Patient Controlled Fluid Administration

The purpose of the study is to investigate whether participant dictated fluid bolus administration in response to their symptom of experienced thirst is a viable basis to guide a clinical practice of fluid maintenance and correction of hydration status. To this end the experiment will compare the implementation of this fluid maintenance mechanism on volume depleted healthy participants to a program of routine fluid maintenance. The null hypothesis is that the hydration state of the participants, as measured by change in body weight and plasma osmolality, will be no better corrected and managed by a thirst dictated management system than by routine maintenance. The study has a cross-over design, used to ensure differences in hydration status, or lack there of, can be attributed to the methods of fluid administration in question, without differences between individuals confounding the results. The participants will be required to attend the laboratory on two occasions for approximately 5 hours each visit, for arm A and B of the study. The two visits will be separated by 7 to 14 days. On each visit standard IV fluids will be administered The evening before each visit participants will be required to take 40mg of the water tablet called furosemide and refrain from drinking fluids. This is used in order to dehydrate the participant and reduce body mass by between 2 - 4%. The participant needs to be dehydrated in order to promote a thirst response so that the interventions can be studied in a cohort of participants representative of hypovolemic patients post surgery On both visits an indwelling cannula will be placed into a vein in the participants' arm, to administer IV fluid on the participants' non dominant side. Before fluid administration this will be used to draw a blood sample for plasma osmolality measurements. A second blood sample with be drawn from a vein on the opposite arm following the fluid infusion. For arm A: the participant will request the administration of 200ml boluses of IV fluid at any point that they experience thirst. This administration will be limited to one bolus every 15 minutes. For arm B: participants will receive routine fluid maintenance as dictated by the NICE guidelines. During both trials, low intensity exercise will be permitted (walking, standing, sitting) although high intensity exercise is not allowed. Entertainment in the form of a computer with internet access and DVDs will be provided. The arm of the study the patient will undergo in the first week will be determined according to a randomised list. However, due to the nature of the investigation the arm of the study be undergone by the patient can not be blinded from the researchers or participant. All measurements, except the perception of thirst questioning, are objective measures, such as weight, plasma osmolality, haematocrit and blood sodium levels. This will minimise any researcher bias.