1. A. Unless supplemented with strong analgesic drugs such as opioids, most general anesthetics allow reflex reactions to painful stimuli, which may include movement and autonomic reflex changes. Even though these reflex changes occur, if adequately anesthetized, patients will not experience the noxious stimulus. To give this patient a neuro-muscular blocking agent without initially evaluating the adequacy of anesthesia would be a mistake. A lawsuit is almost certain, should the patient be inad equately anesthetized and complain postoperatively of being aware but paralyzed. If it is determined that the patient is receiving adequate anesthesia (i.e., evaluate the delivery of gas, and check other reflexes such as corneal), the use of a neuromuscu-lar blocking drug may be acceptable if movement is interfering with the procedure. Morphine may be a reasonable supplement to anesthetic management to inhibit reflex reactions to noxious stimuli. Raising the inspired concentration of isoflurane may further blunt reflex reactions to noxious stimuli. However, it may not be a wise choice, since multiples of MAC may cause greater instability of physiological functions (i.e. cardiovascular function). Use a balanced anesthetic approach with adjunctive agents. The gut is quite responsive to noxious insult, but the reflex responses are still inhibited with proper analgesics, so muscular movement is avoidable.
2. B. Perfusion of the brain is preserved when hemorrhage occurs. Thus, a greater proportion of the initial dose of anesthetic should appear in the brain, and a dose smaller than what is needed for a nor-movolemic patient is all that is required. Also, since flow to tissues associated with redistribution of the drug and termination of anesthesia is compromised, anesthesia should be deep and extended. Titrate this patient to a safe level of effect. While poor perfusion of the liver may reduce the exposure of drugs to metabolic enzymes, most intravenous anesthetics rely very little on hepatic clearance to terminate the anesthetic effect when a single bolus is administered. Furthermore, the question implies a direct influence of blood pressure on the efficiency of hepatic enzymes, and there is no evidence to support such a contention. Option C is not true. The opposite of option D is true. No evidence exists that binding of anesthetics is altered by these conditions.
3. D. Anesthetics with low blood and tissue solubility require minimal uptake from the lung, as alveolar partial pressure equilibrates with tissue. Remember, alveolar partial pressure is the driving force to establish tension gradients throughout the body. Thus, when uptake is low and alveolar tension rises quickly, blood and brain (which receives a high blood flow) equilibrate with gaseous agents quickly, and anesthesia is induced relatively rapidly. A gas that is highly soluble in tissues requires a greater accumulation from the lung before partial pressure equilibria are attained, since with greater uptake the rate of rise of the alveolar tension to the inspired level is slower. Although a relationship exists between MAC and blood solubility with respect to anesthetic concentration in the tissues, the association suggested by choice B is opposite the expectation. Consider the implications of the Meyer Overton rule. An agent with a high Ostwald solubil ity coefficient is one of the more soluble agents in tissue, so the explanation of option A applies. Option E has no apparent bearing on the rate of rise of the alveolar partial pressure in brain, alveolus, or any other tissue.
4. C. Remifentanil has become popular as a component drug in the technique of total intravenous anesthesia as a consequence of this feature. It is distribution of blood to the brain, not specific pharmacological properties, that primarily controls the rate of induction of anesthesia with IV agents. Phenyl-piperidines as a class of opioids are less likely to produce histamine release. Moreover, histamine release may complicate anesthetic management (e.g. bronchoconstriction and hypotension), so if it were an action of remifentanil it would be a negative feature. Remifentanil's duration of action is short because it is rapidly metabolized. Chest wall rigidity is associated with high doses of phenylpiperidine opi-oids in particular, and no evidence suggests that remifentanil would be any less likely to cause such an effect.
5. E. Reduced peripheral vascular resistance occurs with most halogenated hydrocarbons, and reflex tachycardia may be a concern. Halothane may be the clearest exception, since there appears to be a balance between relaxation and constrictor influences in various vascular beds with this agent so that total peripheral resistance changes very little. Halothane is the agent of concern when sensitiza-tion of the myocardium to catecholamine-induced arrhythmias may be important, such as during incidences of hypercapnia. Sevoflurane does not directly influence sympathetic function. However, reflex tachycardia can occur. Reflex sympathetic stimulation is blocked by halothane. In fact, this may be an advantage of the drug in physiologically risky patients when swings in blood pressure are likely to be frequent.
6. D. Although few contend that a unitary hypothesis will explain anesthesia, the Meyer Overton rule was among the first explanations provided by the scientific community. The correlation remains significant, as it suggests that sites of action for various anesthetics may reside near (or the agent must pass though) hydrophobic tissue components. Also, physical disruption of membrane function may yet be found to play a role for at least some agents. Option A is the reverse of the true interaction. Several sites on the GABA receptor complex may be involved. Clmoves inward to cause cells to become less excitable. Enantiomers, which have nearly identical physical properties but different potencies, challenge the Meyer Overton rule.
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