Obstetrics

General anaesthesia for operative obstetricsAmelia banks

David Levy

AbstractAlthough the fraction of caesarean sections performed under general

anaesthesia has decreased greatly over the past 40 years, the caesar-

ean section rate has increased. therefore, the actual number of general

anaesthetics may not have declined greatly year by year. However, there

is an increasing likelihood that a trainee’s first experience of caesarean

section under general anaesthesia will be an emergency case. Mortality

associated with general anaesthesia for caesarean section is virtually

confined to emergency cases; airway problems predominate. cord pro-

lapse and placenta praevia are not absolute contraindications to general

anaesthesia. A scarred uterus (e.g. after previous caesarean section) is a

key predictor of intraoperative major haemorrhage. Accurate and timely

multidisciplinary communication is vital during general anaesthesia for

obstetrics. Avoidance of aortocaval compression (by left-lateral tilt) is

of paramount importance for maintenance of feto-placental perfusion.

At induction of general anaesthesia, head-up tilt is recommended as

routine, both for prevention of regurgitation and for optimization of

preoxygenation and airway management. Gas monitoring lends objectiv-

ity to preoxygenation: the endpoint is an end-tidal fractional expired

oxygen concentration approaching 90%. thiopental is the induction

agent of choice. in pre-eclampsia, it is vital that the pressor response

to intubation is obtunded to prevent intracerebral haemorrhage. the

opioids alfentanil and remifentanil are suitable adjuncts to thiopental.

0.75 minimum alveolar concentration end-tidal vapour concentration

(plus 50% nitrous oxide) is required for a bispectral index of less than

60. there is no rationale for risking awareness with light anaesthetic

regimens. rocuronium is an acceptable (and licensed) alternative to

succinylcholine for caesarean section. training opportunities in obstetric

general anaesthesia (particularly elective cases) should be encouraged.

Keywords aspiration; awareness; caesarean section; failed intubation;

pre-eclampsia; rapid-sequence induction

Amelia Banks, FRCA, is Anaesthetic Specialist Registrar in the

Nottingham and East Midlands School of Anaesthesia. She trained

at St Bartholomew’s, London and has undertaken her anaesthetic

training in Nottingham. She has a keen interest in obstetric

anaesthesia.

David Levy, FRCA, is Consultant Anaesthetist at Queen’s Medical Centre,

Nottingham. He qualified from the University of Edinburgh and trained

in Aberdeen, Sheffield and Nottingham. His interests include obstetric

anaesthesia and neuroanaesthesia.

ANAestHesiA AND iNteNsiVe cAre MeDiciNe 8:8 31

There has been a dramatic increase in the caesarean section rate over the past 40 years, from less than 4% in the early 1960s to 21% in 2000.1 In the 1960s and 1970s general anaesthesia was used for most elective and emergency cases. Although regional techniques now predominate, the actual number of general anaes-thetics may not have declined greatly year by year. The National Sentinel Caesarean Section Audit found that 23% of emergency and 9% of elective cases were performed under general anaes-thesia.1 There is an increasing likelihood that a trainee’s first experience of caesarean section under general anaesthesia will be an emergency case.

Caesarean section is the commonest operative obstetric proce-dure. Other procedures may be undertaken antepartum, such as cervical suture, or postpartum, such as removal of retained pla-centa and perineal repair. Surgical management of postpartum haemorrhage can include uterine brace suture, hysterectomy, or laparotomy to identify and control the source of bleeding.2 The salient aspects of general anaesthesia for caesarean sec-tion can be applied to other operative situations, although the need for avoiding aortocaval compression by the gravid uterus is obviously not an issue postpartum.

Indications for general anaesthesiaThe anaesthetic technique for operative delivery is dependent on the clinical situation, and will be determined by maternal and fetal considerations.

The few absolute indications for general anaesthesia include:• contraindication to regional anaesthesia (e.g. uncorrected

coagulopathy)• maternal refusal of regional anaesthesia• insufficient time to establish or extend regional anaesthesia

(e.g. in the event of profound fetal bradycardia)• failure of regional anaesthesia (accounts for 10% of general

anaesthetics for caesarean section). Cord prolapse and placenta praevia were previously considered absolute indications for general anaesthesia. However, cord pro-lapse may not require general anaesthesia provided that the cord is decompressed and there is no significant fetal compromise. For placenta praevia there should be discussion amongst the mother, the obstetrician, and anaesthetist. Uterine scarring (e.g. after previous caesarean section) is a key predictor of intraoperative major haemorrhage.3

Anaesthetic regimenA summary of the procedures involved in general anaesthesia for operative obstetrics is shown in Table 1.

