Presentation on theme: "PHARMACOKINETICS AND PHARMACODYNAMICS IN THE ELDERLY AND THEIR IMPACT ON ANESTHETIC AGENTS Samantha P. Jellinek, PharmD, BCPS, CGP Clinical Pharmacy."— Presentation transcript:
1PHARMACOKINETICS AND PHARMACODYNAMICS IN THE ELDERLY AND THEIR IMPACT ON ANESTHETIC AGENTS Samantha P. Jellinek, PharmD, BCPS, CGP Clinical Pharmacy ManagerAGSTHE AMERICAN GERIATRICS SOCIETYGeriatrics Health Professionals.Leading change. Improving care for older adults.Topic
2The problem Elderly patients require dose reductions for most agents Become more sensitive to the therapeutic and adverse effectsIncreased sensitivity results from a combination of pharmacokinetic/pharmacodynamic (PK/PD) alterationsPathophysiology may also affect the PK/PD of anesthetic agents
3Physiologic vS. Calendar Age Wide variability in dose-response relationships occur with increasing agePhysiologic age and comorbidity are the primary influences on postoperative outcomeThere are very healthy elderly patients who exhibit the physiology, and thus the PK and PD, of the young. On the other hand, very aged elderly patients may exhibit compromised CV and CNS systems. Thus, there is wide variability in the dose-response relationships that occur with increasing age. Recent literature indicates that physiological age and comorbidity, and not calendar age itself, are the primary influences on postoperative outcome in the elderly.
4ObjectiveS To review the physiological changes that occur with age To review how these changes affect the PK/PD of the agents used in anesthetic practice in the elderly
5Changes in Body Composition: Men Total body weight declinesContraction of total body water and loss of lean tissue massBody fat fraction returns toward young adult valuesBy the geriatric years, total body weight in physically active older men has declined as a result of the contraction of total body water and the loss of lean tissue mass, returning the body fat fraction toward young adult values. In the elderly, muscle mass falls to about 50% of adolescent values.
6Changes in Body Composition: Women Little change in total body weightMore persistent trend of increasing body fatOffsets resorption of skeletal elements and loss of total body waterResult: increment in the fat fraction of the total body weightOlder women typically experience little change in total body weight. Women have a more persistent trend of increasing body fat, which offsets resorption of skeletal elements and loss of total body water, producing an increment in the fat fraction of the total body weight.
7ALTERED VOLUME DISTRIBUTION of Drugs (1 of 2) A decrease in total body water causes a decrease in the central compartment (V1)Results in higher peak drug concentrations following boluses or rapid infusionsA decrease in lean body mass causes a decrease in the rapid equilibrating compartment (V2)Body composition changes alter the volume of distribution (Vd) of drugs. This will result in a longer duration of effect and higher peak drug concentration following boluses or rapid infusions.
8ALTERED VOLUME DISTRIBUTION of Drugs (2 of 2) An increase in body fat causes an increase in the slow equilibrating compartment (V3)Results in an increase in total volume of distribution and alterations in the duration of drug effectComputer simulations are used to interpret how these changes affect dose and time course of drug effectAlthough we are aware that these changes in Vd occur, it is nearly impossible to interpret how they will affect dose and time course of drug effect without computer simulations.
9How can we apply this to clinical practice? Neuromuscular blocking agents given on a weight-related basis may have a more prolonged effect in the elderlySteady-state Vd (Vdss) of thiopentone increases to 125% of the adult value, yet the initial Vd is reducedSame is seen with soluble anesthetic vapors such as halothaneWater-soluble drugs such as cimetidine have a reduced VdssAs muscle is the target organ for neuromuscular blocking agents, any dose given on a weight-related basis may be expected to have a more prolonged effect in the elderly. The steady-state Vd of thiopentone increases to 125% of the adult value, yet the individual Vd is reduced, increasing the apparent sensitivity of the elderly to this drug.
