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Keywords:

  • acid-base;
  • blood gas;
  • blood pressure;
  • HBOCS

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. Footnotes
  9. References

Objective – To establish the efficacy of Oxyglobin (HB-200) in canine babesiosis and compare it to standard therapy, packed red blood cell transfusion (pRBCT) with respect to improvements in specific parameters of blood gas, acid-base, blood pressure, and subjective evaluations.

Design – Prospective, randomized, clinical trial.

Setting – Onderstepoort Veterinary Academic Hospital.

Animals – Twelve dogs (8–25 kg) naturally infected with Babesia rossi and a hematocrit of 0.1–0.2 L/L (10–20%).

Interventions – Treatment groups were randomized to receive either 20 mL/kg of Oxyglobin or pRBCT over 4 hours via a central venous catheter. Transfusions were followed by lactated Ringer's solution infusion. Rectal temperature, femoral arterial and mixed venous blood sampling, oscillometric blood pressure, and subjective assessment of patient status (habitus), and appetite were performed at time points 0, 1, 4, 8, 24, 48, and 72 hours.

Main Results – Dogs presented with a hypoalbuminemic alkalosis; hyperchloremic, dilutional acidosis; normotensive tachycardia; pyrexia; depression; and anorexia. Both treatments produced similar results, with the exception of significant differences in pH (4 h); PCO2 (4 h); hemoglobin (8 h, 24 h); mean arterial pressure (48 h); albumin (4 h, 8 h); habitus (8 h, 48 h); and appetite (24 h). Arterial O2 content was higher for pRBCT than Oxyglobin at 72 hours, but central venous PO2 did not differ between groups or over time and was consistently subnormal.

Conclusions – Oxyglobin provides similar overall improvements to pRBCT in dogs with anemia from babesiosis, with respect to blood gas, acid-base and blood pressure, although patients receiving packed cells tended to have more rapid normalization of habitus and appetite.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. Footnotes
  9. References

Anemia caused by the hemoprotozoan Babesia rossi in the dog is an important cause of morbidity and mortality in South Africa.1–4 The other consequences of this severe anemia include tissue hypoxia, acid-base disturbances, hypotension, and malaise.2,3,5,6 Blood transfusion addresses many of these problems by improving oxygen carrying capacity and intravascular volume; supporting blood colloidal pressure; and improving tissue perfusion. Importantly, blood replacement normalizes the body's buffering capacity, which is crucial in states of lactic acidosis and mixed acid-base disturbances and which is depleted in states of severe anemia.7 Blood transfusion has been a cornerstone in the treatment of this disease in South Africa for over 40 years.7,8

The advance of novel transfusion technologies promises to deliver many of the benefits of blood transfusion, with fewer associated risks.9 Use of hemoglobin-based oxygen-carrying solutions (HBOCS) in the treatment of hemoprotozoal anemia has not been studied in a clinical trial. Oxyglobin (HB-200) is the first and only licensed veterinary HBOCS. A similar product for use in humans (Hemopure [HB-250]) is also available in South Africa. Some studies have demonstrated HBOCS corpuscle-free, polymerized hemoglobin structure is capable of providing equal or superior benefits for anemic patients in comparison to isovolumic packed red blood cell transfusions (pRBCT) for traumatic injury and a number of disease states,4,10–12 while others have showed its inadequacies.5,13–15 The advantages of a stroma- or corpuscle-free transfusion solution include absence of transfusion reactions, reduced disease transmission risk, improved shelf life, and no need for refrigeration.

The efficacy of Oxyglobin has never been prospectively demonstrated for canine babesiosis. There have been some concerns regarding the safety profile of HBOCS, particularly with regards to their nitric oxide (NO) scavenging and subsequent hypertensive effects and a possible association with increased mortality.14–16 Other researchers have noted the almost complete absence of immunopathology caused by repeated Oxyglobin infusion or have refuted the teleological basis of the study by Barton and Grundy, which implied increased deaths with HBOCS transfusion.17–19

Canine babesiosis is endemic and widespread in South Africa and is the most common reason for admission to the Onderstepoort Veterinary Academic Hospital (OVAH) of the University of Pretoria's Veterinary Faculty.3,20 The high caseload combined with the severity of the endemic form of canine babesiosis (B. rossi) provided an ideal model for evaluation of comparative efficacy of Oxyglobin versus the current standard of pRBCT, for the alleviation of the anemia and blood gas and acid-base disturbances. Although Oxyglobin is described as an oxygen bridge, the study was not restricted to aspects of oxygenation alone as the pathogenesis of babesiosis includes severe acid-base perturbations.

