Blood collection tubes fill correctly during venipuncture due to which of the following factors?
The high pressure in the arterial system
The high pressure in the venous system
The positive pressure created by the tourniquet
The negative pressure within the tube
The Correct Answer is D
Choice A reason:
The high pressure in the arterial system is not a factor in the filling of blood collection tubes during venipuncture. Arterial blood is not typically collected using evacuated tubes; these are used for venous blood collection, where the pressure is lower.
Choice B reason:
While the venous system does have pressure that aids in blood flow, it is not the high pressure that causes blood collection tubes to fill. Venous pressure is relatively low compared to arterial pressure, and on its own, it is not sufficient to fill the vacuum tubes used in venipuncture.
Choice C reason:
The positive pressure created by the tourniquet can help engorge the veins, making them easier to access, but it does not directly cause the blood collection tubes to fill. The tourniquet's role is to assist in vein visualization and palpation rather than in the filling of the tube.
Choice D reason:
The negative pressure within the tube is the correct factor that causes blood collection tubes to fill during venipuncture. When the needle punctures the patient's vein and then the tube stopper, the vacuum in the tube pulls blood into it until the vacuum is exhausted or the tube is filled. This is why it is essential not to allow the tube contents to contact the stopper, as backflow into the venous system can cause adverse reactions.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Choice A Reason:
Shaking the tubes vigorously can cause hemolysis, which is the rupture of red blood cells, leading to inaccurate test results. It is not recommended as it does not provide gentle mixing and can damage the blood cells.
Choice B Reason:
Moving the tubes in a figure-eight motion is not a standard practice for mixing blood samples. This method may not provide the consistent and gentle inversion needed to mix the anticoagulant with the blood effectively.
Choice C Reason:
Rolling the tubes between the palms of the hands 4 to 8 times after collection is the recommended method. This technique allows for gentle and thorough mixing of the blood with the anticoagulant, preventing clotting without causing hemolysis. The number of inversions ensures that the anticoagulant coats the inner surface of the tube and mixes with the blood, which is essential for accurate laboratory results.
Choice D Reason:
Passing the tubes from hand to hand is not an effective method for mixing blood samples. This action may not provide the necessary inversion and can lead to inadequate mixing, resulting in clotted specimens.
Correct Answer is D
Explanation
Choice A Reason:
Withdrawing the needle completely would be an incorrect action because it would end the procedure prematurely and require a new venipuncture, causing unnecessary discomfort to the patient. It should only be done if the venipuncture has been completed or if there is a need to stop due to a complication.
Choice B Reason:
Rotating the bevel of the needle could potentially reposition the needle for better blood flow if it has become occluded or is not properly aligned with the vein. However, this action should be done with caution to avoid causing injury to the vein or discomfort to the patient.
Choice C Reason:
Increasing tourniquet pressure is not advisable once blood flow has been established, as it could cause damage to the vein or hemolysis of the blood sample. The tourniquet should be released once the blood starts flowing into the first tube to avoid these issues.
Choice D Reason:
Activating a new evacuated tube is the correct action to take when blood flow stops upon attaching a second tube. This could indicate a problem with the vacuum in the tube rather than with the needle or the venipuncture site. Trying a new tube can resolve the issue without needing to adjust the needle or the patient's position.
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