Anaesthetic Management of Morbidly Adherent Placenta (MAP / Placenta Accreta Spectrum)

MD Examination Answer

1. Definition and Classification

"Placenta accreta spectrum, formerly known as morbidly adherent placenta, refers to the range of pathologic adherence of the placenta, including three subtypes of accreta, increta, and percreta." — Miller's Anesthesia, 10e

2. Risk Factors (Anaesthetic Relevance)

• Prior uterine surgery — most important: previous caesarean section + anterior placenta previa
• Risk of accreta with previa: 3% (0 CS) → 11% (1 CS) → 40% (2 CS) → >60% (≥3 CS)
• Other: endometrial ablation, myomectomy, pelvic irradiation, IVF, advanced maternal age
• Ultrasound sensitivity ~80–90%; MRI useful for posterior placenta or bladder involvement

3. Antenatal Preparation — Multidisciplinary Team (MDT)

• Obstetric anaesthesiologist
• Maternal-fetal medicine specialist
• Neonatologist
• Gynaecologic/pelvic oncology surgeon
• Urologist (risk of bladder involvement in percreta)
• Vascular/general surgeon (as needed)
• Interventional radiologist
• Blood bank and transfusion medicine

4. Pre-operative Assessment

History

• Parity, number of CS, prior uterine surgery
• Comorbidities (cardiac, respiratory — relevant to fluid loading and vasopressors)
• Religious/ethical considerations (e.g., Jehovah's Witness — plan for cell salvage, normovolaemic haemodilution)

Investigations

5. Operating Room Setup

• Large-bore IV access: ≥2 × 16G (or larger) peripheral cannulae
• Arterial line: mandatory — for beat-to-beat BP monitoring and serial blood sampling (ABG, Hb, coagulation)
• Central venous access: CVP monitoring, rapid infusion of vasopressors and fluids
• Rapid infusion device and fluid warmer (e.g., Level 1, Belmont)
• Cell salvage machine (intraoperative autologous transfusion) — set up and ready
• TEG/ROTEM: viscoelastic point-of-care coagulation monitoring
• Massive Transfusion Protocol (MTP) activated: pre-ordered pRBC:FFP:Platelets in 1:1:1 ratio
• Warm blankets, forced-air warming device — prevent hypothermia
• Main operating room (not labour room) with full surgical team present

6. Choice of Anaesthesia

A. Neuraxial Anaesthesia (Preferred in elective, planned cases)

• CSE allows awake delivery with the patient's partner present
• Epidural component allows incremental dose extension for prolonged hysterectomy
• Regional anaesthesia avoids airway management risks in the obese parturient
• Associated with lower operative blood loss and reduced transfusion need compared to GA (likely because volatile agents cause uterine relaxation)
• A UK retrospective series showed regional anaesthesia used in 60% of planned PAS cases with good outcomes
• Conversion from neuraxial to GA was rarely required (only when spinal duration was insufficient during hysterectomy)

• Low-dose intrathecal component (hyperbaric bupivacaine 8–10 mg + fentanyl 15–25 mcg ± morphine 100–200 mcg)
• Epidural catheter for top-ups (0.5% bupivacaine boluses or infusion)
• Block level: T4 required

B. General Anaesthesia (Indicated when:)

1. Uncontrolled, massive haemorrhage — haemodynamic instability
2. Severe coagulopathy (contraindication to neuraxial)
3. Patient refusal of neuraxial
4. Failed/inadequate neuraxial block
5. Emergency (unplanned) surgery with no time for regional
6. Suspected bladder/bowel percreta requiring complex resection

• Rapid Sequence Induction (RSI) — full stomach precautions apply
  • Pre-oxygenation for 3–5 minutes (parturient has reduced FRC, increased O₂ consumption)
  • Cricoid pressure (controversial but still recommended in obstetrics)
  • Induction: Propofol or thiopentone + Suxamethonium 1.5 mg/kg (or Rocuronium 1.2 mg/kg if sugammadex available)
  • Ketamine is an excellent alternative induction agent if patient is haemodynamically unstable — provides sympathomimetic BP support
• Intubation: use videolaryngoscope as primary device (anticipated difficult airway in obese/obstetric patient)
• Maintenance: TIVA or balanced with low-dose volatile (0.5–1 MAC isoflurane/sevoflurane); note volatile agents cause dose-dependent uterine relaxation — a disadvantage for haemostasis
• Avoid: deep volatile anaesthesia before delivery (fetal depression)
• Ventilation: protect against aspiration; consider PEEP in prolonged cases

7. Intraoperative Anaesthetic Management

Haemodynamic Monitoring

• Invasive arterial BP monitoring (A-line) — essential
• CVP (internal jugular or subclavian)
• Consider pulmonary artery catheter or transoesophageal echocardiography (TOE) if severe haemodynamic compromise or cardiac comorbidity

Blood Loss Management

Anticipate massive haemorrhage

• Average blood loss in caesarean hysterectomy for PAS: 3–5 litres; can exceed 10 litres in percreta

Transfusion Strategy

• Massive Transfusion Protocol: 1:1:1 pRBC:FFP:Platelets (adapted from trauma evidence)
• Serial TEG/ROTEM to guide component therapy

Tranexamic Acid (TXA)

