The Effects Of Dexmedetomidine On Respiratory Mechanics And Oxygen Consumptionin Orthopedic Surgical Patients Under General Anesthesia

Objective:To compare the effects ofdexmedetomidine（with loading doses of 0.3μg/kg or 0.5μg/kg）and midazolam（0.02mg/kg）on the hemodynamics,respiratory mechanics and energy metabolism in patients undergoing orthopedic surgery under general anesthesia.Methods:Ninety American Society of Anesthesiologists physical status I or II adults were randomized to dexmedetomidine 0.3μg/kg group（group D₁）,dexmedetomidine 0.5μg/kg group（group D₂）and midazolam group（group D₀）.Before anesthesia induction,various loading dosage of dexmedetomidine（0.5μg/kg or 0.3μg/kg）or midazolam 0.02 mg/kg were injected intravenously.After anesthesia induction with fentanyl and propofol,LMA was inserted and desflurane was inhaled.Before surgery（T₁）and 10 minutes after skin incision（T₂）,MAP（mean arterial pressure）,HR（heart rate）,SpO₂（pulse oxygen saturation）,VT（tidal volume）,MV（minute ventilation volume）,Compl（lung compliance）,RAW（airway resistance）,Ppeak（peak pressure）,Pplat（plate pressure）,Pmean（mean pressure）,VO₂（oxygen consumption）,VCO₂（carbon dioxide emissions）and RQ（respiratory quotient）were all recorded respectively.At the same time,the number of adverse reactions occurred in each group were also counted.Results:For hemodynamics,HR and MAP of group D₀ and D₁both increased significantly after skin incision（P<0.05）,while only MAP of group D₀ were significantly higher than preoperative value（P<0.05）.Whenever at T₁ or T₂,HR of group D₀ were higher than those in group D₁ and D₂,while MAP ofgroup D₂ were lower than those in group D₀ and D₁（P<0.05）.Otherwise,the increment of MAP in group D₂ with skin cutting was significantly lower than that ingroup D₀（P<0.05）.For respiratory mechanics,Ppeak,Pplat and Pmean of the three groups were all significantly higher than the preoperative ones,with Compl significantly decreased（P<0.05）.However,RAW were only increased in group D₀and D₁ after skin incision（P<0.05）.For energy metabolism,VO₂ increased significantly in group D₀ at T₂,with RQ decreased（P<0.05）.And VCO₂decreased only in group D₂ after surgery（P<0.05）.After skin incision,VO₂of group D₀ was significantly higher than that ingroup D₁ and D₂（P<0.05）.And the increment of VO₂causing by skin incision in group D₀ was much higher than that in group D₂.Conclusion:Compared with midazolam,dexmedetomidine is more helpful to reduce the stress reaction causing by surgical stimulation,maintain the stability of hemodynamics,and reduce the oxygen consumption effectively,which is dose-dependent.However,it still make little influence on the respiratory mechanics.