10Changes in the Central Nervous System (1 of 2) Between the ages of 20 and 80 years there is approximately a:30% reduction in cerebral blood flow36% reduction in cerebral oxygen consumption30% reduction in cortical neuronal densityNeuronal activity, autoregulation, and cerebrovascular response to CO2 remain intactNeuronal composition, cell number, and regeneration capacities in the CNS diminishThe target organ for all anesthetic agents is the CNS. Between the ages of 20 and 80 years there is approximately a 30% reduction in central blood flow, a 36% reduction in cerebral oxygen consumption, and a 30% reduction in cortical neuronal density. Neuronal activity, autoregulation, and cerebrovascular response to CO2 remain intact in the absence of disease. However, in recent years, it has been discovered that neuronal composition, neuronal cell number, and neuronal regeneration capacities in the CNS diminish with increasing age.
11Changes in the Central Nervous System (2 of 2) Depletion of brain neurotransmittersNumber of receptor sites and composition of receptors decrease and changeMay explain why most anesthetic agents exert their effects in the elderly at lower blood and effect-site concentrationsThere is a depletion of brain neurotransmitters (catecholamines, serotonin, and acetylcholine). These are associated with mood, memory, and motor function and may partly account for their loss. The number of receptor sites and the composition of these receptors that are involved in memory formation and the propagation of anesthesia, such as N-methyl-d-aspartate, also decrease and change in the elderly. These alterations may explain why most anesthetic agents exert their effects in the elderly at lower blood and effect-site concentrations.
12Changes in the Cardiovascular System (1 of 5) Decreased number of myocytesStiffening of myocardial cellsReduced response to β-adrenergic stimulationLarge arteries dilateIncreased wall thickness and smooth muscle toneAge-related changes in CV function explain the increased cardio-depressant effects of many anesthetics in the elderly. The decreased number of myocytes, the stiffening of myocardial cells, and the reduced response to β-adrenergic stimulation result in clinically obvious decreased contractile properties of the heart with increasing age. In parallel with these cardiac changes, the large arteries dilate, with increased wall thickness and increasing smooth muscle tone.
13Changes in the Cardiovascular System (2 of 5) Results in an increase in systolic BP, elevated left ventricular (LV) afterload, and LV wall thickeningReduces LV compliance, causing impairment of diastolic functionMore sensitive to the arrhythmogenic effects of anestheticsIncreased tendency to develop pulmonary edemaClinically this results in an increase in systolic blood pressure and an elevated LV afterload, resulting in LV wall thickening. This is turn reduces LV compliance and causes impairment of diastolic function. As a consequence, the elderly are more sensitive to the arrhythmogenic effects of anesthetics, with an increased tendency to develop pulmonary edema.
14Changes in the Cardiovascular System (3 of 5) No age-associated decline in cardiac output in healthy older adultsSedentary lifestyle or degenerative changes would produce a decline in cardiac outputDecreases in cardiac output with a lower tissue perfusion may lengthen the time required to transport drugs to tissues and delay the time to peak effectAlthough it was previously believed that a progressive decrease in cardiac output occurs, newer longitudinal studies fail to show a significant age-associated decline in cardiac output at rest or during exercise in healthy adults between the ages of 25 and 79 years. It appears that in the elderly, a sedentary lifestyle or degenerative diseases would produce a decline in cardiac output, but an active lifestyle and good health would maintain it at relatively normal levels.
15Changes in the Cardiovascular System (4 of 5) Reduction in perfusion is unevenResults in increased duration of action of anesthetic agentsVirtually all anesthetics decrease cardiac output to some degreeDose needed for induction is reducedSlower onset of block seen with neuromuscular blocking agentsThe reduction in perfusion is uneven, with decreases in hepatic and renal blood flow and an increase of cerebral, coronary and skeletal blood flow. A reduction in perfusion of the organs responsible for drug metabolism and elimination has important PK implications for IV anesthetic agents, generally increasing their duration of action.If we consider the effect of anesthetic drugs on cardiac output, virtually all decrease it to some degree. As a result of the decreased cardiac output, the dose of anesthetic agents needed for induction is reduced, because a relatively larger fraction of the dose is distributed to the brain. A decrease in cardiac output would also result in slower distribution of neuromuscular blocking drugs to the neuromuscular junction, explaining the slower onset of block often seen in elderly patients.