The study hypothesis was that the transfusion of Oxyglobin would provide similar blood gas, acid-base, systemic blood pressure, and subjective clinical improvement in dogs with severe anemia caused by natural infection with B. rossi, compared with packed red cell transfusion.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. Footnotes
  9. References

Study population

Twelve dogs admitted through the Outpatients clinic of the OVAH between February 2005 and March 2006 with a thin capillary blood smear diagnosis of B. rossi.

Inclusion criteria

Dogs were included in the study if they had a hematocrit between 0.1 and 0.2 L/L (10–20%), were negative for insaline red cell agglutination, and were between 8 and 25 kg (18–55 lbs).

Exclusion criteria

Dogs with complicated forms of babesiosis (acute renal failure, immune-mediated hemolytic anemia, acute respiratory distress, cerebral forms, muscular and gut forms, pancreatitis), patients with hypoglycemia (blood glucose<3.3 mmol/L [60 mg/dL]), dogs with Ehrlichia canis coinfection or suspicion thereof, dogs <6 months of age, dogs on medication for a preexisting medical condition, or dogs showing intractable behavior, were excluded.

Selection and processing

The trial protocol was approved by both the Research and the Animal Use and Care Committees of the University of Pretoria (trial V001/04). Dogs were client-owned animals admitted to the OVAH and were enrolled in the trial with the owner's consent. Patients were then randomized using O- or B-marked cards in an envelope into 1 of the 2 treatment groups and cared for according to the standard protocols of the OVAH and stipulations of the Animal Use and Care Committee. A multilumen jugular cathetera was aseptically placed using local anesthesia and a jugular cut-down technique (standard protocol for this catheter type and in our institution). The first 2 mL of blood that was removed was replaced after all other samples had been collected. This was to prevent iatrogenic sampling-induced anemia. The baseline samples collected included 1 mL for venous blood gas analysis, 2 mL for serum chemistry analysis, and 1 mL in EDTA for baseline hematology; later sampling was only 1 mL for venous blood gas analysis. Arterial blood (1 mL) was collected from the femoral artery into a heparinized syringe, placed on ice and analyzed within 5 minutes of collection. Blood gas and acid-base analysis,b clinical chemistry,c and hematologyd were performed on baseline (t=0) samples. All reference intervals were established in the laboratory of the OVAH or obtained from a study by Leisewitz et al.21 Total hemoglobin rather than hematocrit/PCV was used as a measure of oxygen carrying capacity. The presence of Oxyglobin in the plasma confounded any reasonable attempts to use PCV as a measure with which to compare groups. With regard to respiratory compensation for acidosis, in order to determine if the drop in PCO2 was appropriate to the base deficit measured for each patient, the bicarbonate was compared at each time point for each patient. The differential between the expected respiratory compensatory response22 for nonrespiratory acidosis (0.7 mm Hg PCO2 decrease per 1 mmol/L HCO3 decrease) was calculated from the formula [(HCO3−18.7) × 0.7]−(PCO2−31.5) where 18.5 and 31.5 were the average values for the OVAH laboratory reference intervals. Oscillometric blood pressure readingse were taken 5 times (on the right antebrachium with patients in left lateral recumbency) simultaneously with a femoral pulse count by palpation, and readings averaged. Cuff width was estimated at 40% of the diameter of the proximal antebrachium. Rectal temperature was measured using the same digital thermometerf throughout the study.

A custom-designed, standardized rubric was used to grade habitus from 0 to 4 (0, moribund; 1, severely depressed; 2, depressed; 3, normal; 4, excitable), and a uniform dietg was fed according to the manufacturer's feeding guidelines. Appetite was also graded using a rubric (0, no interest; 1, licks food; 2, eats <50% of food offered in <10 min; 3, eats 50–100% of food offered; 4, eats all food and begs for more). After t=0 (baseline) samples were taken, dogs were treated with 3.5 mg/kg of intramuscular diminazene,h oral fenbendazole,i and topical fipronil-methoprene.j A packed red cell or Oxyglobin transfusion at 5 mL/kg/h for 4 hours was administered according to the randomization. Thus, patients in each groups received an identical transfusion volume. Researchers were not blinded to the treatment group once the random allocation had been made. After transfusion was complete, dogs were switched to maintenance rates of a lactated Ringer's solutionk for the remainder of the trial. Sampling and assessments were performed at 1, 4, 8, 24, 48, and 72 hours. Dogs were housed in the intensive care unit (ICU) of the OVAH for the remainder of the triall; all survivors were discharged from ICU at 72 hours.

