In the clinical setting some biomedical engineers have eliminated the J point in their computerized ST-segment analysis software algorithms ( Figure 16-2). The ST junction is defined as the point at which the QRS complex ends and the ST segment begins. The PR segment extends from the end of the P wave to the start of ventricular depolarization (e.g., appearance of a Q wave) (Figure 16-1). The degree of elevation (or depression) is relative to an isoelectric line, which is commonly referenced as the PR segment. Otherwise the proportion of false positives would increase. 8- 11 In particular, two chest leads (V 2 and V 3) have been shown to exhibit the greatest shift of the ST junction and as such must be accounted for in applying diagnostic criteria for myocardial injury. 4Ĭurrent recommendations for ST-segment deviation thresholds account for the influence of gender, ECG lead, age, and race on position of the ST segment. 7 When used in high-risk cardiac patients to guide early treatment, they may reduce morbidity. Compared with Holter monitors, ST-segment trending monitors have on average a sensitivity of 74% and specificity of 73% in detecting myocardial ischemia. 5, 6īecause of its low cost, noninvasiveness, widespread availability, and designation as a standard of care for monitoring of all anesthetized patients, 1 the ECG remains a common and required diagnostic tool in the operating room. 4 The overall incidence of perioperative ischemia in patients with CAD scheduled for cardiac or noncardiac surgery ranges from 20% to 80%. 3 Research has shown prolonged stress-induced ischemia (i.e., ST-segment depression) to be the major cause for cardiac morbidity (myocardial infarction) after major vascular surgery. Approximately one third of patients scheduled for noncardiac surgery have risk factors for coronary artery disease (CAD), and postoperative myocardial infarction is three times as frequent in patients with ischemia. Many factors support this trend, including the development of practice guidelines by professional societies that advocate such monitoring techniques in select patient populations 2 and the demographics of the general surgical population. Computerized real-time ST-segment analysis continues to be incorporated in operating rooms (ORs), intensive care units (ICUs), and postanesthesia care units (PACUs) across the country. This includes assessment of heart rate, rhythm, and in particular for some patients, ST segments. The continuous monitoring of the cardiovascular status via the electrocardiogram (ECG) is a requirement for any patient receiving an anesthetic. This chapter reviews the more commonly used noninvasive and invasive cardiovascular monitors in anesthesia practice. In addition, it is well known that errors in anesthesia care are minimized when clinicians remain alert and vigilant. Palpation can aid in assessing the quality of the pulse and degree of skeletal muscle relaxation, as well as locating major vascular structures when placing central venous lines or performing regional anesthesia techniques.Ĭritical thinking skills are cardinal prerequisites for successful monitoring of a patient’s anesthetic. Auscultation is used to verify correct placement of airway devices such as the endotracheal tube and laryngeal mask airway, to assess arterial blood pressure, and to continually monitor heart sounds and air exchange through the pulmonary system. Inspection of the patient can provide information regarding the adequacy of oxygen delivery and carbon dioxide elimination, fluid requirements, and positioning and alignment of body structures. They provide essential objective and subjective data not available from advanced monitoring modalities and can alert the anesthetist to occult problems in select patients. Consequently, the application of critical thinking skills, thorough physical assessment, vigilance, and the appropriate selection and application of monitors are key requirements in the process of anesthesia monitoring.įundamental monitoring/assessment techniques include inspection, auscultation, and palpation. 1 Many different monitors are commonly used to assist in the delivery of an anesthetic, and clinicians assimilate the data provided to make appropriate clinical judgments. Monitoring of anatomic and physiologic variables during an anesthetic procedure is vital to patient safety and meeting established standards of care.
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