The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts


Paul Luehrs RRT, BSRT, BSEd, John Wolfe MD CoxHealth, Springfield MO

Introduction:  Obesity is an independent risk factor for intensive care unit death and should be regarded as a severe comorbidity in such units.(1)  Lung protective ventilation strategies should be implemented in this patient population.  The use of Bi-Vent (APRVT), for the management of morbidly obese respiratory failure patients whose failure is not the result of ALI/ARDS, has not been widely reported.  The Bi-Vent mode is available on the Servoi.  The mode is most commonly associated with those patients suffering from ALI/ARDS who require lung recruitment and alveolar stabilization provided by an increased mean airway pressure (MAP).  Bi-Vent allows the clinician to inverse the I:E ratio while preserving the patient's ability to spontaneously breathe throughout the ventilatory cycle, improving patient-ventilator synchrony and promoting lung recruitment. 

Case Summary:  On 3/09/06 a 46-year-old male patient weighing 500 lbs. presented to the ED orally intubated with an 8.0 ET receiving bag ventilation with FiO2 1.0.  On admission the patient's WBC count was 15.5, the sputum was positive for staphylococcus aureus, liver enzymes were elevated, echocardiogram showed a normal LVEF, cardiomegaly and severe pulmonary hypertension.  With cardiomegally, pulmonary hypertension and a normal LVEF an elevated BNP (b-type natriuretic peptide) of 547, is compatible with right heart failure.  The initial chest x-ray showed gross obesity and bilateral 'white out' with evidence of cardiomegally. The patient was placed on the Servoi ventilator at 1410 on PC 20 cmH2O, PEEP 15 cmH2O, f 15, FiO2 1.0.  The first ABG at 1425 revealed pH 7.06, PaCO2 106, PaO2 72, O2Hb 85%, COHb 5.1, P/F 72 on a MVe 5.2 l/m.  Over the next 104 minutes the patient was placed in Bi-Vent mode 3 times resulting in dramatic hypotension.  At 1745 the patient was successfully changed to Bi-Vent, without dramatic hypotension, on PHigh of 35 cmH2O, THigh 3.4 s, TPEEP 0.4 s, f 16, with a PEEPtot. measured at 23 cmH2O, MAP 34 cmH2O.   At 1817 the ABG showed an improving respiratory acidosis and a P/F ratio of 73.  On 3/10/06 at 0540 the patient's ABG showed a pH 7.47, PaCO2 45, PaO2 265 and P/F 279 on Bi-Vent: PHigh 33 cmH2O, THigh 4.1 s, TPEEP 0.3 s, PEEP 0, f 14, MVe 7.8 l/m.  Over the following 10 days the patient was maintained in Bi-Vent mode in order to maintain alveolar patency with high MAPs in the context of a large abdominal compartment.  On day 11 the patient was changed to PS 10 cmH2O, PEEP 20 cmH2O and eventually transitioned over to unassisted ventilation with flow-by to the tracheostomy on day 33.  On day 40 the patient was discharged to home with 2 l/m oxygen.

Discussion:  This patient suffered from acute decompensation of CHF and fluid overload as evidenced by the ED admission BNP of 547.  As a consequence of his BMI his respiratory and ventilatory status declined.  The patient was placed on a bariatric bed enabling the caregivers to inflate portions of the bed for skin maintenance. The extremely obese abdomen put pressure on the chest while in the recumbent or semi-recumbent position common to the intubated ICU patient.  This abdominal pressure increases the likelihood that the lower lungs may develop atelectasis.  Sedation and analgesics also increase the opportunity for alveolar collapse under the weight of the abdominal compartment.  We chose the mode Bi-Vent so the MAP could be increased while maintaining control of the Plp or PIP, which has been associated with less ventilator associated lung injury (VALI).  Extending the inspiratory time and limiting the expiratory time, to less than 0.5 s, maintains the patient in the inspiratory phase for the majority of their ventilatory cycle.  This leads to a sustained inflation and a higher MAP to combat the intruding abdomen.  The use of Bi-Vent in the morbidly obese patient should be studied as a means of reducing morbidity and mortality.

1.  Bercault, Nicolas Md et al.  Obesity-related excess mortality rate in an adult intensive care unit: A risk

     adjusted matched cohort study *.Critical Care Medicine. 32(4):998-1003, April 2004.