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Review Note

Last Update: 03/27/2025 09:44 PM

Current Deck: ACG Part 2::Obstetrics

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SS_OB 1.35 Discuss the pathophysiology and anaesthetic management of the following medical conditions particular to pregnancy:

- Hypertensive disorders of pregnancy/preeclampsia
Definitions:
  • Hypertension: SBP >140mmHg or diastolic BP > 90mmHg
  • Chronic hypertension: HTN that existed before 20 weeks (or those on anti-HTN meds)
  • Gestational hypertension: HTN after 20 weeks
  • Pre-eclampsia: New onset HTN + one or more other features:
    • Renal:
      • Proteinuria (urine PCR > 30mg/mmol or ACR >8mg/mmol or >1g/L (2+) on dipstick)
      • Oliguria <80ml/hr
      • Serum or plasma Cr > 90
    • Haematological involvement (thrombocytopenia <100, haemolysis (schistocytes or red cell fragments on blood film, raised bilirubin, raised lactate dehydrogenase >600mIU/L, decreased haptoglobin), DIC)
    • Uteroplacental dysfunction (Fetal growth restriction, abnormal blood flow on USS)
    • Other maternal organ dysfunction:
      • CNS: headache, visual disturbance, papilloedema, clonus/hyperreflexia
      • CVS: Pulmonary oedema
      • GIT/Liver: Elevated transaminase enzymes (HELLP), liver tenderness, N&V, epigastric pain
  • Onset before 35 weeks considered ‘early’ and has poorer outcomes
  • Severity:
    • BP: SBP >160 or DBP >90 = severe, SBP >180 or DBP > 110 = hypertensive crisis
Pathophysiology of PET:
It is generally accepted that impaired trophoblastic cell invasion results in failure of spiral artery dilatation, leading to placental hypoperfusion, and consequently hypoxia. In response to hypoxia, the placenta releases cytokines and inflammatory factors into the maternal circulation triggering endothelial dysfunction. The subsequent increase in vascular reactivity and permeability, and coagulation cascade activation, results in organ dysfunction.
  • CVS/resp:
    • HTN + increased sensitivity to catecholamines (and vasopressors)
    • Reduced circulating volume
    • Increased SVR, reduced CO
    • Increased vascular permeability: Prone to pulmonary oedema, laryngeal and pharyngeal oedema
  • Haem:
    • Thrombocytopenia with plt consumption and hypercoagulability with increased fibrin activation and breakdown - may develop DIC
    • Increased Hct due to low circulating volume
  • Renal
    • Reduced GFR
    • Proteinuria (increased permeability)
    • Oliguria severe disease
  • CNS:
    • Headache, visual changes, hyperreflexia
    • Cerebrovascular haemorrhage
    • Eclampsia (from cerebral oedema or vasoconstriction)
    • Clonus indicates high risk of imminent eclampsia
  • Fetaplacental unit:
    • Reduced fetal growth and oligohydramnios
    • Poor placenta perfusion, sensitive to changes in maternal BP
    • Reduced umbilical arterial diastolic blood flow (esp. reverse diastolic flow) indicates poor fetal outcome -> early intervention needed

PET management:
  • Prevention:
    • Antiplatelets (aspirin) for patients at high risk (chronic HTN, T1 or T2DM, previous HTN disease) with two or more risk factors (e.g. BMI >36 at booking, age >40 years) from 12 weeks’ gestation until 36–37

  • Pre-op management:
    • BP control:
      • Aim to control BP below 160/90 (or will need early delivery), ideally below 140/90
      • Oral agents: 1st line:  Labetalol, 2nd line: nifedipine (10mg), methyl-dopa
      • IV agents if severe hypertension:
        • Labetalol 5-10mg IV every 10 minutes
        • Hydralazine 5mg IV up to 20mg
  • Protection from eclampsia:
    • MgSO4 4g over 15 minutes, then maintenance 1g/hour for 12-24hrs
    • Use magnesium if any of the following: clonus, persistent or recurrent headaches, visual scotoma, nausea and vomiting, epigastric pain, oliguria, severe hypertension or progressive deterioration in renal or liver function tests.
    • If eclamptic seizures develop: Load with 4g, then another 2g bolus
  • Other:
    • Continuous CTG monitoring
    • MDT discussion around delivery timing with senior obstetrician, anaesthetist, midwife, patient (especially if pre-term)
    • Consider A-line for BP monitoring (and if inserted then best place for monitoring)
    • Should eb in monitored environment especially if IV agents being used
    • Can also used an early epidural to help with BP management and avoiding sympathetic surges
    • Recent bloods especially platelets and coags as needed
    • Usual obstetric hx, ex, fasting, airway
  • Intra-op:
    • Vaginal vs LSCS delivery
    • Vaginal:
      • Epidural controls excessive surges in BP in labour and is recommended if not contraindicated
      • Platelets count >100 go for it
      • Platelets > 75 and normal clotting screen - go for it
      • Platelets <75 - careful assessment with senior colleague and risks and benefits discussed with patient
      • Usually bloods within 6 hours but if clinically deteriorating rapidly or platelets falling rapidly then before FBC immediately prior to block
      • No fluid loading prior to epidural (but have vasopressor on hand)
    • LSCS:
      • GA or neuraxial
      • GA if significant thrombocytopenia, coagulopathy or other contraindication
      • GA:
        • Goals: Secure airway safely, avoid spike in BP with laryngoscopy, facilitate fetal delivery as soon as safe
        • A: Careful airway assessment, facial oedema common, stridor concerning, have selection of smaller ETT’s available and consider AFOI if severe. 
        • B: Usual strategies
        • C: 2x wide bore IVL’s, arterial line for severe PET. Induction: Need to obtund sympathetic response to laryngoscopy - alfentanil 1-2mg and/or labetalol 10-20mg, remi TCI or bolus also very effective. Fluid management: delicate balance - do not over do fluids as will cause pulmonary oedema, consider low volume oxytocin infusion.
        • If magnesium has been used remember it will prolong action of NDMR’s and may exacerbate uterine atony
        • Extubation: Ensure adequate analgesia, may need to control BP response with labetalol again (10-20mg bolus)
      • Neuraxial: Less prone to hypotension with spinals than usual pregnant population, better analgesia. Must ensure clotting/coags/plts safe.
        • Fluids: Reduced volume co-load. By end of procedure fluid given should not exceed blood loss.
        • Vasopressor: Phenylephrine or ephedrine as needed (may be sensitive to effects so trial lower doses)
        • Avoid NSAIDs as prone to renal impairment (and platelet function impaired)
  • Post-op:
    • Best cared for in HDU/ICU for monitoring of haemodynamics, eclampsia especially if on going magnesium infusion
Ref:
Oxford handbook
National women's guideline

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