An 83 YO man is being treated in the ED. his wife, who brought him in, states, "he's so SOB and pale, I was worried." Oxygen by 28% air-entrainment mask is begun. The patient is given an IPPB treatment with albuterol. Despite continued therapy, the patient does not improve and continues to use accessory muscles to breathe. He is diaphoretic and pale and his temperature is 102 degrees F. The decision in made to begin NIV. A BIPAP unit is set up with initial pressures of IPAP = 6 and EPAP of -2. These are then adjusted based on pulse oximetry and the patient's RR. With an IPAP to EPAP ratio of 12 cm H2O to 4 cm H2O and a measured FiO2 of 0.3, the patient has a rate of25 bpm and an SpO2 of 87%. Vital signs, SpO2 and RR remain fairly stable. Two hours later the patient's RR has increased to 35 bpm. ABG's reveal Ph 7.21 pCO2 05 pO2 47 HCO3 40. Repeated adjustments to the IPAP:EPAP ratio fail to improve the patient's condition. The decision is made to intubate him and proide him with volume-targeted ventilation. The patient is 5'8" and weighs 148 lbs (IBW = 70 kg). BSA = 1.78 m2. The SIMV mode is selected. What initial Vt, VE and f would your select? After initiating ventilation, the following paramaters are noted: PIP 33 cm H2O Pplat 25 cm H2O Pta = 33-15 = 8 cm H2O. The patient is spontaneously breathing an additional 10 bpm with a Vt of 200 ml. The decision is made to add pressure support for the spontaneous breaths to overcome the WOB imposed by the artificial airway. What is an estimate resistance on this patient, assuming a constant flow of 80 lpm is used for calculation? Where would you set pressure support?
A number of solutions are possible for this problem. The following answer is provided as one option. Initial Vt is selected at 6 ml/kg (420 ml). Because this patient has a hx of COPD, a lower Vt was selected to reduce the risk of lung injury. VE is set at 8 lpm: 4 x BSA = 4 x 1.78 = 7.12 lpm, Increase VE by 5% oer degree F. Increase by 1.05 lpm to a total VE of 8.2 lpm. Rate is set at 19 bpm (VE/Vt = f) Flow is set at 80 lpm using the descending flow pattern. FiO2 is set at 0.5 initially. (NoteL because this patient is breathing spontaneously, a lower g and VE could be used, depending on the clinician's preference. The FiO2 could be lower, as well. The setting selected here would provide a minimum safe initial form of ventilation and could be adjusted based on patient assessment. Resistance is estimated at Pta/Flow or 8cm H2o/80 lpm = 8cm H2o/1.33 lps = 6 cm H2o.L/sec. The answer is only an estimate because the flow is not constant. Pressure support is set at 6 cm H2O.