This study demonstrated that early infusion of DEX following CABG operations was associated with a reduction of morphine usage, a decrease in pain severity, and improvement of sedation, which encouraged early extubation. Pain control is crucial after cardiac surgery. The release of catecholamine causes the increase of the peripheral vascular resistance, heart rate, and risk of myocardial infarction, arrhythmias, and mortality. From our observations, we noticed a transient rise in main arterial pressure (MAP) during the 1st postoperative hour in both groups, followed by a decrease in MAP.
Arain and associates  found a brief increase in blood pressure in the DEX group, which was related to activation of α2 agonist on the smooth muscle of the vessel wall, which leads to transient vasoconstriction and increased in mean arterial pressure. We have noticed this in both groups. However, we thought these initial hemodynamic changes in MAP and HR were most probably related to post-surgical stress, the surgical procedures itself, or pre-existing hypertension as it happened in both groups . The decrease in MAP and HR was related to more gradual central effect of DEX in patients who received it, while the reduction of MAP for patients who did not receive DEX and depended on morphine as main analgesic most probably was related to decreasing catecholamine and direct vasodilatation effect of morphine considering that there was no significant difference in the number of patients receiving inotropes and vasodilators between the two groups.
Our findings were in line with Liu and coworkers’  meta-analysis, which stated that DEX lead to a shorter length of intubation, but it can be associated with bradycardia in patients after cardiac surgery compared with propofol. This tendency to lower the heart rate and systolic blood pressure with decreased incidence of tachycardia and arrhythmias have a cardioprotective effect, as stated by another meta-analysis by Gong and coauthors .
On the other hand, Mukhtar and colleagues  concluded in their study that intraoperative DEX infusion attenuated the hemodynamic and neuroendocrine response to surgical trauma and cardiopulmonary bypass. The same findings were declared by Priye and associates , who concluded that DEX infusion, even those without the loading dose, have a safe, effective adjuvant analgesic effect. It can reduce narcotic consumption without undesirable hemodynamic effects in cardiac surgery patients.
Shehabi and coworkers  found that DEX reduced vasopressors’ requirement after cardiac surgery with effective analgesia sedation, less hypertension, and more bradycardia versus morphine regimen. In our study, we did not find any difference between the two groups with regard to MAP and HR (p = 0.561 and 0.017, respectively). Barletta and associates  stated that DEX decreased cardiac index and HR for patients undergoing lengthy procedures which remained reduced at the time of discharge; our results did not support this conclusion as there was no significant difference between the two groups in HR. On the other hand, Maldonado and coworkers  concluded that DEX was associated with a lower rate of respiratory depression. It caused a higher rate of adverse hemodynamic events, which might be a concern in a hemodynamically unstable patient, but we did not observe any adverse effect on hemodynamic stability; this can be attributed to the low number of patients who needed inotropic support or vasodilator during the post-operative period in our cohort. Moreover, we have estimated opioid administration as analgesics postoperatively, which could reflect passively on the patients’ hemodynamics post-CABG. We observed that 10% of the patients were in need of opioids in the DEX group. These patients could be considered to have a low pain threshold or the post-operative managing doctors had a low threshold to give his patients more analgesia.
It worth mentioning that, while 95% of the control group were depended on opioids, 5% only of them only received non-steroidal anti-inflammatory (NSAID), according to the assessment of the post-operative ICU doctors who considered most of these patients with high pain threshold, and so, NSAID was enough to control their pain. Moreover, the dose of opioids given in the DEX group was significantly less than those of the other group [20, 21].
The pattern of pain in both groups was almost the same, which means that DEX does not alter the trend of the pain but decreased the intensity, and both groups needed to receive analgesics at the same point according to pain score between 4 and 5. These results agreed with Cheng and associates’ study .
Some authors mentioned that the use of DEX decreased the length of ICU stay in comparison with the use of other sedative and analgesics like midazolam and morphine, and we did not observe in our study significant differences in ICU stay as it was 2 ± 0.5 and 3 ± 0.1 days (p = 0.512). There are many factors other than pain and analgesics which could influence the ICU stay, including the patient’s hemodynamics, which can be affected by other etiologies other than pain.
From the clinical point of view, Lin and coworkers  suggested that DEX gave a suitable condition through which it facilitated weaning process from mechanical ventilator as it did not depress spontaneous ventilation, as well as it decreased the risk of delirium, ventricular tachycardia, and hyperglycemia following cardiac surgery; however, it could cause significant bradycardia. In our study, there was no significant difference between the two groups in intubation time.
The primary limitation of the study is the retrospective nature, and several factors may have affected the outcomes other than the treatment. A randomized clinical trial is required to adjust for the measured and unmeasured variables that could confound the results. However, because the administration of DEX in our cohort was not related to patients’ specific risk factors, the two groups had comparable baseline data.