NMS. Surgery

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Part I ♦ Foundations c. PS: This mode pressurizes the ventilator circuit to a preset level when the patient initiates a breath and maintains that level until the patient stops inhaling. (1) Inspired tidal volume: Determined by the amount of PS and the patient’s intrinsic work of breathing capacity. (2) Increasing PS reduces the work of breathing for the same tidal volume. (3) PS facilitates weaning from the ventilator. (4) Usual starting point: 5–10 mm Hg above the baseline pressure (continuous positive airway pressure [CPAP]/PEEP) and can be used alone or in combination with SIMV. d. CPAP and PEEP: These result in the ventilator circuit being pressurized to a specified level above atmospheric at all times, during inspiration and expiration. (1) This primary means of increasing oxygenation increases mean airway pressure and the number of inflated alveoli, which increases lung surface area available for gas exchange and decreases intrapulmonary shunt. (2) Usually, CPAP/PEEP of 5 mm Hg above atmospheric pressure is used and is increased as necessary to improve oxygenation. (3) Because these modes increase intrathoracic pressure at higher levels, they can decrease venous return to the heart and therefore cardiac output. (4) PEEP is used with SIMV and AC, whereas CPAP is used with PS. 4. Rate: After mode, the next parameter to set is rate (10–12 bpm). a. Higher rates may be necessary to decrease the Pco 2 if higher minute ventilation or lower tidal volumes are required. b. No rate is needed for PS. 5. Tidal volume: Normal tidal volume is 5 mL/kg, but ventilated patients are usually set at 6–8 mL/kg. a. Higher volumes overcome dead space and to ensure alveolar filling. b. With decreasing lung compliance (e.g., with ARDS), smaller tidal volumes of 4–6 mL/kg have been shown to reduce mortality. c. Occasionally, permissive hypercapnia is beneficial to avoid barotrauma. 6. Routine ventilator support starting point a. Mode: SIMV; however, if no work of breathing is desired, use the AC mode. b. Rate: 10–12 bpm. c. Tidal volume: 6–8 mL/kg (4–6 mL/kg if the patient has acute lung injury [ALI] or ARDS). d. PS: 5–10 mm Hg (not used in AC/VC). e. PEEP/CPAP: 5–10 mm Hg. f. Fio 2 : 0.4. g. Modify settings for the patient’s condition