Comparison of Gravity Collection Versus Suction Collection for Transfusion Purposes in Dogs
Blood donation is an essential step in transfusion medicine that must take into account the donor’s welfare, collection effectiveness, and blood product quality. This prospective study enrolled 13 canine blood donors, each subjected to both gravity and suction collection methods, in a randomized order. Clinical parameters, including heart rate (HR), respiratory rate (RR), systolic blood pressure (SBP), and rectal temperature (RT), were evaluated at four time points, including when the donor was on the floor and on the collection table, and before and after blood donation. The number of times the donor and needle required repositioning, the duration of the donation, the noise created by the apparatus, and the presence of a hematoma were evaluated. The weight, index of hemolysis, and hematocrit of each unit of blood were recorded. There was no significant difference between collection methods for either the clinical parameters at each time point or the prevalence of hematoma formation, the frequency of needle repositioning, the hemolysis index, or hematocrit. Collection by suction was noisier (P < 0.0001), faster (P = 0.004), and associated with significantly less donor repositioning (P = 0.007). Suction appears to be a safe and cost-effective method that should be considered to optimize blood donation.
Introduction
Blood transfusion is an important therapeutic ally in emergency and critical care medicine. Fortunately, it does not require sophisticated equipment. Blood donation is a pivotal step that must be performed while ensuring both donor welfare and optimal quality of the blood product. In veterinary medicine, blood collection may be achieved by either gravity or suction.1–5 Blood collection by gravity is a relatively easy procedure that can be performed in any veterinary facility. Collection by suction is faster than gravity and consequently appears to be an attractive option, especially in veterinary hospitals with a significant demand for blood products.1,3,4,6 To the authors’ knowledge, although several papers and book chapters refer to a suction-based method of blood collection, the quality of the blood product obtained has only been reported in one abstract.1,3,5,6 In addition, no information is available concerning the impact of the technique on the welfare of the blood donor. The aims of this study were to confirm that blood collection by suction does not alter the quality of the blood product and to evaluate the impact of suction blood collection on the welfare of blood donors.
Before implementing the suction method for blood collection, the blood bank of the Faculty of Veterinary Medicine, University of Montreal, decided to establish its impact on already enrolled canine blood donors and on the resulting blood product. The authors wanted to evaluate whether faster collection was associated with significant hypotension in the donor. In addition, the noise generated by the suction apparatus may cause more stress to the donor, an important factor to consider if sedation is not encouraged. Furthermore, mechanical injury to red blood cells and hemolysis may occur in the collection bag due to significant aspiration velocity.7 Similarly, an increased red blood cell fragility was reported when using certain volumetric and syringe pumps during blood administration.8 This prospective study was conducted to evaluate the efficacy of suction versus gravity-based methods of blood collection and to examine their comparative effects on the canine blood donors and on the blood products produced.
Materials and Methods
Participants
Thirteen canine blood donors enrolled in the blood bank of the Faculty of Veterinary Medicine, University of Montreal, participated in this prospective study from November 2009 to March 2010. Participants were subjected to both blood collection methods (i.e., gravity and suction). The order for blood collection method was done randomly (i.e., the dogs were numbered sequentially and then randomly allocated either to suction followed by gravity [n = 7] or gravity followed by suction [n = 6] in a near 1:1 ratio). All dogs were healthy according to previously published blood bank guidelines.3,5,9,10 As part of the donor program, complete blood count and serum biochemistry profile were performed annually and were within normal limits. All participants tested negativea for Ehrlichia canis, Anaplasma phagocytophilum, Borrelia burgdorferi, and Dirofilaria immitis and were up-to-date on vaccinations and deworming.
Dogs enrolled in the Canine Blood Donor Program are selected based on their calm and docile disposition as no sedation is used for blood collection. The Canine Blood Donor Program has an established Animal Use Protocol approved by the Ethical Committee of the Faculty of Veterinary Medicine, University of Montreal. Each donation was standardized using the same protocol.
