Reduced tidal volumes and lung protective ventilatory strategies: where do we go from here?

[Extracorporeal Lung Support in Thoracic Surgery: Basics and Pathophysiology]

Extracorporeal lung support (ECLS) is of increasing importance in general thoracic surgery. Different modes of ECLS may be applied in several situations throughout the perioperative phase and are adapted to the individual patient's needs and the planned surgical procedures. ECLS is not a static procedure and should be always evaluated according to the present condition of the patient. Therefore, it is essential to understand the pathophysiology of the disease and the different ECLS modes, as well as the different cannulation options, in order to be able to use the different escalation and de-escalation techniques in accordance with the clinical situation.

Lung protective ventilation strategy for the acute respiratory distress syndrome

BACKGROUND

Patients with acute respiratory distress syndrome and acute lung injury require mechanical ventilatory support. Acute respiratory distress syndrome and acute lung injury are further complicated by ventilator-induced lung injury. Lung protective ventilation strategies may lead to improved survival. This systematic review is an update of a Cochrane review originally published in 2003 and updated in 2007.

OBJECTIVES

To assess the effects of ventilation with lower tidal volume on morbidity and mortality in patients aged 16 years or older affected by acute respiratory distress syndrome and acute lung injury. A secondary objective was to determine whether the comparison between low and conventional tidal volume was different if a plateau airway pressure of greater than 30 to 35 cm H20 was used.

SEARCH METHODS

In our previous 2007 updated review, we searched databases from inception until 2006. In this third updated review, we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL and the Web of Science from 2006 to September 2012. We also updated our search of databases of ongoing research and of reference lists from 2006 to September 2012.

SELECTION CRITERIA

We included randomized controlled trials comparing ventilation using either a lower tidal volume (Vt) or low airway driving pressure (plateau pressure 30 cm H2O or less), resulting in a tidal volume of 7 ml/kg or less, versus ventilation that used Vt in the range of 10 to 15 ml/kg in adults (16 years old or older) with acute respiratory distress syndrome and acute lung injury.

DATA COLLECTION AND ANALYSIS

We independently assessed trial quality and extracted data. Wherever appropriate, results were pooled. We applied fixed-effect and random-effects models.

MAIN RESULTS

We did not find any new study which were eligible for inclusion in this update. The total number of studies remained unchanged, six trials involving 1297 patients. Five trials had a low risk of bias. One trial had an unclear risk of bias. Mortality at day 28 was significantly reduced by lung-protective ventilation with a relative risk (RR) of 0.74 (95% confidence interval (CI) 0.61 to 0.88); hospital mortality was reduced with a RR of 0.80 (95% CI 0.69 to 0.92). Overall mortality was not significantly different if a plateau pressure less than or equal to 31 cm H2O in the control group was used (RR 1.13, 95% CI 0.88 to 1.45). There was insufficient evidence for morbidity and long-term outcomes.

AUTHORS' CONCLUSIONS

Clinical heterogeneity, such as different lengths of follow up and higher plateau pressure in control arms in two trials, makes the interpretation of the combined results difficult. Mortality was significantly reduced at day 28 and at the end of the hospital stay. The effects on long-term mortality are unknown, although the possibility of a clinically relevant benefit cannot be excluded. Ventilation with lower tidal volumes is becoming a routine strategy of treatment of acute respiratory distress syndrome and acute lung injury, stopping investigators from carrying out additional trials.

Lower tidal volume at initiation of mechanical ventilation may reduce progression to acute respiratory distress syndrome: a systematic review

INTRODUCTION

The most appropriate tidal volume in patients without acute respiratory distress syndrome (ARDS) is controversial and has not been rigorously examined. Our objective was to determine whether a mechanical ventilation strategy using lower tidal volume is associated with a decreased incidence of progression to ARDS when compared with a higher tidal volume strategy.

METHODS

A systematic search of MEDLINE, EMBASE, CINAHL, the Cochrane Library, conference proceedings, and clinical trial registration was performed with a comprehensive strategy. Studies providing information on mechanically ventilated patients without ARDS at the time of initiation of mechanical ventilation, and in which tidal volume was independently studied as a predictor variable for outcome, were included. The primary outcome was progression to ARDS.

RESULTS

The search yielded 1,704 studies, of which 13 were included in the final analysis. One randomized controlled trial was found; the remaining 12 studies were observational. The patient cohorts were significantly heterogeneous in composition and baseline risk for developing ARDS; therefore, a meta-analysis of the data was not performed. The majority of the studies (n = 8) showed a decrease in progression to ARDS with a lower tidal volume strategy. ARDS developed early in the course of illness (5 hours to 3.7 days). The development of ARDS was associated with increased mortality, lengths of stay, mechanical ventilation duration, and nonpulmonary organ failure.

