Crystalloids and colloids If blood products are not required, then fluid replacement will consist of either a crystalloid or colloid solution.There has been much debate over recent years as to which of these is preferable (Rizoli, 2003). In a systematic review conducted by the Cochrane Library,no evidence was found to support the use of colloids over crystalloids in the critically ill patient (Alderson etal,2004).However,fluid choice remains a clinical decision based on individual patient requirements and responses.