Pharmacology in Anesthesia Section 1.

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Pharmacokinetics. Pharmacokinetics (PK): depicts relationship b/w dosage of medication given
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Pharmacology in Anesthesia Part 1 Juan E. Gonzalez, CRNA, MS Assistant Clinical Professor

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Pharmacokinetics (PK): depicts relationship b/w dosage of medication given & its watched [plasma] and/or [tissue]. PK: what the BODY "does" to the medication Clinical PK: depicts Absorption (A), Distribution (D), Metabolism (M), Elimination (E) of medications. (ADME) Information about PK parameters (e.g. Vd ss , CL tot ) permits the forecast of [plasma] taking after various dosing regimens (dosage individualization)

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Pharmacodynamics (PD): portrays relationship b/w [drug] and the reaction (pharmacological impact) PD: what the DRUG "does" to the body PD impacts: in charge of coveted (helpful adequacy) and undesired (harmfulness) clinical results Examples of PD estimations: changes in BP amid HTN Tx, diminishes in HR amid Beta-blocker Tx, changes in PT and INR amid coumadin Tx drug + receptor drug-receptor complex reaction

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PK & PD Both PK & PD are wellsprings of variability in medication reactions among pts (between patient variability: e.g., age, simultaneous ailment, associative medicines)

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PK & PD Dosing regimen PK [drug] in the body (introduction) PD reaction Therapeutics Clinical result

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PK ideas When a medication is given extravascularly it must be consumed crosswise over natural layers to achieve systemic dissemination PO: from GI tract into vessels longer Transdermal: from skin into vessels Transfer of medication crosswise over layers in light of: medication properties: sub-atomic size, level of ionization, lipid dissolvability, protein restricting different elements: measure of blood stream to target tissue, [gradient] of medication over the layers Vasculature = transport of medication particle to site of movement

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Ionization Most medications are salts of powerless acids or feeble bases For both frail acids and frail bases the aggregate grouping of a medication is more noteworthy in favor of the film on which the medication is more ionized Degree of ionization of a medication (whether acidic or fundamental medication) at a specific site is dictated by the separation consistent (pKa) of the medication and the pH of the environment the medication is in

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Weak base If pH>pKa: unionized structure prevails If pH=pKa: unionized=ionized If pH<pKa: ionized structure prevails eg: Basic Drug (diazepam) pKa 3.3 In stomach: pH=1.3 In plasma: pH=7.4 Greater [diazepam] in GI compartment than in plasma Weak corrosive If pH>pKa: ionized structure prevails If pH=pKa: unionized=ionized If pH<pKa: unionized structure prevails pH, pKa, ionization

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PK ideas Once intravascular (IV): Drug can leave vasculature (enter tissues) or Drug can stay stuck blood Drug may scrape to endogenous proteins (e.g. egg whites) Binding is generally reversible (balance b/w protein-bound medication and unbound medication) Unbound medication in blood is main impetus of circulation of operator into body tissues

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PK ideas If unbound medication leaves the circulatory system and appropriates to tissue: medication may get to be tissue-bound medication may tie to receptor (pharmacologic or harmful reaction) medication may tie to a nonspecific site (no impact) medication may stay unbound in tissue medication might be rendered inert and/or disposed of from the body (if tissue can metabolize or wipe out the medication)

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PK ideas Organs (e.g. liver, GI tract divider, lung) have chemicals that metabolize drugs. Coming about metabolites might be dynamic (organic impact) or idle (no impact) Blood has esterases: proteins that separate ester securities in medication atoms  latent

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Metabolism (as a rule in the liver) through one or both sorts of responses" Phase I responses make the medication more polar and water solvent  more inclined to end by the kidney (e.g. oxidation, hydrolysis, diminishment) Phase II responses Inactivate the pharmacologic movement of the medication and may make it more inclined to disposal by the kidney (e.g., conjugation to shape glucuronides, acetic acid derivations, sulfates)

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Linear PK Most medications take after straight pharmacokinetics: [drug] in serum change relatively with day by day dosing (e.g., If "X" [drug] were multiplied from 400mg/d to 800mg/d, the patient\'s serum [drug] would twofold If medication is given through ceaseless IV mixture, serum [drug] will increment until harmony b/w drug measurements rate and the rate of medication end e.g., if pt getting theophylline at a rate of 40mg/hr (dosage), the serum [theophylline] will increment until the pt\'s body was dispensing with theophylline at 40mg/hr. At the point when [serum] achieves a consistent worth  STEADY STATE

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Compartmental PK Describes the body as an arrangement of speculative compartments connected by exchange rate forms (thought to be first-arrange: relative to the focuses in their underlying compartments) Linear or dosage corresponding PK (e.g. [drug] is corresponding to the dosage given) These PK compartments aggregate together a few physiological compartments (tissues) that have comparative active properties Each compartment is described by its size (volume). Every compartment has homogeneous focuses.

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One-compartment demonstrate Only one Compartment Drug given Drug Eliminated

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Two-compartment model Peripheral Compartment (vessel-poor gathering) 90% body mass 25% heart yield Central Compartment (vessel-rich gathering) 10% body mass 75% cardiovascular yield Drug given Drug Eliminated - Central Compartment: Can be tested through the blood. Comprised of intravascular liquid and organs/tissues exceedingly perfused with blood, e.g: lungs, liver, kidneys, heart, cerebrum (fast harmony dissemination with blood) - Peripheral Compartment: Cannot be typically examined. Comprised of organs/tissues ineffectively perfused with blood, e.g: muscle, skin, fat, bone (moderate harmony circulation with blood)

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Fluid Composition There are essentially two water compartments in the body: Extracellular 17% of body weight (12 liters)* Plasma 4% of body weight (3 liters) Interstitial 13% of body weight (9 liters) Intracellularly 41% of body weight (28.5 liters) *Total body water (58% of body weight) or (40.5 liters) (taking into account 70 kg man)

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Definitions Volume of Distribution (Vd): volume important to represent the aggregate sum of medication in the body if the medication were available all through the body in the same fixation as in plasma. Retention must be quick and one expect there is no end. Vd is the evident volume in which the medication is circulated after it has been brought into the framework. This speculative quality is figured from the aggregate measurements partitioned by the plasma focus at zero time. Vd = Q/C T=0 where Q: measurements of medication C T=0 : [drug] in plasma at time 0 Units: liters/kg

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Definitions Clearance (Cl): hypothetical volume of plasma that is totally cleared of medication at a given time. Measure of the body\'s capacity to dispose of medication. Units: ml/min Elimination Half-Time (T 1/2 beta ): time it takes for the [drug] in plasma to fall by one half (records for time to a half decline in focal compartment focus) Elimination Half-Life : (t 1/2 ) time it takes for the aggregate sum of medication in the body to diminish by half after assimilation and circulation are finished. Plasma convergence of a medication achieves consistent state in 4 to 5 half-lives. Disposal additionally takes 4 to 5 half-lives

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References The Chemistry of Drugs for Nurse Anesthetists (2005) by L.B. Kier & C.S. Dowd, AANA Publishing , Inc. Accessible just through AANA Bookstore: shop/books.asp Nagelhout & Zaglaniczny: Nurse Anesthesia, 3 rd version

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