Abstract

Blood gas and acid base measurements are an essential means of assessing respiratory function and homeostasis. Blood levels of oxygen and carbon dioxide are closely related to and affected by acid base balance and electrolyte concentrations. This delicate balance can be altered by minute changes in respiratory patterns, body temperature, and metabolic demands. If unrecognized, severe consequences may result including neurologic or myocardial dysfunction and multiorgan failure. Blood gas evaluation has been reported for only a few nondomestic species.

Studies to evaluate blood gas parameters in bongo (Tragelaphus eurycerus) and eland (Tragelaphus oryx) antelope were conducted at The Audubon Center for Research of Endangered Species, the Audubon Park Zoo, and the Mt. Kenya Game Ranch. Thirteen adult female captive bongo, 11 adult female captive eland and six adult female free-ranging elands were bled under three different circumstances: 1) Manual restraint in a drop floor chute (Fauna Research Inc. Red Hook, NY, USA). 2) Manual restraint following sedation. Animals received haloperidol (Geneva Pharmaceuticals Inc. Broomfield, CO, USA) at an approximate dose of 1 mg/kg per OS SID for 3 days prior to sampling and 3 hours prior to restraint on the day of sampling. 3) Chemical immobilization using narcotic combinations of carfentanil-xylazine, etorphine-xylazine, carfentanil-xylazine-ketamine, or etorphine-xylazine-ketamine delivered intramuscularly via dart to produce sternal recumbency. Oxygen was supplemented intra-nasally (3–5 L/minute) in 25 of 35 immobilization events.

Samples were collected from the caudal auricular artery via a 20-ga needle into pre-heparinized syringes. Analyses were done within 10 minutes of collection using an I-STAT portable blood gas analyzer (I-STAT Corporation, Princeton, NJ, USA), or an IRMA blood analysis system (Diametrics Medical Inc. St. Paul, MN, USA) or stored on ice for 3 hours and analyzed using CIBA-Corning 283 pH/blood gas analyzer (Bayer Diagnostics, Diagnostic Division Tarrytown, NY, USA). Parameters evaluated were pH, P_aCO₂, P_aO₂, HCO₃ˉ and base excess (BE). Values were compared to acid base normals established for domestic cattle (Table 1).

Table 1. Domestic cow reference values (George 1994)

Statistical Methods

The blood gas data were considered continuous and were evaluated for normality using the Kolmogorov-Smirnov test with the null hypothesis of normality rejected at p<0.05.

Analyses were performed to compare arterial blood gas data for manual, haloperidol, and immobilized groups excluding animals with nasal oxygen supplementation. Within group comparisons for the immobilization group were made at time 0 between animals supplemented and not supplemented with nasal oxygen. In addition, paired comparisons were made between time 0 and time 30 for animals supplemented and not supplemented with oxygen. Multiple events on the same animals were averaged.

Data that followed a normal distribution were compared between multiple groups using a one way, fixed effect, analysis of variance. Where groups were different, multiple comparisons were performed using Tukey’s test with experiment-wise error set at alpha = 0.05. Data were compared between two groups using a t-test. Data that did not follow a normal distribution were compared between multiple groups using the Kruskall-Wallis test. Where groups were different, multiple comparisons were performed using Dunn’s method with experiment-wise error set at alpha = 0.05. Data were compared between two groups using the Wilcoxon Rank Sum Test. Paired comparisons were made using a paired t-test for normal data and a Sign rank test for non-normal data.

All tests were performed against a two-sided hypothesis (SigmaStat v 5.0, SPSS Science, Tallahassee, FL). A p<0.05 was considered significant.

Results and Discussion

Results are reported in Table 2. Samples from all manually restrained bongos and elands indicated metabolic acidosis (pH<7.35 and HCO₃ˉ<20). Hypocapnia (P_aCO₂<35) was observed in six of seven animals reflecting the expected compensatory response.

Table 2. Blood gas measurements in bongo and eland using three different restraint methods.

Haloperidol treated manually restrained animals (two bongos and one eland) maintained a normal pH status and oxygenation but had a lower HCO₃ˉ (mean = 13.95) and BE (mean = -8.95) when compared to the manually restrained acidotic animals. It is likely that haloperidol treated animals were able to compensate for the acid production (most likely lactic acid) by lowering P_aCO₂ to <35, whereas compensatory mechanisms in manually restrained animals were overwhelmed.

Normal acid base values were observed in 42% of the immobilization events. Forty-one percent of the oxygen supplemented animals had a P_aO₂≤92 mm Hg, whereas all unsupplemented animals were hypoxemic. In 44% of the events, animals had a respiratory acidosis (pH<7.35 and P_aCO₂>44) but showed little compensation (HCO₃ˉ>30), presumably, because these disturbances were slight or moderate. Two elands exhibited a respiratory alkalosis (pH>7.45 and P_aCO₂<35). One was euthanatized due to capture myopathy. One eland exhibited a metabolic alkalosis (pH>7.45 and HCO₃ˉ>30). This animal died the day following immobilization and was found to have an enlarged, flaccid heart. Histopathology was not performed. Arterial pH, PCO₂, and HCO₃ˉ were much closer to normal in the majority of the immobilized animals vs. the manually restrained animals that had a more severe metabolic acidosis. Haloperidol, an anti-anxiety drug used in humans, may have reduced stress during manual restraint allowing animals to maintain a normal acid base balance. Further evaluation of acid base status under various restraint condition is encouraged. A flow chart to facilitate acid base interpretation is included (Fig. 1).

Figure 1 Acid base interpretation flow chart.2

Literature Cited

1.  George JW. Water electrolytes and acid base. In: Duncan RJ, Prasse KW, Mahaffey EA, eds. Veterinary Laboratory Medicine Clinical Pathology, 3rd ed. Ames, IA: Iowa State University Press; 1995:94–111.

2.  Wingfield WE. Acid-base disorders. In: Veterinary Emergency Secrets. Philadelphia, PA: Hanley and Belfus, Inc.; 1997:288–293.