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Mechanical ventilation has inherent risks, including infection, barotrauma, volutrauma, bronchopulmonary dysplasia, and lung injury.
Increased levels of supplemental oxygen during mechanical ventilation can result in retinopathy of prematurity and lung injury from excessive arterial oxygen levels.
The basic goals of mechanical ventilation are to improve oxygen delivery to meet metabolic demand and eliminate carbon dioxide, while reducing the work of breathing (WOB). The basic aim of assisted ventilation is to meet the goals while minimizing the associated deleterious effects.undefined#ref1">1
Modes of mechanical ventilation provide positive pressure ventilation (PPV) in an attempt to improve oxygenation and ventilation, prevent cardiovascular failure, manage intracranial pressure, protect the airways, and improve oxygen delivery to the tissues. PPV can be either pressure mode or volume mode.
Most conventional ventilators are equipped with graphics that enable the practitioner to understand how the lungs are responding to treatment. Changes in mechanical ventilation should be made in response to the patient’s status.
The respiratory therapist (RT) must use critical thinking skills around these key factors related to mechanical ventilation:
Additional facts about PPV include:
Although an appropriate PEEP level may result in clinical benefits, both inappropriately low and high levels may cause harm. An appropriate PEEP level may also be best achieved by an individualized approach, based on the patient’s disease process. PEEP should be set at the lowest level to achieve an acceptable level of PAO2 within a lung protective strategy. An open-lung model with a stepwise progression of PEEP to recruit atelectatic lung segments should be used in pediatric patients with restrictive lung disease (i.e., acute lung injury [ALI]) (Table 1).
Normal glottic closure at end-exhalation is prevented when an artificial airway is present; therefore, minimal PEEP (approximately 5 cm) maintains physiologic FRC, which is the amount of air left in the lungs at end-expiration.1
Common modes of ventilation:
It is important to understand how and when to make ventilator adjustments to improve oxygenation and ventilation (Figure 1). Patients with severe acute respiratory distress syndrome (ARDS) may require even lower VT (4 to 5 ml/kg). In addition, PIP, plateau pressure, or both should be maintained at less than 28 cm H2O and driving pressure at less than or equal to 15 cm H2O.1
Rationale: Pressure-controlled ventilation is selected when a ventilation strategy focused on maintaining an exact PIP-to-PEEP ratio is the goal.
Rationale: Parameters are based on previous ventilator settings and the RT’s assessment after reviewing ventilator graphics.
Rationale: The cycle mechanism determines the termination of inspiration with a preset inspiratory time, VT, or flow.
Rationale: The goal is to set the ventilator to deliver the target VT with the least amount of pressure, which may be preset or variable (with a high-pressure limit). The patient’s size and condition guide the I:E ratio.
Rationale: Alarm settings are based on the cycling mechanism chosen. Low-pressure alarms are used to detect disconnections in the system. High-pressure alarms are used for notification of increased pressure in the system.
In some cases, a spontaneous breathing trial may not be feasible because a reduction in sedation may result in the patient pulling the ET tube and IV lines, and unplanned extubation may occur.4
Rationale: Increased intrathoracic positive pressure may reduce venous return and cardiac output. Likewise, positive pressure may cause a pneumothorax, which may also decrease cardiac output.
Rationale: Asynchrony causes increased WOB and distress. Asynchrony in a small child is commonly associated with flow regulation; access to flow and speed of delivery influence the patient’s ability to breathe comfortably.
Rationale: Body temperature can be significantly altered by the temperature of inspired gas.
Make sure that the parameters being set meet the patient’s physiologic demands by allowing sufficient flow, FIO2, and PEEP without compromising hemodynamics and reducing the WOB.
Rationale: Early intervention when inadequate ventilator support and hemodynamic instability occur may prevent further clinical deterioration.
Rationale: Changes in lung compliance may change the PIP or VT.
Rationale: An alarm indicating an increased PIP or change in VT may be associated with a need for suctioning or an airway obstruction. A low-pressure alarm may indicate that the ventilator tubing has been disconnected.
Rationale: Suctioning the artificial airway maintains airway patency and removes secretions.
Rationale: Sedation and neuromuscular blockade may be necessary to achieve ventilator synchrony, but paralytics mask the patient’s underlying neurologic state. Daily sedation interruption improves outcomes and significantly reduces the duration of mechanical ventilation and intensive care.4
Klingenberg, C. and others. (2017). Volume-targeted versus pressure-limited ventilation in neonates. Cochrane Database of Systematic Reviews, 10, Art. No.: CD003666. doi:10.1002/14651858.CD003666.pub4
van der Staay, M. Chatburn, R.L. (2018). Advanced modes of mechanical ventilation and optimal targeting schemes. Intensive Care Medicine Experimental, 6(1), 30. doi:10.1186/s40635-018-0195-0
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