Quiz 9

A 35 year old male is brought to the ER from home. He is drowsy. There is a bottle that the ambulance crew have brought to the ER that they found at his bedside. There was also a suicide note by his side.

You find that his pupils are reactive and normal in size.   Lab values are as follows: Na 142, K 3.9, HCO3 18 , Cl 102 , BUN 20 , Creatinine 0.8, Glucose 95. pH 7.18  pO2 81 pCO2 26, HCO3 12, Osmolality 326, CXR few bibasilar infiltrates , CT Brain  Normal,

Q1. Which of the following is an unlikely cause of this patient's pH imbalance 

Ethylene glycol

ETOH

Methanol

Paraldehyde

Answer is choice 4 (Paraldehyde) Paraldehyde  gives anion gap acidosis but does not give an osmolar gap. Isopropyl alcohol is iso-pH i.e. no change in pH but gives an osmolar gap (it is not a choice in this question).
In this patient there is an anion gap. There is also an osmolar gap.
Anion gap is calculated as Sodium - (Chloride + Bicarbonate). It should  be in the range of 10 ± 2. High anion gap is due to acids that do not reflect in chloride. Thus the only acid that will not cause anion gap must be HCl. If it is due to loss of alkali, it must be due to loss of bicarbonate. All other acids cause anion gap.

Alcohol causes keto-acidosis, as does diabetes. Methanol gives Formic acid. Ethylene glycol gives oxalic acid and forms oxalate crystals which explains choice 3 of Q2.

Now to understand osmolar gap - it is the difference between measured and calculated osmolality - please check out nephro .

Q2. Which of the following statements is FALSE ?

Bicarbonate values from the ABG are less reliable than the bicarbonate values found on the Serum electrolytes.

Isopropyl alcohol is unlikely to be the cause of the pH alteration

Crystals in the urine are a good finding to look for.

If methanol is the cause, bicarbonate is the first drug to be given to prevent blindness.

Sodium Bicarbonate, given IV would improve the mental status of this patient significantly

Answer is choice 5 (Sodium Bicarbonate, given IV would improve the mental status of this patient significantly).

NaHCO3 does not improve a patient significantly if the pH is around 7.2 already - like it is in this case. Another criteria used for determining the utility of giving bicarb just to correct acidosis is bicarb less than 15. In this case, the true measured bicarb is 18 (not 12 as shown in the ABG).

I always wrongly thought that in terms of treatment/prevention of blindness due to methanol, Ethanol was the treatment of choice. It actually is Bicarbonate. This hardly known fact MUST be made well known to doctors due to its rapidity of benefiting a patient who would otherwise become blind. To confirm this answer, you may read Harrison's or just believe me. The other statements that are true in this question are  self explanatory or have already been explained in the answer to Q1.