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Paper text:
anesthesia machine check is an integral part of the anesthesiologist 's daily routine . in 1993 , a joint effort between the american society of anesthesiologists and the u.s .
food and drug administration ( fda ) produced the anesthesia apparatus checkout recommendations , which included both low and high pressure systems checks .
newer anesthesia machines offer an electronic and automatic self - testing capability and led some providers to believe that these advanced testing can partially or totally replace those outdated recommendations .
we recently experienced a case in which the expiratory bacterial filter was completely blocked by a plastic membrane .
the cause of machine failure could not be identified until a complete preanesthesia machine manual check was performed .
a 71-year - old woman with history of coronary artery disease , hypertension , and chronic obstructive pulmonary disease presented for a substernal hernia repair from her coronary bypass surgery .
this was the second case of the day and the drager fabius gs anesthesia machine was reported to have been checked by another provider right before the case started . a circle breathing circuit with inspiratory , expiratory limbs bacterial filters , and a heat and moisture exchanger ( vital signs , totowa , nj ) was attached to the ventilator .
after tracheal intubation , the patient was then placed on volume - controlled ventilation mode with tidal volume of 600 ml , rate of 10 , 3 cmh2o positive - end expiratory pressure , and 100% fraction of oxygen . almost immediately
, peak airway pressure was noted to rise to 65 cmh2o with the delivered tidal volume less than 300 ml .
direct laryngoscopy was performed and endotracheal tube ( ett ) position was confirmed by direct visualization .
mucus plug , severe bronchospasm , and tension pneumothorax were considered in the differential diagnosis .
when the circuit was disconnected from the ett for suction , a high pressure exhalation was noticed with immediate improvement of blood pressure to 90 mmhg .
we removed the circuit from the ett and manually ventilated the patient with an ambu bag and backup oxygen source .
the anesthesia circuit was suspected to be source of the problem and a new circuit was installed .
after the completion of the case , the circuit , all apparatus , and machine were examined closely and extensively to identify possible causes .
however , a plastic film was found in the expiratory bacterial filter on the machine end [ figure 1 ] .
it was assumed that this plastic film caused the inability to exhale and resulted in high peak airway pressures with inability to deliver adequate tidal volume .
a plastic membrane completely covered the fault bacterial filter to simulate our case scenario , we attached a breathing bag to the y - piece of same breathing circuit used in the case and initiated volume - controlled ventilation with preset tidal volume of 600 ml and rate of 12 with a fresh gas flow of 2 l / min .
the airway pressure increased continuously and reached a peak airway pressure of 50 cmh2o after 34 cycles .
since the film could be easily put on the inspiratory filter , we then attached the faulty filter into the inspiratory limb and repeated the same test .
the inspiratory airway pressure immediately reached 60 cmh2o with a low expiratory airway pressure and normal airway pressure cycling .
the anesthesia provider only performed leak test since it was the second case of the day .
after occluding the y - piece of the same circuit and flushing the oxygen valve , the pressure gauge did not decrease confirming that no leak was found and the system was fine .
we then attempted to determine whether a complete preanesthesia machine check could have correctly identified this problem .
self - tests of the same anesthesia machine , as recommended by drager with the faulty filter in either the expiratory or inspiratory limb , passed except during the leak test , which took longer than usual to perform and gave a warning ventilator fail afterward . using the fda recommendation , we performed the leak test by closing the pop - off valve , occluding the y - piece , and pressurizing the circuit to 30 cmh2o with the oxygen flush valve .
when the faulty filter was in the expiratory limb , the value on the pressure gauge continuously increased and the breathing bag on the bag mount kept increasing in size .
when the faulty filter was in the inspiratory limb , a pressure of 30 cmh2o could not be achieved by flushing the oxygen flush valve and the bag remained deflated .
three cases of bacterial filter blockage have been reported in the literature.[24 ] in all three cases , the obstruction occurred after the case had started normally . in our patient , the plastic film stayed in a fixed position immediately above the filter material during manufacture and caused complete occlusion of the expiratory limb filter .
many new anesthesia workstations now incorporate technology that allows the machine to either automatically or manually walk the user through a series of self - tests to check for functionality of the electronic , mechanical , and pneumatic components .
however , our case emphasizes the importance of manual checking the low and high pressure systems in all anesthesia workstations in addition to self - test .
a leak test should be performed by closing the pop - off valve , occluding the y - piece , and pressurizing the circuit to 30 cmh2o with the oxygen flush valve .
a flow test with a breathing bag attached at the y - piece should be evaluated by initiating the desired ventilation mode for the coming case .
backup ventilation equipments and familiarity with signs of expiratory and inspiratory limb obstruction should not be underestimated .
we describe a case where the expiratory bacterial filter was completely blocked by a plastic membrane . 
 significantly increased airway pressures and inability to deliver adequate tidal volume to the patient were experienced . 
 the cause of machine failure could not be identified until a complete preanesthesia machine manual check was performed . 
 all machines and circuits should be checked manually , even with the availability of new and advanced self - tests in machines . 
 backup ventilation equipments and familiarity with signs of expiratory and inspiratory limb obstruction should not be underestimated .