American Journal of Respiratory and Critical Care Medicine

We studied endotracheal suctioning-induced alveolar derecruitment and its prevention in nine patients with acute lung injury. Changes in end-expiratory lung volume measured by inductive plethysmography, positive end-expiratory pressure-induced alveolar recruitment assessed by pressure–volume curves, oxygen saturation, and respiratory mechanics were recorded. Suctioning was performed after disconnection from the ventilator, through the swivel adapter of the catheter mount, with a closed system, and with the two latter techniques while performing recruitment maneuvers during suctioning (40 cm H2O pressure-supported breaths). End-expiratory lung volume after disconnection fell more than with all other techniques (−1,466 ± 586, −733 ± 406, −531 ± 228, −168 ± 176, and −284 ± 317 ml after disconnection, through the swivel adapter, with the closed system, and with the two latter techniques with pressure-supported breaths, respectively, p < 0.001), and was not fully recovered 1 minute after suctioning. 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 performing recruitment maneuvers during suctioning (71 ± 37 and 60 ± 30 ml) (p < 0.001). Changes in alveolar recruitment correlated with changes in lung volume (ρ = 0.88, p < 0.001) and compliance (ρ = 0.9, p < 0.001). Oxygenation paralleled lung volume changes. Suctioning-induced lung derecruitment in acute lung injury can be prevented by performing recruitment maneuvers during suctioning and minimized by avoiding disconnection.

It has been suggested that ventilator-associated lung injury can be caused by high transpulmonary pressures at the end of inspiration and/or insufficient recruitment at the end of expiration, in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) (1). Preventing alveolar overdistension and derecruitment are the goals of more recently proposed protective ventilatory strategies. In this context, the periodic derecruitment induced by endotracheal suctioning could be harmful in patients with ALI/ARDS. In addition, the application of a subatmospheric pressure generates alveolar injury in cases of surfactant dysfunction (2). Most of the studies on endotracheal suctioning have concentrated on reversing or preventing hypoxemia resulting from such a procedure. Few data exist about the effect of endotracheal suctioning on lung volumes (35), and no study has assessed the consequences of suctioning on alveolar recruitment in ALI/ARDS. In patients with various etiologies of acute respiratory failure, Brochard and coworkers demonstrated that one major mechanism causing hypoxemia during suctioning was the decrease in lung volume induced by the loss of positive alveolar pressure. This phenomenon could be prevented by the use of continuous oxygen insufflation via a special endotracheal tube generating a positive pressure during suctioning (3). The need to use a modified endotracheal tube, however, limits the clinical application of this technique. Cereda and coworkers reported that using a closed suctioning system allowed partial prevention of the fall in end-expiratory lung volume and hypoxemia observed when endotracheal suctioning was performed after disconnection from the ventilator, in patients with ALI (4). The effect of the closed system on the recruitment induced by positive end-expiratory pressure (PEEP) was not studied. Lu and coworkers have shown that a recruitment maneuver performed after endotracheal suctioning could reverse atelectasis resulting from such a procedure, in an animal model (5). However, the prevention of the endotracheal suctioning-related lung volume loss could be more clinically relevant (6, 7). In addition, whether better prevention could be obtained by the use of special maneuvers during suctioning needed to be studied.

The aims of our study were (1) to assess the magnitude of lung volume fall during endotracheal suctioning and to determine the respective roles of PEEP loss and negative pressure, (2) to assess the impact of endotracheal suctioning performed with different techniques on alveolar recruitment/derecruitment in patients with ALI/ARDS, and (3) to try to prevent derecruitment by performing a special recruitment maneuver during endotracheal suctioning. We hypothesized that such a maneuver could prevent alveolar derecruitment and the decrease in oxygenation. The effect of different suctioning techniques on lung volumes, alveolar recruitment/derecruitment, arterial oxygenation and respiratory mechanics was assessed and compared in nine patients with ALI/ARDS.

Patients

The local institutional ethics committee approved the protocol. Written informed consent was obtained from the patients' next of kin. Patients fulfilling criteria for ALI/ARDS (8) were eligible. Patients were not included in case of a leaking chest tube, contraindication to sedation or paralysis, and respiratory or hemodynamic instability over the last 6 hours. Nine patients were studied (Table 1)

TABLE 1. General characteristics of the patients


Patient No.

