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Anaesthesia for Caesarean section
Anaesthesia for Caesarean section David M Levy FRCA
Table 1 Classification of the urgency of Caesarean section
Caesarean section
Grade
Incidence
Definition (at time of decision to operate)
[1] Emergency Immediate threat to life of woman or fetus
A UK-wide survey of over 60,000 Caesarean sections in 1997 revealed that 78% were performed under regional anaesthesia (Fig. 1), although this varied from centre to centre. It is likely, however, that the increasing Caesarean section rate has kept the overall number of general anaesthetics broadly the same as when regional techniques were in the minority. Across 14 hospitals of the South Thames (West) region, the Caesarean section rate increased by 10% from 1993-1998. Although the proportion of Caesarean sections performed under general anaesthesia fell by two-thirds, the actual number decreased by only one-third.
Categorisation of urgency A new 4-point classification of urgency of Caesarean section (Table 1), similar to that used by the National Confidential Enquiry into Perioperative Deaths, has been validated by close agreement between anaesthetists’ and obstetricians’ gradings of over 400 cases. Mutual adoption of this classification should aid decisions as to which mode of anaesthesia is appropriate in nonelective cases. The Association of Anaesthetists of Great Britain and Ireland and the Obstetric Anaesthetists’ Association have together decreed
GA 22%
CSE 9%
Spinal 47%
[2] Urgent
Maternal or fetal compromise, not immediately life-threatening
[3] Scheduled
Needing early delivery but no maternal or fetal compromise
[4] Elective
At a time to suit the woman and maternity team
that the time from informing the anaesthetist to the start of operative delivery should not exceed 30 min. A decision to delivery interval of 30 min has become adopted widely as an audit standard, despite lack of any evidence that 30 min is a critical threshold in the development of intrapartum hypoxia. Spinal anaesthesia is often appropriate for urgent (Table 1) Caesarean section, although a recent Confidential Enquiry into Stillbirths and Deaths in Infancy (CESDI) has deemed repeated attempts inadvisable in the absence of significant risk factors for general anaesthesia.
Consent Women must receive an explanation of the proposed anaesthetic technique and its limitations. The possibility of regional anaesthesia proving inadequate and the measures that will be taken to remedy the situation must be dealt with. Written consent in difficult circumstances is not essential, although the risks/benefits that have been discussed and the fact that oral consent was obtained should be documented. A mentally competent obstetric patient has an absolute right to refuse to consent to medical treatment for any reason (rational or irrational) or for no reason at all. This pertains even though the consequence may be her own death or the death or serious handicap of the child she bears.
Mortality
Epidural 22%
Fig. 1 Anaesthesia for Caesarean sections in the UK (1997).
Maternal mortality attributed to anaesthesia has fallen steadily in the last 30 years (Fig. 2). In the Report on Confidential Enquiries into Maternal
British Journal of Anaesthesia | CEPD Reviews | Volume 1 Number 6 2001 © The Board of Management and Trustees of the British Journal of Anaesthesia 2001
Key points In 1997, 78% of Caesarean sections were performed under regional anaesthesia in the UK General anaesthesia is indicated for all emergency Caesarean sections (i.e. when there is an immediate threat to life of mother or fetus) and when a regional technique is absolutely contra-indicated or has failed When an epidural catheter is placed after the spinal injection in a needlethrough-needle combined spinal-epidural (CSE), the position of the epidural catheter tip cannot be tested immediately Continuous (incremental) spinal anaesthesia offers a high degree of haemodynamic control for parturients with serious cardiac lesions For general anaesthesia in pre-eclampsia/eclampsia, a neuro-anaesthetic regimen is essential to protect the maternal cerebral circulation from hypertensive surges
David M Levy FRCA Consultant Obstetric Anaesthetist Anaesthetics Directorate C Floor East Queen’s Medical Centre Nottingham NG7 2UH, UK
171
Anaesthesia for Caesarean section
20
output from autotransfusion of blood as the uterus contracts after delivery might precipitate circulatory overload. Strict avoidance of aortocaval compression, prompt boluses of a vasopressor and infusion of crystalloid immediately after intrathecal injection will avert significant hypotension in most cases.
10
Level of injection
Number of deaths
60 50 40 30
0 '53 '56 '59 '62 '65 '68 '71 '74 '77 '80 '83 '86 '89 '92 '95 Mid-year of triennium
Fig. 2 Maternal mortality (number of deaths) from anaesthesia 1952–1996.
Deaths (CEMD) in the UK for 1994–1996, there were no deaths from general anaesthesia: the solitary anaesthetic death followed combined spinal-epidural anaesthesia. However, CESDI has highlighted 4 cases from 1994–1995 in which general anaesthesia was associated with life-threatening hazards (2 anaphylaxis, 2 airway crises). Fasting intervals of 6 h for food and 2 h for fluids (tea/coffee with semi-skimmed milk, or fruit squash) are appropriate for women scheduled for elective Caesarean section. Ranitidine 150 mg should be prescribed 2 h before an elective operation and administered 8hourly to women in labour with risk factors for Caesarean section to reduce gastric acid secretion. The administration of a measure of sodium citrate 0.3 M immediately before every Caesarean section is almost universal practice. The risk of aspiration is not confined to general anaesthesia: protective reflexes may be obtunded in the event of an excessively high regional block.
