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Once the mode of ventilation is selected, EMS clinicians will need to set several variables. In AC and SIMV modes, tidal volume, respiratory rate, and PEEP are all determined by the clinician. Tidal volumes are normally chosen to be 6–10 mL/kg of ideal body weight based on patient height. Tidal volumes of 6–8 mL/kg are preferred for patients with acute respiratory distress syndrome, whereas 8–10 ml/kg may be better for other conditions such as trauma and COPD [11]. Respiratory rate should be adjusted based upon the patient’s clinical situation, with low tidal volume strategies usually associated with higher rates. Higher than standard minute ventilation should be assured in patients who are dependent upon respiratory compensation of a metabolic acidosis.

PEEP may also be applied to improve oxygenation via mechanisms similar to NIPPV, discussed above, and is often initially set at 5–10 cm H₂O. For patients with obstructive physiology (e.g., asthma and COPD), care should be taken to maximize expiratory time to avoid incomplete expiration and breath stacking, which can lead to increased airway pressures. If air trapping is suspected, excess pressure can be alleviated by disconnecting the endotracheal tube from the ventilator for a few seconds and compressing the patient’s chest.

Peak inspiratory pressure (PIP) represents the maximum pressure developed during the inspiratory phase. Changes in PIP are a common source of ventilator alarms. Low PIP usually indicates a leak in the ventilator circuit. High PIP may represent either an increase in airway resistance (e.g., blocked tube, bronchospasm, secretions) or a decrease in lung compliance (e.g., pulmonary edema, atelectasis, pneumothorax, pleural effusion, hyperinflation). These two states can be distinguished by performing an inspiratory hold test to measure a plateau pressure. This test is performed by pressing the hold button on the ventilator for approximately 5 seconds during inspiration without allowing the patient to exhale. This effectively eliminates the airway resistance from the measured pressure and allows independent assessment of pressure being developed in the lungs with a given tidal volume. This is equivalent to a measurement of lung compliance. If the plateau pressure rises along with PEEP, clinicians should look for correctable causes of decreased lung compliance.