What are the differences in pharmacodynamics between sevoflurane and isoflurane?

Pharmacodynamic Differences Between Sevoflurane and Isoflurane

Sevoflurane offers faster induction and recovery with fewer airway complications compared to isoflurane, while both agents provide similar cardiovascular stability at equivalent MAC doses. 1, 2

Cardiovascular Effects

• Both sevoflurane and isoflurane cause dose-dependent depression of myocardial contractility and afterload reduction, with more similarities than differences in their cardiovascular profiles 3
• Isoflurane tends to cause greater increases in heart rate during induction compared to sevoflurane (92±2 bpm vs 90±4 bpm), potentially making sevoflurane more suitable for patients where tachycardia should be avoided 2
• Both agents demonstrate cardioprotective effects, decreasing troponin release and enhancing left ventricular function compared to propofol or midazolam in cardiac surgery patients 3, 4
• At equivalent MAC doses (0.49 for sevoflurane vs 0.53 for isoflurane), there are no significant differences in hemodynamics, cardioactive drug use, or ischemia incidence between the two agents during CABG surgery 5

Induction and Recovery Characteristics

• Sevoflurane has lower blood-gas solubility than isoflurane, resulting in faster induction and recovery times 1, 6
• Sevoflurane's non-pungent odor makes it significantly better tolerated during mask induction compared to isoflurane, with fewer complications such as coughing, breath-holding, and laryngospasm 2, 7
• Single vital capacity breath induction is faster with sevoflurane than isoflurane (45±21 sec vs 71±22 sec), with higher success rates (100% vs 75.8%) and fewer induction-related complications (11.8% vs 84.8%) 8
• Recovery of response to commands is significantly faster with sevoflurane than isoflurane (7.5±0.5 min vs 18.6±2.0 min) 6
• Patients open their eyes at lower end-tidal MAC-fractions with sevoflurane (0.12±0.01 MAC) compared to isoflurane (0.15±0.01 MAC) 2

Immunomodulatory Effects

• Both sevoflurane and isoflurane suppress immune cell function, but with some agent-specific differences 3
• Both agents decrease neutrophil adhesion to human endothelial cells, which may provide beneficial effects in ischemic settings 3
• Isoflurane and sevoflurane bind to lymphocyte function-associated antigen-1 (LFA-1), blocking its interaction with ICAM-1 and inhibiting immune cell adhesion 3
• Isoflurane, but not sevoflurane, has an inhibitory effect on Macrophage-1 antigen (MAC-1), demonstrating a difference in their immunomodulatory profiles 3
• Both agents can induce lymphocyte apoptosis via the mitochondria-triggered pathway, though propofol may attenuate sevoflurane-induced mitochondria-related apoptosis 3

Neurological Effects

• Both sevoflurane and isoflurane show similar effects on intracranial pressure (ICP) at equivalent MAC concentrations during neurosurgical procedures 5
• ICP response to hypocarbia during progressive hyperventilation is preserved with sevoflurane at both 0.5 and 1.0 MAC concentrations 5
• During recovery, patients receiving sevoflurane report feeling less clumsy and less confused than those receiving isoflurane, suggesting potentially better cognitive recovery 2

Clinical Considerations and Pitfalls

• For patients at risk of ICP elevations, both agents should be administered cautiously in conjunction with ICP-reducing maneuvers such as hyperventilation 5
• Sevoflurane is preferred over isoflurane for mask induction in both pediatric and adult patients due to its non-pungent odor and lower incidence of airway complications 1, 2
• In patients with hepatic impairment, neither sevoflurane nor isoflurane adversely affects hepatic function, though sevoflurane patients may have prolonged terminal disposition of fluoride (23 hours vs 10-48 hours in normal hepatic function) 5
• For patients with renal insufficiency, both agents should be used with caution, as creatinine level increases have been observed in 7% of sevoflurane patients and 8% of isoflurane patients 5
• The French Society of Anesthesia and Resuscitation strongly recommends sevoflurane over isoflurane when choosing an inhalational anesthetic, when clinical benefits are equal 3

Environmental Considerations

• While not directly related to pharmacodynamics, it's worth noting that both sevoflurane and isoflurane have environmental impacts as greenhouse gases, though with different carbon footprints 3
• Sevoflurane has a higher metabolism rate (4-5%) compared to isoflurane (0.2%), resulting in less unmetabolized agent being released into the atmosphere 3

In summary, while both agents share many pharmacodynamic properties, sevoflurane offers distinct advantages in terms of induction quality, recovery profile, and patient comfort, making it generally preferred over isoflurane for most clinical scenarios when inhalational anesthesia is indicated.