Age
 (yr)

Cause of ALI/ARDS

Underlying Disease

PaO2/FIO2
 (mm Hg)

PEEPext
 (cm H2O)

PEEPi
 (cm H2O)

FIO2

LIS

Days of Mechanical
 Ventilation

Days of
 ALI/ARDS

Outcome
132Acute pancreatitisNephrotic syndrome93102.11.003.25222Died
277Alveolar hemorrhageAortic stenosis180104.51.002.5033Survived
357PneumoniaDiabetes75132.61.003.0011Survived
476PneumoniaAortic stenosis226122.50.502.5088Survived
538Subarachnoid hemorrhageViral hepatitis190101.90.502.7511Survived
655Massive blood transfusionAortic aneurysm176163.10.503.0022Survived
735SepsisAcute lymphoid leukemia100141.80.603.50118Died
846PneumoniaAlcoholism92124.61.003.5044Died
957PneumoniaRenal cancer157123.40.702.7533Survived
Mean531431230.752.9764
SD
17


54
2
1
0.24
0.38
7
3

Definition of abbreviations: ALI = acute lung injury; ARDS = acute respiratory distress syndrome; LIS = lung injury score; PEEPext = external positive end-expiratory pressure; PEEPi = intrinsic positive end-expiratory pressure.

.

Patients were sedated, paralyzed, and mechanically ventilated in volume-controlled mode. All had an 8.0-mm endotracheal tube. Tidal volume was 6–8 ml · kg−1, respiratory rate was 18–25 per minute−1, and PEEP was chosen by the attending physician. The inspired oxygen concentration was set to have a pulse-oximeter oxygen saturation (SpO2) of 92% or more.

Measurements

Changes in end-expiratory lung volume were measured by inductive plethysmography, as previously described (9). 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 (Figure 1)

. Lung volume change was also measured after suctioning, at the first breath after resuming baseline ventilation, and after 1 minute, before elastic pressure–volume (Pel–V) curve recording.

Pel–V curves from PEEP and from the static equilibrium volume at zero end-expiratory pressure (ZEEP) were acquired before and 1 minute after each suctioning procedure, using the low sinusoidal flow technique, as described (10, 11). Linear compliance at ZEEP and PEEP-related alveolar recruitment/derecruitment at the elastic pressure of 20 cm H2O were measured (1015).

SpO2 changes were calculated as the difference between the value before suctioning and the minimum value recorded up to 1 minute after each suctioning procedure.

Signals were recorded and stored in a computer for subsequent analysis.

Details on measurement of end-expiratory lung volume, Pel–V curve, alveolar recruitment, airway pressures, and respiratory resistance are given in the online supplement.

Protocol

(For details, see the online supplement.) A flowchart of protocol and measurements is shown in Figure 2

. Endotracheal suctioning was performed:
  1. After disconnection from the ventilator (DISCONNECTION)

  2. Without disconnection, introducing the suction catheter through the swivel adapter of the catheter mount (SWIVEL)

  3. With a closed suctioning system (CLOSED) (Hi-Care; Mallinckrodt DAR-Tyco Healthcare Group, Mirandola, Italy)

  4. During SWIVEL, while triggering pressure-supported breaths at a peak inspiratory pressure of 40 cm H2O during suctioning (SWIVELPSV)

  5. During CLOSED, while triggering 40 cm H2O pressure-supported breaths during suctioning (CLOSEDPSV) (Figure 1)

Trigger function was inhibited during Procedures 1 to 3 and was set at −1 cm H2O during Phases 4 and 5. Suctioning techniques were performed in random order and were separated by at least 30 minutes. The suction catheter (Fr 14) was inserted into the airways 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 seconds. Negative pressure was set at −200 cm H2O.

Statistical Analysis

Results are reported as means ± SD. Comparison of suctioning techniques was made by analysis of variance (Friedman test), and two-by-two comparisons were made using the Wilcoxon test for paired samples. Regression analysis (Spearman ρ) was used when required. p < 0.05 was considered statistically significant.

