ANAESTHESIA FOR OBSTETRIC EMERGENCIES

ANAESTHESIA FOR OBSTETRIC EMERGENCIES

Brit. J. Anaesth. (1971), 43, 864 ANAESTHESIA FOR OBSTETRIC EMERGENCIES BY J. S. CRAWFORD This topic is most conveniently discussed with reference ...

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Brit. J. Anaesth. (1971), 43, 864

ANAESTHESIA FOR OBSTETRIC EMERGENCIES BY J.

S. CRAWFORD

This topic is most conveniently discussed with reference first to Caesarean section and secondly to vaginal surgery, regard being paid in each instance to the use of general anaesthesia and of regional block.

Maternity Hospital, Birmingham, England.

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More recently the author has grafted certain precautionary measures on to this technique, namely: the invariable routine of "pre-oxygenating" the patient for 3-4 minutes before induction, in order to reduce the hazard to mother and (1) EMERGENCY CAESAREAN SECTION foetus of an episode of hypoxia; The maternal requirements are: efficient oxygenathe application of cricoid pressure (vide infra); tion, a reasonable degree of stability of cardiothe injection of hyoscine (0.6 mg) rather than vascular dynamics, protection against the aspiraatropine, immediately before that of thiopention of regurgitated or vomited gastro-oesophageal tone, in order to reduce the incidence of contents, freedom from distress, and adequacy of awareness during operation (Crawford, myometrial contractility following delivery. 1971a); The foetal requirements are: maintained adethe administration of either 0.5 per cent haloquacy of uteroplacental perfusion with oxygenated thane throughout the operation (Moir, 1970) blood and efficient exchange of respiratory gases, or of 0.1 per cent methoxyflurane subsequent and the avoidance of depression due to drugs to delivery of the infant (Crawford, 1971a) administered to the mother. further to reduce the incidence of awareness; (A) General Anaesthesia. and positioning of the patient on the operating The technique of general anaesthesia incorporates table in a manner which will ensure that measures which should be put into effect—in all the gravid uterus does not compress the but the very rare case—a considerable time beinferior vena cava (Crawford, 1971b). fore the patient reaches the anaesthetic room: in most cases, indeed, before the decision to operate When this amended technique is employed, has been made. Specifically, this makes reference each of the requirements detailed in the opening to the protection of the mother against regurgita- paragraphs will have been met: the anaesthetic tion-aspiration, and as the topic is relevant to the risk to the mother—and the hazard of discomfort entire field of obstetric anaesthesia it will be dealt during operation—should be negligible, and the neonate should suffer neither drug-induced with separately towards the end of this paper. The basic technique of general anaesthesia depression nor depression due to asphyxia inwhich has gained widespread acceptance during cremental to that which was present before the the past decade consists of induction with thiopen- start of the anaesthetic. One further important tone (250-300 mg in 2.5 per cent solution), aspect of the technique must, however, be emfollowed by suxamethonium (100 mg) and swiftly- phasized. Arrangements must be made to replace accomplished endotracheal intubation (without promptly an appreciable degree of blood loss prior inflation of the lungs using a mask); sub- occurring during the operation. If the section is sequently, anaesthesia is maintained using a mix- being undertaken in response to antepartum ture of nitrous oxide and oxygen, provided by haemorrhage, it is likely in most cases that crossintermittent positive pressure ventilation, and matched blood will be already available. In other circumstances the anaesthetist, in his role as aided by the maintenance of muscle relaxation. resuscitation officer, has the responsibility of ensuring before the start of the procedure, that J. SELWYN CRAWFORD, F.FJLRX.S,. Birmingham blood will be available for immediate infusion

ANAESTHESIA FOR OBSTETRIC EMERGENCIES if and when required. Furnishing of the operating theatre with a blood-wanning device is an essential part of these preparations.

the technique, the production of maternal hypotension is almost inevitable unless active measures are taken to guard against it. If matpmai systolic blood pressure falls by 30 per cent, or below 100 mm Hg—and is maintained at this level for more than a very short time—foetal asphyxia will develop (Moya and Smith, 1962; Marx, Cosmi and Wollman, 1969). The administration of a vasopressor might succeed in reversing the fall in blood pressure, but by causing uterine arterial vasoconstriction, will fail to return the efficiency of perfusion of the placental site to the pre-anaesthetic level [the qualification that ephedrine is an exception to this is a matter of some dispute (Shnider et al., 1968; James, Greiss and Kemp, 1970)]. Recently, Cosmi and Marx (1968) have demonstrated that an effective way of guarding against both maternal hypotension and reduced placental perfusion is by "pre-loading" of the maternal circulatory blood volume. This is accomplished by infusing 1 litre of Ringer lactate solution during the 30-minute period before initiation of the regional block. The influence of lateral tilt upon the welfare of mother and infant during the course of section conducted under regional block has not been well investigated. Quite possibly it will be found to reduce considerably the hazards discussed above. (c) Comparative Evaluation of General Anaesthesia and Regional Anaesthesia. Under certain circumstances, the use of regional block for emergency section is either contraindicated or highly inadvisable. These are: in the presence of actual, or strongly threatened severe maternal haemorrhage; if a severe grade of foetal distress, or impending foetal distress (indicated, for example, by a prolapsed, or presenting, loop of umbilical cord) dictates the urgency of operation; if it appears likely that myometrial relaxation will be required to permit a relatively atraumatic delivery (examples: the presence of a constriction ring; an oblique, or transverse foetal lie, especially if little liquor remains); if eclampsia or a severe grade of pre-eclamptic toxaemia is present (the threatening neurological and cardiovascular complications are more easily governed under conditions of general anaesthesia);

