52 research outputs found
Theoretical effect of hyperventilation on speed of recovery and risk of rehypnotization following recovery - a GasMan<sup>Âź</sup> simulation
<p>Abstract</p> <p>Background</p> <p>Hyperventilation may be used to hasten recovery from general anesthesia with potent inhaled anesthetics. However, its effect may be less pronounced with the newer, less soluble agents, and it may result in rehypnotization if subsequent hypoventilation occurs because more residual anesthetic will be available in the body for redistribution to the central nervous system. We used GasMan<sup>Âź</sup> simulations to examine these issues.</p> <p>Methods</p> <p>One MAC of isoflurane, sevoflurane, or desflurane was administered to a fictitious 70âkg patient for 8âh with normoventilation (alveolar minute ventilation [V<sub>A</sub>] 5âL.min<sup>-1</sup>), resulting in full saturation of the vessel rich group (VRG) and >95% saturation of the muscle group. After 8âh, agent administration was stopped, and fresh gas flow was increased to 10âL.min<sup>-1</sup> to avoid rebreathing. At that same time, we continued with one simulation where normoventilation was maintained, while in a second simulation hyperventilation was instituted (10âL.min<sup>-1</sup>). We determined the time needed for the partial pressure in the VRG (F<sub>VRG</sub>; representing the central nervous system) to reach 0.3 MAC (MACawake). After reaching MACawake in the VRG, several degrees of hypoventilation were instituted (V<sub>A</sub> of 2.5, 1.5, 1, and 0.5âL.min<sup>-1</sup>) to determine whether F<sub>VRG</sub> would increase above 0.3 MAC(= rehypnotization).</p> <p>Results</p> <p>Time to reach 0.3 MAC in the VRG with normoventilation was 14âmin 42âs with isoflurane, 9âmin 12âs with sevoflurane, and 6âmin 12âs with desflurane. Hyperventilation reduced these recovery times by 30, 18, and 13% for isoflurane, sevoflurane, and desflurane, respectively. Rehypnotization was observed with V<sub>A</sub> of 0.5âL.min<sup>-1</sup> with desflurane, 0.5 and 1âL.min<sup>-1</sup> with sevoflurane, and 0.5, 1, 1.5, and 2.5âL.min<sup>-1</sup> with isoflurane. Only with isoflurane did initial hyperventilation slightly increase the risk of rehypnotization.</p> <p>Conclusions</p> <p>These GasMan<sup>Âź</sup> simulations confirm that the use of hyperventilation to hasten recovery is marginally beneficial with the newer, less soluble agents. In addition, subsequent hypoventilation results in rehypnotization only with more soluble agents, unless hypoventilation is severe. Also, initial hyperventilation does not increase the risk of rehypnotization with less soluble agents when subsequent hypoventilation occurs. Well-controlled clinical studies are required to validate these simulations.</p
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