Induction of anaesthesia: rapid-sequence induction should be used for all women requiring general anaesthesia from the middle of the second trimester onwards to reduce the risk of aspiration of gastric contents. The woman should be positioned with left-lateral tilt and slight head-up position. Full monitoring should be in place. The lungs should be pre-oxygenated with a close-fitting facemask, to a fractional end-tidal oxygen concentra-tion approaching 0.9. A cricoid force of 10 N should be applied awake and increased to 30 N on induction of anaesthesia.

The induction agent of choice is thiopental (5–7 mg/kg), but other agents such as propofol, ketamine and etomidate are suit-able alternatives. Ketamine (1 mg/kg) and etomidate (0.3 mg/kg)

7 © 2007 elsevier Ltd. All rights reserved.

Obstetrics

are useful in women with haemodynamic instability (e.g. in ante-partum haemorrhage secondary to placental abruption). Succinyl-choline is used to facilitate tracheal intubation in most women. A dose of 1–1.5 mg/kg should be used to ensure optimal intubating conditions. Rocuronium (0.6 mg/kg) is an acceptable alternative in situations where avoidance of succinylcholine is warranted.4

Maintenance of anaesthesia: anaesthesia is maintained using a volatile halogenated agent (e.g. isoflurane or sevoflurane) delivered in oxygen/nitrous oxide. Fractional inspired oxygen is guided by pulse oximetry – there is no need to adhere to a ‘default’ of 0.5. If a circle system is used, overpressure (with high fresh-gas flows) should be used initially to ensure adequate end-tidal concentrations of volatile agent to prevent intraoperative awareness. To ensure adequate depth of anaesthesia (bispectral index < 60) an end-tidal vapour concentration of more than 0.75 minimum alveolar concentration (as well as 50% nitrous oxide)5 should be maintained before the administration of opioid analge-sia. Past concerns about uterine atony secondary to a protracted

A summary of the procedures involved in general anaesthesia for operative obstetrics

communication • Vital throughout

• Multidisciplinary

Preoperative

assessment

• thorough airway assessment essential

Aspiration

prophylaxis

• 0.3 M sodium citrate 30 ml (orally) with

ranitidine 150 mg (orally) or ranitidine

50 mg intravenously

Location • in operating theatre

• surgeons present and scrubbed

• Abdomen draped if emergency

Assistance • trained anaesthetic assistant

Positioning • Left-lateral tilt

• slight head-up position

Monitoring • As AAGbi guidelines

Preoxygenation • Facemask with good seal

• Aim for end-tidal oxygen > 0.9

induction • thiopental (5–7 mg/kg)

• succinylcholine (1–1.5 mg/kg)

intubation • cuffed oral tracheal tube

• rehearsed failed intubation drill

Maintenance • end-tidal vapour concentration > 0.75

MAc with 50% oxygen/50% nitrous oxide

extubation • Awake and responsive

• Left-lateral or semi-recumbent position

Postoperative • Analgesia with oral paracetamol plus

NsAiD

• PcA morphine

• regular review

AAGbi, Association of Anaesthetists of Great britain and ireland; MAc, minimum alveolar concentration; NsAiD, non-steroidal anti-inflammatory drug; PcA, patient-controlled analgesia

Table 1

ANAestHesiA AND iNteNsiVe cAre MeDiciNe 8:8 318

relaxant effect of halothane have been allayed by the rapidity of offset of more modern, less soluble vapours.

Neuromuscular blockade should be maintained using incre-ments of non-depolarizing agents, guided by response to peri-pheral nerve stimulation.

Analgesia: opioids (e.g. morphine 10–20 mg) should be adminis-tered following delivery of the fetus. An expectant policy should be adopted if neuraxial opioids have been given previously (i.e. for labour analgesia) because additional opioids may not be necessary. Intravenous patient-controlled analgesia is ideal for the first 12–24 postoperative hours. Regular oral paracetamol and a non-steroidal anti-inflammatory drug should be given routinely in the absence of contraindications.

