Chemistry of dehydration, The

Our cells have a high water content and the decrease in total body water causes reductions in both the intracellular and extracellular fluid volumes. Clinical manifestations of dehydration are most closely related to intravascular volume depletion. In effect blood volume goes down as water is ‘siphoned off’ from the veins to the body cells. As the blood volume goes down, the volume of oxygen it can carry goes down and eventually we suffer a form of hypoxia. 

Dehydration is not quite as simple as this, however, as the loss of ‘electrolytes’ also has an effect and the loss of sodium and calcium in particular .

Channels are found in all cell membranes. They are tiny. The archetypal channel pore is just one or two atoms wide at its narrowest point and is selective, accepting only one type of ion, such as sodium, calcium or potassium. These ions move through the channel pore single file nearly as quickly as the ions move through free fluid.

Ion channels are key components in a wide variety of biological processes that involve rapid changes in cells, such as cardiac, skeletal, and smooth muscle contraction, epithelial nutrient transport {epithelial cells are tissue cells that perform functions like secretion, selective absorption, protection, transcellular transport and detection of sensation), T-cell activation (our system of immunity) and pancreatic beta-cell insulin release.

As the volume of electrolytes decreases, therefore, numerous extra physiological effects can then arise affecting the heart muscles, blood vessels, neurons and so on.

For example, as intracellular calcium decreases there is a reduction in muscle contraction. In the heart, a decrease in calcium available for each beat results in a decrease in cardiac contractility. In blood vessels, a decrease in calcium results in less contraction of the vascular smooth muscle and therefore an increase in arterial diameter [vasodilation]. Vasodilation decreases total peripheral resistance, while a decrease in cardiac contractility decreases cardiac output. Since blood pressure is determined by cardiac output and peripheral resistance, blood pressure drops. So the overall effect of loss of electrolytes due to dehydration is to reduce blood pressure!

In effect one side effect of dehydration caused by the loss of electrolytes is hypotension, low blood pressure. Hypotension may then lead itself lead to hypoxia.

Overall, therefore the end result of dehydration, if we follow through all its threads is in many cases due to hypoxia, but the routes by which this occurs can be many and complex and can be as much due to electrolyte loss as water loss.

Side effects may include one or more of the following at various levels of dehydration according to severity

• Extreme thirst and discomfort
• Constipation
• decreased urine volume and abnormally dark urine
• unexplained tiredness, lethargy, overwhelming fatigue
• irritability, moodiness
• increased body temperature because of decreased sweating
• lack of tears when crying
• dry mouth
• insomnia
• headaches similar to those experienced during a hangover
• decreased blood pressure (hypotension) and dizziness or fainting when standing up due to orthostatic hypotension
• nausea
• delirium, hallucinations or visions
• unconsciousness/coma

References

Ellis S. J. Severe hyponatraemia: Complications and treatment. QJM. 1995;88(12):905–9.
Ellinas P. A, Rosner F, Jaume J.C. Symptomatic hyponatremia associated with psychosis, medications, and smoking. J Natl Med Assoc. 1993;85(2):135–41
Giupponi G, Erfurth A. Transient psychosis in lisinopril-induced hyponatremia. Psychiatr Prax. 1998;25(4):204.
Sharma H, Pompei P. Antidepressant-induced hyponatraemia in the aged. Avoidance and management strategies. Drugs Aging. 1996;8(6):430–435.
Haensch C. A, Hennen G, Jörg J. Reversible exogenous psychosis in thiazide-induced hyponatremia of 97 mmol/l. Nervenarzt. 1996;67((4):319–22.