By Richard Kallet, MS, RRT, FCCM

Director of Quality Assurance, Respiratory Care Services, Department of Anesthesia, San Francisco General Hospital

Mr. Kallet reports that he is a major stockholder in the Asthma & Allergy Prevention Company and receives grant/research support from Nihon-Kohden.

SYNOPSIS: In postoperative cardiac surgery patients with hypoxemia at admission to the ICU, the brief application of an intensive recruitment maneuver followed by lung-protective ventilation was associated with reduced occurrence and severity of pulmonary complications.

SOURCE: Costa Leme A, Hajjar LA, Volpe MS, et al. Effect of intensive vs. moderate alveolar recruitment strategies added to lung-protective ventilation on postoperative pulmonary complications. JAMA 2017;317:1422-1432.

In this single-center prospective trial, 320 patients undergoing elective cardiac surgery and who had hypoxemia upon ICU admission were randomized to receive either a moderate or intensive recruitment maneuver (RM). Then, they were managed with a tidal volume of 6 mL/kg and positive end-expiratory pressure (PEEP) of 8 cm H2O. Hypoxemia was defined as an arterial oxygen tension-to-inspired oxygen fraction ratio (PaO2/FiO2) < 250 mmHg on PEEP > 5 cm H2O. The age range studied was 18-80 years and excluded those with a history of chronic obstructive lung disease, pulmonary hypertension, neuromuscular disease, or prior cardiac surgery.

The primary outcome was the incidence and intensity of pulmonary complications during hospitalization. The severity was quantified using an ordinal scale between 0-5, with scores > 3 signifying major pulmonary complications. Secondary outcomes included both ICU and hospital length of stay and hospital mortality.

In the moderate RM strategy group, continuous positive airway pressure (CPAP) of 20 cm H2O was applied for 30 seconds for a total of three applications. The intensive RM consisted of applying PEEP of 30 cm H2O with pressure control ventilation with a driving pressure of 15 cm H2O (i.e., achieving a plateau pressure or Pplat of 45 cm H2O) that was sustained for 60 seconds for a total of three applications.

All 320 patients completed the study, and there were no differences in baseline characteristics. Those who received an intensive RM exhibited higher PaO2/FiO2 and chest compliance with a lower driving pressure than those who received a moderate RM. Moreover, those treated with an intensive RM demonstrated both a lower incidence (15.3% vs. 26.4%) and severity (1.7 vs. 2.0) of postoperative complications compared to the moderate RM group (both of which were statistically significant).

Both ICU and hospital lengths of stay were significantly lower in those who received intensive vs. moderate RMs to treat postoperative hypoxemia (3.8 vs. 4.8 days and 10.9 vs. 12.4 days, respectively). In addition, the need for oxygen therapy, prolonged use of non-invasive ventilation, and reinstitution of mechanical ventilation all were significantly lower in those randomized to the intensive RM group. The incidence of postoperative pneumonia and septic shock was not different between treatment groups. Hospital mortality was not significantly different between treatment groups.

COMMENTARY

In 1992, an editorial by Lachmann proposed an open lung ventilation strategy for patients with acute respiratory distress syndrome (ARDS), which emphasized aggressive recruitment of collapsed lung followed by low-stretch tidal ventilation and minimizing shear injury by applying sufficient levels of PEEP.1 Early studies on RM produced mixed results in terms of gas exchange and chest mechanics, explained by different approaches to RM as well as patient selection criteria.

Over the past two decades, investigators have produced more than 120 publications studying the nature and prevalence of shear-related lung injury in ARDS and its response to RMs and higher PEEP levels. It has become increasingly apparent that repetitive closure and reopening of peripheral airways (i.e., compliant collapse and formation/destruction of liquid bridges), along with de-recruitment/recruitment of alveoli, probably are a major source of ventilator-induced lung injury in severe ARDS. In turn, this may partly explain why mortality in severe ARDS remains stubbornly high (42-50%) despite great strides in reducing the effect of stretch-related injury.

Recently, a multicenter pilot study of 200 subjects compared lung-protective ventilation incorporating an RM (similar to that described above) along with a decremental PEEP trial to the ARDSNet low tidal volume protocol. The lung-protective approach that incorporated an RM showed significant improvement in oxygenation and lower elastic driving pressure over 72 hours of study. Although not significant, those randomized to the RM treatment group demonstrated a 14% lower hospital mortality rate and lower incidence of death attributed to progressive respiratory failure (12% vs. 33%).

Taken together, both studies are consistent with the conceptual approach first proposed by Lachmann. Both in ARDS and other conditions with similar mechanical derangements (i.e., severely reduced chest wall compliance), transient application of high plateau pressure is necessary to reopen collapsed lung tissue, along with sufficient PEEP to counteract superimposed compressive forces related to lung edema as well as reduced chest wall compliance. Emerging evidence over the past 15 years behooves us to re-examine the wisdom of adhering to the “least PEEP” philosophy that has guided clinical practice since the early 1980s.

REFERENCES

  1. Lachmann B. Open up the lung and keep the lung open. Intensive Care Med 1992;18:319-321.
  2. Bellani G, Laffey JG, Pham T, et al. Epidemiology, patterns of care and mortality for patients with acute respiratory distress syndrome in intensive care units in 50 countries. JAMA 2016;315:788-800.
  3. Kacmarek RM, Villar J, Sulemanji D, et al. Open lung approach for acute respiratory distress syndrome: A pilot, randomized controlled trial. Crit Care Med 2016;44:32-42.