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Sitting position does not alter minimum alveolar concentration for desflurane

[La position assise ne modifie pas la concentration alvéolaire minimale du desflurane]

Chun-Ming Lin, MD^*, Chieh-Tsai Wu, MD, Shih-Tseng Lee, MD, Tai-Ngar Lui, MD, Chia-Chun Huang, MD^*, Allen Hon-Lun Li, MD PhD^* and Anthony G. Doufas, MD, PhD

^* From the Departments of Anesthesiology and
Neurosurgery, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Tao Yuan, Taiwan; and the
Department of Anesthesia, Stanford University School of Medicine, Stanford, California, USA; and the Outcomes Research Group.

Address correspondence to: Dr. Chun-Ming Lin, Department of Anesthesiology, Chang Gung Memorial Hospital, 5, Fu-Hsing St., Tao Yuan, Taiwan. E-mail: sam2498{at}adm.cgmh.org.tw

Purpose: 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).

Conclusion: The sitting position does not change desflurane anesthetic requirements for immobility.

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The sitting position in neurosurgery – unresolved hemodynamic consequences!/La position assise en neurochirurgie – conséquences hémodynamiques non résolues !

Anthony J. Cunningham and David Hourihan
CJA 2007 54: 497-500. [Full Text]  

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				A. J. Cunningham and D. Hourihan The sitting position in neurosurgery - unresolved hemodynamic consequences!/La position assise en neurochirurgie - consequences hemodynamiques non resolues ! Can J Anesth, July 1, 2007; 54(7): 497 - 500. [Full Text] [PDF]