Short Communication Received: December 21, 2009 Accepted after revision: June 8, 2010 Published online: August 24, 2010
Neonatology 2011;99:78–82 DOI: 10.1159/000316854
Volume Not Guaranteed: Closed Endotracheal Suction Compromises Ventilation in Volume-Targeted Mode Nicholas J. Kiraly a David G. Tingay a–c John F. Mills a, b Peter A. Dargaville a, d Beverley Copnell a, b, e
a
Neonatal Research, Murdoch Childrens Research Institute, b Department of Neonatology, Royal Children’s Hospital, and c Department of Paediatrics, University of Melbourne, Parkville, Vic., d Department of Paediatrics, Royal Hobart Hospital and University of Tasmania, Hobart, Tas., and e School of Nursing and Midwifery, Monash University, Melbourne, Vic., Australia
Key Words Endotracheal suction ⴢ Mechanical ventilation ⴢ Neonatal intensive care ⴢ Newborn infant
Abstract Background: Closed endotracheal suction interferes with mechanical ventilation received by infants, but the change to ventilation may be different when ventilator modes that target expired tidal volume (VTe) are used. Objective: To measure airway pressure and tidal volume distal to the endotracheal tube (ETT) during and after closed suction in a volume-targeted ventilation mode with the Dräger Babylog 8000+, and to determine the time until VTe returns to the baseline level. Methods: In this benchtop study, closed suction was performed on 2.5- to 4.0-mm ETTs connected to a test lung. 5–8 French suction catheters were used at suction pressures of 80–200 mm Hg during tidal-volume-targeted ventilation. Results: During catheter insertion and suction, circuit inflating pressure increased and tidal volume was maintained, except when a large catheter relative to the ETT was used, in which case tidal volume decreased. End-expira-
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tory pressure distal to the ETT was reduced during suction by up to 75 cm H2O while circuit end-expiratory pressure was unchanged. Reduction in end-expiratory pressure distal to the ETT was greatest with large catheters and high suction pressures. Following suction, circuit and tracheal inflating pressures increased and tidal volume increased before returning to baseline in 8–12 s. Conclusions: Closed endotracheal suction interferes with ventilator function in volumetargeted mode, with substantially negative intratracheal pressure during suction, and the potential for high airway pressures and tidal volumes following the procedure. These effects should be considered and pressure limits set appropriately whenever using volume-targeted ventilation. Copyright © 2010 S. Karger AG, Basel
Introduction
Closed endotracheal tube (ETT) suctioning is frequently performed in infants receiving mechanical ventilation to clear secretions from the airway while avoiding disconnection of the ventilator circuit. However, conNicholas J. Kiraly Neonatal Research, Murdoch Childrens Research Institute Department of Neonatology, Royal Children’s Hospital Flemington Road, Parkville, Vic. 3052 (Australia) Tel. +61 3 9345 4023, Fax +61 3 9345 5067, E-Mail nicholas.kiraly @ mcri.edu.au
cerns exist that the procedure could interfere with ventilator function in modes in which an expired tidal volume (VTe) is targeted (TTV) with the result that ventilation may not be preserved [1, 2]. A recent report highlighted the effect of partial or complete ETT obstruction during ventilation of newborn infants using the Dräger Babylog 8000+ in TTV mode, demonstrating that tidal volume was often not achieved due to ventilator programming or settings [3]. Another study found overshoot in tidal volume using TTV mode after a rapid decrease in airway resistance, a change which occurs when suctioning ends [4]. We previously found that airway pressure distal to the ETT can become considerably negative (while circuit pressure remains unaffected) during closed suction with time-cycled, pressure-limited ventilation, but no published neonatal study to date has investigated the effect of ETT suction on ventilation in a TTV mode [5]. Our objective was to determine the effects of ETT suction on airway pressure and VTe measured distal to the ETT during TTV ventilation using a neonatal lung model, and to determine the time until VTe returned to the baseline level following suction.
