Obstetric Anaesthesia Flashcards
How much does the cardiac output change in pregnancy and after labour
Pregnancy: increases by 50%
Immediately after labour: 75% increase from pre-labour value
How does pregnancy affect blood pressure
Drops in the first trimester and returns to normal by term.
Diastolic BP is more significantly affected especially in 2nd trimester
How does utero-placental blood flow differ before pregnancy and at term
Before pregnancy: 50 - 100 ml/min
At term: 700 - 900 ml/min
What happens to Hb and why
Plasma volume increases 50%
Red cell mass increases 30%
—-> Dilutional anaemia
Describe the changes to the coagulation system in pregnancy
From early in the 1st TM
- Increased factors: 1, 7, 9, 10, 12
- reduced antithrombin 3
Hypercoagulable state and increased risk of VTE
From when can a gravid uterus cause compression of the IVC and aorta and when should a wedge be used during surgery of a pregnant patient
From 14 weeks it is possible
Insert wedge for GA > 20 weeks
What are the challenges to laryngoscopy in the obstetric patient
- Large breasts
2. Mucosal oedema (pregnancy hormones)
How does the FRC change in pregnancy
Reduced by 20% due to expanding abdominal contents.
When supine, small airways collapse and atelectasis occurs during tidal breaths in 50% of pregnant woman at term
How does oxygen consumption change in pregnancy and how does the physiology adapt to accommodate this increase oxygen consumption
VO2 increases by 60%
Va needs to increase
- Vt increases –> 30% drop in PaCO2
- Compensation for respiratory alkalosis leads to HCO3 of approximately 20 mEq/L (this is incomplete and the pH increases slightly)
Why is there an increased risk of regurgitation and aspiration with a pregnant patient general anaesthetic?
- Reduced LES tone
- Altered anatomical relationships between diaphragm/oesophagus/stomach
- Increased intra-abdominal pressure
How is gastric emptying, pH and volumes affected by pregnancy
All unchanged.
Except gastric emptying during labour which is reduced by pain, anxiety and opioids.
Returns to normal after 18 hours
How does drug handling differ in pregnancy
- MAC decreased by 40% (Progesterone = sedative)
- LA dose decreased by 40%
- Pharmacodynamics changed by decreased albumin
- Pseudocholinesterase reduced but normal dose of sux because increased blood volume counteracts this
Which nerve roots carry uterine pain
T10 - L2
Which nerve roots carry vaginal pain
S2 - S4
Describe the options for analgaesia during labour
PHARMACOLOGICAL
- Neuraxial analgaesia/anaesthesia (Spinal-Epidural)
- Lumbar epidural with bupivacaine 0.1%
- May prolong the second stage of labour - Opioids + antiemetics (±paracetamol)
- PCA (best: fentanyl/remifentanil)
- Intermittent bolus doses (Morphine
- Requires monitoring for RSP depression
- Crosses placenta: neonate often needs naloxone (duration of action = ±30 mins) - ENTONOX (50:50)
NON-PHARMACOLOGICAL
(Less consistent analgaesia)
- Transcutaneous Electrical Nerve Stimulation (TENS)
- Massage/Relaxation/Breathing techniques
- Aromatherapy/Warm water baths
Why is spinal anaesthesia preferred to GA for anaesthesia for Caesarian Section
Avoid risks of GA
- Increased risk of difficult intubation
- More rapid desaturation and hypoxaemia
- Increased risk of regurgitation in pregnant woman
- Effects of GA on unborn fetus
Benefits of Spinal
- Partner can be present
- Mom can participate in birth (early bonding and breastfeeding)
List the premedications given to all pregnant patients
- Metoclopramide 10mg PO within 2 hrs (or 30 mins IV)
- Sodium Citrate 30 ml PO 30 mins preop
- Ranitidine 300mg PO within 2 hours
- Cefazolin 1g (<80kg) or 2g (>80kg) 30 - 60 mins before
Summarise the contraindications for neuraxial anaesthesia relevant to pregnancy
- Coagulopathy (Plt < 75, DOAC, INR>1.5, Uraemia, HELLP)
- Hypotension
- Placenta praevia/abruptio
- Valvular heart disease
- Peripartum cardiomyopathy
- Supine hypotensive syndrome - RICP and seizures
- Eclampsia
Which interspaces can be used for Neuraxial anaesthesia
Spinal cord ends at L1/L2 in adults
So:
L2/L3 or L3/L4 can be used
What angle should be accomplished by the wedge
30 degrees left lateral tilt to prevent aortocaval compression
Why is phenylephrine the preferred vasopressor in the case of spinal induced hypotension
Phenylephrine causes less fetal acidosis than ephidrine
Uterine perfusion is proportional to maternal blood pressure
