Anesth Analg 2008; 107:941-944
© 2008 International Anesthesia Research Society
doi: 10.1213/ane.0b013e3181804a5d
CRITICAL CARE AND TRAUMA
Functional Residual Capacity Changes After Different Endotracheal Suctioning Methods
Hermann Heinze, MD,
Beate Sedemund-Adib, MD,
Matthias Heringlake, MD,
Ulrich W. Gosch, MD, and
Wolfgang Eichler, MD
From the Department of Anesthesiology, University of Luebeck, Luebeck, Germany.
Address correspondence to Dr. Hermann Heinze, Department of Anesthesiology, University of Luebeck, Ratzeburger Allee 160, 23538 Luebeck, Germany. Address e-mail to Hermann.heinze{at}uk-sh.de.
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Abstract
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BACKGROUND: Our primary objective was to investigate the effects of three different endotracheal suctioning procedures on functional residual capacity (FRC).
METHODS: Using a crossover design, postoperative cardiac surgery patients (n = 20) received three different suctioning methods in randomized order: closed suctioning during pressure-controlled ventilation, closed suctioning during volume-controlled ventilation, and open suctioning. FRC was measured before and 20 min after the intervention.
RESULTS AND CONCLUSIONS: FRC is reduced in postcardiac surgery patients after suctioning, regardless of which method is used. Certain patients may have very pronounced changes of FRC. Routine FRC measurements could complement respiratory monitoring to optimize respiratory therapy.
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Introduction
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Endotracheal suctioning (ETS), a common procedure during mechanical ventilation, may counteract the open lung concept.1 Closed suctioning (CS) systems were therefore introduced, and have been shown to prevent lung volume loss during suctioning in acute lung injury.2–4 However, CS during volume-controlled ventilation (CS-VCV) may be dangerous because of a risk of high intrinsic positive end-expiratory pressure (PEEP) levels at insertion of the catheter and extreme negative pressures during suctioning, effects that are less pronounced when CS is used with pressure-controlled ventilation (CS-PCV).5 Nevertheless, CS-VCV seems to be clinically established and widely accepted.2–4,6
The primary objective of our study was to investigate the effects of three different ETS procedures: CS-PCV, CS-VCV, and open suctioning (OS) on functional residual capacity (FRC).
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METHODS
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After obtaining approval from the local ethics committee and written informed consent from patients, we studied 20 postoperative cardiac surgery patients. All patients' lungs were mechanically ventilated (inner diameter 7.5 mm [women] and 8 mm [men]) after transfer to the intensive care unit.
A crossover design was used. The patients received three different suctioning maneuvers in randomized order: CS-PCV, CS-VCV, and OS. During OS, the patients were disconnected from the ventilator. The 14F suctioning catheter was inserted into the endotracheal tube, advanced until resistance was met, and withdrawn 2–3 cm. Negative pressure of 200 cm H2O was applied for 20 s. The patients were then reconnected to the ventilator. During the CS procedures, patients remained connected to the ventilator. A CS system (Size 14F, Kendall Comp., Mansfield, USA) was used. The ETS maneuver was the same as that applied during OS.
Before the start of the study protocol, a standardized recruitment maneuver was applied to the patients' lungs (PEEP 15 cm H2O, positive inspiratory pressure 35–40 cm H2O for 30 s) and the patients were allowed to stabilize hemodynamically for 10 min. Respiratory settings were as follows: tidal volume (VT) 6–8 mL/kg predicted body weight; PEEP 10 cm H2O; I:E 1:1. Respiratory rate was adjusted to achieve normocapnia.
FRC was measured at baseline. At the end of the FRC measurement, the mean value of compliance of the respiratory tract during continuing ventilation of the last 10 breaths (Crs) (VT divided by the pressure difference between plateau pressure and PEEP) and Vt were obtained, and ETS was started. After ETS, each patient was allowed to stabilize for 10 min before another FRC measurement was started. Again, respiratory variables were obtained in the same fashion. Arterial blood gases were obtained right before ETS (baseline) and 20 min after ETS (post ETS). After each measuring interval, the standardized recruitment maneuver was used again.
