DIFFERNTIAL DIAGNOSIS

   When I was in medical school, we had a visiting professor named DR, French .His father had written a book on Differential Diagnosis. The book had various causes of certain symptoms. So if one looks  at the cause of headaches, we will see many causes of headaches from simple tension headache to sinus infection to brain tumor. So it gave a list of possible causes of certain symptoms. One has to understand that the physician or the medical student has to take a detain history  and do physical examination and then narrow it down to 'few' causes.  In those days the lab tests  and radiology was not that advanced  and the Ultrasound examination and CT scan  and PET scan  and angiography etc. were not there. So everything was CLINICAL. Now a days we have many tools at our disposal and that has changes things and helped  and also made it worse. We are depending upon TESTS and not on history and physical examination and then we are going on wrong track. That brings me to the story for today. 

     I have seen this male patient for last few years  and he had smoked many many years ago and had COPD.. Over period of time he had gotten worse  and he was on oxygen and he also had cardiac problem - Atrial Fibrillation. He had few episodes of increased heart rate and i had to admit and then he had ablation and he did better. He lived by himself  and he was some what noncompliant with follow up. I checked his blood oxygen and carbon dioxide  and as expected he had elevation of CO2. In the early part of lungs not working or doing their job- which is to take in oxygen and wash out carbon di oxide, both these are normal. As the disease advances, the oxygen lack starts and then patient needs oxygen . As disease gets worse, the CO2 starts getting elevated. So in his case the oxygen had dropped  and CO2 was now elevated . The sum of these 2 gases in blood is constant ( one of the laws of partial pressure of gases in a mixture) So when CO2 increases the oxygen drops  and if we can reduce CO2, the oxygen will increase. So I started him on a machine - NIV -Non Invasive Ventilator . So he has been on it for a year and seems to have done better . His compliance was not great . I would have liked him to use it for 8 hours or more and he was using it for 4 hours  and that to not daily. So one day he had a fall in bathroom and so he came to ER . He was slightly confused  and had tremors  and the ER physician did CT scan of the brain  and admitted him for altered mental status  and may be TIA - mini stroke. NOONE BOTHERED TO CHECK BLOOD CO2.when we did do the check on it his CO2 was more than the double of normal value. and having oxygen supplementation his oxygen level was too high. THAT WAS THE CAUSE OF HIS CONFUSION AND  THE Fall. We have respiratory center in brain and it is stimulated by LACK of oxygen and Elevated CO2. So when the oxygen level drops , we breath more to compensate for it  and same with CO2 elevation. But with COPD patients the sensitivity to elevated CO2 is gone  and the patients breath only due to lack of oxygen. The elevated CO2 acts like sedative  and cause altered mental status. When one takes away lack of oxygen, the patients will not breath much . So one has to be careful as to how much oxygen should be given. In this case if one would have done HISTORY , they would have known that he was on home NIV  and that means his CO2 must be elevated  and they would have checked blood CO2  and that would have helped .But the knee jerk reaction was to do CT scan of the Brain. Certainly doing a CT scan in any patient with fall  and altered mental status is indicated  and appropriate, but checking blood oxygen and CO2 levels would have clinched the diagnosis .So the differential diagnosis has a list of many conditions that could cause the fall and the altered mental status  and the HISTORUY would have narrowed it down  and on the top of the list would have been retention of CO2!