Posted by Scott on March 05, 2003 at 23:46:38:In Reply to: Hypoxemia posted by Dr. Wexler on March 12, 1998 at 22:01:33:
First-time caller, this sounds like fun.
Your patient needs a real polysomnogram, not a portable study. The ICSD is silent on this type of patient unless his central ventilatory control is congenitally defective (Congenital Central Hypoventilation Syndrome and Central Alveolar Hypoventilation Syndrome). These are diagnoses of exclusion. Most hypoventilation is not central, but the result of lung disease. In the obese or severely kyphotic, the lung is compressed and diaphragmatic function is reduced. Sometimes(especially if they are short), this is enough to cause insufficient ventilation and hypercarbia, but not always. All obese people do not have hypercarbia. The term obesity-hypoventilation syndrome (Pickwickian) is a non-ICSD term and refers to those obese patients who do have hypercarbia. Not all obesity-hypoventilation syndromes have Obstructive Sleep Apnea and many have Central Sleep Apnea which is not hypoventilation. The key is daytime hypercarbia. If present, the patient is a hypoventilator. The next step is to find out why (all the tests everybody suggested). Then treat that the best way you can to lower the hypercarbia. Then do a real PSG. Then do a BiPAP titration because BiPAP is a kind of ventilator and will further lower his daytime hypercarbia. Don't forget a back-up rate of 10 or so on the BiPAP because when you improve their hypercarbia, their oxygen improves and they lose their drive to breathe. Is that clear?
You can put him on any old CPAP while all this is going on. If he does not have hypercarbia, he is just an obese OSA, use CPAP.
By the way, respiratory stimulants like progesterone don't do much. If you go that route, you can prove it with a pre/post ABG. Acetazolamide is tricky to use. It uncouples the CO2-bicarbonate linkage. Be careful in renal patients, be careful of other meds especially diuretics. The real problem is that we don't know what it does to CSF pH.
Finally, protriptyline has been used both as a respiratory stimulant and for OSA. It is poorly tolerated, but may be safer and more effective than the other two. Personally, I would avoid trying to regulate ventilation with drugs.