Errors in flow and pressure related to the arterial filter purge line.

The purge line is a necessary component on arterial filters, although its presence may affect the amount of flow reaching the patient as well as the pump outlet pressure in the extracorporeal circuit. In-vitro and clinical studies conducted to investigate these effects with a commonly used purge line showed that at flows less than 1.5 L/min, rates for pediatric or infant patients, the purge line diverts as much as 40% of the intended pump flow away from the patient. A small diameter resistance tube connected in series with the purge line reduced purge flow such that over 80% of the pump flow reached the patient. Pressure monitored at the arterial filter port with the purge line open could be as much as 45 mmHg lower than the pressure measured with the purge line closed to the filter. Studies should be done to determine if the arterial filter purge line compromises flow to the patient, and if an additional resistance to the purge line is appropriate to reduce the flow through it.

New roller pump disposable provides safety and simplifies occlusion setting.

A new disposable insert for the arterial roller pump, the Better-Header, provides safety and functionality beyond what standard tubing provides. It automatically limits pump outlet pressure to a level determined by the user and provides a self-contained, simple means to set pump occlusion. The Better-Header consists of a Starling-like pressure relief valve connected across standard header tubing. As long as arterial line pressure at the pump outlet remains below a set limit, the valve is closed. If line pressure approaches the pressure limit, the valve opens, preventing overpressurization by shunting blood from pump outlet to inlet. The Better-Header can also be used to set occlusion by the "dynamic method" to obtain nonocclusive settings. The Better-Header was evaluated in the lab for its pressure-flow characteristics. Even when the arterial line was completely clamped at a pump flow of 7 L/min, line pressure was limited to a safe level and all circuit connections were preserved. The Better-Header has been used successfully at North Shore University Hospital in over 500 clinical cases covering a wide range of patients and procedures. In several instances, the user was alerted to high pressure situations by fluid flow through the valve and by an audible alarm, allowing rapid correction of the source of pressure. Compared to the standard setup, the Better-Header maintains outlet pressure within safe, user-settable limits, and permits consistent, nonocclusive settings with predictable retrograde flow.