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Anaesthetic FRCA Primary - eLFH Obstetrics > eLFH - Pregnancy and Drugs used by Anaesthetists > Flashcards

eLFH - Pregnancy and Drugs used by Anaesthetists Flashcards

1
Q

Categories of effects of of pregnancy on anaesthetic drugs used

A

General effects

Uterine effects (including placental blood flow)

Neonatal effects (of maternally administered drugs)

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2
Q

General effects of volatile agents in pregnancy

A

MAC is reduced in pregnancy

With controlled ventilation, alveolar equilibration is slowed due to higher pulmonary blood flow

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3
Q

Uterine effects of volatile agents in pregnancy

A

Reversible decrease in uterine muscle tone is clinically important at MAC 1.5 - 2

May contribute to PPH at delivery
Resistant to oxytocin

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4
Q

Neonatal effects of volatile agents in pregnancy

A

Small, highly lipid soluble molecules of volatile agents cross the placenta freely

But are very rapidly exhaled by the newborn within first few minutes of life

No prolonged effects in newborn

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5
Q

General effects of induction agents in pregnancy

A

IV bolus initially delivered to vessel rich group of organs causing initial effects.

Initial effects wear off due to redistribution to lower blood flow but larger tissues (eg skeletal muscle)

Uteroplacental unit has very high blood flow at term so receives high proportion of initial IV bolus

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6
Q

Vessel rich group of organs

A

CNS
Heart
Hepatic
Renal
Splanchnic bed

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7
Q

Uterine effects of induction agents in pregnancy

A

No effect on uterine tone

Placental perfusion is related to maternal BP

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8
Q

Effect of induction agents on maternal BP

A

Propofol - most maternal hypotension

Ketamine - least hypotension

Thiopental - intermediate effects

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9
Q

Neonatal effects of induction agents in pregnancy

A

Thiopental + Propofol are highly lipid soluble - cross placenta freely

Maternal redistribution causes rapid decreasing blood concentrations in mother and foetus before delivery

No major neonatal depression seen beyond first few minutes of birth

Foetal neurobehavioral scores reveal subtle decreases that last for up to 48 hours

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10
Q

General effects of neuromuscular blockers in pregnancy

A

Serum cholinesterase activity is decreased at term and for 48 hours post partum - usually not enough to affect duration of suxamethonium clinically

Magnesium used for eclampsia prolongs action of non-depolarising neuromuscular blockers

Rocuronium has biliary clearance so may have prolonged effects due to cholestasis caused by oestrogens

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11
Q

Uterine effects of neuromuscular blockers in pregnancy

A

No effect on uterine smooth muscle tone

Only affect skeletal muscle

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12
Q

Neonatal effects of neuromuscular blockers in pregnancy

A

Neuromuscular agents are highly ionised so very low concentrations cross the placenta

No clinical effects in the newborn

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13
Q

General effects of neuraxial opioid use in pregnancy

A

No impairment of breastfeeding

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14
Q

Uterine effects of neuraxial opioid use in pregnancy

A

No significant uterine effects

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15
Q

Neonatal effects of neuraxial opioid use in pregnancy

A

Lipophilic opioids (eg fentanyl) with doses closer to systemic levels and rapid absorption are more likely to produce effects (eg side effect profile inc respiratory depression) as more placental transfer occurs

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16
Q

General effects of local anaesthetics in pregnancy

A

In late pregnancy, compression of IVC and subsequent engorgement of epidural venous plexus decreases volume of spinal canal
Therefore neuraxial LA spreads further

Decreased alpha1 acid glycoprotein and albumin so increased levels of unbound portion of LAs
Therefore potential greater risk of systemic toxicity

Systemic absorption also greater due to higher local blood flow

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17
Q

Uterine effects of LAs in pregnancy

A

No direct effects

Changes in placental perfusion related to maternal BP drop

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18
Q

Direct neonatal effects of local anaesthetics in pregnancy

A

Dose and agent dependent

Less protein bound and ionised agents (eg lidocaine) cross placenta more and can sedate baby

Bupivacaine highly protein bound and has few neonatal effects

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19
Q

Indirect neonatal effects of local anaesthetics in pregnancy

A

Drop in maternal BP causing reduced placental perfusion

Spinal cause slightly lower foetal pH than epidural or GA

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20
Q

Tocolytic agent effects

A

Decrease uterine tone and contractions

Often in context of premature labour

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21
Q

Duration of tocolytic agent use and intended benefit

A

24-48 hours

Goal to give time to complete steroids for foetal lung maturity and counselling

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22
Q

Tocolytic agents used for postponement of premature labour

A

Nifedipine

Atosiban

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23
Q

Nifedipine mechanism of action

A

Calcium channel blocker

Causes smooth muscle relaxation

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24
Q

Nifedipine initial dose for tocolysis

A

20 mg

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25
Q

Side effects of nifedipine

A

Tachycardia
Hypotension
Headaches
Dizziness

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26
Q

Atosiban mechanism of action

A

Oxytocin receptor antagonist

27
Q

Atosiban administration

A

IV bolus followed by infusion

28
Q

When is Atosiban preferred to Nifedipine

A

When there is CVS instability due to nifedipine side effects

29
Q

When are tocolytic agents used for acute management of uterine hypertonicity

A

When causing foetal distress - eg during induction or augmentation of labour (when stopping uterotonics alone is insufficient)

