Difficulty: Hard

Average Score: 38%

Blood collection tubes fill correctly during venipuncture due to which of the following factors?

Rationale

The negative pressure within the tube.

Blood collection tubes fill correctly during venipuncture primarily due to the negative pressure created inside the tube. This negative pressure facilitates the drawing of blood from the vein into the tube, enabling a successful collection process.

A (The high pressure in the arterial system) YOUR ANSWER

The arterial system operates under significantly higher pressure compared to the venous system, but this pressure does not directly contribute to the filling of blood collection tubes. During venipuncture, blood is drawn from veins, not arteries, and therefore arterial pressure is not a relevant factor in this context.

B (The high pressure in the venous system) YOUR ANSWER

While the venous system does have some pressure, it is much lower than that of the arterial system and is not a contributing factor in the filling of blood collection tubes. The process relies on the creation of a pressure differential, rather than on venous pressure itself, to facilitate blood flow into the tube.

C (The positive pressure created by the tourniquet) YOUR ANSWER

The use of a tourniquet may temporarily increase venous pressure and help engorge the veins, making them more visible and accessible for venipuncture. However, the positive pressure generated does not assist in the filling of the blood collection tubes; instead, it is the negative pressure within the tubes that allows for the actual collection of blood.

D (The negative pressure within the tube) CORRECT

This choice accurately describes the mechanism behind blood collection tube filling. The negative pressure inside the tube creates a vacuum that draws blood from the vein once the needle is inserted and the tube is properly positioned. This is the crucial factor that ensures successful blood collection during venipuncture.

Conclusion

The filling of blood collection tubes during venipuncture is primarily facilitated by the negative pressure inside the tubes, which creates a vacuum effect. Other factors such as arterial pressure, venous pressure, or tourniquet application do not directly contribute to the blood collection process. Understanding this mechanism is essential for effective venipuncture and successful blood sample collection.

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