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Monitored anaesthesia care

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Monitored anaesthesia care

  2. 2. <ul><li>Involves administering a combination of drugs for anxiolytic , hypnotic , amnestic , and analgesic effect </li></ul>
  3. 3. <ul><li>Refers to instances in which an anaesthesiologist has been called upon to provide specific anaesthesia services to a particular patient undergoing a planned procedure, in connection with which a patient receives local anaesthesia , or in some cases, no anaesthesia at all . </li></ul>
  4. 4. <ul><li>In such a case the anaesthesiologist is providing specific services to the patient and is in control of the patient non-surgical or non-obstetrical medical care, including the responsibility of monitoring the patient’s vital sign , and is available to administer anaesthetics or provide other medical care as appropriate. </li></ul>
  5. 5. <ul><li>Conscious sedation </li></ul><ul><li>= minimally depressed level of consciousness that retain the patient’s ability to independently and continuously maintain an airway and respond appropriately to physical stimulation and verbal command </li></ul>
  6. 6. MAC GRAY ZONE GENERAL ANESTHESIA Monitored Anesthesia Care
  7. 7. <ul><li>To maintain patient safety & sense of well-being </li></ul><ul><li>To alleviate pain, minimise discomfort </li></ul><ul><li>To minimise psychological response </li></ul><ul><li>- anxiolysis, analgesia, amnesia </li></ul><ul><li>To control behaviour </li></ul><ul><li>To return to pre-procedural state </li></ul><ul><li>- recognised criteria </li></ul><ul><li>- safe discharge </li></ul>
  8. 8. <ul><li>Should be no different than for other patients </li></ul><ul><li>Assess ability to remain motionless and cooperate, verbally communicate </li></ul><ul><li>Important in monitoring level of sedation and cardiorespiratory function </li></ul><ul><li>cardiorespiratory disease is often the indication for MAC over GA </li></ul><ul><li>However, problem such as persistent cough or orthopnoea may prevent immobility </li></ul>
  9. 10. <ul><li>End points: </li></ul><ul><li>Providing patient comfort </li></ul><ul><li>Maintaining cardiorespiratory stability </li></ul><ul><li>Improving operating condition </li></ul><ul><li>Prevent recall of unpleasant perioperative event </li></ul>
  10. 11. <ul><li>MAC usually involves IV administration of drugs- alone/supplemental to LA/RA </li></ul><ul><li>Drug should allow rapid+complete recovery, min N&V </li></ul><ul><li>A level of sedation that allows verbal communication is optimal </li></ul><ul><li>Increased pt agitation may be due to pain or anxiety </li></ul>
  11. 12. <ul><li>Agitation </li></ul><ul><li>causes: pain, hypoxia, hypercarbia, impending local toxicity, cerebral hypoperfusion </li></ul><ul><li>others: bladder distension, hypothermia, hyperthermia, pruritus, nausea, positional discomfort, IV site, tourniquet inflation, and member of the surgical team leaning on the patient </li></ul>
  13. 15. <ul><li>Endoscopic procedures such as gastro-duodenoscopy, colonoscopy, sigmoidoscopy </li></ul><ul><li>Minor surgical procedures performed under LA </li></ul><ul><li>Painful diagnostic or treatment procedures such as BMA, trephine biopsy, change of burn dressing </li></ul><ul><li>Special situation such as IV administration of X-ray contrast medium in a patient considered to be susceptible to anaphylaxis </li></ul>
