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dc.contributor.authorSashmita Kumari Padhy-
dc.description.abstractNeurosurgical procedures involving craniotomy and resection of brain tumors are usually carried out under general anaesthesia. The goals of anaesthesia during neurosurgical procedures are smooth induction, stable intra operative haemodynamics, providing optimal surgical condition, adequate brain relaxation, smooth and rapid recovery after end of surgery. (1,2) Ideal anesthetic agent for neurosurgery should reduce cerebral metabolism, maintain cerebral blood flow, maintain flow metabolism coupling, reduce intracranial pressure, maintain auto regulation, maintain cerebrovascular reactivity to carbon dioxide, maintain hemodynamic stability, rapid onset and early recovery. (3) Rapid recovery after end of surgery leads to early neurologic examination and early detection of any complications with appropriate treatment for it reduces mortality and morbidity. Anaesthetic agent used in neurosurgery can have significant effect on neurological outcome. (4) The commonly used techniques for conduct of anaesthesia for neurosurgical patients are either using inhalation or intravenous anaesthesia using total intravenous anesthesia (TIVA). Total intravenous anaesthesia is achieved using an intravenous hypnotic agent administered along with opioid whereas the inhalational technique involves the use of halogenated anesthetics along with opioid. Drugs with rapid onset and offset like propofol and remifentanil are most commonly used for TIVA. (5) As remifentanil is not available in our hospital, we use routinely combination of propofol and fentanyl for TIVA. Among the inhalational agents we routinely use Sevoflurane for neurosurgical procedures. Each of the techniques has its own advantages and disadvantages. Propofol can be used through manual infusion or target controlled infusion pump. When propofol infusion is given in manual infusion pumps, pharmacokinetics of drug to be utilized during infusion otherwise a fixed infusion rate may result in rising, declining or stable concentration leading to underdosage or overdosage. For a stable plasma concentration varying rate of infusion may be required. Availability of TCI pumps which uses pharmacokinetics of the drug and microprocessor-based software helps to achieve target plasma concentration and effect site concentration easily. (6) Using TCI pumps for TIVA helps real time titration of effect site concentration and can be adjusted according to processed EEG monitor for adequate depth of anesthesia. (7) TIVA has advantages of rapid, smooth induction, reduced intracranial pressure, hemodynamic stability and less incidence of PONV. (8) Propofol causes dose dependent reductions of cerebral metabolic rate and blood flow so coupling of flow metabolism is maintained. It also causes reduction of intracranial pressure. Carbon dioxide reactivity and autoregulation are maintained. (9,10) It has property of rapid onset and is short acting, rapid recovery, reduces ICP, antiemetic and anticonvulsant action which is beneficial in neurosurgery. (11,12) It has no analgesic activity, so propofol combined with intravenous opioids for maintenance of anaesthesia. All volatile anesthetics decreases cerebral metabolism in dose related manner. It has also intrinsic vasodilator capacity due to direct action on vascular smooth muscle. Final effect depends upon the balance between two effects. At 0.5 MAC, CMR suppression predominates leading to decreased cerebral blood flow. At 1 MAC, CMR suppression and vasodilatory effects are balanced so there is no net change. At more than 1 MAC vasodilatory effects are predominant leads to increase in blood flow and ICP. Order of vasodilating potency is approximately halothane ≫ enflurane > desflurane ≈ isoflurane > sevoflurane. Sevoflurane is least vasoactive. Sevoflurane is fluorinated methyl isopropyl ether. Vapor pressure is 160 mm of hg, so used in conventional nonheated vaporizer. Blood gas partition coefficient is 0.69, so rapid induction and recovery. At concentrations below 1.0 MAC has nearly no effect on cerebral blood volume and intracranial pressure. (13,14,15) Cerebral metabolism is reduced to the same extent when compared with equipotent concentrations of sevoflurane and propofol. (13) Coupling between regional cerebral blood flow and metabolism is maintained with sevoflurane and propofol. Autoregulation remains intact with 1.0 MAC sevoflurane (16). Cerebrovascular autoregulation is maintained with 0.5 and 1.0 MAC sevoflurane, although the fast dynamic component of autoregulation is slightly impaired with 1.0 MAC. (16,17,18) This suggests that concentrations below 1.0 MAC sevoflurane should be suitable for neuroanesthesia. At high concentration when used for induction, seizure like EEG pattern may be observed particularly in children having history of febrile convulsion. (19) Concentration <1.5 MAC can be safely used in patients with Seizure disorder. It has also neuroprotective effect due to inhibition of excitatory glutamate sensitive NMDA receptor and activation of inhibitory GABA receptor. (20). Though both the anesthetic regimens are being used for intracranial tumor surgery, literature is inconclusive on which agent is better, due to low quality evidence. In a recent Cochrane review, Prabhakar et al, have concluded that propofol and sevoflurane have equivalent effect on emergence from anaesthesia, propofol has lesser incidence of side effects like PONV with no difference in brain relaxation scores between propofol and sevoflurane group. (21) So, they could not draw any firm conclusions on the benefits of any technique over another for use during brain tumour surgery. One of the major drawbacks of the existing studies is that the authors have not utilized the equivalent depth of anaesthesia for comparison as guided by processed electroencephalogram (EEG). Hence the existing studies could not have a proper comparison. It is important to use both the regimens to a common end point namely the depth of anaesthesia. In the present study we have intended to compare the two regimens using a targeted value of depth of anesthesia using Patient state Index (PSI) in patients undergoing neurosurgical procedures on various perioperative indices.en_US
dc.titleComparison of two anaesthetic regimens TIVA (Propofol-fentanyl) versus Inhalation (Sevoflurane-fentanyl) on perioperative haemodynamic, operating conditions and immediate postoperative outcomes in patients undergoing elective neurosurgical procedures involving brain tumorsen_US
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