Obstetric anaesthetic pharmacology Flashcards
Define postpartum haemorrhage
Cumulative blood loss of > 1000 ml or bleeding associated with signs/symptoms of hypovolaemia within 24 hours of birth process regardless of delivery route.
What are the four T’s which detail the four most common causes of post partum haemorrhage
Tone - Uterine atony
Trauma - Laceration / hematoma / inversion / rupture
Tissue - Retained products or invasive placenta
Thrombin - Coagulopathy
How much blood can be lost before there is an increase in heart rate and/or decrease BP
25% of patient’s blood volume
± 1500 mls
Why are Hb and Hct levels poor indicators of acute blood loss if no plasmalyte is given
The levels would take 24 - 48 hours to reflect the true concentration of Hb / haematocrit
Which blood marker is predictive of severe PPH and what are the problems with sampling this parameter in PPH?
Fibrinogen < 200 mg/dL
Problems
- Fibrinogen assays have a long turn around time
- Large variation in baseline levels: 210 - 900 mg/dL
Define severe PPH
Need for:
- Multiple blood products
- Angiographic embolization
- Surgical intervention
- Maternal death
Summarise the risk factors for PPH
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
Which four risk factors are associated with the highest odds for predicting the need for massive transfusion
- Abnormal placentation
- Placental abruption
- Severe preeclampsia
- Intrauterine fetal demise
Outline the stepwise management of major obstetric haemorrhage
- Pre-empt and predict with risk factors
- Recognize, declare, communicate, get help
- High capacity IV access (2 x large bore)
- Crystalloids / colloids / Packed cells
- ETT ± CVC ± A-line
- Forced air-warming blanket
- Oxytocin bolus 2.5 –> 3U by slow IV bolus injection
- Oxytocin infusion 40 U in 1000mls at 250 ml/hr
(Prophylactic oxytocin is 20 u in 1000 mls at 125 ml/hr) - 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 - Prostaglandin E1 = misoprostal 200 mcg tablets: 2 - 3 tablets PR or SL(better no first pass)
- Prostaglandin F2 alpha –> 1 mg into 4 ml = 0.25mg/ml –> 1 ml intramyometrally into each of four quadrants
What is the ED 90 for oxytocin in uncomplicated low-risk labour.
What is the ED 90 for oxytocin in arrested/obstructed labour
uncomplicated = 0.35 U
Complicated = 3U
List the problems with oxytocin administration
- Tachyphylaxis (rapidly diminishing response to successive doses of a drug rendering it less effective)
- Vasodilatation (caution in shock)
- ADH properties –> water retention and hypoNa (with infusions)
How long does oxytocin bolus dose last
± 1 hour
What are the problems with ergometrine
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
What is the onset of ergometrine and how long do the effects last
IV - immediate
IM - 5 minutes
Duration: 3 hours
What are the advantages and disadvantages of misoprostal (PG E1)
Advantages
- Cheap
- No refrigeration (c.f. oxytocin/ergometrine)
- SL more reliable (less first pass metabolism)
Disadvantages
1. Less effective than oxytocin and ergometrine
What are the problems with PGF2alpha
- Bronchospasm –> V/Q mismatch –> hypoxaemia
- Systemic hypertension
- Pulmonary hypertension if used IV
- Cannot be given IV
- Can only be used intramyometrally as a last line agent
What is the % error with subjective assessment of blood loss at 300 ml and at 2000 ml
300 ml blood loss - error = 16%
2000ml blood loss - error = 41%
What is the rule of 30
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
What is the shock index? What is the normal shock index in obstetric and non-obstetric patients
Shock index is HR/SBP
Non-obstetric patients > 0.7 is abnormal
Obstetric patients > 0.9 is abnormal
Describe the definitions of severity of postpartum haemorrhage
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.
Describe the massive transfusion products ordered
- Fixed-ratio 5 RCC + 5 FFP + 1 pooled platelets + Cryoprecipitate
Maintain platelet count> 50 x 10^9/L
Give tranexamic acid: 1g repeatable once
When should the surgeon proceed straight subtotal hysterectomy
- Uterine rupture that is irreparable
2. Placenta increta or percreta
What are the surgical techniques used for:
- Atonic uterus
- Uterine tears
- Placental site bleeding
- Atonic uterus - B-Lynch compression suture or STAH
- Uterine tears - Stepwise uterine artery devascularization / Uterine artery ligation or STAH
- Placental site - Stepwise uterine artery devascularization / Balloon tamponade / STAH
What is the lloyd davis position
Trendelenburg lithotomy
