Critical Care, Critical Care Alert, Cardiology

Critical Care Alert: Low Tidal Volume Ventilation for Emergency Department Patients

Critical Care Alert

A 52-year-old woman presents to the ED after being found altered by her neighbor. On arrival, she is not alert and is disoriented. Vitals show a heart rate of 135 bpm, blood pressure 107/55, temperature 102.3° F, respiratory rate 24, and oxygen saturation 78%. The patient receives an emergent chest x-ray demonstrating bilateral and diffuse pulmonary infiltrates. Patient’s bedside ultrasound demonstrates effective and appropriate contractility, and no diastolic dysfunction is noted. The patient is placed on non-invasive positive pressure ventilation (NIPPV), but after a few minutes, the patient continues to have a decreased oxygen saturation and increased altered mental status.

Now, the team decides to intubate the patient. The intubation is uneventful, and the patient is transitioned from BVM to the ventilator. At this time, the attending asks, "What settings would you like on the ventilator?"

Article
De Monnin K, Terian E, Yaegar LH, et al. Low Tidal Volume Ventilation for Emergency Department Patients: A Systematic Review and Meta-Analysis on Practice Patterns and Clinical Impact. Crit Care Med. 2022;50(6):986-998.

Objective
To evaluate the impact of ED-based Low Tidal Volume Ventilation (LTVV) on outcomes and ventilator settings in the ED and ICU

Background
Patients experiencing critical illness necessitating mechanical ventilation have high mortality rates. Additionally, survivors of critically ill mechanical ventilation experience high morbidity. Several studies have established that lung-protective ventilation decreases risks of ventilator-associated lung injury (VALI) and improves outcomes in patients with acute respiratory distress syndrome (ARDS).1,2 There is now increasing data to suggest that Lung Protective Ventilation (LPV) provides benefit for patients without ARDS as well.3

LPV is multi-factorial. One important aspect of LPV is low tidal volume ventilation (LTVV). LTVV has been one of the most effective strategies in reducing mortality in ARDS. Given the increasing lengths of stay in EDs and longer ED mechanical ventilation times, the use of LTVV in the ED may provide several potential benefits. Ventilator settings in the early phase of respiratory failure have demonstrated impact on outcomes for both patients with ARDS, as well as those at risk for developing ARDS. Interestingly, initial ventilator settings in the ICU tend to change minimally during the first few days of stay. Additionally, studies have shown that ventilator settings in the ED directly influence ICU ventilator settings. Thus, the ED is posited to be a "high-impact area" to target goals of LTVV.4

Studies have shown that LPV is under-utilized in the ED. Many of these studies are almost a decade old and here the authors explore the existing and new literature, immediately noting an increase in publications regarding mechanical ventilation in the ED.

Hypothesis
Implementing a LTVV strategy in the ED improves outcomes and decreases risks of VALI in mechanically ventilated patients

Design
Systematic review and meta-analysis to compare outcomes between patients receiving ED-based LTVV versus non-LTVV. The definition of LTVV in this meta-analysis was that used for “LTVV” or “LPV” in the included studies: typically tidal volume less than or equal to 8mL/kg predicted body weight (PBW)

Inclusion criteria: Studies of adults receiving invasive positive pressure mechanical ventilation during the study period. Inclusion of nonrandomized studies was decided a priori. Studies had to report delivered ED tidal volume settings to be considered.

Exclusion criteria: Case studies, reviews, correspondences.

Primary outcome: Hospital mortality

Secondary outcomes: mechanical ventilation duration, ICU length of stay, hospital length of stay, occurrence rate of ARDS after admission

RESULTS

  • 21 studies were included in the final analysis
    • 11 studies provided outcome data and were part of the meta-analysis
    • 10 studies provided tidal-volume data
  • Of the 10 studies providing tidal-volume data:
    • 3 were rated as good quality on the Newcastle-Ottawa Scale
    • 7 were rated as poor quality
  • Of the 11 studies providing outcome data:
    • 3 were quasi-experimental before-and-after studies
    • 6 were cohort studies
    • 8 were rated as good quality on the Newcastle-Ottawa Scale
    • 3 were rated as poor quality

Outcomes

  • The before-and-after studies providing outcome data demonstrated an increase in ED-initiated LTVV with implementation of ED-based ventilator protocol with a significant reduction in ED-provided tidal volumes over time.
  • Use of LTVV in the ED was associated with an increased use of LTVV in the ICU, with a significant reduction in ICU tidal volumes.
  • 10 studies (with an n = 11086) were included in the pooled analysis for mortality, demonstrating a 24.5% mortality in the LTVV group vs a 23.1% mortality in the non-LTVV group (p=0.23).
  • However, a post hoc "leave-one-out" subgroup analysis (9 studies, n = 8127) that excluded an outlier study (Prekker et al.) demonstrated a mortality of 26.5% in the LTVV group vs a 31.1% mortality the non-LTVV group (p<0.001). Note that heterogeneity was reduced from 76% to 0% in this subgroup analysis.
  • Occurrence rates of ARDS after admission was reported in 5 studies (n=7042) and was 4.5% in the LTVV group vs 8.3% in the non-LTVV group (p<0.001).
  • ED LTVV was associated with shorter hospital length of stay and ICU length of stay.
  • ED LTVV had greater ventilator-free days compared to non-LTVV.
  • In a subgroup analysis of 2 studies that addressed the impact of LTVV on ED patients with ARDS, mortality was 33.6% in the LTVV cohort vs 47.9% in the non-LTVV cohort (p=0.03).

Limitations

  • No randomized controlled trials were included in the review.
  • The leave-one-out analysis that demonstrated a significant mortality improvement was a post-hoc analysis.

EM Take-Aways

  • Mechanical ventilation is a common intervention started in the Emergency Department for critically ill patients.
  • Initial tidal volume and ventilator settings have repeatedly demonstrated an important impact on patient-centered clinical outcomes.
  • LTVV, a facet of LPV, improves patient outcomes for in patients both with and without ARDS, and may decrease occurrence or progression to ARDS.
  • The Emergency Department ventilator settings are often maintained and minimally changed in the ICU, thus making the ED an high-impact area to initiate and adhere to LTVV.
  • The results of this meta-analysis suggest that LTVV should be the default and initial ventilator settings for mechanically ventilated patients.

References

  1. 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. N Engl J Med. 2000;342(18):1301-1308.
  2. ​​Determann RM, Royakkers A, Wolthuis EK, et al. Ventilation with lower tidal volumes as compared with conventional tidal volumes for patients without acute lung injury: a preventive randomized controlled trial. Crit Care. 2010;14(1):1-14.
  3. Serpa Neto A, Oliveira Cardoso S, Manetta JA, et al. Association between use of lung-protective ventilation with lower tidal volumes and clinical outcomes among patients without acute respiratory distress syndrome: a meta-analysis. 2012;308(16): 1651-1659.
  4. Fuller BM, Ferguson IT, Mohr NM, et al. Lung-protective ventilation initiated in the emergency department (LOV-ED): a quasi-experimental, before-after trial. Ann Emerg Med. 2017;70(3):406-418.

 

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