Mechanical Ventilation: Pressure Support and Control and Volume-Assured Pressure Support (Respiratory Therapy)

ALERT

Setting alarm limits appropriately is important to preventing harm. Verify alarm settings when ventilator parameters are adjusted and with each patient–ventilator safety check. Never disable ventilator alarms.

Always plug a ventilator into an electrical outlet (labeled or colored red) that is supplied by an emergency generator.

OVERVIEW

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, is an indication 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 (ventilator-free days).

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 (i.e., length of intensive care unit stay, ventilator-free days to discharge, mortality, morbidity).

With traditional pressure ventilation, the practitioner selects the desired pressure level, and the inspired tidal volume (VT) is determined by the selected pressure level and the patient's resistance and compliance. This is an important characteristic to note when caring for an unstable patient on a pressure mode of ventilation. Careful attention to exhaled VT is necessary to prevent inadvertent hyperventilation or hypoventilation. Permissive hypercapnia should not be attempted in patients with elevated intracranial pressure (ICP) or patients with myocardial ischemia, injury, or arrhythmias. Some patients receiving low-pressure ventilation, leading to permissive hypercapnia, require sedation to decrease spontaneous effort.

Many modes of pressure ventilation are available. These modes include assist-control (A/C), synchronized intermittent mandatory ventilation (SIMV), pressure support ventilation (PSV), positive end-expiratory pressure (PEEP) and continuous positive airway pressure (CPAP), pressure-control/inverse ratio ventilation (PC-IRV), proportional assist ventilation (PAV), adaptive support ventilation (ASV), airway pressure release ventilation (APRV), and biphasic (Table 1).

Summary descriptions of modes, mode parameters, and ventilator alarms are provided within this procedure (Table 1) (Table 2).

Humidity

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 are inexpensive and single use. Most HME units are passive, capturing both heat and moisture from expired gas and returning it to the patient at approximately 70% efficiency.^{undefined#ref3">3}

Complications

Complications of PPV include pulmonary barotrauma, volume-pressure trauma, hemodynamic changes, and ventilator-associated pneumonia (VAP).

• Pulmonary barotrauma is manifested by pneumothorax, pneumomediastinum, pneumopericardium, pneumoperitoneum, and subcutaneous emphysema.
• Volume-pressure trauma is evidenced by large volumes being translated into high plateau pressures and subsequent acute lung injury.
• Hemodynamic changes can be caused by PPV, which can reduce venous return and decrease cardiac output. Auto-PEEP is a common complication of mechanical ventilation that can result in hemodynamic compromise and even death.

EDUCATION

• Provide developmentally and culturally appropriate education based on the desire for knowledge, readiness to learn, and overall neurologic and psychosocial state.
• Clarify advance directives with the patient and family.
• During a life-threatening emergency, mechanical ventilation may need to be initiated quickly, with no time for staff to speak with the patient or family beforehand. As soon as possible, educate the patient and family about mechanical ventilation.
• Ensure that the patient and family understand the implications of intubation and mechanical ventilation specific to the situation, including why a ventilator is being used. Communicate in a way they understand; "respirator" and "life support" are commonly understood terms.
• Explain the procedure to the patient and family.
• Discuss the potential benefits of mechanical ventilation that the patient may experience (e.g., less shortness of breath, less difficulty with the breathing process).
• Discuss the unpleasant sensations that the patient may experience (e.g., gagging, anxiety). Explain to the patient that medications are given to promote relaxation and tolerance of the treatment. Explain that some patients may require sedation during mechanical ventilation.
• Explain that the patient will be unable to speak. Establish a method of communication in conjunction with the patient and family before initiating mechanical ventilation, if necessary.
• Explain to the patient and family what they should expect while the patient is ventilated.
• Educate the patient and family about ventilator alarms and their meanings. Assure them that staff do hear the alarms and will respond accordingly.
• Encourage questions and answer them as they arise.

