eLFH - General Anaesthesia for Caesarian section Flashcards
Summary of key risks caused by physiological changes during pregnancy
Regurgitation higher risk
Increased O2 demand with lower FRC
Higher risk intubation
Aortocaval compression and reduced venous return
Medications commonly used to reduced gastric acid volume and pH for elective C sections
Metoclopramide 10 mg orally
Sodium citrate 0.3 Molar (30 ml) orally
PPIs
Medications commonly used to reduced gastric acid volume and pH for emergency C sections
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
What causes increase in maternal basal oxygen consumption at term
Increased maternal metabolic rate
Consumption in foeto-placental unit
By how much is maternal basal oxygen consumption increased at term
~ 20%
By how much is FRC reduced in mother at term
~ 20%
Typically falls from 1.7L to 1.35L
Possible reasons for risk of awareness being greater in GA for C section vs non-obstetric population
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
Key changes to RSI procedure for obstetric patient
Polio / short handle laryngoscopes available
Table of 15 degree left lateral tilt from prior to induction
Sodium citrate orally
Dose of Thiopentone for RSI
4 - 5 mg/kg
Dose of Suxamethonium for RSI
1.5 - 2 mg/kg
Maximum number of intubation attempts before starting difficult intubation drill
2 attempts including one with alternate laryngoscope
Inspired gas concentrations used in GA for emergency C section
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
Important considerations with of using inhalational anaesthetic agents for GA in obstetric patients
Time dependent neonatal depression - largely avoided with 1 MAC
Dose dependent uterine relaxation
Reduced sensitivity to Oxytocin
Use of opioids in obstetric RSI
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)
Approximate conversion of different opioid agent dosing
10 mg Morphine = 100 micrograms Fentanyl = 1 mg Alfentanil
When might opioids be used for obstetric RSI
Exception when opioids may be used in RSI are pre-eclampsia
Paediatrician / neonatologist must be informed if doing so
Target CO2 with ventilator for obstetric GA
Maintain normocarbia
Normal arterial CO2 in late pregnancy is 4 kPa
Reason for lower maternal arterial PCO2 in late pregnancy
To maintain concentration gradient for CO2 clearance by foetus
Maternal arterial PCO2 ~ 4 kPa
Foetal PCO2 ~ 6 kPa
Extubation of obstetric patients
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
Possible indications for GA for C section
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
Disadvantages and risks of GA for C section
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
Extra features in pregnancy that may predict difficult airway
Morbid obesity
Large breasts
Voice changes (laryngeal oedema)
Women considered high risk for Caesarean section
Previous C section
Suboptimal CTG (cardiotocograph)
Poor labour progress
Unfavourable foetal position
Multiple pregnancy
Pre-eclampsia
Barrier pressure definition
Barrier pressure = Lower oesophageal sphincter pressure - intragastric pressure