  14. 17. <ul><li>Predict the effect of drugs </li></ul><ul><li>Understand p/kinetic & p/dynamic properties ( context-sensitive half time, effect site equilibration time, drug interactions ) </li></ul><ul><li>Cont infusion are superior to intermittent bolus </li></ul><ul><li>-less-fluctuate in drug conc, prompt recovery </li></ul>
  15. 18. <ul><li>Accumulation of drugs in the poorly perfused fatty tissues during a long case can contribute to a prolonged recovery </li></ul><ul><li>It is difficult to predict duration of action based on elimination half life alone </li></ul>
  16. 19. <ul><li>Describes the time required for the plasma drug concentration to decline by 50% after terminating an infusion of a particular duration </li></ul><ul><li>The CSHT increases as the duration of infusion increases (particularly fentanyl & STP) </li></ul><ul><li>-thus STP is not ideal drug for ambulatory procedures </li></ul>
  17. 20. <ul><li>There is no constant relationship between elimination half-life and context-sensitive half-time </li></ul><ul><li>eg: fentanyl’s elimination is shorter than sufentanil (462 vs 577 minutes), its CSHT is twice that of sufentanil at 2H and 8-10x longer at 5H </li></ul>
  18. 21. <ul><li>Q: How does the CSHT relate to the time of recovery? </li></ul>
  19. 22. <ul><li>Describes the time from rapid iv admin of a drug until its clinical effect is manifest </li></ul><ul><li>Half time of equlibration between drug concentration in the blood and drug effect = t1/2 keo </li></ul><ul><li>Smaller values correspond with rapidity of onset </li></ul>
  20. 23. <ul><li>Drugs with shorter values: </li></ul><ul><li>thiopental, propofol, alfentanil </li></ul><ul><li>Drugs with longer values: </li></ul><ul><li>midazolam (0.9-5.6 m), sufentanil, and fentanyl </li></ul><ul><li>t1/2keo is a key factor in determining bolus spacing </li></ul><ul><li>eg: even using the shortest value for midazolam, 2.7 minutes is required for 87.5% effect-site equlibration of a bolus dose </li></ul><ul><li># low cardiac output is another factor that will slow onset time </li></ul>
  21. 24. <ul><li>No one inhaled/IV can provide all the component of MAC </li></ul><ul><li>Combination of drugs that act synergistically needed </li></ul><ul><li>eg opiod-benzodiazepine combination to achieve the components of hypnosis, amnesia & analgesia </li></ul>
  22. 25. <ul><li>Cpss50 = plasma concentration at a steady state required to abolish purposeful movement upon skin incision in 50% of patients </li></ul>
  23. 26. <ul><li>It has a context-sensitive half-time that is short even after a prolonged infusion, and a short effect-site equlibration-time </li></ul><ul><li>As it doesn’t posses analgesic properties, analgesia is provided by means of local infiltration or small doses of opiod. </li></ul><ul><li>Initial bolus 0.5mg/kg then 10mg intermittent bolus as necessary </li></ul>
  24. 27. <ul><li>Alternatively, </li></ul><ul><li>-continuous infusion at a rate 4mg/kg/h </li></ul><ul><li>-Patient-controlled sedation (PCS) </li></ul><ul><li>-Targer-controlled infusion, maintain target plasma concentration 0.5-1.5mcg/ml, titrating to response </li></ul><ul><li>Ramifentanil may also be administered at rate 0.01-0.05mcg/kg/min </li></ul><ul><li>#there is evidence that a single 10mg dose possess direct antiemetic properties </li></ul>
  25. 28. PROPOFOL DEXMEDETOMIDINE Pain upon injection Yes Minimal Analgesic properties with subhypnotic dose Minimal Yes Amnestic properties with subhypnotic dose Significant Insignificant Type of onset with typical administration Rapid 5-10 minutes Use by anaest provider Yes No Potential for significant bradycardia Minimal significant
