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Obstetric Anaesthesia Flashcards

1
Q

How much does the cardiac output change in pregnancy and after labour

A

Pregnancy: increases by 50%

Immediately after labour: 75% increase from pre-labour value

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2
Q

How does pregnancy affect blood pressure

A

Drops in the first trimester and returns to normal by term.

Diastolic BP is more significantly affected especially in 2nd trimester

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3
Q

How does utero-placental blood flow differ before pregnancy and at term

A

Before pregnancy: 50 - 100 ml/min

At term: 700 - 900 ml/min

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4
Q

What happens to Hb and why

A

Plasma volume increases 50%
Red cell mass increases 30%
—-> Dilutional anaemia

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5
Q

Describe the changes to the coagulation system in pregnancy

A

From early in the 1st TM

  • Increased factors: 1, 7, 9, 10, 12
  • reduced antithrombin 3

Hypercoagulable state and increased risk of VTE

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6
Q

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

A

From 14 weeks it is possible

Insert wedge for GA > 20 weeks

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7
Q

What are the challenges to laryngoscopy in the obstetric patient

A
  1. Large breasts

2. Mucosal oedema (pregnancy hormones)

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8
Q

How does the FRC change in pregnancy

A

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

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9
Q

How does oxygen consumption change in pregnancy and how does the physiology adapt to accommodate this increase oxygen consumption

A

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)
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10
Q

Why is there an increased risk of regurgitation and aspiration with a pregnant patient general anaesthetic?

A
  1. Reduced LES tone
  2. Altered anatomical relationships between diaphragm/oesophagus/stomach
  3. Increased intra-abdominal pressure
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11
Q

How is gastric emptying, pH and volumes affected by pregnancy

A

All unchanged.

Except gastric emptying during labour which is reduced by pain, anxiety and opioids.

Returns to normal after 18 hours

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12
Q

How does drug handling differ in pregnancy

A
  1. MAC decreased by 40% (Progesterone = sedative)
  2. LA dose decreased by 40%
  3. Pharmacodynamics changed by decreased albumin
  4. Pseudocholinesterase reduced but normal dose of sux because increased blood volume counteracts this
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13
Q

Which nerve roots carry uterine pain

A

T10 - L2

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14
Q

Which nerve roots carry vaginal pain

A

S2 - S4

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15
Q

Describe the options for analgaesia during labour

A

PHARMACOLOGICAL

  1. Neuraxial analgaesia/anaesthesia (Spinal-Epidural)
    - Lumbar epidural with bupivacaine 0.1%
    - May prolong the second stage of labour
  2. 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)
  3. ENTONOX (50:50)

NON-PHARMACOLOGICAL
(Less consistent analgaesia)

  1. Transcutaneous Electrical Nerve Stimulation (TENS)
  2. Massage/Relaxation/Breathing techniques
  3. Aromatherapy/Warm water baths
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16
Q

Why is spinal anaesthesia preferred to GA for anaesthesia for Caesarian Section

A

Avoid risks of GA

  1. Increased risk of difficult intubation
  2. More rapid desaturation and hypoxaemia
  3. Increased risk of regurgitation in pregnant woman
  4. Effects of GA on unborn fetus

Benefits of Spinal

  1. Partner can be present
  2. Mom can participate in birth (early bonding and breastfeeding)
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17
Q

List the premedications given to all pregnant patients

A
  1. Metoclopramide 10mg PO within 2 hrs (or 30 mins IV)
  2. Sodium Citrate 30 ml PO 30 mins preop
  3. Ranitidine 300mg PO within 2 hours
  4. Cefazolin 1g (<80kg) or 2g (>80kg) 30 - 60 mins before
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18
Q

Summarise the contraindications for neuraxial anaesthesia relevant to pregnancy

A
  1. Coagulopathy (Plt < 75, DOAC, INR>1.5, Uraemia, HELLP)
  2. Hypotension
    - Placenta praevia/abruptio
    - Valvular heart disease
    - Peripartum cardiomyopathy
    - Supine hypotensive syndrome
  3. RICP and seizures
    - Eclampsia
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19
Q

Which interspaces can be used for Neuraxial anaesthesia

A

Spinal cord ends at L1/L2 in adults

So:
L2/L3 or L3/L4 can be used

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20
Q

What angle should be accomplished by the wedge

A

30 degrees left lateral tilt to prevent aortocaval compression

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21
Q

Why is phenylephrine the preferred vasopressor in the case of spinal induced hypotension

A

Phenylephrine causes less fetal acidosis than ephidrine

Uterine perfusion is proportional to maternal blood pressure

22
Q

Describe how oxytocin should be administered

A

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

23
Q

What are the names and doses of the other uterotonic agents

A
  1. 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)

