A hemodynamically unstable patient being ventilated in the volume-controlled continuous man-datory ventilation (VC-CMV) mode is triggering inspiration at a rate of 25 breaths/min and has the following arterial blood gas results:

Question

pH 7.50, partial pressure of carbon dioxide (PaCO2) 30 mm Hg, partial pressure of oxygen (PaO2) 98 mm Hg, arterial oxygen saturation (SaO2) 100%, bicarbonate (HCO3?) 24 mEq/L. The respira-tory therapist should perform which of the following?
a. Extubate and administer noninvasive posi-tive pressure ventilation (NIV).
b. Change the mode to pressure-controlled continuous mandatory ventilation (PC-CMV).
c. Change the mode to volume-controlled intermittent mandatory ventilation (VC-IMV).
d. Sedate and paralyze the patient.

Answer 1

ANS: C
This patient has ventilator-induced hyperventilation as evidenced by the partial pressure of car-bon dioxide (PaCO2) of 30 mm Hg with a trigger rate of 25 breaths/min. Switching to the vol-ume-controlled intermittent mandatory ventilation (VC-IMV) mode will decrease the number of ventilator breaths the patient triggers by allowing the patient to breathe spontaneously between the mandatory ventilator breaths. This will reduce the patient's minute ventilation and normalize the PaCO2 and pH. Another potential advantage is to put less of a strain on an already hemody-namically unstable patient. There is nothing in this patient's scenario that suggests extubation and use of noninvasive positive pressure ventilation (NIV). Switching to the pressure-controlled con-tinuous mandatory ventilation (PC-CMV) mode will most likely not correct the patient's problem because the patient will still be able to trigger ventilator set breaths and could continue to hyper-ventilate. Although sedating and medically paralyzing the patient could normalize the patient's acid-base balance, it is not the treatment of choice because of the hemodynamic instability of the patient.