  26. 29. <ul><li>Anxiolytic, amnestic & hypnotic properties </li></ul><ul><li>Midazolam has many advantages over diazepam </li></ul><ul><li>There is often significant and prolonged psychomotor impairment following conscious sedation techniques using midazolam as their main component </li></ul><ul><li>Cpss50 decresases significantly as a function of age , reduce threefold in an 80 year-old compared to 40 year-old </li></ul>
  27. 30. MIDAZOLAM DIAZEPAM Water soluble Lipid soluble Painless on injection Venoirritant Thrombophlebitis is rare Thrombophlebitis is common Short elimination half time (4 hours) Long elimination half time (> 20 hours) Clearance is unaffected by H2 antagonists Clearance is reduced by H2 antagonists Inactive metabolites (1-hydroxy midazolam) Active metabolites (desmethy-diazepam, oxazepam) Resedation is unlikely Resedation is more likely
  28. 31. <ul><li>#Flumazenil has a very short elimination half-life ~60 minutes, shorter than that most clinically used BDZ. In one study the effect of midazolam recurred 90 minutes following administration of flumazenil </li></ul>
  29. 32. <ul><li>Initial recommended dose is 0.2mg IV </li></ul><ul><li>If the desired level of consciousness is not achieved within 45 seconds, repeat 0.2mg IV </li></ul><ul><li>If necessary, repeat 0.2mg IV every 60 seconds to a maximum of 1.0mg </li></ul><ul><li>Recognise the potential for resedation </li></ul>
  30. 33. <ul><li>α 2- adenoreceptor agonists, anxiolytic and sedatives </li></ul><ul><li>Clonidine- good analgesia at high dose 4mcg/kg iv or 5mcg/kg orally w/out effect on respiration / PONV </li></ul><ul><li>slow on & offset –necessitating given well before surgery and possible delay in discharge after operation </li></ul>
  31. 34. <ul><li>Dexmedetominidine provides dose-related sedation and prolongation of sensory block </li></ul><ul><li>but cause significant haemodynamic impairemet & PONV </li></ul><ul><li>Elimination half-life of 2H indicates a fast offset, which is the major advantages over clonidine </li></ul>
  32. 35. <ul><li>Low-dose (0.5-1mg/kg) ketamine reported to provide weak sedation but excellent analgesia </li></ul><ul><li>Didn’t reduce propofol requirement </li></ul><ul><li>But +ve effect on haemodynamic stability and counteract propofol-induced resp depression </li></ul><ul><li>due to its sympatomimetic properties & CNS effects </li></ul><ul><li>Bad dreams/hallucination were not reported at sedatives dose </li></ul>
  33. 36. <ul><li>Among opiods ramifentanil is a potent analgesic with excellent p/kinetic profile: TPE 1.5min, p/dynamic offset 5.8min, short elmination half-life & time-independent CSHT. </li></ul><ul><li>s/e: n&v, pruritus, muscular rigidity at high dose (>1mcg/kg/min) </li></ul><ul><li>infusion rate of 0.1mcg/kg/min suggested as optimal balance between sedatives/side-effects </li></ul>
  34. 37. <ul><li>Initial injection of LA </li></ul><ul><li>Retrobulbar block </li></ul><ul><li>Patient discomfort unrelated to the procedure </li></ul><ul><li>Uncomfortable position </li></ul><ul><li>Propofol injection </li></ul><ul><li>Pneumatic tourniquet pain </li></ul>
  35. 38. <ul><li>In paediatric patient, chloral hydrate, paraldehyde and syrup diazepam or trimeprazine are used to provide sedation. However dose and onset of action of these drugs are often unreliable & unpredictable. </li></ul>
  36. 39. DRUG TYPICAL ADULT IV DOSE (TITRATED TO EFFECT IN INCREAMENT0 BDZ Midazolam Diazepam 1-2mg before propofol or ramifentanil infusion 2.5-10mg OPIODS Alfentanil Fentanyl Ramifentanil 5-20mcg/kg bolus 2 minutes before stimulus 0.5-2mcg/kg bolus 2 minutes before stimulus 0.1mcg/kg/min infusion 5 minutes before stimulus then weaned to 0.05mcg/kg/min as tolerated (adjust increment up or down in 0.025mcg/kg/min Propofol 250-500 mcg/kg bolus, 25-75 mcg/kg/min infusion Ketamine 4-6 mg/kg PO, 2-4 mg/kg IM, 0.25-1mg/kg IV Dexmedetomidine 0.5-1.0mcg/kg over 10-20min followed by 0.2-0.7mcg/kg/h
