A 45-year-old man with no significant past medical history presents to the intensive care unit (ICU) status post motor vehicle collision. Upon presentation to the emergency department (ED), he was endotracheally intubated for airway protection, with a Glasgow Coma Scale (GCS) score of 7 (eye 1, verbal 2, motor 4). Intubation was accomplished without any incidence of hypotension or hypoxia; however, the patient was actively vomiting at presentation and vomitus was noted at his vocal cords during direct laryngoscopy. His trauma workup included computed tomography (CT) scans of the head, cervical spine, chest, abdomen, and pelvis, as well as a chest radiograph. Bifrontal contusions and suspected diffuse axonal injury (DAI) were demonstrated on CT. No other injuries were discovered. He presents to your ICU early in the night with the following settings on the mechanical ventilator: assist-control/volume-targeted mode (AC/VC), tidal volume of 650 mL, positive end-expiratory pressure (PEEP) of 5 cm H2O, respiratory rate of 14, and a fraction of inspired oxygen (Fio2) of 0.50. On these settings, you note that his peak inspiratory pressure is 29 cm H2O and his inspiratory plateau pressure is 25 cm H2O. The patient's vital signs are as follows: heart rate 115 bpm, blood pressure 120/80 mm Hg, respiratory rate 14 breaths/min, oxygen saturation 92%, and temperature 37.5°C (99.5°F). Also, as you review the graphics package on the ventilator, you note smooth waveforms, with no evidence of intrinsic PEEP or dyssynchrony. As you receive the report from the emergency medicine physician, you note the concerns for aspiration and you review his chest radiograph and chest CT, which both suggest aspiration to the bilateral lower lobes. You are happy with his current status, but you wonder how his head injury and potential lung injury will progress. As you settle in for an interesting call night, you notice that his inspiratory plateau pressure is now 35 cm H2O and his Fio2 is 0.80.
General overview of mechanical ventilation
Regardless of the indication for endotracheal intubation and initiation of mechanical ventilation, a mechanical ventilator, in and of itself, does not treat much. However, it does have great potential for harm. Effective mechanical ventilation should prioritize limitation of ventilator-induced lung injury (VILI) almost as much as oxygenation and maintenance of normal carbon dioxide levels should take less priority in the majority of patients.1 Keen knowledge of basic and advanced principles will allow the clinician to use the mechanical ventilator for its maximum therapeutic potential and minimize iatrogenic injury while the process that led to respiratory failure is allowed to heal. It cannot be stressed enough that knowledge of cardiopulmonary physiology, heart-lung interactions, and the effects of mechanical ventilator settings on cerebral oxygenation and blood flow will allow the clinician flexibility when titrating support to an individual patient at the bedside. While the clinician should be intimately familiar ...