Fluid therapy remains an essential treatment for ill reptiles, although best practices for fluid administration have not been established and controversy remains regarding the most appropriate electrolyte solution for dehydrated reptiles.1 Current recommendations include the administration of isotonic crystalloid solutions with a sodium concentration and pH similar to reptile plasma values.1 However, some authors recommend a nonlactated RRS, which is a 1:1 mixture of isotonic crystalloid solution and 5% dextrose solution, as the ideal rehydration fluid for reptiles.2 These recommendations have been made on the basis of the assumption that most fluid loss in reptiles is free water loss that should be replaced with a low-osmolarity electrolyte solution.2
Although the current reptile literature3 indicates that RRSs continue to be used as recommended, little research has been reported on whether those types of solutions are more appropriate for the treatment of dehydration than are other electrolyte solutions.4 In stranded juvenile loggerhead sea turtles (Caretta caretta), intracoelomic administration of a 1:1 mixture of 5% dextrose solution and saline (0.9% NaCl) solution (20 mL/kg, q 24 h for 3 doses) versus other evaluated electrolyte solutions resulted in hyperglycemia and an increased incidence of metabolic derangements in blood gas values.5
Historically, administration of LRS has not been recommended for reptiles because of concern that this would lead to hyperlactatemia2 owing to the presumed inability of the liver to process the influx of lactate. However, no published evidence exists to support this claim, and in stranded juvenile loggerhead sea turtles, intracoelomic administration of LRS at a dosage of 20 mL/kg every 24 hours for 3 doses caused no increase in blood lactate concentration.5 Sea turtles are unique reptiles that live in a marine environment; therefore, that finding5 may not be generalizable to other groups of reptiles, particularly reptiles that are adapted to arid environments, such as commonly kept inland bearded dragons (Pogona vitticeps).
The purpose of the study reported here was to evaluate the effects of a single SC injection of LRS, PLA, and RRS on commonly measured plasma biochemical values, plasma osmolarity, and blood lactate concentration when administered to bearded dragons experimentally dehydrated by furosemide administration. We hypothesized that LRS administration would not result in an increase in blood lactate concentration and that RRS administration would result in an increase in plasma glucose concentration.
Materials and Methods
Animals
Nine adult (1 to 2 years old) inland bearded dragons (5 males and 4 females) with a mean ± SD body weight of 0.28 ± 0.05 kg were obtained from a breeder. They were housed individually or with conspecifics in glass tanks in a climate-controlled room with a 12-hour light-dark cycle. Room temperature was maintained between 25°C and 27°C, and UV-B light was provided for 12 h/d over 1 end of the tank, providing a basking area of approximately 34°C. The bearded dragons were offered gut-loaded insects or mixed leafy greens once a day, 6 d/wk, on a rotating schedule. Fresh water was provided in a bowl, and all bearded dragons were placed in shallow warm water twice a week for further water supplementation.
All animals were deemed healthy on the basis of repeated physical examinations and monitoring of food intake, fecal output, body weight, and plasma biochemical and CBC values prior to and throughout the study. The study protocol was approved by the University of Wisconsin-Madison School of Veterinary Medicine Institutional Animal Care and Use Committee.
Study design
A complete crossover study was performed involving 3 treatment sessions separated by a minimum 14-day washout period. The treatment sequence was randomized.a Food was withheld from bearded dragons for 36 hours prior to each treatment session, and during each session, no food or water was provided. At the start of each session, body weights were measured, and then furosemideb (10 mg/kg, SC) was administered in the axillary area every 12 hours for 4 doses.
Twelve hours after the last furosemide dose was administered in each session, body weight was recorded, and then a 0.4-mL blood sample was obtained from the ventral tail vein by use of a 25-gauge needle and a 1-mL syringe that contained lithium heparin.c This initial blood sample was used to measure baseline (dehydration) blood (PCV, total solids, and lactate) and plasma biochemical (total protein, uric acid, sodium, potassium, calcium, phosphorus, and glucose) values and plasma osmolarity. After blood sample collection, a single dose of LRS,d PLA,d or RRS (1:1 mixture of 5% dextrose solutiond and PLA) equivalent to approximately 5% of the animal's body weight prior to furosemide administration (ie, 50 mL/kg) was administered SC along the lateral aspect of the body wall. The 50-mL/kg dose was chosen because approximately 5% of body weight had been lost by bearded dragons receiving four 10-mg/kg doses of furosemide in a previous study.6 Blood samples were again collected 4 and 24 hours after fluid administration for measurement of the same analytes as measured in baseline samples.
