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Common Intensive Care Unit (ICU) Monitors

22 March, 2012 | intensive care, Surgery Equipment

ICU Monitors -

Intensive care units (ICU) employ a variety of different monitoring techniques in patient care. Monitoring equipment is used in ICUs when care demands more accurate monitoring than bedside physical examination. Equipment can be tailored to monitor a variety of vital signs on a patient, such as, cardiac, pulmonary, hemodynamic, or volume status. Monitors can also be invasive or noninvasive. There are generally seven major types of monitoring devices: blood pressure cuffs, oxygen saturation monitors, cardiac event monitors, arterial lines, central venous lines, swan-ganz catheters (also known as PACs), and end-tidal CO2 monitors.

Blood pressure cuffs come in all shapes and sizes and its important to select a cuff that fits the patient’s arm. A rule of thumb is that the cuff should be 80% of the upper arm circumference and width should be 40% of the upper arm circumference. Having a cuff that is too small leads to falsely elevated pressures. Low-flow states can lead to underestimation of blood pressure. Pulse oximeters are another type of non-invasive monitoring device that measures peripheral arterial blood oxygen saturation. When clipped onto a finger, the device can distinguish reflections of light of oxygenated versus deoxygenated blood, allowing detection of percent oxygen saturation. Cardiac monitors are usually set up similarly to an electrocardiogram, with 12 leads recording electrical activity continuously. They are connected to a computer monitor that reads usually one lead at a time. The computer system can calculate potentially dangerous rhythms and can alarm the medical team during these events.

Noninvasive monitoring is very helpful, however, invasive monitoring in the ICU is usually required for more accurate readings of blood pressure and oxygenation, particularly in patients who are in shock and/or on mechanical ventilation. Arterial lines provide a good way to monitor pressures in the periphery. Central venous pressure lines, aka Central Lines, can give better measures of volume status as well as provide a port to administer medication that cannot be given peripherally. There are generally four locations to gain access to the central venous circulation: the internal jugular vein, subclavian vein, supraclavicular vein, and femoral vein. Major complications from line placement include pneumothorax (air getting into the pleural space, compressing the lung), arterial puncture, vein thrombosis, malposition of catheters, venous air embolism, and infection. There are two main types of catheters for central venous access: multilumen (usually triple-lumen) that can be used for different infusate solutions and an introducer catheter, large bore catheters with side-arm infusion ports for infusion at rapid rates.

Swan-Ganz (PAC) catheters provide the most accurate measurement of a patient’s volume status. These catheters are threaded into the pulmonary artery via the superior vena cava and have a balloon tip that carries the catheter into the pulmonary vasculature until it gets “wedged” into a small artery. Wedging the balloon allows the catheter tip to sample pressures that are very close to the left atrium of the heart and therefore, equivalent to left ventricular end diastolic pressure. In general, there are five different ports of a PAC: Distal injection port, balloon inflation valve, proximal injection port, extra injection port, and the thermistor connector. PAC’s are indicated if there is uncertainty regarding fluid status, especially in heart or kidney failure. Also, when right-sided cardiac pressures do not correlate with left-sided pressures, or to assess left ventricular function when this is unknown. There are four main complications of PACs. Ventricular ectopy can occur when the His fibers at the right ventricle outflow tract are irritated as the balloon advances. The pulmonary artery could rupture causing severe bleeding, which is rare and usually fatal. There is a chance the occluded artery could damage tissue downstream (this is called infarction). Finally, right bundle branch block may occur, which may lead to complete heart block in the presence of pre-existing left bundle branch block. These are the basic strategies that clinicians employ when monitoring patients in the ICU.