The electrolyte bracket contains a mixture of the old staples of nephrology mixed with some new kids on the block trying to muscle in on established territory, Vaptans vs hypertonic saline and ZS-9 vs Kayexalate. Hypertonic saline is well established and works when used correctly. In my experience inadequate monitoring and insufficient lab testing always complicates the correction of severe and acute hyponatremia. Severe hyponatremia has potentially devastating consequences and so should be managed in an ICU setting where frequent labs can be drawn and most importantly acted upon. The role of Vaptans is probably more in the chronic setting, in particular for longstanding hyponatremia in the setting of heart failure. In fact the SALT 1+2 trials excluded patients with acute symptomatic hyponatremia. Dr Berl wrote a nice review in KI.
Bicarbonate is center stage in the 2 and 7 seed match up. Bicarbonate for acute acidosis such as lactic acidosis, when extreme, is widely used I would imagine. This is despite lack of good evidence to suggest it improves outcomes. However, when faced with severe acidosis it makes physiological sense to give alkali. Another area were iv bicarbonate has fallen out of favor is in cardiopulmonary resuscitation. The 2010 ACLS guidelines recommended against the routine use of iv bicarbonate. This was due to fears of it causing intracellular acidosis, hypernatremia, respiratory depression and metabolic acidosis once perfusion is restored.
One study from the 1990s looked at 273 successful out of hospital cardiac arrest outcomes. 58 patients got no HCO3 and had short CPR times (7.4 +/- 5.5 minutes). 215 patients did receive HCO3 and had significantly longer CPR times (23.3 +/- 13.5 minutes, (P =< 0.001). Initial emergency department blood gas results of both groups were not significantly different. No patients in the no HCO3 group had hypernatremia (sodium [Na]+ greater than 150), whereas four patients (2%) in the HCO3 group were hypernatremic. Eight patients (14%) in the no HCO3 group and 37 patients (17%) in theHCO3 group were alkalotic with pH values greater than 7.49 (P = NS). Six patients (10%) of the no HCO3 group and 24 patients (11%) of the HCO3 group had a metabolic component to the alkalosis as defined by a positive base excess value (P = NS). These are interesting findings given that these patients are the sickest and probably most acidemic you will encounter!
Despite this entire blurb I went for serum anion gap in this bracket!Very useful equation.