Embedded Files
vascular surgery patients, such that isoflurane requirements were low in all groups. Therefore, cannot evaluate the potential reductive effect of dexmedetomidine on anesthetic requirements in vascular surgery patients. A study with minimal background anesthesia will be required to achieve this. Several studies have reported dose-dependent sedative effects with dexmedetomidine. During the 1-h dexmedetomidine infusion preceding induction of anesthesia, the patients in our medium- and high-dose groups fell asleep but were easily arousable. Although the dexmedetomidine infusion had a sedative effect before induction, sedation was not observable the day after surgery. This is consistent with recent findings of tachyphylaxis to the anesthetic effects of dexmedetomidine in rats. Our study is limited by the small number of patients. This study was designed as a dose-finding pilot study in high-risk surgical patients and, as such, provides useful information on the safety and hemodynamic effects of three different infusion doses of dexmedetomidine in surgical patients with preexisting vascular disease. This study was not designed to detect all adverse cardiac outcomes nor does it have enough power to draw definite conclusions on the safety and anti-ischemic effects of dexmedetomidine. A large-scale study is necessary to validate these preliminary results and, based on our ischemia data, should be conducted using a targeted 0.45 ng/ml plasma dexmedetomidine concentration. Whether a greater dexmedetomidine concentration will provide additional benefits without excessive side effects remains to be determined. Administration of vasoactive drugs based on hemodynamic values limits the interpretation of hemodynamic data. In addition to the hemodynamic values, the hemodynamic variability was reflected in the quantity of vasoactive medications required to treat changes in hemodynamics that exceeded our protocol-defined limits. We infused dexmedetomidine for 48 h postoperatively, when the natural incidence of myocardial ischemia is greatest. A briefer infusion might have been as effective and should be investigated. Although a longer infusion period might benefit some patients, it would not be appropriate for those who could not ambulate and would increase their risk of pulmonary embolism. The lack of concordance between intraoperative TEE and Holter ECG detection of ischemia is consistent with the findings of previous studies comparing the sensitivity of echocardiography with ECG in patients undergoing angioplasty. Although regional contractile abnormalities are more sensitive than ST-segment changes for the early detection of myocardial ischemia, the use of TEE is limited intraoperatively mainly to patients who receive general anesthesia. Thus, the potentially high-risk periods of anesthetic induction and emergence cannot be monitored by TEE. However, Holter ECG is relatively insensitive in detecting ischemic changes in the posterior and lateral quadrants of the left ventricle, where 56% of the echocardiographic ischemic changes occurred in our patients. Multiplane TEE and multilead ECG monitoring ultimately may enhance the sensitivity of each monitoring modality. Whether the true incidence of perioperative ischemia equals the sum of ECG and TEE ischemia remains to be determined. We did not measure cardiac output and pulmonary artery pressure. However, the effects of dexmedetomidine on these parameters and on the baroreflex should be studied to further validate the safety of dexmedetomidine in patients with vascular disease. Finally, we have studied only vascular surgery patients and only males. Further studies should include other surgical patient populations with or at risk for CAD as well as females to verify that these results are applicable to the high-risk cardiac population in general. The hemodynamic effects of dexmedetomidine in vascular surgery patients appear to be similar to those in healthy volunteers. A dose of 0.45 ng/ml appeared to be most effective in blunting hemodynamic responses to perioperative stress but required greater intraoperative pharmacologic intervention to support blood pressure and heart rate. Further
Report abuse