Regional anaesthesia Single-shot spinal anaesthesia Single-shot spinal anaesthesia has become the most popular anaesthetic technique for Caesarean section (Fig. 1). This is largely a consequence of the widespread adoption of pencil-point tip needles, which have reduced the incidence of headache requiring epidural blood patch to 0.5% or less. Preload
A crystalloid fluid preload has become recognised as an ineffective means of preventing hypotension after spinal injection. In contrast to colloid, its short intravascular half-life prevents the necessary sustained increase in cardiac output before sympathetic blockade. In one study, a litre of hydroxyethyl starch produced a mean increase in cardiac output of over 40% and prevented hypotension in over 80% of women. However, all colloids incur a risk of anaphylaxis and concern has been raised that the further increase in cardiac 172
Magnetic resonance imaging has shown that the conus medullaris of the spinal cord extends below the level of the body of L1 in 20% of patients. Moreover, anaesthetists commonly underestimate the height of their approach. A series of reports describing damage to the conus medullaris has led to an authoritative recommendation that spinal needles should not be inserted higher than the L3/4 interspinous space – practically, the space at or immediately above a line joining the highest points of the iliac crests. Dose of local anaesthetic
Virtually all UK obstetric anaesthetists use bupivacaine 0.5% in dextrose 80 mg ml–1. Gestation should be considered when deciding upon the dose for a single-shot spinal. In one study, loss of cold sensation to T4 was achieved with 2.25 ml in all of a group of women at term but only 16% of women at 28–35 weeks’gestation. The progressively gravid uterus causes increasing vena caval compression, epidural venous engorgement and consequent displacement of the dura and reduced subarachnoid space volume. Postural manoeuvres after intrathecal injection, such as moving from right to left lateral or flexing the knees and thighs, promote cephalad spread of the injectate by influencing vertebral canal blood volume. Most UK anaesthetists ascertain block height by defining loss of temperature sensation with ethyl chloride spray. However, there is evidence that loss of light touch sensation to T5 is a better predictor of pain-free Caesarean section under (opioid-free) spinal bupivacaine anaesthesia. Light touch can be tested by gently dabbing the skin with cotton wool. The extent of the block and modality of testing should be recorded routinely. Opioids
The addition of intrathecal fentanyl, diamorphine or morphine can reduce the incidence of intra-operative visceral pain, although fentanyl does not contribute significantly to postoperative analgesia. Over 70% of respondents to a recent survey of UK obstetric anaesthetists added an opioid, most often fentanyl. Diamorphine was used by less than a quarter of those using an opioid, morphine by <10%. Reports of respiratory depression after intrathecal doses of opioids in obstetric practice are conspicuous by their absence. Intra-operative pain should be treated promptly by i.v. alfentanil (0.5 mg increments), inhaled isoflurane 0.25% in an N2O/O2 50:50 mixture or conversion to general anaesthesia.
British Journal of Anaesthesia | CEPD Reviews | Volume 1 Number 6 2001
Anaesthesia for Caesarean section
Vasopressors
Ephedrine (α- and β-sympathomimetic) is generally regarded as the vasopressor of choice in obstetrics. Persisting reservations about the effects of α-agonists on uteroplacental blood flow have endured from a 30-year-old study of Columbian ewes – which did not undergo regional anaesthesia. A randomised comparison of i.v. boluses of ephedrine and phenylephrine in women undergoing Caesarean section found similar changes in maternal systolic pressure and cardiac output and no changes in umbilical artery (UA) Doppler waveforms. Mean UA pH was significantly greater in neonates whose mothers had received phenylephrine. Moreover, another study has demonstrated that hypotension occurring after prophylactic ephedrine 10 mg i.v. was associated with significant fetal acidaemia. However, if phenylephrine is used alone to treat hypotension, it is liable to cause maternal bradycardia necessitating i.v. atropine or glycopyrrolate. Phenylephrine is most useful in 50–100 µg increments for the treatment of hypotension in the presence of tachycardia. Doses of this magnitude offset the haemodynamic effects of bolus doses of syntocinon given after delivery. Supplied only in 1 ml, 10 mg ampoules, phenylephrine must be diluted (e.g. to 100 µg ml–1) before use. Pre-eclampsia
Over the last few years, it has become accepted by many that preeclampsia is not necessarily a contra-indication to single-shot spinal anaesthesia. It stands to reason that if the abnormal vasoconstriction is of humoral rather than neural aetiology, sympathetic blockade should not cause precipitous hypotension. Prior vasodilatation by effective anti-hypertensive treatment (e.g. oral methyldopa or i.v. hydralazine), with limited intravascular volume expansion, seems to avert problematic hypotension. Judicious increments of either ephedrine or phenylephrine do not cause arterial pressure overshoot. Postoperative analgesia
Supplementation of intrathecal diamorphine or morphine by regular oral or rectal paracetamol (1 g, 6-hourly) and diclofenac (50 mg, 8-hourly, 12 h after an initial 100 mg postoperative dose), with oral dihydrocodeine if required (60 mg 4-hourly), makes patient-controlled i.v. morphine unnecessary for most women. The Royal College of Anaesthetists has stated in a clinical guideline that nonsteroidal anti-inflammatory drugs (NSAID) should not be used in pre-eclampsia. This was Grade C evidence – based on expert consensus. In pre-eclampsia with mild renal involvement (good urine output and no serum indices of renal failure), there seems little reason to deny women the benefit of the opioid-sparing effect of an NSAID, although successive doses should not be given without
repeated confirmation of sustained satisfactory urine output. There is no doubt that NSAIDs are always contra-indicated in the initial postoperative period if Caesarean section has been complicated by excessive bleeding or there is concern about adequacy of haemostasis (e.g. uterine atony).
Epidural anaesthesia Few elective Caesarean sections are now performed under epidural anaesthesia because the quality of anaesthesia is generally poorer than that afforded by subarachnoid block. In the 1997 survey, the rate of conversion to general anaesthesia (6%) was 3 times greater for epidurals than spinals. Epidural anaesthesia is still favoured by many when gradual establishment of block is desired to minimise hypotension, although combined spinal-epidural (CSE) techniques are gaining in popularity and continuous (incremental) spinal anaesthesia may represent the best technique. In severe preeclampsia, postoperative infusion of epidural bupivacaine/fentanyl in a high-dependency area will confer optimal analgesia and contribute to blood pressure control. A recent South African study demonstrated that women who were fully conscious and co-operative after an eclamptic seizure could safely undergo Caesarean section under epidural anaesthesia. All women had platelet counts >100 × 10–9 l–1 and had been treated with magnesium sulphate. Conversion of labour analgesia Women in labour deemed at high risk for Caesarean section – and those with potentially difficult airways – should have epidural analgesia instituted early. It should be established that the block is working well with no missed segments. If analgesia in labour has been poor, anaesthesia for Caesarean section is unlikely to be satisfactory. Conversion of analgesia for labour to surgical anaesthesia for Caesarean section is not the same as establishing epidural anaesthesia de novo. Plain bupivacaine 0.5% alone has been shown to convert low-dose bupivacaine/fentanyl labour epidural analgesia to surgical anaesthesia for Caesarean section as swiftly and effectively as lidocaine 2% with epinephrine, or a 50:50 mixture of the two solutions. The impact of adding bicarbonate has not been studied in this situation. Use of bupivacaine 0.5% alone circumvents the time spent and risks inherent in the hurried preparation of alkalinised drug mixtures. Good communication among midwives, obstetricians and anaesthetists should make general anaesthesia for the woman with a working epidural a rarity. Even in the event of cord prolapse, traditionally managed without question by general anaesthesia, there might be time for an epidural top-up, provided upward pressure on the presenting part is effective in avoiding cord compression.
