I had an interesting question today from a correspondent in sunny Spain; is colloid preferable as the bolus challenge in goal-directed therapy? I have always supposed the rationale of increasing stroke volume by fluid challenge is to increase oxygen delivery, though this is rarely mentioned. Goal directed therapy with anything less than red blood cells always seemed intrinsically daft to me because any increase in stroke volume is achieved by increasing the plasma volume, which haemodilutes the red cells to a similar magnitude. More recently it occurred to me that as crystalloid is less anaemia-genic than colloid, it might be better as a booster of oxygen delivery. Taking a look at the data of Yates & colleagues in York, Yates, you’ll see my 3D drawing of their Hb and DO2 data confirms the superiority of crystalloid over colloid in their hands. But the bigger question of goal-directed therapy with either remains open. We just do not know if optimising or even normalising any hemodynamic parameter makes any difference, for better or for worse, to patient outcome. Avoid tachycardia and Avoid hypotension seem to be the only established tenets. Plenty of anaesthetists find that difficult enough… why oh why do we not have self-tuning control in theatre?