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LETTER TO EDITOR
Year : 2010  |  Volume : 54  |  Issue : 6  |  Page : 576 Table of Contents     

An unusual cause of altered airway pressure during surgery under general anaesthesia


Department of Neuroanesthesiology, All India Institute of Medical Sciences, New Delhi, - 110 029, India

Date of Web Publication22-Nov-2010

Correspondence Address:
Hemanshu Prabhakar
Department of Neuroanaesthesiology, Neurosciences Centre, All India Institute of Medical Sciences, New Delhi - 110 029
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0019-5049.72653

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How to cite this article:
Dube SK, Bharati SJ, Prabhakar H. An unusual cause of altered airway pressure during surgery under general anaesthesia. Indian J Anaesth 2010;54:576

How to cite this URL:
Dube SK, Bharati SJ, Prabhakar H. An unusual cause of altered airway pressure during surgery under general anaesthesia. Indian J Anaesth [serial online] 2010 [cited 2020 Oct 25];54:576. Available from: https://www.ijaweb.org/text.asp?2010/54/6/576/72653

Sir,

A 17-year-old male, weighing 50 kg, of American Society of Anesthesiologists physical grade I, was scheduled for exploration and repair of right pan-brachial plexus injury under general anaesthesia (GA). Inside the operation theatre, we connected routine monitors to the patient. GA was induced with propofol 100 mg and fentanyl 100 mcg. Patient's airway was secured with a size 3 proseal Laryngeal Mask Airway (LMA). Anaesthesia was maintained with infusion of propofol 100 mcg/kg/min and fentanyl 1 mcg/kg/hr using a single intravenous cannula of 18G on the dorsum of left hand, along with nitrous oxide in oxygen (2:1 ratio). As the surgery needed intraoperative use of nerve stimulator, use of muscle relaxant was avoided. Mechanical ventilation was adjusted to maintain an end-tidal carbon dioxide (EtCO 2 ) of 35-37 mmHg. After 50 minutes of stable proceeding, we noticed a sudden drop in maximum and mean airway pressure along with a ventilator alarm of "high drive gas pressure" [Figure 1]a, but the EtCO 2 reading remained unaltered. We tried looking for any leak or obstruction in the breathing system, inadequate fresh gas flow, displaced LMA, the position of the bag/ventilator selector valve, proper connections and functioning of the ventilator. When all possibilities were ruled out, we noticed that the breathing tubes were squeezed by the patient's hand [Figure 1]b. Immediately, a bolus of 40 mg of propofol was administered. The patient's grip over the breathing tube loosened and the airway pressures returned to normal. Our search for the cause revealed that there was an obstruction in the extension line of the propofol and fentanyl infusion was blocked. At the same time, the infusion pump failed to give alarm. The obstruction was cleared and rest of the surgery went uneventful.
Figure 1: (a) Altered airway pressure alarms (b) Squeezed breathing tubes in the patient's hand

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High or low airway pressure conditions in the breathing system have been a major cause of anaesthesia related mortality and morbidity. [1] Conditions that can cause low airway pressure alarm include: a disconnection or major leak in the breathing system; inadequate fresh gas flow; leaking tracheal tube cuff; extubation; the bag/ventilator selector valve in bag position; faulty or unconnected ventilator; gas or power supply failure to the ventilator or obstruction upstream to the pressure sensor. [2] In our situation, EtCO 2 reading was unaltered in spite of altered airway pressure In the presence of dangerously abnormal airway pressures the exhaled carbon dioxide may remain relatively normal. [1] The airway pressure alarms detect the high or low air way pressure conditions in the breathing system. In our case, because of the airway pressure alarm, the obstruction of the propofol and fentanyl infusion was timely detected and subsequent events of inadequate anaesthetic depth could be avoided. We suggest a careful observation of airway pressure alarms in the intraoperative period where we avoid the use of muscle relaxants.

 
   References Top

1.Dorsch JA, Dorsch SE. Airway volumes, flows and pressures. Understanding Anesthesia Equipment. In: Dorsch JA, Dorsch SE, Editors. 5th ed. Philadelphia: Lippincott Williams and Wilkins; 2008. p. 741.  Back to cited text no. 1
    
2.Raphael DT, Weller RS, Coran DJ. A response algorithm for the low pressure alarm condition. Anesth Analg 1988;67:876-83.  Back to cited text no. 2
    


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