Sudden pump stop may cause air release in oxygenators, 'The Hammer Effect': An in vitro evaluation.

Area of Science:

• Cardiopulmonary bypass (CPB) technology
• Biomedical engineering
• Medical device safety

Background:

• Oxygenators in CPB circuits are designed for air removal.
• Semipermeable hollow fibers in oxygenators can allow unintended air entry.
• The 'hammer effect,' a pressure drop from sudden flow cessation, is a potential cause.

Purpose of the Study:

• To investigate and reproduce the hammer effect in CPB oxygenators.
• To determine if the hammer effect causes air release through oxygenator fibers.
• To raise awareness of this phenomenon in CPB procedures.

Main Methods:

• An in vitro setup simulating CPB was used with four test oxygenators.
• The hammer effect was induced by suddenly stopping an occluded roller pump.
• Pressure waves were measured, and residual air in oxygenators was quantified post-test.

Main Results:

• The hammer effect was successfully reproduced, causing a relative negative pressure drop.
• Two of the four tested oxygenator brands exhibited air release through semipermeable fibers.
• This indicates a potential for air entrainment during CPB operations.

Conclusions:

• The hammer effect can occur in CPB circuits prior to patient connection.
• Sudden pump stops or clamping combined with centrifugal pumps can trigger this effect.
• Awareness of the hammer effect is crucial to prevent air embolism in CPB.