Medications That Affect Preload
Nitroglycerin is the primary medication that reduces preload by causing venodilation and decreasing venous return to the heart. 1
Nitrates (Nitroglycerin and Related Compounds)
Nitroglycerin acts predominantly through venodilation, which lowers preload and rapidly reduces pulmonary congestion. 1 The mechanism involves:
- Venous dilation, particularly in the mesenteric bed, which decreases venous pressure at any given vascular volume 2
- Reduction in left ventricular filling pressure (LVEDP) by diminishing venous tone 3
- Lowering of intrathoracic inferior vena cava volume, demonstrating decreased venous return 4
The preload-reducing effect is most pronounced in patients with normal arterial elastance and ventricular function, where nitroglycerin causes a predominant preload reduction rather than afterload reduction. 5 However, in patients with excessive afterload or heart failure, nitroglycerin may have mixed effects on both preload and afterload. 5
Formulations and Duration
- Sublingual nitroglycerin provides 30 minutes of venodilation 3
- Cutaneous nitroglycerin ointment extends action for 4-6 hours 3
- Oral isosorbide dinitrate and sustained-release preparations provide longer-acting preload reduction 3
Levosimendan
Levosimendan reduces cardiac preload in cardiogenic shock, achieving lower preload compared to dobutamine. 1 This inotrope increases contractility while simultaneously decreasing preload, making it useful in specific heart failure scenarios. 1
Diuretics
Loop diuretics reduce preload by decreasing intravascular volume through sodium and water excretion. 1 For patients with heart failure and significant fluid overload:
- Initial intravenous dose should equal or exceed chronic oral daily dose 1
- Can be administered as intermittent boluses or continuous infusion 1
- Effectiveness is enhanced by limiting sodium intake and dosing continuously or multiple times daily 1
Important Clinical Distinctions
Norepinephrine paradoxically increases venous return by shifting unstressed to stressed volume, thereby increasing preload rather than decreasing it. 1 This represents an important contrast to the preload-reducing agents.
Dobutamine decreases systemic and pulmonary vascular resistance but does not primarily reduce preload through venodilation. 1