Invasive Monitors – Anesthetic Systems

by Brian Warriner, MD, FRCPC

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    00:00 There are a number of invasive monitors that are used in specific procedures and for high risk patients. So, invasive monitors are any monitor in which we have to put a line into the patient in some fashion, and then connect to one of these colored transducers outside the patient. And each of these transducers has to be calibrated at the time we connect it to the patient. And this allows us to measure the actual pressure the patient is generating. This can be blood pressure, this is a very common use of this.

    00:32 We just place some freezing in the wrist and we pass a catheter into the radial artery, and we connect the radial artery to a transducer, and we can measure the actual blood pressure every time the patient's heart beats. Plus, we can take blood samples without sticking more needles in the patient. But there are a lot of other pressures we also measure, including cerebral, excuse me, central venous pressure, which is the pressure of the venous blood within the body. We put a catheter through the external, internal jugular vein, usually into the superior vena cava or even into the right atrium, and we can measure pressures there. We can pass a catheter down through the heart and through the tricuspid valve, out into the pulmonary circulation and measure pressures in the lung. This kind of device can also measure cardiac output, can measure mixed venous saturation, which is an indication of oxygen used by the patient. Very sophisticated, very, very impressive, very helpful monitors.

    01:38 And patients who have intracranial hemorrhages or trauma to their head, and have bleeding into their, into their skull, can have monitors placed that measure their intracranial pressure. So, that kind of monitor is placed by a neurosurgeon, but we're the ones who hook it up, and we often monitor it.

    01:56 In certain cardiac cases, or in other cases where we're concerned about the patient's overall hemodynamic stability, we can pass a trans-esophageal echocardiogram through the esophagus of the patient. And we can do ultrasounds from the esophagus, through the heart anteriorly. And we can measure cardiac output. We can look at the actual contraction of the ventricle. And we can look at the function of the various cardiac valves. This is extremely valuable in cardiac surgery, but can also be used in other high risk forms of surgery where the patient may be hemodynamically unstable. Sensory and motor evoked potentials are used in spinal cord surgery to make sure that nervous connections between the spine and the lower limbs don't get damaged during the surgery. Electroencephalogram is sometimes used in surgery. In one of the hospitals I work in, we use it all the time when we're doing carotid endarterectomy. In other words, cleaning out the carotid artery. We use an EEG to make sure that the patient's not having a decrease in the cerebral circulation, which might be a precursor to a stroke. In addition, there are new cerebral monitors. A very well known one in the United States is the BIS monitor. It's not widely used elsewhere, because it's actually never been shown to be very useful. But the BIS monitor is widely used in the United States and is supposed to be an indicator of depth of anesthesia, and is supposed to help the anesthesiologist prevent recall during anesthesia. Cerebral oximetry monitoring actually allows us to look at the blood going into the brain, and determine its oxygen saturation. We can do fetal heart monitoring through the abdominal wall of the mother towards birth. And we do uterine contraction monitoring, particularly when we're doing emergency Cesarean sections on patients who are in labour.

    About the Lecture

    The lecture Invasive Monitors – Anesthetic Systems by Brian Warriner, MD, FRCPC is from the course Anesthesiology: Introduction.

    Included Quiz Questions

    1. It is used in patients with head trauma.
    2. It is used in patients at high risk for stroke.
    3. It is typically used during surgery as an indicator of the depth of anesthesia.
    4. It can ensure that there is no lack in the cerebral circulation system.
    5. It can assess oxygen saturation in the major cerebral arteries.
    1. Volume of blood pumped by the left ventricle
    2. Mixed venous oxygen saturation
    3. Tricuspid valve function
    4. Left ventricle contractility
    5. Systolic blood pressure

    Author of lecture Invasive Monitors – Anesthetic Systems

     Brian Warriner, MD, FRCPC

    Brian Warriner, MD, FRCPC

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