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Mechanical ventilation weaning: An evidence-based review

Hetland, Breanna, PhD, RN, CCRN-K; Heusinkvelt, Jennifer, BSN, RN; Krabbenhoft, Lisa, MSN, RN; Grotts, Erin, BSN, RN

doi: 10.1097/01.CCN.0000544397.74806.9a
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Abstract: Mechanical ventilation weaning remains a challenge in critical care nursing. Nurses can review the evidence-based guidelines provided in this article to gain a better understanding of common ventilator modes and settings, the weaning process, common complications, and symptom management. Five nursing-care recommendations for achieving optimal patient outcomes are also shared.

Mechanical ventilation weaning is an ongoing challenge in critical care nursing. This article reviews evidence-based guidelines on common ventilator modes and settings, the weaning process, complications, and symptom management.

Breanna Hetland is an assistant professor at the University of Nebraska Medical Center College of Nursing, Omaha, Neb.

Jennifer Heusinkvelt is a DNP student at the University of Nebraska Medical Center College of Nursing, Omaha, Neb.

Lisa Krabbenhoft is a PhD student at the University of Nebraska Medical Center College of Nursing, Omaha, Neb.

Erin Grotts is a clinical ICU nurse at Nebraska Medicine, the Fred & Pamela Buffett Cancer Center, Omaha, Neb.

The authors have disclosed no financial relationships related to this article.

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Mechanical ventilation (MV), an invasive respiratory support intervention, is necessary when a patient has difficulty breathing normally due to an inability to maintain a patent airway, adequate gas exchange, or both.1 It is estimated that over one million patients require MV each year at a combined annual cost of $27 billion.2,3 Patients who undergo this life-saving intervention may experience significant physiologic and psychological symptoms. Some patients only need ventilator support for a short time, but others may require weeks or months of MV.

Before a ventilator can be safely removed, the patient must first undergo ventilator weaning. Ventilator weaning is a gradual withdrawal of ventilator support that encourages a return to independent, spontaneous respirations. This process can occur in a single day or over several weeks to months.1,4 Ventilator weaning is one of the most challenging aspects of ICU care management; on average, 40% of a patient's time on a ventilator is spent undergoing ventilator weaning.5 Efforts to reduce the amount of time a patient spends on the ventilator, specifically during ventilator weaning, are critical to reduce the physical and financial burden of MV.

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This article describes the process of MV and ventilator weaning with an emphasis on current practice guidelines. An overview of ventilator modes, ventilator weaning, common complications, and the assessment and management of patient symptoms are provided. A discussion of nursing considerations in the context of clinical practice guidelines for sedation management and ventilator weaning is also given.

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MV: From intubation to extubation

MV may be necessary for a variety of medical conditions that cause respiratory failure or prevent a patient from maintaining a patent airway, such as surgery or neurologic compromise. Respiratory failure is characterized by inadequate gas exchange in the lungs and is clinically assessed by measuring specific parameters in arterial blood (pH less than 7.35, carbon dioxide concentration greater than 50 mm Hg, oxygen concentration less than 50 mm Hg).1 (See Causes of acute respiratory failure.) MV is often needed to treat acute respiratory failure because it supports adequate ventilation, provides oxygen delivery, restores acid–base balance, reduces overall work of breathing, and ultimately enables survival.1,4 Acute respiratory failure is typically classified into two main types—Type I (hypoxemic) and Type II (hypercapnic)—both of which cause hypoperfusion of the respiratory muscles.6-8

Nurses often are the first to recognize the initial signs and symptoms of acute respiratory failure, such as shortness of breath and tachypnea. If respiratory failure is not addressed, the patient's condition will worsen and any of the following may be observed: nasal flaring, use of accessory muscles, paradoxical abdominal movements, prolonged expiratory phase, expiratory grunting, cyanosis, decrease in the pulse oximetry oxygen saturation despite increasing the administration of supplemental oxygen, anxiety, diminished lung sounds, inability to speak in full sentences, tripod positioning to further expand the chest, feelings of impending doom, and altered mental status. Any of these signs may indicate the need for MV.8

