Anaesthetics & Pregnancy

Question 1

What major changes occur by week 12?

Answer 1

1) hormonal changes
2) mechanical effects
3) increased metabolic demand
4) presence of placenta

Question 2

What does cardiac output do?

Answer 2

Increases by up to 50% in the 3rd trimester

Question 3

What cardiac parameters increase?

Why do these increase?

Answer 3

1) CO
2) HR
3) SV

CO= SV x HR

SV increases by 30% mainly due to increased bloody volume

The increase in circulating E + P causes vasodilation and a fall in TPR. Because of this, HR increases.

CO increase because both SV and HR increase

Question 4

What happens to the heart in pregnancy?

Answer 4

You get LVH and dilatation (to facilitate increase in CO)

Diaphragm is displaced upwards by 4cm.

Both of these together cause apex to move UP and LEFT.

Question 5

ECG findings in pregnancy

Answer 5

1) L axis deviation
2) ST depression
3) inverted T waves (II, V1 and V2)

Question 6

What is aortocaval compression?

Answer 6

The enlarging uterus compressing both IVC and lower aorta when patient is supine

Question 7

What are some consequences of aortocaval compression?

Answer 7

Compression of IVC reduces VR and thus leads to fall in pre load and CO

Question 8

How is AC compression compensated?

What is a potential problem with GA and epidurals?

Answer 8

1) increase HR (tachycardia)
2) increase systemic vascular resistance (vasoconstriction)
3) diversion of blood from LL to return through epidural and azygous system

GA and epidural blocks abolish the sympathetic response and increase risk of supine HypoTN (can cause bradycardia, N, sweating, pallor and fainting)

Question 9

What respiratory parameters increase?

Answer 9

1) tidal volume (40%)
2) respiratory rate (15%)

These increase because P mediated hypersensitivity to CO2 occurs

Question 10

What resp parameters decrease?

Answer 10

1) airway resistance (by 35%, due to P mediated bronchial and tracheal smooth muscle relaxation)
2) FRC (20%)

Question 11

What anatomical changes to resp tract occur?

Answer 11

Hormonal changes to mucosal vasculature lead to engorgement and orders of upper airway down to pharynx and glottis. This can be exacerbated in HTN and pre eclampsia

Question 12

What haem parameters increase?

Why?

Answer 12

1) Total blood volume (40%)
2) Total plasma volume (50%)
3) RBC volume (30%)
4) Clotting factors (800%)

Blood Volume increases from 6-8 weeks. Reaches max ~32-34 weeks with little change thereafter.

Plasma volume increase is mediated by P and E acting on the kidneys initiating RAAS.

Total body water increases 2’ to renal sodium retention.

Question 13

What haem parameters decrease?

Answer 13

1) Hb
2) Platelets

Renal EPO increases red cell mass by 20-30% which is a smaller rise than the plasma volume, resulting in haemodilution and a decrease in Hb concentration.

This is termed the physiological anaemia of pregnancy.

Platelet production is increased but the platelet count falls because of dilution and consumption. Platelet function remains normal.

Question 14

What GIT changes occur?

Answer 14

1) GIT Tone and motility decrease
2) Increased acid production
3) Relaxation of LOS
4) Reflux present >80%
5) Increase aspiration risk under GA

Question 15

What happens to the GFR in pregnancy?

Answer 15

Increased blood volume and CO cause increased renal blood flow and GFR (50-60% higher).

Question 16

Renal changes in pregnancy

Answer 16

1) Increased UTI risk (because of P-mediated ureteric smooth muscle relaxation)
2) lower renal threshold for glucose
3) Increased aldosterone (causes fall in plasma osmolality bc of water retention 2’ to this, and also increased P)
4) Dilatation of ureters and renal pelvis

Nb: After the 12 wks enlarging uterus can compress the ureters as they cross the pelvic brim and cause further dilatation by obstructing flow.

Question 17

What is autotransfusion?

Answer 17

During labour, there is an increase in intravascular volume from the contracting uterus to the venous system.

Following delivery this autotransfusion compensates for the blood losses and tends to further increase CO by 50% of pre-delivery values

Question 18

Features of NO as an anaesthetic agent

Answer 18

1) Potent analgesic gas
2) Low blood solubility, so you get rapid uptake
3) Inspired concentration 30 -70%
4) Takes 50s to achieve effective analgesic concentration
5) Need to start using before contractions start

Question 19

Features of pethidine

Answer 19

1) Most common opioid used during labour
2) 100mg IM 2-3 hourly
3) Cheap, safe and easy to use
4) BUT: maternal N + V, dysphoria
5) Can produce respiratory depression in the fetus

Question 20

Features of fentanyl

Answer 20

1) Shorter acting synthetic opioid
2) Highly lipophilic with rapid analgesia
3) 50-100μg IV
4) PCA

Question 21

CI of epidurals

Answer 21

1) Patient refusal
2) Hypovolaemia
3) Coagulopathy / anticoagulant treatment
4) Sepsis - localised v generalised
5) Obstetrical – eg fetal distress (relative)

Question 22

Advantages of epidurals

Answer 22

1) Very effective pain relief
2) No sedation
3) Improves placental blood flow in some cases (eg pre-eclampsia)
4) Allows instrumental delivery/LUSCS

Question 23

Immediate epidural complications

Answer 23

1) HypoTN
2) Dural puncture
3) High block
4) Intravascular injection

Question 24

Delayed epidural complications

Answer 24

1) PDPH
2) Backache
3) Neurological
4) Infective complications
5) Haematoma