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Prevent Excessive Inspiratory Plateau Pressures

Prevent Excessive Inspiratory Plateau Pressures

Corresponding Bundle Element:

Inspiratory plateau pressures maintained < 30 cm H2O for mechanically ventilated patients.

Related Measures

Inspiratory Plateau Pressure Goal

Background:

Patients with sepsis are at increased risk for developing acute respiratory failure, and most patients with severe sepsis and septic shock will require endotracheal intubation and mechanical ventilation.  Nearly 50 percent of patients with severe sepsis will develop acute lung injury (ALI)/acute respiratory distress syndrome (ARDS).  Patients with lung injury will have bilateral patchy infiltrates on chest x-ray, low paO2:FIO2 ratios (less than 300 for ALI or less than 200 for ARDS), and pulmonary capillary wedge pressure less than 18 cm H20, although this last measure is often clinically not available. 

High tidal volumes that are coupled with high plateau pressures should be avoided in ALI/ARDS.  Clinicians should use as a starting point a reduction in tidal volumes over 1 to 2 hours to a “low” tidal volume (6 mL·kg-1·lean body weight-1) as a goal in conjunction with the goal of maintaining end-inspiratory plateau pressures of < 30 cm H2O. 

Mortality Reduction:

The largest trial of a volume- and pressure-limited strategy showed a 9 percent decrease of all-cause mortality in patients ventilated with tidal volumes of 6 mL/kg of estimated lean body weight (as opposed to 12 mL/kg) while aiming for a plateau pressure of < 30 cm H2O. (1)

The formal ARDSnet protocol for mechanical ventilation is available at http://www.ardsnet.org/lowvtrefcard.pdf and is encouraged for use in septic patients.

Permissive Hypercapnea:

Hypercapnia (allowing PaCO2 to increase above normal, so-called permissive hypercapnia) can be tolerated in patients with ALI/ARDS if required to minimize plateau pressures and tidal volumes.

Although an acutely elevated PCO2 may have physiologic consequences that include vasodilatation and increased heart rate, blood pressure, and cardiac output, allowing modest hypercapnia in conjunction with limiting tidal volume and minute ventilation has been demonstrated to be safe in small, nonrandomized series. (2,3)  No upper limit for PCO2 has been established. Some authorities recommend maintaining pH at > 7.20 to 7.25, but this has not been prospectively established. The use of hypercarbia is limited in patients with preexisting metabolic acidosis and is contraindicated in patients with increased intracranial pressure. (4)  Sodium bicarbonate infusion may be considered in select patients to facilitate use of permissive hypercarbia. (5) Experimental models suggest that respiratory acidosis may confer protection against various forms of inflammatory injury. (6)

Positive End-Expiratory Pressure (PEEP):

Provide adequate supplemental oxygen to maintain a pulse oximetric saturation of > 90 percent. A minimum amount of PEEP should be set to prevent lung collapse at end expiration. Setting PEEP based on severity of oxygenation deficit and guided by the FIO2 required to maintain adequate oxygenation is one acceptable approach.

For patients supported by mechanical ventilation or who are appropriate candidates for a pressurized face mask, PEEP or continuous positive airway pressure may be used to increase mean and end-expiratory airway pressures, allowing the reduction of the oxygen concentrations below potentially toxic levels (FIO2 < 0.60).

References:

  1. The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. New Engl J Med. 2000;342:1301–1308.
  2. Hickling KG, Henderson S, Jackson R. Low mortality rate in adult respiratory distress syndrome using low-volume, pressure-limited ventilation with permissive hypercapnia: A prospective study. Crit Care Med. 1994;22:1568–1578.
  3. Bidani A, Cardenas VJ, Zwischenberger JB. Permissive hypercapnia in acute respiratory failure. JAMA. 1994;272:957–962.
  4. Tasker RC. Combined lung injury, meningitis and cerebral edema: How permissive can hypercapnia be? Intens Care Med. 1998;24:616–619.
  5. The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. New Engl J Med. 2000;342:1301–1308.
  6. Laffey JG, et al. Therapeutic hypercapnia reduces pulmonary and systemic injury following in vivo lung reperfusion. AJRCCM. 2000;162:2287–2294.

Content adapted extensively from:

  • Dellinger RP, Carlet JM, Masur H, et al. Surviving Sepsis Campaign guidelines for management of severe sepsis and septic shock. Crit Care Med. 2004;32:858-873.
  • Sevransky JE, Levy MM,  Marini JJ. Mechanical ventilation in sepsis-induced acute lung injury/acute respiratory distress syndrome: An evidence-based review. Crit Care Med. 2004;32[Suppl.]:S548–S553.

Tips

  1. Create a standardized protocol that prompts users to use tidal volumes no greater than 6 ml/kg IBW and to maintain plateau pressures less than 30 cm H20.  
  2. Make execution of an ARDSnet-like protocol the primary responsibility of the respiratory therapists, if possible.
  3. Have stakeholders work in concert with the respiratory therapy department to create and deploy a clinical protocol for ALI/ARDS ventilation.
  4. Avoid synchronized intermittent mandatory ventilation (SIMV) during the acute phase of illness.  Instead, use mandatory modes of ventilation such as assist control (ACV) or pressure control (PCV) to prevent spontaneously large tidal volumes.
  5. Do not allow peak pressures to govern ventilator management.  The key value is the plateau pressure.
  6. The weight for determining the Vt should be the ideal body weight, not the fat or over-hydrated weight. The ideal body weight is calculated from the patient’s height.
  7. Do not worry about the pCO2 unless the pH is less than a threshold the clinical team cannot accept.   Some intensivists are comfortable with pH as low as 7.10.  Most clinicians like to see pH greater than 7.21.  Timid clinicians use pH in the range of 7.25 or 7.30.  Where renal dysfunction prevents compensation, bicarbonate can be used to help maintain the pH.  However, constant bicarbonate infusions can also contribute to CO2 production.  THAM does not have this side effect.