Preflush

Preflush is a preparatory flushing procedure used in various settings to remove air, stagnant fluids, or contaminants from a system before a subsequent operation, sampling, or administration. The goal is to establish representative conditions and reduce the risk of contamination or carryover from previous contents.

In medical care, a preflush commonly involves infusing a small volume of sterile saline through an intravenous line, catheter, or access port before administering medications or drawing blood. This helps clear the line of residual drug, blood, or air, reduces the risk of dilution of the intended dose, and improves accuracy of sampling. The exact volume and rate depend on the device, patient, and protocol, and must follow institutional guidelines to minimize infection risk.

In water quality testing and environmental sampling, preflush refers to purging the distribution system with water before taking a sample to avoid capturing water that has been sitting in the pipe. Field practices may involve running water for a defined period or until key parameters stabilize, ensuring a representative sample of the active supply.

In industrial and process engineering, preflush is used for pipeline or reactor startup to clear residues from cleaning stages, to cool lines, or to establish steady-state flow, often using a compatible fluid. It helps protect equipment and maintains process integrity during commissioning or maintenance.

Benefits include improved sample integrity and reduced cross-contamination; potential downsides include added fluid volume, cost, and the need for strict adherence to sterile or chemical compatibility requirements to prevent unintended effects. See also flushing, purging, line priming, dead space.