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Monitored Anesthesia CareDarma Wirawan Soeredi, MDAnesthesia DepartmentAdventist Medical Center ManilaSource: Clinical Anesthesia 7th EditionDistinguishing MAC From Moderate Sedation/Analgesia (Conscious Sedation) Understand the purpose of Monitored Anesthesia Care (MAC)Discuss levels of MAC and appropriateness by type of caseDiscuss special circumstances in which MAC may not be appropriateDiscuss techniques of MAC anesthesia

ObjectivesMAC Sedation / AnalgesiaMAC is a specific anesthesia service for a diagnostic / therapeutic procedure, it has the potential to convert to a general or regional anesthetic as needed

TerminologySedation/ analgesia is the term currently used by the ASA in their recently published Practice Guidelines for Sedation and Analgesia by Non-AnesthesiologistsThe standards for preoperative evaluation, intraoperative monitoring, and the continuous presence of a member of the anesthesia care team, and so forth, are no different from those for general or regional anesthesiaMonitored anesthesia care may include varying levels of sedation, analgesia, and anxiolysis as necessary. The provider of monitored anesthesia care must be prepared and qualified to convert to general anesthesia when necessary. If the patient loses consciousness and the ability to respond purposefully, the anesthesia care is a general anesthetic, irrespective of whether airway instrumentation is required3Monitored Anesthesia Care

MAC GRAY ZONE GENERAL ANESTHESIAUsual noninvasive cardiocirculatory and respiratory monitoring.Oxygen administration, when indicated.Administration of sedatives, tranquilizers, antiemetics, narcotics, other analgesics, beta-blockers, vasopressors, bronchodilators, antihypertensives, or other pharmacologic therapy as may be required in the judgment of the anesthesiologist.

Usual Services Performed by the AnesthesiologistAs usual preop evaluationAdditional:ability to remain motionless and actively cooperate?Patients psychological aspect?Is there sensorineural of cognitive deficit?

Preoperative AssessmentMACGENERAL ANESTHESIAVerbal communication is very important for three reasons: as a monitor of the level of sedation and cardiorespiratory functionas a means of explanation and reassurance for the patientas a mechanism of communication when the patient is required to actively cooperate6the desired end points is being able to provide patient comfort, maintaining cardiorespiratory stability, improving operating conditions, and preventing recall of unpleasant perioperative eventsadministration of either individual or combinations of analgesic, amnestic, and hypnotic drugs.Always vigilant

Techniques of Monitored Anesthesia CareClinical experience suggests that a level of sedation that allows verbal communication is optimal for the patient's comfort and safetyIf the level of sedation is deepened to the extent that verbal communication is lost, most of the advantages of monitored anesthesia care are lost and the risks of the technique approach those of general anesthesia with an unprotected and uncontrolled airwayOther causes of discomfort and agitation include a distended bladder, hypothermia, hyperthermia, pruritus, nausea, positional discomfort, uncomfortable oxygen masks and nasal cannulae, intravenous (IV) cannulation site infiltration, a member of the surgical team leaning on the patient, and prolonged pneumatic tourniquet inflation.7Observer's Assessment of Alertness/Sedation Scale

MACConsciousnessSafety RiskPatent Airway Spontaneous BreathingFactors That Contribute the Success of MACPATIENTSURGEONPROCEDUREANESTHESIOLOGIST?ConsciousCooperativeCommunicativeFunctional capacityASA PC I IVManageable anxietyManageable pain Able to follow commandsAble to lie still / flatKnows difference between MAC and GAKnows role of sedative vs pain managementCool CalmBedside MannersAble to manage pain CooperativeCommunicativeClinical experienceAppropriate case selection & patient preparationKnows difference between MAC and GAKnows role of sedative vs pain managementCool CalmTalks vs SedatesAble to manage pain & sedation CooperativeCommunicativeKnows Dr / Patient limitsKnows how / when to convertCataract extractionBone marrow biopsyLumpectomyPacemaker - AICD insertionInguinal Hernia repairsKnee arthroscopyTEE CardioversionRhinoplasty3rd Molar extractionFace/Brow liftShort Manageable Pain Position