Although MV is not curative, it can help support the patient until the initial cause of respiratory failure can be treated. For the ventilator to be applied, a patient must first be intubated, which involves the insertion of an artificial airway, an endotracheal tube, into the patient's mouth or nose; occasionally a patient may require surgical intervention to establish an advanced airway with a tracheostomy and placement of a tracheostomy tube. After an airway is established, MV is initiated to facilitate the delivery of oxygen to the tissues. Healthcare providers (physicians, NPs, critical care nurses, and respiratory therapists) work collaboratively to determine the appropriate type and amount of support the ventilator should provide to aid respiratory function while the underlying cause of respiratory distress is addressed.

The mechanical ventilator delivers air by pushing it through the artificial airway and into the lungs, subsequently creating positive intrathoracic pressure. Compliance refers to the lungs' ability to distend during inspiration to allow for the increase in pressure. Due to physiologic conditions such as inflammation, fibrotic changes, or edema, lungs become “stiff” and require more force to inflate. In addition, compliance is influenced by airway factors, including internal obstructions (tumor, mucus plug), external obstructions (kinked ventilator tubing), or decreased airway size. In addition, chest wall factors such as compression of the chest wall (distended abdomen, obesity) or patient position can also affect compliance. Decreased lung compliance leads to increased inspiratory pressure and can ultimately lead to significant lung damage secondary to barotrauma (too much pressure) or volutrauma (too much volume).1

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Common ventilator modes and settings

Ventilator modes. Most ventilators currently used in ICUs are classified as positive-pressure ventilators, and they allow providers to use a variety of modes and settings depending on the physiologic needs of the patient. Ventilators can be programmed to deliver a targeted volume, a constant pressure, or a combination of both with each breath. Most ventilator modes allow for spontaneous breathing, but vary in the level of control they give patients over their own breaths (see Ventilator mode advantages and disadvantages).1,4

Volume control ventilation is the most frequently used ventilation type in the ICU. The ventilator is programmed to deliver a preset volume of air and concentration of oxygen with each breath, regardless of the amount of pressure required to deliver the designated volume of air. The amount of pressure required to deliver the targeted volume is variable and depends on the patient's lung compliance. The patient's inspiratory pressure must be monitored closely in volume ventilators to avoid barotrauma. Several different volume modes are used, including assist-control and synchronized intermittent mandatory ventilation.1,4

Pressure control ventilation is being used more frequently in the ICU because of the reduced risk for causing acute lung injury, secondary to barotrauma. The ventilator delivers breaths at a specific pressure (rather than volume), which allows the amount of air brought into the lungs with each breath to vary based on the patient's needs. This means inspiration ends when a preset pressure is reached, regardless of the volume delivered, which ultimately reduces patient effort and improves overall comfort. It is important to monitor the amount of air exhaled with each breath to ensure the patient receives an adequate amount of oxygen. Common pressure modes include pressure support ventilation (PSV), pressure-controlled ventilation, and airway pressure release ventilation.1,4

Ventilator settings. Specific ventilator settings are based on the patient's underlying condition and reason for mechanical ventilatory support. These settings include tidal volume, positive end-expiratory pressure (PEEP), fraction of inspired oxygen (FiO2), and pressure support. Tidal volume is the amount of air delivered with each breath. The recommended tidal volume is approximately 5 to 8 mL/kg.1 PEEP is applied at the end of exhalation and is used to improve oxygenation. Optimal PEEP is achieved when the maximum amount of oxygen is delivered using the lowest amount of FiO2. FiO2 is the amount of oxygen the ventilator delivers to the patient. Room air has an FiO2 of 21%, whereas ventilators can be set to deliver an FiO2 of up to 100%. The amount of FiO2 varies dependent on the patient's condition and severity of hypoxemia. Pressure support is a small amount of preset pressure delivered during inspiration to assist the patient in spontaneous breathing. It can be used alone or added to other ventilator modes and is often used during weaning to help reduce the work of breathing.1,4