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Local anaesthetic toxicity
The use of low-dose bupivacaine solutions for labour analgesia has confined the risk of local anaesthetic toxicity in obstetrics to the establishment of epidural anaesthesia for Caesarean section. Lbupivacaine 0.5% is equally effective as bupivacaine 0.5%, with less risk of CNS or cardiac toxicity in the event of high plasma concentrations after inadvertent intravascular injection. It has emerged that ropivacaine 0.75%, which is licensed for Caesarean section, is approximately equipotent with bupivacaine 0.5%. Any diminution of motor block with ropivacaine would be of little benefit to women undergoing Caesarean section.
Combined spinal-epidural anaesthesia Studies over the last 15 years have confirmed the superior quality of CSE anaesthesia compared with that of epidural anaesthesia alone for Caesarean section. Many units have adopted CSE as their standard technique for Caesarean section, despite lack of evidence of overall superiority compared with single-shot spinals in respect of the following variables: (i) speed of establishment of surgical anaesthesia; (ii) incidence of hypotension; (iii) incidences of nausea/vomiting and shivering; (iv) requirement for i.v./inhalational supplementation and conversion to general anaesthesia; (v) quality of muscle relaxation; (vi) incidence of dangerously high block requiring emergency airway management; and (vii) incidence of postoperative headache, neuropathy and CNS infection. Potential morbidity
Use of a Tuohy needle inevitably incurs a risk of accidental dural puncture and its consequences. In a needle-through-needle technique, the spinal needle is typically advanced up to 15 mm beyond the tip of the Tuohy needle. Unlike a single-shot spinal, the needle is not gripped by successive tissue layers during its passage. Moreover, the tip of a pencil-point needle is 1 mm or so distal to the aperture. Compared with a bevel-tipped needle, unrestrained deeper insertion before flashback of CSF might predispose to the alleged greater incidence of paraesthesia and possible increased risk of neural damage. The risk of meningitis is conceivably greater for CSE compared with single-shot spinals because of the proximity of a catheter to a dural hole. Spinal dose of local anaesthetic
Using the same intrathecal dose of bupivacaine as for a single-shot spinal and keeping the epidural catheter ‘in reserve’ gains no haemodynamic advantage. If avoidance of hypotension is a priority, a deliberately small intrathecal dose (e.g. 1 ml of bupivacaine 0.5%) can be administered. Assuming successful intrathecal injection (a failure rate of 3% has been described for a locking spinal
174
needle-through-Tuohy needle technique), the desired block height can be achieved by increments of epidural local anaesthetic (or saline, which can extend a block by compression of the thecal sac). The smaller the spinal dose, the greater the reliance upon the epidural component and likelihood of unsatisfactory anaesthesia. Catheter misplacement
The position of a catheter placed directly after spinal injection in a needle-through-needle technique cannot be tested immediately. At the very time the catheter might be required (e.g. to prolong the block), it might not be functional, necessitating conversion to general anaesthesia. Both subarachnoid or subdural migration risk a dangerously high block and consequent emergency airway management. If difficulty is encountered threading an epidural catheter after spinal injection, intrathecal hyperbaric bupivacaine will fix as time elapses and limit the extent of block to the dependent area. The most recently described approach to CSE anaesthesia circumvents many of the potential problems of needle-through-needle techniques. Subarachnoid puncture is made with a standard spinal needle and the stylette replaced immediately. Only after satisfactory placement of an epidural catheter through a separate Tuohy needle, at the same space or space above, is spinal injection performed. Restriction of opioid to the spinal component of a CSE eliminates the risk of an unpredictably large fraction of an epidural dose reaching the CSF if the catheter is partially subarachnoid. Intrathecal diamorphine 0.25 mg provides the same quality and duration of analgesia as epidural diamorphine 5 mg. Placenta praevia
CSE anaesthesia is useful when surgery is predicted to outlast a single-shot spinal block. In the event of protracted surgery (e.g. Caesarean hysterectomy in a woman with placenta praevia), an epidural catheter will allow extension of the block, typically around 90 min after a standard intrathecal dose. Recent UK and American retrospective studies have compared regional and general anaesthesia for Caesarean section with placenta praevia. The commonly held obstetric view that placenta praevia dictates general anaesthesia is not supported. Regional anaesthesia was associated with reduced estimated blood loss and transfusion requirements. However, anterior placenta praevia in a women over 35 who has had previous Caesarean sections suggests a particularly high risk of massive haemorrhage. General anaesthesia with provision for postoperative ICU admission might be considered prudent.
Continuous spinal anaesthesia Placement of a catheter in the subarachnoid space allows the slow establishment of the highest quality of anaesthesia with the
British Journal of Anaesthesia | CEPD Reviews | Volume 1 Number 6 2001
Anaesthesia for Caesarean section
greatest degree of haemodynamic control. Tiny increments (e.g. 0.25 ml) of local anaesthetic solution can be titrated against block height and haemodynamic effects. There is no risk of systemic local anaesthetic toxicity. A series of patients undergoing Caesarean section was described almost 30 years ago, when 24-gauge catheters were threaded through 21-gauge spinal needles. The authors claimed the following advantages of inducing spinal anaesthesia with the patients supine: (i) elimination of unpredictably high spread by patient movement; (ii) no discontinuation of physiological monitoring during repositioning from lateral or sitting to supine; and (iii) immediate treatment of any hypotension. However, the incidence of postoperative headache was 16%. Potential morbidity
An endoscopic cadaver study demonstrated that all catheters inserted >30 mm into the subarachnoid space developed loops. Limiting the length of catheter threaded to <20 mm will reduce the risks both of snaring a nerve root and directing the catheter tip caudally. It is thought that the caudal positions of microspinal catheter tips led to attempts to achieve cranial extensions of low blocks by repeated doses of 5% lidocaine in hyperbaric dextrose. If not diluted by CSF, this solution is potentially toxic to the poorly insulated nerves of the cauda equina. A series of cases of cauda equina syndrome led the US Food and Drug Administration to ban microspinal (<24-gauge) catheters in 1992. It has been suggested that only solutions with a tonicity near to that of CSF should be used for continuous spinal anaesthesia. Reducing the concentration of glucose in solution with bupivacaine 0.5% from 80 mg ml–1 to 8 mg ml–1 (by mixing plain and hyperbaric solutions in the proportion of 9:1) does not affect the immediate characteristics of single-shot spinal blocks in pregnant women at term. There seems little need, therefore, to use repeated doses of hyperbaric 0.5% bupivacaine in glucose 80 mg ml–1 in a continuous spinal technique. Indication
Continuous spinal anaesthesia has never become popular in UK obstetric anaesthetic practice, although recent case reports have described successful management of parturients with serious cardiac lesions (e.g. aortic stenosis and Eisenmenger’s syndrome) using cautious incremental dosing. Kits comprising a 28-gauge catheter through 23-gauge needle and 22-gauge catheter over 27gauge needle with pull-wire are available (see Burnell & Byrne, Key reference). The incidences of infection, neuropathy and postdural puncture headache remain to be defined.
