Obstetric Anaesthesia

Physiological changes in pregnancy Mechanical Hormonal Increased metabolic demands Fetoplacental circulation

Respiratory changes FRC decreased 20% Ventilation increased (progesterone) At term minute ventilation increased 50% O2 consumption increases 40 – 60% and 100% in labour Blood gas: compensated resp alkalosis O2 dissociation curve shifted to right

Consequences Greater risk of hypoxaemia Decreased O2 stores Increased O2 demand

CVS Changes Blood volume increases 30 – 40% CO increased 43% SVR decreased 21% During labour CO increases a further 43% (Pain) Aortocaval compression Delivery – autotransfusion < 500ml

Blood Constituents Plasma protein concentration decreases Decreased A/G ratio COP decreases 13% Pulmonary oedema Hypercoagulable state

Consequences Airway difficulties Oedema Worse Malampatti Score

GIT Function Increased gastric acid Delayed gastric emptying Decreased lower oesophageal sphincter tone Increased risk of G-O reflux Increased aspiration risk Prophylactic measures mandatory

Placenta Not autoregulated Hypotension can lead to severe uteroplacental insufficiency and fetal distress

GA vs Regional for C/S?

Regional Anaesthesia is SAFER But……… Mortality with both

National Committee on Confidential Enquiries into Maternal Death of SA 1999 – 2001 25 deaths under Spinal

Advantages of Regional Improved safety Risk of Intubation averted Hypoxia Aspiration Bonding between mother & baby

Regional Techniques Spinal Anaesthesia Epidural Anaesthesia Combined Spinal - Epidural

Regional anaesthesia SPINAL Fast onset Small dose Good quality block Single shot EPIDURAL Slow onset Large dose Missed segments Top-ups possible Post op analgesia

Contraindications to Regional Patient refusal Operator inexperience Absent resuscitation equipment However…… The above applies to any procedure!!

Contraindications to Regional Specific Hypovolaemia Coagulation abnormalities Thrombocytopaenia (<75 x 109/L) Local sepsis CVS co-morbidity – MS, AS Raised intracranial pressure Allergy

Spinal Anaesthesia History / examination / explanation / consent Antacid prophylaxis IV access and crystalloid at the time of block 10 - 20 ml Kg-1 (co-loading) Spinal at L 3/4: 25 G pencil point needle 2 ml 0,5% Bupivacaine (10 mg), plus 10 g Fentanyl (0,2 ml) T4 block in most cases Position supine with 150 L lateral wedge/tilt i.e. L side down GREATER SPLANCHNIC NERVE SYMPATHETIC NERVE AFFERENTS (PAIN) EXITS AT T5

Spinal (continued) Facemask oxygen Rx hypotension At delivery Ephedrine / Phenylephrine Increase L uterine displacement Fluid At delivery Oxytocin 2,5 iu over 30 seconds Oxytocin infusion 10 iu in 1000 ml

Inadequate block Pre – Sx Intra-operatively Inhaled nitrous oxide Alfentanil 250 μg or Fentanyl 50 μg BZD small dose (Midazolam 1 - 2 mg) NB Amnesia and respiratory depression LA Convert to GA

Complications of Spinal Hypotension Sympathetic block Bradycardia Aorto-caval compression Occult haemorrhage High motor blockade Failed block Headache

Spinals and Epidurals

Spinal Anaesthesia

Spinal Needles Quincke Whitacre

Epidural Anaesthesia Tuohy needle

Epidural Set

General Anaesthesia for C/S Two patients with differing requirements

Indications for GA Maternal request Urgent surgery Regional anaesthesia contraindicated Failed regional anaesthesia

Technique History / examination Antacid prophylaxis Monitoring L lateral tilt Preoxygenate Rapid Sequence Induction / Intubation (RSI or “Crash Induction”) with Thiopentone / Suxamethonium

Rapid Sequence induction

Technique Pre delivery At delivery At end of case Nitrous oxide / oxygen 50% Volatile agent (Halothane or Iso) At delivery Oxytocin 2.5 iu Ergometrine 0,1 mg incrementally to 0,5 mg (PGF2 must never be given IV) if required Opiate: Morphine or Fentanyl Nitrous oxide 65% At end of case Extubate awake on side if feasible

Malampatti Score

Suspected difficult intubation Senior anaesthetist Optimise position of head Different blades Full range of ETTs Manipulate larynx Gum elastic bougie Well functioning suction

Failed Intubation Drill Need to continue? Mother’s life at risk Regional not feasible – coagulation etc Severe fetal distress – prolapsed cord If not - wake patient up Spinal or epidural

Mother comes first!!

Severe pre-eclampsia Arterial BP > 160 mm “Hg” systolic or >110 mm “Hg” diastolic Proteinuria >3+ Oliguria Cerebral signs Pulmonary oedema Impaired liver function or hepatic rupture Thrombocytopenia HELLP Syndrome (Haemolysis, Elevated Liver enzymes, Low Platelets)

Pre-eclampsia

Severe pre-eclampsia Management Fluid & vasodilator therapy Seizure prophylaxis Expeditious delivery <120 ml per hour Spinal: < 10 ml / kg Emphasis on vasopressors

Severe pre-eclampsia Spinal anaesthesia method of choice if no contraindications even if NRFHT Platelet count > 75 x 109 l-1 Fetal bradycardia is an indication for GA Use normal doses for spinal anaesthesia Similar doses of vasopressors <120 ml per hour Spinal: < 10 ml / kg Emphasis on vasopressors

Major anaesthetic problems Airway management Pre O2, range of ETTs, bougie, LMA Intubation response MgSO4, Alfentanil Neuromuscular blockade MgSO4 prolongs NDMRs

Eclampsia GA favoured Postoperative ventilation, depending on presence of cerebral oedema

References Prevention & Rx of CVS instability during spinal anaesthesia for C/S Dyer et al. SAMJ 94;3: 367-372 Oxford Handbook of Anaesthesia Allman & Wilson