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Ventilator weaning

As soon as a patient is intubated, considerations to facilitate ventilator weaning are priority.1 After the cause of acute respiratory failure has been adequately addressed, the patient must be able to demonstrate the ability to breathe and maintain adequate oxygen exchange independent of the ventilator before they can be extubated. To determine readiness for extubation, patients must undergo a series of weaning trials, also called spontaneous breathing trials (SBTs), in which healthcare staff gradually adjust the ventilator modes and settings to require increased patient respiratory effort. A variety of methods can be used to initiate an SBT on the ventilator, including T-piece, continuous positive airway pressure (CPAP) trials, and gradual PSV reduction. SBTs can last anywhere from a few minutes to 2 hours. When the SBT is completed, the ventilator is placed back on its baseline settings. The healthcare team reevaluates the need for continued support based on the patient's performance. As a rule, SBTs should be attempted at least once per day. Some institutions have implemented specific weaning protocols, but generally the initiation and duration of SBTs as well as the specific methods and settings employed for weaning trials is patient-specific and at the discretion of the attending physician.1,4

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Extubation failure is characterized by the need for reintubation within 48 to 72 hours of extubation and occurs in up to 47% of patients on MV.9 Advanced age, prolonged MV, severity of illness, multiple organ dysfunction, and the use of continuous sedation are all risk factors for extubation failure. Reintubation is associated with prolonged hospital and ICU stays, increased rates of tracheostomy placements, and increased mortality. Due to the high economic and personal costs of prolonged weaning and extubation failure, it is imperative that the critical care nurse monitor factors such as patient discomfort, fatigue, sweating, work of breathing, mental status, and vital signs during weaning. In addition, measures such as these can be taken prior to the start of an SBT to encourage successful breathing:1,4

  • optimizing muscle strength by providing adequate nutrition, avoiding neuromuscular-blocking agents, decreasing corticosteroids, and normalizing electrolytes.
  • decreasing respiratory work by placing the patient in an upright position, decreasing respiratory demand and resistance, and increasing compliance.
  • optimizing ventilator drive by reducing or stopping sedative medications.
  • increasing oxygen-carrying capacity by avoiding factors that cause atelectasis, correcting anemia and acid–base imbalances.
  • addressing cardiac dysfunction and oxygen-carrying capacity.
  • promoting sputum clearance.
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Complications

Many complications can result from MV, so ventilator-associated events and conditions need to be assessed and monitored frequently. Complications associated with MV may be related to the artificial airway, the patient's response to MV, or the processes of intubation and extubation. Two of the most notable, preventable complications include pneumonia and self-extubation.10,11

Ventilator-associated pneumonia (VAP), one of the most common hospital-acquired infections in the ICU, can increase morbidity and mortality, length of stay, and hospital costs. VAP is diagnosed by the recognition of changes in respiratory assessments such as lung sounds, the amount and thickness of secretions, and alterations in laboratory tests and chest X-rays. The most effective way to prevent VAP is limiting the time patients spend on MV, when possible. Nurses can aid in reducing VAP-related complications by following the care bundles geared to risk reduction. A care bundle, such as the one listed below, provides a routine, coordinated series of interventions that, when performed together, can result in a better outcome than any one intervention alone.10

  • Head of bed elevation—Reduce aspiration of gastric content, thus reducing risks for infection.
  • Oral care with chlorhexidine—This oral antiseptic has been shown to reduce rates of acquiring VAP.
  • Sedation holidays and weaning protocols—Daily weaning trials and sedation holidays are strategies that limit the duration of MV.
  • Care provider education—VAP prevention education should be provided to all healthcare providers involved in the care of patients requiring MV.

