Oxygen: Effect on Acid Base Balance – Hemostasis and Acid Base Balance

00:00 acidosis with bicarbonate, which the kidney produces, is impaired. This is a slide of the Oxyhemoglobin dissociation curve. And the way this is represented, is that on the vertical axis shows the oxyhemoglobin saturation, and on the horizontal axis we have the oxygen level in the blood. Under normal circumstances, the oxygen level in the blood is around 90 to 100. So, you can see that there's a period during which oxygen is very rapidly taken up by the hemoglobin, that's the steep part of the curve, and then there's a relative flattening of the curve, and there's little change in the oxygen level at that point. Conditions in the body can either interfere, or actually improve the delivery of Oxygen, by shifting the Oxyhemoglobin curve either to the left, or to the right. If it's shifted to the left, the hemoglobin becomes much more avid for oxygen, it doesn't release oxygen well. So this occurs when there's alkalosis, when there is hypothermia, and when DPG is decreased.

01:12 The shift is to the left, oxygen is not delivered to tissues well. On the other hand, a shift to the right will allow more easy delivery of oxygen to tissues.

01:24 It's easier for oxygen to be released by hemoglobin, when the Oxyhemoglobin dissociation curve moves to the right. And this can occur with acidosis, with hyperthermia, and with increases in DPG. What most of us try to do is try to keep the Oxyhemoglobin dissociation curve from moving at all. So we maintain normal blood pressure, normal temperature, and we try to maintain normal pH. But if you have a choice between alkalosis in this situation, or a little bit of acidosis, acidosis at least improves offloading of oxygen to tissues. So, the anesthesiologist role in maintaining acid-base balance is to provide a well controlled anesthesia, with minimal negative effects upon respiratory and cardiac function. Major hemodynamic changes are always a negative in this situation, because they'll nearly always cause acidosis. In addition, the anesthesiologist must aggressively resuscitate patients who have become volume depleted through trauma, or other bleeding disorders, or who are dehydrated through diarrhea, or too much heat prior to coming to the operating room. Kidney disease is a common problem in society, and it's becoming more common all the time. These patients require monitoring of their acid-base status during surgery, and correction of the dangerous changes such as metabolic acidosis and metabolic alkalosis that can occur. Unfortunately, it's not easy to change these things, it's not always easy to fix them, but at least you should know what's happening and be prepared to attempt to fix them.

03:12 Fortunately, anesthesia itself, except for its expected effects upon respiratory and cardiac function, does not adversely affect acid-base status. However, it is the duty of the anesthesiologist to monitor acid-base status, and to correct adverse changes wherever possible.

03:30 So in summary, in this lecture we've talked about some of the physiologic effects of anesthetic vapours, opiates and induction agents. We've talked specifically and primarily about respiratory function and cardiac function, because that's where the major effects are.

03:48 We've alluded to some of the effects that occur on hemostasis and on acid-base balance.

03:54 The bottom line for every anesthesiologist is that, it's his or her duty to constantly monitor the patient for all of these conditions, and to adjust the patient's condition in the appropriate direction when any of these areas go out of line. The constant monitoring is absolutely critical and is really the duty of every anesthesiologist.