Volume depletion
Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management
Definition
Volume depletion refers to a reduction in intravascular fluid volume due to fluid loss, inadequate intake, or fluid redistribution.
Aetiology
- Gastrointestinal losses: diarrhoea, vomiting, gastrointestinal bleeding.
- Renal losses: diuretics, adrenal insufficiency, osmotic diuresis (e.g., diabetes mellitus).
- Third space losses: burns, peritonitis, pancreatitis.
- Inadequate intake: reduced fluid consumption due to illness or neurological impairment.
Pathophysiology
- Loss of intravascular fluid decreases venous return and cardiac output, leading to hypotension and organ hypoperfusion.
- Activation of the renin-angiotensin-aldosterone system (RAAS) promotes sodium and water retention to compensate for volume loss.
- Severe depletion results in hypovolaemic shock and multi-organ failure if untreated.
Risk Factors
- Advanced age or frailty.
- Chronic kidney disease.
- Use of diuretics or laxatives.
- Diabetes mellitus (osmotic diuresis).
- Conditions causing excessive sweating (e.g., heat exposure, fever).
Signs and Symptoms
- General: thirst, dry mucous membranes.
- Neurological: dizziness, confusion, syncope.
- Cardiovascular: hypotension, tachycardia, postural dizziness.
- Renal: oliguria, concentrated urine.
- Skin: decreased skin turgor.
Investigations
- Serum electrolytes: assess sodium, potassium, urea, and creatinine levels.
- Urine osmolality and specific gravity: elevated in volume depletion.
- Blood urea nitrogen (BUN)/creatinine ratio: increased in prerenal azotaemia.
- Haematocrit: may be elevated due to haemoconcentration.
- Arterial blood gas (ABG): to assess for metabolic alkalosis (vomiting) or metabolic acidosis (diarrhoea).
Management
1. Fluid Replacement:
- Oral rehydration: preferred for mild cases (e.g., oral rehydration solutions).
- IV fluid therapy: isotonic crystalloids (e.g., normal saline, Ringer’s lactate) for moderate to severe depletion.
2. Correct Underlying Cause:
- Stop diuretics if contributing to volume loss.
- Treat infections, adrenal insufficiency, or gastrointestinal losses appropriately.
3. Monitoring:
- Monitor vital signs (BP, HR) and urine output.
- Repeat electrolyte and renal function tests to guide ongoing fluid replacement.
4. Referral:
- Acute medical team: for patients with haemodynamic instability or severe depletion.
- Nephrology: if renal impairment or electrolyte disturbances persist.
- Endocrinology: if adrenal insufficiency is suspected.