Postoperative hypertension is common and can be difficult to manage. When other vital signs are normal, including normal pulse oximetry and normal respiratory rate, it is common to assume that the hypertension is due to poorly treated pain and should be treated with opioids. This may be a dangerous approach.

Hypoventilation is a not uncommon postoperative occurrence. Frequent causes of hypoventilation include residual effects of inhaled anesthetics and opioids, as well as persistent neuromuscular blockade, suboptimal ventilation due to pain or surgical site factors, and coexisting chronic obstructive pulmonary disease (COPD). As hypoventilation worsens, it can lead to carbon dioxide retention and hypercarbia. As hypercarbia worsens, direct cardiac and vascular depression occurs, and in order to compensate for this depression, hypercarbia can also stimulate catecholamine release. There is a linear correlation between increases in PaCO₂ and increases in heart rate and cardiac output. The overall effect of the catecholamine release is hypertension, along with increased pulse pressure, stroke volume, myocardial contractility, and heart rate. Treating hypertension with opioids, therefore, may worsen the situation, as opioids may lead to further hypoventilation, hypercarbia, hypertension, and eventually respiratory insufficiency or failure.