Safer Suctioning with Pressure Support
Abstract & Commentary
In this study, the effect of endotracheal suctioning-induced alveolar derecruitment was studied. The study population consisted of 9 sedated and paralyzed patients with acute lung injury. Five endotracheal suction techniques were compared in random order in each patient, with at least 30 min between each: 1) suctioning after disconnection from the ventilator; 2) suctioning without disconnection, introducing the suction catheter through the swivel adapter of the catheter mount; 3) suctioning with a closed suctioning system; 4) suctioning through the swivel adapter while triggering pressure-supported breaths at a peak inspiratory pressure of 40 cm H2O; and 5) suctioning with a closed suction catheter while triggering pressure support at a peak inspiratory pressure of 40 cm H2O during suctioning.
Trigger pressure on the ventilator was set at -1 cm H2O during pressure support. The suction catheter (14 French) was inserted into the airway until resistance was met and then pulled back 2 cm. Intermittent suctioning was started while the catheter was gradually removed. Each suctioning maneuver lasted 25-30 s. Negative pressure was set at -200 cm H2O (150 mm Hg). Changes in end-expiratory lung volume were measured by inductive plethysmography. The end-expiratory lung volume change was calculated as the difference between the volumes measured at the end of expiration just before and at the end of each suctioning procedure. SpO2 changes were calculated as the difference between the value before suctioning and the minimum value recorded up to 1 min after each suctioning procedure.
End-expiratory lung volume after disconnection fell more than with the other techniques (-1466 ± 586, -733 ± 406, -531 ± 228, -168 ± 176, and -284 ± 317 mL after disconnection, through the swivel adapter, with the closed system, and with the 2 latter techniques and pressure support, respectively, P < 0.001). Recruitment decreased after disconnection and using the swivel adapter (-104 ± 31 and -63 ± 25 mL, respectively) was unchanged with the closed system (-1 ± 10 mL) and increased when using pressure support during suctioning (71 ± 37 and 60 ± 30 mL) (P < 0.001). Oxygenation paralleled lung volume changes. Maggiore and colleagues concluded that suctioning-induced alveolar derecruitment in acute lung injury can be minimized avoiding disconnection prevented by using pressure support at a peak inspiratory pressure of 40 cm H2O, which serves as a recruitment maneuver during suctioning. (Maggiore SM, et al. Am J Respir Crit Care Med. 2003;167:1215-1224.)
Comment by Dean R. Hess, PhD, RRT
Endotracheal suctioning is a necessary component of the care of mechanically ventilated patients. However, it is associated with complications, the most common of which is hypoxemia. Suction-related hypoxemia is likely related to alveolar derecruitment during the procedure in patients with acute lung injury. Cereda and associates previously reported that lung volume changes during suctioning can be ameliorated by use of closed suction.1 Until recently, a focus of closed suction technique has been the avoidance of suction-related hypoxemia. However, suction-related hypoxemia may be the symptom of larger issue. Indeed, hypoxemia resulting from suctioning can often be avoided by simply increasing the FIO2 setting on the ventilator. It is now widely accepted that alveolar derecruitment and subsequent rerecruitment (closing and re-opening) is a form of ventilator-induced lung injury. Thus, avoiding derecruitment (and associated hypoxemia) during suctioning should be considered part of a lung-protective ventilation strategy. In fact, I routinely use closed suction in mechanically ventilated patients with acute lung injury.
In this study, alveolar derecruitment was essentially eliminated if pressure support at a peak inspiratory pressure of 40 cm H2O was used in conjunction with closed suction. With this clever technique, the ventilator is triggered when suction is applied and a pressure of 40 cm H2O is applied for the duration of the suction maneuver. This achieves at least 3 potentially beneficial effects. First, positive end-expiratory pressure is not removed because the patient is not disconnected from the ventilator. Second, the ventilator servo-controls flow to maintain a constant airway pressure during pressure support (or pressure control). Thus, the application of suction aspirates flow (and volume) from the ventilator circuit (which is immediately replenished) rather than from the distal lung. This has been previously demonstrated in my laboratory.2 Third, the application of 40 cm H2O to the proximal airway serves as a recruitment maneuver during the suction procedure. One might envision the suction procedure removing airway plugging and the 40 cm H2O recruiting collapsed alveoli distal to the previously obstructed airway. Although this technique was studied during a routine suction maneuver in this study, it begs the question of whether such a maneuver might also be beneficial during bronchoscopy.
This study provides additional evidence of the benefits of closed suction catheter use. Another benefit related to the use of a closed suction technique is a decreased risk of nosocomial pneumonia, and this should be considered part of a strategy to reduce the incidence of ventilator-associated pneumonia.3 However, there remains considerable resistance among some clinicians to the use of closed suction catheters. It has been argued that closed suction is less effective at removal of secretions than open suction, but this has been reported not to be true.4 Some have cited the cost of closed suction catheters as an obstacle to their use. However, these catheters do not need to be changed daily (as recommended by the manufacturer), which considerably reduces the cost related to their use.3
This well-done study provides strong evidence to support the use of closed suction in patients with acute lung injury.
Dr. Hess is Assistant Professor of Anesthesia, Harvard Medical School; Assistant Director of Respiratory Care, Massachusetts General Hospital, Cambridge, MA.
1. Cereda M, et al. Intensive Care Med. 2001;27:648-654.
2. Hess DR, et al. Respir Care. 2003;48:869-879.
3. Wong SY, et al. Respir Care. 2001;46:1070.
4. Witmer MA, et al. Respir Care. 1991;36:844-848.