A new inhaled anesthetic under development by a pharmaceutical company is tested in a series of experiments to determine its pharmacokinetic properties. During one of the experiments, the anesthetic agent is administered at a constant partial pressure while arterial and venous concentrations are monitored. The study results show that the anesthetic has a very large arteriovenous concentration gradient shortly after beginning inhalation. Which of the following best describes the properties of the new anesthetic?

Question

A new inhaled anesthetic under development by a pharmaceutical company is tested in a series of experiments to determine its pharmacokinetic properties.  During one of the experiments, the anesthetic agent is administered at a constant partial pressure while arterial and venous concentrations are monitored.  The study results show that the anesthetic has a very large arteriovenous concentration gradient shortly after beginning inhalation.  Which of the following best describes the properties of the new anesthetic?

Quizplus · Accepted Answer

Before gas anesthetics can reach the target organ (brain), they must move through a number of compartments (inhaled air → lungs → blood→ brain). The onset of anesthesia occurs when a sufficient quantity of anesthetic is transferred to the brain. The factors shown in the table influence the rate of transfer of anesthetic through the compartments and determine the onset of action. 11ec160b_3c06_c2b3_9249_9fd73014ce0f_MD0001_00 The arteriovenous concentration gradient is the difference between the concentration of a gas anesthetic in arterial and venous blood. The solubility of the anesthetic in the peripheral tissues is a major factor in determining the size of the arteriovenous gradient. If tissue solubility is high, a large amount of anesthetic is taken up from arterial blood, which results in low venous concentration. As a result, saturation of the blood requires further absorption of anesthetic in order to replace that which is absorbed by the peripheral tissues. Because blood saturation takes longer, brain saturation is also delayed and onset of action is slower. In contrast, anesthetic gases with low peripheral tissue solubility have smaller arteriovenous gradients as there is less peripheral tissue uptake (Choices B and C). Less anesthetic is required to replace the amount absorbed by the peripheral tissue and so blood saturation occurs quickly, allowing concentrations in the brain to equilibrate faster (Choice A). (Choice D) Potency of the anesthetic is defined by the minimal alveolar concentration (MAC), the alveolar concentration that prevents movement in 50% of patients exposed to noxious stimuli. Potent anesthetics have low MACs. The arteriovenous concentration gradient influences the rate of induction, not anesthetic potency. Educational objective: The arteriovenous concentration gradient reflects the overall tissue solubility of an anesthetic. Anesthetics with high tissue solubility are characterized by large arteriovenous concentration gradients and slower onsets of action.

A New Inhaled Anesthetic Under Development by a Pharmaceutical Company