Materials and Methods The benchtop experimental model used a Dräger Babylog 8000+ ventilator (Dräger, Lübeck, Germany) connected via an ETT (a series of different sizes; Mallinckrodt, Rowville, Vic., Australia) to an infant test lung (model 560li; Michigan Instruments, Grand Rapids, Mich., USA; compliance 1 ml/cm H2O). Between the circuit and the ETT was a closed suction system (Ballard TrachcareTM; Kimberly-Clark, Roswell, Ga., USA); a wall suction unit (PM3000; Precision Medical, Northampton, Pa., USA) was used to apply a negative pressure to the suction catheter. The experimental model has been described previously [5]. Ventilator circuit pressure was measured proximal to the ETT, and tracheal pressure was measured 1 cm distal to the ETT tip (Scireq SC-24, Montreal, Que., Canada). Tracheal gas flow was measured 2 cm distal to the ETT tip using a hot wire anemometer (Florian respiration monitor; Acutronic Medical Systems, Zug, Switzerland). These signals were digitally acquired at 200 Hz using LabVIEWTM 6.0 (National Instruments, Austin, Tex., USA) and were averaged over the last three inflations of each phase to reduce error. After suction, dramatic breath-to-breath changes occurred, so only the maximum value was used for analysis to show the largest inflation in that phase. VTe was used in the analysis and the time until VTe stabilised to within 10% of baseline VTe was also determined. The ventilator’s own flow sensor (data not recorded) was positioned between the ventilator circuit and ETT, proximal to the suction catheter. Ventilation was applied using volume guarantee mode with the following settings: set VTe 6 ml; positive end-expiratory pressure (PEEP) 5 cm H2O; peak inspiratory pressure (PIP) limit 50 cm H2O; rate 60 breaths/min; inspiratory time 0.4 s; circuit gas
Closed Suction with Volume-Targeted Ventilation
flow 8 l/min, and FIO2 0.4. After 6 s of baseline ventilation (baseline phase), the catheter was passed to the tip of the ETT and remained there for 6 s without suction (catheter insertion phase). Suction was then applied for 6 s, the standard duration in our institution (suction phase). Suction was then ceased and the catheter withdrawn (post-suction phase). This experimental protocol was performed six times on each combination of ETT (inner diameter: 2.5, 3.0, 3.5 and 4.0 mm), catheter (5, 6, 7 and 8 French gauge (Fr)) and suction pressure (80, 120, 160 and 200 mm Hg), except when the catheter was too large for the ETT. Data were compared using Student’s t test, and multiple regression analyses were performed with the method of least squares using Stata 9.0 (Stata, College Station, Tex., USA).
Results
Circuit PEEP was largely undisturbed by the suction procedure; the greatest reduction (0.5 cm H2O) occurred with use of the largest ETT and catheter during the suction phase. The pooled data for changes from baseline in circuit inflation pressure (IP), tracheal IP and tracheal PEEP are shown in table 1 (a positive number in table 1 indicates an increase in pressure compared to the baseline phase). With a 4.0-mm ETT, an 8-Fr catheter, and 160 or 200 mm Hg suction pressure, the ventilator ceased generating inflations during the suction phase; therefore VTe, circuit IP and tracheal IP were reduced to zero with these combinations. Successive increases in VTe were observed in the catheter insertion, suction and post-suction phases compared to baseline (fig. 1), except when the largest catheter for each ETT was used. In these cases, VTe was reduced during the suction phase. In all cases, VTe increased significantly from baseline in the post-suction phase (p ! 0.001 in each case), as did tracheal IP (p ! 0.001 in each case; table 1). Multiple regression analyses showed that ETT size, catheter size and suction pressure were poor predictors of both post-suction maximum VTe (R 2 = 0.09) and the time after suction until VTe returned to baseline (R 2 = 0.36, table 1). Data in figure 1 and table 1 are pooled containing all four suction pressures. Varying suction pressure had little effect on circuit and tracheal IP, but higher suction pressures were associated with lower tracheal PEEP during the suction phase (data not shown; p ! 0.001; multiple regression analysis R 2 = 0.64). This effect was more pronounced where the ratio of catheter to ETT diameter was high and thus interaction between variables was observed (p ! 0.001). ETT and catheter sizes were also significant in determining tracheal PEEP during suction (p ! 0.001 for each). Neonatology 2011;99:78–82
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Table 1. Changes in ventilation parameters from the baseline phase during the catheter insertion, suction and post-suction phases
(changes vs. baseline) Catheter size
2.5-mm ETT 5 Fr 6 Fr 3.0-mm ETT 5 Fr 6 Fr 7 Fr 3.5-mm ETT 5 Fr 6 Fr 7 Fr 8 Fr 4.0-mm ETT 5 Fr 6 Fr 7 Fr 8 Fr
Catheter insertion phase
Suction phase
Post-suction phase
circuit IP
tracheal IP
tracheal PEEP
circuit IP
tracheal IP
5.780.4 23.885.5
1.380.3 0.480.7
0.580.1 4.181.0
18.582.1 37.087.7
2.580.9 9.784.5
0.881.3 4.080.2 14.281.2
0.780.2 1.480.2 1.380.4
0.080.2 0.280.1 2.480.2
10.382.4 16.681.3 27.682.7
0.180.8 0.980.2 2.181.1 11.180.9
0.380.2 0.580.2 0.880.2 0.980.3
0.080.1 0.080.0 0.180.1 1.880.4
0.680.9 0.381.0 0.480.1 0.781.0
0.480.6 0.380.2 0.380.1 0.380.7
0.080.2 0.080.2 0.080.1 0.080.2
tracheal PEEP
maximum tracheal IP
time to stable VTe, s
–10.282.5 –65.2823.4
14.080.8 16.081.7
10.281.0 11.781.0
1.980.9 3.780.5 8.783.3
–4.180.9 –16.284.2 –65.3818.2
13.281.2 17.985.4 18.986.0
9.381.0 9.880.9 11.681.3
6.881.7 9.281.3 11.182.7 16.188.0
2.281.2 3.681.1 2.281.9 6.386.4
–2.080.5 –6.881.5 –21.386.1 –75.1821.4
13.181.3 12.981.6 13.681.1 14.880.9
9.080.9 8.581.1 8.981.3 11.781.3
5.180.9 4.681.3 4.982.2 –2.185.9
3.280.9 2.180.9 2.481.9 –3.784.2
–0.980.2 –2.780.7 –6.881.8 –21.389.3
12.582.0 14.183.0 15.483.3 6.888.9
8.380.8 9.481.1 8.880.8 8.781.2
Data (means 8 SD) are pooled from suction pressures of 80, 120, 160 and 200 mm Hg. All pressure measurements are in cm H2O.
