Assessment of Dehydration and Efficacy of Rehydration With Subcutaneous Saline in the Pigeon (Columba livia)
Identification of key clinically applicable signs correlating directly with dehydration severity could allow clinicians to accurately define the degree of dehydration they are encountering in an avian patient at presentation, when fluid therapy is commonly initiated. Certain signs have been reported to indicate clinical dehydration, although their use in predicting severity has led to uncertainty. When delivering fluid therapy to a dehydrated debilitated bird, the risk of aspiration with oral administration and the stressful and often cumbersome maintenance of intravenous or intraosseous catheters might be avoided if subcutaneous administration were effective. Moreover, avian species may not follow the mammalian standard of 7% dehydration as the decision point for determining if subcutaneous fluids can be effectively absorbed. The purpose of this study was to assess the effect of controlled dehydration on the reliability of clinical sign development, and to determine if subcutaneous fluid administration rehydrates pigeons when dehydration progresses beyond 7.5%.
Thirty-six mixed sex pigeons were purchased from a local breeder and housed singly under controlled photoperiod, ambient temperature, and humidity. All birds had food withheld from 12 hours before, and water was provided until immediately before study. Once on study, all pigeons were deprived of water and weighed frequently until a target weight (percent dehydration) was reached, when corrected for maintenance energy losses. Target groups consisted of 0%, 4%, 7.5%, 9.5%, 11%, and 13.5% dehydration. Dehydrated birds in each group were assessed in regard to the following physical diagnostic characteristics: ulnar vein changes (diameter, shape-round or flattened, and refill time), body temperature changes (cloacal, carpal contact, and middle toe base contact), lower eyelid pinch recovery time, presence of oral mucous strings with repeated closed mouth opening, and clinical biochemical changes (hematocrit, blood urea nitrogen (BUN), albumin). Each bird had the same assessments repeated following 5% rehydration with 0.9% sodium chloride (NaCl) delivered subcutaneously divided equally into each medial leg web. Two 1 ml heparinized blood samples were collected from the medial tarsal or ulnar wing veins opposite to the site of sign assessment. After the hematocrit was determined, plasma samples for albumin (improved biuret for birds) and BUN were collected into O-ring tubes and stored at -70°C until analyzed on a Hitachi 917 chemistry analyzer.
The following clinical signs were found to be significantly influenced by dehydration: eye pinch time (p<0.0001), presence of oral string(s) (p=0.0051), albumin (p=0.0289), and BUN (p=0.0031). Carpal contact temperature (p=0.1349), cloacal temperature (p=0.3354), middle toe base contact temperature (p=0.2350), ulnar vein diameter (p=0.0670), ulnar vein refill time (p=0.0774), ulnar vein flattening (p=0.0863), and hematocrit (p=0.9344) were not reliable markers over the dehydration range studied. When 11–13.5% dehydrated birds were compared to hydrated controls with regard to these same parameters, the same signs were significant. In addition, carpal contact temperature (p=0.0280), ulnar vein diameter (p=0.0010), ulnar vein refill time (p=0.0010), and ulnar vein flattening (p=0.0080) became significant markers, whereas, albumin (p=0.3990) became nonsignificant. Delayed eyelid pinch time (p=0.005), presence of oral strings (p=0.008), ulnar vein diameter (p=0.0010), ulnar vein refill (p=0.0010), ulnar vein flattening (p=0.008), and BUN (p=0.001) were the best predictors of more severe dehydration. As previously reported, individual birds did not exhibit all dehydration signs at any one level of dehydration, necessitating the evaluation of greater than one sign during clinical assessment. Likewise, change rather than the absolute value of a parameter was often most indicative of dehydration, sometimes limiting its usefulness at presentation. Paired T testing revealed that all signs except oral string formation (p=0.2930) were corrected toward normal by subcutaneous rehydration in birds 9.5% or more dehydrated, and in 2.5 hours or less. At all sites measured, body temperature reliably decreased in response to rehydration.
Delayed eyelid pinch time, presence of oral strings, decreased ulnar vein diameter, longer ulnar vein refill, increased ulnar vein flattening, and elevated BUN were the best predictors of more severe dehydration from this study when used in combination. Dehydration up to 13.5% percent can be readily corrected with relatively simple subcutaneous rehydration, without the need for more invasive procedures. Further work is needed in avian species to explore the use of subcutaneous fluid administration for dehydration of greater severity than reported here. However, from the present study, it appears the mammalian subcutaneous rehydration cutoff of 7.0% may not apply in avian species.