Another common complication of MV is self-extubation, which occurs when a patient deliberately or accidently removes his or her own endotracheal tube. Studies have found that up to 22.5% of mechanically ventilated patients in the ICU will experience an unplanned self-extubation.11 A variety of risk factors are associated with self-extubation, including increased patient consciousness, changes in mental status (confusion), patient discomfort, inadequate sedation, and agitation (possibly due to the use of restraints). Self-extubation may negatively impact patient health and the process of weaning.12,13 Nurses should be cognizant of the risk factors that contribute to unplanned extubations to provide tailored care to mitigate these risks. To best manage agitation, nurses may use the Confusion Assessment Method-ICU (CAM-ICU) to detect delirium in its early stages.14 By recognizing the signs of delirium early, nurses can adjust sedative and analgesic medications as well as leverage other nonpharmacologic interventions to keep patients calm. Many unplanned self-extubations occur during the weaning process.11,13 Healthcare teams can ensure timely extubation by leveraging weaning protocols. Providing adequate staffing to properly monitor patients and reducing the use of restraints during ventilator weaning are also important.11,13 Previous studies have indicated that ICUs with fewer staff experience a higher number of unplanned self-extubations, and patients who self-extubate are physically restrained at the time of the incident.11,13 The risk of these events can be reduced by up to 51% by staffing one additional nurse per patient per day.11 Simply decreasing a nurse's workload alone could reduce the risk by 45%.11 Although restraints are widely thought to help prevent self-extubation incidents, research indicates that an increase in patient surveillance is the more effective intervention.11,13

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The patient experience

MV carries a tremendous physiologic and psychological symptom burden. Physical symptoms such as pain, thirst, dyspnea, and fatigue are frequently reported by patients receiving MV.15 In addition to severe physical discomfort, patients may also feel psychological symptoms like helplessness, isolation, and fear.15-17 Frequent suctioning causes gagging and coughing, which results in worsening physical and mental discomfort.11 Unfortunately, anxiety continues to be one of the most common, persistent, and debilitating symptoms caused by MV.15 Anxiety is exacerbated by fluctuating states of consciousness and the inability to effectively communicate needs. In addition, agitation and delirium are common in up to 80% of patients receiving MV and these symptoms are associated with adverse outcomes, including longer duration of MV and ICU lengths of stay as well as increased mortality.2,18

Obtaining accurate symptom assessment is difficult during MV due to patients' altered levels of consciousness, fluctuating severity of illness, and high doses of sedatives, analgesics, or neuromuscular-blocking agents. Although the use of patient self-report of symptoms is considered the “gold standard,” nurses may have to rely on proxy reports from the patient's caregiver or implement specific symptom assessment tools to accurately assess and describe patient symptoms.19,20

If patients are awake and alert, direct communication should be encouraged. It is imperative that nurses are responsive to the patient's communication efforts and respond clearly to the patient.21 There are various methods nurses can use to communicate with mechanically ventilated patients, such as using a letter board, word board, picture board, pain-rating scale, pen and paper, marker board, asking yes or no questions, and allowing the use of electronic devices. Effective communication allows nurses to reorient the patient. Reorientation can also be promoted through the return of hearing aids and eyeglasses and additional measures that allow patients to reestablish meaningful contact with their surroundings and with other people.21

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Pharmacologic and nonpharmacologic management techniques

The MV symptom experience is unique for each patient, which further complicates the task of symptom management for healthcare providers. In addition to a foundational understanding of the common symptoms experienced by mechanically ventilated patients, an in-depth knowledge of a variety of pharmacologic and nonpharmacologic management techniques is imperative to providing quality care during MV and ventilator weaning.15,16,19,22

Sedative and analgesic medications are often the first treatment option to reduce physical and psychological symptoms. Common sedatives include midazolam, propofol, and dexmedetomidine, and common analgesic medications include morphine, fentanyl, hydromorphone, and remifentanil.1 The overuse of these medications can be detrimental to patients in the ICU by causing adverse reactions such as respiratory depression and prolonged duration of MV, prolonged ICU and hospital lengths of stay, reduced survival, altered gut function, reduced ability for early mobility, increased risk of ICU-acquired muscle weakness, increased psychological stress, reduced interaction with family and environment, and increased cognitive dysfunction.23 Treatment goals should focus on keeping the patient calm and cooperative and using the smallest amount of sedation medication needed to maintain comfort.19

