Anaesthesia for Obstetric Surgery

Anaesthesia for Obstetric Surgery

• Spinal anaesthesia is recommended as the standard procedure for caesarean section.
• General anaesthesia is used when spinal anaesthesia is contraindicated.
• Local infiltration This can be used in desperate situations, e.g. the absence of a trained anaesthetist, or a moribund patient.

Spinal Anesthesia for Caesarean Section

This method is considered dangerous by some but it is used as the standard anaesthetic technique in hospitals with limited facilities for the following reasons:

Advantages

If it is done cautiously and if the anaesthetist is aware of (and watching out for) complications, it has the following advantages:

• It gives effective pain relief very quickly with almost 100% success.
• There is no maternal depression of CNS. The cough reflex is intact.
• There is no direct foetal depression.
• Only a very small dose of local anaesthetic is needed, so systemic toxicity is low.
• The anaesthetist is free to resuscitate the baby if necessary.
• There is no direct effect on uterine contractility unlike high doses of volatile agent.
• There is good relaxation of abdominal muscles.

Disadvantages

• Hypoxia. The enlarged uterus interferes with the movement of the diaphragm. Respiratory difficulties can arise with a high block but rarely cause serious problems. If the spinal block interferes with intercostal movement then there is a definite danger of hypoxia.
• Hypotension. During pregnancy the circulation of the CSF is altered because of high intra-abdominal pressure. The injected local anaesthetic travels higher up, causing a block of sympathetic nerves. Because of this smaller doses of LA are used in pregnancy and most hypotension is caused by aorto-caval compression and sympathetic block.
• Post spinal headache - the incidence of this is low especially if a 25/27G needle is used.
• Danger of total spinal.
• Shivering -Treat with oxygen and if not relieved give 25 mg of pethidine

Precautions to Take While Using a Spinal Anaesthetic for Caesarean Section

• Pre-operative preparation as described for general anaesthetic.
• Take steps to prevent supine hypotensive syndrome. The patient must be lying on her side or with a left tilt at this stage. If her blood pressure is lower than her normal blood pressure then you must not start any kind of anaesthesia until the blood pressure has been corrected. (See page 331).
• Insert a 16G needle and give at least 1 litre of Hartmann's solution before inserting the spinal.
• Use an appropriate dose of local anaesthetic:

• Don't inject the local anaesthetic while a uterine contraction is in progress.
• Check the blood pressure every 60 seconds for the next 15 minutes.
• Give the mother oxygen by mask, to breathe.
• Place a wedge under her right hip when she is turned to the supine position as described above.

• Increase fluids
• Give oxygen by mask
• Manual displacement of uterus
• Place in lateral position
• Give ephedrine 5 - 10 mg IV in repeated doses or phenylphrine 0.5-1 mcg/kg.

The use of Ephedrine

Ephedrine does not interfere with uterine blood flow and is recommended as the vasopressor of choice for the treatment of hypotension during spinal anaesthesia. Dose: 5 - 10 mg in repeated doses up to 30mg IV.

For resistant hypotension, assuming that caval compression and hypovolemia have been corrected a small dose of metaraminol (0.5 -1 mg) may be used. If this is not available a low dose of dilute adrenaline may be required.

General Anesthesia for Caesarean Section

Potential Anesthetic Problems

• Inhalation of Gastric Contents: This is a special hazard in the pregnant patient for the following reasons: There is a high gastrin level and a delayed gastric emptying time during pregnancy; The increased intra-abdominal pressure predisposes to vomiting; The oesophago-gastric sphincter is less efficient during pregnancy; The lithotomy position (in which a lot of obstetric procedures are performed) predisposes to regurgitation. Many obstetric procedures are emergencies and the patient may present for an anaesthetic after a recent meal. Pulmonary aspiration of gastric contents (incidence: 1:500-400 for obstetric patients versus 1:2000 for all patients) and failed endotracheal intubation (incidence: 1:300 versus 1:2000 for all patients) during general anesthesia are the major causes of maternal morbidity and mortality. Every effort should be made to ensure optimal conditions prior to the start of anesthesia and to follow measures aimed at preventing these complications.
• Anticipation of a difficult endotracheal intubation may help reduce the incidence of failed intubations. The higher incidence of failed intubations in pregnant patients compared with nonpregnant surgical patients may be due to airway edema, or large breasts that can obstruct the handle of the laryngoscope in patients with short necks. A variety of laryngoscope blades, a short laryngoscope handle, at least one extra styletted endotracheal tube (6 mm), Magill forceps (for nasal intubation), a laryngeal mask airway (LMA), an intubating LMA should be readily available.
• Depression of the foetus by drugs given to anaesthetise the mother.
• Supine hypotensive syndrome or obstruction of the inferior vena cava. This is not uncommon. Always watch out for it! It is caused by the pregnant uterus pressing on the inferior vena cava and reducing the venous return on which the blood pressure depends. The blood pressure therefore falls. Occasionally blood pressure remains normal but tachycardia and sweating occur.

The signs and symptoms of this syndrome should always be corrected before an anaesthetic is given. Several anaesthetic deaths have resulted from this. The hypotension must first be corrected by the following methods:

Administer intravenous fluids rapidly.

Place a pillow under the right hip and tilt 15 degrees to the left.