General anaesthesia General anaesthesia is indicated for all ‘emergency’Caesarean sections (Table 1) and other cases for which a regional block is absolutely contra-indicated or has failed. If the history or evaluation of the airway suggests that tracheal intubation might be difficult, awake fibre-optic intubation should be considered.
Depth of anaesthesia The regimen of thiopental, succinylcholine and intubation has remained standard and largely unchanged since it superseded mask and ether 40 years ago and permitted a lighter plane of inhalational general anaesthesia. Although babies born to mothers anaesthetised with ether were undoubtedly sleepier than those whose mothers who underwent light anaesthesia facilitated by neuromuscular block, they were not necessarily compromised. General anaesthesia is ‘innocuous and reversible’ for the baby provided maternal oxygenation and normocarbia are maintained, aortocaval compression avoided and a paediatrician is present to support ventilation. Fetal compromise to which uterine hyperstimulation has been contributory might actually be relieved by uterine relaxation conferred by a volatile agent. In contrast, a maternal stress response to excessively light general anaesthesia will be to the detriment of uteroplacental blood flow. With inhalational agent monitoring now universally available, the risk of awareness in obstetric anaesthesia should have been consigned to history. No adverse maternal or neonatal effects were found when sevoflurane and desflurane were evaluated for maintenance of anaesthesia. These agents offer the advantage of more rapid approximation of alveolar to inspired tensions as the anaesthetic effect of the i.v. induction dose declines.
Inhalational induction Obstetric general anaesthesia was not made ostensibly safer by the introduction of i.v. induction, neuromuscular blockade and intubation – the number of deaths attributable to anaesthesia increased markedly in the 1964–1966 triennium (Fig. 2). Sevoflurane has been use successfully for inhalational induction of anaesthesia for Caesarean section in the absence of vascular access and in status asthmaticus. The smooth, rapid onset and lack of coughing or vomiting suggest that the technique does not necessarily impose an increased risk of aspiration.
Pre-eclampsia Uncorrected coagulopathy, or symptoms consistent with impending eclampsia (severe headache or visual disturbance) are potential indications for general anaesthesia. Prior communication with a
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paediatrician is essential in order that preparation can be made for antagonism of opioid and provision of ventilatory support for the neonate. Laryngeal oedema is a real risk – beware the patient with recent voice change. Any dubious notion of light general anaesthesia for the baby’s benefit should be overridden by efforts to protect the maternal cerebral circulation. Although the onset and duration of succinylcholine are unaffected by therapeutic serum magnesium concentrations, the durations of action of all nondepolarising drugs are potentiated. The following points should be borne in mind: 1. Have a low threshold for direct arterial pressure monitoring. 2. Attenuate the pressor response to intubation with alfentanil 10 µg kg–1 or remifentanil 2 µg kg–1 (preceded by glycopyrrolate 0.4 mg to prevent bradycardia) before rapid sequence neuro-anaesthetic induction with a generous dose of thiopental. 3. A peripheral nerve stimulator is essential to ascertain the degree of neuromuscular block. 4. Before extubation, consider additional anti-hypertensive therapy (e.g. labetalol in 10–20 mg increments) to avert a dangerous pressor response. Any patient whose larynx was noted to be swollen at laryngoscopy or in whom intubation was traumatic is at particular risk of laryngeal oedema. Postoperative care must be in an ICU or highdependency area with an anaesthetist immediately available. Midwives should be alerted to the ominous significance of stridor.
Current controversy The use of succinylcholine for Caesarean section remains standard teaching. However, anaphylaxis to succinylcholine has been responsible for maternal deaths at Caesarean section and many ‘near misses’. Rocuronium 0.6 mg kg–1 is licensed for Caesarean section and has been shown to produce acceptable intubating conditions after thiopental 6 mg kg–1 within 90 s without untoward neonatal effects. UK data suggest that the risk of anaphylaxis to rocuronium is much lower than that for succinylcholine. However, an important potential disadvantage is that the duration of block rules out the possibility of abandoning the anaesthetic in the event of failed tracheal intubation. Controversially, some argue that inserting a laryngeal mask airway (LMA) and ventilating the lungs with cricoid pressure is no less safe overall, in this situation, than using succinylcholine and attempting to proceed with inhalational anaesthesia by spontaneous respiration. Unlike the case with succinylcholine, optimal 176
Fig. 3 ProSeal laryngeal mask airway.
conditions for airway management and maintaining oxygenation will be sustained and vomiting cannot occur. Maintenance of a slight head-up tilt will allow gravity to reduce the risk of regurgitation of gastric contents. The ProSeal LMA (Fig. 3) holds great promise for airway management in obstetric anaesthesia. A second tube makes a sealed junction against the upper oesophageal sphincter, allowing continuity with the gastrointestinal tract and isolation from the airway. Gastric insufflation during IPPV is minimised and passage of a gastric tube facilitated.
Failed and difficult intubation The management of difficult and failed intubation in obstetrics has been reviewed recently in this journal (see key references).
Key references Abouleish E,Abboud T, Lechevalier T, Zhu J, Chalian A,Alford K. Rocuronium (Org 9426) for Caesarean section. Br J Anaesth 1994; 73: 336–41 Brain AIJ,Verghese C, Strube PJ.The LMA ‘ProSeal’ – a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4 Burnell S, Byrne AJ. Continuous spinal anaesthesia. BJA CEPD Rev 2001; 1: 134–7 (Fig. 1, p134) Focus group. Obstetric anaesthesia delays and complications. In: Confidential Enquiry into Stillbirths and Deaths in Infancy. 7th Annual Report. London: Maternal and Child Health Research Consortium, 2000; 41–52 Gabbott DA. Recent advances in airway technology. BJA CEPD Rev 2001; 1: 76–80 Hamer Hodges RJ, Bennett JR, Tunstall ME, Knight RF. General anaesthesia for operative obstetrics. Br J Anaesth 1959; 31: 152–63 Lucas DN,Yentis SM, Kinsella SM, Holdcroft A, May AE,Wee M et al. Urgency of caesarean section: a new classification. J R Soc Med 2000; 93: 346–50 Morris S. Management of difficult and failed intubation in obstetrics. BJA CEPD Rev 2001; 1: 117–21 Shibli KU, Russell IF.A survey of anaesthetic techniques used for caesarean section in the UK in 1997. Int J Obstet Anesth 2000; 9: 160–7 See multiple choice questions 108–110.
