Nitrates are used for the management of an acute episode of AD as they relax vascular smooth muscle, thus producing vasodilator effects on peripheral arteries and veins. Dilation of post-capillary vessels, including large veins, promotes peripheral pooling of blood and reduces venous return to the heart, thereby reducing left ventricular end-diastolic pressure (pre-load) and arterial blood pressure. On the other hand, arteriolar relaxation reduces systemic vascular resistance, which leads to reduced arterial pressure (after-load). If sildenafil has been used within the previous 24 hours in an individual with SCI presenting with acute AD, use of an alternative short acting, rapid-onset antihypertensive agent is recommended. Nitrates are the second most commonly used agent after nifedipine for management of AD in individuals with SCI (Consortium for Spinal Cord Medicine 2001; Braddom & Rocco 1991). However, with the exception of one case report with intravenous use of nitroprusside (Ravindran et al. 1981) and expert opinions (Consortium for Spinal Cord Medicine 2001), no studies exist to support their use in SCI.
There is level 5 evidence (clinical consensus) (Consortium for Spinal Cord Medicine 2001; Braddom & Rocco 1991), but no clinical studies which support the use of nitrates in the acute management of AD in SCI.