16Changes in the Cardiovascular System (5 of 5) Increased risk of hypotensionDecreased baroreceptor sensitivityDecreased response to β-stimulationDecreased response of renin/aldosterone/angiotensin systemElderly patients are also at an increased risk of developing hypotension because of the decreased baroreceptor sensitivity, decreased response to β-stimulation, and decreased response of the renin/aldosterone/angiotensin system.
17Changes in the Respiratory System (1 of 2) Vital capacity, maximum voluntary ventilation, and total lung capacity decrease with increasing ageFunctional residual capacity and closing volume increaseResults in collapse of small airways and air trappingA number of striking anatomic changes occur in the respiratory system with age. Vital capacity, maximum voluntary ventilation, and total lung capacity all decrease with age, whereas functional residual capacity and closing volume (the volume about FRC at which the airways begin to close off) increase, resulting in the collapse of small airways and air trapping.
18Changes in the Respiratory System (2 of 2) Marked suppression of hyperventilation in response to imposed hypoxia or hypercapniaAnesthesia, supine position, and use of narcotics worsen hypoxiaIncreased risk of aspiration and postoperative pneumoniaIn the elderly there is marked suppression of hyperventilation in response to imposed hypoxia or hypercapnia, putting these patients at a higher risk of respiratory failure. Anesthesia, supine position, and use of narcotics worsen hypoxia by increasing the ventilation perfusion mismatch in an age group that already has blunted ventilatory reflexes. Impaired cough and laryngeal reflexes, decreased immune response, and decreased mucociliary clearance increase the risk of aspiration and postoperative pneumonia.
19Changes in the Hepatic System (1 of 2) Decrease in liver volume40% reduction in liver blood flowAnesthesia and abdominal surgery also reduce blood flowReduced maintenance requirements for drugs that are rapidly cleared by the liverModest reduction in the rate of hepatic metabolism for drugs slowly cleared by the liverFall in metabolism for other anestheticsA decrease in liver volume and a 40% reduction in liver blood flow occurs as individuals approach the end of the ninth decade. Anesthesia and abdominal surgery decrease liver blood flow themselves. These effects result in reduced maintenance dose requirements for drugs that are rapidly cleared by the liver (eg, propofol) but a modest reduction in the rate of hepatic metabolism for drugs that are cleared slowly by the liver (eg, alfentanil and vecuronium). For vecuronium, the elimination half-life is prolonged from 78 minutes in the young to 125 minutes in the elderly. There is an overall decline in metabolism of some anesthetics, such as etomidate, whose clearance falls by about 37%.
20Changes in the Hepatic System (2 of 2) Intrinsic hepatic capacity unchangedNo significant age-dependent difference in the activity of hepatic phase 1 and 2 drug metabolismHepatic cytochrome P450 activity unchangedProduction of albumin decreasedIncreased free fraction of drugs that bind primarily to it, with reduced dose requirementsAlpha-1 acid glycoprotein increasedDecreased free fraction of drugs and reduced eliminationA decrease in the intrinsic hepatic capacity is not supported by recent studies that show an absence of significant age-dependent differences for the activity of hepatic phase 1 and 2 drug metabolism. Hepatic cytochrome p450 activity remains unchanged. Production of albumin by the liver is decreased, resulting in decreased plasma protein binding of drugs. A decreased albumin concentration increases the free fraction of drugs that bind primarily to it (eg, diazepam), with reduced dose requirements. An increased α-1 acid glycoprotein concentration decreases the free fraction of drugs that bind to it (eg, lidocaine) and reduce the drugs’ ability to be cleared.
21Changes in the Renal System Delay in the offset of renally excreted drugsGlomerular filtration rate decreases by about 1% per year over 40 years of ageResult of decreased cardiac output and glomerular sclerosisElimination of drugs undergoing renal excretion is prolongedTubocurarineOne of the consequences of age-related changes in renal function is a delay in the offset of renally excreted drugs such as pancuronium. It would therefore be prudent to choose a different neuromuscular blocking agent for an elderly patient with signs of renal disease.As a result of decreased cardiac output and age-related glomerular sclerosis, GFR decreases by about 1% per year over the age of 40. Elimination of drugs that undergo renal excretion may therefore be prolonged in the elderly. For example, the elimination half-life of tubocurarine is 268 minutes in the elderly but 137 minutes in younger patients.
