Hyponatremia after Autologous Breast Reconstruction: A Cohort Study Comparing Two Fluid Management Protocols.

Background:  Perioperative fluid management is an important component of enhanced recovery pathways for microsurgical breast reconstruction. Historically, fluid management has been liberal. Little attention has been paid to the biochemical effects of different protocols. This study aims to reduce the risk of postoperative hyponatremia by introducing a new fluid management protocol.

Methods:  A single-institution cohort study comparing a prospective series of patients was managed using a new "modestly restrictive" fluid postoperative fluid management protocol to a control group managed with a "liberal" fluid management protocol.

Results:  One-hundred thirty patients undergoing microsurgical breast reconstruction, at a single institution during 2021, are reported. Hyponatremia is demonstrated to be a significant risk with the original liberal fluid management protocol. At the end of the first postoperative day, mean fluid balance was +2,838 mL (± 1,630 mL). Twenty-four patients of sixty-five (36%) patients had low blood sodium level, 14% classified as moderate-to-severe hyponatremia. Introducing a new, "modestly-restrictive" protocol reduced mean fluid balance on day 1 to +844 mL (±700) ( ≤ 0.0001). Incidence of hyponatremia reduced from 36 to 14% ( = 0.0005). No episodes of moderate or severe hyponatremia were detected. Fluid intake, predominantly oral water, between 8am and 8pm on the first postoperative day is identified as the main risk factor for developing hyponatremia (odds ratio [OR]: 7;  = 0.019). Modest fluid restriction, as guided by the new protocol, protects patients from low sodium level (OR: 0.25; confidence interval: 95%; 0.11-1.61;  = 0.0014).

Conclusion:  The original "liberal" fluid management protocol encouraged unrestricted postoperative oral intake of water. Patients were often advised to consume in excess of 5 L in the first 24 hours. This unintentionally, but frequently, was associated with moderate-to-severe hyponatremia. We present a new protocol characterized by early cessation of intravenous fluid and an oral fluid limit of 2,100 mL/day associated with a significant reduction in the incidence of hyponatremia and fluid overload.