End-expiratory Lung Volume

Data are shown in Figures 1 and 3

, and Table 2

TABLE 2. Individual values of change in end-expiratory lung volume during and just after endotracheal suctioning, with the studied suctioning technique



ΔEELV during Suctioning (ml)

ΔEELV Just after Suctioning (One Breath) (ml)
Patient No.
DISCONNECTION
SWIVEL
CLOSED
SWIVELPSV
CLOSEDPSV
DISCONNECTION
SWIVEL
CLOSED
SWIVELPSV
CLOSEDPSV
1−1,416−666−502−213−213−1,114−115−96 42−154
2−884−276−222−106−46−578−40−80142100
3−1,962−1,155−833−115−157−1,280−95−169 4 31
4−1,452−839−705−471−841−1,067−260 73−301 2
5−571−466−295 15−141−556−230−83153−76
6−1,846−1,195−553−442−789−1,325−491−299−79−130
7−843−394−693−112−9−671−168−190−11 19
8−2,092−1,307−253−26−31−1,921−1,017−102 51 65
9−2,124−301−726−47−325−1,530−70−155 65−5
Mean−1,466−733*−531*−168*,,−284*,§,−1,116−276*−122* 7*,§−16*,§,
SD
586
406
228
176
317
460
310
101
136
86

* p < 0.01, compared with DISCONNECTION.

p < 0.01, compared with SWIVEL.

p < 0.01, compared with CLOSED.

§ p < 0.05, compared with SWIVEL.

p < 0.05, compared with CLOSED.

p = 0.05, compared with CLOSED.

Definitions of abbreviations: DISCONNECTION = endotracheal suctioning performed after the disconnection from the ventilator; CLOSED = endotracheal suctioning with the closed system; CLOSEDPSV = endotracheal suctioning performed with the closed system, while triggering pressure-supported breaths during suctioning; ΔEELV = change in end-expiratory lung volume; SWIVEL = endotracheal suctioning performed through the swivel adapter of the catheter mount; SWIVELPSV = endotracheal suctioning performed through the swivel adapter of the catheter mount, while triggering pressure-supported breaths during suctioning.

. End-expiratory lung volume decreased during endotracheal suctioning, whatever the technique used. The largest end-expiratory lung volume fall was observed with DISCONNECTION, and it was significantly different from SWIVEL and CLOSED (−1466 ± 586, −733 ± 406, and −531 ± 228 ml, respectively, p < 0.001). The drop in end-expiratory lung volume during suctioning was minimal with SWIVELPSV and CLOSEDPSV (−168 ± 176 and −284 ± 317 ml, respectively, p = NS), and significantly smaller (p < 0.001) than with the three other techniques without pressure-supported breaths. When suctioning was performed with DISCONNECTION, the simple disconnection from the ventilator and the application of negative pressure contributed equally to the total end-expiratory lung volume drop (728 ± 377 and 737 ± 383 ml, respectively). However, large variations existed in the individual patients: in some patients, disconnection alone contributed the most whereas, in others, suctioning was the main determinant of the total loss of lung volume (Figure 1). A correlation between the level of external PEEP and the fall in lung volume observed after disconnecting patients from the ventilator, before suctioning, was found: the higher the external PEEP, the higher the lung volume drop observed after disconnection alone, before applying the negative pressure (ρ = 0.7, p < 0.05). One breath after resuming normal ventilation, the residual lung volume loss was still large after DISCONNECTION, whereas it was minimal after SWIVEL and CLOSED (−1116 ± 460, −276 ± 310 and −122 ± 101 ml, respectively, p < 0.001). One breath after SWIVELPSV and CLOSEDPSV, the minimal drop in end-expiratory lung volume observed during endotracheal suctioning was completely recovered (7 ± 136 and −16 ± 86 ml, respectively, p < 0.001 compared with the other techniques). One minute after endotracheal suctioning, just before Pel–V curves recording, the end-expiratory lung volume was still not fully recovered with DISCONNECTION, whereas it was almost totally restored with both SWIVEL and CLOSED and increased with both SWIVELPSV and CLOSEDPSV (−278 ± 239, −89 ± 58, −44 ± 53, 93 ± 53, and 64 ± 38 ml, respectively, p < 0.001).