  37. 40. <ul><li>Increase pt satisfaction </li></ul><ul><li>Eliminate unpredictable variability in dose requirement between patients </li></ul><ul><li>eg: 0.5 mg midazolam and 25mcg fentanyl with 5min lockout interval </li></ul><ul><li>Alfentanil as 5mcg/kg IV bolus with 3min lockout period </li></ul>
  38. 42. <ul><li>During normal inspiration is subatmospheric creating a tendency to collapse </li></ul><ul><li>This tendency is opposed by upper airway muscles which contract just prior to diaphragmatic contraction </li></ul><ul><li>This control appears sensitive to sedative-hypnotic drug administration </li></ul><ul><li>Eg: sedatives dose of midazolam have been reported to increase upper airway resistance 3-4 fold, an effect exaggerated in elderly.. </li></ul>
  39. 43. <ul><li>Protective pharyngeal and laryngeal reflexes are depressed by sedation, debilitation and advanced age </li></ul><ul><li>Complete recovery of swallowing reflex occur ~15 minutes after the return of consciousness from propofol anaesthesia </li></ul><ul><li>It is depressed up to 2H after midazolam </li></ul>
  40. 44. <ul><li>In an otherwise norman man whose PCO2 is increased by hypoventilation sec to opiod administration, the alveolar gas equation predicts a PAO2 ~50mmHg (SpO2 75%) </li></ul><ul><li>If fio2 increases to 28%, the PAO2 increases to 100mmHg (Spo2 100%) </li></ul><ul><li>Recap: PAO 2 = PIO 2 - 1.2 (PaCO 2 ) where PIO 2 = FIO 2 (P B – 47 mm Hg) </li></ul>
  41. 47. <ul><li>ASA Standards for Basic Anaesthetic monitoring </li></ul><ul><li>-applicable to all levels of anesthesia care </li></ul><ul><li>Communication & Observation </li></ul><ul><li>Preparedness to recognise and treat LA toxicity </li></ul>
  42. 48. <ul><li>Visual, tactile and Auditory assessment </li></ul><ul><li>-rate, depth & pattern of breathing </li></ul><ul><li>-palpation of arterial pulse </li></ul><ul><li>-peripheral perfusion, Cap refill </li></ul><ul><li>-diaphoresis </li></ul><ul><li>-pallor </li></ul><ul><li>-shivering </li></ul><ul><li>-cyanosis </li></ul><ul><li>-acute change in neurological status </li></ul>
  43. 49. <ul><li>Auscultation </li></ul><ul><li>-heart & breath sounds (precordial stethoscope) </li></ul><ul><li>Pulse oximetry (an ASA standard) </li></ul><ul><li>Capnography </li></ul><ul><li>Electrocardiography </li></ul><ul><li>Temperature </li></ul><ul><li>Bispectral index (value <80 minimise recall) </li></ul>
  44. 51. <ul><li>This study was designed to determine the optimal infusion rates of propofol and alfentanil when administering during LA </li></ul><ul><li>Randomised, double-blind study </li></ul><ul><li>effect of different propofol infusion rates on the alfentanil requirement, level of sedation, intraoperative recall, respiratory and cardiovascular variables, and recovery evaluated. </li></ul><ul><li>72 ASA I or II female outpatients undergoing breast biopsy procedures with local anesthesia were randomly assigned to 1 of 4 treatment groups </li></ul>
  45. 52. <ul><li>All patients received IV midazolam 2mg for premedication </li></ul><ul><li>Propofol was infused at 0, 25, 50 or 75 mcg/kg/min </li></ul><ul><li>Sedation was evaluated using OAA/S scale at 5 min intervals by blinded observer </li></ul><ul><li>2 minutes before infiltration of LA, bolus of alfentanil 2.5mcg/kg IV given, folllowed by infusion 0.5mcg/kg/min </li></ul><ul><li>Alfentanil infusion titrated varied to patient comfort and stable cardiovascular and respiratory fx. </li></ul>