ASSESSMENT AND PREPARATION

Assessment

1. Perform hand hygiene before patient contact. Don appropriate personal protective equipment (PPE) based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
2. Introduce yourself to the patient.
3. Verify the correct patient using two identifiers.
4. Assess the need for mechanical ventilation before initiating ventilator support.
   1. Signs and symptoms of respiratory insufficiency or failure (e.g., hypercapnia secondary to hypoventilation, hypoxia)
   2. Decreased peripheral oxygen saturation (SpO₂) and arterial oxygen saturation (SaO₂)
   3. Altered level of consciousness
   4. Adventitious breath sounds
   5. Acid-base imbalance
   6. Cyanosis
   7. Hypotension or hypertension
   8. Increased work of breathing
   9. Hemodynamic instability

Preparation

1. Before initiating mechanical ventilation, ensure that the ventilator and associated equipment are functioning properly per the manufacturers' specifications and the organization's practice. Check the system microprocessor or ventilation system, circuit compliance, HME or humidifier, and filters, and perform a circuit leak test.
2. Ensure that the patient is positioned with the head of the bed elevated at or greater than 30 degrees, unless specifically contraindicated.³

PROCEDURE

Pressure Support Ventilation (PSV)

1. Perform hand hygiene and don gloves. Don additional PPE based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
2. Verify the correct patient using two identifiers.
3. Explain the procedure and ensure that the patient agrees to treatment.
4. Select the PSV level in order to lower the spontaneous respiratory rate to 12 to 16 breaths/min and to attain a VT of 6 to 8 ml/kg ideal body weight (IBW).³ If necessary, increase the VT if the partial pressure of carbon dioxide (PaCO₂) increases or decreases below normal values, causing the patient to become hypercarbic or alkalotic.

   Rationale: Increasing the pressure support (PS) allows for a larger VT, which decreases the risk for hypercarbia. Decreasing the PS leads to increased acidosis and a smaller VT.

5. Set the trigger sensitivity between –0.5 and –1.5 cm H₂O pressure.³

   Rationale: If the sensitivity is set too low, increased patient effort is necessary to initiate a ventilator breath. Dyssynchrony can result.

6. Select the PEEP level. In many cases, the initial setting is 5 cm H₂O.³
   1. Adjust PEEP as needed after evaluation of tolerance (e.g., SaO₂, arterial partial pressure of oxygen [PaO₂], physical assessment).
   2. Increase PEEP levels to restore functional residual capacity (FRC) and allow reduction of fraction of inspired oxygen (FIO₂) to safe levels (i.e., less than or equal to 0.6).²

      Rationale: A PEEP level of 5 cm H₂O is considered physiologic.¹ High levels of PEEP rarely should be interrupted because reestablishing FRC (and PaO₂) may take hours, especially in a patient with acute respiratory distress syndrome (ARDS).

7. Place the patient on 100% oxygen unless information is available that identifies a precise FIO₂.³ Adjust the FIO₂ downward, as tolerated, using SaO₂ and arterial blood gas (ABG) values to guide level selection. Titrate the FIO₂ to ensure that the PaO₂ is 55 to 80 mm Hg and/or the SpO₂ is 88% to 95%¹ or per the organization’s practice.

   Rationale: Most patients in the acute care setting should be placed on 100% oxygen unless information is available identifying a precise FIO₂.³ High levels of FIO₂ 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.

8. Ensure that the ventilator alarms are set appropriately (Table 2).
9. Provide circuit humidification.
   1. For conventional humidifiers, make sure the humidifier has adequate fluid (sterile distilled water) and that the thermostat setting is adjusted according to the manufacturer's recommendations.
   2. When using a humidifier, maintain the gas temperature at 35°C plus or minus 2°C (95°F plus or minus 3.6°F) at the circuit Y-piece with a relative humidity of 100%.³

      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 should be maintained at or near body temperature.