22Neuromuscular Blocking Agents Onset of action is prolongedCisatracuriumDuration of action is prolongedSuccinylcholine, rocuronium, mivacurium, vecuroniumAtracurium and cis-atracurium not prolongedLong-acting agents are associated with longer PACU stays and postoperative pulmonary complicationsMaintenance infusion rate for adequate neuromuscular blockade is reducedVecuroniumRecovery from muscle relaxation is delayedWhat is known about the PK/PD of neuromuscular blocking agents? First, their onset of action is prolonged secondary to reduced muscle blood flow. We also know that their duration of action is prolonged. This is seen with succinylcholine and mivacurium because of lower rates of hydrolysis caused by decreased levels of plasma cholinesterase in the elderly.Therefore, neuromuscular blocking agents should be limited to short- acting or intermediate-acting (vecuronium and rocuronium) in all elderly patients in whom extubation is planned. Long-acting neuromuscular blocking agents are associated with long PACU stays and increased postoperative pulmonary complications.The maintenance infusion rate for adequate neuromuscular blocking is reduced. The primary route of elimination of vecuronium is via hepatic metabolism, and the decline in hepatic blood flow with age will reduce the plasma clearance. This implies that a constant level of blockade in the elderly is reduced by about 30% and the patient will recover about 30% to 40% more slowly than a younger patient.Finally, recovery from muscle relaxation is delayed. Elderly patients have reduced tissue distribution and clearance, which causes increased plasma drug concentrations and an increased effect.
23Volatile Anesthetic Agents (1 of 2) 66%75% anesthetic concentration is required by an 80-year-old compared to a young adultRate of induction may be slowedDose should not be hastened to induce inductionLarger decrease in BP seen in elderlyImpairment of reflex heart rate responses to BPReduced myocardial contractility by inhalation anestheticsVolume contractionReduction in inhalation anesthesia requirements is due to fundamental neurophysiological changes in the brain. Typically 66% to 75% anesthetic concentration is required by an 80-year-old as compared to a young adult. Rate of induction may be slowed because of reduced ventilation, but the dose of inhalation agent should not be hastened to induce induction.There is a general perception that inhalation agents can cause a larger decrease in blood pressure at a given concentration in the elderly than in the young. Many factors account for the perceived greater hemodynamic sensitivity, but age-related impairment of reflex heart rate responses to blood pressure, decreased myocardial contractility by inhalation anesthetics, and volume contraction might enhance the decrease.
24Volatile Anesthetic Agents (2 of 2) Isoflurane and desflurane are metabolized lessAdvantages of sevoflurane and desflurane:More rapid control of anesthetic depthFaster emergence from anesthesiaMore rapid recovery of mental function to pre-anesthesia levelsIsoflurane and desflurane are metabolized less than other potent inhalation anesthetics; therefore, the concentration of potentially toxic metabolites (inorganic fluoride, which can cause nephrotoxicity) is lower.The lower solubility of sevoflurane and desflurane has important advantages in the elderly, for example, more rapid control of anesthesia depth to meet varying intraoperative conditions, faster emergence from anesthesia for desflurane as compared to isoflurane, and theoretically a more rapid recovery of mental function to pre- anesthetic levels, although studies have failed to demonstrate this.
25Intravenous Agents Must cross the blood-brain barrier Non-ionized and protein-boundSmall changes in pH greatly alter the availability of the drugSlow infusion rates are saferToo slow a rate may increase the dosage requirementTo be effective, IV anesthetic drugs must cross the blood-brain barrier and be non-ionized. They are usually protein-bound, which allows some penetration of the blood-brain barrier. The degree of ionization is related to their pKa values. Changes in the degree of ionization will have profound effects on the efficiency of anesthetic drugs. Small changes in pH will greatly alter the availability of the drug. The elderly have a deterioration in renal acid-base balance control, and any such fall in pH will increase the relative potency of the drug, often to dangerous levels.Slower infusion rates appear to be much safer. The amount of drug given at faster rates is up to 50% more than actually needed for induction. You need to take into account the circulation time or the time it takes for the drug to be delivered to the brain to induce anesthesia. The longer the circulation time, the more drug that will be infused before anesthesia occurs. Even after recognition of the onset of anesthesia, there will be more drug still to be presented to the brain. There may come a time with very slow infusion rates when either the redistribution into the lean body mass or metabolism exerts an effect on the induction dose and may increase the dose required.
