Overview
Dehydration is a potentially life threatening condition in which the body has an insufficient amount of water for normal functioning. Volume depletion refers to the loss of electrolytes and water.
7-8 % of body weight is comprised of blood. Sodium levels in the blood is approximately 135 – 145 mEq/L. Dehydration can be described according to the level of sodium (hypo-, iso-, and hypernatremic).
Percentage of body weight composed of water according to age group
| Age group | Percentage of body weight composed of water |
|---|---|
| Premature | 85% |
| Neonate | 80% |
| 3 months | 75% |
| 9 months | 70% |
| 12 years and older | 60% |
Normal circulating volume (blood volume) according to age group
| Age group | Circulating volume | Percentage of body weight |
|---|---|---|
| Neonate | 90 ml/kg | 9 % of body weight |
| Infant | 80 ml/kg | 8% of body weight |
| Child | 70 ml/kg | 7 % of body weight |
Classification of dehydration
| Classification | Examples |
|---|---|
| In relation to sodium content | Isonatremic, hyponatremic, and hypernatremic |
| Clinical | Mild, moderate, and severe dehydration |
| According to WHO | No dehydration, some dehydration, and severe dehydration |
Classification of dehydration in relation to sodium content
| Sodium level | Description |
|---|---|
| Isonatremic | Proportion of water and sodium lost is equal |
| Hyponatremic | Proportion of sodium lost is more than water |
| Hypernatremic | Proportion of water lost is more than sodium |
Classification of dehydration according to volume depletion
| Volume depletion | Corresponding body weight loss | Signs and symptoms |
|---|---|---|
| Mild volume depletion (3-10%) | Corresponds to about 50 ml/kg of body weight loss. Physical signs are minimal or absent | Thirsty, pulse slightly increased, urine output normal or slightly decreased, mucous membranes moist and tears present, normal skin turgor, normal capillary refill |
| Moderate volume depletion (7-10%) | Corresponds to 100 ml/kg loss of body weight | Resting tachycardia but normal blood pressure, capillary refill time > 2 seconds, weak peripheral pulses, irritability → lethargy, dry mucous membranes, depressed anterior fontanelle, sunken eyes, and dry skin |
| Severe volume depletion (10 – 15%) | Corresponds to more than 100 ml/kg loss of body weight. | Cannot drink properly, poor response to painful stimulus → comatose, resting tachycardia, hypotension, prolonged capillary refill time, weak central pulses, cold mottled skin |
Diagnosing dehydration
| Component | Checklist |
|---|---|
| Ask | Diarrhea, vomiting, thirst, urine |
| Look | General appearance (irritable, lethargic or coma), eyes, mouth and tongue, breathing |
| Feel | Skin, pulse, fontanelle in infants |
Causes of dehydration – basically causes of vomiting and diarrhoea
| System | Causes |
|---|---|
| CNS | Projectile vomiting due to raised ICP seen in – infections (meningitis, encephalitis, brain abscess and severe anaemia), space-occupying lesions (brain tumors, neurocysticercosis, intracranial hemorrhage), neurocysticercosis |
| Gastrointestinal | Gastreoenteritis, malabsoprtion (coeliac disease), obstruction, hepatitis, volvulus, pyloric stenosis, short gut syndrome (e.g. treating ischemic mesenteric disease) |
| Endocrine | Diabetic ketoacidosis, congenital adrenal hyperplasia, thyrotoxicosis |
| Renal | Pyelonephritis |
| Infections | Pneumonia, otitis, sinusitis, sepsis |
| Psychiatric | Anxiety |
- Patient history
- Feeding pattern and fluids given: usually dehydration from diarrhoea and vomiting is part of malnutrition
- Fluid loss e.g. vomiting, reduced urine output, loose stools: the child not passing urine in the past 24 hour is a critical sign for oliguria/anuria)
- Level of activity
- Medications given to the child: most causes of watery diarrhoea in children is viruses and generally no medication is needed. ORS and IV fluids can be given depending on the level of dehydration. Dysentery is an indication for antibiotics
- Heat and sunlight exposure
- Signs and symptoms
- Tachycardia: This can be an ealrly sign of volume depletion. If the child has fever, remember that pulse rate increases 10 beats per degree centigrate of temperature elevation above reference range
- Tachypnoea
- Hypotension: develops late when there is severe depletion
- Weight loss: an important measure of the degree of volume depletion
- Change in level of activity e.g. drowsiness, poor interaction: may reflect decreased cerebral perfusion or significant electrolyte abnormalities (hypo- or hypernatremia)
- Mild dehydration = irritable
- Moderate to severe dehydration = lethargy or coma
- Sunken fontanelle
- Sunken and tearless eyes: noticed by the parent
- Dry mucous membranes
- Reduced capillary refill time: normally < 2 seconds
- Cool and clammy extremities
- Reduced skin turgor: normally immediate return
- Oliguria
Management of Dehydration
- Investigations
- Urea, electrolytes and creatinine: assess for renaly dysfunction – acute kidney injury. Electrolyte abnormalities (especially hypokalemia and hyponatremia) can result from most causes of volume depletion.
