Functional Residual Capacity
The volume of air remaining in the lungs at the end of normal expiration. Significantly reduced in pregnancy, affecting preoxygenation and anesthetic management during airway procedures.
Full Definition
Functional residual capacity (FRC) is the volume of air that remains in the lungs at the end of a normal, passive expiration, representing the balance point between the inward elastic recoil of the lungs and the outward elastic recoil of the chest wall. In obstetric anesthesia, understanding FRC changes is crucial because pregnancy causes a progressive decrease in FRC of approximately 20% by term due to elevation of the diaphragm by the enlarged uterus and increased chest wall mass. This reduction in FRC, combined with increased oxygen consumption during pregnancy, results in faster desaturation during apnea, making effective preoxygenation essential before general anesthesia or sedation. The decreased FRC also affects the uptake and elimination of inhaled anesthetics, requiring modifications in anesthetic technique. Supine positioning further reduces FRC, emphasizing the importance of optimal positioning during obstetric procedures.
Usage
Usage note: Abbreviate as FRC after first use. Always consider in context of pregnancy-related physiologic changes.
In Context
- "The reduced functional residual capacity in pregnancy necessitates thorough preoxygenation before rapid sequence induction." — Anesthesia planning note
- "Functional residual capacity decreases progressively throughout pregnancy, reaching a 20% reduction at term." — Physiology textbook