Statistical analysis: Sample size was calculated using a software program.m Post-hoc power analysis was performed to validate that the tests used provided an 80% power at a P of <0.05 for all major parameters used, and their limits of detection. All statistical analyses were done using a software program.n Student t-tests with Welch's correction for unequal variances were used to compare pH, PCO2, PO2, central venous PO2 (CVPO2), HCO3, mean arterial pressure (MAP), plasma proteins, and anion gap (AG), at each of the 7 sampling times. Habitus and appetite were tested with Wilcoxon's rank sum test. Post hoc power analyses were done by using the average of all 14 means and standard deviations for each measurement (7 sampling times multiplied by 2 treatments).

Additionally, to control for confounding effects of treatment and illness on the subsequent measurements, an analysis of covariance (ANCOVA) was performed for each of the parameters. This was performed by fitting a linear model to the data (eg, pH at time t={b1+b2}×{pH at time t−1}+{b3× value}). b1, b2 and the residual standard error was calculated as the average for each of these values for the 7 sampling times. When b2 was not significant, it was deleted from the model and only the effect of treatment was retained. All models were checked for normality of errors and homoscedasticity. If these were violated, outliers were deleted or data transformed. Post-hoc power analyses for b3 were done using the average of all 7 means and standard deviations for each measurement time (combining treatments) to obtain a mean and standard deviation for time t−1.

The tests demonstrated that the study had 80% power to detect a difference of 0.056 units in pH, 8.26 mm Hg in PCO2, 18.7 mm Hg in PO2, 9.2 mm Hg in CVPO2, 5.8 mmol/L in HCO3, and 31.6 mm Hg in MAP.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. Footnotes
  9. References

Average patient age was 9 months (range, 6–48 mo) for pRBCT patients and 18 months (range, 7–36 mo) for Oxyglobin-treated dogs. Mean body mass was 20.45 and 15.31 kg (45 and 33.7 lbs, respectively). Eleven of 12 dogs completed the study. One dog in the Oxyglobin group (patient 11) died suddenly between 8 and 24 hours. A full postmortem and histopathology of all organs was performed by a veterinary pathologist.

Subjective criteria: habitus and appetite

Dogs entering the trial were uniformly depressed, pyrexic, and anorexic. Both groups' final temperature was significantly different to their initial temperature (Figure 1). Dogs receiving pRBCT were noticeably brighter and had a greater interest in food by 8 hours, than those receiving Oxyglobin. By 72 hours, this difference was no longer significant and the 2 patient groups were equivalent (Table 1). A significant difference in habitus (8–48 h) was noted, with pRBCT patients feeling better (Table 1).

image

Figure 1.  Patient rectal temperatures in Celsius. Significant differences (P<0.05) shown as *, #. Error bar=1 standard deviation.

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Table 1.   72-hour trends of habitus and appetite (median score)
 OBOBOBOBOBOBOB
  • Significant differences between groups indicated by

  • *,**,#,§

    (P<0.05).

  • O, Oxyglobin; B, pRBCT.

Time (h)00114488242448487272
Habitus1.521.52232*3*2**3**3#4#34
Appetite00000.53.50.500§3.5§33.533.5

Hemoglobin, blood gas, and acid-base status

Total hemoglobin levels had improved significantly by 72 hours (Figure 2). At 8 and 24 hours, pRBCT dogs had a significantly higher total hemoglobin than Oxyglobin-infused dogs. By 48 hours, there was no longer a significant difference between the 2 groups.

image

Figure 2.  Total hemoglobin with significant differences shown as symbols *, **, #, § (P<0.05). Error bar=1 standard deviation.

