Edyta Gołąbiewska PhD

Transcription

1 Edyta Gołąbiewska PhD

2 The depth of anesthesia has been divided into four sequential stages: Stage 1: Analgesia (induction) Stage 2: Excitement Stage 3: Surgical anesthesia Stage 4: Medullary paralysis

3 Induction - period of time from the onset of administration of the anesthetic to the development of effective surgical anesthesia - essential to avoid phase II Maintenance - period during which the patient is surgically anesthetized - monitor the patient s vital signs Recovery - postoperatively, withdrawal the anesthetic mixture and monitor the return of the consciousness

4 relieve anxiety ; sedation (benzodiazepines) prevent allergic reactions (antihistamines) prevent aspiration of stomach contents and postsurgical nausea and vomiting (antiemetics) provide analgesia (opioids) prevent bradycardia and secretion of fluids into the respiratory tract (anticholinergic drugs) facilitation of intubation and relaxation (muscle relaxants)

5 GENERAL ANESTHESIA INHALATIONAL INTRAVENOUS GAS - Nitrous oxide VOLATILE LIQUIDS -Halothane -Isoflurane -Desflurane -Enflurane -Sevoflurane -Ketamine -Etomidate -Propofol -Barbiturates (Thiopental) -Beznodiazepines -Opioids

6 Mainstay of anesthesia, often given after IV agent The depth of anesthesia can be rapidly altered by changing the concentration of the drug (this is not possible with IV agent) Reversible agents, rapidly eliminated from the body Modern inhalation anesthetics are nonflammable, nonexplosive Halothane, Nitrous oxide, Isoflurane, Enflurane, Desflurane, Sevoflurane, (ether, chloroform)

7 MAC median alveolar concentration (measure of potency, this is ED 50 of the anesthetic) end-tidal concentration of anesthetic gas needed to eliminate movement among 50 % of patients challenged by a standardized skin incision small MAC for the potent anesthetics such as halothane; large MAC for less potent agents, such as nitrous oxide Usually expressed as the percentage of gas in a mixture required to achieve the effect

8 MAC Hypotension Hypothermia Hyponatremia Hypoxia Pregnancy age CNS depressants MAC Hyperthermia Hypernatremia Chronic alcohol Increased CNS transmitters (MAOi, Amphetamine, Cocaine, Ephedrine)

9 Oil/gas partition coefficients: It indicates the amount of gas that is soluble in oil phase. - It s a measure of lipid solubility of anesthetic - it s a measure of anesthetic potency Higher the solubility of general anesthetics in oil (higher the oil/gas partition) - greater the potency

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11 Blood/gas partition coefficient solubility of the agents in the blood Measure the rate of induction and recovery of inhalational anesthetics (how quickly the inhalation anesthetic equilibrate between lungs and blood and ultimately the target site in the brain) Low blood/gas partition coefficient equilibrate quickly faster the induction, faster the recovery (nitrous oxide) High blood/gas partition coefficient slower the induction, slower the recovery (halothane)

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13 Elimination redistribution of the drug from the brain to the blood and elimination through the lungs Inhaled gas alveoli blood tissue (including brain)

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15 Non-flammable, non-explosive at room temperature Stable in light Stable at room temperature, with a long shelf life Environmentally friendly - no ozone depletion Cheap and easy to manufacture Pleasant to inhale, non-irritant, induces bronchodilatation Low blood:gas solubility - i.e. fast onset High oil:water solubility - i.e. high potency Minimal effects on other systems - e.g. cardiovascular, respiratory, hepatic, renal or endocrine No biotransformation - should be excreted ideally via the lungs, unchanged Non-toxic

16 Potent analgesic and weak general anesthetic, colourless odourless gas at room temperature Does not induce respiratory depression Employed at concentrations of 30% in combination with oxygen (especially in dental procedures) For anesthesia at 80% with oxygen (must be used with other anesthetics for surgical anesthesia not used as a single agent) Poorly soluble in blood and other tissue (rapid induction and recovery) Safe, nonirritating

17 volatile liquid at room temperature, light sensitive, pleasant odour, non-irritating weak analgesic (administered together with other analgesic drugs) relaxes skeletal and uterine muscle very potent small MAC, high oil/gas partition coefficient slower induction, slower recovery - high blood/gas partition coefficient eliminated unchaged via lungs often used in children; agents of choice in asthmatics