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(B) Regional Block. Skin analgesia should extend from T6 to S5 when regional block analgesia is employed for Caesarean section. An extradural block may be provided specifically for the operation, or by extending a lumbar epidural block which had been in progress during labour. It is doubtful if a pre-existing caudal block can expeditiously be extended in this manner. If a lumbar epidural block is used, the analgesic drug should be injected through a catheter, and not directly via the needle: injection via the catheter avoids the extra hazard of depositing the drug in the subarachnoid space; the operation might last longer than the duration of action of a single dose of the drug. When epidural block is given, the established route into the epidural space may conveniently be used to provide postoperative analgesia. Alternatively, a spinal block may be initiated pre-operatively, but in this case, the majority opinion favours the single-dose technique. Whilst the use of regional block does not guarantee complete freedom from the danger of regurgitation-aspiration, it renders this hazard a very minor consideration. If the technique (either epidural or spinal) is correctly employed, the choice also ensures that the infant will not be subjected to drug-induced depression, or the mother to hypoxia. However, the avoidance of maternal distress is by no means guaranteed. The incidence of total failure to provide analgesia has been reported by one competent investigator as being 4 per cent, with insufficient analgesia to permit the operation to continue in a further 6 per cent of cases (Shnider, 1970a). The relatively poor relief from discomfort, pain and nausea associated with the use of regional block for Caesarean section is such that depressant drugs— frequently, even, general anaesthesia—are administered almost routinely subsequent to delivery of the infant. Of great import, however, is the effect of regional block on maternal cardiovascular dynamics and, as a reflection of this, upon uteroplacental perfusion. Owing to the extensive autonomic blockade which is an inherent attribute of

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being satisfied, it is quite acceptable to provide— or to extend—a regional block for the operation. If the choice of regional block is made, facilities for undertaking cardiopulmonary resuscitation of the mother—and an attendant qualified to use them—must be constantly present throughout the procedure. (2)

VAGINAL SURGERY

(A) Forceps Delivery. In modern obstetric surgery, forceps delivery may be categorized as: outlet, low (with or without rotation of the foetal head) and mid-forceps. Here the relative merits of the different forms of anaesthetic technique are much more sharply defined than is the case with respect to emergency Caesarean section. There should be few occasions annually in the practice of any hospital upon which general anaesthesia is administered for a forceps delivery. The demerits of general anaesthesia when administered for forceps delivery are no less than those associan indication that endotxacheal intubation will ated with its use for Caesarean section; whilst, on the other hand, the factors which argued against prove to be difficult. the use of regional block for section are applicThere is an acceptable substitute for each of able to a much smaller extent in consideration of the drugs recommended, for the general anaes- forceps delivery. The reason for the latter contrast thetic technique if the patient is sensitive to one is that analgesia is required to be extended only up to T10-11 for vaginal delivery, and thus the of those recommended. On balance, therefore, in terms of numbers of threat of undue hypotension is limited (some categories of cases, it is apparent that general authorities would claim that it is averted), and anaesthesia is more likely to be the preferred the requirements of urgency may be satisfied. technique in the interests of both maternal and There is a choice between three methods of foetal well-being. This is so even when the mother regional block: extradural, spinal and pudendal. has been in receipt of a regional block during If the patient has been in receipt of an extradural labour: in such a case, urgency will be dictated block during labour, there is obviously no problem either by haemorrhage or by foetal distress. If the to be answered. former, extension of the regional block further Pudendal block continues to be the most frecephalad is contraindicated; if the latter, rapid quently used method in Britain, but it provides upward extension of the block without "pre- analgesia of a very poor quality in the majority loading" could well markedly jeopardize the of cases. It is quite likely that the persistence chance of foetal survival. with which it is employed reflects in large measure However, the most commonly occurring indica- the inadequacy of anaesthetic staffing of obstetric tion for an emergency Caesarean section—in the units. The name itself is a misnomer (Scudamore United Kingdom, if not in the United States and Yates, 1966), for in order to provide reason(Shnider, 1970b)—is "failure to progress in able analgesia of the lower birth canal and perlabour" in conjunction usually with a somewhat ineum, the posterior cutaneous nerves of thigh poor obstetric background or an indication of early should be blocked in addition to the pudendal foetal distress. In this circumstance, haste is not nerves, and the proposed line of the episiotomy of paramount importance and, all other criteria should be infiltrated with local analgesic solution.

