Dehydration

Question 1

What is dehydration?

Answer 1

“losing more fluids than you take in”
- Water loss dehydration (hyperosmolar, due either to increased sodium or glucose)
- Salt and water loss dehydration (hyponatremia). 

Question 2

Describe the aetiology and risk factors for dehydration

Answer 2

• Decreased Fluid intake: severe illness, anorexia, malnutrition 
• Pyrexia/excess sweating 
• GI loss: diarrhoea, vomiting 
• Polyuria (e.g. diabetes mellitus, diabetes insipidus, hypercalcaemia)  
• Heatstroke
• drunk too much alcohol 
• diuretics

Question 3

What presenting symptoms of dehydration can be found in the history?

Answer 3

• Extreme thirst 
• Less frequent urination 
• Dark-coloured urine 
• Fatigue 
• Dizziness 
• Confusion 

Question 4

What signs of dehydration can be found on physical examination?

Answer 4

• Dark urine
• Fatigue
• Thirst
• Dry skin + lips
• Headaches
• Muscle cramps
• Syncope
• Palpitation

Question 5

What investigations are used to diagnose/ spot dehydration?

Answer 5

• Increased urea (or raised urea-to-creatinine ratio), albumin and Haematocrit (Haematocrit is the ratio of RBCs to the volume of blood. Therefore, if fluid is lost from the blood (i.e. in dehydration) this ratio will increase).
• Reduced urine volume and skin turgor.
• Water deprivation test - diabetes insipidus 

Question 6

How is dehydration managed?

Answer 6

• IV fluids, resuscitation 
• Blood pressure, heart rate, serum lactate, haematocrit (if bleeding, there is no blood loss), and urine output may be used to assess the volume deficit and to assess response to fluids. 
• In patients with dehydration and severe hyponatremia, rapid volume repletion may cause a rapid rise in sodium. This can cause central pontine myelinolysis (CPM-damages regions of the brain). The clinician must weigh the risks of continued dehydration against the risks of CPM. The patient’s volume status and serum sodium must be followed closely. 

Question 7

What complications can arise from dehydration?

Answer 7

• Heat injury
• Urinary and kidney problems.Prolonged or repeated bouts of dehydration can cause urinary tract infections, kidney stones and even kidney failure. 
• Seizures .Electrolytes — such as potassium and sodium out of balance.
• Low blood volume shock (hypovolemic shock).

Question 8

Describe the prognosis of dehydration

Answer 8

Good 

Question 9

Describe the pathophysiology behind dehydration

Answer 9

1. The primary control of water homeostasis is through osmoreceptors in the brain.
2. As perceived by these osmoreceptors, dehydration stimulates the thirst centre in the hypothalamus, which leads to water consumption.
3. These osmoreceptors can also cause the conservation of water by the kidney.
4. When the hypothalamus detects lower water concentration, it causes the posterior pituitary to release antidiuretic hormone (ADH), which stimulates the kidneys to reabsorb more water.
5. Decreased blood pressure, which often accompanies dehydration, triggers renin secretion from the kidney.
6. Renin converts angiotensin I to angiotensin II, which increases aldosterone release from the adrenals.
7. Aldosterone increases the absorption of sodium and water from the kidney.
8. Using these mechanisms, the body regulates body volume and sodium and water concentration.