eLFH - General Anaesthesia for Caesarian section

Question 1

Summary of key risks caused by physiological changes during pregnancy

Answer 1

Regurgitation higher risk

Increased O2 demand with lower FRC

Higher risk intubation

Aortocaval compression and reduced venous return

Question 2

Medications commonly used to reduced gastric acid volume and pH for elective C sections

Answer 2

Metoclopramide 10 mg orally
Sodium citrate 0.3 Molar (30 ml) orally
PPIs

Question 3

Medications commonly used to reduced gastric acid volume and pH for emergency C sections

Answer 3

Labouring women at high risk are kept NBM

Medications as for elective C sections if admitted early enough

0.3M sodium citrate PO before anaesthesia

Question 4

What causes increase in maternal basal oxygen consumption at term

Answer 4

Increased maternal metabolic rate
Consumption in foeto-placental unit

Question 5

By how much is maternal basal oxygen consumption increased at term

Answer 5

~ 20%

Question 6

By how much is FRC reduced in mother at term

Answer 6

~ 20%
Typically falls from 1.7L to 1.35L

Question 7

Possible reasons for risk of awareness being greater in GA for C section vs non-obstetric population

Answer 7

Use of lower inspired anaesthetic agents due to concerns of relaxant effect on uterus and neonatal sedation

Surgery starting very soon after induction

Avoidance of IV opioids before induction

Question 8

Key changes to RSI procedure for obstetric patient

Answer 8

Polio / short handle laryngoscopes available

Table of 15 degree left lateral tilt from prior to induction

Sodium citrate orally

Question 9

Dose of Thiopentone for RSI

Answer 9

4 - 5 mg/kg

Question 10

Dose of Suxamethonium for RSI

Answer 10

1.5 - 2 mg/kg

Question 11

Maximum number of intubation attempts before starting difficult intubation drill

Answer 11

2 attempts including one with alternate laryngoscope

Question 12

Inspired gas concentrations used in GA for emergency C section

Answer 12

Nitrous oxide commonly used as carrier gas
50% nitrous oxide + 50% O2 with volatile to maintain MAC of 1

Exception is GA for foetal distress where 100% O2 administered with increased inhalational agent concentration until delivery

Question 13

Important considerations with of using inhalational anaesthetic agents for GA in obstetric patients

Answer 13

Time dependent neonatal depression - largely avoided with 1 MAC

Dose dependent uterine relaxation

Reduced sensitivity to Oxytocin

Question 14

Use of opioids in obstetric RSI

Answer 14

Rarely used

Cross the placenta and affect neonatal respiratory effort
Also delay return of spontaneous ventilation of mother in failed intubation

Once baby is delivered mother is given adequate dose of opioid (eg 15-30 mg morphine)

Question 15

Approximate conversion of different opioid agent dosing

Answer 15

10 mg Morphine = 100 micrograms Fentanyl = 1 mg Alfentanil

Question 16

When might opioids be used for obstetric RSI

Answer 16

Exception when opioids may be used in RSI are pre-eclampsia

Paediatrician / neonatologist must be informed if doing so

Question 17

Target CO2 with ventilator for obstetric GA

Answer 17

Maintain normocarbia

Normal arterial CO2 in late pregnancy is 4 kPa

Question 18

Reason for lower maternal arterial PCO2 in late pregnancy

Answer 18

To maintain concentration gradient for CO2 clearance by foetus

Maternal arterial PCO2 ~ 4 kPa
Foetal PCO2 ~ 6 kPa

Question 19

Extubation of obstetric patients

Answer 19

Fully reverse neuromuscular blockade prior to lightening anaesthesia

High risk of aspiration during extubation

Full left lateral position

Trolley that can go immediately head down

May deflate cuff to ensure air leak prior to extubation - especially if laryngeal oedema or difficult intubation

Question 20

Possible indications for GA for C section

Answer 20

No time for regional method

Failure / worn off regional anaesthesia

CVS instability with major haemorrhage or fixed cardiac output states (eg severe aortic stenosis) - sympathetic blockade with regional

Maternal choice

CI to regional

Likely long surgery

Question 21

Disadvantages and risks of GA for C section

Answer 21

Increased post op pain compared to regional techniques

Maternal and Neonatal sedation

Risk of uterine relaxation and increased PPH

Awareness risk

Aspiration risk

Difficult intubation

Question 22

Extra features in pregnancy that may predict difficult airway

Answer 22

Morbid obesity
Large breasts
Voice changes (laryngeal oedema)

Question 23

Women considered high risk for Caesarean section

Answer 23

Previous C section
Suboptimal CTG (cardiotocograph)
Poor labour progress
Unfavourable foetal position
Multiple pregnancy
Pre-eclampsia

Question 24

Barrier pressure definition

Answer 24

Barrier pressure = Lower oesophageal sphincter pressure - intragastric pressure

Question 25

Why does lower oesophageal sphincter pressure drop in pregnancy

Answer 25

Increased progesterone

Question 26

Factors which reduce gastric emptying

Answer 26

Labour pain
Anxiety
Opioid use

Note pregnancy itself does not affect gastric emptying

Question 27

Management of regurgitation during induction

Answer 27

If spont breathing: Head down + lateral and suction

If parralysed: Head down + suction and secure airway - then suction catheter before ventilating to avoid dispersing gastric contents

Question 28

Associated of GA with Apgar scores

Answer 28

GA associated with lower Apgar scores at 1 minute but not at 5 mins

Question 29

Why is awareness of mother bad

Answer 29

Psychological impact inc PTSD

Maternal catecholamine release can affect placental perfusion