PEEP-induced Alveolar Recruitment

Pressure–volume curves obtained from ZEEP and from PEEP and the quantification of alveolar recruitment, before and after the different suctioning techniques, in a representative patient (Patient 4) are shown in Figure 4

.

PEEP-induced alveolar recruitment decreased in all patients 1 minute after endotracheal suctioning with both DISCONNECTION and SWIVEL (239 ± 114 ml before versus 135 ± 101 ml after suctioning with DISCONNECTION, p < 0.01, and 236 ± 111 versus 173 ± 92 ml with SWIVEL, p < 0.01) (Figure 5)

. Alveolar recruitment did not change after endotracheal suctioning performed with a closed system (233 ± 114 ml before versus 232 ± 113 ml after suctioning, p = NS), whereas it increased when endotracheal suctioning was performed while triggering pressure-supported breaths (232 ± 110 ml before versus 303 ± 108 ml after suctioning with SWIVELPSV, p < 0.01, and 233 ± 110 versus 294 ± 109 ml with CLOSEDPSV, p < 0.01) (Figure 5). The changes in alveolar recruitment correlated with the end-expiratory lung volume variations observed during endotracheal suctioning (ρ = 0.68, p < 0.001), one breath after suctioning (ρ = 0.75, p < 0.001), and 1 minute after suctioning (ρ = 0.88, p < 0.001) (Figure 6) .

Arterial Oxygen Saturation

Data on arterial oxygen saturation were not available for Patient 2. In eight patients, SpO2 values before the different suctioning techniques were identical (96.1 ± 2.8, 96.2 ± 2.9, 95.7 ± 2.2, 96.2 ± 2.7, and 96.1 ± 2.2% before DISCONNECTION, SWIVEL, CLOSED, SWIVELPSV, and CLOSEDPSV, respectively, p = NS). As shown in Figure 7

, SpO2 decreased with all the techniques used. However, the drop in SpO2 was much greater when endotracheal suctioning was performed after the disconnection from the ventilator than with all the other techniques (−9.2 ± 7.6, −1.7 ± 0.9, −2.2 ± 2.7, −1.5 ± 0.6, and −1.3 ± 0.6% with DISCONNECTION, SWIVEL, CLOSED, SWIVELPSV, and CLOSEDPSV, respectively, p < 0.01). The decrease in SpO2 correlated with the changes in alveolar recruitment (ρ = 0.44, p < 0.01) and the changes in end-expiratory lung volume during endotracheal suctioning (ρ = 0.43, p < 0.01), one breath after suctioning (ρ = 0.53, p < 0.001) and 1 minute after endotracheal suctioning (ρ = 0.46, p < 0.01).

Respiratory System Mechanics

Pressure at the lower inflection point of the Pel–V curve from ZEEP decreased, albeit not significantly, after DISCONNECTION (p = 0.06), it did not change after SWIVEL and CLOSED, whereas it increased significantly after SWIVELPSV (p < 0.05) and tended to increase after CLOSEDPSV (p = 0.06) (see Table 3

TABLE 3. Changes in pressure–volume curve from zero end-expiratory pressure and respiratory mechanics with the different endotracheal suctioning techniques



