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 Anesthetic Monitoring
Which would you rather have, a lousy surgeon and a great anesthetist, or a great surgeon and a lousy anesthetist?
I think I would go with the lousy surgeon and the great anesthetist, because at least I would survive the operation to sue Dr. Fumblefingers later for his botched surgery. The realities of surgery are that your anesthetist has a far greater opportunity to kill you than your surgeon does.
Some of us will remember a music group called the Bee Gee's. In 1997 they wrote a smash hit called Stayin' Alive. What was Stayin' Alive about? Hard to tell, really. The Bee Gee 's were famous for a lot of things, but clear diction and crisp enunciation weren't among them. I could never really tell what Stayin' Alive was about.
In an anesthesia setting, it's a lot easier to tell what stayin' alive is all about. Stayin' alive is all about the body's ability to get oxygen to the tissues and get carbon dioxide away from them, at least on a short-term basis. It's that simple. To do that, it takes breathing and it takes blood flow.
But not just any breathing and not just any blood flow. The breathing must be deep enough to actually exchange gasses, and it must be regular. We supplement oxygen during surgery, and that helps get oxygen in to the blood, but oxygen does nothing to help carbon dioxide get out of the blood. You have to be breathing.
Then the bloodflow must have blood adequate pressure to reach all the tissues. The maximum pressure can't be too high, and the minimum must not be too low or you can get into trouble. That means that you have to have a heart beating in a normal rhythm and a normal rate, with normal strength, and you must have normal vascular tone.
How do we make sure all this is happening? It's a little thing I call anesthetic monitoring. Every body, both human and animal, is different. Although there are "standard doses" of anesthetic drugs, the reality is that the response to these standard doses is different between individuals. For that reason, anesthetic drugs are given "to effect," meaning that you give only as much as is needed to produce the desired effect and no more. It takes constant monitoring to be sure that we have given enough but not too much.
As part of this monitoring, we check the following:
Heart Rate Heart Rhythm Pulse Quality
Oxygen Stauration Capillary Refill Time Jaw Tone
Eye Position Muscle Tone Body Temperature
Blood Pressure Mucous Membrane Color
Some of this checking is done with our eyes, ears, and hands. While this is a low-tech approach, vital information is obtained this way that could not be obtained any other way. Mechanical and electronic monitors are important, but nothing can replace trained eyes and hands and ears. Our anesthetic monitoring is done by a dedicated technician. Here, the word "dedicated" is not talking about his or her devotion or work ethic. It means that our anesthesia techs are in the surgery room doing nothing but monitoring. They are not running back and forth to the next room doing laundry.
To supplement our techs' trained ears and eyes and hands, we use a variety of electronicmonitors. For instance, we have two instruments which measure blood pressure.
 
The instrument on the right is a doppler unit used to measure blood pressure in the smaller patients. The instrument on the left is a dynamap, an oscillometric unit used to measure blood pressure in the larger patients. Measuring blood pressure is vital to stayin' alive, since low blood pressure, or hypotension, can be devastating to the patient. If the blood pressure is low, not enough blood will circulate to provide oxygen and remove carbon dioxide. The tissues begin to die. This is not good, especially if those tissues are in the brain or kidney, the first two organs to suffer when blood pressure drops. As CO2 accumulates, blood pH cahnges, and so none of the complex biochemistry that happens in the body works right. As the heart suffers from lack of oxygen and CO2 build-up, it becomes weaker and able to pump even less blood, then eventually goes into abnormal rhythms and then arrest. You get the picture.
Low blood pressure is a common finding in anesthetized patients. We estimate that as many as 30% to 40% of our anesthesia patients will experience hypotension at some point. This is not due to something we are doing wrong. It happens to humans under anesthesia too. Uncorrected, it can pose serious problems. Follow the link Intra-Op Hypotension for a detailed explanation.
Breathing is the second thing we monitor electronically. Besides counting the number of respirations in a minute, we also monitor the actual gasses in the blood. The instrument below is a pulse oximeter. It measures how much oxygen is dissolved in the blood.  If the patient is breathing adequately, the oxygen saturation (or SaO2) will be high, near 100%. This means that the blood is carrying all the oxygen that it can. To tip the scales in our favor, we supplement oxygen to anesthetized patients. Under anesthesia, patients are breathing 99% oxygen ( plus 1% anesthetic gas), as compared to room air which in only about 21% oxygen. If breathing is not adequate, the percent of oxygen saturation in the blood will drop, and our pulse oximeter will tell us when this happens. You can have regular breathing at a normal rate, but if the breathing is not deep enough or if there are some lung problems, not enough gas will be exchanged and oxygen saturation will drop.
Another type of respiration monitor is the capnograph. The capnograph measures the amount of  CO2 that is expired. Because our patients are breathing 99% oxygen, it really takes some serious breathing problems to make the oxygen saturation go down. However, supplementing oxygen does nothing for helping the body expel CO2. Thus, when the breathing first starts to get a little marginal, the oxygen saturation will not change much, but expired CO2 (end-tidal CO2, or etCO2 as it is called), will start to rise. Rising end-tidal CO2 is a very sensitive early warning sign of respiratory problems.
The last monitor we will discuss in the electrocardiogram. Also called an ECG for short, this TV-like device can also provide vital information. Just because the heart beating in a normal cadence, it does not mean that the heart is actually working correctly. Sometime abnormal rhythms happen, often in response to low oxygen and high CO2 situations, that seriously imterfere with the heart's ability to pump blood, and which can sometimes progress to actual cardiac arrest. To monitor the heart's rhythm, we sometimes we use an ECG machine. The ECG machine measures the electrical wave form of the heart.
Each monitor has it's good points and it's bad points. The ECG, for instance, can appear perfectly normal for up to ten minutes after the patient is clinically dead. The Pulse Oximeter can register normal readings even though blood pressure has dropped to harmful levels. The blood pressure monitors can give normal readings even though there is no oxygen in the blood. A patient can appear normal to a trained technician but be one heart beat away from arrest with an abnormal heart rhythm. It takes a combination of close observation plus thoughtful interpretation of all the monitoring numbers to provide safe anesthetic monitoring.
Clik the link to return to the Consumer Guide to Elective Surgery
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