- Glucose: rule out diabetic ketoacidosis and hypoglycaemia
- Serum osmolality
- Arterial blood gases: in patients with severe volume depletion (hypovolemic shock). Can diagnose metabolic acidosis
- Urinalysis: rule out pyelonephritis
- Principles of managing dehydration
- Maintenance fluids
- Prevent dehydration
- Prevent electrolyte disorders
- Prevent ketoacidosis
- Prevent protein degradation
- Maintenance electrolytes
- Daily requirement of sodium Sodium: 2 – 3 mEq/kg/d
- Daily requirement of potassium: 1 – 2 mEq/kg/d
- Maintenance fluids
- Treatment of dehydration (IV fluids)
- Restore intravascular volume: Normal saline or Ringers lactate 20 ml/kg bolus over 20 minutes. May need 2 – 3 repeat boluses until intravascular volume is restored
- Calculate 24 fluid needs:
- Maintenance water according to body weight (Holliday-segar formula)
- Deficit water (% dehydration x weight)
- Calculate 24 hours electrolyte needs
- Select appropriate fluid
- Administer half the calculated amount during first 8 hours
- Administer remaining over the next 16 hours
- Replace ongoing loss as they occur
- Monitor vitals, intake and output, weight, and electrolytes
- Oral rehydration therapy
- 50 ml/kg ORS within 4 hours for mild dehydration
- 75 – 100 ml/kg over 4 hours for moderate dehydration
- 10 ml/kg ORS for each loose stool
- Breast feeding and other usual feeding allowed after rehydration
- How to prepare ORS
- 1 Litre of water (boiled and cooled) + 1 packet of ORS
- Prepare fresh. Discard if child finishes
Body weight method for calculating fluid volume (Holliday-segar formula)
| Body weight | Maintenance fluid volume over 24 hours |
|---|---|
| 0 – 10 kg | 100ml/kg |
| 11 – 20 kg | 1000 ml + 50ml/kg for each kg > 10 kg |
| > 20 kg | 1500 ml + 20ml/kg for each kg > 20 kg |
Complications of Dehydration
- Complications of dehydration
- Severe volume depletion in infants or children risk cardiovascular collapse (hypovolemic shock) and death.
- Seizures
- Hyponatremia resulting from replacement of free water alone may also cause seizures
- Hypernatremia
- Decreased cerebral perfusion
- Pre-renal failure: can be corrected if recognised early. Can also progress to intrarenal failure through acute tubular necrosis if there is delay in treatment
- Heart failure: ff the child is mild-to-moderately dehydrated and large amounts of fluids are given they may get fluid overload
- Coma
WHO guidelines for treating dehydration in children
Due to a high number of children with diarrhoea and limited bed space, WHO made guidelines to manage children with dehydration in **6 hours for infants and 3 hours for older children)**instead of 24 hours
Treatment of dehydration according to WHO
| Degree of dehydration | Treatment |
|---|---|
| No dehydration | ORS after loose stools |
| Some dehydration | ORS |
| Severe dehydration | IV or IO fluid replacement needed rapidly |
Administration of IV normal saline or Ringers lactate
| Age | 30 ml/kg | 70 ml/kg |
|---|---|---|
| Infants (< 12 months) | 1 hour | 5 hours |
| Older children | 0.5 hours | 2.5 hours |
| NS or RL | Infants ( < 12 months) | Older children |
|---|---|---|
| 30 ml/Kg | 1 hour | 0.5 hours |
| 70 ml/kg | 5 hours | 2.5 hours |
ORS vs plain water for treating dehydration due to diarrhoea
| Feature | ORS (Oral Rehydration Solution) | Plain Water |
|---|---|---|
| Purpose | Treats dehydration and electrolyte loss, especially in diarrhea | Provides fluid only, but does not correct electrolyte imbalances |
| Electrolytes | Contains sodium, potassium, and chloride to restore balance | No electrolytes, can cause dilutional hyponatremia |
| Glucose Content | Contains glucose to enhance sodium and water absorption | No glucose, less efficient absorption |
| Water Absorption | Uses sodium-glucose cotransport for better hydration | Slower absorption, may not restore hydration effectively |
| Prevention of Hyponatremia | Maintains proper sodium levels | Large amounts can dilute blood sodium and cause hyponatremia |
| Effectiveness in Diarrhea | Reduces diarrheal fluid loss and helps gut recovery | Can worsen osmotic fluid shifts, increasing dehydration |
| WHO Recommendation | Gold standard for treating dehydration | Not recommended alone for dehydration, only as a supplement |
| Risk of Overhydration | Low, as it maintains fluid-electrolyte balance | High, as it dilutes body electrolytes |
24-hour Fluid Requirements Practice Questions
- A 25 kg child presents with severe dehydration
- Maintenance fluid: 1500 ml + 20 x 5 = 1600 ml
- Deficit fluid: 25 x 100ml/kg = 2500 ml
- Total fluid requirement in 24 hours = 2500 + 1600 = 4100 ml
- Boluses: 25 x 20 = 500 ml x 2 = 1000 ml (already given as bolus)
- First 8 hours: 2050 ml – 1000 ml = 1050 ml
- Remaining 16 hours: 2050 ml