Nonpharmacologic treatment options have been shown to be effective at reducing the overall symptom burden during MV and should be considered as an adjunct to sedative and analgesic medications.22 For example, music can decrease the physiologic and psychological symptoms and reduce sedative exposure in mechanically ventilated patients.24 Physical presence of family, friends, and healthcare staff may positively benefit patients undergoing MV. Specifically, nurse presence during ventilator weaning elicits an emotional, caring connection with the patient, which can aide in decreasing the patients' anxiety.22 Animal-assisted therapy may also aid in reducing stress responses, decrease feelings of isolation, and improve mood.25 The use of imagery is a nonpharmacologic intervention that may enhance healing and relieve symptoms such as stress, fear, and anxiety.26,27 In addition, simple interventions such as oral swabs, water spray, and menthol moisturizers may be helpful in combatting dry mouth and thirst.28

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Nursing considerations

Critical care nurses are vital to ensuring patient safety and promoting overall comfort during MV and weaning from MV. Recently, the American Thoracic Society and the American College of Critical Care Medicine released clinical practice guidelines to help direct efforts to treat symptoms and liberate critically ill patients from MV safely and efficiently.19,29 From the moment of intubation, nurses are instrumental in adopting and applying these guidelines to ultimately drive positive patient outcomes.

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Recommendation #1: Minimize the use of sedatives and analgesics through continual symptom assessment. The amount of sedation and analgesic agents being delivered to the patient is an important consideration during MV and ventilator weaning. These medications may impede the ability to wean patients, so it is recommended that medication administration protocols are followed to minimize sedation in patients who will be mechanically ventilated for more than 24 hours. From the moment the patient is intubated and placed on MV, monitoring using reliable assessment tools for sedation level, pain, agitation, and delirium are the foundation for future weaning success (see Common ICU symptom assessment tools). Continuous monitoring ensures patients receive appropriate pain relief and that sedation is titrated to allow for responsiveness. When nurses assess and intervene appropriately, complications from oversedation, such as muscle atrophy, pneumonia, ventilator dependency, thromboembolic disease, nerve compression, and pressure injury, can be avoided.19,29

Specific recommendations for pain management include:19

  • using preemptive analgesia and/or nonpharmacologic interventions for an invasive and potentially painful procedure.
  • treating nonneuropathic pain for patients in the ICU with I.V. opioids as the first-line drug class of choice.
  • considering nonopioid analgesics to decrease the number of opioids administered and to decrease adverse reactions of opioids.

Prior to proceeding to specific interventions for agitation and delirium, it is important to first identify possible underlying causes, such as pain, confusion, hypoxemia, hypoglycemia, hypotension, or withdrawal from alcohol and drugs. Symptoms of agitation and delirium may be augmented by using both pharmacologic and nonpharmacologic treatments; however, nonpharmacologic approaches should be considered before the use of sedatives and/or antipsychotic agents. If sedation is needed, it is important to frequently monitor the depth of sedation and screen for the presence of delirium due the increased rates of mortality associated with its occurrence during MV. Nurses can help reduce the need for sedatives, analgesics, and antipsychotic medications as well as augment the negative outcomes associated with these medications by promoting normal sleep patterns, routine assessments, implementing frequent repositioning, and providing frequent reorientation.19,29

Recommendation #2: Implement daily wakefulness and early mobility initiatives. Encouraging a period of maximum patient wakefulness may reduce the risks of prolonged deep sedation, provide beneficial effects of higher peak stimulations, and allow patients to engage in physical and cognitive activities.30 Daily spontaneous awakening trials (SATs) should be completed prior to initiating SBTs.19 However, the most ideal timing and duration of SATs and SBTs remains unknown. The benefits of performing them on night shift include workload-related issues such as less “off unit” time performing tests and other procedures (MRIs, computed tomographies, scopes), distractions, and tasks, but performing SATs and SBTs during the night shift may interfere with sleep patterns and wakefulness of the patient.30,31 Alternatively, performing them during the day shift allows providers to be present to directly observe patients' readiness to extubate. Day shift offers more staff members to provide assistance, but the challenge of task management and care coordination can take away from nurses' ability to properly supervise the patient during SATs and SBTs.30,31 Ultimately, collaboration among nurses, respiratory therapists, physicians, and other therapeutic providers (dietitians and physical, occupational, or speech therapists) is critical to ensure the most appropriate timing for SATs and SBTs and to coordinate care that promotes patient success. In addition to SATs and SBTs, implementation of early mobility protocols has been shown effective in decreasing duration of MV and patients were more likely to be able to walk at time of hospital discharge.29-31 In addition, promoting early mobility for patients in the ICU can reduce the incidence and duration of delirium and improve functional outcomes. Achieving light sedation levels will further increase the success of early mobility protocols.19

