSON, I. (1954), Jbid., 9, 13. attributability 45. EDRIDGE, A. W. (1954), Broadway Clin. Supp., 1, 7. valuable and interesting series of fatal case reports70 46. LEARMONTH, J. (1953), Brit. med. J., 1, 743. reveals in almost instance the of C. F. Acta 2, every danger 47. SCURR, (1951), Anaesthesiologica, 243. http://pmj.bmj.com/ anaesthetic ' incidents ' when hypotensive methods 48. ENDERBY, G. E. H. (I951), Proc. Roy. Soc. Med., 44, 82g. are 49. ENDERBY, G. E. H. (1954), Lancet, I, I85. used. It appears certain that the reserve or 50. HUGHES, G. (1954), Ibid., I, 311. margin of safety is greatly lessened in the hypo- 51. JAMES, A., COULTER, R. L., and SAUNDERS, J. W. tensive of the (1953), Ibid., I, 412. state, any mismanagement 52. BROMAGE P. R. (1953), Proc. Roy. Soc. Med., 46, 919. anaesthetic or infringement of the rules will 53. SCHALLEK, W., and WALZ, D. (1954), Anesthesiology, I5,. be paid for at the highest price-the life of the 673. For this reason induced 54. NILSSON, E. (1953), Brit. J. Anaes'h., 25, 24. patient. hypotension 55. MILES, B. E., et al. (I952), Clin. Sci., II, 73. is only permissible when there are direct and 56. DE WARDENER, H. E. (1955), Anaesthesia, I0, 18. on September 24, 2021 by guest. positive indications, when the anticipated benefit 57. EVANS, B., and ENDERBY, G. E. H (1952), Lancet,, 1045. to the the risk and when first- 58. BROMAGE, P. R. (1952), Ibid., 2, I0. patient outweighs 59. ENDERBY, G. E. H. (1953), Trans. Med. Soc. Lond., 68, 68. class anaesthetic conditions are assured. 60. SCURR, C. F., and WYMAN J. B (1954), Lancet, 1, 338. REFERENCES 61. HAMPTON L. J., et al. (1954), Surgery, 35, 857. 62. MASON A. A., and PELMORE, J. F. (1953), Brit. med. J.,. I. WRIGHT, S., Applied Physiology, London, 1953. I, 250. 2. PRIMROSE, W. B. (I954), Brit. J. Anaesth., 26, Ioo. 63. SAUNDERS, J. W. (1952), Lancet, x, 1286. 3. EDITORIAL (I954), Ibid., 26, II8. 64. SCURR, C. F. (1951), Ibid., i, 1020. 4. SCURR, C. F. (I95I), Curr. Res. Anesth. & Analg., 30, 2II. 65. BOYAN, P. (1953), Brit. med. J., I, 728. 5. PIERCE, V. K., BOYAN, P., and MASTERSON, J. G. 66. C. S.G.O., 96, 3IO-3I4. WIGGERS, J. (1950). Physiology of Shock, p. 243. (I953), 67. GRIFFITHS, J. A. (1953), Quart. J. Med., 22,. 405. 6. ANDERSON, M. E., and LUNDY, J. S. (x949), Anesthesiology, 68. WYMAN, J. B. (1953), Proc. Roy. Soc. Med., 46, 605. 10, I45. 69. HAMPTON, L. J., and LITTLE, D. M. (1953), Lancet, I,. 7. BISHOP, H. F., CILIBERTI, B. J., and BARENDRICK, 1299. E. H. (I952), Ibid., 13, 297. 70 . (I953), Anaesthesia, 8, 263.. 8. HOWARD, P., LEATHART, G. L., DORNHORST, A. C., 71. SCURR, C. F. (1950), Ibid., 5, 67.