Intavenous Anesthesia Flashcards
What is the order of tissues in which concentrations of different IV anesthetics peak?
Concentrations peak in the following order:
- Plasma: peaks upon injection
- Vessel rich groups, e.g. liver and spleen: peaks at 1 min
- Muscles: peaks at 10 min
- Fat: peaks after 100 min
What is propofol used for? What dose is used for each situation?
Propofol is used for induction of anesthesia. It is used as a bolus for induction in doses ranging from 1.0-2.5 mg/kg.
It is also used for maintenance of anesthesia (given via continuous infusion rather than multiple boluses) using a loading dose of 1-2 mg/kg followed by an infusion of 100 mcg/kg/min to be titrated to effect. If multiple boluses are used, the dose range is 0.3-0.5 mg/kg.
Propofol is also useful in lower doses for sedation during regional and monitored anesthesia care and for pts in the ICU. The sedation dose range is 25-75 mcg/kg/min.
What are the advantages and disadvantages of propofol?
Advantages:
- Pleasant, rapid loss of consciousness and rapid awakening
- Easily titratable
- Fewer residual effects on the pt’s brain
- Antiepileptic
- Antiemetic
- Never associated with malignant hyperthermia
Disadvantages:
- Anaphylaxis in pts with egg allergy
- Apnea: pt must be intubated and assisted with ventilation
- Hypotension
- Burning pain upon injection, which can be attenuated by using an IV catheter placed in a large vein and/or by coadministering lidocaine 0.5-1.0 mg/kg IV just prior to injecting propofol
What is thiopental used for? What are the advantages and disadvantages?
It was mainly used for pts undergoing neurosurgery, but is now banned in the USA.
It has the advantage of of reducing the brain’s oxygen consumption and may reduce ischemia-induced brain damage.
It is also used intraoperatively for burst suppression (decreases EEG activity) in neurosurgery and status epilepticus and for treatment of increased ICP.
What is etomidate used for? What are its advantages and disadvantages?
Etomidate is the agent of choice for induction whenever cardiovascular instability is a potential issue. This is because it has the unique advantages of causing little or no effect on systemic or pulmonary artery pressure, little or no effect on heart rate, and only a mild effect on cardiac output.
Disadvantages:
- Adrenocortical suppression
- Myoclonus
- Activation of seizure foci
What is ketamine used for? What dose is used for each situation?
Ketamine is used for induction of anesthesia with a dose of 0.1 mg/kg.
It is used for maintenance of anesthesia with a dose of 2-4 mcg/kg/hr.
*It is not ever given using multiple boluses for maintenance.
What is the onset of action, duration of action, and half-life elimination of propofol?
Onset: 15-45 seconds
Duration: 5-10 min
T1/2: 2-24 hr
What is the onset of action, duration of action, and half-life of etomidate?
Onset: 15-45 seconds
Duration: 3-10 min
T1/2: 3-5 hrs
What is the onset of action, duration of action, and half-life of thiopental?
Onset: 15-30 sec
Duration: 5-10 min
T1/2: 12 hr
What is the onset of action, duration of action, and half-life of ketamine?
Onset: 30-60 sec IV; 3-4 min IM; 20-40 min PO
Duration: 5-10 min IV; 12-25 min IM
T1/2: 2-4 hr
What are the doses used for ketamine?
Induction/bolus dose:
- 1-2 mg/kg IV
- 4-6 mg/kg IM
- 6-10 mg/kg PO
Infusion dose:
- GA: 30-90 mcg/kg/min
- Adjunct: 0.1 mg/kg/hr
What is dexmedetomidine (Precedex) used for? What doses are used?
Precedex is a selective a2-adrenergic agonist primarily used for short-term (<24 hrs) sedation in the ICU. It has minimal respiratory depression compared to propofol and thus can be used for pts who aren’t intubated.
For sedation, a loading dose of 0.5-1 mcg/kg is given over 10 minutes followed by an infusion of 0.2-1 mcg/kg/hr.
What is methohexital used for? What doses are used?
Methohexital is a barbiturate with similar cardiorespiratory effects to thiopental.
It uniquely activates epileptic foci facilitating ECT and identification of seizure foci during ablation therapy.
Induction/bolus dose: 1-2 mg/kg.
GA maintenance dose: 50-150 mcg/kg/min
What unique properties does ketamine have compared to other IVAs?
- Increases HR (thiopental also does but less so)
- Increases MAP (precedex does but only as a bolus)
- Increases cerebral blood flow
- Increases cerebral metabolic rate of O2
- Increases ICP
- No change in ventilatory drive (all others decrease it)
When is ketamine contraindicated?
- Patients with intracranial pathology b/c it increases ICP and CBF
- Direct myocardial depressant in pts with catecholamine depletion (sepsis, trauma)