30
Q

Tocolytic agents used for acute management of uterine hypertonicity

A

Terbutaline

Nitrates

31
Q

Terbutaline mechanism of action

A

Beta agonist

32
Q

Terbutaline dose and administration

A

0.2 to 0.5 mg subcutaneously can be repeated

33
Q

Terbutaline side effects

A

Tachycardia

34
Q

Nitrates mechanism of action

A

Directly acting smooth muscle relaxant

35
Q

Nitrates administration

A

Sublingual
Buccal

36
Q

Tocolytic agents used for intraoperative uterine relaxation

A

Volatile agents

Terbutaline

37
Q

Volatile agent mechanism of action for uterine relaxation and dose

A

Directly actine smooth muscle relaxant

Increasing MAC to 1.5 - 2 causes uterine relaxation

38
Q

Other tocolytic agents

A

Magnesium

Crystalloid IV fluid bolus 10-15 ml/kg

39
Q

Magnesium mechanism of action of tocolysis

A

Directly acting smooth muscle relaxant

Not licensed for tocolysis but often used for pre-eclampsia

40
Q

Side effects of magnesium

A

Muscle weakness

Prolongation of neuromuscular blockade

41
Q

Crystalloid IV bolus mechanism of action of tocolysis

A

Unknown mechanism but may have posterior pituitary effect that reduces oxytocin secretion

42
Q

Uterotonic agent effects

A

Increase uterine tone and contractions

43
Q

Uterotonic agent uses

A

Induction and augmentation of labour

Active management of third stage of labour

Prophylaxis and management of PPH

44
Q

Most common cause of PPH

A

Atonic uterus

45
Q

Risk factors for PPH where prophylactic uterotonics should be considered

A

Prolonged or augmented labour

Instrumental or operative delivery

Multiple gestation

Previous PPH

46
Q

Uterotonic agents

A

Oxytocin

Ergometrine

Prostaglandins

47
Q

Oxytocin mechanism of action

A

Syntocinon - synthetic polypeptide identical to human oxytocin

Mediates uterine contraction in normal labour

48
Q

Syntocinon presentation

A

Clear colourless solution

5 or 10 IU in 1 ml

49
Q

Syntocinon administration

A

IV or IM

Give slowly IV as bolus can cause hypotension and reflex tachycardia

Use separate line if transfusing blood or plasma as oxytocin is rapidly metabolised but plasma oxytocinase

50
Q

Syntocinon dose

A

5 IU by slow IV bolus
Repeated once (total 10 IU)

Followed by infusion
Eg. 40 IU in 500 ml saline at 125 ml/hour (10 IU per hour)

51
Q

Syntocinon side effect

A

Similar in structure to ADH

Can cause water retention and hyponatraemia

52
Q

Ergometrine mechanism of action

A

Alkaloid of the ergot fungus

Potent smooth muscle constrictor

53
Q

Ergometrine side effects

A

Vasoconstriction / HTN

Potent emetic

54
Q

Ergometrine contraindications

A

Pre-eclampsia
Cardiac / vascular disease
Porphyria

55
Q

Ergometrine presentation

A

Clear colourless solution of 0.5 mg in 1 ml

56
Q

Ergometrine dose and administration

A

0.5 mg IV or IM

Usually given in combination with syntocinon as syntometrine

57
Q

Syntometrine

A

Combination of Syntocinon 5 IU + Ergometrine 0.5 mg

If ergometrine contraindicated then usually give syntocinon 5 IU alone

58
Q

Prostaglandin examples and route of administration

A

Dinoprostone - PV

Misoprostol - PV or PO or PR

Carboprost - IM

59
Q

Prostaglandin mechanism of action

A

Direct uterotonic effect
Potent smooth muscle constrictors

60
Q

Prostaglandin side effects

A

Bronchospasm

61
Q

Relative contraindication of prostaglandins (especially carboprost)

A

Asthma

62
Q

Carboprost dose

A

0.25 mg IM repeated every 15 mins up to a total of 2 mg

63
Q

Typical dose of misoprostol

A

0.6 to 0.8 mg rectally

64
Q

Order in which uterotonic medications should be administered for prophylaxis and management of PPH

First line to fourth line treatments

A

Syntocinon - IV

Ergometrine - IM / IV

Carboprost - IM

Misoprostol - PR

Anaesthetic FRCA Primary - eLFH Obstetrics (6 decks)

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