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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
Choice A Reason:
The red top tube is typically used for serum determinations in chemistry, serology, and blood bank. It contains no additive or may contain a clot activator. The red top tube is not the first choice for capillary puncture order of draw because it is designed for tests that require serum and not whole blood.
Choice B Reason:
The lavender top tube is used for whole blood hematology determinations, as it contains EDTA as an anticoagulant. According to the order of draw for capillary punctures, the EDTA tube should be collected first to ensure adequate volume and accurate hematology test results. This makes the lavender top tube the correct choice for the first collection in this scenario.
Choice C Reason:
The light blue top tube contains sodium citrate and is used for coagulation tests. In venipuncture, it is drawn after the blood culture bottle and before other tubes to prevent contamination with additives from other tubes. However, for capillary punctures, it is not the first choice as hematology tests take precedence.
Choice D Reason:
The royal blue top tube is used for trace element, toxicology, and nutrient determinations². While it may be used for lead and toxicology screens mentioned in the question, it is not the first tube to be drawn in a capillary puncture sequence. The EDTA tube (lavender top) is drawn first to prevent clotting and ensure accurate CBC results.
Correct Answer is A
Explanation
Choice A reason:
Asking another phlebotomist to obtain the specimen is a prudent step after multiple unsuccessful attempts. It can reduce the patient's discomfort and anxiety. A fresh perspective from another professional might increase the chances of a successful draw, especially in challenging situations like small, fragile veins often found in diabetic patients.
Choice B reason:
Performing the draw on a foot is not typically recommended due to the increased risk of infection and complications, especially in diabetic patients who may have reduced sensation and slower healing in their extremities. This option should only be considered when other more proximal sites have been deemed unsuitable.
Choice C reason:
Repeating the draws until successful is not advisable as it can cause undue stress to the patient and increase the risk of hematoma or vein damage. It is essential to minimize the number of attempts to prevent patient discomfort and potential complications.
Choice D reason:
Performing the draw on a leg is another option that is generally avoided unless absolutely necessary, due to similar reasons as drawing from a foot—risk of infection and complications. Additionally, it can be an uncomfortable position for the patient.
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