HYPOTENSIVE ANrESTHESIA

By ROBERT Cox, M.B.E., F.R.C.S.

A.uistant Surgeon, Westminster Hospital : Surgeon, All Saints Hospital

THE performance of a major surgical operation under a general or spinal anresthetic is always accompanied by some fall in blood-pressure ; it may not be of very great extent but it is always there if proper observation is kept for it. Even the administration of the drugs commonly used for routine premedication will bring about a small but important and observable fall in tension.

Some types of anresthetic, especially spinal anresthetics, and some types of operations, such as those associated with considerable blood loss or severe tissue trauma, are notably accompanied by marked hypotension.

Because lowered blood-pressure is one of the cardinal evidences of surgical shock and because it is a deviation from normality, it has become a matter of sinister portent to both surgeon and anlesthetist, and to be avoided or corrected if at all possible. This attitude is engrained in all of us from our earliest clinical training, and it is not surprising therefore that the idea of deliberately seeking a lower level of blood-pressure, whatever may be the reason for this course of action, has met with much opposition, suspicion, and misunderstanding.

The reason that underlies the desire deliberately to produce a hypotensive state is to reduce loss of blood and aid the surgeon by reducing the amount and rate of hremorrhage. There is an important point here which is often not appreciated : when the rate of bleeding is reduced, it is very much easier to see the points that are bleeding and therefore their control is more easily and rapidly accomplished. This is well exemplified in the operation of prostatectomy.

With conventional anasthesia the amount of bleeding is such that often the surgeon cannot define with accuracy the actual bleeding points and has to resort to mass ligature or suture of capsular tissues, plus hydrostatic bag pressure, in order to bring about hremostasis, whereas with hypotensive anlesthesia the bleeding points can be accurately located and dealt with by diathermy coagulation or whatever method the surgeon may choose.

Another advantage soon became apparent with the increasing use of hypotensive drugs. These drugs act by reason of their ability to block t k passage of impulses through autonomic nerve ganglia, thereby preventing vasopressor impulses reaching the peripheral resistance. At the same time afferent impulses are also blocked and thereby the production of shock is greatly diminished (Freeman et al., 1938 ; Paton and Zaimis, 1951). Thus operations of considerable surgical magnitude can be performed using hypotensive drugs with only a light level of general anasthesia, whereas with more conventional methods a much deeper general anasthetic would be required with consequent delay in the patient's recovery. Again instancing prostatectomy, the advantages of having a patient awake and able to drink as soon as he is back in bed from the theatre are obvious.

The difference between the hypotension which accompanies the development of shock and that which is deliberately induced is most important and an understanding of this difference is the basis for the belief that the proper use of hypotensive drugs is not only safe but beneficial. In the hypotension of shock the reduction of blood-pressure is uncontrolled and haphazard and is accompanied by attempts on the part of the body at readjustment by vasoconstriction, with consequent reduction of blood flow through vital organs. In induced hypotension, vasodilatation in the visceral and 'peripheral areas occurs with consequent maintenance of blood flow.

Read at the Thirteenth Annual Meeting of the British Association of Urological Surgeons at London on 28th June 1957.

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Three chief methods of deliberately producing hypotension have been used. I . High Spinal Anesthesia (Griffiths and Gillies, 1948).-This is a method which undoubtedly

can bring about a profound depression of the blood-pressure, but it is not readily controllable and has certain unpleasant features, especially from the patient’s point of view. We at Westminster Hospital have not used this method, and I propose to say no more about it.

2. The pentamethonium and hexamethonium drugs were introduced about 1948 and came into use in the following year and have been used extensively (Cox, 1953 ; Wyman, 1953), so that there is now available a considerable body of experience in their use. These drugs, used either in one large dose or in divided doses, are capable of causing considerable falls in blood-pressure, but the degree of hypotension and its duration were not entirely predictable and control was not always easy.

