The Effects of Bolus and Slow Fluid Infusions in Healthy Volunteers with Shock

INTERVENTION: After the venesection of 10 ml/kg Ideal Body Weight of blood over a 15 minute period from healthy fit adult subjects, participants will be randomised to receive a intravenous crystalloid fluid (Plasma‐Lyte 148) for resuscitation. The type of fluid used is Plasma‐Lyte 148 solution (Baxter Healthcare). The amount of Plasma‐Lyte 148 solution that will be administered is 13 ml/kg (Ideal Body Weight) . Plasma‐Lyte 148 solution will be infused continuously via the intravenous route through a peripheral intravenous cannula. The Plasma‐Lyte 148 infusion will commence exactly 15 minutes after completion of the venesection. Plasma‐Lyte 148 solution will infused over 2 time periods/arms depending on randomisation. 1. Over a 10 minutes period (Bolus infusion group) 2. Over a 30 minutes period (Slow infusion group) The ratio of 1:1.3 ratio of the volume of blood to the volume of Plasmalyte is adopted from the landmark clinical trial, The Saline versus Albumin Fluid Evaluation Study (SAFE). Once the Plasma‐Lyte 148 solution has been infused, data collection will be conducted for 60 minutes. Once data collection is completed, the venesected blood will be re‐infused back to the participant over a 30 minute period. The study will then be concluded. Participants will then be crossed over to the other infusion period/arm between 7 ‐14 days later i.e there will be a washout period of between 7‐14 days between the 2 interventions. CONDITION: Haemorrhagic Shock PRIMARY OUTCOME: The primary outcome is: Oxygen delivery (mls/kg/min) ; ; This is easily measured by using non‐invasive technology which continuously measure cardiac output, O2 saturation and haemoglobin levels throughout the study. ; ; Determinants of oxygen delivery will be directly measured using state of non‐invasive technology (Edwards Life Science ClearSight Device). These will include: ; 1. Stroke volume index (independent of heart rate) ; 2. Haemoglobin concentrations ; 3. Blood arterial saturation ; 4. Heart rate ; ; Venous blood gas including (pH,Pa02,PaCO2, base deficit) using an ABL 800 Blood Gas Monitor INCLUSION CRITERIA: 1. Healthy adults 2. No regular medication other than contraceptive pill 3. Normal Haemoglobin level SECONDARY OUTCOME: Cardiac index using the Edwards Lifesciences ClearSite Advanced haemodynamic monitor Diastolic blood pressure using the Edwards Lifesciences ClearSite Advanced haemodynamic monitor Heart Rate using the Edwards Lifesciences ClearSite Advanced haemodynamic monitor Indocyanine green, which will be measured with PULSION non‐invasive LiMON–Technology Mean arterial pressure using the Edwards Lifesciences ClearSite Advanced haemodynamic monitor Plasma Atrial natriuetic peptide Plasma Interleukin 6 Plasma Tumour necrosis factor (Alpha) Plasma haemoglobin using an ABL 800 Blood Gas Monitor Plasma lactate using an ABL 800 Blood Gas Monitor Stroke volume index using the Edwards Lifesciences ClearSite Advanced haemodynamic monitor Systemic vascular resistance using the Edwards Lifesciences ClearSite Advanced haemodynamic monitor Systolic blood pressure using the Edwards Lifesciences ClearSite Advanced haemodynamic monitor Vascular reactivity index using a VENDYs non invasive vascular reactivity machine.