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There are very few medical or obsteric considerations which mitigate against the choice of general anaesthesia, and they are met with only rarely. These are: acute, or severe chronic, pathology of the respiratory system; sickle cell disease, because of the risk that during the induction of general anaesthesia, there might be a brief period of hypoxaemia (a hazard which will be of greater moment if it occurs whilst the patient has a low cardiac output, due to caval occlusion); the risk of inducing hypoxaemia is relatively low when regional block is used;

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dural block, and may be performed more easily and with greater expedition. It requires very little equipment and only a brief period of training, and provides satisfactory operating conditions within 5-6 minutes of the start of the procedure (which is described in detail elsewhere—Crawford, 1971c). The major drawback to the use of the technique is the occurrence of post-spinal headache, the incidence of which should be less than 3 per cent if a 23 or 24 gauge needle is used. This method of analgesia will surely emerge as the one of choice as the staffing of obstetric units by anaesthetists improves. It should be noted that neither extradural nor spinal block will obtund the distressing—often painful—dragging sensation which the patient experiences during a difficult forceps delivery. Relief The initiation of an extradural block is an from this should be provided by inhalational acceptable and appropriate technique. If the lum- analgesia. bar route is used, a catheter is best inserted into General anaesthesia is likely to be required the epidural space as a preliminary to the injection for a forceps delivery under the following cirof the analgesic solution, lest the latter is inad- cumstances : vertently placed in the subarachnoid space. It is if the patient is extremely unco-operative, or doubtful if more than a few highly skilled—and it is virtually impossible to communicate inherently fortunate—practitioners can successwith her; fully initiate a lumbar epidural block in each of if the patient has eclampsia, and a regional a series of patients who are in the second stage block is not already in progress; of labour. Under the latter circumstance, the caudal route is much the more likely to be chosen if there is a specific contraindication to the use by most obstetric anaesthetists. If an Irish type of of regional block; argument may be forgiven, except for those cases if the proposed operation is a "trial of forceps" in which anatomical difficulties make it impossible, —an anachronistic procedure in which the caudal block is technically a much easier proobstetrician considers that delivery by cedure, and more rapidly accomplished, than is Caesarean section might be required in the lumbar epidural block. Two observations require event of failure to deliver vaginally. to be made with regard to caudal block. Firstly, a relatively large volume of anaesthetic solution If general anaesthesia is administered, the premust be injected in order rapidly to obtain the ferred technique is that as described for Caesarean desired spread. Secondly, as the foetal head is, section. Each of the precautions against regurgitain the circumstances under discussion, through tion-aspiration enumerated elsewhere in this rethe pelvic brim, extra caution must be exercised view must be rigorously observed. Anaesthesia when the needle is advanced through the sacro- should not be induced whilst the patient is in the coccygeal ligament to impinge on the posterior lithotomy position. wall of the body of the sacral vertebrae—a laterally directed needle, or one whose point is (B) Ventouse Delivery. slipped beyond the sacrum, could be propelled into the foetal scalp without the anaesthetist's The order of preference of anaesthetic technique for this operation is the same as that for forceps being aware of it. delivery. Spinal and extradural block each proThe use of a low spinal block for forceps vides good operating conditions and excellent delivery has all of the advantages of an extra- analgesia, except for the dragging sensation, which

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If this full procedure is carried out, outlet forceps delivery may be effected without causing much distress to the patient. However, a more formidable forceps delivery conducted under these conditions will, in the considerable majority of cases, cause pain. The pain is twofold in origin: arising from the uterus, and from the peri-uterine and peri-pelvic diaphragmatic tissues. It may be subdued—in some cases totally obtunded—by the administration of inhalational analgesia. Paracervical block will effectively guard against the pain in a large proportion of cases, but the use of this technique is now thought by many to be inadvisable (Editorial, 1970). An additional cause of discomfort is the dragging sensation which accompanies a strongly-exerted pull with the forceps.

