Never disable ventilator alarms.
Always plug a ventilator into a power outlet that is supplied by an emergency generator.
Positive pressure ventilation (PPV) through an artificial airway is used to maintain or improve oxygenation and ventilation. Respiratory insufficiency or failure, evidenced by apnea, hypoxia, hypercarbia, and increased work of breathing, are indications for mechanical ventilation. Selection of volume or pressure modes is dependent on the available evidence, clinical goals, availability of modes, and the practitioner's preference. There is very little evidence indicating that one mode of ventilation is more effective than another in terms of clinical outcomes (i.e., mortality) and ventilator hours needed.
Positive pressure modes of ventilation have traditionally been categorized into volume mode and pressure mode. However, with the advent of microprocessor technology, sophisticated iterations of traditional volume and pressure modes of ventilation have evolved. Ventilator manufacturers have created different names for the modes, and parameters that require adjustment vary somewhat among the ventilators. Although many of the modes have names that are different from traditional volume and pressure modes, they are similar in function in many cases. There is little evidence that the newer modes improve outcomes.
Summary descriptions of modes, mode parameters, and ventilator alarms are provided within this procedure (Table 1) (Table 2).
Volume-limited ventilation has traditionally been the most popular form of PPV, largely because tidal volume (VT) and minute ventilation (MV) are ensured. MV is defined as VT multiplied by respiratory rate. With volume ventilation, a predetermined VT is delivered with each breath, regardless of resistance and compliance. VT is stable from breath to breath but airway pressure may vary.
Several modes of volume-limited ventilation can be delivered. Those modes include controlled mechanical ventilation (CMV), assist-control (A/C) ventilation, and synchronized intermittent mandatory ventilation (SIMV).
Most ventilators have pressure-sensing mechanisms that trigger flow. This means that the patient must generate a decrease in the system pressure with an inspiratory effort. When the ventilator senses the drop in pressure, flow is delivered. If the ventilator has a flow-triggering option, the flow trigger is selected in L/min. The smaller the number of L/min selected, the more sensitive the ventilator capabilities. Flow triggering is set in conjunction with a base flow (flow in L/min that is provided between ventilator breaths). Flow rate is monitored in the expiratory limb of the ventilator. When flow is disrupted during a spontaneous breath, a decrease in flow downstream is sensed; additional flow is delivered.
Humidity is essential to prevent the drying effect of the gases provided by the ventilator. Inspired gases may be humidified with the use of standard cascade or high-volume humidifiers. Many organizations use disposable heat-moisture exchangers (HMEs) in place of conventional humidifiers because HMEs decrease the risk of infection and are inexpensive. HMEs prevent hypothermia, evaporation and thickening of secretions, atelectasis, and destruction of the epithelium in the airway.undefined#ref1">1 The use of HMEs has been associated with decreased incidence of ventilator-associated pneumonia (VAP) in ventilated patients.
Complications of PPV include pulmonary barotrauma, volume-pressure trauma, hemodynamic changes, and VAP.
Rationale: Mode selection varies depending on the clinical goal and the practitioner's preference.
Rationale: The use of IMV plus PSV has been associated with prolonged weaning times. If respiratory muscle rest is the goal of using IMV plus PSV, the level of PSV should be high enough to provide a V
T of 4 to 8 ml/kg and to maintain a total rate (IMV plus PSV breaths) of less than or equal to 20 breaths/min.
Do not attempt permissive hypercarbia in a patient with elevated intracranial pressure or a patient with myocardial ischemia, injury, or arrhythmias.
Rationale: The frequency rate selected depends on whether or not the clinical goal is to rest or work the respiratory muscles.
Rationale: Inspiratory flow refers to the speed with which a V
T is delivered during inspiration. Increasing the flow rate shortens the T
I. Conversely, slowing the flow rate lengthens the T
I. Adjusting the inspiratory flow achieves the desired I:E ratio and comfortable breathing patterns.
A short T
I and a longer expiratory time (T
E) may be necessary in a patient with an obstructive lung disease (e.g., emphysema, asthma). In contrast, a patient with a restrictive disease such as ARDS has noncompliant lungs; longer T
I enhances recruitment and prevents derecruitment in this patient.
Rationale: If the sensitivity is set too low, increased patient effort is necessary to initiate a ventilator breath. Dyssynchrony can result.
Rationale: Most patients in the acute care setting should be placed on 100% oxygen unless information is available identifying a precise F
4 High levels of F
2 result in increased risk of oxygen toxicity, absorption atelectasis, and reduction of surfactant synthesis. By initiating PPV with maximum oxygen concentration, hypoxemia can be avoided while optimal ventilator settings are being determined and evaluated. This also permits measurement of the percentage of venous admixture (shunt), which provides an estimate of the severity of the gas-exchange abnormality.
Rationale: A PEEP level of 5 cm H
2O is considered physiologic.
4 High levels of PEEP should rarely be interrupted because reestablishing FRC (and Pa
2) may take hours, especially in a patient with ARDS.
Rationale: Gases are generally humidified before entering the artificial airway.
In a patient with thick or tenacious secretions, pay attention to the inspired temperature to prevent mucus plugging. In this situation, circuit temperature may need to be closer to body temperature.
Rationale: The moisture in warmed, exhaled gases passes through the vast surface area of the HME and condenses. With inspiration, dry gases pass through the HME and become humidified.
Rationale: The longer the HME is inline, the more efficient the humidification; however, inspiratory resistance increases over time. In weaning patients, the additional resistive load added by these humidifiers may preclude their use.
Rationale: Secretions may cause obstruction; an HME is contraindicated when secretions are copious or bloody.
Rationale: There is a risk of thermal injury from overheated inspired gas and risk of poor humidity from underheated inspired gas.
Rationale: Condensation in the tube that is drained toward the patient may cause a respiratory infection if the patient inhales contaminated water droplets.
Rationale: Ventilation and oxygen may be needed immediately to relieve acute respiratory distress caused by hypoxemia or acidosis.
Rationale: Acute changes in PIP or V
T may indicate mechanical malfunction, such as tubing disconnection, cuff or connector leaks, tubing or airway kinks, or changes in resistance and compliance.
Always consider the possibility of a tension pneumothorax if the patient has a shift in the trachea, decreased breath sounds on one side, and increased peak pressures. If a tension pneumothorax occurs, perform a needle thoracotomy.
Rationale: An oral airway serves the same purpose as a bite block.
An oral airway may not be tolerated as well as the bite block because it may induce gagging.
Rationale: Continuous lateral rotation therapy may be helpful in improving oxygenation. Elevation is one of the most modifiable factors related to VAP.
Rationale: Dyssynchrony occurs when the patient's intrinsic breaths oppose or challenge the ventilator and may occur because of patient fatigue or restlessness.
Rationale: Hemodynamic changes may indicate functional changes in circulating volume caused by positive intrathoracic pressure.
Always consider the potential for pneumothorax with acute changes, such as a tracheal shift, decreased breath sounds, and increased PIP readings on the ventilator.
Gallagher, J.J. (2018). Alternative modes of mechanical ventilation. AACN Advanced Critical Care, 29(4), 396–404. doi:10.4037/aacnacc2018372
Weiss, C.H. and others. (2017). Summary for clinicians: Mechanical ventilation in adult patients with acute respiratory distress syndrome clinical practice guideline. Annals of the American Thoracic Society, 14(8), 1235–1238. doi:10.1513/AnnalsATS.201704-332CME
*In these skills, a "classic" reference is a widely cited, standard work of established excellence that significantly affects current practice and may also represent the foundational research for practice.
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