A 55-year-old man undergoes an elective surgery under general anesthesia. Two hours into the surgery, his left ventricular pressure-volume loop has changed from the solid line to the dashed line, as shown in the image below (the loop is unchanged in areas where there is no dashed line): Which of the following is most likely responsible for this patient's hemodynamic change?

Question

A 55-year-old man undergoes an elective surgery under general anesthesia.  Two hours into the surgery, his left ventricular pressure-volume loop has changed from the solid line to the dashed line, as shown in the image below (the loop is unchanged in areas where there is no dashed line):  Which of the following is most likely responsible for this patient's hemodynamic change?

Quizplus · Accepted Answer

11ec160b_3c8b_82fb_9249_6fc2f3e68097_MD0001_00 The left ventricular (LV) pressure-volume loop in this patient shows a rightward shift in end-diastolic volume (point 1), indicating increased preload, which occurs with infusion of normal saline or other causes of increased blood volume (eg, blood transfusion, renal failure). Following the Frank-Starling law, the increased LV stretch from increased preload leads to increased stroke volume (the horizontal distance between points 1 and 3) and a slight increase in afterload (ie, the peak LV pressure reached during blood ejection). Contractility is unchanged. (Choice A) Clamping of the abdominal aorta increases aortic pressure to increase afterload. Stroke volume decreases because the left ventricle is unable to eject as much blood against the increased aortic pressure. Preload is unchanged. (Choice B) Blood loss decreases intravascular volume and leads to decreased preload. The decreased preload causes reduced stroke volume and a slight decrease in afterload (Frank-Starling). (Choice C) Dobutamine primarily acts as a beta 1 receptor agonist and stimulates increased contractility. The increased contractility increases stroke volume and leads to a slight increase in afterload. (Choice D) Acute myocardial infarction disrupts myocardial function and often decreases contractility. The decreased contractility decreases stroke volume and causes a slight decrease in afterload. Preload is unchanged initially but is likely to increase if the decrease in contractility is sustained. Educational objective: A rightward shift of the bottom right corner (point 1) of the left ventricular (LV) pressure volume loop indicates increased end-diastolic volume or preload, which occurs with infusion of normal saline. The increased preload causes increased LV stretching and leads to increased stroke volume and a slight increase in afterload (Frank-Starling law).

A 55-Year-Old Man Undergoes an Elective Surgery Under General Anesthesia