An intubated patient with no known history of congestive heart failure is in the ICU

Question

The patient is comatose and currently receiving mechanical ventilation via volume-controlled continuous mandatory ventilation (VC-CMV), set rate 12 breaths/min, set tidal volume (VT) 400 mL, positive end-expiratory pressure (PEEP) 18 cm H2O, fractional inspired oxygen (FIO2) 0.35, and the patient is not assisting. Hemodynamic measurements show the following: central venous pressure (CVP) 5 mm Hg, pulmonary artery pressure (PAP) 33/20 mm Hg, and pulmonary artery occlusion pressure (PAOP) 16 mm Hg. Arterial blood gas (ABG) results are: pH 7.43, arterial partial pressure of carbon dioxide (PaCO2) 38 mm Hg, arterial partial pressure of oxygen (PaO2) 90 mm Hg. The physician asks for recommendations to improve this patient's hemodynamics. The most appropriate recommendation for this patient is which of the following?
a. Initiate pressure support ventilation (PSV) 10 cm H2O with CPAP 10 cm H2O, and check cardiac output.
b. Decrease the PEEP incrementally and re-check hemodynamic measurements.
c. Change to volume-controlled synchro-nized intermittent mandatory ventilation (VC-SIMV) with the same settings, and recheck hemodynamic measurements.
d. Change to pressure-controlled continuous mandatory ventilation (PC-CMV), peak inspiratory pressure (PIP) 25 cm H2O, PEEP 18 cm H2O, FIO2 0.35, and check PAP.

Answer 1

ANS: B
The patient's central venous pressure (CVP) is within normal limits. The pulmonary artery pres-sure (PAP) and pulmonary artery occlusion pressure (PAOP) are both elevated. These hemody-namic results are consistent with left ventricular failure. However, when looking at the ventilator settings it should be noted that the set positive end-expiratory pressure (PEEP) is >15 cm H2O. This setting will prolong changes in lung zones and produce erroneously elevated pressure read-ings by squeezing the pulmonary vessels and overinflating the lungs. Changing the mode to pressure support ventilation (PSV) or synchronized intermittent mandatory ventilation (SIMV) will lower the mean inspiratory pressures and minimize the hemodynamic effects of positive in-trathoracic pressure. However, this patient is comatose so PSV is not an option (choice "A") and changing to volume-controlled synchronized intermittent mandatory ventilation (VC-SIMV) with the same PEEP level (choice "C") will have little effect on the hemodynamics. Pressure ventilation (choice "D") will have about the same effect on the patient's hemodynamic values as the current settings. Decreasing the PEEP incrementally and checking the hemodynamic meas-urements can be used to optimize the PEEP level for this patient.