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All dogs entering the trial had a normal pH except dog 9 (Oxyglobin group, pH 7.2, PCO2 15.2 mm Hg and PO2 114 mm Hg), which returned to within the reference interval by 1 hour and recovered within the trial time frame. pH values also demonstrated a statistically significant difference between treatment groups (Figure 3). Some dogs were hypocapneic (PCO2<23.1 mm Hg) at baseline, but all had returned to within the laboratory reference interval by 72 hours (Figure 4). Only pRBCT-treated dogs had a significant increase in PCO2 during the trial, and were also less hypocapneic than Oxyglobin dogs at 4 hours (Figure 4). Although a few dogs in both groups were hypoxemic (PO2<74.2 mm Hg, Figure 5) at various times, this was never clinically significant and at no times were dogs deemed to be severely hypoxemic (PO2<50 mm Hg); thus, supplemental oxygen was never administered. Dog 11 developed peracute respiratory distress between 8 and 24 hours and died suddenly before an arterial blood gas sample could be collected. Pulmonary thromboembolism was suspected based on clinical signs and rapidity of death, but was not confirmed by the postmortem examination.

image

Figure 3.  pH values with significant difference shown as * value (P<0.05). Error bar=1 standard deviation.

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image

Figure 4.  PCO2 values with differences over time shown as * and between groups as # (P<0.05). Error bar=1 standard deviation.

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image

Figure 5.  PO2 values. Error bar=1 standard deviation.

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CVPO2 was decreased throughout the trial and did not increase or reach the reference interval (47.9–56.3 mm Hg) for either treatment group (Figure 6). Although results of arterial O2 content (aO2ct) were confounded by small sample sizes, significant differences existed between baseline and 72 hours in the pRBCT group (P=0.02). Significance was approached between the two groups at 24 hours (P=0.07) and 48 hours (P=0.052) and due to unequal variances at 24 hours, Student t-tests with Welch's correction were performed to take this into account. At baseline, aO2ct was 4.1±2.4 mL/dL for pRBCT-treated patients and 4.6±0.4 mL/dL for Oxyglobin patients, while at 72 hours it was 10.8±4 mL/dL for pRBCT and 6.0±3.7 mL/dL for Oxyglobin dogs.

image

Figure 6.  Central venous oxygen tension (CVPO2) values; no significant differences exist between groups or over time, and both groups were below reference intervals. Error bar=1 standard deviation.

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For all patients, bicarbonate and PCO2 means stayed within reference intervals (with some outliers), although they were different to initial values (Figure 7). As has been described in a previous study,21 dogs presented with mixed acid-base disorders generally identifiable by a normal pH, respiratory alkalosis, and evidence of compensation for the lactic acidosis. Statistical evaluation of the respiratory compensation for acidosis demonstrated that pRBCT 72 hours values were different to the initial values, while Oxyglobin-treated dogs' were not, although the groups differed from each other at 4 hours (Figure 8).

image

Figure 7.  Bicarbonate (HCO3) levels with significant differences over time (*, #) and between groups (§,†) (P<0.05). Error bar=1 standard deviation.

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image

Figure 8.  Differential between observed PCO2 and measured bicarbonate and the expected compensatory shift. Significant differences over time for pRBCT (*) and between groups (#) (P<0.05). Error bar=1 standard deviation.

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At no time was there a statistically significant difference between the AG values, and averages were uniformly below reference intervals (Figure 9). One patient (Oxyglobin group, patient 9) had a high AG from baseline to 4 hours, but then normalized. In conjunction with a low chloride gap (Figure 10), this acid-base state is classified as a hyperchloremic acidosis.21,23

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Figure 9.  Anion gap (AG). No significant differences exist. Error bar=1 standard deviation.

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Figure 10.  Chloride gap. No significant differences exist. Error bar=1 standard deviation.

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Plasma protein analyses

At presentation all dogs had a mild hypoalbuminemic alkalosis.21 A marked increase in total serum proteins, mainly attributable to hyperalbuminemia, was noted in dogs treated with Oxyglobin from 4 to 8 hours (Figure 11). By 24 hours, this difference was not significant again. The initial hypoalbuminaemia probably contributed most to the low AG for both groups.

image

Figure 11.  Plasma albumin and globulin levels. Significant differences shown as (*) or (#) between differing groups (P<0.05).

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Blood pressure and heart rate

In this trial, all dogs were noticeably tachycardic at admission, and significantly less so by 72 hours. The correlation obtained from a Pearson's product-moment analysis of the femoral pulse count and machine-measured data was strong (r2=0.86, P<0.001) indicating that the machine-measured pulse was accurate, and lending weight to oscillometric blood pressure measurements made simultaneously by the same device. At 4–8 hours, Oxyglobin patients' pulse rates rose again, and were significantly higher than those of patients receiving pRBCT. Diastolic blood pressure (DBP) was low for all patients at the outset, and systolic blood pressure (SBP) was high, giving a low-normal MAP. Through the trial, patients in the Oxyglobin group had higher blood pressure measurements although significance was only reached at 2 points (Figure 12).

