Which clinical sign is most consistent with hypovolemic shock?

In the context of hypovolemic shock, low cardiac output is indeed a critical and consistent clinical sign. Hypovolemic shock occurs when there is a significant loss of blood volume, which can be due to hemorrhage or fluid loss from other causes. This reduction in blood volume leads to inadequate blood return to the heart, resulting in decreased stroke volume and consequently low cardiac output. The body attempts to compensate for this low output through various mechanisms, but the underlying issue remains a deficiency in circulating blood volume.

The other options do not align with the physiological state observed in hypovolemic shock. For instance, high blood pressure is typically not present; rather, blood pressure tends to drop as the body struggles to maintain perfusion. Bradycardia is also counterintuitive, as the heart rate usually increases as a compensatory response to falling blood volume and blood pressure. Increased cardiac output contradicts the fundamental definition of hypovolemic shock, as the blood volume deficit would not support a higher output from the heart. Thus, low cardiac output effectively represents the heart's response to attenuated preload due to hypovolemia.