Introduction
Monitoring in anesthesia had been in place long before the introduction of clinical anesthesia. The importance of respiratory pattern was known since antiquity. Work by William Harvey, Stephen Holes, and Claude Bernard led to the discovery of cardiovascular monitoring. Despite advancing technology and the availability of sophisticated monitoring tools, anesthesia practitioners continue to witness anesthesia-related morbidity and mortality in patients receiving anesthesia. This fact highlights the central role of monitoring the patients during the perioperative period to improve the patient’s safety and outcomes.
The expert recommendations to improve patient safety and outcomes during the perioperative period have been evolving continuously, and the latest one is by the American Society of Anesthesiologists (ASA), 2015.
Standards of ASA Monitoring (AS4.4, AS4.5)
It was first introduced in 1986 by ASA and last amended in October 2015. It includes two sets of recommendations:
Qualified anesthesia personnel shall be present in the room throughout the conduct of all general anesthetics, regional anesthetics, and monitored anesthesia care.
Objective: Because of the rapid changes in patient status during anesthesia, qualified anesthesia personnel shall be continuously present to monitor the patient and provide anesthesia care.
During all anesthetics, the patient’s oxygenation, ventilation, circulation, and temperature shall be continually evaluated.
The objectives and techniques to monitor oxygenation, ventilation, circulation, and temperature are summarized in Table 6.1.
Cardiovascular Monitoring
Monitoring of the cardiovascular system (CVS) helps to identify disturbances in rhythm, myocardial injury, and fluctuation in blood pressure. Detailed information about pulmonary vasculature and cardiac function can be obtained with the help of advanced monitoring devices. It can be done in the following three ways:
Noninvasive: Electrocardiogram (ECG), noninvasive blood pressure (NIBP).
Semi-invasive: Transesophageal echocardiography (TEE).
Invasive: Invasive blood pressure, central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP).
Electrocardiogram
Electrocardiogram monitoring helps in detecting rhythm abnormalities, myocardial injury, and cardiac arrest during the perioperative period.
Lead II is the preferred lead for arrhythmia detection.
Lead V5 alone will detect 75% of the ischemic episode; adding lead V4 increases this to 90%, and the combination of lead II, V4, and V5 add up to 96% detection rate.
The use of monitors with features of automatic ST analysis is highly recommended.
Noninvasive Blood Pressure
Works on the principle of oscillometry and record blood pressure at a set interval (interval should not be more than 5 mins).
Oscillometry principle calculates mean arterial pressure first and derives systolic and diastolic pressure utilizing set algorithm.
The length and width of the cuff should be 80 and 40% of the arm circumference, respectively.
Too large cuff underestimates blood pressure while too small cuff overestimates it.
Invasive Blood Pressure
It is more accurate compared to NIBP and is the gold standard for blood pressure monitoring. It works on the principle of “Wheatstone bridge” and requires cannulation of one the accessible arteries like radial (most common site), ulnar, brachial, femoral, posterior tibial, and dorsalis pedis. The cannulation of any of such arteries can lead to complications like bleeding, local hematoma, thrombosis, arterial spasm, digital ischemia, sepsis, and aneurysm formation. Being an invasive procedure with a myriad complications, invasive monitoring should be employed in cases where indicated, for example, the following:
Patients requiring vasopressors/inotropes.
Frequent blood analysis is needed.
Unavailability of appropriate size BP cuff.
Measurement of advanced dynamic parameters such as pulse pressure variation (PPV), stroke volume variation (SVV), and cardiac output using Flotrac device.
Although Allen’s test has been in use for many years to assess the adequacy of contribution to circulation of hand by the ulnar artery, it is not foolproof against the prevention of complications. It is performed by occluding the radial and ulnar artery after complete exsanguination of the patient’s hand. The time taken for the color of the hand to become normal after the release of pressure from the ulnar artery while maintaining pressure over the radial artery is interpreted as follows:
Transesophageal/Transthoracic Echocardiography
Echocardiography is a real-time and highly sensitive tool in detecting cardiac functions and regional wall motion abnormality during the perioperative period. The use of echocardiography can aid in:
Detection of any regional wall motion abnormality.
Assessment of valvular dysfunction.
Diagnosing heart failure (systolic, diastolic).
Transthoracic echocardiography (TTE) is noninvasive but limited by the window through the chest wall; on the other hand, TEE offers an excellent window, but being invasive requires the patient to be intubated.
Central Venous Pressure
CVP tracing is obtained by placing a venous catheter in central veins. The preferred vein is internal jugular, because it is valveless and in direct communication with the right atrium. The other sites are subclavian, basilic, and femoral veins. The CVP trace consists of “a,” “c,” “x,” “v,” and “y” waves, as shown in Fig. 6.1.
The waves of CVP are described as below:
a = due to atrial contraction.
c = due to the backward movement of tricuspid valves during its closure.
x = due to ventricular systole.
v = due to ventricular filling.
Normal CVP in adult is 3 to 10 cm H2O (2–8 mm Hg).
The various conditions which can affect CVP values are tabulated in Table 6.2.
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