Anesthesia Pharmacology and Special Populations Flashcards
aging patients anesthesia considerations
- fast growing population
- less organ reserve
- many prescriptions + medications (polypharmacy that could interact with our anesthetics)
- more prone to adverse reactions to medications
body water % in elderly
decreases
50-55%
lean body mass % in elderly
decreases
12%
body fat % in elderly
increases
women 38-45%
men 36-38%
serum albumin in elderly
decreases
3.8 g/dL
kidney weight in elderly
decreases
80% that of a young adult
hepatic blood flow in elderly
decreases
55-60% that of a young adult
alpha 1 glycoprotein in elderly
increased, unknown mechanism
anesthesia plan for elderly requirements
- meticulous preoperative assessment
- detailed management of intraoperative variables and disease states
- cautious titration of drug administration and doses [slower circ time; decrease doses]
- age related increase in pharmacodynamic sensitivity to anesthesia agents [mechanism unknown]
- additional monitor for anesthetic depth potentially indicated (BIS)
why are dose reductions for IV meds required in the elderly?
- longer half-lives
- 30% decrease dose Q10 years
- increased brain sensitivity to narcotics
- plasma drug concentrations immediately after injection usually higher due to decreased level of plasma proteins
optimization of post operative pain management in the elderly can be complicated by…
- preexisting cognitive impairment
- fear of opioid related side effects
regional anesthesia for pain control in the elderly
- anatomic changes in epidural and subarachnoid space
- diameter and # of myelinated fibers decreased
- increase permeability of dura and decreased volume of CSF
- occlusion of intervertebral foramina with fibrous connective tissue
- spread of block higher in elderly
- regional can be patchy due to calcifications in the spinal column
muscle relaxants in the elderly
- reduced skeletal muscle mass
- onset of action delayed [slower circ time, increased amount of extrajunctional cholinergic receptors]
- DOA extended (metabolism/elimination delayed due to decreased organ function)
- antagonsim remains unchanged
- reduced plasmacholinesterase (more reduction in males vs. females)
post-operative delirium
- acute confusional state characterized by inattention, abnormal level of consciousness, thought disorganization, and a fluctuating course
- one of the most common post-operative complications for elderly patients undergoing surgery
- can be prevented in up to 40% of cases
pre-op review of medications in elderly
- d/c or sub meds with potential drug interactions with anesthesia
- d/c meds that increase surgical risk
- identify meds to be discontinued based on Beer’s criteria
- continue meds with withdrawal potential
- avoid starting new benzos + reduce dose for those at risk for POD
- avoid meperidine + morphine (active metabolites)
- caution with antihistamines + meds with anticholinergic effects
- consider starting B blocker/statin to decrease post-op CV adverse events
- adjust renally excreted meds
drugs that can induce post-op delirium
- tricyclic antidepressants
- antihistamines
- antimuscarinics
- antispasmodics
- first-generation antipsychotics
- H2 receptor antagonists
- skeletal muscle relaxants
- antiemetics
- corticosteroids
- meperidine
- sedative hypnotics
- polypharmacy
main considerations for elderly population
- renal impairment
- decreased plasma protein [albumin]
- reduced gastric motility and acidity
- altered distribution
- increased total body fat
- decreased hepatic blood flow
- decreased GFR
Pharmacology in obese patients influenced by…
- different tissue distribution
- hemodynamics
- blood flow to tissue types (organs, adipose, splanchinic)
- plasma composition
- liver and kidney function
Pharmacokinetics in obese influenced by…
- lipid solubility of drug
- diffusion through body compartments
things to consider when dosing medications for obese
- volume of distribution for loading dose [IBW for drugs that are preferential for lean tissue; TBW for drugs with equal distribution to lean and adipose tissue]
- clearance for maintenance dose
- lean body weight (LBW)
what is lean body weight
measurement of weight in those who are obese that accounts for the extra development of muscle tissue to support large amounts of fat
Thiopental in obese patients
- dose on TBW
