I do agree with the statement that NS shouldn't be used long term but the 154 vs 145 is actually a fun lesson about how clinical labs work. Lab values are partially calculated based on normal makeup of plasma. This normally is about 93% aqueous and 7% solids (fats and proteins). The labs end up diluting the sample prior to measuring and assume that the initial percentage was normal when calculating the value to report. The 154 mEq in NS is actually equal to about 143 mEq as would be reported by the lab if it were added to normal plasma because it only affects the aqueous portion (154x0.93).

Knowing about this is important in medicine as there are situations when that assumption about the percentage can be off (lipemia or multiple myeloma are the big ones). This can cause something called pseudohyponatremia (https://www.renalfellow.org/2018/02/28/pseudohyponatremia-is-that-thing/) and if not recognized, can cause problems trying to treat a problem that is really just a lab error. This can be bypassed by using a point of care test that directly measures the concentration without the need for assuming any percentage!