Blood Volume & PPH Assessment
Hướng dẫn chi tiết sắp ra mắt
Chúng tôi đang chuẩn bị hướng dẫn giáo dục toàn diện cho Blood Volume in Pregnancy. Quay lại sớm để xem giải thích từng bước, công thức, ví dụ thực tế và mẹo từ chuyên gia.
Obstetric haemorrhage is one of the leading causes of maternal mortality worldwide, responsible for approximately 25% of all maternal deaths globally. It encompasses antepartum haemorrhage (APH), occurring from 24 weeks of gestation, and postpartum haemorrhage (PPH), the most common severe obstetric emergency. Postpartum haemorrhage is defined as blood loss of 500 mL or more from the genital tract within 24 hours of a vaginal delivery, or 1000 mL or more after a caesarean section. Major PPH is defined as blood loss above 1000-1500 mL, and massive PPH as above 1500-2000 mL or sufficient to cause haemodynamic compromise. Blood volume in pregnancy increases by approximately 40-50% above baseline, reaching approximately 100 mL/kg at term — totalling 6000-7000 mL for an average woman at 39 weeks. This physiological hypervolaemia means that pregnant women can sustain considerable blood loss before manifesting haemodynamic compromise, making early recognition challenging. The four commonest causes of PPH are captured in the Four T's mnemonic: Tone (uterine atony — responsible for approximately 75% of PPH), Trauma (genital tract lacerations or uterine rupture), Tissue (retained placenta or products), and Thrombin (coagulopathy, including disseminated intravascular coagulation). Management follows the HAEMOSTASIS mnemonic: bimanual uterine massage, oxytocin, ergometrine, magnesium, surgical options including compression sutures and hysterectomy. Massive transfusion protocols using a fixed ratio of packed red blood cells, fresh frozen plasma, and platelets (typically 1:1:1) prevent the coagulopathy of haemorrhage.
Blood volume in pregnancy ≈ 100 mL/kg body weight (~6000-7000 mL at term); PPH ≥500 mL (vaginal) or ≥1000 mL (CS); Major PPH >1000-1500 mL; Massive PPH >1500-2000 mL; Shock Index = Heart Rate / Systolic BP (>1.0 suggests significant haemorrhage; >1.7 = critical); Transfusion ratio: pRBC:FFP:Platelets = 1:1:1
- 1Measure and estimate blood loss: weigh swabs and drapes (1g = 1mL blood), use calibrated blood collection drapes under the mother, note the volume in suction canisters. Visual estimation consistently underestimates blood loss by 30-50%.
- 2Classify haemorrhage severity: Class I (10-15% blood volume, ~750-1050 mL) — minimal symptoms; Class II (15-30%, 1050-2100 mL) — tachycardia, narrowing pulse pressure; Class III (30-40%, 2100-2800 mL) — tachycardia, hypotension, altered consciousness; Class IV (>40%, >2800 mL) — critical, life-threatening.
- 3Identify the cause using the Four T's: Tone (palpate uterus — atonic if soft and boggy); Trauma (inspect entire genital tract systematically); Tissue (manual exploration of uterus for retained products, review placenta for completeness); Thrombin (check clotting status — clinical oozing, laboratory coagulation tests).
- 4Apply the HAEMOSTASIS mnemonic in sequence: H=ask for Help and bimanual uterine massage; A=Assess resuscitation and Anaesthesia; E=Establish IV access and fluid replacement; M=Massage uterus and oxytocin infusion; O=Oxytocin bolus 5 IU IV; S=Syntometrine (ergometrine+oxytocin) or carboprost (Haemabate); T=Tamponade — intrauterine balloon; A=Apply compression sutures (B-Lynch); S=Systematic pelvic devascularisation; I=Interventional radiology; S=Subtotal hysterectomy as last resort.
- 5Activate the massive transfusion protocol (MTP) when blood loss exceeds 1500 mL or haemodynamic compromise is present. Initial MTP: 4 units pRBC + 4 units FFP + 1 pool platelets. Repeat packs based on clinical status and TEG/ROTEM-guided therapy.
- 6Monitor: pulse, BP, urine output (catheterise), SpO2, temperature, and serial haematocrit/coagulation every 30-60 minutes during active haemorrhage. Prevent hypothermia, acidosis, and coagulopathy — the lethal triad.
- 7Document all interventions, blood products transfused, drug doses, and timings contemporaneously on an obstetric haemorrhage pro-forma.
Oxytocin 5 IU slow IV + syntocinon infusion 40 IU in 500mL at 125mL/hr; bimanual massage; ergometrine if no contraindication
Uterine atony (soft uterus failing to contract) is responsible for 75% of PPH. Immediate bimanual uterine massage plus sequential uterotonic drugs — oxytocin, ergometrine, carboprost — are first-line. Insert large-bore IV, take bloods, cross-match 4 units.