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868 should be treated in the manner previously described. Pudendal block is an extremely poor provider of relief from pain during this operation. Unless regional block is specifically contraindicated, general anaesthesia should not be used, except for the pernicious and very rarely occurring procedure of "trial of ventouse".

breech extraction invokes a greater degree of danger to the foetus than does assisted breech delivery; for the second stage of labour to proceed, with reasonable speed, to the point at which an assisted breech delivery may be carried out, the maternal bearing-down power—and the force of myometrial contractions—must be undimi rushed; the pain of a breech delivery is the sum of uterine pain, plus perineal pain, plus the pain caused by manipulations within the lower birth canal (including, in most cases, the application of forceps to the aftercoming head). Obviously, the employment of general anaesthesia is quite inappropriate in a case in which an assisted breech delivery is the aim. If progress during the second stage is poor, due to flagging myometrial and maternal voluntary efforts, or if evidence of foetal distress dictates that delivery be rapidly accomplished, a breech extraction will

be required, and this should call for general anaesthesia. Anaesthesia is needed not only to provide analgesia and pelvic floor relaxation, but also to induce myometrial relaxation. The reason for the latter objective is to reduce the difficulty of intra-uterine manipulations, and hence to diminish the threat of trauma to the infant Under this circumstance the basic technique of anaesthesia as described previously may be employed, with the addition of halothane (2.0 per cent) until the infant has been delivered. If general anaesthesia is needed solely to permit the rapid delivery of the aftercoming head, halothane will not be required. This is one of the only two situations in obstetric surgery in which anaesthesia has to be induced whilst the patient is in the lithotomy position. The precautions against aspirationregurgitation, listed later in this review, must be adhered to rigorously. The use of regional block—either extradural or spinal—in cases of breech presentation has been discouraged because it is directly correlated with an increased incidence of perinatal mortality. The association reflects the fact that, because of diminution in maternal expulsive efforts, there is an increase in the need to perform a breech extraction, and added to this are two further facts of ominous import: uterine tone is not reduced by the regional block, and the adequacy of analgesia is such that the unwary obstetrician is tempted to be too forceful in his manipulations because the patient does not protest. These remarks certainly apply to spinal block, the use of which should not be encouraged. In the writer's hospital we have observed that when 0.25 per cent bupivacaine is used for lumbar epidural block, the bearing-down reflex is obtunded in approximately 50 per cent of cases. Furthermore, in a smaller proportion of patients a reduction in the power of the lower abdominal muscles is produced. These effects, in our experience, make little significant difference to the ability of a patient to deliver spontaneously a foetus presenting by the vertex, although the second stage is longer when the patient has to be encouraged to bear down than it is when the reflex urge is present. It must, however, be assumed that they will reduce the chances of avoiding the necessity of performing a breech extraction. Certainly the prospect of providing, with a regional block, an

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(c) Breech Delivery. This continues to provide one of the major challenges to both obstetrician and anaesthetist The challenge to the obstetrician is met, with increasing frequency, by the decision to perform an elective Caesarean section—or emergency section before a late stage of labour has been reached—and this effectively reduces the challenge to the anaesthetist and, most probably, brightens the prospects for the infant. Much of the generally held assessment of the perinatal risks attendant upon breech delivery is confused by the fact that in a very considerable proportion of these cases the infant is premature. Accepting the fact that the perils of prematurity (including the factors which can cause premature delivery) artificially exaggerate the dangers inherent in breech delivery, the following considerations demand recognition:

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undistressed mother with a fully relaxed pelvic be required, and the entire delivery will be condiaphragm presents a rosy picture. However, a ducted under it. breech presentation persists in only 3 per cent of The second twin is at much greater risk. It pregnancies which are maintained beyond 32 presents not infrequently by the breech or as a weeks, and only a proportion of these will be compound presentation. Also, it is exposed to permitted to come to vaginal delivery. Hence the double hazard of a reduced placental site it will be a matter of years before any one (due to myometrial retraction) and a prolonged obstetric unit can assess reasonably well the extent second stage (reflective of a period of uterine to which regional block exposes such an infant to quiescence following delivery of the first twin). increased hazard. Caution must be employed. Prolapse of the umbilical cord is an additional The anaesthetist should not provide a regional complication to which the second twin is subject. block for breech delivery unless there is the Because the co-operative efforts of the mother absolute guarantee that an obstetrician highly are required to reduce delay in delivery, and skilled in the art of breech extraction (a dying because intra-uterine manipulations have so frebreed of practitioners) will be present at the quently to be undertaken (and recalling, too, delivery. If an extradural block is given to a that these infants generally are premature), the patient with a breech presentation, and breech use of extradural or spinal block in these cases extraction is found to be required, a general is most inadvisable. For similar reasons, the anaesthetic should be given. The use of extra- administration of pudendal block should also not dural block for first-stage labour, and its discon- be advocated. Perineal field block plus intertinuance when the second stage approaches, is a mittent inhalational analgesia is again the least technique which cannot be discussed here. offensive technique. If general anaesthesia is rePudendal block is not a satisfactory alternative quired to assist in the second delivery, the techto extradural block in these cases. If administered nique is as described with respect to breech too early, it will reduce or obtund the bearing- delivery. This is the other situation referred to in down reflex, and by the time that it would be which anaesthesia must be induced whilst the patient is in the lithotomy position. wholly beneficial, it is difficult to insert. Probably the least unsatisfactory technique consists of a perineal field block (perhaps aug(E) Retained Placenta. mented by block of the posterior cutaneous General anaesthesia is certainly required for this nerves of thigh) plus intermittent inhalational operation if the obstetrician cannot gain entry analgesia. to the uterus. Under this circumstance, anaesWhatever the proposed method of analgesia, thesia should be induced whilst the patient is in it is not to be doubted that an anaesthetist must the horizontal position, as intragastric pressure be present from the start of the second stage of is increased by adoption of the lithotomy position. a breech delivery. His equipment should be in The basic technique as described may be used, readiness for the immediate provision of general halothane being administered until such time as anaesthesia, and, if the patient is not already the obstetrician is satisfied that all the products receiving an infusion, he should establish entry of conception have been removed from the into a conveniently located vein. uterus. If an epidural block has been in progress during (D) Multiple Delivery. labour, manual removal of the placenta—if necesAlthough these are usually spontaneous, their sitated—can be performed without causing disoccurrence demands the presence of an anaes- comfort to the patient, unless the cervix has closed down tightly. However, to administer an extrathetist and a paediatrician. Delivery of the first infant is rarely com- dural block or a spinal block solely for this operaplicated. If it presents by the breech, either a tion would be an example of misguided zeaL A spontaneous or an assisted breech delivery is the combination of paracervical block and pudendal general rule. In cases of locked twins, or of some block would be a much more appropriate way other rare complication, general anaesthesia will of providing analgesia for this operation.

