Editing Anatomy and Physiology – RN Practice Questions (section)

==Question 6==
A patient in the intensive care unit has a cardiac output of 3.0 liters per minute, a heart rate of 128 beats per minute, a blood pressure of 84/62 mmHg, flat neck veins, and a central venous pressure of 1 mmHg. Which physiologic problem best explains this presentation?
# Excessive afterload from systemic vasoconstriction.
# Inadequate preload from decreased circulating volume.
# Impaired contractility from myocardial ischemia.
# Excessive preload from fluid overload.

'''Answer:''' 2 (B). Inadequate preload from decreased circulating volume.

''Rationale:'' Cardiac output is heart rate multiplied by stroke volume, and stroke volume depends on preload, afterload, and contractility. Flat neck veins and a very low central venous pressure indicate low right-sided filling pressure, meaning there is too little volume returning to the heart. By the Frank-Starling law, less ventricular stretch produces a weaker contraction and a smaller stroke volume, and the tachycardia is a compensatory attempt to preserve cardiac output. Option 1 is unlikely because high afterload typically accompanies a normal or elevated blood pressure. Option 3 would not produce flat neck veins and a central venous pressure of 1 mmHg; failing contractility usually causes backup and elevated filling pressures. Option 4 is contradicted by the low central venous pressure and flat neck veins.