When calculating total blood volume for a full-term, 2-day-old infant, which of the following information should a phlebotomist consider?

Choice A Reason:
For blood donation, a 16- to 18-gauge needle is typically used because it is large enough to allow the rapid flow of blood without causing hemolysis (destruction of red blood cells). The larger gauge needle also helps in minimizing the time the donor has to spend during the donation process. Using a needle that is too small could slow down the blood flow and potentially damage the blood cells, which is not ideal for the recipient of the blood donation.

Choice B Reason:
A 19- to 21-gauge needle is commonly used for routine venipuncture but is not ideal for blood donation. These needles are smaller than the 16- to 18-gauge needles and would not facilitate the quick collection of the volume of blood typically required for a donation. They are more suitable for collecting blood samples for testing rather than for donation purposes.

Choice C Reason:
A 22- to 24-gauge needle is even smaller and is often used for patients with smaller veins, such as children or elderly patients. These needles would not be appropriate for blood donation as they could significantly slow the blood flow and increase the donation time, which could be uncomfortable for the donor.

Choice D Reason:
A 25- to 28-gauge needle is the smallest size commonly used in medical practice and is suitable for patients with extremely small or fragile veins. These needles would be impractical for blood donation due to their small size, which would not allow for the efficient flow of blood required for a donation.

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.