26HYPNOTICS: PropofolAnesthetic depth synergistically increased when administered with other induction agentsDecreased maintenance requirement with increasing ageSlowly administer a reduced dose to avoid hypotensive effects11.5 mg/kg without opioids; 0.51 mg/kg with opioidsMask induction with sevoflurane causes less hypotension than IV propofol inductionHypotensive response of propofol is offset by intubation responseDose reductions for propofol are required with concurrent administration of any other induction agent, narcotics, or benzodiazepines, as anesthetic depth is synergistically increased.Age-related decreases in clearance of propofol result in a decreased maintenance requirement with age.The hypotensive side effects of propofol require slow administration of a reduced dose, titrated to effect, rather than a bolus of a preselected standardized dose. The dose of propofol should be 1 to 1.5 mg/kg without opioids or 0.5 to 1 mg/kg with opioids, especially when midazolam or ketamine is given. Mask induction with sevoflurane causes less hypotension in the elderly than IV propofol induction. Hypotensive response of propofol is offset by intubation response.
27HYPNOTICS: Thiopental Higher concentrations are seen for any given doseRecovery can be significantly prolonged after continuous infusions or repeated bolus dosesElderly require a 20% reduction in infusion rateConcentration will decline nearly as rapidly when infusion is turned offHigher concentrations are seen for any given dose of thiopental, caused by a reduction in the Vd. Recovery can be significantly prolonged after repeated boluses or continuous infusion, because metabolism becomes dependent on intrinsic hepatic enzyme activity and the degree of protein binding. Healthy elderly patients need only a modest reduction in the infusion rate, 20% or less, when compared to younger adults. If the appropriate adjustment is made, then the concentration will decrease nearly as rapidly when the infusion is turned off.
28HYPNOTICS: Methohexital Clearance is greater and elimination half-life is shorter than that of thiopentalClearance largely dependent on hepatic blood flowElimination will be prolongedThe clearance of methohexital is greater than that of thiopental and its resultant elimination half-life is shorter. However, its clearance is largely dependent on hepatic blood flow, which declines with age, so elimination will be prolonged in comparison to that in younger individuals.
29HYPNOTICS: Etomidate Initial volume of distribution is decreased Requires less than half the dose to reach the same stage EEG endpoint as younger patientsThe initial Vd of etomidate is reduced. An 80-year-old patient requires less than half the dose of etomidate to reach the same EEG endpoints as a 20-year-old patient.
30Benzodiazepines: Midazolam Increased potency30% reduction in clearance in the elderlyTakes twice as long for concentration to fall50%75% dose reduction required when administered as a bolusMidazolam has increased potency in the elderly. Pharmacokinetic studies show a reduction in clearance, approximately 30% in a 80-year-old compared to a 20-year-old, and it takes nearly twice as long for the concentration to fall in an 80-year-old as in a 20-year-old. Anywhere from a 50% to 75% dose reduction is required in the elderly when midazolam is administered as a bolus.
31Benzodiazepines: Diazepam Desmethyldiazepam has more CNS activity than diazepamAccumulation with long-term use can prolong its clinical effects in the elderlyThe hepatic oxidative metabolism of diazepam by hydroxylation results in desmethyldiazepam, which has more CNS activity than the parent compound. With long-term use, the accumulation of the more potent metabolite can prolong its clinical effects in the elderly.
32Benzodiazepines: Ketamine Can exert a negative inotropic effect on ischemic myocardiumLower induction dose for elderly critically ill patientsDecreased clearance and prolonged duration of action expectedBecause ketamine can exert a negative inotropic effect on ischemic myocardium, it is prudent to lower the induction dose for critically ill elderly patients. A decreased clearance and prolonged duration of action in the elderly is expected.
