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 managed using a new 'modestly restrictive' fluid post-operative fluid management protocol to a control-group managed with a 'liberal' fluid management protocol.

RESULTS: 130-patients undergoing microsurgical breast reconstruction, at a single institution during 2021, are reported. Hyponatraemia is demonstrated to be a significant risk with the original liberal fluid management protocol. At the end of the first post-operative day, mean fluid balance was +2838 ml (+/- 1630ml). 24/65 (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 one to +844 ml (+/-700) (p=<0.0001). Incidence of hyponatraemia reduced from 36% to 14% (p=0.0005). No episodes of moderate or severe hyponatraemia were detected. Fluid intake, predominantly oral water, between 8am and 8pm on the first post operative day is identified as the main risk factor for developing hyponatremia (OR 7; p=0.019). Modest fluid restriction, as guided by the new protocol, protects patients from low sodium level (OR 0.25; CI 95%; 0.11-1.61; p=0.0014) Conclusion: The original 'liberal' fluid management protocol encouraged unrestricted post-operative oral-intake of water. Patients were often advised to consume in excess of 5-litres in the first 24-hours. This unintentionally, but frequently, was associated with moderate to severe hyponatraemia. We present a new protocol, characterised by early cessation of intravenous fluid and an oral fluid limit of 2100ml/day associated with a significant reduction in the incidence of hyponatraemia and fluid overload.