Sample analysis
Plasma total protein, uric acid, sodium, potassium, calcium, phosphorus, and glucose concentrations were measured with a commercial biochemical panel marketed for used in reptiles.e Packed cell volume and refractometer-determined blood total solids concentration were measured by means of standard laboratory methods. Plasma osmolarity was measured via freezing-point osmometry.f Blood lactate concentration was measured with a commercial blood gas analyzer.g Temperature corrections were performed for pH to reflect the ambient temperature of 27°C as body temperature by use of the standard calibration formula for the blood gas analyzer.
Statistical analysis
Statistical softwareh was used for data analysis. All data were evaluated for normality of distribution with the Shapiro-Wilk test and for equality of group variances with the Brown-Forsythe test. Results are reported as mean ± SD unless otherwise noted. Two-way repeated-measures ANOVA was performed to evaluate the effects of electrolyte solution type and time on measured clinicopathologic values. Within each treatment, data were evaluated for differences between baseline values and values at 4 and 24 hours after solution administration. To account for differences in baseline values, between-group comparisons of values at 4 and 24 hours were performed by use of differences in those values from baseline. The Holm-Sidak method was used for post hoc analysis. A value of P < 0.05 was considered significant.
Results
Administration of furosemide resulted in a mean ± SD loss in body weight of 4.9 ± 3.5% (Table 1). Changes in evaluated clinicopathologic variables were summarized (Table 2). Plasma total protein and blood total solids concentrations decreased after fluid administration and were significantly lower at the 24-hour assessment point for all 3 electrolyte solutions. No differences among solutions were identified for those variables. No difference from baseline or among solutions at any assessment point was identified for blood lactate concentration.
Mean ± SD body weight of 9 inland bearded dragons (Pogona vitticeps) before and after experimental induction of dehydration with furosemide (10 mg/kg, SC, q 12 h for 4 doses) and 24 hours after SC administration of a single dose (50 mL/kg) of 3 electrolyte solutions in a crossover study design.
| Solution | Initial body weight (g) | Dehydration body weight (g) | Percentage dehydration | Body weight after fluid administration (g) |
|---|---|---|---|---|
| RRS | 272 ± 48 | 262 ± 49 | 4 ± 3 | 271 ± 51 |
| LRS | 275 ± 50 | 261 ± 50 | 5 ± 4 | 272 ± 53 |
| PLA | 278 ± 49 | 263 ± 49 | 6 ± 3 | 274 ± 51 |
Mean ± SD values of clinicopathologic variables and changes from baseline (after induction of dehydration; ‡) at various points for the bearded dragons of Table 1.
| 4 hours after fluid administration | 24 hours after fluid administration | |||||
|---|---|---|---|---|---|---|
| Variable | Solution | Baseline | Mean ± SD | Δ | Mean ± SD | Δ |
| PCV (%) | RRS | 31 ± 5 | 29 ± 5 | −1.8 ± 1.8 | 27 ± 5* | −3.8 ± 2.9 |