24
Q

How long should it take sensation to return after a spinal

A

4 hours. Monitor for recession –> if no recession or worsening motor function –> MRI and Neurosurgery within 6 hours

25
What is your approach to inadequate spinal anaesthesia
1. 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
26
How to anticipate and diagnose a high spinal
1. Progressive dyspnoea 2. Weak hand grip strength (C8/T1) 3. Inability to touch the nose (C5/C6) 4. Ineffective cough/speak (C4/C5) 5. Apnoea (C3) Associated with profound hypotension ± bradycardia (Sympathectomy and block of cardiac accelerator fibers)
27
What are the management principles of a high spinal
1. Always be prepared for high spinal - Equipment/drugs/positioning 2. Get help early 3. ABCDE (Manage airway - Etomidate + ETT and administer ephidrine/adrenalin infusion after ETT if CO is not immediately restored. 4. Supportive care until spinal wears off
28
Why is epidural anaesthesia not used as the primary anaesthetic for caesarian section
1. Less predictable 2. More time consuming 3. Less dense and less reliable
29
What are situations in which epidural anaesthesia may be used for caesarian section as the sole technique
1. 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. 2. 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.
30
When is combined spinal-epidural anaesthesia particularly useful
Prolonged surgical duration - Intra-abdominal adhesions - Morbid obesity
31
When is GA indicated for C/S
1. Significant bleeding (praevia/abruptio/rupture) 2. Severe fetal distress/bradycardia 3. Cord prolapse 4. HELLP syndrome 5. Coagulapthy
32
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)
33
What agents provide sufficient analgaesia prior to delivery of the fetus
N2O ± perfalgan
34
Summarise the unique aspects of GA for C/S
1. 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) 2. 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) 3. Emergence/extubation - Same caution for airway protection as for induction DONT's 1. No NSAIDS (Premature closure of the ductus arteriosus) before delivery 2. Avoid opioids/sedatives before delivery 3. Avoid Nitrous in fetal distress
35
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 1. Wound sepsis 2. Higher rates of uterine atony and PPH
36
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
37
What dose of intrathecal drugs should be used in an obese parturient
Standard dose
38
When does Pre-eclampsia develop
1. Pregnancy specific hypertensive disease with multi-system involvement. 2. Develops after 20 weeks, most often near term 3. It can occur for the first time during labour or the peurperium
39
What is the peurperium
From delivery of placenta until 6 weeks postpartum
40
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 1. Proteinuria > 0.3g/24 hr (PCR >30) or dipstix prot >2+ 2. Platelet < 100 000/microlitre 3. SCr >97.2 (or doubling of SCr) 4. LFT: double upper limit of normal 5. Pulmonary oedema 6. New onset persistent headache refractory to analgaesia 7. Visual symptoms (Blurred/flashing lights/scotomata)
41
Why is oedema not part of the diagnostic criteria for PET
It normally occurs in 80% pregnancies
42
What is the main direct cause of maternal death
Hypertensive diseases of pregnancy
43
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
44
What are the risk factors for Pre-eclampsia
Maternal 1. Previous Hx PET 2. Family Hx PET 3. Primigravida 4. Age < 20 or > 35 5. Microvascular disease - Migraine - HPT - DM - SLE/APL (collagen vascular disease) Fetal 1. Multiple pregnancies 2. Hydatidiform mole 3. Placental hydrops
45
What are the features that indicate pre-eclampsia with severe features
Any one of the following 1. BP > 160/110 2. New onset CNS dysfunction (Visual Sx/Headache) 3. Transaminitis > x2 upper limit of normal 4. Thrombocytopaenia 5. SCr > 92.7 or double normal 6. Pulmonary oedema So PET without severe features is HPT with proteinuria --> anything else is a severe feature.
46
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
47
Compare the treatment of moderate PET to Severe disease
MODERATE PET 1. Admit for observation: - BP/CTG/Reflexes/UO/Dipstix/Plts/Urate 2. Maternal and fetal conditions will determine timing of delivery PET with SEVERE FEATURES 1. Administer fluid cautiously (incl. Blood products) - Diastolic LV dysfunction - leaky pulmonary capillaries - Abnormal renal function - ---> pulmonary oedema 2. Antihypertensives until delivery - Alpha-methyldopa (Aldomet) - Nifedipine (Adalat) 3. Peripartum - MgSO4 (prevent seizures) - BP control with Labetalol/dihydralazine (Nepresol) - Rx DIC with FFP/Cryoprecipitate/platelets/blood guided by repeated clotting studies
48
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
49
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
50
What does ESMOE stand for
Essential Steps to Manage Obstetric Emergencies
51
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

DA (50 decks)

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