Isotonic Dehydration

Definition, Etiology, PathogenesisTop

Isotonic dehydration is loss of water with preserved normal effective osmolality of body fluids.

Causes include loss of isotonic fluids via the gastrointestinal tract, kidneys, or skin (burns); loss of blood; or as a result of fluid sequestration in the “third space” (eg, the peritoneum).

Clinical FeaturesTop

Manifestations include features of hypovolemia (decreased blood pressure and central venous pressure, tachycardia), features of central nervous system ischemia, oliguria (prerenal acute kidney injury), dry mucous membranes, dry skin, and reduced skin turgor. In case of extremely severe dehydration, the patient develops hypovolemic shock.

DiagnosisTop

Diagnosis is based on a positive history of current or prior loss of body fluids as well as the presence of clinical features of dehydration and hypovolemia, and in some cases prerenal azotemia (see Acute Kidney Injury). Differential diagnosis includes all conditions associated with hypotension, such as cardiovascular or central nervous system diseases, poisonings, or other disorders.

TreatmentTop

1. Volume resuscitation using balanced (our preference) or unbalanced (saline) crystalloid fluids,Evidence 1Strong recommendation (benefits clearly outweigh downsides; right action for all or almost all patients). Moderate Quality of Evidence (moderate confidence that we know true effects of the intervention). Quality of Evidence lowered due to indirectness. Self WH, Semler MW, Wanderer JP, et al; SALT-ED Investigators. Balanced Crystalloids versus Saline in Noncritically Ill Adults. N Engl J Med. 2018 Mar 1;378(9):819-828. doi: 10.1056/NEJMoa1711586. Epub 2018 Feb 27. PMID: 29485926; PMCID: PMC5846618. unless there are specific indications for blood or plasma, to compensate for the prior and current volume loss.

2. Intensive treatment of causes of dehydration.