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Mechanical Ventilation in ARDS Due to Sepsis
Sepsis is one of the main causes of acute respiratory distress syndrome (ARDS), in which the lungs are injured by circulating inflammatory mediators, resulting in severely impaired gas exchange usually requiring invasive mechanical ventilation. ARDS also results in poor lung compliance in a hetereogeneous distribution, making less-affected lung areas more vulnerable to ventilator-induced lung injury. Sepsis-induced ARDS is a form of severe organ failure, and is a major contributor to the high mortality from severe sepsis and septic shock. Sepsis-induced ARDS most often results from pneumonia, but ARDS can develop as a sequela from sepsis of any infectious source.
Mechanical ventilation in ARDS has been examined in numerous well-conducted randomized controlled trials, most of which included patients with severe sepsis and septic shock. Only a handful of studies have considered sepsis-induced ARDS as a distinct entity; most of the evidence supporting the Surviving Sepsis Guidelines for mechanical ventilation in sepsis-induced ARDS derive from evidence collected in ARDS trials in general. The Surviving Sepsis Guidelines for mechanical ventilation of ARDS due to sepsis don't diverge significantly from the general management of ARDS; here is a summary.
Low Tidal Volume Ventilation for Sepsis-Induced ARDS
Traditional high tidal volumes (10-12 mL/kg) provided during mechanical ventilation can cause barotrauma and are harmful to people with ARDS. Use low tidal volumes of 6 mL/kg of predicted body weight for people with sepsis-induced ARDS (or from any cause). (Strength: Grade 1A, as compared against 12 mL/kg).
Predicted body weight is calculated by height; use an online chart or calculator to help you. A 5' 9" man would receive 424 mL tidal volumes; a 5' 3" woman, only 314 mL. These uncomfortably-low-seeming values may be partly why physicians commonly use inappropriately high tidal volumes in ARDS; it's been suggested that women with ARDS are especially likely to receive excessive tidal volumes.
The plateau pressure in people with ARDS should be measured and ideally maintained ≤ 30 cm H2O with passive inflation of the lungs during mechanical ventilation (Grade 1B).
If plateau pressures ≤ 30 cm H2O can't be achieved with 6 mL/kg tidal volumes, try reducing them even lower, to 5 or 4 mL/kg (as low as 280 mL for a 5' 9" man).
Low tidal volumes and plateau pressures should not just be used in people with full-blown ARDS, but virtually everyone with sepsis, because observational trials suggest a decreased risk for ARDS when lower tidal volumes are used (Ungraded).
Why: The landmark ARDSNet trial demonstrated a 9% absolute reduction in mortality in people with ARDS treated with tidal volumes 6 mL/kg compared to 12 mL/kg predicted body weight. They also targeted a plateau pressure ≤ 30 cm H2O. Subsequent meta-analyses supported these findings of benefit from low tidal volume ventilation for ARDS.
But: Individual patient factors should be considered when choosing the tidal volume in sepsis-induced ARDS, such as:
- Reduced chest wall / abdominal compliance (most often due to obesity), which may necessitate higher plateau pressures to achieve minimal gas exchange parameters;
- Amount of PEEP being applied (adds to plateau pressure);
- Patients' breathing efforts (which increase transalveolar pressure for any given plateau pressure) and ventilatory demand, such as from metabolic acidosis.
High frequency oscillatory ventilation (HFOV) was not been shown to be beneficial as first-line therapy for ARDS in two large randomized trials.
Positive End-Expiratory Pressure (PEEP) for ARDS due to Sepsis
Positive end-expiratory pressure (PEEP) should be used during mechanical ventilation for ARDS, to prevent atelectotrauma (shear stress as alveoli expand and collapse during mechanical ventilation) (Grade 1B). For people with moderate-to-severe ARDS due to sepsis, higher PEEP is suggested (Grade 2C). Higher PEEP can be titrated according to bedside measurements of respiratory compliance, or more simply according to oxygenation using the ARDSNet strategy.
Why: Animal experiments show PEEP prevents ventilator-induced lung injury when high plateau pressures are present. In a 2010 meta-analysis, people with moderate or severe ARDS (PaO2/FiO2 ≤ 200 mm Hg) appeared to benefit from a higher PEEP strategy (but those with less severe ARDS did not).
Recruitment Maneuvers and Prone Positioning for ARDS from Sepsis
Surviving Sepsis Guidelines suggest trying recruitment maneuvers in people with sepsis and ARDS with severe refractory hypoxemia (Grade 2C). For institutions with experience with prone positioning for ARDS, prone positioning is suggested for those with severe ARDS (PaO2/FiO2 < 100 mm Hg) (Grade 2B).
