INTRODUCTION: During a cerebrovascular procedure, diligent care is made to ensure no air is present in lines and connectors. Should air enter the cerebral vasculature, cerebral air emboli can cause worsening neurological outcome or death. This communication outlines how a process change of refrigerating mixed heparin for storage lead to the presence of unintentional air, or off-gassing of the fluid. MATERIAL & METHOD: The off-gassing phenomenon was noted during procedure. Various hypotheses were considered, including fluid preparation and manufacturing defects of lines and tubes. Further investigation identified a new process in mixing of heparin bags that were then refrigerated. The off-gassing was noted during the procedure when cold fluid flowed through tubing draped across a warming blanket. This article utilizes the explanatory research method to describe the cause and effect relationship. The aim is to provide knowledge of this phenomenon to prevent future occurrences. RESULT: Fluids used for neuro endovascular procedures should be warmed to prevent off-gassing, which can lead to cerebral air embolus. CONCLUSION: Air formation or out-gassing can occur when cold fluids are warmed. During neuro endovascular procedure, this unintentional air can cause significant morbidity or mortality to the patient. Understanding and recognizing this phenomenon is important to prevent patient harm.