Expert: Ronald Levy, M.D. - 12/9/2007

Question
Dr. Levy,

I have been trying to find an answer to two serious questions for months and cannot get an answer from my sources.  Hopefully you can assist me in finding the answers.

Patient is a 59 year old male in relatively good health.  He does have early stages of PAD and some hearing loss with tinnitus.  Weight 190 lbs., 5'10".

Questions 1:

How long would it take for an individual's O2 level to drop from the mid 90's (94%) to 86% if they were Pseudocholinesterase Deficient and did not know they were Pseudocholinesterase Deficient once they were taken off a respirator after surgery?

Cholinesterase Serum level 2 hours after surgery was 3270 (classified as Low).

Questions 2:

Does a Cholinesterase Level of 3270 suggest that this individual is Pseudocholinesterase Deficient and since it is hereditary he should notify his children to make their doctors aware of this since they too could have this deficiency?

Any assistance you can give me would be helpful.

Regards,
Bill

Answer
Let me start with the second question. First of all, I am not familiar with an absolute value of cholinesterase enzyme. We usually determine Pseudocholinesterase Deficiency (PD) with a Dibucaine Number (DN) where normal enzyme has a DN of 75 and above, heterozygous atypical enzyme has a DN of 40-70, and homozygous atypical enzyme has a DN of less than 20. Whatever the case, his children should definitely be aware of this and should be tested for it prior to any surgery.

As to the first question, there is no definitive answer to this question. The reason is as follows. The oxygen saturation follows a sigmoidal curve meaning that from about 91 to 100 the curve is flat and changes in oxygen saturation do not significantly influence the number of oxygen molecules attached to the hemoglobin molecule. But below 91 the curve falls of sharply so that very small changes in the # of oxygen molecules attached to hemoglobin will significantly change the saturation. So if someone stops breathing, their saturation will slowly fall from 100 to 91 an then start to fall very quickly after that. The speed that it falls is related to the oxygen concentration in their blood before they stopped breathing. So if the patient was breathing 100% oxygen for 5 minutes before being extubated, they could probably go for 5-10 minutes before their saturation would fall into the low 90s. I would be surprised that the anesthesiologist didn't check for spontaneous breathing strength before he extubated the patient. This is one of our golden rules.

Hope this helps,

Ronald Levy, MD
Associate Professor of Anesthesiology
UTMb-Galveston