Published on 07/02/2015 by admin
Filed under Anesthesiology
Last modified 07/02/2015
This article have been viewed 2598 times
Kent H. Rehfeldt, MD, FASE
Anesthesiologists frequently administer opioids preoperatively, intraoperatively, and postoperatively, most often to provide analgesia or as part of a balanced anesthetic. A predominantly opioid-based anesthetic may be selected for hemodynamically unstable patients because, compared with other classes of anesthetic drugs, opioids usually cause fewer unwanted changes in the hemodynamic profile. Nonetheless, opioids, especially in large doses, can alter hemodynamics. Changes in heart rate, cardiac conduction, blood pressure, and myocardial contractility are possible. Whether these effects are beneficial or detrimental depends on the clinical setting.
The administration of opioids (with the exception of meperidine) usually results in decreased heart rate. The tendency of meperidine to increase heart rate has been attributed to its atropine-like structure or to the effect of its principal metabolite, normeperidine. The reduction in heart rate that typically accompanies the use of opioids other than meperidine is seen in conjunction with reduced sympathetic tone and may be desirable in some patients, such as those at risk for developing coronary ischemia. When compared with the use of fentanyl and sufentanil, the use of alfentanil less reliably prevents increases in heart rate and blood pressure in response to surgical stimulation during cardiac operations. Additionally, opioids directly stimulate μ receptors in medullary vagal nuclei, an effect that can be attenuated by bilateral vagotomy. Some investigators have also noted decreases in heart rate with the use of remifentanil, even in the absence of enhanced parasympathetic tone, suggesting a direct effect on cardiac conduction tissue. Severe bradycardia and even asystole have been reported following the administration of opioids, such as remifentanil; fortunately these serious reactions are rare and may be more likely to occur when remifentanil is given as a bolus or when administered to patients who are also receiving β-adrenergic receptor or calcium channel blocking agents. Similarly, profound bradycardia may be more likely to occur when opioids are given during vagotonic procedures. For example, fentanyl, sufentanil, and alfentanil significantly augment the oculocardiac reflex, contributing to intraoperative bradycardia during some eye operations. Pretreatment with drugs such as pancuronium or atropine diminishes the likelihood of occurrence of opioid-induced decreases in heart rate.
Fausts Anesthesiology Review Expert Consult 4e
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