These drugs work by increasing nitric oxide levels in the blood and inducing coronary vasodilation which will allow for more coronary blood flow due to a decreased coronary resistance, allowing for increased oxygen supply to the vital organs (myocardium). The nitric oxide increase in the blood resulting from these drugs also causes dilation of systemic veins which in turn causes a reduction in venous return, ventricular work load and ventricular radius. All of these reductions contribute to the decrease in ventricular wall stress which is significant because this causes the demand of oxygen to decrease. In general organic nitrates decrease oxygen demand and increase oxygen supply. It is this favourable change to the body that can decrease the severity of ischemic symptoms, particularly angina. Other medications used to reduce the occurrence and severity of vasospasm and ultimately ischemia include L-type calcium channel blockers (notably nimodipine, as well as verapamil, diltiazem, nifedipine) and beta-receptor antagonists (more commonly known as beta blockers or β-blockers) such as propranolol. L-type calcium channel blockers can induce dilation of the coronary arteries while also decreasing the hearts demand for oxygen by reducing contractility, heart rate, and wall stress. The reduction of these latter three factors decreases the contractile force that the myocardium must exert in order to achieve the same level of cardiac output. Beta-receptor antagonists do not cause vasodilation, but like L-type calcium channel blockers, they do reduce the hearts demand for oxygen. This reduction similarly results from a decrease in heart rate, afterload, and wall stress.
A count of 250 neutrophils per ml or higher is considered diagnostic for spontaneous bacterial peritonitis. Cultures of the fluid can be taken, but the yield is approximately 40% (72-90% if blood culture bottles are used). Contraindications
Mild hematologic abnormalities do not increase the risk of bleeding. The risk of bleeding may be increased if:
prothrombin time > 21 seconds
international normalized ratio >  1.6
platelet count < 50,000 per cubic millimeter.Absolute contraindication is the acute abdomen that requires surgery. Relative contraindications are:
Pregnancy
Distended urinary bladder
Abdominal wall cellulitis
Distended bowel
Intra-abdominal adhesions. See also
Anterior chamber paracentesis

References
External links

WebMD: Patient guide