Blood Collection Protocol
Before blood donation, all canine blood donors received a physical exam and their packed cell volume and total solids were determined. The jugular vein area was clipped and the side prepared was recorded to alternate sides at each donation. A topical anesthetic gelb was applied 30–45 min before venipuncture. The dogs were walked outside and allowed to become accustomed to the blood donation room for 5–10 min before collection. For the purpose of this study, a first set of measurements was performed on the floor (PRE-FLOOR). For blood donation, the dogs were placed in lateral recumbency on the donation table. A second set of physical parameters was collected at that point (PRE-TABLE). Cleaning and disinfection of the jugular venipuncture site was performed using a chlorhexidine-based productc. The same phlebotomist (J.B.) and veterinarian collecting the physical parameters data (B.C.) were used throughout the study. Two animal care attendants participated in the study, but care was taken so that the same person handled each dog for both collection methods.
An electric mixer with an integrated scaled was used to collect blood by gravity. For blood collection by suction, a vacuum chambere set above a digital scalef and connected to a vacuum wall mount was used. Depression of the vacuum was set at 101.6 mm Hg for each donation. Triple bags in closed circuitg were used for both collection methods.
The duration of each donation was recorded, from the time of puncture of the jugular vein until the blood collection was completed (i.e., when about 450 mL of blood had been collected or if the blood flow had stopped and a minimum of 425 mL of blood had been collected). More precisely, when collecting blood by gravity, the blood donation automatically ceased when 450 mL of blood filled the bag (weighing 473 g) as the electric blood mixer had an automated device that blocked the collection line at that point, preventing additional blood collection. When collecting by suction, the plastic vacuum chamber was placed on a digital scale. Tarring the scale to 0 was performed after the onset of the suction while the collection line remained clipped, just prior to venipuncture. The collection line was manually clipped when the phlebotomist observed that a minimum of 450 g of blood had been collected by suction.
Following the removal of the needle, compression of the venipuncture site was maintained for 3 min. During that time, a third set of physical parameters was collected (POST-TABLE). The venipuncture site was then rinsed with clear water and inspected for the presence of a hematoma. The blood donor was then placed on the floor and a last set of measurements (POST-FLOOR) was collected. Finally, all dogs received a highly digestible canned food meal.
Data Collected for Each Canine Donor
Several parameters were evaluated to compare the impact of both collection methods on the donor. Heart rate (HR), respiratory rate (RR), rectal temperature (RT), and systolic blood pressure (SBP) were measured at four time points: on the floor and on the table before (PRE-FLOOR and PRE-TABLE) and after (POST-FLOOR and POST-TABLE) blood collection. As recommended by the American College of Veterinary Internal Medicine, an average of five consecutive measurements using a Dopplerh was used to assess the SBP.11–15
If the blood flow either decreased or stopped during the blood collection, the needle was either rotated or slightly withdrawn. The number of times the needle was repositioned was noted. Similarly, the number of times the donor was repositioned, which was defined as any movement (head, limbs, etc.) of the dog or any readjustment in restraint, was also recorded. The presence of a hematoma despite an extended compression of the puncture site for 15 min was also recorded.
Data Collected for Each Blood Product
The amount of hemolysis present in the collection bag was measured by the serum index of hemolysis, which is a semiquantitative measure determined by spectrophotometryi.14 The values of this index can range from 0 to 10j. For each index value, there was a corresponding interval value of serum hemoglobin, which was predetermined by the manufacturer (Table 1). This semiquantitative measurement of hemolysis, is an acceptable alternative to a quantitative method such as HemoCue and more accurate than simple visual evaluation.15–17
Hb, hemoglobin; ND, not detected.
The volume of blood collected was determined by weighing the collection bag at the end of each donation. The hematocrit of the unit of blood was assessed using blood from the collection line (“bag hematocrit”).
Evaluation of the Effectiveness of Each Method
In addition to recording the duration of each donation, the noise generated by each apparatus (i.e., the agitator and vacuum) was quantified using a sound level meterk at a distance of .5 m, 1 m, and 1.5 m from the equipment. Ten measures were collected for each device and each distance.