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Figure 12.  Systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP). Significant differences between treatment groups shown as (*, #, §). (P<0.05).

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. Footnotes
  9. References

The babesiosis caused by the dominant Southern African species, B. rossi,24 is particularly virulent and thus serves as an excellent model for study of all the dog babesias and human falciparum malaria.2,25,26 The primary pathophysiology and most treatable aspect of infection is a severe anemia.7,27 Better understanding of the treatment responses of the more complex forms of babesiosis and falciparum malaria will hopefully flow from the observations made in this study.

All dogs in this study presented with moderate anemia; a mixed acid-base abnormality (respiratory alkalosis; hypoalbuminemic alkalosis; hyperchloremic acidosis; dilutional acidosis); pyrexia; anorexia; tachycardia; hemodynamic changes; and depression. The marked difference in total hemoglobin at critical time points (4 hours, 24 h) might justify the selection of pRBCT over Oxyglobin. The criteria for such a choice might be made based on many of the parameters evaluated in this study (eg, PCO2 or CVPO2). It is surprising that Oxyglobin did not elevate hemoglobin as much as or even more than pRBCT.

Siggaard-Andersen's28 method of assessing acid-base balance would have described these dogs as having a metabolic acidosis with compensatory respiratory alkalosis ‘with many hidden water and electrolyte disorders,’ and not ascribed the alterations as being due to the changes in water, electrolytes and proteins. In the face of a normal pH, this is evidently a gross oversimplification. A Stewart-based (strong ion difference [SID]) approach, however, draws attention to the law of maintenance of electroneutrality and the influences of strong ions and free water on the acid-base status.23

The Stewart-based approach expands the Henderson-Hasselbach philosophy of a ‘metabolic acidosis balanced by compensatory respiratory alkalosis’21–23 by including the influences of electrolytes, albumin, and free water. All dogs in this study had mixed acid-base disorders, although none as severe as those in the study by Leisewitz et al,21 probably because that study evaluated a broader range of dogs. In the current trial, all patients had a normal pH on presentation, but the respiratory compensatory drive was apparently mildly excessive (2.8±2.9 mm Hg) relative to the degree of base deficit, although not to the extent described in the more severe dogs in Leisewitz et al's 2001 study. Because overcompensation is not physiologically rational, this respiratory alkalosis indicates a mixed disturbance due to a respiratory alkalosis,22 but may also represent influences of the hypoalbuminemia on central respiratory receptors, hypotension, pulmonary afferent vagal influences, and peripheral oxygen sensor drives.21,29 What is important is the large difference in respiratory drive needed to compensate for the acidosis at 4 hours. Patients receiving pRBCT would be less likely to suffer ventilatory fatigue, while trying to maintain a normal blood pH. It is worthwhile noting that as long ago as 1976, Malherbe and colleagues stated that in canine babesiosis ‘[t]he “actual” pH of the blood [had] been found to be of less importance than the extent of base deficit.’30

CVPO2 was decreased in both groups and did not increase to within the normal range, even by trial completion. The mixed venous oxygen tension is an indicator of the end-capillary PO2. The greater the tissues' ability to extract oxygen, the lower the CVPO2, as this also represents the diffusion gradient from the capillary to the mitochondria in the tissues.31,32 These results suggest an increased oxygen extraction by the tissues in both treatment groups, and that neither treatment significantly decreased peripheral oxygen debt. Apart from acid-base disturbances, the derangements in lactate metabolism and evidence of tissue and organ hypoxia arising from SIRS33 imply altered tissue extraction of oxygen from the circulation. The best manner of assessing tissue oxygen extraction is evaluation of central venous oxygen.34,35 Another experimental study suggested that, during cardiopulmonary resuscitation in humans, mixed venous blood was superior to arterial samples, and better reflected tissue oxygen extraction from the circulation.31 It is a central tenet of the therapy of both babesiosis and malaria that tissue oxygenation be improved, and hypoxic tissues may not be able to extract oxygen from the circulation. Therefore, molecules with a right-shifted P50 (such as Oxyglobin or hemoglobin under the influence of the Bohr effect and 2,3-DPG), which offload O2 easier would aid cellular metabolism more. In both groups, aO2ct increased over the course of the trial, although only pRBCT group had a significant improvement over 72 hours. This was an unexpected finding, given that hemoglobin increased in both groups, as did clinical parameters. It might imply that Oxyglobin is not as effective an oxygen bridge as reported, or that some aspect of canine babesiosis either interferes with test results or oxygen carriage by Oxyglobin. Alternately, low sample numbers might have influenced results.

