What may indicate that a needle has hit a blood vessel during an IP injection?

When performing an intraperitoneal (IP) injection, aspirating the syringe is a crucial step to confirm that the needle has not entered a blood vessel. If blood enters the syringe upon aspiration, it indicates that the needle has punctured a blood vessel. This may happen if the needle passes through a vascular structure while attempting to inject into the peritoneal cavity. The presence of blood in the syringe suggests a need to withdraw the needle to avoid complications associated with injecting into a blood vessel, such as hemorrhage or other adverse reactions.

In contrast, yellow or greenish fluids in the syringe typically do not signify that a blood vessel has been hit. Yellow fluid could indicate a mix of air and peritoneal fluid, while greenish fluid may suggest other substances but are not indicative of vascular puncture. Resistance in the plunger may occur for various reasons, such as hitting an organ or dense tissue, but it does not specifically indicate vascular puncture either. Therefore, aspirating blood is the most definitive indication that the needle has struck a blood vessel during the injection process.