3. ATfonac/.-This ganglion-blocking agent has an action of only short duration, a single injection producing a fall of blood-pressure lasting only three to five minutes, and repeated doses do not produce tachyphylaxis. It can therefore be administered in a continuous intravenous drip infusion ( 1 mg. of Arfonad per millilitre), and by altering the rate of the drip the degree of hypotension can be controlled (Magill et a/., 1953); when the drip infusion is stopped, recovery is rapid and complete, the pressure remaining stable unless other factors are at work. We have in this drug, then, a method of producing controlled hypotension, whereas the pentamethonium drugs gave only induced hypotension.

We have used Arfonad extensively and in many types of operation since its introduction i n 1953. Its use has become more or less routine in urological operations such as prostatectomy, cystectomy, and partial nephrectomy. For massive procedures such as pelvic viscerectomy I consider its use to be strongly indicated. When properly and intelligently used it appears from our experience to be safe and devoid of unpleasant side effects.

There are, of course, contraindications to the use of hypotensive anasthesia, though with greater experience and growing confidence anasthetists tend to accept more and more cases for this technique.

The most important and absolute contraindication is anoxia. I t is vital that a patient with a low pressure should be fully oxygenated, and it follows that the anasthetist must have perfect and complete control of the airway. Failure to observe this rule resulted in at least two deaths in our earlier pentamethonium series. Arfonad allows of greater safety because, should difficulties with the airway threaten, the drip can be shut off with rapid recovery of the blood-pressure.

Severe‘coronary artery or aortic heart disease are also contraindications, but minor degrees of stenosis or old infarction are not generally considered a bar. Renal disease also, if severe, is taken to be a contraindication. Gross anzmia should be corrected before hypotensive anasthesia is used, and when serious blood loss occurs it must be promptly and effectively made good.

There are certain other requirements which I think should be met before these methods are safe from the patient’s point of view. Hypotensive drugs clearly are not desirable agents in the hands of unskilled or unthinking anasthetists, and both surgeon and anasthetist must be prepared to take a little extra trouble ; the surgeon particularly must be meticulous about his hamostasis, while the anasthetist similarly is attentive to full oxygenation. Moreover, if either partner is unhappy or unwilling in the use of the method, it is better abandoned.

If it had not been that I have observed such derelictions taking place, it would seem unnecessary to lay down that the patient’s blood-pressure must be constantly and frequently observed and recorded. I have seen patients being given hypotensive drugs during anasthesia without control from a blood-pressure recording apparatus. Such folly is criminal and invites disaster.

We have used these methods extensively since 1950, Arfonad being the agent of choice since 1953, and have not had occasion to regret it. From 1953 to 1956 I performed 170 prostatectomies using Arfonad. There were four deaths in this series, but none could be attributed to the anresthetic or to the induced hypotension. The number of patients requiring blood transfusion

3 64 B R I T I S H J O U R N A L O F U R O L O G Y

at the time of operation or within the next forty-eight hours has been very materially reduced as compared with pre-hypotensive anaesthetic days. My impression, and it can be no more since the notes are not always complete on this point, is that there is a slightly increased rate of late hremorrhage, but this has only necessitated the reintroduction of a catheter three times in the last two years. 1 think this complication is due to the use of diathermy to control bleeding points, which under hypotension can be seen but otherwise are left in the hope that they will stop spontaneously. Prostatectomy is probably unique in modern surgery in that it is stili bedevilled by the problem of bleeding. For myself, I can say that the use of hypotensive anzsthesia and an irrigating catheter have much reduced the anxieties which I have about my patients bleeding after prostatectomy.

REFERENCES

COY, R. ( 1953) Pro,- R . SOC. Med., 46, 608.

GRlrFmis H. W . c., and GILLIES, J. (1948). Amsthesia, 3, 134. M N ~ I L I , 1. W , SCURR, C. F., and WYMAN, J. B. (1953). Lancer, 1, 219. PATW. W D M., and ZAIMIS, E. J. (1951). Brit. J . Pharmacol., 6 , 155.

kKELMAY, W. I?, S H A F I L K . s. A., and HOLLING, H. E. (1938). J . c/m. In lev / . , 17, 359.

W \ h l A N 1 H (1953). Proc. R . SOC. Med.., 46, 605.