Describe how oxytocin should be administered
After umbilical cord clamping, administer oxytocin 3U IV slowly. Then add 10IU into the remaining IV fluid and allow infusion at 125 ml/hour. The bolus can be repeated once after 3 minutes if inadequate uterine tone
What are the names and doses of the other uterotonic agents
- Misoprostol 600ug PR or 200 SL and 400 PR
2. Ergometrine 0.1 mg slow IV over 2 mins repeatable once (C/I: HPT, PET, IHD)
How long should it take sensation to return after a spinal
4 hours. Monitor for recession –> if no recession or worsening motor function –> MRI and Neurosurgery within 6 hours
What is your approach to inadequate spinal anaesthesia
- Wait at least 20 minutes
If ZERO effect –> repeat the spinal
If partial block then depending on the situation
- GA
- Supplementation with: fentanyl/ketamine/Nitrous ±
Local anaesthetic infiltration by surgeon
How to anticipate and diagnose a high spinal
- Progressive dyspnoea
- Weak hand grip strength (C8/T1)
- Inability to touch the nose (C5/C6)
- Ineffective cough/speak (C4/C5)
- Apnoea (C3)
Associated with profound hypotension ± bradycardia
(Sympathectomy and block of cardiac accelerator fibers)
What are the management principles of a high spinal
- Always be prepared for high spinal
- Equipment/drugs/positioning - Get help early
- ABCDE (Manage airway - Etomidate + ETT and administer ephidrine/adrenalin infusion after ETT if CO is not immediately restored.
- Supportive care until spinal wears off
Why is epidural anaesthesia not used as the primary anaesthetic for caesarian section
- Less predictable
- More time consuming
- Less dense and less reliable
What are situations in which epidural anaesthesia may be used for caesarian section as the sole technique
- If already sited for planned vaginal delivery (emergency C/S) - takes 20 minutes to work
- —-> If no time then a spinal can be sited below the level of the epidural catheter and the catheter can be kept for postoperative analgaesia. - Certain cardiac lesions where gradual afterload reduction would be more beneficial or safer than the dramatic afterload reduction encountered during spinal anaesthesia (AS and MS never get neuraxial anaesthesia.
When is combined spinal-epidural anaesthesia particularly useful
Prolonged surgical duration
- Intra-abdominal adhesions
- Morbid obesity
When is GA indicated for C/S
- Significant bleeding (praevia/abruptio/rupture)
- Severe fetal distress/bradycardia
- Cord prolapse
- HELLP syndrome
- Coagulapthy
What can be done to minimise volatile agent related uterine atony
Use synergistic agents - N2O - Fentanyl (once baby is out) - Midazolam (once baby is out) And use less volatile to minimise uterine atony and PPH
Combine the above with oxytocin infusion (±5U/hour)
What agents provide sufficient analgaesia prior to delivery of the fetus
N2O ± perfalgan
Summarise the unique aspects of GA for C/S
- Induction
- RSI
- Full induction doses of agent appropriate for mother
(avoid opioids before birth but can be given i.e. PET to blunt intubation response)
- SUX (quickest/no interaction Mg/NDMR not needed for surgery but can be used as don’t cross placenta) - Maintenance
- MAC 1
- After delivery: Give Midaz 2mg/Fent 100ug/N2O 60%/ and reduce MAC to 05 - 0.75
- keep ETCO2 = 4 (this is normal at end of preg) - Emergence/extubation
- Same caution for airway protection as for induction
DONT’s
- No NSAIDS (Premature closure of the ductus arteriosus) before delivery
- Avoid opioids/sedatives before delivery
- Avoid Nitrous in fetal distress
What are the major issues related to diabetes and pregnancy
Maternal glucose crosses placenta Maternal insulin does not cross ------> fetal pancreatic beta cell hypertrophy 1. Macrosomia (Increased C/S) 2. Neonatal hypoglycaemia
Maternal risks
- Wound sepsis
- Higher rates of uterine atony and PPH
What are the major issues related to obesity and pregnancy
Increased maternal risk
- Hypertension
- OSA
- Gestational Diabetes
- Increased need for C/S
Anaesthetic challenges
- Difficult BVM/intubation
- Difficult regional anaesthesia
- Difficult IV access
- Difficult monitoring (esp. BP)
Surgery often prolonged
- Combined spinal-epidural often indicated
What dose of intrathecal drugs should be used in an obese parturient
Standard dose
When does Pre-eclampsia develop
- Pregnancy specific hypertensive disease with multi-system involvement.
