Anaesthetics & Pregnancy Flashcards
What major changes occur by week 12?
1) hormonal changes
2) mechanical effects
3) increased metabolic demand
4) presence of placenta
What does cardiac output do?
Increases by up to 50% in the 3rd trimester
What cardiac parameters increase?
Why do these increase?
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
What happens to the heart in pregnancy?
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.
ECG findings in pregnancy
1) L axis deviation
2) ST depression
3) inverted T waves (II, V1 and V2)
What is aortocaval compression?
The enlarging uterus compressing both IVC and lower aorta when patient is supine
What are some consequences of aortocaval compression?
Compression of IVC reduces VR and thus leads to fall in pre load and CO
How is AC compression compensated?
What is a potential problem with GA and epidurals?
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)
What respiratory parameters increase?
1) tidal volume (40%)
2) respiratory rate (15%)
These increase because P mediated hypersensitivity to CO2 occurs
What resp parameters decrease?
1) airway resistance (by 35%, due to P mediated bronchial and tracheal smooth muscle relaxation)
2) FRC (20%)
What anatomical changes to resp tract occur?
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
What haem parameters increase?
Why?
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.
What haem parameters decrease?
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.
What GIT changes occur?
1) GIT Tone and motility decrease
2) Increased acid production
3) Relaxation of LOS
4) Reflux present >80%
5) Increase aspiration risk under GA
What happens to the GFR in pregnancy?
Increased blood volume and CO cause increased renal blood flow and GFR (50-60% higher).
Renal changes in pregnancy
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.
What is autotransfusion?
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
Features of NO as an anaesthetic agent
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
Features of pethidine
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
Features of fentanyl
1) Shorter acting synthetic opioid
2) Highly lipophilic with rapid analgesia
3) 50-100μg IV
4) PCA
CI of epidurals
1) Patient refusal
2) Hypovolaemia
3) Coagulopathy / anticoagulant treatment
4) Sepsis - localised v generalised
5) Obstetrical – eg fetal distress (relative)
Advantages of epidurals
1) Very effective pain relief
2) No sedation
3) Improves placental blood flow in some cases (eg pre-eclampsia)
4) Allows instrumental delivery/LUSCS
Immediate epidural complications
1) HypoTN
2) Dural puncture
3) High block
4) Intravascular injection
Delayed epidural complications
1) PDPH
2) Backache
3) Neurological
4) Infective complications
5) Haematoma