  46. 53. <ul><li>Results: </li></ul><ul><li>Propofol produced dose-dependant increases in the level of sedation (with median OAA/S scores of 2-4, P<0.05. </li></ul><ul><li>Higher infusion rates of propofol (50-75mcg/kg/min) produced significant amnesia, opiod-sparing effect (alfentanil 0.3±0.2 vs 0.6±0.2 mcg/kg/min) and less PONV. </li></ul><ul><li>Thus in healthy outpatients premedicated with IV midazolam 2mg, a propofol infusion 25-50mcg/kg/min in combination with an alfentanil infusion 0.2-0.4mcg/kg/min is recommended for sedation and analgesia during MAC in the ambulatory setting. </li></ul>
  47. 55. <ul><li>Study found that 13 of 98 (12%) patients with an UL block without sedation for hand surgery would like to be sedated for future similar surgery </li></ul><ul><li>Sedatives can help to decrease the requirement of opiod analgesics, reduce PONV </li></ul><ul><li>Sedation allows the choice of shorter anaesthetic method (local or RA vs spinal or GA) </li></ul><ul><li>Sedation does involve risks especially respiratory depression, haemodynamic instability or uncontrolled movement </li></ul>
  48. 56. <ul><li>Patient factors: </li></ul><ul><li>Dose requirement for sedative agents are decreased in elderly patients </li></ul><ul><li>Risk of desaturation/haemodynamic instability is increased I patients >70 yr </li></ul><ul><li>Similar in ASA III/IV or ASA I/II </li></ul><ul><li>Elderly people are expected to be less anxious </li></ul><ul><li>Thus sedation should be more restricted in the elderly </li></ul>
  49. 57. <ul><li>Factors influencing the level of sedation.. </li></ul><ul><li>Several studies have shown that spinal and epidural can reduce anaesthetic requirement and induce sedation </li></ul><ul><li>The peak sedation effect is usually detected 30-45 minutes after starting the block </li></ul><ul><li>Enhance sedation by adding adrenaline </li></ul><ul><li>Listen to music.. </li></ul>
  50. 58. <ul><li>Ideal pharmacokinetic & pharmacodynamic properties </li></ul><ul><li>Rapid onset, easy titration and high clearance </li></ul><ul><li>p/dynamic dep on actions w/in the effect-site compartment = constant k </li></ul><ul><li>Time to peak effect (TPE) seems to be a better measure as it is independent of the p/kinetic model, and the time course is predictable </li></ul><ul><li>Elimination half life is of limited use </li></ul>
  51. 59. <ul><li>A short Context-sensitive half-time and a high clearance are essential for rapid offset of sedation and fast recovery </li></ul><ul><li>The ideal sedative agent should also have minimal side effect </li></ul>
  52. 61. <ul><li>326 patients were randomised to DEX 0.5, DEX 1 mcg/kg or saline placebo as initial loading dose </li></ul><ul><li>Followed by maintenance 0.2-1.0 mcg/kg/h, titrate until <4 on OAA/S </li></ul><ul><li>Midazolam given for OAA/S >4, and fentanyl for pain </li></ul><ul><li>Primary end point - % of patients not requiring rescue midazolam </li></ul>
  53. 62. <ul><li>Results: </li></ul><ul><li>Significantly fewer pts in the 0.5 and 1.0mcg/kg DEX group required supplemental midazolam compared with placebo (59%,45.7% vs 96.8%), </li></ul><ul><li>at a lower dose to achieve OAA/S <4 before and during surgery </li></ul><ul><li>Both DEX group required significantly less fentanyl 84.8&83.6mcg vs 144.4mcg </li></ul><ul><li>Patient satisfaction was higher </li></ul>
  54. 63. <ul><li>Common adverse events ie bradycardia and hypotension were predominately mild to moderate in severity </li></ul>
  55. 64. <ul><li>Thank you for listening… </li></ul>