DISCONNECTION

SWIVEL

CLOSED

SWIVELPSV

CLOSEDPSV

Before
After
Before
After
Before
After
Before
After
Before
After
Plip, cm H2O13.5 ± 312.5 ± 2.412.9 ± 3.313.1 ± 3.214.6 ± 2.814.1 ± 1.713.1 ± 3.116 ± 2.7*14.1 ± 3.616 ± 3
Vlip, ml241 ± 171152 ± 83208 ± 126201 ± 131280 ± 202209 ± 146196 ± 111356 ± 210*257 ± 173297 ± 173
C1, ml/cm H2O28.1 ± 15.921 ± 7.1*25.7 ± 11.226.6 ± 11.328.9 ± 18.123.8 ± 15.824.9 ± 8.836.3 ± 23.8*26.7 ± 14.228.6 ± 16
Clin, ml/cm H2O71.1 ± 23.165.5 ± 20.770.6 ± 19.165.9 ± 18.168.3 ± 19.368 ± 19.667.9 ± 20.875.5 ± 22.767.6 ± 20.472.8 ± 22
Ppeak, cm H2O32.8 ± 3.834 ± 4.532.9 ± 434.2 ± 5.432.8 ± 3.732.3 ± 3.233 ± 3.731 ± 3.432.7 ± 3.830.7 ± 3.8
Pplat, cm H2O26.6 ± 426.9 ± 3.626.7 ± 3.926.6 ± 4.826.7 ± 3.625.9 ± 3*26.8 ± 425.2 ± 3.8*27 ± 3.925.1 ± 3.9
Rrs, cm H2O · L−1 · s−1
10.2 ± 1.4
11.9 ± 3.5*
10.3 ± 1.6
12.6 ± 3*
9.8 ± 2.2
10.5 ± 2.3
10.3 ± 1.2
9.6 ± 2.1
9.2 ± 2
9.2 ± 2.1

* p < 0.05, compared with before suctioning.

p < 0.01, compared with before suctioning.

Definitions of abbreviations: C1 = compliance of the first part of the pressure–volume curve from zero end-expiratory pressure, below the lower inflection point; Clin = compliance of the linear segment of the pressure–volume curve from zero end-expiratory pressure, above the lower inflection point; CLOSED = endotracheal suctioning performed with the closed system; CLOSEDPSV = endotracheal suctioning performed with the closed system, while triggering pressure-supported breaths during suctioning; DISCONNECTION = endotracheal suctioning performed after the disconnection from the ventilator; Plip = pressure at the lower inflection point of the pressure–volume curve from zero end-expiratory pressure; Ppeak = peak airway pressure; Pplat = end-inspiratory plateau pressure; Rrs = total respiratory resistance; SWIVEL = endotracheal suctioning performed through the swivel adapter of the catheter mount; SWIVELPSV = endotracheal suctioning performed through the swivel adapter of the catheter mount, while triggering pressure-supported breaths during suctioning; Vlip = volume at the lower inflection point of the pressure–volume curve from zero end-expiratory pressure.

and the online supplement). Similarly, the volume at the lower inflection point of the Pel–V curve from ZEEP tended to decrease after DISCONNECTION (p = 0.06) and increased significantly after SWIVELPSV (p < 0.05), whereas it did not change with the other techniques (see Table 3 and the online data supplement).

Compliance of the first segment of the pressure–volume curve from ZEEP, below the lower inflection point, decreased significantly after DISCONNECTION (p < 0.05). It increased after SWIVELPSV (p < 0.05), whereas it did not change with the other techniques (see Table 3 and the online data supplement). Compliance of the linear segment of the Pel–V curve from ZEEP, above the lower inflection point, decreased after both DISCONNECTION (p < 0.01) and SWIVEL (p < 0.01), whereas it did not change after CLOSED, and even increased when endotracheal suctioning was performed while triggering pressure-supported breaths (p < 0.01) (see Table 3 and the online data supplement). The changes in linear compliance correlated with the changes in end-expiratory lung volume 1 minute after endotracheal suctioning (ρ = 0.84, p < 0.001), with the changes in alveolar recruitment (ρ = 0.90, p < 0.001) (Figure 8)

, and with the changes in oxygen saturation (ρ = 0.47, p < 0.01).

Peak airway pressure increased, albeit not significantly, after DISCONNECTION and SWIVEL. It did not change with CLOSED, and decreased significantly after SWIVELPSV and CLOSEDPSV (p < 0.01) (Table 3).

End-inspiratory plateau pressure decreased significantly after CLOSED (p < 0.05), SWIVELPSV (p < 0.05), and CLOSEDPSV (p < 0.01), whereas it did not change with the other techniques (Table 3).

Total respiratory resistance increased significantly after DISCONNECTION (p < 0.05) and SWIVEL (p < 0.05), suggesting that endotracheal suctioning could have induced bronchoconstriction. It tended to increase with CLOSED (p = 0.06), whereas it did not change after SWIVELPSV and CLOSEDPSV (Table 3).

