Different methods of ventilation (controlling pressure vs volume) for people with acute respiratory failure due to lung injury

Review question

We reviewed available evidence for the safety and efficacy of controlling pressure versus controlling volume of air delivered during mechanical ventilation in critically ill adults with acute respiratory failure due to lung injury. We found three relevant studies.

Background

Acute respiratory failure due to acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is a common reason for admission to intensive care units (ICUs) worldwide. A third to half of people with ALI/ARDS die in the ICU, in hospital or during follow-up. People with ALI/ARDS are put on ventilator machines to give the lungs time to recover. However, lung damage can worsen if the volume of air delivered by these machines is too large, or if the pressure reached in the lungs during ventilation is too high.

We wanted to know whether controlling pressure in the lung during ventilation by varying the volume of air delivered (pressure-controlled ventilation, or PCV) was better than allowing varying lung pressures when a fixed volume of air is delivered (volume-controlled ventilation, or VCV).

Study characteristics

The three randomized trials compared PCV versus VCV in a total of 1089 adults with ALI/ARDS from 43 ICUs in five high-income countries. None of the trials were industry-funded. The evidence is current to October 2014.

Key results

We could not be sure whether the proportions of patients who died in hospital were very different between those treated with PCV and with VCV. For every 1000 persons treated with VCV, 636 deaths were reported. On the basis of our results, we could expect to see between 210 fewer deaths and 13 more deaths with PCV. We found that effects on mortality in the ICU and on mortality at 28 days were similarly uncertain. Our results include the possibility that VCV or PCV could be better for reducing the duration of ventilation or the development of traumatic lung damage caused by ventilation (barotrauma). None of the studies provided reliable information regarding to what extent failure of other organs would be impacted by the type of ventilation, nor did they provide information on differences in infection risk or quality of life following discharge from intensive care.

Quality of the evidence

The overall evidence for mortality was of moderate quality. For outcomes such as duration of ventilation, barotrauma and organ failure, evidence was limited by the small numbers studied, the different methods used in the studies or differences in reporting of results, which made interpretation difficult.

Conclusions

Available evidence is insufficient to confirm whether PCV offers any advantage over VCV in improving outcomes for people with acute lung injury on ventilator machines. More studies including a larger number of people given PCV and VCV may provide reliable evidence on which more firm conclusions can be based.

Authors' conclusions: 

Currently available data from RCTs are insufficient to confirm or refute whether pressure-controlled or volume-controlled ventilation offers any advantage for people with acute respiratory failure due to acute lung injury or acute respiratory distress syndrome. More studies including a larger number of people given PCV and VCV may provide reliable evidence on which more firm conclusions can be based.

Read the full abstract...
Background: 

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) account for one-quarter of cases of acute respiratory failure in intensive care units (ICUs). A third to half of patients will die in the ICU, in hospital or during follow-up. Mechanical ventilation of people with ALI/ARDS allows time for the lungs to heal, but ventilation is invasive and can result in lung injury. It is uncertain whether ventilator-related injury would be reduced if pressure delivered by the ventilator with each breath is controlled, or whether the volume of air delivered by each breath is limited.

Objectives: 

To compare pressure-controlled ventilation (PCV) versus volume-controlled ventilation (VCV) in adults with ALI/ARDS to determine whether PCV reduces in-hospital mortality and morbidity in intubated and ventilated adults.

Search strategy: 

In October 2014, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2014, Isssue 9), MEDLINE (1950 to 1 October 2014), EMBASE (1980 to 1 October 2014), the Latin American Caribbean Health Sciences Literature (LILACS) (1994 to 1 October 2014) and Science Citation Index-Expanded (SCI-EXPANDED) at the Institute for Scientific Information (ISI) Web of Science (1990 to 1 October 2014), as well as regional databases, clinical trials registries, conference proceedings and reference lists.

Selection criteria: 

Randomized controlled trials (RCTs) and quasi-RCTs (irrespective of language or publication status) of adults with a diagnosis of acute respiratory failure or acute on chronic respiratory failure and fulfilling the criteria for ALI/ARDS as defined by the American-European Consensus Conference who were admitted to an ICU for invasive mechanical ventilation, comparing pressure-controlled or pressure-controlled inverse-ratio ventilation, or an equivalent pressure-controlled mode (PCV), versus volume-controlled ventilation, or an equivalent volume-controlled mode (VCV).

Data collection and analysis: 

Two review authors independently screened and selected trials, assessed risk of bias and extracted data. We sought clarification from trial authors when needed. We pooled risk ratios (RRs) for dichotomous data and mean differences (MDs) for continuous data with their 95% confidence intervals (CIs) using a random-effects model. We assessed overall evidence quality using the GRADE (Grades of Recommendation, Assessment, Development and Evaluation) approach.

Main results: 

We included three RCTs that randomly assigned a total of 1089 participants recruited from 43 ICUs in Australia, Canada, Saudi Arabia, Spain and the USA. Risk of bias of the included studies was low. Only data for mortality and barotrauma could be combined in the meta-analysis. We downgraded the quality of evidence for the three mortality outcomes on the basis of serious imprecision around the effect estimates. For mortality in hospital, the RR with PCV compared with VCV was 0.83 (95% CI 0.67 to 1.02; three trials, 1089 participants; moderate-quality evidence), and for mortality in the ICU, the RR with PCV compared with VCV was 0.84 (95% CI 0.71 to 0.99; two trials, 1062 participants; moderate-quality evidence). One study provided no evidence of clear benefit with the ventilatory mode for mortality at 28 days (RR 0.88, 95% CI 0.73 to 1.06; 983 participants; moderate-quality evidence). The difference in effect on barotrauma between PCV and VCV was uncertain as the result of imprecision and different co-interventions used in the studies (RR 1.24, 95% CI 0.87 to 1.77; two trials, 1062 participants; low-quality evidence). Data from one trial with 983 participants for the mean duration of ventilation, and from another trial with 78 participants for the mean number of extrapulmonary organ failures that developed with PCV or VCV, were skewed. None of the trials reported on infection during ventilation or quality of life after discharge.

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