Tracheal extubation should be undertaken in the left-lateral or semi-recumbent position after awakening and return of protec-tive airway reflexes.

ComplicationsThe safety of obstetric anaesthesia has improved dramatically during the past 50 years. However, anaesthesia was the cause of death in nearly 6% of direct maternal deaths in the 2000–2002 Confidential Enquiry into Maternal and Child Health report.6 Complications of emergency general anaesthesia accounted for all deaths attributed to anaesthesia.

Failed tracheal intubation: the incidence of failed intubation in the obstetric population is about 1 in 300, 10 times that in the general population.7 A thorough airway assessment must be made before every general anaesthetic. A failed intubation drill must be rehearsed, and followed in the event of diffi-culty. Correct endotracheal tube placement must be confirmed by capnography, and oesophageal intubation recognized and corrected promptly.

Awareness: low concentrations of volatile agent to preserve uterine tone and the avoidance of opioid analgesia to prevent neonatal respiratory depression have been responsible for a high incidence of awareness. In the late 1960s and early 1970s general anaesthesia for caesarean section was associated with a very high incidence of explicit recall.8 The psychological morbidity associ-ated with awareness should not be underestimated. Awareness is eminently preventable, even in the event of hypovolaemic shock, when 100% oxygen is administered without vapour. Anaesthesia can be maintained with increments of intravenous ketamine.

Aspiration of gastric contents: pregnant women are at increased risk of aspiration of gastric contents. Prophylaxis should con-sist of H2 antagonist agents (orally or intravenously) and 0.3 M sodium citrate (30 ml orally). Rapid-sequence induction with cri-coid pressure and slight head-up tilt at induction should further reduce the chance of aspiration.

General anaesthesia and maternal comorbidityThe choice of general anaesthetic will be determined by the maternal condition, particularly when there is maternal co- morbidity. Comorbidities may pre-exist or may be related to the pregnancy.

© 2007 elsevier Ltd. All rights reserved.

Obstetrics

Increasingly, women with significant comorbidities are hav-ing children, and this poses challenges for the anaesthetist. The anaesthetic must be appropriate to the underlying patho-physiology rather than a standard regimen of thiopental and succinylcholine.

Pre-eclampsia: the pressor response to intubation must be obtunded to avoid intracerebral haemorrhage. Thiopental used alone is not sufficient. Opioids (either alfentanil, 10 μg/kg, or remifentanil, 2 μg/kg) are effective adjuncts.2 Neonatal respira-tory depression may occur, but can be easily reversed by nal-oxone. The neonatal paediatrician must be made aware that an opioid has been administered before delivery.

Laryngeal oedema can make tracheal intubation more diffi-cult, and predispose to postoperative stridor.

Pre-eclamptic women may be receiving magnesium by infu-sion. Non-depolarizing neuromuscular blockade is potentiated by therapeutic serum magnesium concentrations. Monitoring with peripheral nerve stimulation is mandatory.

CommunicationAccurate and timely multidisciplinary communication is vital in obstetric anaesthesia.9 High-risk women should be identi-fied early, and comprehensive peripartum management plans formulated. For women in whom emergency induction of gen-eral anaesthesia would be particularly hazardous (e.g. morbid obesity) early establishment of neuraxial analgesia may be appropriate. Consideration should be given to whether a planned operative delivery would be safer than embarking on an unpre-dictable labour.

Discussions with neonatal paediatricians should include details of the opioids administered. Communication with the mother and her birth partner is of paramount importance and is frequently overlooked in emergency situations.

The futureAlthough the caesarean section rate has increased, use of general anaesthesia has declined and trainee hours of work have been decreased. Most anaesthesia trainees have minimal experience of general anaesthesia in obstetrics, and should take every opportu-nity to practise the technique. Increased presence of consultant

ANAestHesiA AND iNteNsiVe cAre MeDiciNe 8:8 31

anaesthetists on obstetric units should help optimize training opportunities. Training adjuncts, including medical simulation, may have a useful role.

General anaesthesia for operative obstetrics, especially elec-tive cases, is not inherently unsafe. If trainees are instilled with excessive anxiety about the potential hazards of general anaes-thesia, complications (especially failed intubation) will remain prevalent.7 ◆

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9 © 2007 elsevier Ltd. All rights reserved.