The main results of this study can be summarized as follows: (1) the drop in lung volume observed during endotracheal suctioning resulted from both the loss of PEEP and the application of a negative pressure; (2) avoiding disconnection during suctioning partially avoided a large fall in lung volume, whereas performing a recruitment maneuver during suctioning fully prevented a lung volume drop; (3) PEEP-induced recruitment decreased with any suctioning techniques requiring the opening of ventilator circuit, but could be preserved by using a closed system, and increased when performing a recruitment maneuver during suctioning; (4) changes in arterial oxygen saturation paralleled changes in end-expiratory lung volume, and oxygen saturation was virtually unaffected by endotracheal suctioning when the drop in lung volume was avoided; and (5) endotracheal suctioning-induced increase in airway resistance was small and fully prevented by performing a recruitment maneuver during suctioning.

Endotracheal Suctioning-induced Changes in End-Expiratory Lung Volume

Endotracheal suctioning performed after disconnection from the ventilator may induce a large lung volume drop and alveolar collapse, particularly in patients with ALI/ARDS ventilated with PEEP (4, 16). Indeed, endotracheal suctioning with disconnection induced almost 1.5-L volume loss (Figures 1 and 3), similarly to the findings of Cereda and coworkers (4) in patients with ALI/ARDS ventilated with comparable levels of PEEP (about 11 cm H2O, on average). Brochard and coworkers, working with patients (3), and Lu and coworkers, working with sheep (5), found a smaller decrease in lung volume when endotracheal suctioning was performed with disconnection from the ventilator (about 400 ml), partly because low levels of PEEP (5 cm H2O) or no PEEP was used. The large volume fall observed after disconnection, may suggest that PEEP could have produced some degree of alveolar overdistension (17). As well, disconnection may have allowed the exhalation of gas, which was previously trapped in the lung as a result of dynamic hyperinflation (1820). The fall in lung volume during endotracheal suctioning after ventilator circuit disconnection results both from the loss of the positive airway pressure generated by mechanical ventilation with PEEP, and from the negative pressure applied during suctioning (3, 5) (Figure 1). Interestingly, the lung volume fall due to the application of negative pressure alone, after disconnection, was identical to the drop in lung volume observed when suctioning was performed without disconnection, suggesting that avoiding disconnection from the ventilator allows the prevention of approximately 50% of the lung volume fall observed during suctioning after disconnection.

Performing endotracheal suctioning without disconnection from the ventilator, through the swivel adapter of the catheter mount and with a closed system, limited the lung volume fall but not to the full extent (Figures 1 and 3). This confirms that both loss of the positive airway pressure due to disconnection and application of a negative pressure are involved in the occurrence of alveolar collapse associated with endotracheal suctioning. This suggests that the use of a closed suctioning system could be recommended in patients ventilated with high PEEP levels, who are at greater risk of large lung volume fall during suctioning by conventional techniques.

The use of in-line suction catheters has been found effective in limiting or preventing endotracheal suctioning-induced hypoxemia and lung volume fall (4, 21, 22). We observed a decrease in end-expiratory lung volume with the closed-suction system, which was larger than previously reported by Cereda and coworkers in similar patients (4). In the latter study, however, the trigger sensitivity was set at −2 cm H2O and the ventilator was thus allowed to autocycle during suctioning with the closed system, whereas this phenomenon did not occur in our study. Ventilator autocycling during endotracheal suctioning could be efficient to compensate for some volume lost during suctioning and contribute to further prevent lung volume drop with the closed system, explaining the differences from the present study. This hypothesis is confirmed by the fact that SpO2 did not change during suctioning with the closed-suction system in the study by Cereda and coworkers, whereas we found a small SpO2 decrease (Figure 6). Our results showed the pure effect of the closed system use on lung volume during endotracheal suctioning, whereas the findings of Cereda and coworkers were the result of the combined effects of the closed-suction system and specific ventilatory settings. In fact, the effect of a closed-suction system on lung volume during suctioning may depend on the ventilatory mode and settings, the suctioning technique and duration, as well as the ratio between the diameters of the suction catheter and the endotracheal tube (2325).