870 Hypoaesthesia—provided by the slow intravenous injection of a well-diluted mixture of pethidine (100-150 mg) and a tranquillizing agent, for example, 50 mg promazine—has much to commend it. This is especially so in the situation in which regional block is not favoured, as hypoaesthesia will then limit the demand for general anaesthesia to cases in which myometrial relaxation is required. The technique should not be used upon a patient who is hypotensive or is considered to be hypovolaemic.

OTHER CONSIDERATIONS OF ANAESTHETIC INTEREST

Amniotic embolism. There has been little progress during the past decade in the facility with which a patient who has suffered an amniotic embolism may be successfully treated. The combination of pulmonary embolism and accompanying pulmonary arteriolar vasospasm leads to acute respiratory distress which, in the current absence of a specific pulmonary vasodilator, can be countered only by the administration of 100 per cent oxygen, usually via an endotracheal tube. The other outstanding feature of

the patient's condition is excessive blood loss from all sites of vessel trauma This reflects a marked reduction in blood coagulability, which in turn is dominantly due to acute hypofibrinogenaemia. The pulmonary lesions provide the most dramatic evidence of a condition of widely disseminated intxavascular fibrin deposition, and it is the continuing progress of this state which causes the reduction in the level of concentration of plasma fibrinogen. Urgent and massive blood transfusion (using a blood-warming device) is demanded to keep pace with the blood loss. When the diagnosis is made, fibrinogen (3 g) should be given as an initial measure, and subsequent doses of this protein—and possibly of epsilon aminocaproic acid—should be prescribed by the haematologist. Continual monitoring of the patient's central venous pressure is mandatory in this condition. Pre-eclampsia: eclampsia. The emergency treatment of the patient with very severe pre-eclampsia, and of the eclamptic patient, cannot be discussed at length here; it is considered in more detail elsewhere (Crawford, 1971c). Increasingly it is being appreciated that this reflects, in obstetrics, the prototype intensive care situation. The investigation and treatment of such a patient must have multidisciplinary support. Although the obstetrician must always retain the ultimate responsibility for the care of the patient, a haematologist, a biochemist, a physician (possibly two—one renal physician and one cardiologist), physiotherapists, midwives and the anaesthetist all have important skills to offer. The specific roles which the anaesthetist might be called upon to play are: to provide general anaesthesia in the event that emergency delivery is to be undertaken; to administer, or to supervise, the regimen of analgesia if the patient is in labour (this could include the administration of a lumbar epidural block, which might also be used to promote some degree of lowering of the blood pressure); supervision of the regimen of anticonvulsant therapy (which currently consists, not infrequently, of either chlormethiazole or diazepam);

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(F) Acute Inversion of the Uterus. This rare complication leads, in most cases, to a state of intense shock. Two factors contribute to the shock; haemorrhage from the venous sinuses of the placental site, reflecting the venous tourniquet effect of the inversion, and acute tension upon the pelvic structures. If there has been little blood loss, then the painful stimuli are likely to be the main contributing factors to the state of shock and immediate therapy must be directed to repositioning the uterus. General anaesthesia will be required, and the technique must include endotracheal intubation and the administration of halothane. If haemorrhage is an outstanding presenting sign, it is likely that tension on the uterine ligaments and their allied structures is not an important contributor to the state of shock (if it were, one could conjecture that an accompanying uterine vasospasm would cause the uterus to be "dry"). Under such a circumstance, immediate therapy should consist of a (warmed) blood transfusion, the volume requirement being assessed by reference to the central venous pressure. Subsequent repositioning of the uterus will require that the patient be anaesthetized.