• WOMAN trial (RCT, n>20,000): TXA significantly reduced death due to bleeding in PPH when given within 3 hours
• Dose: 1 g IV at delivery, repeat in 30 minutes if bleeding continues
• Now standard of care in PPH resuscitation

Intraoperative Cell Salvage

• Historically avoided due to fear of amniotic fluid embolism (AFE)
• Current evidence: reviews found no serious maternal complication from cell salvage in obstetrics
• A leucocyte-depletion filter is used
• Recommended in high-risk cases (PAS, Jehovah's Witness patients — can be lifesaving if kept in a closed circuit)

Vasopressors

• Phenylephrine (first-line) or noradrenaline infusion to maintain MAP ≥65 mmHg
• Vasopressin in refractory vasodilatory shock
• Avoid excessive crystalloid — dilutional coagulopathy worsens haemorrhage

Uterotonic Agents (post-delivery)

Surgical Considerations Affecting Anaesthesia

• Fundal (vertical) uterine incision — avoiding the placenta — is planned
• Placenta left in situ while hysterectomy proceeds (placenta should not be manually removed)
• Interventional radiology: preoperative bilateral internal iliac artery or aortic balloon catheters — controversial; no proven benefit in RCTs, carries risk of vascular injury and leg ischaemia. Decision individualised.

8. Temperature Management

• Active warming throughout (warm IV fluids, forced-air warming blanket)
• Avoid hypothermia — worsens coagulopathy and prolongs drug metabolism
• Target core temp >36°C (lethal triad: hypothermia + acidosis + coagulopathy)

9. Postoperative Management

• ICU admission — mandatory post-caesarean hysterectomy for PAS
• Continue invasive monitoring (arterial line, CVP)
• Ongoing transfusion guided by TEG/ROTEM and serial Hb
• Watch for:
  • Coagulopathy / DIC — treat with FFP, cryoprecipitate, platelets, TXA
  • Acute renal failure — maintain urine output >0.5 mL/kg/h
  • ARDS — from massive transfusion (TRALI)
  • VTE prophylaxis — once haemostasis secured, early anticoagulation
• Pain management: epidural analgesia (if catheter in situ and no coagulopathy) or IV PCA morphine; TXA + NSAIDs + paracetamol multimodal regimen

10. Special Scenarios

Undiagnosed / Emergency PAS

• Highest blood loss and morbidity
• Immediate MTP activation
• Call for MDT including on-call vascular/urological surgeon
• General anaesthesia likely required
• Consider aortic compression manually by surgeon until vascular control achieved

Jehovah's Witness Patient

• Detailed, documented informed consent
• Maximise pre-op Hb: IV iron + erythropoietin (EPO) as early as possible
• Normovolaemic haemodilution (autologous blood kept in closed circuit)
• Cell salvage in closed circuit (usually acceptable)
• TXA prophylaxis
• Conservative surgical technique; consider delayed hysterectomy after uterine artery embolisation (UAE)

Posterior Placenta / Percreta with Bladder Involvement

• Urology team scrubbed and ready
• Cystoscopy ± ureteric stents pre-operatively
• Higher blood loss expected

11. Summary Algorithm

Suspected MAP → Multidisciplinary Planning (before 34 weeks)
        ↓
Pre-op: Large bore IV × 2 | Arterial line | Cross-match 6 units pRBC
        | Cell salvage ready | MTP activated | TEG/ROTEM available
        ↓
Haemodynamically STABLE?
    YES → CSE preferred (awake, epidural top-up for prolonged surgery)
    NO  → RSI + General Anaesthesia (ketamine for induction if unstable)
        ↓
Intraoperative:
    - Fundal incision, cord clamp, placenta in situ
    - TXA 1g IV on delivery
    - 1:1:1 MTP if haemorrhage > 1500 mL
    - Maintain T° > 36°C, pH > 7.35, fibrinogen > 2 g/L
        ↓
Post-op ICU: Monitoring | DIC surveillance | VTE prophylaxis

Key Exam Points to Remember

1. PAS = morbidly adherent placenta — accreta (no decidua) → increta (into myometrium) → percreta (through serosa)
2. MDT at a Level III/IV centre is the single most important intervention reducing morbidity
3. CSE is preferred for planned elective caesarean hysterectomy; GA is indicated for haemorrhage/coagulopathy
4. TXA 1g IV (WOMAN trial) — give early, reduce mortality from PPH
5. Cell salvage is safe in obstetrics with leucocyte-depletion filter
6. Fibrinogen falls early in obstetric haemorrhage — replace early with cryoprecipitate/fibrinogen concentrate
7. Internal iliac balloon catheters — controversial, unproven benefit, risk of vascular injury
8. Avoid hypothermia — maintains coagulation and minimises transfusion requirement
9. Emergency PAS carries the highest morbidity — maintain high index of suspicion in patients with previa + prior CS

• Miller's Anesthesia, 10e — Ch. 58 (Obstetric Anesthesia)
• Creasy & Resnik's Maternal-Fetal Medicine, 8e — Ch. 43 (Placenta Accreta Spectrum) & Ch. 70 (Peripartum Haemorrhage)
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e — Ch. 41 (Obstetric Anesthesia)
• WOMAN Trial Collaborators, Lancet 2017 [PMID: 28456509] — TXA in PPH