2001 OPEN FORUM Abstracts
A BENCH EVALUATION OF ALVEOLAR PRESSURE CHANGES DURING ENDOTRACHEAL SUCTION.
Steve Y. Wong, MD, Guilherme Schettino, MD, Robert Kacmarek PhD RRT FAARC, Dean Hess PhD RRT FAARC. Massachusetts General Hospital and Harvard Medical School, Boston MA.
Closed suction may avoid alveolar derecruitment (Intensive Care Med 2001; 27:648). However, one study reported negative airway pressures using this procedure (Acta Anaesthesiol Scand 2001;45:167), which we reasoned may result from inadequate ventilator flow to replenish that withdrawn by the suction catheter. We studied the relationship between alveolar pressure and ventilator modes during open and closed suctioning.
Method: A Michigan Instruments TTL simulated a resistance of 5 cm H2O/L/s and compliance of 40 mL/cm H2O (C40/R5), or a resistance of 20 cm H2O/L/s and compliance of 80 mL/cm H2O (C80/R20). An 8 mm endotracheal tube size was used. A Puritan-Bennett 7200 ventilator was used with volume control at a flow of 30 L/min (VCV 30), volume control at 60 L/min (VCV 60), or pressure control (PCV). A VT of 500 mL and rate of 15/min were used (I:E ratio 1:3 for PCV). Trigger sensitivity was ?1 cm H2O or flow trigger of 3 L/min (base flow 10 L/min or 20 L/min). PEEP of 5 and 10 cm H2O were used. Experiments were performed with a 14 French catheter (Ballard Trach Care), which was advanced to the distal end of the endotracheal tube. Suction pressure of 120 mm Hg or 180 mm Hg was applied for 10 s. Pressure was recorded from the entrance to the bellows (Ventrak). The experiment was also performed with the ventilator Y-piece disconnected from the inline suction catheter to simulate open suctioning. Pressure drop below PEEP was measured post-hoc from the pressure waveform.
Results: During closed suction, the pressure drop below the set PEEP in the bellows was not affected significantly by PEEP level (P=0.32), trigger method (P=0.51), or suction pressure (P=0.31). Pressure drop was significantly affected by resistance/compliance setting (P<0.001) and flow setting (P<0.001) as shown in the figure below. With open suction, the pressure drop was ?8 cm H2O.
Conclusions: When flow from the ventilator was adequate (PCV or VCV 60), alveolar pressure drop below PEEP was small. When PEEP is used, this should rarely result in sub-atmospheric pressure in the lung. When open suction is used, which results in no PEEP, the alveolar pressure drop is always sub-ambient. These data suggest that closed suction may useful as a technique to avoid alveolar derecruitment during the suction procedure.