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THE PREVENTION OF ASPIRATION OF GASTRO-OESOPHAGEAL CONTENTS

This continues relentlessly to be the most common cause of anaesthetic death in the field of obstetrics. The measures which must be taken to reduce this deplorably high incidence have been set forth many times. What is required now is the capacity rigorously to put them into effect on a national scale. In contrast to what was the probable situation a couple of decades ago, maternal death from aspiration rarely occurs as a result of asphyxia due to upper respiratory obstruction, but is due rather to chemical bronchopneumonia caused by the aspiration of material the pH of which is lower than approximately 3.0-2.5 (Bannister and Sattilaro, 1962; Taylor and PryseDavies, 1966). Measures must be taken to guard against each of these contingencies throughout the labour of every patient, as there can never be a guarantee that a patient will not urgently require to be given a general anaesthetic at some time between the start of labour and the end of the third stage. Thus it should be accepted routine that patients in labour should receive only a light, fat- and roughage-free, easily assimilated diet. Under certain circumstances, oral intake should be limited to sips of water, medicants and mouth fresheners. These circumstances are: patients who are likely candidates for general anaesthesia; for several hours before surgical induction of labour (prolapsed cord is recognized as a complication of this procedure); most outstandingly, patients who have entered the phase of prolonged labour.

Of even greater importance, it must be the rule that each patient receives 15 ml Magnesium Trisilicate Mixture BPC at 2-hourly intervals throughout her stay in the delivery suite. The hurried administration of a dose of antacid immediately before the induction of anaesthesia, in lieu of the regimen described, is an invitation to disaster. If anaesthesia is required, and the dietary and antacid regimen has been appropriately carried out, gastric emptying will rarely be deemed to be necessary before induction (we have emptied the stomach of 4 patients out of the approximate 1,200 who have been given a general anaesthetic for an emergency procedure during the past 2-3 years). However, if a patient does unexpectedly come to emergency surgery, and has recently taken food, or if a patient requires a general anaesthetic after a very prolonged labour (even though she has had little by mouth during the previous few hours), gastric emptying should be performed if it is compatible with obstetric safety. The most efficient and least unpleasant method of emptying the stomach is by the slow intravenous injection of diluted apomorphine (Crawford, 1971c), but the more fastidious may prefer to ask a nurse to pass a gastric tube. Neither method may be employed in cases of prolapsed cord, severe vaginal haemorrhage, eclampsia or very severe pre-eclampsia, or ruptured uterus. If the question of gastric emptying arises in respect to a mother whose foetus gives evidence of very severe distress, anaesthetist and obstetrician must rapidly decide upon their mutual priorities; the decision will probably be influenced most by an honest appraisal of the respective skills of each. The further steps in the defence against aspiration are: pre-oxygenation; adequate suction immediately to hand; application of cricoid pressure before the start of induction of anaesthesia, and its maintenance until the cuff of the endotracheal tube has been inflated: the attendant who applies the pressure should be rehearsed in the manoeuvre, and if he or she is not familiar with it, the surface marking of the patient's cricoid cartilage should be outlined with a ballpoint pen; endotracheal intubation;

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concern with the adequacy of the patient's ventilation, and with the efficiency of her respiratory gas exchange; the advisability of making use of ventilator therapy (with appropriate humidification) is being increasingly realized as the "intensive care attitude" seeps gradually into obstetric thinking. Furthermore, a characteristic attribute of the condition under review is a remarkable reduction in pulmonary capillary blood flow, which is reflected in part by a reduction in the degree of oxygen saturation of arterial blood (Birmingham Eclampsia Study Group—to be published).

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872 gastric aspiration during operation (after delivery) if the foeto-maternal condition contraindicated its application pre-operatively; the routine precautions appropriate to the phase of extubation.

