ASSESSMENT OF EXERCISE-INDUCED DEHYDRATION AND REHYDRATION: EFFECTIVENESS OF USING PREDICTION EQUATIONS FOR PLASMA OSMOLALITY
Chiagoziem K. Ohamadike, Lia Teng, HyunGyu Suh, Mindy L. Millard-Stafford, FACSM. Georgia Institute of Technology, Atlanta, GA.
ASSESSMENT OF EXERCISE-INDUCED DEHYDRATION AND REHYDRATION: EFFECTIVENESS OF USING PREDICTION EQUATIONS FOR PLASMA OSMOLALITY BACKGROUND: Plasma osmolality (POsm) is a gold standard for assessing hydration status; however, osmometers are primarily found in research labs and therefore POsm is not typically measured in clinical or athletic settings. PURPOSE: To compare the accuracy in assessment of dehydration versus rehydration states following the ingestion of oral rehydration solution (ORS) between published equations estimating POsm from Na+, K+, glucose, and blood urea nitrogen (BUN) versus direct measured POsm. METHODS: Seventeen healthy men cycled 90 min in the heat losing ~2.5% body mass and then ingested Pedialyte ORS ([Na+] = 42.6 mmol/L; [K+] = 30.9 mmol/L) replacing 100% of sweat loss over 30 min (~2 liters). Blood samples were collected at dehydration, then 30, 60, and 90 min post rehydration. POsm was directly measured with 50 µl samples (Micro Osmette osmometer, Precision System Inc). These values were compared to three highly cited equations estimating POsm (mmol/L): 1) 2 x (Na++ K+) + BUN+ Glucose (Gerich, Diabetes, 1971); 2) 1.86 x (Na+ + K+) + (1.15 x Glucose) + BUN + 14 (Hooper, British Medical Journal Open, 2015); and 3) 2 x Na+ + Glucose + BUN (Worthley, Anaesthesia and Intensive Care, 1987). RESULTS: All estimation equations were significantly correlated with measured POsm (p < 0.0001, R2ranging from 0.64-0.72). At dehydration and 90 min post-rehydration, measured POsm was 294.6 ± 3.4 and 285.0 ± 3.1 mosmol/L, respectively. At dehydration, Worthley was lower (p < 0.05) than the other equations and measured POsm (mean osmole gap = -3.4 mosmol/L). Conversely, at 90 min post rehydration, Gerich and Hooper equations were higher than Worthley and measured POsm (mean osmol gaps = -4.9 and -3.7 mosmol/L). CONCLUSION: Dehydration due to sweat losses in the heat results in underestimation of POsm when using equations excluding plasma K+ (e.g. Worthley). However, rehydration is not accurately assessed with equations including K+(e.g. Hooper and Gerich) when ORS is ingested to fully restore fluid balance. Therefore, selection of an appropriate published equation to estimate POsm depends on the nature of dehydration and/or fluid replenishment. Supported by a grant from Einsof Biohealth, Miami, FL.
Ohamadike, CK; Teng, L; Suh, HG; and Millard-Stafford, FACSM, ML
"ASSESSMENT OF EXERCISE-INDUCED DEHYDRATION AND REHYDRATION: EFFECTIVENESS OF USING PREDICTION EQUATIONS FOR PLASMA OSMOLALITY,"
International Journal of Exercise Science: Conference Proceedings: Vol. 16:
1, Article 269.
Available at: https://digitalcommons.wku.edu/ijesab/vol16/iss1/269