The mu-agonist opioids, morphine, hydromorphone, and fentanyl, are the most commonly used for initial IV titration for the treatment of postoperative pain. Important patient characteristics to consider when selecting an opioid include previous exposure and tolerance of opioids, current organ function, and hemodynamic stability. For example, fentanyl is favored in patients with any type of end-organ failure. It also produces minimal hemodynamic effects, which adds to its appeal in patients with unstable blood pressure (Pasero, Quinn, Portenoy, McCaffery, & Rizos, 2011).
In addition to patient characteristics, the pharmacokinetics of the opioid and the goals of treatment are considered when deciding which opioid is best for titration in a particular patient (Pasero, Quinn, Portenoy, McCaffery, & Rizos, 2011). Whereas morphine, which is hydrophilic, requires several minutes (15-30) to cross the blood-brain barrier and yield peak effects after IV administration, the more lipophilic opioids, such as fentanyl, cross very quickly and produce peak effects almost immediately when given intravenously. Hydromorphone is less hydrophilic than morphine and so has an intermediate onset (see Table 5-2). Fentanyl tends to be a first-choice opioid for procedural pain and is a logical selection in ambulatory surgery PACU where the goal is to transition the patient quickly to the oral analgesic that the patient will take after discharge. For patients who have undergone major surgery, some PACU nurses like to administer a few doses of fentanyl and then follow with either hydromorphone or morphine for longer-lasting analgesia. However, although it makes sense to use a fast-onset opioid such as fentanyl in patients presenting with severe, escalating pain, it may not be necessary and can complicate the assessment process in those with less severe pain; when opioids are combined and adverse effects occur it is difficult to interpret which one might be the culprit. Therefore, a general principle of initial titration in patients with acute pain is to keep in mind the patients’ ongoing pain treatment plan. As an example, consider the patient who is admitted to the PACU and will have hydromorphone IV patient-controlled analgesia (PCA) for ongoing postoperative pain management. Unless the patient has severe, rapidly escalating pain on admission, it makes sense to begin titration with hydromorphone so that the effects (both pain relief and adverse effects) of the drug that will be used by PCA can be evaluated more easily.