Obstetrics

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CHAPTER 8 Obstetrics

Anaesthesia for non-obstetric surgery during pregnancy

A total of 1% of patients require GA during pregnancy. In the first trimester, there is a risk of organogenesis; in the third trimester there is a risk of premature labour. Therefore, the second trimester is the safest.

In descending order of preference:

Regional anaesthesia

Epidurals give excellent/satisfactory analgesia in 91% of mothers. Increased use of regional techniques probably accounts for the continuing reduction in maternal mortality by avoiding risks of failed intubation and aspiration. Comparative Obstetric Mobile Epidural Trial (COMET) 2001 showed that women requesting analgesia for pain relief were more likely to require instrumental delivery if receiving 0.25% bupivacaine boluses rather than low dose bupivacaine infusion or combined spinal/epidural, but no significant difference in LSCS rates between groups (Table 8.1).

Table 8.1 Advantages and disadvantages of epidural anaesthesia

Advantages Disadvantages
Maternal participation at delivery May take too long to perform if there is fetal distress
Avoids risk of failed intubation Hypotension
Reduced risk of aspiration Risk of patchy, incomplete block
Avoids morbidity from GA drugs Backache
Avoids risk of awareness Urinary retention
Earlier breast-feeding  
Good postoperative analgesia  
Less postnatal depression  

Epidural test dose

Recommended to avoid complications of inadvertent intravenous injection of bupivacaine. Usually use a dose insufficient to cause total spinal anaesthesia if injected into the intrathecal space.

Regional anaesthesia

Platelet count <100 000, abnormal clotting or prolonged bleeding time is a relative contraindication to regional anaesthesia.

Epidurals are best established early and generally unsuitable for emergency procedures. Provide less effective anaesthesia than subarachnoid block and are more likely to require conversion to GA. Epidurals are the technique of choice for labour or LSCS in pre-eclamptic toxaemia (PET), where they provide better haemodynamic stability and improved uteroplacental flow, with avoidance of intubation risks from laryngeal oedema. l-bupivacaine 0.5% is as effective as bupivacaine 0.5% with less risk of CNS or CVS toxicity. Ropivacaine 0.75% is equipotent with bupivacaine 0.5%.

Spinals are the commonest form of anaesthesia for LSCS. Pencil point needles now reduce incidence of post-dural puncture headache requiring blood patch to <0.5%. Colloid fluid preload is more effective than crystalloid in preventing hypotension, but greater risk of anaphylaxis. Avoidance of aortocaval compression and use of vasopressor (e.g. phenylephrine 50–100 μg) significantly reduces hypotension. 2.25 mL 0.5% heavy bupivacaine achieves an adequate block to T4 at term, but larger volumes may be required earlier in pregnancy because of less venous congestion reducing the volume of the epidural space. Addition of opioids (fentanyl/morphine/diamorphine) reduces the incidence of intraoperative visceral pain with little risk of respiratory depression.

Combined spinal-epidural anaesthesia (CSE) may provide better anaesthesia than epidural alone. In a needle-through-needle technique, the spinal needle is advanced <15 mm beyond tip of Tuohy. Alternatively, puncture the subarachnoid space with spinal needle and replace the stylette immediately, then site epidural catheter via Tuohy needle at difference space. Give epidural test dose and then follow with subarachnoid injection. A smaller intrathecal dose (e.g. 1.0 mL 0.5% bupivacaine) followed by epidural increments improves haemodynamic stability; 0.25 mg intrathecal diamorphine ≡ 5 mg epidural diamorphine. There is some concern regarding breaching of the dura increasing infection risk and the complexity of the technique.

Epidural volume extension (EVE) A low subarachnoid block can be extended in a cephalad direction by an epidural injection of 10 mL of normal saline given within 5 min of the initial subarachnoid block. Probably related to compression of the subarachnoid space by the epidural saline, resulting in cephalad spread of local anaesthetic within the subarachnoid space. EVE allows CSE to be performed with small initial intrathecal doses of local anaesthetic and, as saline is used for the epidural ‘top-ups’, the total dose of local anaesthetic used is reduced.

Continuous spinal anaesthesia using an ultra fine bore catheter threaded through a spinal needle has been associated with cauda equine syndrome and is little used in the UK.

Aspiration

Postpartum

Assuming no opioids are present, rate of emptying, gastric pH and volume of stomach contents rapidly return to normal values within about 6–8 h. However, reflux (80% of women at term) may persist for up to 48 h. Therefore, anti-aspiration measures necessary for 48 h postpartum.

Oaa/Aagbi Guidelines for Obstetric Anaesthesia Services

Association of Anaesthetists of Great Britain and Ireland and the Obstetric Anaesthetists Association 2005

Bibliography

American Society of Anesthesiologists. Practice guidelines for obstetrical anesthesia. A report by the American Society of Anesthesiologists. Task Force on Obstetrical Anesthesia. Anesthesiology. 1999;90:600-611.

