Investigations
1st investigations to order
clinical diagnosis
Test
Patients presenting with mild to moderate volume depletion do not require specific tests beyond a careful history and physical exam.
Patients who present with inconsistent history, severe volume depletion, or who do not respond to initial fluid resuscitation are a small subset of patients in whom diagnostic testing should be considered.
Use of a clinical scale or scoring system may improve diagnostic accuracy.[17]
Result
clinical findings vary by age and specific aetiology but can include generalised irritability, decreased activity, tachycardia, delayed capillary refill, dry mucous membranes, sunken eyes, decreased skin turgor, and decreased urination
Investigations to consider
serum electrolytes
Test
Differentiating hypernatraemic, isonatraemic, and hyponatraemic volume losses helps to guide subsequent therapy.
Serum bicarbonate is low in many types of hypovolaemia due to direct losses as in diarrhoea or poor tissue perfusion from decreased intravascular volume.
Urea/Cr is >20:1 with renal hypoperfusion.
Serum potassium is low in enteral losses but can be high in crush injuries and burns.
Result
may show hypernatraemia, isonatraemia, or hyponatraemia; enteral losses: associated with hypokalaemia and low bicarbonate level; crush injuries and burns: may be associated with hyperkalaemia.
blood glucose
Test
Young children are at risk for hypoglycaemia with any significant illness. This must be recognised and treated promptly. Hyperglycaemia occurs in diabetic ketoacidosis.
Rapid bedside testing is a readily available, quick, and appropriate initial screen, but should be confirmed with serum glucose to rule out false elevation that may mask hypoglycaemia.
Result
may show hypo- or hyperglycaemia
urea/Cr
Test
Pre-renal azotaemia frequently accompanies volume depletion.
Result
renal hypoperfusion: >20:1
FBC
Test
Anaemia can be seen in non-acute blood loss. Haemoconcentration may be noted in the setting of loss of plasma volume, especially burns.
Leukocytosis or neutropenia is common in the setting of infection. In acute haemorrhage, whole blood is lost and, until plasma volume is expanded by fluids, haematocrit is likely to be normal.
Result
haemoglobin and haematocrit: may be decreased, normal, or increased; abnormal WBC count with predominance of neutrophils or immature band forms
urinalysis
Test
Urine should be examined for signs of urosepsis and ketonuria.
Result
diabetic ketoacidosis: glycosuria, ketonuria; renal dysfunction: proteinuria; urosepsis: may be proteinuria, haematuria
urine specific gravity
Test
Concentration of urine leading to a high urine osmolarity is an appropriate physiological response to volume depletion, but may not reliably predict dehydration.[17][25]
Infants <6 months old are less able to concentrate urine due to renal immaturity, and they may not have a high specific gravity.
Hypovolaemic children with normally functioning kidneys have elevated specific gravity.
In conditions of abnormal renal function, urine specific gravity is normal or inappropriately low.
Result
normally functioning kidneys: >1.025; abnormally functioning kidneys: normal or inappropriately low
urine osmolality
Test
Concentration of urine leading to a high urine osmolality is an appropriate physiological response to volume depletion.
Patients with primary renal losses have inappropriately dilute urine in the face of significant volume depletion.
Result
usually >450 mOsm/kg
urine microscopy and culture
Test
Performed if sepsis suspected.
Result
sepsis: WBCs and pathogens may be seen on microscopy in urinary infection; culture may demonstrate specific infective pathogen
blood culture
Test
Performed if sepsis suspected.
Result
sepsis: may demonstrate specific infective pathogen
arterial blood gas
Test
Disorders of acid-base balance are frequently seen in the setting of volume depletion (e.g., lactic acidosis, DKA).
Result
may be evidence of metabolic acidosis
head ultrasound or CT scan
Test
Blunt trauma, especially to the head and abdominal viscera, is a major cause of haemorrhage-associated volume depletion. Altered mental status in a child known to have sustained trauma or in a young infant should prompt investigation for occult bleeding.
History is often hidden in settings of abuse.
Result
trauma: may demonstrate intracranial bleed
abdominal ultrasound or CT scan
Test
Blunt trauma, especially to the head and abdominal viscera, is a major cause of haemorrhage-associated volume depletion. Altered mental status in a child known to have sustained trauma or in a young infant should prompt an investigation for occult bleeding.
History is often hidden in settings of abuse.
Result
trauma: may demonstrate intra-abdominal bleed
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