past the left heart “preload’ has been reported as the “wedge pressure” in a patient
who had pulmonary arterial monitoring (aka Swan Ganz catheter). This method of
monitoring is not routinely used in the pediatric ICU setting. In the postoperative
cardiac patient, the left heart preload is the left atrial pressure. Optimizing preload
is giving volume-crystalloid or blood products depending on the clinical need.
Afterload refers to the resistance of the vascular bed that receives flow from the
heart. For the purposes of this discussion, afterload is the vascular resistance in
the systemic vascular system. The most common instance where the vascular
tone of the system is “loose” is sepsis. In septic shock, bacteria and host
characteristics contribute to decreased vascular tone. Increasing after load
increases cardiac output and is accomplished by vasoactive medications such as
neosynephrine. One must make certain that the patient has adequate preload
before using medications to augment after load.
Cardiac contractility refers to the force by which the heart ejects blood. As
previously mentioned, preload, as dictated by the Frank Starling curve is
responsible for part of cardiac contractility. Contractility can also be affected by
inherent muscle weakness due to ischemia (MI), trauma (cardiac contusion), stun
(postop state) or even electrolyte/hormonal dysfunction (hypocalcemia,
hypothyroidism). Contractility can be augmented by myotropic agents such as
dobutamine (B2 adrenergic), epinephrine (B1 and B2), milrinone(↑ cyclic AMP).
Decreasing oxygen consumption requires paying attention to the patient’s
metabolic state. Normothermia should be achieved. Decreasing work of breathing,