Call for help; activate MTP; tranexamic acid 1g IV STAT; check for surgical bleeding source; anaesthesia team
Shock index (HR/SBP) above 1.0 indicates significant haemorrhage in obstetric patients. MTP activation brings blood products rapidly. Tranexamic acid (1g IV, repeat if needed) reduces PPH mortality and should be given within 3 hours of delivery.
Oxytocin infusion for uterine tone; prophylactic antibiotics; epidural top-up or spinal if urgent
Retained placenta is the second most common cause of PPH. If the placenta is not delivered spontaneously within 30 minutes (or 60 minutes in some protocols), manual removal in theatre under anaesthesia is required.
Fibrinogen <2 g/L in obstetric DIC requires immediate correction; target >2 g/L
DIC in obstetrics is triggered by placental abruption, amniotic fluid embolism, or massive haemorrhage itself. Fibrinogen below 2 g/L is an independent predictor of severe PPH. Cryoprecipitate or fibrinogen concentrate restores clotting factor levels and stops the consumptive coagulopathy.
Labour ward: immediate risk stratification and management escalation protocol for women with PPH above 500 mL., where accurate obstetric hemorrhage analysis through the Obstetric Hemorrhage supports evidence-based decision-making and quantitative rigor in professional workflows
Operating theatre: activating and executing massive transfusion protocol for surgical or CS-associated haemorrhage., where accurate obstetric hemorrhage analysis through the Obstetric Hemorrhage supports evidence-based decision-making and quantitative rigor in professional workflows
Antenatal risk stratification: identifying women with placenta praevia, PAS, or prior PPH who need delivery planning at a specialist centre with transfusion expertise., where accurate obstetric hemorrhage analysis through the Obstetric Hemorrhage supports evidence-based decision-making and quantitative rigor in professional workflows
Global health: WHO and FIGO PPH prevention protocols using oxytocin and misoprostol in all deliveries, with tranexamic acid for established PPH, targeting the 70,000 maternal deaths from haemorrhage each year.
Simulation training: obstetric haemorrhage drills are mandated in maternity units and test the full team response including drug preparation, MTP activation, surgical escalation, and documentation.
Placenta Accreta Spectrum (PAS)
Placenta accreta, increta, and percreta represent abnormally adherent placentation due to myometrial invasion. The incidence is rising in parallel with caesarean section rates. PAS is associated with catastrophic haemorrhage at the time of placental delivery. Planned delivery at a specialist centre with multidisciplinary team including vascular surgery, interventional radiology, and cell salvage should be arranged from 34-36 weeks when diagnosed antenatally.
Jehovah's Witness Patient
Jehovah's Witness patients who decline blood products present a complex ethical and clinical challenge in obstetric haemorrhage. Intraoperative cell salvage is generally acceptable. Pre-delivery optimisation of haemoglobin, iron stores, and coagulation is essential. A detailed advanced directive and the patient's specific accepted interventions must be documented before delivery, and a senior haematologist involved in the multidisciplinary plan.
Uterine Inversion
Uterine inversion is a rare but life-threatening complication where the uterus inverts through the cervix, causing sudden PPH and neurogenic shock (often disproportionate to blood loss). Immediate manual replacement of the inverted uterus (Johnson manoeuvre) must be attempted before the cervix contracts. Tocolytics (glyceryl trinitrate or terbutaline) may be needed to relax the cervix if the uterus has been inverted for some time.
Postpartum Haemorrhage in Low-Resource Settings
In low-resource settings where oxytocin cold chain cannot be guaranteed, misoprostol (600 mcg sublingual or oral) is a viable alternative uterotonic for PPH prevention and treatment. The WHO recommends misoprostol as first-line in settings where oxytocin is unavailable. Tranexamic acid is also effective, inexpensive, heat-stable, and should be available in all maternity facilities globally.
| Class | Blood Loss (mL) | % Blood Volume | Signs | Action |
|---|---|---|---|---|
| I | Up to 1000 | Up to 15% | Normal HR, BP; may have mild anxiety | Monitor; IV access; cross-match |
| II | 1000-1500 | 15-25% | Tachycardia; narrowed pulse pressure | Oxytocics; transfuse if not improving |
| III | 1500-2500 | 25-35% | Tachycardia; hypotension; AMS | Activate MTP; senior obstetric/anaesthetic team |
| IV | >2500 | >35% | Severe hypotension; obtunded; cold | Emergency resuscitation; consider hysterectomy |
What are the Four T's of PPH?
The Four T's are: Tone (uterine atony — 75% of cases; uterus fails to contract after delivery), Trauma (genital tract lacerations, uterine rupture, broad ligament haematoma), Tissue (retained placenta or products of conception), and Thrombin (coagulopathy — DIC, pre-existing clotting disorders, or coagulopathy secondary to massive haemorrhage itself). Assess all four simultaneously.