33OPIOIDS: Sufentanil Small decrease in Vd of the central compartment Undergoes hepatic metabolismRequires reduction in both loading and maintenance doses with increasing ageA small decrease in the volume of the central compartment is seen with sufentanil in the elderly, which would affect the dose requirements only for the first few minutes. Sufentanil undergoes hepatic metabolism, so a decreased clearance and an increased duration of action are expected, requiring a reduction in both the loading and maintenance doses.
34OPIOIDS: Remifentanil Has twice the intrinsic potency in elderlyCentral compartment volume decreases 20%Clearance decreases 30%Decrease bolus and maintenance dose by 50%Peak effect expected about 23 minutes after bolusRemifentanil has about twice the intrinsic potency in the elderly. Pharmacokinetic studies show that the central compartment decreases 20% and the clearance decreases 30%. These changes translate into dose changes (decrease by 50% by age 65) for bolus and maintenance infusion. In addition, onset is slower in the elderly, with peak drug effect expected about 2 to 3 minutes after the bolus.
35OPIOIDS: Fentanyl and Alfentanil PK does not appear to be changedFentanyl: Increased potency of about 50%Reduce dose by half to achieve the same effectThe pharmacokinetics of fentanyl and alfentanil in the elderly do not appear to be changed. Fentanyl does show an increased potency of approximately 50%, which would translate clinically into a reduction of dose by half to achieve the same effect.
36OPIOIDS: Morphine Clearance decreased by 50% Prolonged duration of actionReductions in maintenance dosingThe clearance of morphine is decreased by 50% in the elderly, suggesting a prolonged duration of action and reductions in maintenance dosing.
37Local Anesthetics PK/PD changes result from: Decline in the neuron population and slowing of conduction velocity in the peripheral nervesDeterioration in myelin sheaths and connective tissue barriersChanges in anatomical configuration of the lumbar and thoracic spineProgressive sclerotic closure of the intervertebral foraminaPharmacodynamic changes in the elderly result from a decline in the neuron population within the spinal cord and slowing of conduction velocity in the peripheral nerves. Pharmacokinetic changes in local disposition with increasing age are caused by deterioration of the myelin sheaths and connective tissue barriers, changes in anatomical configuration of the lumbar and thoracic spine, and progressive sclerotic closure of the intervertebral foramina.
38Bupivacaine Rapid initial absorption followed by a much slower phase Epidural spaceFast: High initial concentration gradient and large vascularitySlow: Slow uptake of local anesthetic sequestered in epidural fatPeak plasma concentrations and peak times do not changeTerminal half-life increasesProtein binding or metabolizing hepatic enzyme activityThe absorption of bupivacaine from the epidural space shows a biphasic profile: a rapid initial phase followed by a much slower phase. The initial fast absorption phase is a reflection of the high initial concentration gradient and the large vascularity of the epidural space. The slower second phase is believed to occur from the slow uptake of local anesthetics sequestered in the epidural fat.The peak plasma concentrations and peak times of bupivacaine do not seem to change with age. The terminal half-life increases, whereas the total plasma clearance decreases. Bupivacaine has a low hepatic extraction ratio, which means that the decline in plasma clearance is more likely due to a change in the metabolizing hepatic enzyme activity and or serum protein binding than to an alteration in liver blood flow.
39Regional vS. General Anesthesia There are no large prospective studies preferentially supporting the use of regional anesthesia in elderlyOutcome studies suggest no difference in mortality and major morbidityRegional anesthesia has the advantages of:Reduced postoperative negative nitrogen balanceAmelioration of stress response to surgeryDecreased incidence of postoperative thromboembolic complicationsDecreased blood lossDecreased postoperative mental confusionDoes the type of anesthesia administered to elderly patients influence the outcome? Is regional anesthesia preferable in this age group?Intuitively, it makes sense that elderly patients would benefit from regional anesthesia because they remain awake during the procedures and are minimally sedated. During certain procedures, regional anesthesia has the advantages listed on the slide. However, there are no large prospective studies preferentially supporting the use of regional anesthesia in elderly patients. In fact, current outcome studies have suggested that there is no difference in mortality and major morbidity between general and regional anesthesia in most patient populations.
