In an observational cohort study, Gajic et al. reported that of patients ventilated for 2 days or longer who did not have ALI/ARDS at the onset of mechanical ventilation, 25 % developed ALI/ARDS within 5 days of mechanical ventilation [8]. In a multivariate analysis, the major risk factors associated with the development of lung injury were the use of a large Vt and transfusion of blood products. Interestingly, female patients were ventilated with larger Vt (per predicted body weight) and tended to develop lung injury more often. Women are generally shorter than men … this may have accounted for this finding. Similarly, in a large prospective observational study, a large Vt and high peak airway pressure were independently associated with development of ARDS in patients who did not have ARDS at the onset of mechanical ventilation [9].

The strongest evidence for the benefit of protective lung ventilation in patients without ALI/ARDS comes from two randomized studies in surgical patients. Intubated mechanically ventilated patients in the surgical ICU randomly assigned to mechanical ventilation with Vt of 12 mL/kg or lower Vt of 6 mL/kg [10]. The incidence of pulmonary infection tended to be lower, and duration of intubation and duration of ICU stay tended to be shorter for non-neurosurgical and non-cardiac surgical patients randomly assigned to the lower VT strategy. Futier and colleagues randomized 400 adults undergoing major abdominal surgery to an intraoperative ventilatory strategy of either 8–10 or 6–8 mL/kg [11]. The primary outcome was a composite of major pulmonary and extrapulmonary complications occurring within the first 7 days after surgery. The mean duration of ventilation was 5.7 h. In the intention-to-treat analysis, the primary outcome occurred 10.5 % assigned to lung-protective ventilation, as compared with 27.5 % assigned to non-protective ventilation (RR 0.40; CI 0.24–0.68; P = 0.001). This remarkable study demonstrates that even short periods of a non-lung protective ventilatory strategy are harmful.

Current nomenclature related to mechanical ventilation are outdated and confusing. For example, the eighth edition of Mosby’s Respiratory Care Equipment lists 56 unique names for ventilator mode labels [12]. However, when analyzing the targeting schemes (the feedback control system the ventilator uses to deliver a specific ventilatory pattern) in detail, only about two dozen of these modes are “unique” and identifiable using six basic targeting schemes.

The intensivist should be familiar with a number of modes of ventilation all of which have specific indications. Standard ventilator terminology and variables are listed in Table 19.1 while initial (default) ventilator settings are listed in Table 19.2. Ventilator phase variables are illustrated in Fig. 19.1. Volume Controlled Continuous Mandatory Ventilation (VC-CMV), also termed “Assist/Control Ventilation” is the most common mode of mechanical ventilation in the ICU and can be considered a “default mode” (see Fig. 19.2). Pressure Controlled Continuous Mandatory Ventilation (PC-CMV), also termed “Pressure Control Ventilation”, is equally considered as a default/standard mode in ICUs that have a highly involved Respiratory Therapy Driven Protocol in which the exhaled V_T is closely monitored (Fig. 19.2). Continuous Spontaneous Ventilation (CSV), also termed Pressure Support Ventilation (PSV) or Continuous Positive Airway Pressure (CPAP) is considered a Level 1 Evidence Based recommendations for ventilator liberation (weaning) and is commonly used in ventilator dependent patients with chronic respiratory failure (Fig. 19.3) [13]. Because the word “assist” describes the elevation of airway pressure above baseline during inspiration, PSV breath types are assisted, whereas CPAP breaths are unassisted.

These setting should then be dynamically adjusted according to:

Volume Controlled Intermittent Mandatory Ventilation (VC-IMV) otherwise known as, “IMV” or “SIMV” has a limited role; mainly in patients with asthma and those with unresolved respiratory alkalosis. It is the only mode of ventilation not recommended for the ventilator liberation process [13] (Fig. 19.4). Due to the ability of all ventilators to be patient triggered, it is no longer necessary to add the letter “S” to designate “synchronized” [14]. Pressure Controlled Continuous Mandatory Ventilation (PC-CMV) and Airway Pressure Release Ventilation (APRV) should be considered in patients with severe ARDS who have “failed” conventional low V_T ventilation in the VC-CMV mode. In some centers APRV is considered the default mode for ALI/ARDS as well as cardiogenic pulmonary edema [15]. APRV is a useful mode in patients with atelectasis and reduced chest wall compliance.