British Journal of Anaesthesia | CEPD Reviews | Volume 1 Number 6 2001
Table 1 Classification of the urgency of Caesarean section
Caesarean section
Grade
Incidence
Definition (at time of decision to operate)
[1] Emergency Immediate threat to life of woman or fetus
A UK-wide survey of over 60,000 Caesarean sections in 1997 revealed that 78% were performed under regional anaesthesia (Fig. 1), although this varied from centre to centre. It is likely, however, that the increasing Caesarean section rate has kept the overall number of general anaesthetics broadly the same as when regional techniques were in the minority. Across 14 hospitals of the South Thames (West) region, the Caesarean section rate increased by 10% from 1993-1998. Although the proportion of Caesarean sections performed under general anaesthesia fell by two-thirds, the actual number decreased by only one-third.
Categorisation of urgency A new 4-point classification of urgency of Caesarean section (Table 1), similar to that used by the National Confidential Enquiry into Perioperative Deaths, has been validated by close agreement between anaesthetists’ and obstetricians’ gradings of over 400 cases. Mutual adoption of this classification should aid decisions as to which mode of anaesthesia is appropriate in nonelective cases. The Association of Anaesthetists of Great Britain and Ireland and the Obstetric Anaesthetists’ Association have together decreed
GA 22%
CSE 9%
Spinal 47%
[2] Urgent
Maternal or fetal compromise, not immediately life-threatening
[3] Scheduled
Needing early delivery but no maternal or fetal compromise
[4] Elective
At a time to suit the woman and maternity team
that the time from informing the anaesthetist to the start of operative delivery should not exceed 30 min. A decision to delivery interval of 30 min has become adopted widely as an audit standard, despite lack of any evidence that 30 min is a critical threshold in the development of intrapartum hypoxia. Spinal anaesthesia is often appropriate for urgent (Table 1) Caesarean section, although a recent Confidential Enquiry into Stillbirths and Deaths in Infancy (CESDI) has deemed repeated attempts inadvisable in the absence of significant risk factors for general anaesthesia.
Consent Women must receive an explanation of the proposed anaesthetic technique and its limitations. The possibility of regional anaesthesia proving inadequate and the measures that will be taken to remedy the situation must be dealt with. Written consent in difficult circumstances is not essential, although the risks/benefits that have been discussed and the fact that oral consent was obtained should be documented. A mentally competent obstetric patient has an absolute right to refuse to consent to medical treatment for any reason (rational or irrational) or for no reason at all. This pertains even though the consequence may be her own death or the death or serious handicap of the child she bears.
Mortality
Epidural 22%
Fig. 1 Anaesthesia for Caesarean sections in the UK (1997).
Maternal mortality attributed to anaesthesia has fallen steadily in the last 30 years (Fig. 2). In the Report on Confidential Enquiries into Maternal
British Journal of Anaesthesia | CEPD Reviews | Volume 1 Number 6 2001 © The Board of Management and Trustees of the British Journal of Anaesthesia 2001
Key points In 1997, 78% of Caesarean sections were performed under regional anaesthesia in the UK General anaesthesia is indicated for all emergency Caesarean sections (i.e. when there is an immediate threat to life of mother or fetus) and when a regional technique is absolutely contra-indicated or has failed When an epidural catheter is placed after the spinal injection in a needlethrough-needle combined spinal-epidural (CSE), the position of the epidural catheter tip cannot be tested immediately Continuous (incremental) spinal anaesthesia offers a high degree of haemodynamic control for parturients with serious cardiac lesions For general anaesthesia in pre-eclampsia/eclampsia, a neuro-anaesthetic regimen is essential to protect the maternal cerebral circulation from hypertensive surges
David M Levy FRCA Consultant Obstetric Anaesthetist Anaesthetics Directorate C Floor East Queen’s Medical Centre Nottingham NG7 2UH, UK
171
Anaesthesia for Caesarean section
20
output from autotransfusion of blood as the uterus contracts after delivery might precipitate circulatory overload. Strict avoidance of aortocaval compression, prompt boluses of a vasopressor and infusion of crystalloid immediately after intrathecal injection will avert significant hypotension in most cases.
10
Level of injection
Number of deaths
60 50 40 30
0 '53 '56 '59 '62 '65 '68 '71 '74 '77 '80 '83 '86 '89 '92 '95 Mid-year of triennium
Fig. 2 Maternal mortality (number of deaths) from anaesthesia 1952–1996.
Deaths (CEMD) in the UK for 1994–1996, there were no deaths from general anaesthesia: the solitary anaesthetic death followed combined spinal-epidural anaesthesia. However, CESDI has highlighted 4 cases from 1994–1995 in which general anaesthesia was associated with life-threatening hazards (2 anaphylaxis, 2 airway crises). Fasting intervals of 6 h for food and 2 h for fluids (tea/coffee with semi-skimmed milk, or fruit squash) are appropriate for women scheduled for elective Caesarean section. Ranitidine 150 mg should be prescribed 2 h before an elective operation and administered 8hourly to women in labour with risk factors for Caesarean section to reduce gastric acid secretion. The administration of a measure of sodium citrate 0.3 M immediately before every Caesarean section is almost universal practice. The risk of aspiration is not confined to general anaesthesia: protective reflexes may be obtunded in the event of an excessively high regional block.
