Numbers

ICU is a specialty driven by numbers. Because many of our patients are sedated or altered, we cannot always rely on symptoms or history. We use laboratory tests to understand the heart, lungs, kidney, liver, infections, blood, and other systems. Much of "rounding" involves reviewing these lab assays, X-rays, microbiology cultures, and other data.

I admitted a rather young patient who presented with the most extreme numbers I've seen. Her arterial blood gas had a pH of 6.99. A normal pH of the blood is around 7.40, and the body regulates this extremely tightly because proteins begin to denature and enzymes begin to fail if this acid-base balance becomes awry. Why did this patient have such a low pH? Her lactate was greater than 20. If you remember back to high school biology, you will recall that the body makes energy through two mechanisms: an aerobic method and an anaerobic one. When cells have oxygen, they prefer the highly efficient aerobic oxidative phosphorylation. But when deprived of oxygen, they revert to anaerobic metabolism, which produces lactic acid. This patient came in bleeding from her gastrointestinal tract and her blood counts dropped so low that she could not carry oxygen sufficiently to her tissues. The cells, suffocating, produced such an overwhelming amount of acid that her pH was less than 7. While I managed to keep her alive overnight, she is currently in multiorgan system failure, and I don't know how she will do.