40SPECIAL CONCERNS: Pre-oxygenation Elderly patients desaturate fasterTime to peak relaxation from succinylcholine is also increasedArteriolar, alveolar, venous, and tissue compartments are filled with oxygenMaximum oxygen in a short period of time8 deep breaths of 100% oxygen in 60 seconds with an oxygen flow of 10 L/minMore likely to suffer a cardiac event from desaturationMaximum pre-oxygenation is required for elderly patients because they desaturate faster, and the time to peak relaxation from succinylcholine is also increased. Maximum pre-oxygenation is attained when along with arteriolar and alveolar compartments, venous and tissue compartments are also filled with oxygen. Maximum oxygen in a short period of time is 8 deep breaths of 100% oxygen in 60 seconds with an oxygen flow of 10 L per minute. Elderly patients are more likely to suffer a cardiac event from desaturation.
41SPECIAL CONCERNS: Hypothermia (1 of 3) Elderly are susceptible to effects of hypothermia:BleedingDecreased immune functionDecreased wound strengthHypothermia is more pronounced and lasts longer because of:Low basal metabolic rateHypothyroidismHigh ratio of surface area to body massElderly patients are not immune to the adverse effects of hypothermia, which are bleeding, decreased immune function, and decreased wound strength. Hypothermia is more pronounced and lasts longer due to intrinsic factors (low basal metabolic rate, hypothyroidism, high ratio of surface to body mass).
42SPECIAL CONCERNS: Hypothermia (2 of 3) Core temperature must fall to 35.2 °C before:ShiveringCold-induced vasoconstrictionAutonomic mechanisms for thermoregulationOxygen consumption increases 38% over nonshivering levelsReduction in skeletal muscle mass decreases post-op shiveringImpairment of autonomic mechanisms for thermoregulation, cold- induced vasoconstriction, and shivering in the elderly is delayed intraoperatively, until core temperature falls to lower than that in young adults. Younger patients shiver at 36.1 °C while patients older than 80 will not shiver until their core temperature decreases to 35.2 °C.Oxygen consumption is increased 38% over non-shivering levels. Reduction in skeletal muscle mass decreases post-op shivering, thus limiting the rate at which temperature homeostasis can be reestablished.
43SPECIAL CONCERNS: Hypothermia (3 of 3) Inhibition of thermoregulatory responses by anesthetics is exaggeratedProlonging clearanceFurther renders the elderly susceptible to post-op hypothermiaRewarming may precipitate sudden hypotensionVasodilationHypovolemiaInhibition of thermoregulatory responses by anesthetics is greatly exaggerated in the elderly, prolonging clearance of anesthetics, which further renders them more susceptible to post-op hypothermia. Rewarming may precipitate sudden hypotension as a result of vasodilation and hypovolemia.
44Practice Points (1 of 4)Induction dose in the elderly should be reducedAdminister only 50% of the induction dose of a hypnotic/opioid or neuromuscular blocking agent in an 80-year old compared to a 20-year old to ensure the same hypnotic/analgesic or neuromuscular relaxant effectTopic
45Practice Points (2 of 4) Onset of most agents is delayed Wait an appropriate period of time for the maximal effect to occur in the elderly, to avoid undesired side effectsTopic
46Practice Points (3 of 4)Maintenance dose requirements should be reduced dramatically in the elderlyFor example, remifentanil by 70%; propofol by 40%Topic
47Practice Points (4 of 4)PK/PD variability appears to increase with age because of the increasing gap between the healthy and the very ill elderlyTitration to effect thus becomes increasingly important with ageTopic
48RECOMMENDATIONS FOR DOSE ADJUSTMENT Drug/ClassDose AdjustmentBarbituratesModest reduction in bolus dose and infusion ratesEtomidateReduction of up to 50% in bolus dosePropofolReduction of up to 30%50% in bolus dose and infusion ratesBenzodiazepinesReduction of up to 75% in bolus dose and infusion ratesOpioidsReduction of up to 50% in bolus dose and infusion ratesNon-depolarizing neuromuscular blocking agentsNo reduction in bolus dose but generally reduced infusion rates depending on drugVolatile agentsReduction in inspired concentrations of 6% per decadeLocal anestheticsSmall to moderate reduction in segmental doseTopic
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