Endotracheal Suctioning-induced Changes in Alveolar Recruitment

Changes in end-expiratory lung volume were measured together with true alveolar recruitment. Although mathematically coupled, changes in end-expiratory lung volume and recruitment are not equivalent (26). End-expiratory lung volume refers to PEEP-induced net increase in lung volume above the elastic equilibrium volume of the respiratory system at ZEEP. Alveolar recruitment is the amount of lung volume exceeding the volume increase predicted by the pressure–volume relationship at ZEEP (27). Indeed, alveolar recruitment expressed at 20 cm H2O, for instance, will vary with the amount of collapsed lung units that can be reopened by prolonged application of continuous positive airway pressure. One could imagine a situation in which the lung volume loss is regained at the expense of a few alveoli kept open and hyperinflated, while the more unstable alveoli cannot be reopened and remain closed. Therefore, in patients with large lung areas remaining open and normally aerated at ZEEP, endotracheal suctioning-induced changes in end-expiratory lung volume and alveolar recruitment might be quite different.

Several findings of the present study are consistent with the fact that the major abnormality encountered with endotracheal suctioning is the fall in lung volume (Figure 5), including the changes in compliance (3). These changes correlated with the changes in alveolar recruitment and with the drop in SpO2. The larger the endotracheal suctioning-induced fall in lung volume, the lower the short-term efficacy of PEEP to recruit collapsed alveoli after suctioning, and the larger the decrease in SpO2. Indeed, the effect of PEEP on alveolar recruitment is a time-dependent phenomenon and depends on how much of the lungs have been recruited during the previous ventilation, as reported (28).

Effect of Endotracheal Suctioning on Oxygen Saturation

We found that suctioning with the closed system and through the swivel adapter of the catheter mount were equally effective in limiting the large oxygen desaturation observed when endotracheal suctioning was performed while the patient was disconnected from the ventilator (Figure 6). Although SpO2 can sometimes poorly reflect the variations in arterial partial pressure of oxygen (29), it is largely used in the clinical setting to monitor mechanically ventilated patients (30). The correlations found between SpO2, alveolar recruitment and end-expiratory lung volume, although weak, tend to reinforce a causal relationship. Other mechanisms could explain the SpO2 drop observed even when lung volume was maintained. Suctioning could have induced hemodynamic changes, which, by modifying the ventilation/perfusion ratio, could explain the transient impairment in SpO2 even when lung volume was preserved. Another explanation could be that endotracheal suctioning-induced bronchoconstriction may result in an increase in venous admixture (5). We observed only a small increase in total respiratory system resistances after suctioning performed with disconnection, through the swivel adapter and with the closed system, whereas it did not change after the two techniques performed while triggering pressure-supported breaths. The small magnitude of these changes in the context of a decrease in lung volume makes it difficult to ascertain whether this corresponded to a true bronchoconstriction or to the effects of lung volume changes on respiratory system resistances. The increase in lung volume and alveolar recruitment observed when a recruitment maneuver was performed during suctioning counterbalanced the increase in total respiratory system resistances observed with the other techniques.

Effect of Endotracheal Suctioning on the Respiratory Pressure–Volume Curve

Endotracheal suctioning-induced changes in alveolar recruitment were strongly correlated with changes in linear compliance at ZEEP (Figure 7). In one study we found that linear compliance above the lower inflection point may reflect the amount of lung areas recruitable with PEEP (15). The tight relationship between suctioning-induced changes in alveolar recruitment and in linear compliance we found in the present study supports this idea. However, derecruitment caused by suctioning with ventilator disconnection was accompanied by a decrease in linear compliance. We have previously shown that derecruitment induced by decremental PEEP levels produced a progressive increase in linear compliance (15). In other terms, the more recruitable the lung during the pressure–volume curve maneuver at ZEEP, the higher the linear compliance. When PEEP is applied and the lung is recruited, there is less recruitable lung area and the linear compliance is lower. In the present study, the duration of suctioning maneuvers and the amount of lung collapse could explain the lower linear compliance observed after suctioning. In our previous study, the pressure–volume curve from ZEEP was recorded after a single 6-second expiration to the elastic equilibrium volume at ZEEP. The lung areas, which collapsed during this expiration, were completely reopened during the following large low-flow insufflation performed to record the pressure–volume curve. In this context, a high linear compliance at ZEEP indicated that the collapsed lung areas were recruited during the large insufflation and could be kept open with PEEP. In the present study, the duration of the suctioning procedure (30 seconds) and the large lung volume loss during suctioning could make the collapsed lung areas much more difficult to recruit during the subsequent pressure–volume curve maneuver. Therefore, the lower compliance at ZEEP may indicate that the lung zones collapsed during suctioning cannot be fully reopened during the following pressure–volume curve determination. The lung volume fall during suctioning, below the functional residual capacity, profoundly modified the pressure–volume relationship of the respiratory system and may explain the bidirectional findings regarding linear compliance.

