Cardiothoracic surgery entails unique, often extreme, conditions in comparison to noncardiac surgery. Profound hemodynamic and physiologic perturbations associated with hypothermic cardiopulmonary bypass (CPB) and circulatory arrest lead to unique dosing considerations for anesthetic drugs, anticoagulants, vasoactives, inotropes, and antifibrinolytics. This chapter will review the pharmacologic considerations of cardiac anesthesia chronologically in stages, from premedication and induction to pre-CPB maintenance, initiation of CPB, separation from CPB, and the post-CPB period. A special discussion will review the unique pharmacologic approach to anticipated deep hypothermic circulatory arrest (DHCA).
Benzodiazepine (eg, intravenous [IV] midazolam 0.02–0.04 mg/kg) may be given prior to arterial line and/or central line placement. Cardiac surgery has among the highest incidence of intraoperative awareness of any elective surgery (1%–2%). Benzodiazepine administration has been shown to decrease the risk of awareness.1 Benzodiazepines also have a relatively slow offset time with respect to their hypnotic effects, particularly in elderly patients. Lorazepam (0.02 mg/kg IV) has a half-life of 12 to 14 hours in healthy young patients, with evidence of residual sedation and electroencephalographic (EEG) changes 8 hours after a single dose.2 In comparison, the half-life of midazolam is 2.8 hours, with EEG returning to near baseline by 3 hours.3 In the setting of cardiac surgery with CPB, delayed awakening attributed to the sedative effects of lorazepam may be more than 9 hours.4 Residual postoperative sedation is of potential concern in patients where early extubation is desired (eg, “fast-track” anesthesia). Midazolam in anxiolytic doses administered preoperatively and pre-CPB is not typically associated with delayed awakening. However, caution should be exercised when considering even a single preoperative dose of lorazepam, or a post-CPB dose of any benzodiazepine, if early extubation is desired.
Beginning slow titration of IV fentanyl 0.5 to 1.0 mcg/kg or sufentanil 0.05 to 0.1 mcg/kg during placement of invasive lines may be considered.
Similar blunting of the autonomic response to intubation and sternotomy has been demonstrated for fentanyl, sufentanil, alfentanil, and morphine at equianalgesic doses. Ideally, laryngoscopy should be performed adequate analgesia is in place to avoid or blunt an adverse hemodynamic effect. Although all these opioids are similar in pharmacologic action (ie, μ-receptor agonists), they each have quite different pharmacokinetics. One major difference is the time to peak effect. This difference is important to consider when dosing an opioid just prior to laryngoscopy. As is described in Chapter 5, Figure 5–1, the time to peak effect varies for each opioid: alfentanil, less than 2 minutes; fentanyl, 4 minutes; sufentanil, 6 minutes; and morphine, more than 80 minutes.
Induction drugs include propofol, etomidate, ketamine, high-dose midazolam, and the combination of ketamine and midazolam. Among the choices of induction agents, propofol leads to the greatest decrease in ...