What intraoperative measures may decrease PH
- As hypoxemia and hypercarbia increase PAPs, optimize the patient's oxygenation and ventilation. In contrast to systemic vessels, pulmonary vessels constrict with hypoxia. Recruitment maneuvers may improve ventilation-perfusion matching, but avoid overinflation. High levels of positive end-expiratory pressure (PEEP) may narrow vessels to well-ventilated areas of the lung, decreasing PO2. Levels of PEEP greater than 15 cm H2O should be avoided.
- Assess myocardial performance; increasing PA pressures may be secondary to a failing left ventricle. If ischemia is associated with a decreasing CO, consider infusing nitroglycerin to improve coronary perfusion. Inotropic drugs such as dobutamine or dopamine may enhance contractility and improve CO.
- Assess volume status. Although the right ventricle is less preload responsive than the left ventricle, CVP values less than 10 mm Hg suggest the need for preload augmentation. Before surgery an endogenous volume loading test can be performed by raising the patient's legs. Responders have an improvement in blood pressure with this maneuver and would be candidates for intraoperative fluid challenge. Nonresponders probably have RV failure, and fluid challenges may worsen this.
- Correct acidosis and ensure the patient is not becoming hypothermic. Both acid-base abnormalities and hypothermia may cause increased PA pressure. The effects of acidosis are worse in the presence of hypoxemia. Moderate hyperventilation (a PaCO2 of about 30 mm Hg) is suggested.
- Deepen the anesthetic. Catecholamine release will increase PA pressure.
- Consider the use of inotropes in the setting of RV failure. The phosphodiesterase III inhibitors milrinone and amrinone prevent the breakdown of cyclic guanosine monophosphate (cGMP) and increase LV contractility while dilating the pulmonary vasculature. Dobutamine is also an option.
- If systemic hypotension and coronary perfusion are problematic, vasoconstrictors may be superior to volume loading and inotropes. Because of the balance between a- and p-adrenergic effects, norepinephrine is the vasoconstrictor of choice. Norepinephrine should be administered carefully because it can increase PA pressure.
- Consider the use of direct-acting vasodilators. This will be discussed in further detail.
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