Classes of Haemorrhagic Shock in Obstetrics
Haemorrhagic shock in obstetrics is classified into four progressive stages based on blood loss volume and physiological decompensation, with multiple obstetric-specific causes requiring immediate recognition and systematic intervention to prevent maternal mortality.
Classification of Haemorrhagic Shock
Haemorrhagic shock represents a condition where inadequate organ perfusion results in insufficient oxygen availability to satisfy tissue metabolic needs, leading to a catabolic state with inflammation, endothelial dysfunction, and disruption of normal metabolic processes 1. The classification system helps guide resuscitation efforts:
Stage I (Compensated Shock)
- Blood loss: Up to 15% of circulating volume (approximately 750 mL)
- Minimal tachycardia, normal blood pressure maintained
- Patient may appear relatively stable due to physiological compensation 2
Stage II (Mild Shock)
- Blood loss: 15-30% of circulating volume (750-1500 mL)
- Tachycardia (100-120 bpm), narrowed pulse pressure
- Delayed capillary refill, mild anxiety
- Urine output begins to decrease 2
Stage III (Moderate Shock)
- Blood loss: 30-40% of circulating volume (1500-2000 mL)
- Marked tachycardia (>120 bpm), hypotension develops
- Altered mental status, oliguria
- Requires aggressive resuscitation 2, 1
Stage IV (Severe/Decompensated Shock)
- Blood loss: >40% of circulating volume (>2000 mL)
- Profound hypotension, severe tachycardia or bradycardia
- Confusion or unconsciousness, anuria
- Life-threatening, often irreversible even with correction of volume deficits 1
Critical caveat: Fit, healthy pregnant women can tolerate significant blood loss prior to showing signs of decompensation, making early recognition challenging 3. Blood loss is often underestimated, particularly with slow, steady bleeding 3.
Important Causes of Obstetric Haemorrhage
1. Uterine Atony
The most common cause of early postpartum haemorrhage, accounting for >75% of cases 4. Uterine atony results from failure of effective uterine contraction after delivery and is typically diagnosed clinically 4. Initial treatment includes uterine massage and uterotonic medications, with most patients responding to these conservative measures 4.
2. Placenta Accreta Spectrum
A major cause of massive obstetric haemorrhage requiring hysterectomy 5. This condition involves abnormal placental attachment to the uterine wall and is associated with previous caesarean sections 5. Patients with placenta accreta spectrum require intensive hemodynamic monitoring and are at particular risk of ongoing abdominopelvic bleeding, fluid overload from resuscitation, and multiorgan damage 5.
3. Genital Tract Trauma
Includes lower genital tract lacerations, vaginal or perineal hematomas, uterine rupture, and caesarean section incision extensions 4. Uterine rupture or scar dehiscence can cause concealed haemorrhage and requires imaging for diagnosis 4. Bladder flap hematomas and subfascial/prevesical hematomas secondary to epigastric vessel injury or direct rectus muscle tears are also important surgical causes 4.
4. Retained Products of Conception (RPOC)
The second most common etiology for postpartum haemorrhage after uterine atony, affecting approximately 1% of third trimester deliveries 4. RPOC may occur with or without superimposed infection and is typically seen in delayed postpartum haemorrhage (>24 hours to 6 weeks post-delivery) 4. Imaging plays a crucial role in diagnosis, and treatment involves curettage 4.
5. Coagulopathy
Can be inherited or acute, related to conditions such as amniotic fluid embolism, placental abruption, severe pre-eclampsia, or HELLP syndrome 4. Hypofibrinogenaemia (fibrinogen <2 g/L) is the most common factor deficiency in postpartum haemorrhage, occurring in 5% of haemorrhages at 1000 mL and 17% at 2500 mL 6. Disseminated intravascular coagulation (DIC) accompanies over 80% of amniotic fluid embolism cases 7.
6. Placental Abruption
A cause of severe early consumptive coagulopathy and concealed haemorrhage 8, 3. Abruption can lead to massive blood loss with minimal external bleeding, making clinical recognition challenging 3. This condition is associated with rapid development of DIC and requires early use of fresh frozen plasma before red blood cells may be necessary 8.
7. Ectopic Pregnancy
Causes ruptured ectopic pregnancy with concealed intra-abdominal haemorrhage 3, 9. This represents a surgical emergency requiring salpingectomy and can lead to rapid decompensation into haemorrhagic shock 9.
8. Vascular Uterine Anomalies (VUA)
Believed to represent subinvolution of the placental bed and may be associated with RPOC 4. Myometrial areas with intense vascularity and peak systolic velocity >83 cm/s are associated with increased risk of significant postpartum haemorrhage 4. Treatment includes embolization or surgical intervention 4.
9. Amniotic Fluid Embolism (AFE)
A rare but catastrophic cause with an incidence of 1.7 per 100,000 maternities 3. AFE presents as acute collapse during labour or within 30 minutes of birth, characterized by acute hypotension, respiratory distress, acute hypoxia, and potential cardiac arrest 3. DIC develops in over 80% of cases, requiring massive transfusion protocols with cryoprecipitate preferred over fresh frozen plasma to minimize volume overload 7.
10. Uterine Inversion
A rare but life-threatening cause of postpartum haemorrhage that can lead to profound shock disproportionate to visible blood loss 3. This requires immediate manual replacement and can be associated with uterine atony 4.
Management principle: Postpartum haemorrhage is defined as any haemorrhage associated with signs or symptoms of hypovolemia within 24 hours of delivery, regardless of delivery type 4. Early recognition using volumetric and gravimetric measurement techniques (rather than visual estimation) incorporated into clear escalation plans reduces the use of blood components and improves outcomes 6.