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Table of Contents
LETTER TO EDITOR  
Year : 2014  |  Volume : 17  |  Issue : 3  |  Page : 255-257
Positive end-expiratory pressure valve malfunctioning detected by capnography and airway pressure waveform


Department of Anesthesiology, Critical Care and Pain, Tata Memorial Hospital, Mumbai, Maharashtra, India

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Date of Web Publication3-Jul-2014
 

How to cite this article:
Solanki SL, Doctor JR, Patil VP, Rana M. Positive end-expiratory pressure valve malfunctioning detected by capnography and airway pressure waveform. Ann Card Anaesth 2014;17:255-7

How to cite this URL:
Solanki SL, Doctor JR, Patil VP, Rana M. Positive end-expiratory pressure valve malfunctioning detected by capnography and airway pressure waveform. Ann Card Anaesth [serial online] 2014 [cited 2019 Dec 9];17:255-7. Available from: http://www.annals.in/text.asp?2014/17/3/255/135896


The Editor ,

A 30-year-old woman weighing 50 kg (ASA I) underwent left simple mastectomy with deep inferior epigastric perforator flap surgery for carcinoma breast. Anesthesia was maintained with isoflurane in oxygen and air. Monitoring included ASA standard monitors. Mechanical ventilation started in volume control mode using Drδger Fabius GS anesthesia workstation with a tidal volume (TV) of 390 ml, respiratory rate (RR) of 12/min and positive end-expiratory pressure (PEEP) of 5 cm H 2 O; peak and mean airway pressures (Paw) were monitored on ventilator. Approximately 1 h after the start of anesthesia, a sudden change in end tidal CO 2 (etCO 2 ) waveform was noticed; the capnograph alternately showed a normal waveform followed by a very small truncated capnograph [Figure 1]a. Concomitantly, Paw waveform showed failure of expiration for every alternate breath [Figure 1]b, expired TV showed double than set TV (709 vs. 390) and the RR showed half of the set RR (6 vs. 12) [Figure 1]c. Initiation of manual ventilation did not suggest excessively high resistance. Resumption of controlled mechanical ventilation showed a return of same waveform on capnography. Possible causes of distortion of etCO 2 waveform such as tracheal tube kinking, airway secretions and bronchospasm were ruled out. Patient circuit and expiratory valve was checked for proper functioning. Suspecting PEEP valve malfunction, PEEP was changed to 0 from 5. Immediately, etCO 2 and Paw waveform normalized for the set parameters [Figure 1]d. PEEP was set again to five and same capnography waveform returned confirming PEEP valve malfunction. On opening the PEEP valve, it was found to be full of moisture; and after changing the PEEP valve, etCO 2 and Paw waveform and TV became equal to the set values [Figure 2].
Figure 1: (a) Abnormal capnographic waveform shows alternate normal and abnormal wave. (b) Alternate normal and abnormal peak and mean airway pressures (Paw) waveform for set positive end-expiratory pressure (PEEP). (c) Abnormally high delivered tidal volume and half of the respiratory rate for set parameter. (d) Normal Paw waveform after PEEP was set to zero

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Figure 2: (a) Normal capnography waveform after changing of positive endexpiratory pressure valve. (b) Normal peak and mean airway pressures waveform. (c) Normal set and delivered parameters

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Positive end-expiratory pressure valves are unidirectional or bi-directional flow valves and both the PEEP valves generate PEEP only when gas flows in the correct direction. Incorrectly orienting a unidirectional flow PEEP valve against the flow of gas in the expiratory limb will occlude gas flow and thus prevent adequate expiratory flow and cause inadvertent increase in airway pressure. [1] Most modern anesthesia ventilators have integrated PEEP valves, so there is less chance of misplacement of PEEP valves, which may occur if external PEEP valves are used. [2] PEEP valves may be magnetic one-way valves, spring loaded valves or electronic valves. Magnetic and spring loaded valves create PEEP by the force exerted on the valve disc by magnet or spring whereas electronic valves create PEEP by a pressure threshold by pneumatic pressurization of the expiratory valve, that allow expiratory flow to occur only when airway pressure equals or exceeds the selected PEEP. [3] In Drδger workstation, the set end expiratory pressure is transmitted to a silicon diaphragm through a pilot tube which seals against the metal rim of expiratory gas opening and when the pressure in the patient circuit overcomes the set end expiratory pressure, this valve lifts-up and allows escape of expiratory gases. PEEP valve malfunction can occur due either to a manufacturing defect, damaged valve in case of poor maintenance or excessive moisture accumulation. Our workstation was installed 7 years ago, and had undergone servicing 7 months prior to the incident and was working satisfactorily. Therefore, we ruled out structural valve problem and considered excessive moisture accumulation as the cause of malfunction. The accumulation of moisture lead to increased adhesion of the diaphragm to the metal rim and thus the pressure needed to open the valve may be more than set PEEP. In Drδger Fabius GS anesthesia workstation PEEP valve is encased on top of the black breathing circuit manifold [Figure 3] and thus cannot be visualized without opening the screw fixed metal plate and moisture accumulation was unnoticed, which resulted in valve malfunction during expiration. During alternate breaths, the airway pressure increased substantially, which overcame this adhesion and allowed expiration manifested as a difference in peak pressure (16 cm H 2 O vs. 18 cm H 2 O) and plateau pressure (10 cm H 2 O vs. 16 cm H 2 O) in alternate respiratory cycles. The sources of moisture generation in the anesthesia circuit include chemical reaction of anesthesia gases with the CO 2 absorbent and contaminated medical gases. In case of faulty dryer control system water content of compressed gases can exceed the safe limit and may lead to condensation; therefore, regular checking of compressed gases should be carried out. Most modern anesthesia workstations now provide internal heating of the manifold to prevent condensation of water in circuit. The moisture generation is more pronounced during low-flow anesthesia. Addition of extra heat and moisture exchange filter in expiratory limb may also help to trap moisture.
Figure 3: Top view of manifold shows positive end-expiratory pressure valve

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Consequences of PEEP valve malfunction can be serious. For patients with cardiac dysfunction or with sudden major blood loss, creation of auto-PEEP due to malfunction of PEEP valve may lead to serious hemodynamic compromise. Furthermore, inadvertent delivery of high TV may put the patient at risk of pneumothorax especially in patients with emphysematous bullae. In conclusion, one should be vigilant during the conduct of anesthesia and interpret each waveform and numbers displayed on monitor wisely thus improving patient safety.

 
   References Top

1.PEEP valves in anesthesia circuits. Health Devices 1983;13:24. Available from: http://www.mdsr.ecri.org. [Last accessed on 2013 May 05].  Back to cited text no. 1
    
2.Eisenkraft JB. Problems with anesthesia gas delivery systems. In: Schwartz AJ, Matjasko MJ, Gross JB, editors. ASA Refresher Courses in Anesthesiology. Vol. 33. Philadelphia: Lippincott, Williams and Wilkins; 2005.  Back to cited text no. 2
    
3.Sulemanji D, Kacmarek RM. Jiang Y. Manual and mechanical ventilators. In: Sandberg W, Urman R, Ehrenfeld E, editors. MGH Textbook of Anesthetic Equipments. 1 st ed. Philadelphia: Elsevier Saunders; 2011.  Back to cited text no. 3
    

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Correspondence Address:
Sohan Lal Solanki
Department of Anesthesiology, Critical Care and Pain, 2nd Floor, Main Building, Tata Memorial Hospital, Mumbai - 400 012, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-9784.135896

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  [Figure 1], [Figure 2], [Figure 3]



 

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