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Transfusion Medicine. Jeffrey McCullough
Читать онлайн.Название Transfusion Medicine
Год выпуска 0
isbn 9781119599562
Автор произведения Jeffrey McCullough
Жанр Медицина
Издательство John Wiley & Sons Limited
Venipuncture
Most blood collection equipment uses 16‐ or 17‐gauge needles, and the entire set is closed and connected so that the needle is integral. The venipuncture is done with a needle that can be used only once to avoid contamination. The phlebotomist must be aware of the needle placement to minimize the likelihood of puncturing a nerve or artery.
Blood collection
Usually the blood container is placed on a scale, which may have a device to cut off the flow when the container reaches a set weight indicating that the desired volume of blood has been collected. The blood must flow freely and be mixed with anticoagulant frequently as it fills the container to avoid the development of small clots. Blood banks often use mechanical devices that continuously mix the blood and anticoagulant during phlebotomy. No more than 15% of the donor’s estimated blood volume should be collected, and the limit of 10.5 mL/kg body weight [1] is intended to meet this limit. In addition, the volume of blood in the container should be between 405 and 550 mL (i.e., 450 or 500 mL ± 10%). Thus, including specimens for testing, the amount of blood drawn could total 575 mL. Units containing 300–404 mL can be used for transfusion but must be labeled as low‐volume units. The amount of blood withdrawn must be within prescribed limits to be in the proper ratio with the anticoagulant, otherwise the blood cells may be damaged or anticoagulation may not be satisfactory (see Chapter 5).
The actual time for phlebotomy and bleeding is usually about 7 minutes and almost always less than 10 minutes. If the blood flow is slow, clots may form in the tubing before the blood mixes with the anticoagulant in the container. Although there is no FDA‐defined maximum allowable time for the collection of a unit of blood, most blood banks establish a maximum, usually no more than about 15 minutes. There is no difference in factor VIII or platelet recovery between units collected in less than 8 minutes versus those collected in 8–12 minutes [51]. Extremely rapid, pulsatile blood flow or the appearance of bright red blood may indicate an arterial puncture. This can be confirmed by feeling the pressure building in the blood container. An arterial puncture is nearly unmistakable because of the very rapid filling and pressure that develops in the blood container.
During blood donation, there is a slight decrease in systolic and a rise in diastolic blood pressure and peripheral resistance, along with a slight decline in cardiac output but little change in heart rate [52]. The regional cerebral oxygen saturation decreases significantly but still remains within the range of individual physiologic variation, while the cerebral tissue hemoglobin concentration increases significantly, probably because of an increase in cerebral blood volume, which appears to be the major compensation mechanism during acute blood loss to maintain cerebral oxygenation [53].
At the conclusion of blood collection, the needle is removed and the donor is asked to apply pressure to the vein in the antecubital fossa for at least 1 or 2 minutes. Many blood centers have a policy of asking the donor to raise his or her arm to minimize the venous pressure while pressure is applied to the vein. When there is no bleeding, discoloration, or evidence of a hematoma at the venipuncture site, the donor should be evaluated for other symptoms of a reaction to donation. If none is present, the donor can move off the donor table to the refreshment area. The donor should be observed during this time, because the movement into an upright posture may bring on lightheadedness or even fainting.
4.4 Postdonation care and adverse reactions to blood donation
Postdonation care
Many donor reactions, especially lightheadedness or syncope, may occur when the donor is having refreshments. Donors are advised to drink extra fluids to replace and maintain lost blood volume. The nature of the fluid is generally left to donor discretion, except that alcoholic beverages are not recommended. Alcohol is a vasodilator and may cause a shift of blood flow to the periphery, resulting in reduced cerebral blood flow and hypotension or fainting. Even after the loss of a few hundred milliliters of blood, some donors are subject to lightheadedness or even fainting if they change position quickly. Therefore, donors are also advised not to return to work for the remainder of the day in an occupation where fainting would be hazardous to themselves or others. Likewise, donors are also advised to avoid strenuous exercise for the remainder of the day [54]. This may also minimize the chance of hematoma development at the venipuncture site.
Adverse reactions
Reactions have been associated with approximately 4% of blood donations, although many either occur or are first noticed when the donor is off‐site, which complicates accurate reporting. Fortunately, most reactions are not serious [55–57]. Minimizing donor reactions begins with the selection of the site for blood collection, the staff training, the general treatment the donor receives from the staff, and the ambience of the blood collection situation. These factors are important because reactions increase when the blood collection situation is crowded, noisy, or hot, or when the donor endures a long wait. Donors who have reactions are more likely to be younger [58, 59], to be unmarried, to have a higher predonation heart rate and lower diastolic blood pressure, and to be first‐time donors or to have donated fewer times than donors who do not experience reactions [59].
Adverse reactions to whole blood donation can be categorized generally as those due to: (a) hypovolemia, (b) vasovagal effects, and (c) complications of the venipuncture (Table 4.4). The most common symptoms of reaction to blood donation are weakness, cool skin, diaphoresis, and pallor. A more extensive but still moderate reaction may involve dizziness, pallor, hypertension, hypotension, and/or bradycardia. Bradycardia is usually taken as a sign of a vasovagal reaction rather than hypotensive or cardiovascular shock, in which tachycardia would be expected. The vasovagal syndrome can have detrimental effects on blood donors and the blood supply [60, 61]. The most common cause of these symptoms is probably due to the psychological stress of the situation or to neurologic factors rather than hypovolemia caused by loss of blood volume. In the past, a common response to a donor reaction was to have the donor rebreathe into a paper bag. This is effective only if the lightheadedness is due to hyperventilation and reduced bicarbonate levels. Most reactions do not have this basis, and the paper bag may only add to the tension of the situation. This is not recommended as routine practice, but should be reserved for situations in which it seems clear that hyperventilation is a major part of the reaction. Other systemic reactions may include nausea, vomiting, and hyperventilation, sometimes leading to twitching or muscle spasms, convulsions, or serious cardiac difficulties. These kinds of serious reactions are rare. Several strategies have been used to reduce donor reactions, especially in populations of young, first‐time donors, such as 16‐to 17‐year‐old students, who are seen as important to building a future donor base [62]. Intervention strategies studied include predonation education, distraction, and additional water intake, which can reduce the rate of vasovagal reactions [63–65]. Minimizing donor reactions is very important because donors who experience adverse reactions are less likely to return [60, 66, 67].
Table 4.4 Adverse reactions to whole blood donation.
| Hypovolemia | Syncope |
| Lightheadedness | |
| Diaphoresis | |
| Nausea | |
| Vomiting | |
| Vasovagal effects |
|