Statistical Analysis
A repeated-measures linear model with four time points (PRE- and POST-TABLE and PRE- and POST-FLOOR) and collection method as within-subject factors, was used for HR, RR, RT, and SBP. A priori contrasts were used to compare methods at different time points and to compare the time points within each method. A repeated-measures linear model with collection method as a within-subject factor was used for the number of donor and needle repositioning, the collection bag’s weight, the bag’s hematocrit, the duration of donation, and the collection output. Repositioning of the donor, the bag’s weight, and the duration of donation were used as individual cofactors. A repeated-measures linear model, with time points (PRE versus POST) and method as within-subject factors, was used for hematocrit values. A McNemar test was used to compare the prevalence of hematoma formation between the two collection methods. Statistical analyses were carried out using a software packagel, and the level of statistical significance was set at P < 0.05. The Bonferroni correction was used to adjust the α level because of multiple comparisons.
Results
Patients
Seven castrated males and six spayed females were included in this study. Age of the donors ranged from 2 yr to 8 yr (mean, 3.7 yr) and body weights ranged from 24.7 kg to 79.1 kg (mean, 34.7 kg). A variety of breeds were represented, including the German shepherd dog (n = 2), Siberian husky (n = 1), Australian shepherd (n = 1), Labrador retriever (n = 1), wirehaired pointing griffon (n = 1), Great Dane (n = 1), giant schnauzer (n = 1), and mixed-breed dog (n = 5).
All dogs had been enrolled in the Canine Blood Donor Program for a minimum of 4 mo (range, 4–22 mo; mean, 12.6 mo) and had participated in an average of 3.6 donations (range, 1–8 previous donations) collected by gravity before the beginning of the study. During the study, the average time between two donations was 62 days (range, 34–114 days). Seven dogs were dog erythrocyte antigen 1.1 positive and six were negative.
Assessing the Impact of Each Method on the Donor
No significant differences in mean HR, RR, RT, and SBP were found beteen collection methods for each given time point (Figure 1). When blood was collected by suction, the mean HR at POST-TABLE (119 beats/min) was significantly higher than at PRE-FLOOR (108 beats/min; P = 0.003).
Citation: Journal of the American Animal Hospital Association 49, 5; 10.5326/JAAHA-MS-5917
Mean SBP comparisons were performed at each time point for both collection methods to evaluate the donor stress in anticipation of the blood collection (i.e., PRE-FLOOR versus PRE-TABLE), the degree of hypotension (i.e., PRE-FLOOR and PRE-TABLE versus POST-TABLE), and the rapidity of resolution of the hypotension (i.e., PRE-FLOOR versus POST-FLOOR and POST-TABLE versus POST-FLOOR). The results and P values were summarized in Figure 2 for both methods.
![FIGURE 2. Systolic blood pressure (SBP) means at each time, in both methods (i.e., gravity [bold text] and suction [italic text]). The P values are reported for comparisons of SBP means for each time and for both methods.](/view/journals/aaha/49/5/301fig2.jpeg)
![FIGURE 2. Systolic blood pressure (SBP) means at each time, in both methods (i.e., gravity [bold text] and suction [italic text]). The P values are reported for comparisons of SBP means for each time and for both methods.](/view/journals/aaha/49/5/full-301fig2.jpeg)
![FIGURE 2. Systolic blood pressure (SBP) means at each time, in both methods (i.e., gravity [bold text] and suction [italic text]). The P values are reported for comparisons of SBP means for each time and for both methods.](/view/journals/aaha/49/5/inline-301fig2.jpeg)
Citation: Journal of the American Animal Hospital Association 49, 5; 10.5326/JAAHA-MS-5917
Donor repositioning was more frequent when blood was collected by gravity (mean, 4.7 times) compared with suction (mean, 0.1 times; P = 0.007). When comparing both methods, there were no statistical differences between the number of needle repositioning (gravity, 1.07 times; suction, 1.3 times; P = 0.82) or the prevalence of hematoma (gravity, 7.7%; suction, 7.7%; P = 1) as summarized in Table 2.
dB, decibel; Min–Max, minimum to maximum; NA, not applicable; SD, standard deviation.