What is tranexamic acid and when should it be given?
Tranexamic acid (TXA) is an antifibrinolytic drug that prevents clot breakdown by inhibiting plasmin. The WOMAN trial (2017) showed that 1g IV TXA given within 3 hours of PPH onset significantly reduced maternal mortality from bleeding. TXA should be given to all women with clinically significant PPH (>500 mL vaginal or >1000 mL CS) within 3 hours of delivery. A second dose of 1g can be given 30 minutes later if bleeding continues.
What is the shock index and how is it used in PPH?
Shock index (SI) = Heart Rate / Systolic Blood Pressure. In obstetric haemorrhage: SI <0.9 = normal; SI 0.9-1.0 = mild compromise; SI 1.1-1.7 = moderate haemorrhage (consider MTP activation); SI >1.7 = severe/critical haemorrhage. The shock index detects haemodynamic compromise earlier than systolic BP or HR alone, and its early elevation predicts those requiring massive transfusion.
When is a B-Lynch suture used?
The B-Lynch compression suture is a surgical technique used for uterine atony that is refractory to uterotonics. It involves applying a continuous suture around the uterus to apply compression and reduce bleeding. It was described by Christopher B-Lynch in 1997. It is typically used after all uterotonics have been tried and before proceeding to hysterectomy, and can be used alongside an intrauterine balloon tamponade (the 'sandwich technique').
What is the HAEMOSTASIS mnemonic?
HAEMOSTASIS: H=ask for Help and bimanual massage; A=Assess resuscitation, Anaesthesia; E=Establish IV access; M=uterine Massage, Misoprostol, Methergine (ergometrine); O=Oxytocin infusion; S=Shift to theatre, Syntometrine, Surgical options; T=Tamponade (balloon); A=Apply compression sutures; S=Systematic devascularisation (pelvic arteries); I=Interventional radiology (uterine artery embolisation); S=Subtotal/total hysterectomy. This is particularly important in the context of obstetric hemorrhage calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise obstetric hemorrhage computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is the ideal blood transfusion ratio in massive PPH?
A fixed 1:1:1 ratio of packed red blood cells : fresh frozen plasma : platelets is recommended in massive obstetric haemorrhage pending laboratory results, based on military trauma evidence adapted to obstetrics. Viscoelastic testing (TEG or ROTEM) guides targeted product replacement once available, typically directing fibrinogen replacement before platelet transfusion in DIC.
Why do pregnant women compensate so well for blood loss initially?
Pregnancy increases blood volume by 40-50% (approximately 1500-2000 mL above baseline). This physiological expansion means women can lose 1000-1500 mL before classic shock signs (hypotension, tachycardia) appear. This compensation is protective but dangerous — it masks the severity of haemorrhage and can delay appropriate escalation. Shock index and early vigilance are critical for timely recognition.
What is amniotic fluid embolism and how does it cause haemorrhage?
Amniotic fluid embolism (AFE) is a rare (1:40,000 deliveries) but frequently fatal complication caused by the entry of amniotic fluid components into the maternal circulation, triggering massive anaphylactoid response, right heart failure, and consumption coagulopathy (DIC). It typically presents with sudden cardiovascular collapse and severe haemorrhage. Treatment is supportive — resuscitation, MTP, and management of DIC. AFE is a leading cause of unexpected maternal death.
Mẹo Chuyên Nghiệp
Calculate the shock index (HR/SBP) at the first sign of increased bleeding. A rising shock index (even if systolic BP remains apparently normal) warns that haemodynamic compromise is developing before frank hypotension appears. In pregnant women — who maintain BP well due to physiological hypervolaemia — the shock index provides earlier warning than BP alone.
Bạn có biết?
The B-Lynch suture was invented after a 24-year-old woman at Milton Keynes General Hospital developed intractable uterine atony during caesarean section in 1989. Her surgeon, Christopher B-Lynch, improvised a compression suture technique that successfully controlled the haemorrhage, avoiding hysterectomy and preserving her future fertility. He published the technique in 1997 after performing it successfully in five cases, and it has since been adopted globally, saving countless uteruses and enabling subsequent successful pregnancies in women who would previously have required hysterectomy.
Tài liệu tham khảo
- ›WOMAN Trial Collaborators. Effect of early tranexamic acid administration on mortality from PPH. Lancet 2017.
- ›RCOG Green-top Guideline 52 — Prevention and Management of Postpartum Haemorrhage. 2016 (updated 2023).
- ›WHO Recommendations for the Prevention and Treatment of Postpartum Haemorrhage. 2012.
- ›B-Lynch C et al. The B-Lynch surgical technique for the control of massive postpartum haemorrhage. Br J Obstet Gynaecol 1997.
- ›Sentilhes L et al. Postpartum haemorrhage: guidelines for clinical practice. Eur J Obstet Gynecol 2016.