18 Side effects: - hepatotoxcity - respiratory depression - bradycardia, cardiac arrhytmias (sensitize the heart to arrhythmogenic effects of sympathomimetic agents) - hypotension - decrease renal blood flow - malignant hyperthermia ( Ca 2+ ) - DANTROLENE

19 Enflurane produces quicker induction and quicker recovery than halothane, causes fewer arrhythmias, less sensitization of the heart to catecholamines but produces CNS excitation (should not be used in patients with seizure disorders) Isoflurane does not cause cardiac arrhytmias, does not sensitize the heart to the action of catecholamines, produces hypotension due to peripheral vasodilation Desflurane irritating to the airway, can cause laryngospasm, coughing, excessive secretions Sevoflurane rapid onset/recovery, not irritating, useful in children

20 Often used for rapid induction of anesthesia, which is then maintained with an appropiate inhalation agent Rapidly induce anesthesia, must be injected slowly Recovery is due to redistribution from sites in the CNS Barbiturates (Thiopental), Benzodiazepines (Midazolam), Opioidy (Morphine, Fentanyl), Etomidate, Ketamine, Propofol

21 Short-acting anesthetic (approx. 15 min), has analgesic properties Induce dissociated state in which patient is unconscious but appears to be awake and does not feel pain Provides sedation, amnesia, immobility Act on NMDA receptor (antagonist), also stimulates sympathetic outflow which causes stimulation of the heart and blood pressure, induces postoperative hallucinations (particularly in adults) Used mainly in children and young adults for short procedures

22 Onset of action after approx. 40 sec. Administered together with narcotics for analgesia Causes muscle twitching, spontaneous movement, hiccups, blood pressure, pain at the site of injection Does not produce postanesthetic nausea and vomiting Used for short procedures

23 Lack analgesic activity Rapid induction, short-acting Usually in patients with coronary artery disease or cardiovascular dysfunction (no effect on heart and circulation) Causes pain, skeletal muscle movements, inhibits adrenal function, respiratory depression

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25 Local anesthetics are weak bases Applied locally and block nerve conduction of sensory impulses from the periphery to the CNS Abolish sensation and in higher concentrations, motor activity in a limited area of the body without producing unconsciousness

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27 Esters Cocaine Procaine Benzocaine Tetracaine Chloroprocaine Amides Lidocaine Bupivacaine Ropivacaine Mepivacaine

28 Local anesthetics are weak bases and activity increases by increasing ph This because if large amount of a drug is unpolar, it will facilitate its penetration through the cell membrane Once the drug has penetrated the lipid barrier and reach its site of action (inside the cell) it ionized and the ionized form is responsible for activity Local anesthetics are usually formulated as the hydrochloride salt to render them water-soluble pka for local anesthetics

29 Acidosis such as caused by inflammation at a wound partly reduces the action of local anesthetics This is partly because most of the anesthetic is ionized and therefore unable to cross the cell membrane to reach its cytoplasmic-facing site of action on the sodium channel

30 The primary mechanism of action of local anesthetics is blockade of voltage- gated sodium channels (Na + ) Local anesthetics bind to receptors near the intracellular end of the channel and block the channel in a time- and voltage-dependent fashion

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32 CNS effects: - low dose: sleepiness, dizziness, anxiety, visual and auditory disturbances, restlessness, tongue numbness - high dose (stimulatory effects): nystagmus, muscular twitching, finally tonic-clonic convulsions, followed by CNS depression death may occur

33 Cardiovascular effects - hypotension (local anesthetics are vasodilators, except cocaine) - bradycardia - decrease in myocardial contractility - arrhythmias - CV collapse

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35 Topical Infiltration Field block Nerve block Intravenous regional block Spinal nerve block Epidural nerve block

36 Mixture of 2.5% lidocaine and 2.5% prilocaine Risk of methemoglobinemia is rare Safe in neonates Effective in anesthetizing the skin for cannulation and skin grafts Must be applied under an occlusive dressing for minutes

37 the first modern local anesthetic agent (xylocaine) relieves pain during the dental surgeries belongs to the amide class, cause little allergenic reaction sets on quickly and produces a desired anesthesia effect for several hours also antiarrhythmic drug

38 General anesthetics Local anesthetics Site of action Central Nervous System Peripheral nerves Area of body involved Whole body Restricted area Conciousness Lost Unaltered Major surgery Preferred Cannot be used Minor surgery Cannot be used Preferred Poor health patient Risky Safer

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40 Loss of dopaminergic neurons in the substantia nigra Progressive neurological disorder of muscle movement, characterized by tremors, muscular rigidity, bradykinesia (slowness in initiating and carrying out voluntary movements), postural abnormalities