The analyzer employed only provided a calculated AG. In order for the Stewart approach to be used, the SID or strong ion gap (SIG) must be known. Although AG and SID/SIG are not synonymous, one study demonstrated an excellent correlation (r=0.91–0.99) between the corrected AG and SIG.36 Calculation of the corrected AG (and thus its substitution for SIG in interpreting the data using the Stewart technique) requires measurement of urate, lactate, and phosphate, which are not part of a standard veterinary acid-base study. Nonetheless, albumin contributes significantly to SID/SIG.36 Of the plasma proteins, only albumin is considered an organic anionic acid.23 Infusion of Oxyglobin led to significant increases in albumin during the early trial period, and artifactual albumin elevations may be due to high plasma Oxyglobin concentrations.o This is possible because it was only at the time of peak serum Oxyglobin concentration (4 h) that albumin differed between groups. Because albumin is a negative acute phase protein,37 it would be reasonable to expect a hypoalbuminemia at the outset for all dogs. Although the dogs evaluated by Leisewitz and colleagues generally fell into a more serious clinical subset of babesiosis, there was some overlap with dogs here. Both studies noted a high prevalence of hypoalbuminemia at admission (70% in Leisewitz et al,21 100% of 11 dogs so evaluated in this study). Using the Stewart terminology, all dogs admitted had a hypoalbuminemic alkalosis. Although globulins do not contribute to acid-base balance according to the Stewart approach,22,38 63% of dogs (7/11) in this study also presented with hyperglobulinemia, compared with 45% in the study by Leisewitz.21 The difference is small and probably unimportant, but reasons for this remain obscure.

The perturbations in albumin are also the most likely cause of the lack of a high AG despite the likelihood of hyperlactatemia.21 Nel and colleagues have demonstrated that babesiosis resulted in a lactic acidosis (probably a high AG acidosis), due to poor perfusion and oxygenation of tissues. The anaerobic conditions created by the anemia result in elevated lactate levels.3,6,7,8,21,22,27,36,37,39,40 Although this trial did not measure lactate concentrations per se due to analyzer substrate availability problems, it is reasonable to expect little deviation from previous results for hyperlactatemia in this condition. A hyperlactatemia in combination with albumin deviations might account, in part, for any AG abnormalities expected, although none were noted.21 Although endpoint lactates could not be determined, resolution of protein, acid-base and subjective criteria, as well as the results of Nel and many others would suggest normalization of lactate due to improved tissue oxygenation and perfusion, in both groups.40

In many respects, both treatment groups were equivalent at the outset and completion of the trial. Differences were noted during the interim, but particularly between the subjective parameters, hemoglobin, and PCO2. Speed of normalization was the key distinguishing difference between treatments, because both groups started without differences, and completed the trial without differences. The resolution of acidosis is a direct consequence of improved circulating volume; improved tissue oxygen delivery; improved hemodynamics; and removal of the inciting agent (the B. rossi parasite). Both treatments achieve this in a similar manner and time frame, although different pharmacological mechanisms were responsible for these similar end points.

The contrast between Oxyglobin- and pRBCT-treated dogs was most marked when the subjective assessment criteria were compared. Dogs in the pRBCT group had a near-normal appetite within 24 hours of admission, whereas those treated with Oxyglobin needed 72 hours to reach the same level of improvement. A slightly lesser effect was seen with regard to habitus. The possible reasons for this remain speculative. The difference argues strongly for positive effects of blood transfusion (other than simple volume and oxygen-carrying replacement). The eventual recovery and equivalence of Oxyglobin-treated dogs may be a result of the appropriate, endogenous, vigorous regenerative responses that would be present in all dogs with anemia from babesiosis. It may, however, also be postulated that the late improvement in the Oxyglobin-treated dogs was due to the completion of its excretion, and that some effect or component of the Oxyglobin actually suppressed appetite and habitus despite clinicopathological and blood pressure improvements.

