Standard Doses of Inhalational Anesthetics 

Several clinical factors influence the standard doses of inhalational anesthetics: age, weight, efficacy and comorbidity in the standard patient group and environmental toxicity. For the general population of reasonable age and weight, “efficacy and comorbidity based on patient group” is the primary consideration when dosing a patient. This patient group may be defined by any factor unifying the disease being treated and the comorbidities associated with the disease and the use of inhalational anesthetics. For example, some patient groups may be defined by the organ system of interest.  

Obata et al. investigates the potential effect of prolonged low-flow sevoflurane anesthesia on renal and hepatic function when compared to high-flow sevoflurane and low-flow isoflurane anesthesia. Even in the same patient, different organ systems can have different responses. After measuring serum creatinine and other biomarkers, Obata et al. did not discover any negative impact on renal activity when comparing the standard doses commonly used in clinical practice of those three forms of inhalational anesthetics. However, Obata et al. observed a mild hepatotoxic effect of low-flow sevoflurane, which suggested that high-flow sevoflurane and low-flow isoflurane anesthesia is superior to low-flow sevoflurane anesthesia. The mild hepatotoxicity seen with low-flow sevoflurane may present challenges for patients who present with a history of liver disease;1 the patient group defined by liver disease has unique considerations when determining standard doses of inhalational anesthetics and other medications. 

Concerns about environmental damage and adverse effects from anesthesia gases have increased research into low-flow doses of inhalational anesthesia, specifically sevoflurane anesthesia. Donepudi’s et al. study examined the impact of early administration of magnesium sulfate on the amount of inhalational anesthesia 84 patients needed during open fetal myelomeningocele repair surgery. Donepudi et al. concluded that the group receiving magnesium sulfate required significantly lower doses of inhalational anesthesia during surgery, thereby reducing potential adverse effects on the mother and fetus. 2 Suttner and Boldt demonstrate how low-flow anesthetics recycle waste gases effectively thereby reducing toxic discharge into the environment and medication cost. As with the previous study, sevoflurane is the primary gas of interest, although their study looks at desflurane too. Suttner and Boldt find that for both gases, low flow reduces waste and costs by using less fresh gas and recycling exhaled gases. This poses no risk to the patients and might enhance their general well-being. 3 Clinically, there is a push towards using low-flow sevoflurane in place of high-flow sevoflurane to reduce patient and environmental impact.  

Greater age and weight influence the standard doses of inhalational anesthetics due to significant changes seen in the physiological baseline of these individuals compared to the rest of the population. Elderly patients display physiological differences which impact drug distribution and sensitivity. Respiratory function in elderly patients increases their sensitivity to respiratory depressants, like opioids (nitrous oxide). Therefore, the standard doses of inhalational anesthetics are lower for older patients compared to younger adults. 4 

One study on anesthesia doses for obese patients did not find obese patients needing larger doses of inhalational anesthetics like isoflurane to fall asleep. Their study did observe faster recovery times when using sevoflurane anesthesia or desflurane when compared to isoflurane, when considering a clinical end point of “time to eye-opening and time to obeying command.” 5 Despite these dosage positives, managing the airway of an obese patient presents a challenge. The small oral cavity, thick neck and reduced pulmonary and total chest size increase the chance of hypoxia during the surgery and afterwards if postoperative atelectasis occurs.6  

References 

  1. Obata R, Bito H, Ohmura M, Moriwaki G, Ikeuchi Y, Katoh T, Sato S. The effects of prolonged low-flow sevoflurane anesthesia on renal and hepatic function. Anesth Analg. 2000 Nov;91(5):1262-8. doi: 10.1097/00000539-200011000-00039. PMID: 11049919. 
  1. Donepudi R, Huynh M, Moise, Jr. K, J, Papanna R, Johnson A, Austin M, Tsao K, Jain R: Early Administration of Magnesium Sulfate during Open Fetal Myelomeningocele Repair Reduces the Dose of Inhalational Anesthesia. Fetal Diagn Ther 2019;45:192-196. doi: 10.1159/000487883 
  1. Suttner S, Boldt J. Low-flow anaesthesia. Does it have potential pharmacoeconomic consequences? Pharmacoeconomics. 2000 Jun;17(6):585-90. doi: 10.2165/00019053-200017060-00004. PMID: 10977395. 
  1. Vuyk J. Pharmacodynamics in the elderly. Best Practice & research. Clinical Anaesthesiology. 2003 Jun;17(2):207-218. DOI: 10.1016/s1521-6896(03)00008-9. PMID: 12817915. 
  1. Ingrande, J., Lemmens, H.J.M. Anesthetic Pharmacology and the Morbidly Obese Patient. Curr Anesthesiol Rep 3, 10–17 (2013). https://doi.org/10.1007/s40140-012-0002-5 
  1. Domi, R., Laho, H. Anesthetic challenges in the obese patient. J Anesth 26, 758–765 (2012). https://doi.org/10.1007/s00540-012-1408-4