Association of Anaesthetists of Great Britain and Ireland and the Obstetric Anaesthetists Association. Revised Guidelines, 2005. OAA/AAGBI guidelines for obstetric anaesthesia services. Reproduced with the kind permission of the Association of anaesthetists of Great Britain and Ireland

Bogod D.G. The postpartum stomach – when is it safe? Editorial. Anaesthesia. 1994;49:1-2.

Comparative Obstetric Mobile Epidural Trial (COMET) Study Group UK. Effect of low-dose mobile vs traditional epidural techniques on mode of delivery: a randomized controlled trial. Lancet. 2001;358:19-23.

Duley L., Neilson J.P. Magnesium sulphate and pre-eclampsia. BMJ. 1999;319:3-4.

Gomar C., Fernandez C. Epidural analgesia–anaesthesia in obstetrics. Eur J Anaesth. 2000;17:542-558.

Levy D.M. Emergency caesarean section: best practice. Anaesthesia. 2006;61:786-791.

McDonnell N.J., Keating M.L., Muchatuta N.A., et al. Analgesia after caesarean delivery. Anaesth Intensive Care. 2009;37:539-551.

McGlennan A., Mustafa A. General anaesthesia for caesarean section. Contin Edu Anaesth, Crit Care Pain. 2009;9:148-151.

Ong K.-B., Sashidharan R. Combined spinal–epidural techniques. Contin Edu Anaesth, Crit Care Pain. 2007;7:38-41.

Levy D.M. Anaesthesia for caesarian section. BJA CEPD Rev. 2001;1:171-176.

Macarthur A.J., Gerard W. Ostheimer ‘What’s new in obstetric anesthesia’ lecture,. Anesthesiology. 2008;108:777-785.

McGrady E., Litchfield K. Epidural analgesia in labour. Contin Edu Anaesth, Crit Care Pain. 2004;4:14-17.

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Morris S. Management of difficult and failed intubation in obstetrics. BJA CEPD Rev. 2001;1:117-121.

Turner J.A. Severe preeclampsia: anesthetic implications of the disease and its management. Am J Ther. 2009;16:284-288.

Maternal and fetal physiology

Maternal physiology

Effect of anaesthetic drugs on the fetus during LSCS

Pregnancy-induced hypertension

Pathophysiology

Thought to be triggered by an autoimmune reaction against the placenta (Fig. 8.2).

Airway. Facial and laryngeal oedema may make intubation difficult. Consider awake fibreoptic intubation in elective patients undergoing GA.

Cardiovascular. In untreated patients, cardiac index (CI) is low/normal, SVR is normal/high and PCWP is low/normal due to contraction of intravascular volume by as much as 30–40% in severe cases. Fluid challenge may improve cardiovascular stability, increase CI and reduce SVR to more normal levels. PCWP becomes normal/high, but CVP correlates poorly. Consider invasive monitoring if oliguria persists following 500 mL fluid challenge.

Treat hypertension with hydralazine 5–10 mg i.v. boluses or 5–40 mg/h infusion. Causes headache, tremor and vomiting, mimicking symptoms of eclampsia. Also consider labetalol up to 1 mg/kg (reports of fetal bradycardia if used in the presence of fetal distress) or sodium nitroprusside 0.3–8 μg/kg/min. Nifedipine may cause severe hypotension if used with magnesium.

Central nervous system. Cerebral vasospasm, microinfarcts, petechial haemorrhage and oedema cause CNS irritability, visual disturbance and headache. May be worsened by hypertension following pressor response to intubation. Fits are more common in teenage mothers and multiple pregnancies. CNS haemorrhage is a major cause of maternal deaths.

Treat CNS irritability with magnesium sulphate 4 g loading dose then 1–3 g/h which suppresses EEG excitatory activity, aiming for therapeutic blood level of 2–4 mmol/L. Titrate against deep tendon reflexes. Also vasodilates uterine vessels and attenuates uterine vascular response to catecholamines. May accumulate in renal failure. Excess (>4 mmol/L) causes respiratory paralysis, heart block and fetal weakness. Treat with calcium gluconate 1 g i.v.

Coagulation. Thrombocytopenia <100 000 is common. Normal platelet counts are associated with prolonged bleeding times in 10–25% of pre-eclamptics; 34% of patients with severe eclampsia have prolonged bleeding times. Low-grade DIC is common.

Recent Collaborative Low Dose Aspirin Study (CLASP) cast doubt on the efficacy of aspirin in reducing the incidence of pre-eclampsia.

Hepatic. Abnormal LFTs due to oedema and hepatic congestion. Associated with HELLP syndrome (Haemolysis, Elevated Liver enzymes, Low Platelets).

Renal. Decreased glomerular filtration, acute tubular necrosis and increased permeability to proteins causing proteinuria.