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Prevalence in the ICU
Prevalence in the ICU
- Commonality: Highly prevalent in critically ill patients across species.
- Horses:
- Hospitalized horses: 49%.
- Surgical colic patients: 54% (often associated with postoperative ileus).
- Enterocolitis cases: 78%.
- Small Animals: 39%–46% of dogs and cats in the ICU.
- Impact: Leads to a longer length of hospitalization and higher rates of concurrent electrolyte imbalances like hypokalemia and hyponatremia.
Pathophysiology & Consequences:
Pathophysiology & Consequences:
- Inflammatory Response: Increases the severity of systemic inflammatory response syndrome (SIRS) and worsens the body's reaction to endotoxin.
- Gastrointestinal Impact: Can lead to ileus (lack of intestinal movement).
- Cardiac Impact: Risk of cardiac arrhythmias.
- Refractory States: Causes hypokalemia and hypocalcemia that may be resistant to standard treatment until the magnesium deficiency is corrected.
Etiology (Causes in Critical Illness)
Etiology (Causes in Critical Illness)
- Redistribution: Cellular or "third-space" redistribution of magnesium.
- Fluid Therapy: Aggressive IV fluid treatment that is unsupplemented with magnesium can lead to diuresis and subsequent loss.
- Gastrointestinal Loss: Loss of magnesium through the GI tract.
- Homeostatic Shift: Altered magnesium homeostasis due to acute illness.
- Note on Diet: Unlike other metabolic issues, diets for horses and small animals are rarely deficient in magnesium; the deficiency is usually secondary to the illness or treatment.
Metabolic & Endocrine Regulation
Metabolic & Endocrine Regulation
- Lack of Endocrine Control: Unlike calcium (which is tightly regulated by PTH), magnesium does not have a complex homeostatic endocrine regulating mechanism.
- Renal Role: Precisely regulated primarily by the kidneys.
- Hormonal Influences: Vasopressin, glucagon, and calcium concentrations influence magnesium absorption and excretion.
- Relationship with PTH:
- Mild hypomagnesemia: Stimulates PTH release.
- Severe magnesium depletion: Actually decreases PTH release, complicating calcium regulation.
Management & Treatment:
Management & Treatment:
- Diagnostic Investigation: Parallel determination of calcium and PTH concentrations is recommended to fully understand magnesium homeostasis in a patient.
- Supplementation Criteria: Magnesium should be supplemented if an inappetent animal requires long-term fluid treatment.
- Dosage:
- Constant Rate Infusion (CRI): Magnesium sulfate at 50–150 mg/kg/day, IV.
- Volume: Equivalent to 0.1–0.3 mL/kg/day of a 50% solution.
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