Why: Recruitment maneuvers (sustained high airway pressures over brief periods) can open collapsed alveoli, but can theoretically injure them as well. Evidence is lacking as to recruitment maneuvers' benefit or harm, so their use is suggested only in those with severe hypoxemia refractory to standard treatment. Prone positioning was shown in a large multicenter randomized trial to improve mortality in ARDS, but implementation requires institutional commitment. HFOV and extracorporeal membrane oxygenation (ECMO) are considered appropriate salvage therapies for ARDS with refractory hypoxemia. Nitric oxide is suspected of being potentially harmful and is not recommended for routine use in ARDS.
Elevate Head-of-Bed to Prevent Pneumonia in ARDS Due to Sepsis
The head of the bed should be elevated to 30-45 degrees (semi-recumbent position) in people with ARDS to prevent ventilator-associated pneumonia (Grade 1B).
Why: A single randomized trial is cited to support this widespread practice; though that trial has been criticized for methodologic flaws, this is an easy and nearly cost-free intervention with good biologic plausibility.
Weaning Protocols and Spontaneous Breathing Trials in ARDS from Sepsis
A mechanical ventilation weaning protocol should be in place including regular spontaneous breathing trials, with extubation considered when certain criteria are met. The patient should be hemodynamically stable (off vasopressors), arousable, without new serious medical problems (e.g., pulmonary embolism, arrhythmia), low PEEP and ventilator support requirements, and FiO2 that can be achieved by nasal cannula or face mask oxygen. If a patient meets these criteria and passes a spontaneous breathing trial, extubation should be considered (Grade 1A).
Why: Weaning from mechanical ventilation is the goal after ARDS from sepsis or any cause, but the process is often delayed unnecessarily. A protocolized approach to identifying patients ready to wean reduces unnecessary ventilator days for patients with respiratory failure. Sedation interruptions were shown to help in 2000, but more recent data suggests that sedation practices in critical care may have improved to the point that sedation interruptions are not as beneficial as they once were.
Restrictive Fluids in ARDS due to Sepsis
A conservative approach to fluid management is recommended in people with ARDS due to sepsis who are not in shock or with signs of tissue hypoperfusion (Grade 1C).
Why: The FACTT trial showed an aggressive approach to fluid management in ARDS patients (giving ~40 mg furosemide daily to maintain a neutral fluid balance) resulted in fewer days of mechanical ventilation and ICU days, without increasing renal failure or mortality. The protocol was held at any time shock was present.
Avoid Beta-Agonists in ARDS
Unless bronchospasm or hyperkalemia is present, the Surviving Sepsis Guidelines recommend against the use of beta-agonists for people with ARDS from sepsis (Grade 1B).
Why: Beta-agonists in ARDS are believed to be harmful. A randomized trial was stopped early for futility with a trend toward harm in the group receiving aerosolized beta-agonists for ARDS. Beta-agonists given IV were shown to be definitely harmful in BALTI-2.
Avoid Using Pulmonary Artery Catheters in ARDS Due to Sepsis
The Surviving Sepsis Guidelines recommend against use of a pulmonary artery catheter as part of routine management for ARDS due to sepsis (Grade 1A).
Why: Pulmonary artery catheters are an example of a theoretically well-grounded intervention that became commonplace before randomized controlled trials were ever performed. The best available evidence strongly suggests that so-called Swan-Ganz catheters do not improve management of patients with ARDS, either with or without shock. PA catheters may still have a role in select patients in whom specific data obtainable only from a PA catheter is necessary to guide particular management decisions.
Noninvasive Mask Ventilation in ARDS: Use Extreme Caution
Noninvasive mask ventilation (NIV) is suggested to be used only in a small minority of patients with sepsis-induced ARDS. The risks of noninvasive ventilation for ARDS (rapid respiratory arrest and urgent/emergent intubation) must be carefully considered, and be outweighed by the potential benefits (avoidance of invasive mechanical ventilation) (Grade 2B).
Why: The vast majority of people with sepsis-induced ARDS with hypoxemia severe enough to require noninvasive ventilation will soon require invasive mechanical ventilation. Delaying this measure runs the risk of sudden respiratory arrest with complications of an emergent intubation. Generally, noninvasive ventilation should be reserved only for people with mild ARDS who are expected to recover rapidly from the underlying cause; high vigilance for worsened respiratory failure is essential.
Guide to Recommendations’ Strengths and Supporting Evidence in the Surviving Sepsis Guidelines:
- 1 = strong recommendation;
- 2 = weak recommendation or suggestion;
- A = good evidence from randomized trials;
- B = moderate strength evidence from small randomized trial(s) or upgraded observational trials;
- C = low strength evidence, well-done observational trials with control randomized controlled trials
- D = very low strength evidence, downgraded controlled studies or expert opinion.
PulmCCM is not affiliated with the Surviving Sepsis Campaign or the Surviving Sepsis Guidelines.