10The ultimate objective of any dosing regimen is to deliver a therapeutic concentration of drug to its site of actionPharmacologic Basis of MAC Techniques

Excessive sedation may result in cardiac or respiratory depressionInadequate sedation may result in patient discomfort and potential morbidity from lack of cooperationContinuous infusions are superior to intermittent bolus dosing because they produce less fluctuation in drug concentration, thus reducing the number of episodes of inadequate or excessive sedation. Administration of drugs by continuous infusion rather than by intermittent dosing also reduces the total amount of drug administered and facilitates a more prompt recovery11The Elimination Half-life (T 1/2)Context-sensitive Half-timePharmacologic Basis of MAC Techniquesdescribes the time required for the plasma drug concentration to decline by 50% after terminating an infusion of a particular durationIs influenced by distribution, metabolism, elimination

Context-Sensitive Half-timedepends on the drug concentration gradients that exist between the various compartmentsFor example, during the early part of an infusion of a lipophilic drug, distributive factors will tend to decrease plasma concentrations as the drug is transported to the unsaturated peripheral tissues

13PlasmaFollowing the administration of IV drugs:Distribution of DrugsPoorly Perfused TissuesVRGsContext-Sensitive Half-Time

T 1/2 :462minT 1/2 :557minT 1/2 :111min In the case of fentanyl, drug that is irreversibly eliminated from the plasma by hepatic clearance is immediately replaced by drug returning from the peripheral compartmentsdespite the longer elimination half-time of sufentanil, its context-sensitive half-time is actually less than that of alfentanil for infusions up to 8 hours in duration. huge distribution volume of sufentanil, unlike alfentanil (small distribution volume)15HypnoticsPropofolFospropofolDexmedetomidineOpioidsFentanylAlfentanilRemifentanilSufentanilBenzodiazepinesMidazolamDiazepamKetamine

Drugs Commonly Used in MACDrugAdvantage(s)Disadvantage(s)PropofolFast in- fast out(+) amnesia(+) effect on PONV Sense of well beingPain at injection siteHypotension effectHyperlipidemiaFospropofol(+) amnesia(+) effect on PONV Sense of well being(-)pain at injectionLonger onset of action than propofol (4 to 13 minutes)DiazepamAnxiolysis, AmnesiaLong duration (>20h)Pain on injectionProlonged cognitive function recoveryMidazolamAnxiolysis, Amnesia, Fast acting, low CSHTProlonged cognitive function recoveryDexmedetomidineSedation + analgesiaMinor effects on respiratory(-)pain at injection(-)amnesia(-)slow onsetPotential for significant bradycardiaDrugs Commonly Used in MACPropofol250-500 mcg/kg boluses25-75 mcg/kg/min infusionFospropofol 6.5 mg/kg bolus followed by 1.6 mg/kgDexmedetomidineLoading infusion: 0.51 g/kg over 1020 minMaintenance infusion: 0.20.71 g/kg/hDiazepam2-10 ,mgMidazolam1-2 mg prior to propofol or remifentanil infusion

Typical Dose RangeFentanyl 0.52.0-g/kg bolus 24 min prior to stimulus Alfentanil 520-g/kg bolus 2 min prior to stimulus Remifentanil Infusion 0.1 g/kg/min 5 min prior to stimulusWean to 0.05 g/kg/min as toleratedAdjust up or down in increments of 0.025 g/kg/minReduce dose accordingly when coadministered with midazolam or propofol

Typical Dose RangeNALOXONEAn initial dose of 0.4 mg to 2 mg, may be repeated every 2-3 minutes, up to 10 mg FLUMAZENIL Initial recommended dose of 0.2 mgIf desired level of consciousness is not achieved in 45 s, repeat 0.2-mg dose, then every 60 s until a maximum of 1 mg is administeredBe aware of the potential for resedationReversalNaloxone Continuous infusion: 0.005 mg/kg loading dose followed by an infusion of 0.0025 mg/kg/hr

20No Reversal agent for Hypnotics other than TIMEUse of antagonists is NOT a sign of failure, but rather PRUDENT PATIENT SAFETY

Reversal

flumazenil-antagonized midazolam sedation was more expensive than propofol sedation ($68.67 vs. $27.80)21

Thank You, Po