CONCLUSIONS

In mechanically ventilated patients without ARDS at the time of endotracheal intubation, the majority of data favors lower tidal volume to reduce progression to ARDS. However, due to significant heterogeneity in the data, no definitive recommendations can be made. Further randomized controlled trials examining the role of lower tidal volumes in patients without ARDS, controlling for ARDS risk, are needed.

Lung protective ventilation strategy for the acute respiratory distress syndrome

BACKGROUND

Patients with acute respiratory distress syndrome and acute lung injury require mechanical ventilatory support. Acute respiratory distress syndrome and acute lung injury are further complicated by ventilator-induced lung injury. Lung-protective ventilation strategies may lead to improved survival.

OBJECTIVES

To assess the effects of ventilation with lower tidal volume on morbidity and mortality in patients aged 16 years or older affected by acute respiratory distress syndrome and acute lung injury. A secondary objective was to determine whether the comparison between low and conventional tidal volume was different if a plateau airway pressure of greater than 30 to 35 cm H20 was used.

SEARCH STRATEGY

In our original review, we searched databases from inception until 2003. In this updated review, we searched The Cochrane Central Register of Controlled Trials (CENTRAL), (The Cochrane Library 2006, Issue 3). We updated our search of MEDLINE, EMBASE, CINAHL and the Web of Science from 2003 to 2006. We also updated our search of intensive care journals and conference proceedings; databases of ongoing research, reference lists and 'grey literature' from 2003 to 2006.

SELECTION CRITERIA

We included randomized controlled trials comparing ventilation using either lower tidal volume (Vt) or low airway driving pressure (plateau pressure 30 cm H2O or less), resulting in tidal volume of 7 ml/kg or less versus ventilation that uses Vt in the range of 10 to 15 ml/kg, in adults (16 years old or older).

DATA COLLECTION AND ANALYSIS

We independently assessed trial quality and extracted data. Wherever appropriate, results were pooled. We applied fixed- and random-effects models.

MAIN RESULTS

We found one new study in this update for a total of six trials, involving 1297 patients, which were eligible for inclusion. Mortality at day 28 was significantly reduced by lung-protective ventilation: relative risk (RR) 0.74 (95% confidence interval (CI) 0.61 to 0.88); hospital mortality was reduced: RR 0.80 (95% CI 0.69 to 0.92); overall mortality was not significantly different if a plateau pressure less than or equal to 31 cm H2O in control group was used: RR 1.13 (95% CI 0.88 to 1.45). There was insufficient evidence about morbidity and long term outcomes.

AUTHORS' CONCLUSIONS

Clinical heterogeneity, such as different lengths of follow up and higher plateau pressure in control arms in two trials, make the interpretation of the combined results difficult. Mortality is significantly reduced at day 28 and at the end of hospital stay. The effects on long-term mortality are unknown, although the possibility of a clinically relevant benefit cannot be excluded.

Effect of low tidal volume ventilation on atelectasis in patients during general anesthesia: a computed tomographic scan

STUDY OBJECTIVE

To determine whether low tidal ventilation in patients without lung injury results in an increase in the amount of atelectasis and a further impairment of gas exchange during general anesthesia.

DESIGN

Randomized, single-blind study.

SETTING

University hospital.

PATIENTS

16 adult, ASA physical status I and II patients, who were scheduled for elective excision of intracranial lesion.

INTERVENTIONS

Patients were randomly allocated to one of two groups: traditional tidal volume (V(T)) ventilation group (V(T), 10 mL/kg) and low V(T) ventilation group (V(T), 6 mL/kg) after the first computed tomographic (CT) scan.

MEASUREMENTS AND MAIN RESULTS

Atelectasis, as determined by CT and arterial blood gas analysis, was measured before induction, after tracheal intubation, and at the end of operation. After tracheal intubation, CT scan showed atelectasis in both groups. The mean atelectasis area was 4.25 +/- 2.05 cm(2) (3.32% +/- 1.94%) in the traditional V(T) ventilation group and 5.56 +/- 3.21 cm(2) (4.19% +/- 2.31%) in the low V(T) ventilation group. At the end of operation, there was no significant increase in the amount of atelectasis within the two groups. Arterial blood gas analysis showed no differences after tracheal intubation or at the end of operation in either group.