Evaluation of Each Method on the Quality of the Blood Product
The blood bag weighed significantly more when collected by gravity (mean, 479 g) than when collected by suction (mean, 434 g; P = 0.002). Three blood donations were interrupted because of poor blood flow (gravity, 2; suction, 1; P = 0.56), although sufficient blood had been collected in all cases to respect proper anticoagulant/blood ratio.
The hemolysis index of all blood units was either 0 or 1, corresponding to a hemoglobin range of 0–0.5 g/L (Table 1). Although the prevalence of detectable hemolysis (hemolysis index = 1) was more frequent with the gravity collection (gravity, 23.08% [n = 3]; suction, 7.69% [n = 1]), the difference was not statistically significant (P = 0.32). The mean donor hematocrit prior to donation (gravity, 51.61%; suction, 51.71%; P = 0.88) and the mean hematocrit from the collection bag (gravity, 39.9%; suction, 39.9%; P = 1) were not different between the two methods. The average hematocrit was significantly higher before (51.59%) than after the donation (bag hematocrit, 39.9%) for both methods (P < 0.0001) as shown in Table 2.
Comparison of Each Method’s Effectiveness
The average duration of collection by suction (4 min 14 sec) was significantly shorter than by gravity (6 min 27 sec; P = 0.004). The average output of blood collection by suction (2.06 g/sec) was significantly faster (P = 0.005) than by gravity (1.32 g/sec). The average decibels (dB) emitted by the suction apparatus (at 0.5 m, 64.69 dB; at 1 m, 61.25 dB; at 1.5 m, 59.29 dB) was significantly higher than those emitted by the gravity apparatus (at 0.5 m, 62.03 dB; at 1 m, 58.58 dB; at 1.5 m, 58.8 dB) for all distances (at 0.5 m, P < 0.0001; at 1 m, P < 0.0001; at 1.5 m, P = 0.03) as shown in Table 2.
Discussion
Donation by suction appears to be a good alternative to donation by gravity, as suggested by previous studies.1,3,6,18 The suction method is safe for the donor, efficient, and does not alter the quality of the blood product.
The prevalence of vasovagal reactions during blood donation is approximately 2.8% in canine medicine and 2–3% in humans.1,2,9,19–21 In the current study, a significant decrease in SBP was recorded immediately following the donation (PRE-TABLE compared with POST-TABLE), but the average and individual SBP measurements remained > 80 mm Hg, the value below which glomerular filtration rate and cerebral perfusion may be compromised.13,22 Three dogs donating by gravity and five dogs donating by suction had a blood pressure ≤ 96 mm Hg immediately after the donation. The experienced hypotension was transitory, and all SBP returned to normal on POST-FLOOR measurements. No dog either showed signs of weakness or required medical attention. The risk of developing transient hypotension was not associated with age, sex, or weight of the donor (P = 0.36, 0.15, and 0.08, respectively). For both methods, the mean SBP immediately following blood collection (POST-TABLE) was significantly lower than the mean SBP at PRE-FLOOR (P = 0.0007 for gravity-based collection; P = 0.0001 for suction-based collection) and at PRE-TABLE (P < 0.0001 for both methods). There was no difference between both methods concerning the severity of the hypotension.
Similar to a previous study, the authors of this study noted a slight increase in the HR during suction-based blood collection.23 Increased HR is observed in the first phase of the human vasovagal reaction, associated with increased cardiac output and peripheral resistance. This situation corresponds to a stress and blood loss response. A vasovagal reaction is followed by a sudden vasodilation and bradycardia in response to a reduction in sympathetic activity and an increase in parasympathetic activity, respectively.2
Dogs enrolled in the Blood Bank of the Faculty of Veterinary Medicine, University of Montreal, are selected based on their calm disposition, as sedation is not used for blood donation. During the study, the donor was less likely to reposition itself when blood was collected by suction. This finding is likely related to the shorter duration of the procedure. In fact, despite being noisier, the donors tended to be more cooperative during the suction collection as they did not have time to become impatient. Objective parameters (HR, RR, RT, and SBP) were always measured by the same person to reduce bias created by multiple person evaluations.11 Subjective stress behavior parameters, including yawning, licking of the lips, self-grooming, and vocalization could have been evaluated to better appreciate stress experienced by the donor, and the videotaping of each donation would have improved the assessment of these behaviors.23,24 This study confirms that blood collection can be done safely in dogs without sedation, thereby removing an additional cause of hypotension.
