Theory of Constraints is an approach that shows how you can manage bottlenecks and their associated constraints. A bottleneck determines the pace at which the whole process can work, whilst the constraint is the bit of kit or resource that causes the bottleneck.
By identifying where the constraints are, it is possible to focus improvement effort and day to day operational management in order to maintain and increase throughout. The Theory of constraints identifies a five-step process to achieve continuous flow and improve throughout:
Read the section on Theory of Constraints in the NHS Improving Quality document: Quality improvement theory and practice in healthcare.