Filters in anaesthesia and intensive care

The use of various types of filters in anaesthesia and intensive care seems ubiquitous, yet authentication of the practice is scarce and controversies abound. This review examines evidence for the practice of using filters with blood and blood product transfusion (standard blood filter, microfilter leucocyte depletion filter), infusion of fluids, breathing systems, epidural catheters, and at less common sites such as with Entonox inhalation in non-intubated patients, forced air convection warmers, and air-conditioning systems. For most filters, the literature failed to support routine usage, despite this seemingly being popular and innocuous. The controversies, as well as guidelines if available, for each type of filter, are discussed. The review aims to rationalize the place of various filters in the anaesthesia and intensive care environment.