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LETTER TO EDITOR
Year : 2013  |  Volume : 57  |  Issue : 1  |  Page : 93  

Dose sparing of opioids and anaesthetics with pre-operative dexmedetomidine


Department of Anaesthesiology and Critical Care, Gauhati Medical College and Hospital, Guwahati, Assam, India

Date of Web Publication14-Mar-2013

Correspondence Address:
Priyam Saikia
Department of Anesthesiology and Critical Care, Gauhati Medical College and Hospital, Guwahati, Assam
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0019-5049.108589

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How to cite this article:
Saikia P. Dose sparing of opioids and anaesthetics with pre-operative dexmedetomidine. Indian J Anaesth 2013;57:93

How to cite this URL:
Saikia P. Dose sparing of opioids and anaesthetics with pre-operative dexmedetomidine. Indian J Anaesth [serial online] 2013 [cited 2019 Dec 9];57:93. Available from: http://www.ijaweb.org/text.asp?2013/57/1/93/108589

Sir,

I have read with great interest the recent article "Attenuation of pressor response and dose sparing of opioids and anaesthetics with pre-operative dexmedetomidine" in this journal of international repute, and I would like to address some concerns. [1] This study stresses that dexmedetomidine decreases the dose of opioid and isoflurane required to achieve adequate analgesia and anaesthesia.

White in his editorial mentioning the work of Ura states that 1.3 minimum alveolar concentrations (MAC) (SD 0.34) isoflurane blocks adrenergic responses to skin incision and it decreases with concomitant use of fentanyl. [2] In the study by Lee, the median time for end-tidal concentration of isoflurane to reach 80% of inspiratory concentration was 19 min with an interquartile range of 12 min. [3]

Carbon dioxide (CO 2 ) production and alveolar ventilation are major determinants of arterial CO 2 if there is no CO 2 rebreathing. [4] As alveolar concentration of CO 2 is determined by production of CO 2 and fresh gas flow (FGF), it can be assumed that if CO 2 production is constant then alveolar CO 2 is determined by FGF to alveoli in optimal conditions. [4] In patients with normal ventilation perfusion ratio, end-tidal carbon-di-oxide (ETCO 2 ) monitoring can be an estimate of arterial CO 2 . [5]

As alveolar ventilation is a major determinant governing uptake of potent inhaled anesthetics, [6] considering the above-mentioned facts, every patient should have been ventilated to a predetermine ETCO 2 with predetermined FGF to remove minute ventilation as the confounding factor in the study by Bajwa et al. The article mentions that the concentration of isoflurane was adjusted in increments of 0.2%, and it was not apparent what the time limit that was allowed to reach equilibrium. [1] Again as the mode (manual or mechanical) of ventilation or the ETCO 2 was not specified at any moment during the study period, I assume that the alveolar concentration of isoflurane may not have been distributed normally among the study population. [1]

Considering the above facts, in the study by Bajwa et al., a predefined period (to allow equilibration time prior to skin incision) with a fixed protocol-based adjustment of inhalational agent, fresh gas flow, and ventilation pattern to maintain a predefined end-tidal CO 2 level was necessary to attain a steady level of depth of anaesthesia, so that meaningful conclusion could be drawn regarding fentanyl or isoflurane sparing effect of dexmedetomidine in the absence of end-tidal isoflurane and bispectral index monitoring facility.

 
   References Top

1.Bajwa SJ, Kaur J, Singh A, Parmar S, Singh G, Kulshrestha A, et al. Attenuation of pressor response and dose sparing of opioids and anaesthetics with pre-operative dexmedetomidine. Indian J Anaesth 2012;56:123-8.  Back to cited text no. 1
[PUBMED]  Medknow Journal  
2.White D. Uses of MAC. Br J Anaesth 2003;91:167-9.  Back to cited text no. 2
[PUBMED]    
3.Lee DJ, Robinson DL, Soni N. Efficiency of a circle system for short surgical cases: Comparison of desflurane with isoflurane. Br J Anaesth 1996;76:780-2.  Back to cited text no. 3
[PUBMED]    
4.Elam JO, Brown ES. Carbon dioxide homeostasis during anesthesia. III. Ventilation and carbon dioxide elimination. Anesthesiology1956;17:115-27.  Back to cited text no. 4
    
5.St John RE. End-tidal carbon dioxide monitoring. Crit Care Nurse 2003;23:83-8.  Back to cited text no. 5
[PUBMED]    
6.Eger EI 2 nd , Saidman LJ. Illustrations of inhaled anesthetic uptake, including intertissue diffusion to and from fat. Anesth Analg 2005;100:1020-33.  Back to cited text no. 6
    




 

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