FRC Measurement
The LUFU system ("lung function," Draeger Medical, Luebeck, Germany) estimates FRC by oxygen wash-in or washout, a variant of multiple breath nitrogen washout7,8 using a step change of oxygen of 0.2.9 The mean of one wash-in and one washout was calculated.10
Statistics
Values obtained were normalized to the baseline value to compare changes over time. Normal distribution was checked by the Kolmogorov–Smirnow test. The one-factorial ANOVA with post hoc unpaired t-test or the nonparametric Kruskal–Wallis tests with Mann–Whitney U-test were used, where appropriate. Changes between the time-points were analyzed within each group using the paired t-test or Wilcoxon's signed rank test. All data are presented as mean ± sd for normally distributed data or median ± quartiles for non-normally distributed data, unless stated otherwise.
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RESULTS
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Twenty postoperative cardiac surgery patients were studied. Patients' characteristics are summarized in Table 1.
Absolute FRC values were reduced 20 min after suctioning, regardless of which method was used (Table 2), although this did not reach significance in group OS (P = 0.060). A reduction of relative FRC values after ETS compared with baseline was detected in group CS-VCV to 94.7% ± 9.8% (P = 0.026). The reductions in groups CS-PCV (to 95.8% ± 9%; P = 0.053) and OS (to 92.4% ± 21.2%; P = 0.127) did not reach significance (Fig. 1).
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Figure 1. Relative changes of the functional residual capacity after endotracheal suctioning. FRC, functional residual capacity; CS-PCV, closed suctioning with pressure-controlled ventilation; CS-VCV, closed suctioning with volume-controlled ventilation; OS, open suctioning. Data are presented as mean ± sd. *P < 0.05 compared with baseline.
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The patients' individual courses of FRC changes after the three suctioning maneuvers are shown in Figure 2. A large intra- and interindividual variability can be seen, with some patients showing no changes, and others showing a large FRC reduction after suctioning. Absolute values of Crs decreased after all three suctioning maneuvers. Vt remained stable during CS-VCV, but decreased after CS-PCV and OS compared with baseline (Table 2).
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Figure 2. Individual relative changes of the functional residual capacity after endotracheal suctioning. CS-PCV, closed suctioning with pressure-controlled ventilation; CS-VCV, closed suctioning with volume-controlled ventilation; OS, open suctioning; Baseline, before suctioning; post ETS, 20 min after suctioning.
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DISCUSSION
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This is the first study dealing with FRC changes after OS and CS with different ventilatory modes after cardiac surgery in humans. We demonstrated that FRC is reduced after ETS, regardless of which suctioning method is used. Certain patients may have very pronounced changes of FRC.
Previous studies have demonstrated a marked reduction of lung volume and decrease of arterial oxygenation after open ETS.2–4,6,11–13 Our data support this view. CS systems have been shown to cause fewer disturbances to lung volume and oxygenation.2–4,6,11,12,14 This difference between our study and others may be explained by the different patient populations, as well as by differences in suctioning catheter and respiratory tube sizes, suctioning pressures, and duration of suctioning. Although the mean values of lung volume or oxygenation did not change in most studies, CS may produce decreases in these variables in certain patients.6,15
FRC changes should be interpreted cautiously, as airway collapse with gas trapping could under-estimate true FRC.16 In addition, a FRC decrease may not only be caused by collapse of lung regions, but also by a decrease in the number of over-inflated alveoli.16 Unfortunately, we did not measure Crs continuously.17 Continuous measurement could differentiate between collapsed alveoli and over-inflation and describe how profound the effects of ETS are on lung mechanics directly after suctioning.15 Because of the long duration of measurements, FRC monitoring may only reveal the late impact of ETS on lung volume. Continuous measurement of oxygen saturation detects only very profound changes of aerated lung tissue, especially during ventilation with high Fio2,18 but misses less pronounced, but nevertheless relevant, changes of lung volume.19
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CLINICAL IMPLICATIONS
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The individual responses of the patients after ETS indicate that routine estimation of FRC in ventilated patients may be useful and should be interpreted in conjunction with other variables, such as Crs and oxygenation. In this way, patients who could benefit from a recruitment maneuver to avoid lung collapse after ETS would be identified, and the possible negative side effects of such a maneuver20 could be avoided in others.
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ACKNOWLEDGMENTS
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The authors thank Dr. Dieter Weismann for his technical support and Draeger Medical, Luebeck, Germany, for providing the LUFU system.
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Footnotes
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Accepted for publication May 1, 2008.
Reprints will not be available from the author.
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REFERENCES
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Abstract
Introduction
