Obstetric anaesthetic pharmacology

Question 1

Define postpartum haemorrhage

Answer 1

Cumulative blood loss of > 1000 ml or bleeding associated with signs/symptoms of hypovolaemia within 24 hours of birth process regardless of delivery route.

Question 2

What are the four T’s which detail the four most common causes of post partum haemorrhage

Answer 2

Tone - Uterine atony
Trauma - Laceration / hematoma / inversion / rupture
Tissue - Retained products or invasive placenta
Thrombin - Coagulopathy

Question 3

How much blood can be lost before there is an increase in heart rate and/or decrease BP

Answer 3

25% of patient’s blood volume

± 1500 mls

Question 4

Why are Hb and Hct levels poor indicators of acute blood loss if no plasmalyte is given

Answer 4

The levels would take 24 - 48 hours to reflect the true concentration of Hb / haematocrit

Question 5

Which blood marker is predictive of severe PPH and what are the problems with sampling this parameter in PPH?

Answer 5

Fibrinogen < 200 mg/dL

Problems

1. Fibrinogen assays have a long turn around time
2. Large variation in baseline levels: 210 - 900 mg/dL

Question 6

Define severe PPH

Answer 6

Need for:

1. Multiple blood products
2. Angiographic embolization
3. Surgical intervention
4. Maternal death

Question 7

Summarise the risk factors for PPH

Answer 7

Retained placenta
Failure to progress
Morbidly adherent placenta
Lacerations
Instrumental delivery
Large for gestational age baby
Hypertensive disorders
Induction of labour
Prolonged 1st or 2nd stage

Previous PPH

Question 8

Which four risk factors are associated with the highest odds for predicting the need for massive transfusion

Answer 8

1. Abnormal placentation
2. Placental abruption
3. Severe preeclampsia
4. Intrauterine fetal demise

Question 9

Outline the stepwise management of major obstetric haemorrhage

Answer 9

1. Pre-empt and predict with risk factors
2. Recognize, declare, communicate, get help
3. High capacity IV access (2 x large bore)
4. Crystalloids / colloids / Packed cells
5. ETT ± CVC ± A-line
6. Forced air-warming blanket
7. Oxytocin bolus 2.5 –> 3U by slow IV bolus injection
8. Oxytocin infusion 40 U in 1000mls at 250 ml/hr
   (Prophylactic oxytocin is 20 u in 1000 mls at 125 ml/hr)
9. Syntometrine (5U oxytocin + 0.5 mg ergometrine)
   –> dilute into 5ml syringe and give 2.5 mls stat and 2.5 mls after 5 minutes if needed
10. Prostaglandin E1 = misoprostal 200 mcg tablets: 2 - 3 tablets PR or SL(better no first pass)
11. Prostaglandin F2 alpha –> 1 mg into 4 ml = 0.25mg/ml –> 1 ml intramyometrally into each of four quadrants

Question 10

What is the ED 90 for oxytocin in uncomplicated low-risk labour.

What is the ED 90 for oxytocin in arrested/obstructed labour

Answer 10

uncomplicated = 0.35 U

Complicated = 3U

Question 11

List the problems with oxytocin administration

Answer 11

1. Tachyphylaxis (rapidly diminishing response to successive doses of a drug rendering it less effective)
2. Vasodilatation (caution in shock)
3. ADH properties –> water retention and hypoNa (with infusions)

Question 12

How long does oxytocin bolus dose last

Answer 12

± 1 hour

Question 13

What are the problems with ergometrine

Answer 13

Elevation in MAP of 11%
Elevation PA pressure 30%
C/I
1. Pre-eclampsia
2. Hypertension
3. Cardiac disease
4. Porphyria

Very high incidence of nausea and vomiting

Question 14

What is the onset of ergometrine and how long do the effects last

Answer 14

IV - immediate
IM - 5 minutes

Duration: 3 hours

Question 15

What are the advantages and disadvantages of misoprostal (PG E1)

Answer 15

Advantages

1. Cheap
2. No refrigeration (c.f. oxytocin/ergometrine)
3. SL more reliable (less first pass metabolism)

Disadvantages
1. Less effective than oxytocin and ergometrine

Question 16

What are the problems with PGF2alpha

Answer 16

1. Bronchospasm –> V/Q mismatch –> hypoxaemia
2. Systemic hypertension
3. Pulmonary hypertension if used IV
4. Cannot be given IV
5. Can only be used intramyometrally as a last line agent

Question 17

What is the % error with subjective assessment of blood loss at 300 ml and at 2000 ml

Answer 17

300 ml blood loss - error = 16%

2000ml blood loss - error = 41%

Question 18

What is the rule of 30

Answer 18

SBP down by 30 mmHg
HR up by 30 bpm
RR more than 30 breaths/min
Hb/Hct drop by 30%
Urine output < 30 ml/hour

Then patient has lost at least 30% of their blood volume and is in moderate leading to severe shock

Question 19

What is the shock index? What is the normal shock index in obstetric and non-obstetric patients

Answer 19

Shock index is HR/SBP

Non-obstetric patients > 0.7 is abnormal
Obstetric patients > 0.9 is abnormal

Question 20

Describe the definitions of severity of postpartum haemorrhage

Answer 20

PPH
> 500ml post vaginal and > 1000 post C/S
(updated to > 1000ml with signs+symptoms of hypovolaemia within 24 hours delivery)

Severe PPH
> 1500
> 4U Packed cells
> 4 g/dL Hb down
or haemorrhage associated with haemodynamic instability 

Major PPH
> 2500 ml

Massive PPH
One blood volume or 10 packed red blood cells in 24 hours.

Question 21

Describe the massive transfusion products ordered

Answer 21

1. Fixed-ratio 5 RCC + 5 FFP + 1 pooled platelets + Cryoprecipitate

Maintain platelet count> 50 x 10^9/L

Give tranexamic acid: 1g repeatable once

Question 22

When should the surgeon proceed straight subtotal hysterectomy

Answer 22

1. Uterine rupture that is irreparable

2. Placenta increta or percreta

Question 23

What are the surgical techniques used for:

1. Atonic uterus
2. Uterine tears
3. Placental site bleeding

Answer 23

1. Atonic uterus - B-Lynch compression suture or STAH
2. Uterine tears - Stepwise uterine artery devascularization / Uterine artery ligation or STAH
3. Placental site - Stepwise uterine artery devascularization / Balloon tamponade / STAH

Question 24

What is the lloyd davis position

Answer 24

Trendelenburg lithotomy