| LRS | 30 ± 7 | 28 ± 6 | −1.9 ± 2.2 | 27 ± 4 | −2.6 ± 5.1† | |
| PLA | 32 ± 9 | 28 ± 7* | −3.3 ± 3.7 | 25 ± 6* | −7.0 ± 5.8 | |
| Total solids (g/dL) | RRS | 5.9 ± 0.8 | 5.7 ± 0.8 | −0.2 ± 0.4 | 4.7 ± 0.6* | −1.2 ± 0.6 |
| LRS | 5.7 ± 1.0 | 5.2 ± 0.9* | −0.6 ± 0.5 | 4.7 ± 0.7* | −1.0 ± 0.5 | |
| PLA | 6.2 ± 1.0 | 5.6 ± 1.1* | −0.5 ± 0.3 | 4.6 ± 0.7* | −1.6 ± 0.6 | |
| Osmolarity (mOsm/L) | RRS | 325 ± 9 | 322 ± 10 | −3.3 ± 4.3 | 318 ± 10* | −7.3 ± 6.3 |
| LRS | 321 ± 10 | 319 ± 8 | −1.8 ± 4.7 | 324 ± 13 | 2.8 ± 9.4†‡ | |
| PLA | 325 ± 8 | 323 ± 10 | −1.9 ± 4.3 | 320 ± 9 | –4.7 ± 5.3 | |
| Total protein (g/dL) | RRS | 5.1 ± 0.6 | 5.0 ± 0.4 | −0.1 ± 0.2 | 4.4 ± 0.4* | −0.8 ± 0.5 |
| LRS | 5.0 ± 0.7 | 4.7 ± 0.6* | −0.3 ± 0.3 | 4.3 ± 0.6* | −0.7 ± 0.4 | |
| PLA | 5.1 ± 0.6 | 4.9 ± 0.6 | −0.2 ± 0.2 | 4.3 ± 0.5* | 0.8 ± 0.2 | |
| Uric acid (mg/dL) | RRS | 2.8 ± 1.0 | 3.2 ± 1.4 | 0.4 ± 0.8 | 2.5 ± 1.9 | −0.3 ± 1.7 |
| LRS | 1.9 ± 0.6 | 1.9 ± 0.6 | 0.02 ± 0.40 | 1.7 ± 0.5 | −0.2 ± 0.6 | |
| PLA | 2.2 ± 1.3 | 2.7 ± 1.8 | 0.4 ± 0.7 | 2.0 ± 1.8 | −0.2 ± 1.2 | |
| Sodium (mmol/L) | RRS | 145 ± 4 | 138 ± 6* | −7.1 ± 3.7 | 139 ± 4* | −6.9 ± 3.3 |
| LRS | 145 ± 5 | 144 ± 4 | −1.2 ± 3.2‡ | 146 ± 7 | 0.9 ± 4.0‡ | |
| PLA | 146 ± 7 | 144 ± 9 | −2.4 ± 2.9‡ | 145 ± 6 | −1.3 ± 4.8‡ | |
| Potassium (mmol/L) | RRS | 4.0 ± 0.9 | 4.2 ± 0.8 | 0.14 ± 0.90 | 3.7 ± 0.5 | −0.4 ± 0.9 |
| LRS | 3.8 ± 0.6 | 3.5 ± 0.6 | −0.32 ± 1 | 4.5 ± 1.1 | 0.7 ± 1.5 | |
| PLA | 4.1 ± 0.8 | 3.9 ± 0.5 | −0.17 ± 0.70 | 4.2 ± 0.8 | 0.2 ± 1.3 | |
| Calcium (mg/dL) | RRS | 11.8 ± 0.8 | 11.8 ± 0.8 | −0.04 ± 0.2 | 11.3 ± 0.9 | −0.5 ± 0.6 |
| LRS | 12.1 ± 1.1 | 11.9 ± 1.1 | −0.20 ± 0.30 | 11.4 ± 1.1* | −0.7 ± 0.4 | |
| PLA | 12.4 ± 1.6 | 12.3 ± 1.7 | −0.12 ± 0.30 | 12.4 ± 2.9 | 0.0 ± 1.6 | |
| Phosphorus (mg/dL) | RRS | 7.2 ± 1.2 | 6.4 ± 1.1* | −0.8 ± 0.8 | 6.2 ± 1.0* | −1.0 ± 0.4 |
| LRS | 7.2 ± 1.3 | 6.4 ± 1.3* | −0.8 ± 0.4 | 7.1 ± 1.3 | −0.1 ± 0.6‡ | |
| PLA | 7.6 ± 0.7 | 6.8 ± 1.0* | −0.8 ± 0.5 | 7.4 ± 0.7 | −0.2 ± 0.6‡ | |
| Glucose (mg/dL) | RRS | 190 ± 32 | 420 ± 62* | 230 ± 45 | 348 ± 55* | 159 ± 31 |
| LRS | 187 ± 27 | 194 ± 25 | 7.0 ± 14‡ | 185 ± 23 | −2.6 ± 11 | |
| PLA | 187 ± 36 | 192 ± 34 | 5 ± 16‡ | 180 ± 36 | −7.2 ± 6.6 | |
| Lactate (mmol/L) | RRS | 1.8 ± 3.1 | 2.5 ± 4.1 | 0.8 ± 1.7 | 1.7 ± 2.7 | −0.1 ± 4.3 |
| LRS | 0.7 ± 0.6 | 1.5 ± 2.3 | 0.7 ± 2.3 | 3.1 ± 3.7 | 2.3 ± 3.7 | |
| PLA | 1.2 ± 1.0 | 1.9 ± 3.1 | 0.7 ± 2.8 | 2.2 ± 2.8 | 1.0 ± 2.8 | |
| pH | RRS | 7.75 ± 0.12 | 7.70 ± 0.12 | −0.05 ± 0.05 | 7.77 ± 0.11 | 0.02 ± 0.19 |
| LRS | 7.74 ± 0.07 | 7.73 ± 0.1 | −0.01 ± 0.06 | 7.73 ± 0.10 | −0.02 ± 0.18 | |
| PLA | 7.73 ± 0.06 | 7.75 ± 0.11 | 0.02 ± 0.10 | 7.76 ± 0.14 | 0.03 ± 0.11 | |
| HCO3- (mmol/L) | RRS | 26.4 ± 4.2 | 24.9 ± 4.6 | −1.4 ± 2.4 | 27.9 ± 4.5 | 1.5 ± 3.4 |
| LRS | 27.1 ± 6.0 | 25.6 ± 5.4 | −1.5 ± 2.1 | 25.3 ± 4.6 | −1.7 ± 4.3 | |
| PLA | 26.7 ± 2.5 | 27 ± 3.6 | 0.2 ± 2.9 | 27.3 ± 3.2 | 0.6 ± 3.4 | |
Within a treatment, the indicated value differs significantly (P < 0.05) from the baseline (ie, after dehydration) value.