Noise is a physical stress factor for an animal. Sounds over 70 dB are considered loud and those between 90 and 120 dB are considered to be in a critical zone.25 The noise generated by the suction was louder than the noise from the agitator, with peak levels of 65 dB. This value remains below the limit of 90 dB set by the Occupational Safety and Health Administration regulation for workers.26 However, because dogs are more sensitive to sound than humans, one should consider placing earplugs in the donors’ ears to further improve their welfare when using a suction device. During the study, all dogs became accustomed to the noise, despite the fact that none of them had been subjected to the suction device previously.
The prevalence of hematoma formation following blood donation was previously reported to be 4.2% in dogs and 0.35% in humans.9,19–21 Similarly, in this study, only one dog presented a persistent hematoma for each collection method (a prevalence of 7.9%).
The mean blood volume collected by suction was less than that collected by gravity, but it remained within the recommended limits for the amount of anticoagulant used (405–495 mL).5,6 This difference is likely related to a systematic problem with conversion from volume to weight rather than the inability to collect additional blood when using suction collection. The electric agitator, which takes into account that the specific gravity of whole blood is 1.053, automatically stops the blood collection after 450 mL of blood has been collected (corresponding to 475.2 g).6 With the suction-based method, the phlebotomist actively watched the scale and stopped the collection when 450 g of blood had been collected, which is equivalent to only 426 mL. As to be expected, the blood units’ mean weight was significantly less when the donation was ended because of poor blood flow (P = 0.04), but this was not responsible for the weight difference because only three donations were ended for this reason (gravity, 2; suction, 1; P = 0.56), all of which contained an acceptable anticoagulant/whole blood ratio for transfusion purpose.
The collection bag’s hematocrit did not differ between methods (P = 1): however, with both methods, the collection bag’s hematocrit was less than the donor’s hematocrit. (P < 0.0001). Although we do not have an explanation for this finding, it is unlikely that the lower collection bag’s hematocrit was the result of red blood cell destruction during collection because the semiquantitative hemolysis index measured (between 0 and 1) was considered negligible throughout the study. In fact, the hemolysis index did not differ between collection methods and the maximum percentage of hemolysis observed during blood collection by suction was 0.23% ([100−Ht] × Hb/ total Hb), which is well below the recommendation for humans determined by The Council of Europe (0.8%) and the U.S. Food and Drug Administration (< 1%).27
Several suction-based protocols for canine blood collection suggest using negative pressure ranging from −127 to −177.8 mm Hg, but the impact on the blood product and the blood donors has not been established.4,6 In the current study, the negative pressure generated by the vacuum was set at −101.6 mm Hg throughout the blood collection by suction, leading to a fast, but well tolerated, blood donation and negligible hemolysis.
Study limitations include small sample size and lack of blinding. Indeed, the technical team may have been biased by their perception of how stressful each method was, but this potential risk was minimized by randomization and by a standardized technical protocol. In addition, it would have been ideal to assess other quality-control parameters for the blood products obtained, such as red blood cell osmotic fragility testing and red blood cell half-life following blood collection.9
Conclusion
Suction-based blood collection is a fast, cost-effective method that is safe both for the canine blood donor and the blood product when using a reasonable negative pressure (−101.6 mm Hg). This procedure should be considered as an alternative to gravity-based collection to minimize the duration of the blood collection and the stress experienced by the donor.
Comparison of heart rate (A), respiratory rate (B), rectal temperature (C), and systolic blood pressure (D), of canine donors undergoing blood donation by either gravity or suction at four different time points. Means and standard deviations are shown. No statistical differences of the means of the four variables were noted between the two groups at each of the four times. With suction, the mean POST-TABLE (*) was significantly higher than PRE-FLOOR (*) for heart rate.
Systolic blood pressure (SBP) means at each time, in both methods (i.e., gravity [bold text] and suction [italic text]). The P values are reported for comparisons of SBP means for each time and for both methods.
Contributor Notes