CONCLUSION

Ventilation using low V(T)s does not cause more pulmonary collapse than mechanical ventilation using standard V(T)s.

SARS in the Intensive Care Unit

Approximately 20% of patients with severe acute respiratory syndrome (SARS) develop respiratory failure that requires admission to an intensive care unit (ICU). Old age, comorbidity, and elevated lactate dehydrogenase on hospital admission are associated with increased risk for ICU admission. ICU admission usually is late and occurs 8 to 10 days after symptom onset. Acute respiratory distress syndrome occurs in almost all admitted patients and most require mechanical ventilation. ICU admission is associated with significant morbidity, particularly an apparent increase in the incidence of barotrauma and nosocomial sepsis. Long-term mortality for patients admitted to the ICU ranges from 30% to 50%. Many procedures in ICUs pose a high risk for transmission of SARS coronavirus to health care workers. Contact and airborne infection isolation precautions, in addition to standard precautions, should be applied when caring for patients with SARS. Ensuring staff safety is important to maintain staff morale and delivery of adequate services.

Ventilation with lower tidal volumes versus traditional tidal volumes in adults for acute lung injury and acute respiratory distress syndrome

BACKGROUND

Patients with acute respiratory distress syndrome and acute lung injury require mechanical ventilatory support. Acute respiratory distress syndrome and acute lung injury are further complicated by ventilator-induced lung injury. Lung-protective ventilation strategies may lead to improved survival.

OBJECTIVES

To assess the effects of ventilation with lower tidal volume on morbidity and mortality in patients aged 16 years or older affected by acute respiratory distress syndrome and acute lung injury. A secondary objective was to determine whether the comparison between low and conventional tidal volume was different if a plateau airway pressure of greater than 30 to 35 cm H20 was used.

SEARCH STRATEGY

We searched The Cochrane Central Register of Controlled Trials (CENTRAL), The Cochrane Library issue 4, 2003; MEDLINE (1966 to October 2003); EMBASE and CINAHL (1982 to October 2003); intensive care journals and conference proceedings; databases of ongoing research, reference lists and 'grey literature'.

SELECTION CRITERIA

Randomized trials comparing ventilation using either lower tidal volume or low airway driving pressure (plateau pressure 30 cm H(2)O or less), resulting in tidal volume of 7 ml/kg or less versus ventilation that uses Vt in the range of 10 to 15 ml/kg, in adults (aged 16 years or older).

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. Wherever appropriate, results were pooled. Fixed and random effects models were applied.

MAIN RESULTS

Five trials, involving 1202 patients, were eligible. Mortality at day 28 was significantly reduced by lung-protective ventilation: relative risk 0.74 (confidence interval 0.61 to 0.88), whereas beneficial effect on long-term mortality was uncertain: relative risk 0.84 (confidence interval 0.68 to 1.05). The comparison between low and conventional tidal volume was not significantly different if a plateau pressure less than or equal to 31 cm H2O in control group was used: relative risk 1.13 (confidence interval 0.88 to 1.45). There was insufficient evidence about morbidity and long term outcomes.

REVIEWERS' CONCLUSIONS

Clinical heterogeneity, such as different lengths of follow up and higher plateau pressure in control arms in two trials make the interpretation of the combined results difficult. Mortality is significantly reduced at day 28 and the effects on long term mortality are uncertain, although the possibility of a clinically relevant benefit cannot be excluded.

Adenosine triphosphate is released during injurious mechanical ventilation and contributes to lung edema

BACKGROUND

Extracellular nucleotides mediate many cellular functions and are released in response to mechanical stress in vitro. It is unknown whether adenosine triphosphate (ATP) is released in vivo during mechanical ventilation (MV). We hypothesized that stress from high-pressure MV would increase airway ATP, contributing to MV-associated lung edema.

METHODS

Rats were randomized to nonventilated control (n = 6) or 30 minutes of MV with low (15 cm H(2)0, n = 7) or high (40 cm H(2)0, n = 6) pressure. Additional groups received intratracheal ATP (n = 7) or saline (n = 7) before low-pressure MV.

RESULTS

Low-pressure MV did not affect lung edema or bronchoalveolar lavage (BAL) ATP levels. In contrast, high-pressure MV significantly increased BAL ATP and produced alveolar edema; lactate dehydrogenase was unchanged. Intratracheal ATP administration significantly increased lung water during low-pressure MV.

CONCLUSION

High-pressure MV increases BAL ATP concentration without altering lactate dehydrogenase, suggesting that release is not from cell lysis. Intratracheal ATP increases lung water, implicating nucleotides in MV-associated lung edema.