Despite all that has been written in this section,

and accounts of a like nature which have appeared from other pens, the fact remains that the most important prophylactic measure against this lethal condition is anaesthetic competence. The tools of prophylaxis have to be provided and consistently maintained, and this, as is suggested in a memorandum drawn up by the Obstetric Anaesthetists' Association, should, in each large obstetric unit, be the prerogative of a small group of consultant anaesthetists who have an interest in and a commitment to obstetrics. But the final common factor is the doctor who actually gives the anaesthetic, and again'reference can best be made to the Obstetric Anaesthetists' Association's memorandum, which declares that obstetric anaesthesia should be administered only by those who have had at least one year's training in anaesthesia of a general nature, and whose competence is of a standard which satisfies the consultant anaesthetists who are responsible for the obstetric service. REFERENCES

Bannister, W. K., and Sattilaro, A. J. (1962). Vomiting and aspiration during anesthesia. Anesthesiology, 23, 251. Cosmi, E. V., and Mara, G. F. (1968). Acid-base status of the fetus and clinical condition of the newborn following Cesarean section. Amer. J. Obstet. Gynec, 102, 378. Crawford, J. S. (1971a). Awareness during operative obstetrics under general anaesthesia. Brit. J. Anaesth., 43, 179. (1971b). Lateral tilt during Caesarean section. (In preparation.) (1971c). Principles and Practice of Obstetric Anaesthesia, 3rd edn. (awaiting publication). Oxford: BlackwelL Editorial (1970). Paracervical block in labour. Brit. J. Anaesth., 42, 657. James, F. M., Greiss, F. C , and Kemp, R. A. (1970). Evaluation of pressor therapy for maternal hypotension during spinal anesthesia. Anesthesiology, 33, 25. Marx, G. F., Cosmi, E. V., and Wollman, S. B. (1969). Biochemical status and clinical condition of mother and infant at Cesarean section. Anesih. Analg. Curr. Res., 48, 986. Orkin, L. R. (1969). Physiology of Obstetric Anesthesia, p. 94. Springfield, I1L: Thomas. Moir, D. D. (1970). Anaesthesia for Caesarean section: an evaluation of a method using low concentrations of halothane and 50 per cent oxygen. Brit. J. Anaesth., 42, 136. Moya, F., and Smith, B. (1962). Spinal anesthesia for Cesarean section. J. Amer. med. Ass., 179, 609. Scudamore, J. H., and Yates, M. J. (1966). Pudendal block—a misnomer? Lancet, 1, 23. Shnider, S. M. (1970a). Anesthesia for elective Cesarean section; in Obstetrical Anesthesia (ed. Shnider, S. M.). Baltimore: Williams and Watkins.

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For many years there has been debate concerning the position of the patient during induction. The writer's opinion is that she should be in the horizontal plane (on the wedge). A head-up tilt offers little anti-gravitational advantage unless it is carried to a grotesque angle; a head-down tilt appears to be a counsel of despair, suggesting that the anaesthetist expects regurgitation to occur and is planning to hover with a suction catheter and try to catch the material before any enters the larynx. The aspiration of add material should be suspected to have occurred if increasing pressure is required to achieve lung inflation, and there is associated evidence of hypoxaemia. Confirmatory evidence may be provided, in the non-asthmatic patient, by the auscultatory diagnosis of bronchospasm. If it is considered that aspiration has—or appears likely to have—-occurred, remedial measures must be instituted immediately. A sufficiently high percentage of oxygen should be given to counteract cyanosis; aminophylline might be required to relieve bronchospasm; and hydrocortisone (200-300 mg) should be given intravenously as soon as possible. If the operation is of lifesaving importance (foetal or maternal) it should be carried out with expedition. Subsequently, there should be no hesitation in maintaining the patient on ventilator therapy if there is any suggestion of pulmonary insufficiency: humidification will be required. Tracheostomy should be considered if the condition of the patient does not show a marked improvement after 48 hours of artificial ventilation. Sodium bicarbonate might be required to reverse metabolic aridosis. Hydrocortisone (100 mg) should be given intravenously 6hourly for the next 48 hours, and 50 mg 6-hourly during the subsequent 48 hours. Antibiotic therapy should be instituted as soon as possible. The consensus of opinion appears to be that bronchial lavage, with either saline or alkali, is either of no benefit or positively harmful (Vandam, 1965; Marx and Orkin, 1969).

BRITISH JOURNAL OF ANAESTHESIA

ANAESTHESIA FOR OBSTETRIC EMERGENCIES Shnider, S. M. (1970b). Emergency Cesarean section; in Obstetrical Anesthesia (ed. Shnider, S. M.). Baltimore: William* and Watkins. de Lorimer, A. A., Holl, J. W., Chapfcr, F. K., and Morishima, H. O. (1968). Vasopressors in obstetrics: I. Amer. J. Obstet. Gynec, 102, 911.

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Taylor, G., and Pryse-Davies, J. (1966). Prophylactic use of antacid in the prevention of the acidpulmonary aspiration syndrome (Mendelson's syndrome). Lancet, 1, 288. Vandam, L. R (1965). Aspiration of gastric contents in the operative period. New Engl. J. Med., 273, 1206.

