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Anesthetic Considerations in Pregnancy

Anesthetic Considerations in Pregnancy: Pathophysiology driving anesthetic management Authors: Calah Myhre Reviewers: Jasleen Brar Luiza Radu Leyla Baghirzada* Yan Yu* * MD at time of publication Airway ↑ Estrogen serum levels Mucosal capillary engorgement ↑Airway tissue friability & edema ↑ Laryngoscopy difficulty & intubation time Secure airway & avoid hypoxemia Consider video laryngoscopy Preoxygenate with ↑100% oxygen Optimize intubation positioning (e.g. “Sniffing position”) ↑ Progesterone serum levels ↓ Esophageal tone & sphincter pressure ↑ Aspiration risk >20 weeks gestation & during labor Aspiration prophylaxis Rapid sequence induction Nonparticulate antacid prophylaxis (e.g., sodium citrate, famotidine) Pre-operative fasting & gastric ultrasound to assess volume Breathing ↑ Minute ventilation ↓ PaCO2 at baseline Uterine artery vasoconstriction with maternal PCO2 levels exceeding 32 mmHg Impaired uteroplacental perfusion Maintain physiologic alkalosis, avoid maternal hypercapnia Maintain maternal arterial PCO2 28–32 mmHg Avoid permissive hypercapnia ↑ Progesterone serum levels Disproportionate ↑ in plasma volume ↓ Serum colloid osmotic pressure Drug-specific alterations in absorption, distribution, metabolism & excretion (e.g. ↑ distribution of acidic drugs due to ↓ albumin; ↑ clearance of renally- metabolized drugs) Optimize anesthetic dosing for altered pharmacokinetics Adjust dosages based on drug recommendations Circulation ↑ Maternal blood volume Peripheral vasodilation ↓In systemic vascular resistance by 25–30% ↓ Blood pressure ↑Abdominal pressure Compression of the aorta & inferior vena cava Supine hypotension Impaired uteroplacental perfusion Fetal ischemia Optimize placental blood flow Position patient on left side to maintain uterine displacement Diaphragmatic elevation & lung compression ↓ Functional residual capacity ↑ Risk of rapid desaturation Fetal hypoxemia Maintain maternal & fetal oxygenation Optimize positioning (e.g., patient on left side to maintain uterine displacement) & supplement oxygen as needed Heart rate ↑ 15-25% ↑ Cardiac output Manifestations of significant blood loss are delayed Avoid hypotension ↑ Stroke volume Avoid fluid overload Treat abnormal variation in blood pressure at lower values Fetus Requirement to assess & treat two patients Achieve optimal anesthetic dosing for mother while maintaining fetus safety Maintain oxygenation of both mother & fetus & ensure adequate uteroplacental perfusion Consider fetal-drug transfer & adjust agent & dose accordingly Monitor maternal vital sign & fetal heart rate Utilize a multidisciplinary team (e.g., pharmacy, nursing, physical & occupational therapy) Legend: Pathophysiology Mechanism Goal Management Published July 5, 2024 on www.thecalgaryguide.com