   3. Place an HME between the patient's airway and the ventilator circuit.

      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.

      1. Change the HME per the manufacturer's instruction.

         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.

      2. Do not use an HME if secretions are copious or bloody.

         Rationale: Secretions may cause obstruction; an HME is contraindicated when secretions are copious or bloody.

10. Place the capnography device and appropriate adapter in the ventilator circuit, if ordered, or per the organization's practice.
11. Discard supplies, remove PPE, and perform hand hygiene.
12. Document the procedure in the patient's record.

Pressure Control (PC)

1. Perform hand hygiene and don gloves. Don additional PPE based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
2. Verify the correct patient using two identifiers.
3. Explain the procedure and ensure that the patient agrees to treatment.
4. Select PC.
5. Select the inspiratory pressure level (IPL).
6. Select the respiratory rate.
7. Select the inspiratory time (TI) or inverse inspiratory-to-expiratory (I:E) ratio (ventilators vary). The patient likely will not tolerate the prolonged TI in inverse ratio ventilation (IRV) without sedation and paralysis.

   Rationale: Because IRV may result in auto-PEEP, evaluating the total amount of PEEP present is important.

8. Select the PEEP level. When transitioning from volume ventilation to PC-IRV, initially maintain PEEP at the level used previously until the IRV’s effect is assessed.

   Rationale: The goal of PC-IRV is to improve oxygenation. This is done in conjunction with PEEP.

   IRV may result in auto-PEEP (which may be a desirable outcome of the mode); regardless, anticipate and measure auto-PEEP regularly.

9. Set the trigger sensitivity to between –0.5 and –1.5 cm H₂O pressure.³

   Rationale: If the sensitivity is set too low, increased patient effort is necessary to initiate a ventilator breath. Dyssynchrony can result.

10. Place the patient on 100% oxygen unless information is available that identifies a precise FIO₂.³ Adjust the FIO₂ downward, as tolerated, using SaO₂ and ABG values to guide level selection. Titrate the FIO₂ to ensure that the PaO₂ is 55 to 80 mm Hg and/or the SpO₂ is 88% to 95%¹ or per the organization’s practice.

    Rationale: Most patients in the acute care setting should be placed on 100% oxygen unless information is available identifying a precise FIO₂.¹ High levels of FIO₂ 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.

11. Ensure that the ventilator alarms are set appropriately (Table 2).
12. Provide humidification of the circuit.
    1. For conventional humidifiers, make sure the humidifier has adequate fluid (sterile distilled water) and that the thermostat setting is adjusted according to the manufacturer's recommendations.
    2. When using a humidifier, maintain the gas temperature at 35°C plus or minus 2°C (95°F plus or minus 3.6°F) at the circuit Y-piece with a relative humidity of 100%.

       Rationale: Gases are generally humidified before entering the artificial airway.

       In a patient with thick or tenacious secretions, pay attention to inspired temperature to prevent mucus plugging. In this situation, circuit temperature may need to be closer to body temperature.

    3. Place an HME between the patient's airway and the ventilator circuit.

       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.

       1. Change the HME per the manufacturer's instruction.

          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.

       2. Do not use an HME if secretions are copious or bloody.

          Rationale: Secretions may cause an obstruction; an HME is contraindicated when secretions are copious or bloody.

13. Place the capnography device and appropriate adapter within the ventilator circuit, if ordered, or per the organization's practice.
14. Discard supplies, remove PPE, and perform hand hygiene.
15. Document the procedure in the patient's record.

Volume-Assured Pressure Support (VAPS)

1. Perform hand hygiene and don gloves. Don additional PPE based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
2. Verify the correct patient using two identifiers.
3. Explain the procedure and ensure that the patient agrees to treatment.
4. Select VAPS.
5. Select the desired VT.
6. Select the parameters (pressure, volume, rate). Consult the specific ventilator manual as needed for additional parameter settings.

