MAC with age extremes - schepel

MAC with age extremes - schepel

Transcript

1. https://i.dailymail.co.uk/i/pix/2014/07/25/article-2705556-1FF9008000000578-895_634x371.jpg
2. Minimum Alveolar Concentration  MAC defined as end-tidal volatile concentration at 1 ATM which prevents 50% of patients from moving during a skin incision  MAC decreases in all ages after 1 year  Some minor differences between Isoflurane and Sevoflurane under 1 year
3. MAC of Isoflurane by Age The minimal alveolar concentration (MAC) for isoflurane in preterm infants, full-term infants, children, and adults. (Note data are plotted in postconceptual years.) James P. Spaeth, C. Dean Kurth, in A Practice of Anesthesia for Infants and Children (Fourth Edition), 2009 Peak MAC at 6mo of age
4. MAC of Sevoflurane by Age Minimum alveolar anesthetic concentration (MAC) of sevoflurane versus age. The mean (+/- SD) end-tidal concentration of sevoflurane in oxygen for neonates, infants, and children. Lerman, Jerrold. Sevoflurane in Pediatric Anesthesia. Anesthesia & Analgesia: December 1995 - Volume 81 - Issue 6S - p 4S-10S Peak MAC at birth
5. Inhalational Induction  Neonates/infants have higher alveolar ventilation per kilogram and lower FRC per kilogram compared with adults  This means higher blood flow to highly perfused organs, speeding inhalational induction. Teens and adults induce slowly by comparison https://i.ytimg.com/vi/Qz4fsKUE_gw/maxresdefault.jpg
6. Volatile Anesthetics in Neonates  Controversy still exists on what long-term effects may exist with anesthetic exposure <3 years of age  Childhood amnesia – most children cannot retain memories before 1 year of age. Most adults cannot retain memories from before 2-4 years of age  If possible, minimum volatile anesthetic should be used to blunt hemodynamic and physical response to surgical stimulation. Can be thought of as an SVR lowering agent also  Not uncommon to use fentanyl and paralytic as the sole anesthetic in neonates
7. Volatile Anesthetics in the Elderly  General anesthetics may be toxic to both young AND aging brains. They are in in vivo animal studies  Postoperative cognitive dysfunction and decline may be related to illness, perioperative stress, medical comorbidities, and/or general anesthetic exposure  In vitro and in vivo animal studies suggest some possible relation  Data remains inconclusive on a relationship between anesthetic neurotoxicity, postoperative cognitive dysfunction, and Alzheimer’s dementia  Bad brain = more sensitivity = slower emergence Bittner, E.A., Yue, Y. & Xie, Z. Brief review: Anesthetic neurotoxicity in the elderly, cognitive dysfunction and Alzheimer’s disease. Can J Anesth/J Can Anesth 58, 216–223 (2011). https://doi.org/10.1007/s12630-010-9418-x
8. Sevoflurane and the Heart  Produces a concentration-dependent inhibitory effect on SA node automaticity and chronotropy  Inhibitory actions on IF , ICaT , ICaL , and Iks  Compared to isoflurane and desflurane, little to no reflex tachycardia occurs with quick increases in volatile concentration  High proportion of sinus rhythm conversion to clinically non- significant junctional rhythm in all ages, especially over 1 MAC. Look carefully next time!  Phenomenon of “myocardial stunning” which can occur in neonates and infants when 8% sevoflurane used  Clinically significant bradycardia and hypotension can be seen with Down syndrome patients during induction Kojima A, Kitagawa H, Omatsu-Kanbe M, Matsuura H, Nosaka S. Inhibitory effects of sevoflurane on pacemaking activity of sinoatrial node cells in guinea-pig heart. Br J Pharmacol. 2012;166(7):2117–2135. doi:10.1111/j.1476-5381.2012.01914.x
9. Volatile Anesthetic Effect on Respiration All volatile anesthetics (in the absence of other agents):  Decrease tidal volume and increase respiratory rate  Overall DECREASE minute ventilation (TV x RR = MV)  Arterial PCO2 is increased by “right shifting” the CO2-ventilatory response curve.  Respiratory depressant effects (by increase in PCO2): desflurane>isoflurane>sevoflurane  Volatile anesthetics abolish the hypoxic respiratory drive in a dose dependent manner, by depressing peripheral chemoreceptor response
10. Neonatal/Infant Intravascular Physiology  Pediatric intravascular AND extracellular fluid compartments are relatively large compared to adults. Higher volume of distribution!  Hepatic biotranformation is immature  Protein binding is decreased due to decreased a1-acid glycoprotein and albumin. Results in more free drug/higher blood concentrations!  Metabolic rate per kilogram is higher  Total body water is higher in infants than adults
11. https://www.maskinduction.com/uploads/3/1/6/4/31643965/6600631_ori g.jpg
12.  Infants need more drug per kg due to a higher volume of distribution  Infants are more sensitive to the medication due to hepatic and renal immaturity  Infants are more likely to experience systemic toxicity due to more free drug as there is less circulating protein to bind it (e.g. bupivicaine) THERAPEUTIC INDEX IS MUCH NARROWER!!!! Overall…
13. Neonatal IV Anesthetics vs Adults Drug Dose per kilogram Clearance Propofol Increased (increased volume of distribution) Decreased (immature liver) Opiates Decreased (crosses blood brain barrier more easily) Decreased (immature liver) Non-depolarizing Muscle Relaxants Same overall (larger volume of distribution, more sensitive NM junctions) Decreased (immature liver) Succinylcholine Increased (larger volume of distribution) Decreased (decreased pseudocholinesterase)
14. Pharmacology in the Elderly  With senescence:  Decreased muscle mass  Increased body fat  Decrease in total body water  Drugs can achieve higher plasma concentration due to decreased body water, and can redistribute into larger body fat compartment  GFR and hepatic function decrease, resulting in longer duration of action due to decreased clearance  Albumin levels decrease, but a1-acid glycoprotein increases
15. Elderly IV Anesthetics vs Healthy Adults Drug Dose per kilogram Clearance Propofol Decreased (decreased volume of distribution) Decreased Opiates Decreased (decreased volume of distribution) Decreased Non-depolarizing Muscle Relaxants Decreased (decreased volume of distribution) Decreased Succinylcholine Decreased (decreased volume of distribution) Decreased
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