The indicated value differs significantly from the corresponding PLA value.
The indicated value differs significantly from the corresponding RRS value.
Administration of RRS resulted in severe hyperglycemia (mean ± SD plasma glucose concentration at 4 hours, 420 ± 62 g/dL), compared with the mean baseline value (190 ± 32 mg/dL), and this hyperglycemia persisted for at least 24 hours (348 ± 55 mg/dL). Administration of RRS also resulted in a significant reduction in plasma osmolarity and sodium and phosphorus concentrations at the 24-hour assessment point, which was not observed after administration of the other 2 electrolyte solutions.
Discussion
In the study reported here, changes in clinicopathologic variables were assessed in experimentally dehydrated bearded dragons after SC administration of a single dose (5% body weight) of LRS, PLA, or RRS. All evaluated electrolyte solutions caused similar decreases in PCV, blood total solids concentration, and plasma total protein concentration, indicating that all fluid types were absorbed from the subcutaneous space into the intravascular space.
The osmolarity of LRS, PLA, and RRS is 273, 294, and 273 mOsm/L, respectively.7 Plasma osmolarity in bearded dragons is reported to be approximately 295 mOsm/L8 or 315 mOsm/L.6 Administration of RRS in the present study resulted in a significant reduction in plasma osmolarity by 24 hours after administration even though the osmolarity of RRS is similar to that of LRS, which had no significant effect on plasma osmolarity.
Administration of RRS also resulted in profound hyperglycemia that persisted for at least 24 hours after the single dose was administered, whereas no changes in plasma glucose concentration were found after administration of LRS or PLA. This finding was consistent with the aforementioned findings5 for loggerhead sea turtles. Not only would induced hyperglycemia alter clinicopathologic test results and interpretation for at least 24 hours after fluid administration, but also hyperglycemia has been shown to be a negative prognostic indicator for critically ill hospitalized humans.9,10 Although the exact mechanism underlying hyperglycemia-associated death has not been fully elucidated, hyperglycemia is believed to increase the risk of fatal arrhythmias and amounts of reactive oxygen species in essential organs, and even small increases in blood glucose concentration have been shown to be harmful.11 For this reason, induction of hyperglycemia in ill bearded dragons via administration of RRS may be inadvisable.
In addition to the iatrogenic hyperglycemia, the bearded dragons of the present study had a decrease in plasma sodium concentration after receiving RRS. This decrease may have been linked to the hyperglycemia because hyperglycemia induces a shift of fluid from the intracellular space to the extracellular space, leading to relative hyponatremia.12 Another possible explanation for the hyponatremia after administration of RRS could be the reduced amount of sodium in the RRS because PLA was administered at half strength, and therefore a solution containing substantially less sodium than typically present in bearded dragon plasma was administered.12 This result regarding plasma sodium concentration after administration of RRS was inconsistent with results reported for loggerhead sea turtles, in which no change was observed.5
A significant decrease in plasma phosphorus concentration occurred in bearded dragons with all 3 types of electrolyte solutions by 4 hours after administration, but this decrease persisted for at least 24 hours only with RRS. Carbohydrate loading (usually by dextrose solution administration) is a common cause of hypophosphatemia in veterinary patients, attributable to insulin encouraging movement of phosphorus into cells.7 Although none of the bearded dragons of the present study had signs of adverse effects from the observed metabolic derangements, it should be noted that these changes were found after RRS had been administered as a single bolus injection and not in multiple doses as would occur in clinical settings. If multiple doses were administered to a clinically ill reptile in the hospital, derangements of greater magnitude with clinical consequences could occur. For example, hypophosphatemia can cause nausea, hemolysis, leukocyte impairment, and neuromuscular effects.7
Concerns have been raised that the livers of reptiles cannot metabolize the lactate present in LRS when it is administered; thus, LRS has not been recommended historically.2 Hyperlactatemia has often been linked to multiple disease processes and metabolic derangements, so avoidance of hyperlactatemia appears prudent.13 No significant increase in blood lactate concentration was observed as a result of SC administration of a single dose of LRS, compared with blood lactate concentrations associated with the other types of electrolyte solutions evaluated, which is consistent with results reported for loggerhead sea turtles following intracoelomic administration of LRS.5 Therefore, avoidance of LRS use in reptiles for this reason does not appear necessary.