Recommendation #3: Use ventilator liberation protocols. Weaning success hinges in part on the ability to assess whether a patient demonstrates readiness for an SBT. Studies show that patients who are managed with ventilator liberation protocols spend less time on MV and discharge from the ICU earlier than those not managed by a protocol. Criteria such as PEEP level, oxygen requirement, and resolution of acute disease state may be key factors in the protocol. It is recommended that liberation protocols be enacted for patients who have been on MV for 24 hours.29 In addition, the Rapid Shallow Breathing Index (RSBI) is a tool that can help assess readiness to wean and extubate. The RSBI is the ratio of respiratory rate to tidal volume. A value greater than 105 breaths/min/L is predictive of weaning failure, while an RSBI less than 105 breaths/min/L is associated with weaning success.32 Although this protocol is simple and found to be effective, it may not accurately predict extubation readiness in certain patient populations, such as those with cardiopulmonary disease (ineffective inspiratory efforts do not trigger the ventilator leading to false results), cardiac issues (positive pressure can improve cardiac function, therefore reducing RSBI), neurosurgical complications (intubated for airway protection and not abnormal lung physiology), pediatric patients (literature is limited and conflicting on this population), patients on prolonged ventilation, and those with a tracheostomy.32

Recommendation #4: Specific ventilator settings to be applied during SBTs. For patients who have been ventilated for more than 24 hours, it is recommended that the initial SBT be conducted with inspiratory pressure augmentation (5-8 cm H2O) rather than without (T-piece or CPAP). An SBT with pressure augmentation is more likely to be successful, resulting in a higher rate of extubation success.29

Recommendation #5: Employ noninvasive ventilation in high-risk patients. Some patients are at a markedly higher risk for weaning failure. Serious comorbidities such as hypercapnia, chronic obstructive pulmonary disease (COPD), and heart failure require special consideration. It is recommended that these high-risk patients are placed on noninvasive ventilation (NIV) immediately after extubation. Examples of NIV include a bilevel positive airway pressure mask or high-flow nasal cannula. Although some patients may meet extubation criteria, they may be considered high risk for postextubation stridor (PES), or abnormal breathing caused by blockage of the airway. Risk factors for PES include traumatic intubation, intubation longer than 6 days, a large endotracheal tube, and multiple reintubations. For these situations, a cuff leak test is recommended. The cuff of the endotracheal tube is deflated to verify that gas can move around the tube. Absence of a cuff leak may indicate airway edema, thus increasing the risks of PES and reintubation. For patients who fail the cuff leak test, systemic corticosteroids should be administered 4 hours prior to extubation. While it is not required to repeat the cuff leak test prior to extubation, another round of testing may be considered.29 Individuals who have an audible stridor and are using accessory muscles for respiration may be treated with inhaled racemic epinephrine.

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Conclusion

The use of MV is expected to rise as the population in the US continues to age. The science regarding best practices of sedative and analgesic administration and ventilator weaning continues to evolve, but the personal, financial, and societal costs of MV further highlight the need for additional research and utilization of the latest evidence-based practices. It is imperative that critical care nurses serve as leaders in the adoption of the above recommendations to ensure that patients receive the highest quality of care during MV and weaning from MV.

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REFERENCES

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    Keywords:

    mechanical ventilation; noninvasive ventilation; pressure control ventilation; respiratory failure; spontaneous breathing trials; ventilator weaning; ventilator-associated pneumonia; volume control ventilation

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