Regional anaesthesia Single-shot spinal anaesthesia Single-shot spinal anaesthesia has become the most popular anaesthetic technique for Caesarean section (Fig. 1). This is largely a consequence of the widespread adoption of pencil-point tip needles, which have reduced the incidence of headache requiring epidural blood patch to 0.5% or less. Preload
A crystalloid fluid preload has become recognised as an ineffective means of preventing hypotension after spinal injection. In contrast to colloid, its short intravascular half-life prevents the necessary sustained increase in cardiac output before sympathetic blockade. In one study, a litre of hydroxyethyl starch produced a mean increase in cardiac output of over 40% and prevented hypotension in over 80% of women. However, all colloids incur a risk of anaphylaxis and concern has been raised that the further increase in cardiac 172
Magnetic resonance imaging has shown that the conus medullaris of the spinal cord extends below the level of the body of L1 in 20% of patients. Moreover, anaesthetists commonly underestimate the height of their approach. A series of reports describing damage to the conus medullaris has led to an authoritative recommendation that spinal needles should not be inserted higher than the L3/4 interspinous space – practically, the space at or immediately above a line joining the highest points of the iliac crests. Dose of local anaesthetic
Virtually all UK obstetric anaesthetists use bupivacaine 0.5% in dextrose 80 mg ml–1. Gestation should be considered when deciding upon the dose for a single-shot spinal. In one study, loss of cold sensation to T4 was achieved with 2.25 ml in all of a group of women at term but only 16% of women at 28–35 weeks’gestation. The progressively gravid uterus causes increasing vena caval compression, epidural venous engorgement and consequent displacement of the dura and reduced subarachnoid space volume. Postural manoeuvres after intrathecal injection, such as moving from right to left lateral or flexing the knees and thighs, promote cephalad spread of the injectate by influencing vertebral canal blood volume. Most UK anaesthetists ascertain block height by defining loss of temperature sensation with ethyl chloride spray. However, there is evidence that loss of light touch sensation to T5 is a better predictor of pain-free Caesarean section under (opioid-free) spinal bupivacaine anaesthesia. Light touch can be tested by gently dabbing the skin with cotton wool. The extent of the block and modality of testing should be recorded routinely. Opioids
The addition of intrathecal fentanyl, diamorphine or morphine can reduce the incidence of intra-operative visceral pain, although fentanyl does not contribute significantly to postoperative analgesia. Over 70% of respondents to a recent survey of UK obstetric anaesthetists added an opioid, most often fentanyl. Diamorphine was used by less than a quarter of those using an opioid, morphine by <10%. Reports of respiratory depression after intrathecal doses of opioids in obstetric practice are conspicuous by their absence. Intra-operative pain should be treated promptly by i.v. alfentanil (0.5 mg increments), inhaled isoflurane 0.25% in an N2O/O2 50:50 mixture or conversion to general anaesthesia.
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Vasopressors
Ephedrine (α- and β-sympathomimetic) is generally regarded as the vasopressor of choice in obstetrics. Persisting reservations about the effects of α-agonists on uteroplacental blood flow have endured from a 30-year-old study of Columbian ewes – which did not undergo regional anaesthesia. A randomised comparison of i.v. boluses of ephedrine and phenylephrine in women undergoing Caesarean section found similar changes in maternal systolic pressure and cardiac output and no changes in umbilical artery (UA) Doppler waveforms. Mean UA pH was significantly greater in neonates whose mothers had received phenylephrine. Moreover, another study has demonstrated that hypotension occurring after prophylactic ephedrine 10 mg i.v. was associated with significant fetal acidaemia. However, if phenylephrine is used alone to treat hypotension, it is liable to cause maternal bradycardia necessitating i.v. atropine or glycopyrrolate. Phenylephrine is most useful in 50–100 µg increments for the treatment of hypotension in the presence of tachycardia. Doses of this magnitude offset the haemodynamic effects of bolus doses of syntocinon given after delivery. Supplied only in 1 ml, 10 mg ampoules, phenylephrine must be diluted (e.g. to 100 µg ml–1) before use. Pre-eclampsia
Over the last few years, it has become accepted by many that preeclampsia is not necessarily a contra-indication to single-shot spinal anaesthesia. It stands to reason that if the abnormal vasoconstriction is of humoral rather than neural aetiology, sympathetic blockade should not cause precipitous hypotension. Prior vasodilatation by effective anti-hypertensive treatment (e.g. oral methyldopa or i.v. hydralazine), with limited intravascular volume expansion, seems to avert problematic hypotension. Judicious increments of either ephedrine or phenylephrine do not cause arterial pressure overshoot. Postoperative analgesia
Supplementation of intrathecal diamorphine or morphine by regular oral or rectal paracetamol (1 g, 6-hourly) and diclofenac (50 mg, 8-hourly, 12 h after an initial 100 mg postoperative dose), with oral dihydrocodeine if required (60 mg 4-hourly), makes patient-controlled i.v. morphine unnecessary for most women. The Royal College of Anaesthetists has stated in a clinical guideline that nonsteroidal anti-inflammatory drugs (NSAID) should not be used in pre-eclampsia. This was Grade C evidence – based on expert consensus. In pre-eclampsia with mild renal involvement (good urine output and no serum indices of renal failure), there seems little reason to deny women the benefit of the opioid-sparing effect of an NSAID, although successive doses should not be given without
repeated confirmation of sustained satisfactory urine output. There is no doubt that NSAIDs are always contra-indicated in the initial postoperative period if Caesarean section has been complicated by excessive bleeding or there is concern about adequacy of haemostasis (e.g. uterine atony).
Epidural anaesthesia Few elective Caesarean sections are now performed under epidural anaesthesia because the quality of anaesthesia is generally poorer than that afforded by subarachnoid block. In the 1997 survey, the rate of conversion to general anaesthesia (6%) was 3 times greater for epidurals than spinals. Epidural anaesthesia is still favoured by many when gradual establishment of block is desired to minimise hypotension, although combined spinal-epidural (CSE) techniques are gaining in popularity and continuous (incremental) spinal anaesthesia may represent the best technique. In severe preeclampsia, postoperative infusion of epidural bupivacaine/fentanyl in a high-dependency area will confer optimal analgesia and contribute to blood pressure control. A recent South African study demonstrated that women who were fully conscious and co-operative after an eclamptic seizure could safely undergo Caesarean section under epidural anaesthesia. All women had platelet counts >100 × 10–9 l–1 and had been treated with magnesium sulphate. Conversion of labour analgesia Women in labour deemed at high risk for Caesarean section – and those with potentially difficult airways – should have epidural analgesia instituted early. It should be established that the block is working well with no missed segments. If analgesia in labour has been poor, anaesthesia for Caesarean section is unlikely to be satisfactory. Conversion of analgesia for labour to surgical anaesthesia for Caesarean section is not the same as establishing epidural anaesthesia de novo. Plain bupivacaine 0.5% alone has been shown to convert low-dose bupivacaine/fentanyl labour epidural analgesia to surgical anaesthesia for Caesarean section as swiftly and effectively as lidocaine 2% with epinephrine, or a 50:50 mixture of the two solutions. The impact of adding bicarbonate has not been studied in this situation. Use of bupivacaine 0.5% alone circumvents the time spent and risks inherent in the hurried preparation of alkalinised drug mixtures. Good communication among midwives, obstetricians and anaesthetists should make general anaesthesia for the woman with a working epidural a rarity. Even in the event of cord prolapse, traditionally managed without question by general anaesthesia, there might be time for an epidural top-up, provided upward pressure on the presenting part is effective in avoiding cord compression.
