Enrolled patients will be randomized postoperatively to receive either one of the following parenteral maintenance solutions: 1) hypotonic PMS, or 2) isotonic PMS. For the purposes of this study the hypotonic PMS will be 0.45%NaCl, and the Isotonic PMS will be 0.9% NaCl. Enrolled patients will receive their allocated treatment (provided there are no safety issues or concerns) until they are fully orally fed and the PMS rate is no greater than a rate required to "keep vein open (KVO)", to a maximum duration of 48 hours. The physician can thereafter administer the maintenance solution of their choice. The following parameters will be monitored in each study participant during the treatment period: hourly urine output, strict intake and output, 12 hourly fluid balances and daily weights. Blood and urine samples will be obtained on study patients every 12 hours until they are fully orally fed and the IV rate is at KVO, for a maximum of 48 hours. Any additional investigations ordered by the caring physician during the treatment and follow up period will also be recorded. Patients will be followed for clinical outcomes for 48 hours after the study intervention is discontinued, or until the time of discharge.