The present study had several limitations when considering clinical fluid therapy for reptiles. Foremost, the bearded dragons were experimentally dehydrated and did not necessarily represent clinically dehydrated reptiles. Furosemide administration to mammals leads to free water and sodium loss through inhibition of the Na-K-Cl cotransporter protein.14 Although the evidence is limited, it appears that in desert reptiles such as bearded dragons, dehydration involves substantial hypernatremia.15 Further clarification is required of the function of reptilian kidneys and their response to furosemide and dehydration via natural means. It is also important to note that because bearded dragons are a desert species, they likely achieve homeostasis and water loss much differently than an aquatic reptile species would, so any conclusions drawn from the present study are unlikely to apply to other reptile species types.
Another limitation was the lack of a control treatment, which was not included because the objective was not to evaluate whether the 3 electrolyte solutions had an effect on clinicopathologic variables relative to no treatment but, rather, to determine whether clinically relevant differences existed in the response of bearded dragons to administration of any of the 3 solutions. It is unlikely that repeated handling and blood sample collection contributed to the observed changes in plasma biochemical variables given that the observed changes (eg, hyperglycemia) were not consistent among solutions. Furthermore, it is unclear what type of control treatment would be appropriate in our experimental setting given that any type of fluid (other than homologous plasma collected prior to treatment), such as saline solution administered SC, oral tap water consumption, or soaking, would be considered another treatment for dehydration and not a control treatment. However, research into the effects of these other treatment options is warranted.
Furthermore, the clinicopathologic values following fluid administration to the bearded dragons were not compared with values prior to induction of dehydration given that the objective of the present study was not to evaluate which type of electrolyte solution could be used to restore values to predehydration statuses. We have previously shown6 that most clinicopathologic values do not significantly differ after induction of dehydration with the furosemide protocol used in the present study.
Overall, although it cannot be known whether the experimentally dehydrated bearded dragons of the present study precisely mimicked ill bearded dragons in clinical reptile practice, the study results suggested the types of electrolyte solutions that would be more appropriate for bearded dragons and similar reptile species. Additional research is needed to compare bearded dragons with dehydration attributable to a pathological process and those with experimental dehydration as induced in the present study. Because of the multiple metabolic derangements that occurred after administration in the present study and in sea turtles in a previous study,5 RRS is not recommended. Isotonic crystalloid solutions such as LRS and PLA appeared to achieve adequate rehydration without producing metabolic derangements. The LRS did not cause hyperlactatemia, contrary to previous concerns. Isotonic crystalloid solutions designed for mammalian patients appeared to provide adequate, and even superior, rehydration to dehydrated bearded dragons, compared with reptile-specific electrolyte solutions.
Acknowledgments
Funded by the University of Wisconsin-Madison School of Veterinary Medicine Companion Animal Fund, the Association of Reptile and Amphibian Veterinarians, Kevin Wright Memorial research grant, and Abaxis Global Diagnostics.
The authors declare that there were no conflicts of interest.
ABBREVIATIONS
| LRS | Lactated Ringer solution |
| PLA | Plasma-Lyte A |
| RRS | Reptile Ringer solution |
Footnotes
Research Randomizer, version 4.0, Urbaniak GC, Plous S. Available at: randomizer.org. Accessed Feb 15, 2017.
Salix, Merck Animal Health, Kenilworth, NJ.
Pro-Vent, Smiths Medical, Keene, NH.
Hospira Inc, Lake Forest, Ill.
VetScan Avian/Reptile Profile Plus, Abaxis, Union City, Calif.
Advanced micro-osmometer model 3300, Advanced Instruments Inc, Norwood, Mass.
iSTAT CG4+, Abbott Laboratories, Chicago, Ill.
SigmaPlot, version 13, Systat Software, San Jose, Calif.
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