Discussion
We found that VTe and airway pressures were affected by closed ETT suction when using the volume-targeted ventilation mode of the Dräger Babylog 8000+ ventilator. This mode adjusts PIP to target VTe. When the measured VTe is lower than the set tidal volume (e.g. when there is significant ETT obstruction), IP increases by up to 3 cm H2O per inflation up to the set pressure limit. Once the obstruction is removed or VTe is greater than set tidal volume, IP decreases by up to 3 cm H2O per inflation until VTe returns to the set value [6]. In response to partial obstruction of the ETT during the catheter insertion phase, the ventilator increased circuit IP sufficiently to maintain VTe in most cases. During suction, tracheal VTe and IP were increased further (except when the largest catheter for each ETT was used), presumably because removal of gas from the airways by the catheter meant that not all of the tracheal VTe was measured by the ventilator’s flow sensor. We propose that the ventilator recorded a lower VTe than the VTe at the tracheal end of the ETT, causing the ventilator to erroneously increase IP. This effect would explain why the VTe we measured was often greater than the set value. 80
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Once the catheter was withdrawn, the high IP generated was delivered in full to the trachea, elevating VTe by 14–20 ml above the baseline value of 6 ml, and it took 8–12 s to return to the baseline level. Analysis demonstrated that this effect was independent of the ETT diameter, catheter size and suction pressure. This increase in VTe following suction may be beneficial if it serves to reinflate the collapsed lung after suction. Furthermore, the atelectatic lung is expected to have considerably reduced compliance, and the dramatic increase in PIP observed in the present study may therefore be partially mitigated by a decreased compliance clinically, leading to a tidal volume lower than we measured. Conversely, the delivered tidal volume may be excessively large and contribute to significant lung trauma [7]. We found two important differences between closed ETT suction with TTV mode tested here and time-cycled, pressure-limited ventilation (TCPL) tested previously [5]: VTe was maintained during catheter insertion and suction with TTV, but was not during TCPL, and IP and VTe were dramatically increased in the post-suction phase with TTV, but not with TCPL. We did not find an increase in intrinsic PEEP as was seen in an adult model with volume control mode [2]. Kiraly /Tingay /Mills /Dargaville /Copnell
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Fig. 1. Changes in VTe during ETT suctioning of ETT sized 2.5, 3.0, 3.5 and 4.0 mm. Measurements were aver-
aged over the last three inflations of each phase, except for the post-suction phase, where the maximum value is shown. Catheter sizes are indicated. Data are means 8 SD.
Our measurements are likely to differ from those found in clinical practice. Secretions in the airway may obstruct the ETT or the catheter during suction, and spontaneous breathing may alter the ventilator response. We used a Dräger Babylog 8000+ ventilator and results may not be applicable to other ventilators, and lung mechanics of infants receiving mechanical ventilation are
likely to differ from the constant-compliance lung we used. Importantly, adjusting the pressure limit closer to the baseline PIP would limit the capacity for the ventilator to maintain VTe during suction and also would reduce the overshoot in IP and VTe following suction. Given these limitations, the effects of TTV in vivo cannot be predicted from the results of this study; clinical studies
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using standard settings are required to determine such effects. The ventilator settings were chosen to examine how suctioning can interfere with ventilator function using a TTV mode, and our findings demonstrate the need to set appropriate pressure limits when using this mode in clinical practice.
Acknowledgements The authors gratefully acknowledge Prof. Colin Morley, the Clinical Technology Service, Royal Children’s Hospital, and Dräger Medical for use of the Dräger Babylog 8000+ ventilator.
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6 McCallion N, Lau R, Dargaville PA, Morley CJ: Volume guarantee ventilation, interrupted expiration, and expiratory braking. Arch Dis Child 2005;90:865–870. 7 Bjorklund LJ, Ingimarsson J, Curstedt T, John J, Robertson B, Werner O, Vilstrup CT: Manual ventilation with a few large breaths at birth compromises the therapeutic effect of subsequent surfactant replacement in immature lambs. Pediatr Res 1997;42:348–355.
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