   Rationale: Volume-guaranteed pressure modes require that the practitioner select the desired VT; some ventilators also require selection of the pressure level. Spontaneous breathing modes and controlled modes are available.

7. Place the patient on 100% oxygen unless information is available that identifies a precise FIO₂.³ Adjust the FIO₂ downward, as tolerated, using SaO₂ and ABG values to guide level selection. Titrate the FIO₂ to ensure that the PaO₂ is 55 to 80 mm Hg and/or the SpO₂ is 88% to 95%¹ or per the organization’s practice.

   Rationale: Most patients in the acute care setting should be placed on 100% oxygen unless information is available identifying a precise FIO₂.¹ High levels of FIO₂ 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.

8. Ensure that the ventilator alarms are set appropriately (Table 2).
9. Provide circuit humidification.
   1. For conventional humidifiers, make sure the humidifier has adequate fluid (sterile distilled water) and that the thermostat setting is adjusted according to the manufacturer's recommendations.
   2. When using a humidifier, maintain the gas temperature at 35°C plus or minus 2°C (95°F plus or minus 3.6°F) at the circuit Y-piece with a relative humidity of 100%.³

      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 circumstance, circuit temperature may need to be closer to body temperature.

   3. Place an HME between the patient's airway and the ventilator circuit.

      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.

      1. Change the HME per the manufacturer's instruction.

         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.

      2. Do not use an HME if secretions are copious or bloody.

         Rationale: Secretions may cause an obstruction; an HME is contraindicated when secretions are copious or bloody.

10. Place the capnography device and appropriate adapter within the ventilator circuit, if ordered, or per the organization's practice.
11. Discard supplies, remove PPE, and perform hand hygiene.
12. Document the procedure in the patient's record.

MONITORING AND CARE

1. Check for secure stabilization and maintenance of the endotracheal (ET) tube. (Commercial ET tube holders are available.)
2. Confirm ET tube placement, ideally by clinical assessment and continuous waveform capnography. If continuous waveform capnography is not available, use a nonwaveform numeric exhaled carbon dioxide monitor.
3. Monitor SpO₂ continuously.
4. Monitor the inline thermometer to maintain the inspired gas temperature at 35°C plus or minus 2°C (95°F plus or minus 3.6°F) at the circuit Y-piece, with a relative humidity of 100%.³

   Rationale: There is the risk of thermal injury from overheated inspired gas and risk of poor humidity from underheated inspired gas.

5. Keep the ventilator tubing clear of condensation. Drain tubing from the patient toward the expiratory limb.

   Rationale: Condensation in the tube that is drained toward the patient may cause a respiratory infection if the patient inhales the contaminated water droplets.

6. Ensure the availability of a self-inflating manual resuscitation bag (MRB) and appropriate-size face mask attached to supplemental oxygen at the head of the bed. Attach or adjust the PEEP valve if the patient is on PEEP.

   Rationale: Ventilation and oxygen may be needed immediately to relieve acute respiratory distress caused by hypoxemia or acidosis.

7. Check the ventilator settings per the organization’s practice to ensure that they match the prescribing order.
8. Explore any change in peak inspiratory pressure (PIP) or decreased (sustained) VT on PSV. Immediately explore the cause of high-pressure alarms.

   Rationale: Acute changes in PIP or VT may indicate mechanical malfunction, such as a 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 pressure. If a tension pneumothorax occurs, perform a needle thoracotomy.

9. Place a bite block between the teeth if the patient is biting on the oral ET tube. If a bite block is unavailable, an oral airway may be used.

   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.

10. Change the patient’s body position as often as possible. Ensure that the patient is positioned with the head of the bed elevated at or greater than 30 degrees, unless specifically contraindicated.³

    Rationale: Continuous lateral rotation therapy may be helpful in improving oxygenation. Elevation is one of the most modifiable factors related to VAP.