- Develops after 20 weeks, most often near term
- It can occur for the first time during labour or the peurperium
What is the peurperium
From delivery of placenta until 6 weeks postpartum
Define Pre-eclampsia
SBP >140 or DBP >90 on 2 occasions more than 4 hours apart after 20 weeks in a previously normotensive patient and the new onset of 1 or more of the following:
Can confirm high BP within minutes if > 160/110
- Proteinuria > 0.3g/24 hr (PCR >30) or dipstix prot >2+
- Platelet < 100 000/microlitre
- SCr >97.2 (or doubling of SCr)
- LFT: double upper limit of normal
- Pulmonary oedema
- New onset persistent headache refractory to analgaesia
- Visual symptoms (Blurred/flashing lights/scotomata)
Why is oedema not part of the diagnostic criteria for PET
It normally occurs in 80% pregnancies
What is the main direct cause of maternal death
Hypertensive diseases of pregnancy
What is the pathophysiology of pre-eclampsia
Unclear.
Failure of deep myometrial trophoblastic invasion of spiral arteries –> placental hypoperfusion —> alters placental villous angiogenesis –> placental secretion of antiangiogenic factors –> bind vascular endothelial growth factor –> widespread maternal vascular dysfunction
What are the risk factors for Pre-eclampsia
Maternal
- Previous Hx PET
- Family Hx PET
- Primigravida
- Age < 20 or > 35
- Microvascular disease
- Migraine
- HPT
- DM
- SLE/APL (collagen vascular disease)
Fetal
- Multiple pregnancies
- Hydatidiform mole
- Placental hydrops
What are the features that indicate pre-eclampsia with severe features
Any one of the following
- BP > 160/110
- New onset CNS dysfunction (Visual Sx/Headache)
- Transaminitis > x2 upper limit of normal
- Thrombocytopaenia
- SCr > 92.7 or double normal
- Pulmonary oedema
So PET without severe features is HPT with proteinuria –> anything else is a severe feature.
Can PET be prevented?
Woman at risk of early onset PET, severe enough to require very preterm delivery are offered low dose aspirin early in the second TM as well as calcium supplementation
Compare the treatment of moderate PET to Severe disease
MODERATE PET
- Admit for observation: - BP/CTG/Reflexes/UO/Dipstix/Plts/Urate
- Maternal and fetal conditions will determine timing of delivery
PET with SEVERE FEATURES
- Administer fluid cautiously (incl. Blood products)
- Diastolic LV dysfunction
- leaky pulmonary capillaries
- Abnormal renal function
- —> pulmonary oedema - Antihypertensives until delivery
- Alpha-methyldopa (Aldomet)
- Nifedipine (Adalat) - Peripartum
- MgSO4 (prevent seizures)
- BP control with Labetalol/dihydralazine (Nepresol)
- Rx DIC with FFP/Cryoprecipitate/platelets/blood guided by repeated clotting studies
What is the ideal analgaesia for a patient with PET delivering vaginally
Exclude coagulopathy
–> epidural (can be converted to neuraxial anaesthesia if C/S is required). keep BP within 20% baseline
When should neuraxial anaesthesia vs GA be used in PET
Neuraxial
- No coagulopathy
- Normal GCS
GA
- Coagulopathy or
- Altered mentation
Main problems with GA is difficult ETT and hypertensive intubation response
What does ESMOE stand for
Essential Steps to Manage Obstetric Emergencies
When can a patient after spinal be discharged from recovery
Normal vital signs persist
No evidence of ongoing bleeding
Spinal level has dropped by two segments
