A 49-year-old man, who is in the post-anesthesia care unit recovering from cardiac ablation for atrial fibrillation, is experiencing chest pain and shortness of breath. The symptoms started suddenly while he was resting and have been rapidly getting worse. The patient has no other medical history. Blood pressure is 74/32 mm Hg, pulse is 140/min, and respirations are 30/min. Pulse oximetry is 92% on room air. On examination, the patient is diaphoretic and appears distressed. He has distant heart sounds and the jugular veins are distended. The lungs are clear to auscultation bilaterally. ECG shows sinus tachycardia and low-amplitude QRS complexes. Which of the following hemodynamic changes are most likely present in this patient?

Question

Quizplus · Accepted Answer

11ec25c8_d8a9_3f5b_bc81_29f9d38ce67f_MD0003_00 IVC = inferior vena cava; JVD = jugular venous distension; LV = left ventricular; SBP = systolic blood pressure. This patient has Beck triad (hypotension, jugular venous distension, distant heart sounds) and low-amplitude QRS complexes on ECG, findings consistent with cardiac tamponade. Acute tamponade is a potential complication of cardiac procedures (eg, ablation), which may cause bleeding into the pericardial space. As blood or fluid fills the low-compliance pericardial sac, pericardial pressure increases and compresses the cardiac chambers; the relatively low-pressure right-sided chambers are primarily affected, with restricted diastolic filling of the right atrium and right ventricle. As these chambers are unable to fill, less blood is pumped to the left side of the heart and cardiac index (CI) (a measure of cardiac output per body surface area) decreases, resulting in hypotension and obstructive shock. Because the obstruction to blood flow is primarily right-sided, an absence of pulmonary edema is expected. Due to compression by the accumulating pericardial fluid, right atrial pressure (RAP) (a reflection of central venous pressure) and pulmonary capillary wedge pressure (PCWP) (a reflection of left atrial pressure) are increased. As tamponade progresses, diastolic pressures in all 4 cardiac chambers increase and equalize with pericardial pressure (and with one another), stagnating blood flow within the heart. (Choice A) Hypovolemic shock involves decreased RAP, PCWP, and CI. In response to the low CI, systemic vascular resistance (SVR) increases to try to maintain blood pressure. Hypovolemic shock (Choice B) Obstructive shock due to acute pulmonary embolism involves increased RAP (proximal to the obstruction) and decreased PCWP and CI (distal to the obstruction). SVR is increased in response to low CI. Tamponade represents a unique scenario in which PCWP is elevated despite decreased blood flow to the left atrium. pulmonary embolism PCWP is elevated (Choice C) Septic shock involves peripheral vasodilation with decreased SVR and decreased RAP. PCWP is also decreased. CI is increased because of sympathetic activation in response to the reduced SVR. Septic shock (Choice E) A marked decrease in SVR is the initial disturbance in high-output heart failure, and a compensatory rise in CI increases venous return (increased RAP). Despite a sustained increase in CI, left ventricular output cannot keep up with the increased flow demand created by reduced SVR and heart failure develops (eg, increased PCWP). high-output heart failure Educational objective: Cardiac tamponade may be recognized by Beck triad (hypotension, jugular venous distension, distant heart sounds). Increasing pericardial pressure restricts diastolic filling of the right-sided heart chambers, leading to decreased cardiac output and obstructive shock. Right atrial pressure and pulmonary capillary wedge pressure (a reflection of left atrial pressure) are increased due to compression. References: Cardiac tamponade. (http://www.ncbi.nlm.nih.gov/pubmed/29025544)

A 49-Year-Old Man, Who Is in the Post-Anesthesia Care Unit