1995 OPEN FORUM Abstracts
RESPIRATORY ALKALOSIS CREATED BY HEART BEAT TRIGGERING OF THE VENTILATOR
Donna Wemhoff BS, RRT, CPFT; Corie Stewart-Hockley BS, RRT; Anthony Vacca DO - University of Missouri Hospital and Clinics, Columbia, Missouri
PATIENT DATA AND CASE SUMMARY: We present two cases of patients in which the pressures generated by their cardiac contractions were significant enough to trigger the ventilators, causing a respiratory alkalosis. Both patients were ventilated with a Siemens Servo 900C. Patient A was a 67 yr old with pneumonia and respiratory failure. Ventilator settings were VC, TV 700, RR 12, Fi02 .40, PeeP 5, sensitivity -1 CWP. Initial ABGs without patient assisting were 7.42/32/95. The next routine AM ABG reported 7.63/18/94 with ventilator being triggered at a rate of 16. The physician requested decreasing TV to 650cc. ABGs were then 7.52/27/109 with the ventilator still being triggered at 16. No apparent efforts were being generated by the patient, and closer observation noted deflection of the pressure manometer needle consistently with every heart beat, creating enough negative pressure to trigger the ventilator. Simultaneous recordings of ECG and airway pressure tracings were taken. This was accomplished by placing an adaptor into the ventilator circuit at the patient wye and connecting to it an air filled arterial line tubing with a transducer that was then connected to the ECG monitor. This allowed printed strips showing ventilator trigger consistent with cardiac contraction. To prevent the heart beat from triggering the ventilator, sensitivity was decreased to -2 CWP. ABG's returned to 7.42/35/107. Patient B was a 64 yr old male with SLE and a prolonged history of immunosuppression with corticosteroids resulting in PCP. This patient required paralysis to maintain optimal oxygenation on settings of PC 30, RR 20, Fi02 .85, Peep 10, sensitivity -2 CWP. Patient assisting the ventilator was noted. However, in the assessment for need of more neuromuscular blockade, it was detected that the heart beat was the triggering mechanism resulting in ABGs of 7.53/21/94. Simultaneous ECG and airway pressure tracings were recorded as described with patient A. The tracing below shows that with decreasing the sensitivity to -3 CWP, the heart beat triggering was eliminated and ABG's revealed 7.43/32/106.
SIGNIFICANCE- Literature survey revealed nothing as reported here regarding the heart beat's ability to create negative intrathoracic pressure significant enough to trigger a ventilator. When ruling out reasons that ventilated patients maintain a respiratory alkalosis (pain, agitation, anxiety, sepsis, etc,) heart beat triggering can be added to the list. We have subsequently seen further cases of this both with the 900C and the Bear 1000 ventilators.
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