Prevention of Endotracheal Suctioning-related Adverse Events

It has been shown that repetitive alveolar collapse and reopening can be injurious to the lung (6, 7, 3133). Mead and coworkers showed, in a model of heterogeneous lung, that atelectatic regions can be exposed to shear stress generated by the recruitment of collapsed alveoli and the overdistension of the alveolar units adjacent to atelectatic zones (31). The application of a negative pressure could further increase shear forces resulting in lung damage (2). Lung injury resulting from repetitive alveolar opening and closing can affect the release of inflammatory mediators into the lung and the systemic circulation (7, 33). Therefore, preventing the periodic alveolar derecruitment induced by endotracheal suctioning could be more clinically relevant than its reversal in patients with ALI/ARDS.

In the present study, using the triggering function of the ventilator during endotracheal suctioning to deliver 40 cm H2O pressure-supported breaths seemingly induced a sort of recruitment maneuver during suctioning. This maneuver fully prevented the suctioning-induced derecruitment and can be incorporated in a global strategy to avoid derecruitment and hypoxemia in patients with the most severe ALI/ARDS (34). A previous study proposed the use of a special, modified endotracheal tube as a method to prevent lung volume fall during suctioning (3). However, the clinical application of that method was greatly limited by the use of special equipment. The present study describes the simplest way to fully prevent, not simply reverse, endotracheal suctioning-related derecruitment.

Study Limitations

The present study did not address the efficacy of the different suctioning techniques in terms of quantity of secretions removed. However, the wall pressure, the catheter size, the duration of suctioning, and the technique for introducing and withdrawing the catheter, all influencing the efficacy of endotracheal suctioning, were kept strictly similar during the study. To our knowledge, no study has clearly shown a greater efficacy of a specific suctioning procedure compared with others. Concern has been expressed about the efficacy of the closed system in removing secretions. Few data exist on this issue, with anecdotal reports suggesting a lower efficacy of the closed system compared with the conventional, open technique (35). Nevertheless, in a study specifically addressing this issue, no significant difference between the amount of secretions removed with the closed-circuit catheter and with a conventional catheter was found (36). Increasing the degree of applied negative pressure can increase the efficiency of suctioning, but also augments the risk for mucosal trauma (37).

Because patients were sedated and paralyzed, the effect of the studied suctioning techniques in spontaneously breathing patients was not assessed. Avoiding paralysis might partly prevent the lung volume fall during endotracheal suctioning, by allowing patients to cough, for instance. On the other hand, introducing the suction catheter into the airways without interrupting mechanical ventilation may impede the ability of the ventilator to efficiently assist the patient during suctioning, causing a major patient–ventilator dissynchrony and patient discomfort (24). Therefore, the interference of the suction catheter with mechanical ventilation in spontaneously breathing patients, as well as the effect of specific ventilatory modes and settings, needs further studies.

In summary, we have found that, in patients with ALI/ARDS, avoiding disconnection from the ventilator and, more efficiently, using a closed-suction system allowed the adverse effects of endotracheal suctioning on lung volume, alveolar recruitment, and oxygenation to be minimized. A recruitment maneuver, performed by triggering pressure-supported breaths during suctioning, fully prevented the lung volume fall and mechanical derangements of the respiratory system, allowing an increase in alveolar recruitment.

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Correspondence and requests for reprints should be addressed to Prof. L. Brochard, Réanimation Médicale, Hôpital Henri Mondor, 94000 Créteil, France. E-mail:

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