Hypothermia Attenuates the Vasodilator Effects of Dexmedetomidine on Pial Vessels in Rabbits In Vivo

Effect of Dexmedetomidine Infusion on Sublingual Microcirculation in Patients Undergoing On-Pump Coronary Artery Bypass Graft Surgery: A Prospective Randomized Trial

OBJECTIVES

Cardiac surgery is characterized by attenuation of microcirculatory perfusion. Dexmedetomidine has been proved to attenuate the microcirculatory derangements evoked by experimental sepsis. The authors investigated the effects of dexmedetomidine infusion on sublingual microcirculation in patients undergoing on-pump coronary artery bypass graft (CABG) surgery.

DESIGN

Prospective, randomized blinded study.

SETTINGS

Tertiary university hospital.

PARTICIPANTS

A total of 70 adults undergoing elective on-pump CABG surgery.

INTERVENTION

After a standard general anesthesia, participants were allocated randomly to receive either propofol continuous intravenous infusion, 50 to 70 µg/kg/min, or propofol infusion, 50 to 70 µg/kg/min plus dexmedetomidine infusion, 0.5 µg/kg/h, during cardiopulmonary bypass. Microcirculation was studied with side-stream dark field imaging at 3 times: immediately before starting bypass (T0), 30 minutes after initiation of bypass (T1), and 30 minutes after weaning from bypass (T2).

MEASUREMENTS AND MAIN RESULTS

Microvascular flow index was significantly higher in the dexmedetomidine group at T2 compared to the control group (2.20 ± 0.29 and 1.47 ± 0.30, respectively; p = 0.001). The perfused vessel density was significantly higher in the dexmedetomidine group at T2 compared to the control group (6.1 [3-8.9] mm/mm² and 3.3 [2.2-4.3] mm/mm², respectively; p = 0.01). The total vascular density was significantly higher in the dexmedetomidine group compared to the control group at T1 and T2 (9.9 [7.8-12.6] mm/mm² v 7.4 [6.1-9] mm/mm², p = 0.005; and 9.27 ± 2.27 mm/mm² v 7.24 ± 1.66 mm/mm², p = 0.003, respectively).

CONCLUSION

This trial demonstrated that dexmedetomidine infusion improved sublingual microcirculation indices in patients undergoing on-pump CABG surgery.

Hypothermia makes cerebral resistance index a poor prognostic tool in encephalopathic newborns

BACKGROUND

Severe neonatal encephalopathy (NE) of hypoxic-ischaemic origin may cause death or life-long disability. Acute encephalopathy may also affect cerebrovascular control. Pourcelot's cerebrovascular resistance index (RI) ≤0.55 was predictive of poor outcome in normothermic NE infants. Recent studies have questioned its predictive power during therapeutic hypothermia (HT).

OBJECTIVE

To assess the predictive power of RI during HT and after rewarming.

METHODS

45 infants with NE treated with HT for 72 h had their RI calculated during early (median 11 h) and late (median 62 h) cooling and after rewarming (median 89 h). Poor outcome was defined as death or abnormalities on day 10 magnetic resonance imaging shown to predict severe neuromotor disability.

RESULTS

RI ≤0.55 during cooling did not differentiate between good and poor outcome (late cooling, p = 0.08), but was powerful after rewarming (p = 0.004). RI ≤0.55 predicted true poor outcome in 43% (95% confidence interval (CI): 12, 80) during late cooling and in 100% (95% CI: 31, 100) after rewarming. RI >0.55 predicted good outcome in 86% (95% CI: 69, 95) during late cooling and in 89% (95% CI: 74, 96) after rewarming.

CONCLUSIONS

Low RI is not predictive of poor outcome during HT in NE infants, but regains the predictive power seen in normothermic infants after rewarming.

Neuroprotective effects of a combination of dexmedetomidine and hypothermia after incomplete cerebral ischemia in rats

BACKGROUND

Dexmedetomidine and hypothermia are known to reduce neuronal injury following cerebral ischemia. We examined whether a combination of dexmedetomidine and hypothermia reduces brain injury after transient forebrain ischemia in rats to a greater extent than either treatment alone.

METHODS

Thirty-eight male Sprague-Dawley rats were anesthetized with fentanyl and nitrous oxide in oxygen. Four groups were tested: group C (saline 1 ml/kg, temporal muscle temperature 37.5 degrees C); group H (saline 1 ml/kg, 35.0 degrees C); group D (dexmedetomidine 100 microg/kg, 37.5 degrees C); and group DH (dexmedetomidine 100 microg/kg, 35.0 degrees C). Dexmedetomidine or saline was administered intraperitoneally 30 min before ischemia. Cerebral ischemia was produced by right carotid artery ligation with hemorrhagic hypotension (mean arterial pressure 40 mmHg) for 20 min. Neurologic outcome was evaluated at 24, 48, and 72 h after ischemia. Histopathology was evaluated in the caudate and hippocampus at 72 h after ischemia.

RESULTS

Neurologic outcome was significantly better in the group DH than the group C (P<0.05), whereas it was similar between the group DH and the groups D or H. Survival rate of the hippocampal CA1 neurons was significantly greater in groups D, H, and DH than group C (P<0.05). Histopathologic injury in the caudate section was significantly less in groups H and DH than group C (P<0.05).

CONCLUSION

The combination of dexmedetomidine and hypothermia improved short-term neurologic outcome compared with the control group, whereas the combination therapy provided comparable neuroprotection with either of the two therapies alone.