Try to push the uterus away from the IVC manually (if above fails).

Place the patient in the left lateral position if above fails (very rare) while fluid is being given.

• Aortic compression interfering with blood supply to the foetus.
• Shock In the obstetric patient: This may have several causes, e.g. haemorrhage; septic shock; traumatic shock; acute inversion of the uterus; amniotic fluid embolism (here the membranes rupture and amniotic fluid enters the circulation causing a "shock like" state). The most common cause of shock is blood loss, the signs of which often present late as these patients have the ability to compensate for a significant degree of blood loss. Therefore vigilance is important, including good IV access (16G) and treatment of the cause before an irreversible situation arises.
• Impairment of uterine contractility due to anaesthetic agents.

Pre-operative preparation

• Check the patient's medical state, e.g. present and past medical problems; anaesthetic history; degree of dehydration; extent of blood loss (if any). Check blood pressure with the patient in the lateral position and again 5 minutes after the left lateral tilt position is assumed. Tell the patient to lie on her side until she comes to theatre. Find out the time of the last dose of analgesia, the reason for the caesarean section and the presence or absence of foetal distress.
• Premedication consists of H2 antagonist, i.e. ranitidine 300mg orally (if available) and metoclopramide 10mg IM, IV or O, 1 hour prior to surgery.
• Give an antacid, 20-30ml sodium citrate (0.3M) 20 minutes before surgery.

Theatre procedure:

Transfer the patient to theatre in the lateral position.

Check when the patient had her last meal. A routine caesarean section should not be done within 6 hours of a meal. Even so, the risk of vomiting is higher in the pregnant patient.

Check the cuff of the endotracheal tube for leaks. Leave the syringe attached.

Check the suction, turn it on and put it under the mattress of the operating theatre.

Explain the technique of cricoid pressure to the assistant and to the patient and why it is necessary.

Check the anaesthetic machine and equipment.

Draw up the drugs.

Intra-operative management

• Anaesthetise the patient in the supine position with a wedge or pillow under her right hip. The table is horizontal.
• Note the blood pressure. If it is low follow the measures described to treat the supine hypotensive syndrome.
• Start an IV infusion of Hartmann's solution (500 -1000ml of fluid). Use a 16G cannula if possible.
• Pre-oxygenate the patient for four minutes (by the clock).
• Give a pre-selected sleep dose of ketamine or thiopentone intravenously (ketamine 1 - 2 mg/kg IV or thiopentone 3 - 4 mg/kg IV). The standard method of titrating the induction agent by checking the eyelash reflex is not used in this instance. Avoid the use of ketamine in pre-eclampsia and eclampsia.
• Follow the induction agent (thiopentone or ketamine) with a dose of short acting relaxant, e.g. suxamethonium 1.5mg/kg.
• Apply cricoid pressure after consciousness is lost.
• Support the jaw until it is relaxed enough. (Note: The patient should not be ventilated after the relaxant. The four minutes pre-oxygenation ensures that there is sufficient oxygen in the lungs to tide over the period of apnoea).
• When the jaw is relaxed, intubate the patient and inflate the cuff. Check the position of the endotracheal tube by auscultation.

Maintain the anaesthetic with air or nitrous oxide, oxygen (50%) and volatile (e.g. halothane 0.5%) or intermittent doses of ketamine 0.5mg/kg. or ether 2 - 3% air/oxygen. When the effect of the suxamethonium wears off give a dose of long-acting relaxant, e.g. vecuronium,0.01-0.05 mg/ kg pancuronium 0.1- 0.06 mg /kg . Intermittent doses of suxamethonium may also be used . However, you should consider the probability of dual and mixed block (if dose >500mg or >7-8 mg/kg).

Control the patient's ventilation, avoiding hyperventilation. Ether/air/oxygen, suxamethonium/intubation followed by spontaneous respiration can also be used if no non-depolarizing relaxants are available.

Once the baby is born the following is carried out:

• Give the mother 25- 50mg pethidine IV or other analgesic.
• Watch for awareness under anaesthesia.
• Use oxytocin: 5 units IV and 30 units/Litre in Hartmann's solution (or normal saline) over 4 hours.
• Have the assistant ventilate the mother (or use a mechanical ventilator).
• Inspect the baby and resuscitate if necessary.

Reversal is carried out in the usual way with atropine and neostigmine. Halothane and high concentrations of ether may cause uterine relaxation and post partum bleeding. The low concentration (2-3%) of ether does not interfere with uterine contractility.

Post-Operative Care

Give routine post-operative care. Watch for post partum bleeding. Encourage early ambulation.

Advantages of a General Aanaesthetic

There is less cardiovascular disturbance than with spinal or epidural anaesthesia. If it is properly performed harmful effects on the mother or fetus are few.

Disadvantages of a General Anaesthetic

• There is a danger of aspiration.
• The incidence of difficult/failed intubation is higher in obstetric patients.
• The anaesthetist is not as free to resuscitate the baby.

General anaesthesia is required when a spinal anaesthetic (recommended as the standard anaesthetic in situations for which this manual is intended) is contraindicated e.g.

• Shocked patient
• Bleeding patient
• Transverse lie where uterine relaxation may be required by the surgeon
• Where other contraindications to a spinal exist