- prolonged DOA and 1/2 life
propofol in obese patients
- LBW for induction
- TBW for maintenance
- highly lipophilic, total clearance and Vd correlate well with TBW
midazolam in obese patients
- loading dose on TBW
- maintenance dose on IBW
- sedative effects correlate better to larger Vd and less to elimination
- need higher dose to achieve initial therapeutic effects
dexmedetomidine in obese patients
- 0.2 mcg/kg/min
- lower than usual infusion rates recommended to minimize cardiac side effects
succinylcholine in obese patients
- dose based on TBW
- large ECF compartment in obese
- psuedocholinesterase activity increases with weight
NDMRs in obese patients
- dose based on IBW
- prolonged DOA with TBW dosing
- hydrophilic drugs given on IBW ensures more predictable recovery
fentanyl in obese patients
- weight based dose inconclusive
- dosing based on TBW overestimates requirements
- measure clearance has non-linear relationship to TBW
sufentanil in obese patients
- loading dose based on TBW
- maintenance dose based on LBW and response
- increased Vd and prolonged e1/2 life correlates with degree of obesity
remifentanil in obese patients
- dose based on IBW
- kinetics not effected by weight
rectal admin in pediatrics
generally a slower absorption, commonly used in kids under 5 yo for sedation
intranasal admin in pediatrics
faster onset, less offensive to children; can give midazolam and fentanyl via this route
IM admin in pediatrics
not recommended because decreased muscle mass and pain that could potentially last for days; emergency drugs and pain medications can be given via this route
IV admin in pediatrics
distribution of the drug depends on circulating blood elements, blood-tissue partition coefficients, distribution of blood flow
drug distribution in pediatric patients
- major proteins involved in binding drugs are albumin and alpha1 acid glycoprotein
- much lower concentration in infants
- presence of substance that can displace drug from proteins will alter pharmacology
- agents that are highly protein bound will have an apparent smaller Vd
- implications for blood gas and blood tissue coefficients for volatile anesthetics
blood flow and pediatric pharmacology
- smaller muscle mass and greater fat stores in neonates and infants
- greater blood flow to central organs (brain, liver, heart, kidneys)
- water soluble drugs may require higher doses (succ)
- mismatch in tissue types effects duration of action
other factors that affect pediatric drug distribution
- integrity of BBB (decreased) = rapid uptake of anesthetics into CNS, higher brain blood flow
- receptor affinity and sensitivity
- developmental changes in hepatic metabolism (may not be mature yet)
- change in renal function
GFR at birth
40 mL/min
GFR at 1 year of age
100 mL/min
chemotherapy patients and anesthesia
focus on how the drugs will affect CV system, pulmonary function, and hematology to know how they will affect your anesthetic
cisplatin
- clinical use = lung cancer, breast cancer, bile duct cancer, ovarian cancer
- toxicity = nephrotoxicity, peripheral neuropathy, nerve dysfunction
methotrexate
- clinical use = breast cancer, lymphomas, bladder cancer
- toxicity = myelosuppresion with neutropenia and thrombocytopenia
bleomycin
- clinical use = Hodgkin’s and non-Hodgkin’s lymphomas, bladder cancer
- toxicity = pulmonary fibrosis
doxorubicin
- clinical use = lung cancer, lymphomas, ovarian cancer, thyroid cancer
- toxicity = cardiotoxicity, myelosuppression
cetuximab
- clinical use = colon cancer, GI cancer
- toxicity = interstitial lung disease
volatile anesthetics, barbs, and ketamine influence on cancer cell activity
suppress NK cell activity and can promote cancer cell mets
nitrous oxide influence on cancer cell activity
- reduces purine and thus DNA synthesis
- suppresses neutrophil chemotaxis, potentially facilitating the spread of cancer
propofol influence on cancer cell activity
- seems to exhibit protective effects through various mechanisms
- anti-inflammatory effect
- inhibition of COX-2 + reduction of PGE-2
- weak beta adrenoreceptor binding
- enhancement of antitumor immunity
- NK function preservation
opioids influence on cancer cell activity
- may produce cellular and humoral immunosuppression
- most = morphine
local anesthetics influence on cancer cell activity
shown to reduce metastatic burden