CORRESPONDENCE EFFECTS OF OSMOTIC DIURETICS ON C.SJ. PRESSURE

particularly Moreno, Murphy and Goldsmith, 1969). Hamburger (1968), Gibson and Fitch (1971) and Mostert et aL (1971) provide documentation in support of abandoning mannitol therapy in favour of more harmless and useful manoeuvres such as infusion of hypertonic glucose and fructose. The principal merit of this is, however, in safeguarding the knowledge that the brain can be shrunk only at the price of body dehydration.

JACOBUS W. MOSTERT

Buffalo, New York REFERENCES

Gibson, R Myles, and Fitch, W. (1971). Central venous pressure and intracranial pressure measurements using hypertonic fructose solution at differing Pco, levels. Proc. roy. Soc. Med., 64, 655. Hamburger, J. (1968). Nephrology. Philadelphia: Saunders. Hooshmand, H., Dove, J., and Houff, S. (1969). Effects of diuretics and steroids on cslf. pressure. Arch. NeuroL, 21, 499. Mostert, J. W., Trudnowski, R J., Evers, J. L., Hobika, G. H., Moore, R H., and Murphy, G. P. (1971). Cardiovascular responses to hypertonic glucose. (An aspect of resuscitation studied in patients with chronic renal failure.) Anaesthesia, 26, 334. Moreno, M., Murphy, C , and Goldsmith, C (1969). Increase in serum potassium resulting from the administration of hypertonic mannitol and other solutions. J. Lab. din. Med., 73, 291.

BOOK REVIEW Pain Relief in Labour. By Donald D. Moir. Published by Churchill Livingstone, Edinburgh and London. Pp. 140; ilhis.; indexed. Price £1.00. The practice of obstetric analgesia has changed radically during the past ten years due to the introduction of new drugs and techniques. The CMB syllabus for midwife training in analgesia has been enlarged to take account of these changes. Unfortunately, the number of lectures allotted to teach this enlarged syllabus has not been increased and so those who lecture to midwives on this subject have had to compromise by outlining the principles of analgesia, leaving the midwife to fill in the details from her own reading This has been difficult due to the lack of an authoritative modern textbook for midwives. This deficiency has now been corrected by the publication of Dr Moir's excellent comprehensive handbook. Dr Moir describes in detail the procedures for which the midwives are responsible, pointing out the causes of failure and any associated dangers. In addition he describes the principles of techniques such as epidural and paracervical block which, although not strictly the province of the midwife, enable her to understand the problems involved and be able to recognize and treat complications. The first two chapters outline the history of pain relief in labour and the methods of psychological pre-

paration for childbirth. These are followed by two excellent chapters on analgesics, sedatives and tranquillizers. In these, side effects, placental transfer, and pain pathways are discussed in addition to formal descriptions of the drugs employed. Where controversy exists, the author carefully and logically gives his own reasoned opinion on the best course to follow. His views on tincture of opium and on the fixed combination of pethidine with levallorphan (Pethilorfan) will be endorsed by most obstetric anaesthetists. An up-to-date description of inhalation analgesic methods is followed by an excellent account of local anaesthetics and regional analgesia. As might be expected from such a well-known authority in this field, this chapter is the best in the book, being clear, concise and comprehensive. The book concludes with a chapter on general anaesthesia in obstetrics which could be read with benefit by Fellowship candidates wishing to study a modern account of practical obstetric anaesthesia. The book is well produced and would be a worthwhile investment for pupil midwives. It will also be required reading for those anaesthetists who are involved in midwife teaching and would be a useful book for undergraduates and postgraduate students wishing to gain some insight into obstetric analgesia and anaesthesia. T. H. L. Bryson

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Shy—Theirs is an elegant report. However, "a fact in our lives is valuable not so far as it is true, but as it is significant" (Goethe) and Walker and Thomson (Brit. J. Anaesth., 43, 445) detract from our understanding of the physiology of shrinking the brain during neurosurgery. They find mannitol superior to fructose-mannitol in the terms of their particular protocoL But I am convinced that the reverse can just as beautifully be said and done by simply changing the rate of administration of the respective solutions. It is of the greatest clinical importance to realize that the development of "overshoot" (a rise of cs.f. pressure at the end of the third to fifth hours) depends on the state of hydration of the dogs and nothing else (Hooshmand, Dove and Houff, 1969). Hooshmand et aL found in detailed experiments that if more than one-third of the volume of urine output secondary to the diuretic effects of the drugs was replaced by intravenous fluids, an "overshoot" resulted. On the other hand, if the dogs were kept dehydrated and intravenous fluid was limited to less than one-third of the volume of diuresis, then "overshoot" of pressure did not appear (the one-third figure was arrived at after trials of one-fourth, one-half, two-thirds, and threefourths replacements of the volume of diuresis). There are no magic effects of mannitol; anything mannitol can do other osmotic diuretics like glucose and fructose can do better because they are safer (see