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Local anaesthetic toxicity
The use of low-dose bupivacaine solutions for labour analgesia has confined the risk of local anaesthetic toxicity in obstetrics to the establishment of epidural anaesthesia for Caesarean section. Lbupivacaine 0.5% is equally effective as bupivacaine 0.5%, with less risk of CNS or cardiac toxicity in the event of high plasma concentrations after inadvertent intravascular injection. It has emerged that ropivacaine 0.75%, which is licensed for Caesarean section, is approximately equipotent with bupivacaine 0.5%. Any diminution of motor block with ropivacaine would be of little benefit to women undergoing Caesarean section.
Combined spinal-epidural anaesthesia Studies over the last 15 years have confirmed the superior quality of CSE anaesthesia compared with that of epidural anaesthesia alone for Caesarean section. Many units have adopted CSE as their standard technique for Caesarean section, despite lack of evidence of overall superiority compared with single-shot spinals in respect of the following variables: (i) speed of establishment of surgical anaesthesia; (ii) incidence of hypotension; (iii) incidences of nausea/vomiting and shivering; (iv) requirement for i.v./inhalational supplementation and conversion to general anaesthesia; (v) quality of muscle relaxation; (vi) incidence of dangerously high block requiring emergency airway management; and (vii) incidence of postoperative headache, neuropathy and CNS infection. Potential morbidity
Use of a Tuohy needle inevitably incurs a risk of accidental dural puncture and its consequences. In a needle-through-needle technique, the spinal needle is typically advanced up to 15 mm beyond the tip of the Tuohy needle. Unlike a single-shot spinal, the needle is not gripped by successive tissue layers during its passage. Moreover, the tip of a pencil-point needle is 1 mm or so distal to the aperture. Compared with a bevel-tipped needle, unrestrained deeper insertion before flashback of CSF might predispose to the alleged greater incidence of paraesthesia and possible increased risk of neural damage. The risk of meningitis is conceivably greater for CSE compared with single-shot spinals because of the proximity of a catheter to a dural hole. Spinal dose of local anaesthetic
Using the same intrathecal dose of bupivacaine as for a single-shot spinal and keeping the epidural catheter ‘in reserve’ gains no haemodynamic advantage. If avoidance of hypotension is a priority, a deliberately small intrathecal dose (e.g. 1 ml of bupivacaine 0.5%) can be administered. Assuming successful intrathecal injection (a failure rate of 3% has been described for a locking spinal
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needle-through-Tuohy needle technique), the desired block height can be achieved by increments of epidural local anaesthetic (or saline, which can extend a block by compression of the thecal sac). The smaller the spinal dose, the greater the reliance upon the epidural component and likelihood of unsatisfactory anaesthesia. Catheter misplacement
The position of a catheter placed directly after spinal injection in a needle-through-needle technique cannot be tested immediately. At the very time the catheter might be required (e.g. to prolong the block), it might not be functional, necessitating conversion to general anaesthesia. Both subarachnoid or subdural migration risk a dangerously high block and consequent emergency airway management. If difficulty is encountered threading an epidural catheter after spinal injection, intrathecal hyperbaric bupivacaine will fix as time elapses and limit the extent of block to the dependent area. The most recently described approach to CSE anaesthesia circumvents many of the potential problems of needle-through-needle techniques. Subarachnoid puncture is made with a standard spinal needle and the stylette replaced immediately. Only after satisfactory placement of an epidural catheter through a separate Tuohy needle, at the same space or space above, is spinal injection performed. Restriction of opioid to the spinal component of a CSE eliminates the risk of an unpredictably large fraction of an epidural dose reaching the CSF if the catheter is partially subarachnoid. Intrathecal diamorphine 0.25 mg provides the same quality and duration of analgesia as epidural diamorphine 5 mg. Placenta praevia
CSE anaesthesia is useful when surgery is predicted to outlast a single-shot spinal block. In the event of protracted surgery (e.g. Caesarean hysterectomy in a woman with placenta praevia), an epidural catheter will allow extension of the block, typically around 90 min after a standard intrathecal dose. Recent UK and American retrospective studies have compared regional and general anaesthesia for Caesarean section with placenta praevia. The commonly held obstetric view that placenta praevia dictates general anaesthesia is not supported. Regional anaesthesia was associated with reduced estimated blood loss and transfusion requirements. However, anterior placenta praevia in a women over 35 who has had previous Caesarean sections suggests a particularly high risk of massive haemorrhage. General anaesthesia with provision for postoperative ICU admission might be considered prudent.
Continuous spinal anaesthesia Placement of a catheter in the subarachnoid space allows the slow establishment of the highest quality of anaesthesia with the
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greatest degree of haemodynamic control. Tiny increments (e.g. 0.25 ml) of local anaesthetic solution can be titrated against block height and haemodynamic effects. There is no risk of systemic local anaesthetic toxicity. A series of patients undergoing Caesarean section was described almost 30 years ago, when 24-gauge catheters were threaded through 21-gauge spinal needles. The authors claimed the following advantages of inducing spinal anaesthesia with the patients supine: (i) elimination of unpredictably high spread by patient movement; (ii) no discontinuation of physiological monitoring during repositioning from lateral or sitting to supine; and (iii) immediate treatment of any hypotension. However, the incidence of postoperative headache was 16%. Potential morbidity
An endoscopic cadaver study demonstrated that all catheters inserted >30 mm into the subarachnoid space developed loops. Limiting the length of catheter threaded to <20 mm will reduce the risks both of snaring a nerve root and directing the catheter tip caudally. It is thought that the caudal positions of microspinal catheter tips led to attempts to achieve cranial extensions of low blocks by repeated doses of 5% lidocaine in hyperbaric dextrose. If not diluted by CSF, this solution is potentially toxic to the poorly insulated nerves of the cauda equina. A series of cases of cauda equina syndrome led the US Food and Drug Administration to ban microspinal (<24-gauge) catheters in 1992. It has been suggested that only solutions with a tonicity near to that of CSF should be used for continuous spinal anaesthesia. Reducing the concentration of glucose in solution with bupivacaine 0.5% from 80 mg ml–1 to 8 mg ml–1 (by mixing plain and hyperbaric solutions in the proportion of 9:1) does not affect the immediate characteristics of single-shot spinal blocks in pregnant women at term. There seems little need, therefore, to use repeated doses of hyperbaric 0.5% bupivacaine in glucose 80 mg ml–1 in a continuous spinal technique. Indication
Continuous spinal anaesthesia has never become popular in UK obstetric anaesthetic practice, although recent case reports have described successful management of parturients with serious cardiac lesions (e.g. aortic stenosis and Eisenmenger’s syndrome) using cautious incremental dosing. Kits comprising a 28-gauge catheter through 23-gauge needle and 22-gauge catheter over 27gauge needle with pull-wire are available (see Burnell & Byrne, Key reference). The incidences of infection, neuropathy and postdural puncture headache remain to be defined.