41 Drugs used in Parkinson s disease: Drugs which increase dopamine (MAOi Selegiline, Rasagiline and COMT inhibitors Entacapone, Tolcapone) Dopamine precursors (Levodopa) Dopamine agonists (Bromocriptine, Pramipexole, Ropinirole, Rotigotine) Dopa decarboxylase inhibitors (Carbidopa, Benserazide) Drugs which block Ach (Benzatropine, Biperiden) Amantadine

42 LEVODOPA - precursor of Dopamine - cross BBB and is converted to DOPAMINE in the brain - decarboxylated peripherally to dopamine, causing side effects (nausea, vomiting, cardiac arrhytmias, hypotension) - together with carbidopa - potent and efficacious drug regimen (Levodopa+Carbidopa)

43 Levodopa side effects: - fluctuations in motor response correlate with the drug plasma concentration (short T 1/2 ) - on-off phenomenon patients suddenly can lose normal mobility and experience tremors, cramps, immobility - anorexia, nausea, vomiting, hypotension peripheral effects - visual and auditory hallucinations, abnormal involuntary movements (dyskinesias), psychosis, depression, anxiety CNS effects

44 CARBIDOPA, BENSERAZIDE - inhibitors of DOPA decarboxylase, diminishes metabolism of levodopa and level of Levodopa which enter the brain thus side effects associated with metabolism of L-DOPA peripherally

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46 SELEGILINE, RASAGILINE - MAO type B inhibitors (MAO type B - which metabolizes dopamine; does not inhibit MAO type A which metabolizes NE and serotonin) increase level of dopamine in the brain - enhances action of Levodopa if administered together - Selegiline - metabolized to amphetamine (may produce insomnia) - Rasagiline 5 times the potency of Selegiline, it is not metabolized to amphetamine

47 ENTACAPONE, TOLCAPONE - COMT inhibitors (catechol-o-methyltransferase) - Leads to decreased plasma concentrations of 3-O-methyldopa (metabolite of levodopa) central uptake of levodopa and greater concentrations of dopamine in the brain - Tolcapone cross BBB and inhibits COMT in the CNS (however the inhibition of COMT peripherally is the primary action) - Adverse effects: diarrhea, hypotension, nausea, anorexia, dyskinesias, hallucinations, sleep disorder Levodopa+Carbidopa+Entacapone

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49 BROMOCRIPTINE (ergotamine alkaloid), ROPINIROLE, ROTIGOTINE, PRAMIPEXOLE (nonergot ) - Dopamine receptors agonist - effective in patients with advanced Parkinson s disease complicated by motor fluctuations and dyskinesias, however ineffective in patients who have shown no therapeutic response to levodopa - they can delay the need to employ levodopa in early Parkinson s disease

50 BENZATROPINE, BIPERIDEN - antimuscarinic agents (anticholinergics) - tremors, but not rigidity and bradykinesia - not used in monotherapy, adjuvant role in antiparkinsonism therapy - induce mood changes, dry mouth, visual problems, high doses cause pupillary dilation, confusion, hallucination, tachycardia, urinary retention, constipation

51 AMANTADINE - antiviral drug - increase release of dopamine, block cholinergic receptors, inhibit NMDA receptor - little effect on tremor, but more effective than the anticholinergics against rigidity and bradykinesia - Side effects: restlessness, agitation, confusion, hallucinations, urinary retention, orthostatic hypotension, dry mouth, at high dosages toxic psychosis

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54 loss of Ach is associated with Alzheimer disease a degenerative disease of the brain resulting in dementia, caused due to irreversible progressive deterioration of brain cells, especially the cerebral cortex and hippocampus loss of cognitive functions such as memory, movement coordination, pattern recognition, judgment and reasoning

55 ACh esterase inhibitors are used to slow progression of Alzheimer disease Donepezil Rivastigmine Galantamine Tacrine Ach esterase inhibitors

56 Typical side effets of Ach esterase inhibitors: - nausea, vomiting - diarrhea - anorexia - tremors - bradycardia - muscle cramps

57 Antagonist of NMDA receptors (partial blockade - allow to limit Ca 2+ influx into the neuron such toxic intracellular levels are not achieved during NMDA receptor overstimulation, while still permitting sufficient Ca 2+ flow to preserve other vital processes that depend on Ca 2+ Neuroprotective effects, prevent the loss of neurons Slow the rate of memory loss Can cause confusion, agitation, restlessness, but usually well tolerated