Sitting position does not alter minimum alveolar concentration for desflurane.
OBJECTIVE
Hypotension is a common complication of the sitting position during anesthesia, and is often counteracted by decreasing anesthetic depth, thereby exposing patients to the risk of being inadequately anesthetized. Baroreceptor unloading and the consequent sympathoexcitation, as during head up tilt, decreases pain threshold and arouses the central nervous system (CNS), whereas hypotension exerts a direct CNS depressant effect. We estimated the minimal alveolar concentration (MAC) of desflurane for immobility in patients undergoing surgery in the sitting position, in comparison to MAC desflurane for patients having a similar type of surgery in the supine position.


METHODS
The Dixon up-and-down method was used to evaluate the MAC for desflurane in patients undergoing cervical spine laminoplasty (n = 24) or discectomy (n = 24) in the sitting and supine positions, respectively. Logistic regression with co-variate adjustment was employed to examine if the two positions (sitting and supine) have different or share the same concentration vs response relationship for immobility. Monte Carlo simulation was used to calculate 95% confidence intervals (CI) for the MAC in each position, and to estimate the difference in MAC (delta MAC) between the sitting and supine positions.


RESULTS
Modeling both sitting [6.54% (6.50-6.66, 95% CI)] and supine [6.70 (6.55-6.81)] patients as having different MAC concentrations did not significantly improve our simplified model, which treats the two patient groups as one [6.61 (6.52-6.70), delta -2 log likelihood = 2.735, P = 0.098]. Mean delta MAC (95% CI) was -0.14 (-0.30, 0.03).


CONCLUSIONS
The sitting position does not change desflurane anesthetic requirements for immobility.
Lin
Chun-Ming
CM
Department of Anesthesiology, Chang Gung Memorial Hospital, 5, Fu-Hsing St., Tao Yuan, Taiwan. sam2498@adm.cgmh.org.tw
Wu
Chieh-Tsai
CT
Lee
Shih-Tseng
ST
Lui
Tai-Ngar
TN
Huang
Chia-Chun
CC
Li
Allen Hon-Lun
AH
Doufas
Anthony G
AG
D000328:Adult; D000465:Algorithms; D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics*; D001794:Blood Pressure / Q000187:drug effects; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D000077335:Desflurane; D004311:Double-Blind Method; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D009010:Monte Carlo Method; D009333:Neck / Q000601:surgery; D019635:Neurosurgical Procedures; D010146:Pain / Q000601:surgery; D011187:Posture / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000378:metabolism*; D013131:Spine / Q000601:surgery; D016683:Supine Position / Q000502:physiology
D018685:Anesthetics, Inhalation; D000077335:Desflurane; D007530:Isoflurane