11. Evaluate for patient–ventilator dyssynchrony.

    Rationale: Dyssynchrony occurs when the patient's intrinsic breaths oppose or challenge the ventilator and may occur because of patient fatigue or restlessness.

12. Observe for hemodynamic changes associated with increased VT, PEEP, or decreased cardiac output.

    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.

13. Suction the patient, using the closed technique if possible, only when needed (i.e., not routinely).
14. On an ongoing basis, monitor the patient for complications of mechanical ventilation, such as barotrauma, volutrauma, VAP, pneumothorax, or accidental extubation.
15. Observe the patient for signs or symptoms of pain. If pain is suspected, report it to the authorized practitioner.

EXPECTED OUTCOMES

• Maintenance of adequate pH, PaCO₂, and PaO₂
• Maintenance of adequate breathing pattern
• Respiratory muscle rest

UNEXPECTED OUTCOMES

• Unacceptable pH, PaCO₂, or PaO₂
• Hemodynamic instability
• Pulmonary barotraumas or volutrauma
• Inadvertent extubation
• Malpositioned ET tube
• Nosocomial lung infection
• Respiratory muscle fatigue
• Excessive condensation in ventilator circuit
• Discrepancy between set and measured ventilator settings

DOCUMENTATION

• Education
• Completed ventilation system test (pass or fail), date, and initials or signature of respiratory therapist (RT) and credentials
• Indication for ventilatory assistance
• Date and time ventilatory assistance was instituted
• Ventilator settings
  • FIO₂
  • Mode of ventilation
  • VT
  • Respiratory frequency (total and mandatory)
  • PEEP level
  • I:E ratio or TI
  • PIP
  • Dynamic lung compliance
  • Static lung compliance
• ABG values
• Oxygen saturation readings
• Patient’s response to PPV
• Hemodynamic values
• Vital signs
• Unexpected outcomes and related interventions
• Respiratory interventions
• Tube location verification

HOME CARE CONSIDERATIONS

• A patient who is eligible for invasive long-term care mechanical ventilation in the home requires a detailed plan, as well as stable cardiopulmonary parameters.⁴

REFERENCES

1. Kacmarek, R.M. (2021). Chapter 47: Physiology of ventilatory support. In R.M. Kacmarek, J.K. Stoller, A.J. Heuer (Eds.), Egan's fundamentals of respiratory care (12th ed., pp. 1013-1052). St. Louis: Elsevier.
2. Kacmarek, R.M. (2021). Chapter 48: Patient-ventilator interactions. In R.M. Kacmarek, J.K. Stoller, A.J. Heuer (Eds.), Egan’s fundamentals of respiratory care (12th ed., pp. 1053-1071). St. Louis: Elsevier.
3. Kacmarek, R.M. (2021). Chapter 49: Initiating and adjusting invasive ventilatory support. In R.M. Kacmarek, J.K. Stoller, A.J. Heuer (Eds.), Egan's fundamentals of respiratory care (12th ed., pp. 1072-1104). St. Louis: Elsevier.
4. Simonds, A.K. (2016). Home mechanical ventilation: An overview. Annals of the American Thoracic Society, 13(11), 2035-2044. doi:10.1513/AnnalsATS.201606-454FR (Level VII)

ADDITIONAL READINGS

Chatburn, R.L., Volsko, T.A. (2021). Chapter 46: Mechanical ventilators. In R.M. Kacmarek, J.K. Stoller, A.J. Heuer (Eds.), Egan’s fundamentals of respiratory care (12th ed., pp. 987-1012). St. Louis: Elsevier.

Elsevier Skills Levels of Evidence

• Level I - Systematic review of all relevant randomized controlled trials
• Level II - At least one well-designed randomized controlled trial
• Level III - Well-designed controlled trials without randomization
• Level IV - Well-designed case-controlled or cohort studies
• Level V - Descriptive or qualitative studies
• Level VI - Single descriptive or qualitative study
• Level VII - Authority opinion or expert committee reports