Sunday, April 29, 2012

Electrolyte Imbalances During Mechanical Ventilation

Numerous factors contribute to ventilator dependence. However, one should focus on identifying factors that are potentially reversible. Electrolyte imbalances have a direct relationship to weaning from mechanical ventilation. 
Below is a summary of different electrolytes and how their imbalances may prolong mechanical ventilation. 

Calcium (Ca)
Normal: 8.4-10.5 mg/dl
LOW- may lead to muscle twitching, muscle spasms, and ECG changes.
HIGH- may lead to fatigue, depression, muscle weakness, nausea & vomiting.
Considerations- these imbalances may hider ventilator weaning & exacerbate muscle fatigue during a Spontaneous Breathing Trial  (SBT). Patients may need  a longer recovery phase between SBT's. 

Chloride (CL)
Normal: 98-110 mmol/L
LOW- can create metabolic acidosis, muscle spasm, and even coma.
HIGH- Minimal symptoms.
Considerations- if low and patient is symptomatic withhold SBT's. A SBT may increase the acidosis and lead to muscle fatigue & injury. 

Magnesium (mg)
Normal: 1.6-2.5 mg/dl
LOW- may cause muscle weakness, irritability, arrhythmia's, convulsions.
HIGH- Creates ECG changes (coupled with hyperkalemia-cardiac arrest).
Considerations- withhold SBT until corrected.

Phosphate (p)
Normal: 2.3-3.7 mg/dl
LOW- may lead to diaphragmatic weakness.
HIGH- Minimal symptoms, usually associated with endocrine disorders.
Considerations- if low allow for longer recovery between SBT's, to decrease risk of muscle damage. 

Potassium (K)
Normal: 3.5-5.1
LOW- may cause muscle weakness, myocardial irritability. If untreated can cause metabolic alkalemia. 
HIGH-arrhythmia's, cardiac arrest. 
Considerations- withhold SBT's until condition is corrected. SBT's is considered a cardiac stress test. 

Sodium (Na)
Normal 136-145 mmol/L
LOW- May cause weakness, hypertension &/or tachycardia.
HIGH- May cause confusion, irritability, seizures, coma. 
Considerations- Patient may be at increased risk for ventilator muscle fatigue. 


[1]. Dooley, J. & Fegley, A. (2007). Laboratory Monitoring of Mechanical Ventilation. Critical Care Clin. 23 (2): 135-148. 
[2]. Marino, P. (2012). The ICU Book: 3rd edition. Lippincott Williams & Wilkins.