Fluid Balance

• Fluid balance is critical in health & especially when there is a specific disease present.
• Individuals vulnerable to fluid dysregulation include:
  1. Intense exercise
  2. Severe disease processes
• Water balance refers to the relationship between Total Body Water (TBW) and body solute.
• Stable cell volume is important for functioning and survival.
• The solute concentration in the extra-cellular and intra-cellular compartments affect the water distribution in these compartments.
• Osmolality refers to the solute concentration and in a steady state the intra-cellular concentration = extra-cellular concentration.
• The distribution of TBW between the intracellular and extracellular compartment is determined by the solute concentration.
• Tonicity refers to the portion of osmolality contributed by solutes distributed in the body fluid compartment. Serum sodium concentration is a measure index of tonicity as sodium chloride constitute ≥ 90% of the extracellular solute.
• In a normal state ECFV= 16l, ICFV=24l, serum [Na]= 140 mmols/l.
• Hypernatraemia is corrected by infusing either water in form of 5% dextrose solution or if hypovolaemia is present, hypotonic saline (Roumelioti et al).

Exercise & fluid balance

• Athlete perceived indices of fluid balance by perceiving fluid intake & sweat losses during exercise training is difficult and inaccurate at times. In a study done by Love et al, players under-estimated sweat losses (73% ±17%) to a greater than fluid intake (37%±28%) which resulted in players to perceive that they were in a positive fluid balance rather than in negative balance. Conversely, at times, athletes may overhydrate.
• Hydration status can be assessed using body mass while monitoring the cardiovascular parameters that include HR and BP. Serum electrolyte concentration, with osmolality, together with renal electrolyte concentration, accurately reflects the changing concentration in the extracellular compartment.
• It is important to differentiate immediate post-exercise hypovolaemia that may be a physiologic drop in BP due to the immediate cessation of the muscle pump action that causes temporary blood pooling from dehydration.

Hydration

• Maintain cardiac output (CO) & prevent injury to body organs.
• Maintain CO by appropriate fluid balance: output = intake, maintain fluid balance by replacing fluid losses during the day and especially when exercising by consuming appropriate fluids. Exercising in the heat and individuals with medical conditions & the elderly are at higher risk of dehydration.
• Prevent fluid dehydration & also prevent over-hydration during exercise.
• ASSIC resting HR app allow heart rate measurement to track baseline HR.
• ASSIC recovery & fitness app allow fitness monitoring when exercising.

To Measure Hydration you can look at: HR & BP, Electrolytes: Na⁺¹, k⁺¹, Urea And Creatinine.

References

• Fluid balance concepts in medicine: principles and practice. Maria-Eleni Roumelioti, Robert H Glew, Zeid J Khitan, Helbert Rondon-Berrios, Christos P Argyropoulos, Deepak Malhota, Dominic S Raj, Emmanuel I Agaba, Mark Rohrscheib, Glen H Murata, Joseph I Shapiro and Antonios H Tzamaloukas. World J Nephrol. 2018 Jan 6; 7(1): 1-28
• Measured and perceived indices of fluid balances of fluid balances in professional athletes. The use and impact of hydration assessment strategies. T.D. Love, D.F. baker, P. Healey & K.F. Black. Eur J Sport Sci Jan 24: 1-8.