The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

AN UNUSUAL CASE OF RESPIRATORY ALKALOSIS

Jeffrey Brown, Christopher Hirsch, Kevin Crowley, Stephen Mette; Maine Medical Center, Portland, ME

Introduction Unexplained ventilator autocycling poses a challenge for the respiratory care practitioner Case Summary A 25 year old woman 5 days postpartum presented to our emergency department complaining of severe chest pain. Cardiac catheterization revealed acute left main coronary artery dissection. The patient was brought emergently to the operating suite for coronary artery bypass grafting and ultimately required nitric oxide, an Intra Aortic Balloon Pump (IABP) and a Thoratec IVAD® (Thoratec, Pleasonton, Ca.) Left Ventricular Assist Device (LVAD) for left ventricular support. Postoperatively the patient was brought to the cardiothoracic intensive care unit and placed on the Drager Evita XL® (Drager, Lubeck, Germany). Slight hyperventilation was requested for pulmonary vasodilation. Initial settings were CMV rate 16, 600 ml (9.4 ml/kg). The first postoperative ABG was 7.42/26/17/336. Over the next 24 hours a respiratory alkalosis with hyperchloremic (serum chloride 113-120 mEq/l) metabolic acidosis persisted. The patient received propofol 80 mg/hr. but continued to hyperventilate (mandatory rate 14, total rate 16-20, PaCO2 18-27). The patient was paralyzed with vecuronium bromide, confirmed with nerve stimulation. The ventilator rate was decreased from 14 to 8 sequentially. The total breath rate remained 16. Trigger sensitivity was minimized and ultimately turned off. Analysis of the flow/ time waveform continued to depict regular “spontaneous efforts” (60 ml). The mode was changed to SIMV, rate 8, PSV 5 cm H2O. Minute volume dropped from 9.6 to 6 lpm. ABG after 45 minutes was 7.33/33/17/160. The patient’s ABGs continued to improve and she was extubated the following day. Discussion No factors characteristically associated with ventilator autocycling (ETT cuff leak, inappropriate ventilator sensitivity, bronchopleural fistula, diaphragmatic pacing) were noted. Given that the LVAD is both a pump and a sump the possibility arises that intrathoracic pressure fluctuations could occur which may cause the ventilator to cycle. Although a literature search failed to reveal other instances of ventilator autocycling related to LVAD use, further study of factors contibuting to autocycling would be useful. Sponsored Research - None

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