General anaesthesia General anaesthesia is indicated for all ‘emergency’Caesarean sections (Table 1) and other cases for which a regional block is absolutely contra-indicated or has failed. If the history or evaluation of the airway suggests that tracheal intubation might be difficult, awake fibre-optic intubation should be considered.
Depth of anaesthesia The regimen of thiopental, succinylcholine and intubation has remained standard and largely unchanged since it superseded mask and ether 40 years ago and permitted a lighter plane of inhalational general anaesthesia. Although babies born to mothers anaesthetised with ether were undoubtedly sleepier than those whose mothers who underwent light anaesthesia facilitated by neuromuscular block, they were not necessarily compromised. General anaesthesia is ‘innocuous and reversible’ for the baby provided maternal oxygenation and normocarbia are maintained, aortocaval compression avoided and a paediatrician is present to support ventilation. Fetal compromise to which uterine hyperstimulation has been contributory might actually be relieved by uterine relaxation conferred by a volatile agent. In contrast, a maternal stress response to excessively light general anaesthesia will be to the detriment of uteroplacental blood flow. With inhalational agent monitoring now universally available, the risk of awareness in obstetric anaesthesia should have been consigned to history. No adverse maternal or neonatal effects were found when sevoflurane and desflurane were evaluated for maintenance of anaesthesia. These agents offer the advantage of more rapid approximation of alveolar to inspired tensions as the anaesthetic effect of the i.v. induction dose declines.
Inhalational induction Obstetric general anaesthesia was not made ostensibly safer by the introduction of i.v. induction, neuromuscular blockade and intubation – the number of deaths attributable to anaesthesia increased markedly in the 1964–1966 triennium (Fig. 2). Sevoflurane has been use successfully for inhalational induction of anaesthesia for Caesarean section in the absence of vascular access and in status asthmaticus. The smooth, rapid onset and lack of coughing or vomiting suggest that the technique does not necessarily impose an increased risk of aspiration.
Pre-eclampsia Uncorrected coagulopathy, or symptoms consistent with impending eclampsia (severe headache or visual disturbance) are potential indications for general anaesthesia. Prior communication with a
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paediatrician is essential in order that preparation can be made for antagonism of opioid and provision of ventilatory support for the neonate. Laryngeal oedema is a real risk – beware the patient with recent voice change. Any dubious notion of light general anaesthesia for the baby’s benefit should be overridden by efforts to protect the maternal cerebral circulation. Although the onset and duration of succinylcholine are unaffected by therapeutic serum magnesium concentrations, the durations of action of all nondepolarising drugs are potentiated. The following points should be borne in mind: 1. Have a low threshold for direct arterial pressure monitoring. 2. Attenuate the pressor response to intubation with alfentanil 10 µg kg–1 or remifentanil 2 µg kg–1 (preceded by glycopyrrolate 0.4 mg to prevent bradycardia) before rapid sequence neuro-anaesthetic induction with a generous dose of thiopental. 3. A peripheral nerve stimulator is essential to ascertain the degree of neuromuscular block. 4. Before extubation, consider additional anti-hypertensive therapy (e.g. labetalol in 10–20 mg increments) to avert a dangerous pressor response. Any patient whose larynx was noted to be swollen at laryngoscopy or in whom intubation was traumatic is at particular risk of laryngeal oedema. Postoperative care must be in an ICU or highdependency area with an anaesthetist immediately available. Midwives should be alerted to the ominous significance of stridor.
Current controversy The use of succinylcholine for Caesarean section remains standard teaching. However, anaphylaxis to succinylcholine has been responsible for maternal deaths at Caesarean section and many ‘near misses’. Rocuronium 0.6 mg kg–1 is licensed for Caesarean section and has been shown to produce acceptable intubating conditions after thiopental 6 mg kg–1 within 90 s without untoward neonatal effects. UK data suggest that the risk of anaphylaxis to rocuronium is much lower than that for succinylcholine. However, an important potential disadvantage is that the duration of block rules out the possibility of abandoning the anaesthetic in the event of failed tracheal intubation. Controversially, some argue that inserting a laryngeal mask airway (LMA) and ventilating the lungs with cricoid pressure is no less safe overall, in this situation, than using succinylcholine and attempting to proceed with inhalational anaesthesia by spontaneous respiration. Unlike the case with succinylcholine, optimal 176
Fig. 3 ProSeal laryngeal mask airway.
conditions for airway management and maintaining oxygenation will be sustained and vomiting cannot occur. Maintenance of a slight head-up tilt will allow gravity to reduce the risk of regurgitation of gastric contents. The ProSeal LMA (Fig. 3) holds great promise for airway management in obstetric anaesthesia. A second tube makes a sealed junction against the upper oesophageal sphincter, allowing continuity with the gastrointestinal tract and isolation from the airway. Gastric insufflation during IPPV is minimised and passage of a gastric tube facilitated.
Failed and difficult intubation The management of difficult and failed intubation in obstetrics has been reviewed recently in this journal (see key references).
Key references Abouleish E,Abboud T, Lechevalier T, Zhu J, Chalian A,Alford K. Rocuronium (Org 9426) for Caesarean section. Br J Anaesth 1994; 73: 336–41 Brain AIJ,Verghese C, Strube PJ.The LMA ‘ProSeal’ – a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4 Burnell S, Byrne AJ. Continuous spinal anaesthesia. BJA CEPD Rev 2001; 1: 134–7 (Fig. 1, p134) Focus group. Obstetric anaesthesia delays and complications. In: Confidential Enquiry into Stillbirths and Deaths in Infancy. 7th Annual Report. London: Maternal and Child Health Research Consortium, 2000; 41–52 Gabbott DA. Recent advances in airway technology. BJA CEPD Rev 2001; 1: 76–80 Hamer Hodges RJ, Bennett JR, Tunstall ME, Knight RF. General anaesthesia for operative obstetrics. Br J Anaesth 1959; 31: 152–63 Lucas DN,Yentis SM, Kinsella SM, Holdcroft A, May AE,Wee M et al. Urgency of caesarean section: a new classification. J R Soc Med 2000; 93: 346–50 Morris S. Management of difficult and failed intubation in obstetrics. BJA CEPD Rev 2001; 1: 117–21 Shibli KU, Russell IF.A survey of anaesthetic techniques used for caesarean section in the UK in 1997. Int J Obstet Anesth 2000; 9: 160–7 See multiple choice questions 108–110.
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