The tachycardia is an appropriate physiological response to severe anemia. Babesiosis is well-described cause of the systemic inflammatory response syndrome and multiple organ dysfunction syndrome.41 Inflammatory cytokines,42 inducible NO,43 and hypoxemia may all result in a maldistributive state, if it were not for the appropriate physiological responses. All dogs maintained a normal MAP, although it may be seen that MAP remained largely within normal limits of 87–127 mm Hg established by Jacobson and colleagues.44–46

The lack of a clear difference between the 2 agents' effects on MAP (barring one divergence at 48 h) is noteworthy. This is despite the potent NO scavenging and inactivating properties of the Oxyglobin polymers, and their possible activity as endothelin-1 antagonists.13,16,46,47 NO is a potent vasodilator produced both constitutively and inductively by the vascular endothelium,45 and one would expect a NO scavenger to elevate blood pressure more than a less effective scavenger or placebo. In contrast, the findings of this study would imply that either these properties are less potent in this setting than others have proposed, or that isovolumic blood and Oxyglobin transfusions possess equivalence in this regard. Although the results showed that Oxyglobin did produce elevations in blood pressure (particularly in the first 8 h), obvious hypertension (SBP>184 mm Hg, MAP>138 mm Hg, diastolic blood pressure>113 mm Hg) did not occur. Even individuals' SBP never exceeded the borderline hypertensive cutoff values of Jacobson et al.45 Significant differences did not occur during this period due to wide variations in response between dogs causing overlapping data distributions. It is the authors' inference that although both treatments help to maintain and normalized hemodynamics, this benefit is similar and cannot be dissected out from the beneficial effects of the parasiticidal treatment, volume of transfusion, or some other effect. In fact, Jacobson et al45 showed that NO may not be as important in canine babesiosis as once speculated.

This particular study cohort was defined in order to limit the costs of the study (large dogs) and any danger to dogs arising from multiple sampling times (small dogs). Exclusion of all complicated forms of babesiosis allowed the cohort to be as homogenous as possible with respect to presenting abnormalities and demographics. It also allowed the study to retain a high degree of power despite a small sample size. It was not the authors' intention to study every aspect of the clinical efficacy of these remedies in all permutations of babesiosis, but rather to focus primarily on the treatment of the anemia caused by babesiosis as a disease, and on transfusion as the most important supportive treatment measure. The evaluation of changes in blood gas and acid-base status is a valid means of evaluating the efficacy of transfusion therapy for anemia.7 In this respect, the use of Oxyglobin in the management of canine babesiosis seems to have some promise. Clinicians could reasonably expect comparable blood gas, acid-base, and blood pressure improvement results to those produced by pRBC transfusion, with only transient differences in subjective criteria of assessment and certain parameters of oxygenation, hemoglobin, and respiration.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. Footnotes
  9. References

Our gratitude is extended to Dr V. Rentko, Mrs Elsbé Myburgh, the Onderstepoort Blood Bank Service, Prof. J. Schoeman, Prof. P. Stadler, Sr M. Maree, Sr Y. de Witt, Sr L. Coetzer, Prof. J. Greeff, Mr C. Murdoch, Dr E. Rozanski, Prof. A. Guthrie, and the veterinary students who assisted with sample collection at strange hours.

Footnotes

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. Footnotes
  9. References

aCS-22703-E triluminal catheter, Arrow International, Reading, PA.

bBlood Gas 865, Bayer Healthcare, Leverkusen, Germany.

cNexct, Alpha Wassermann, Bayer Healthcare.

dCell-dyne 3700, Abbott Laboratories, Queenborough, Kent, UK.

eCardell Model 9402 BP & SpO2 model, Minirad International, Orchard Park, NY.

fHartmann Thermoval Rapid, Hartmann Australasia, Homebush, NSW, Australia.

gHill's Prescription Diet a/d, Hill's Pet Nutrition, Topeka, KS.

hDizene, Virbac, Midrand, South Africa.

iPanacur BS, Intervet, Isando, South Africa.

jFrontline Plus, Merial SA, Halfway House, South Africa.

kSabax ringer lactate, Adcock Ingram Critical Care, Aeroton, South Africa.

lTrial V001/04.

nR Development Core Team (2005). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria.

oBiopure Corporation, Cambridge, MA.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. Footnotes
  9. References
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