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Original article
Lung volume and cardiorespiratory changes during open and closed endotracheal suction in ventilated newborn infants
  1. A B Hoellering1,
  2. B Copnell1,2,
  3. P A Dargaville3,
  4. J F Mills1,
  5. C J Morley1,2,
  6. D G Tingay1,2,4
  1. 1
    Department of Neonatology, Royal Children’s Hospital, Melbourne, Victoria, Australia
  2. 2
    Murdoch Children’s Research Institute, Melbourne, Victoria, Australia
  3. 3
    Department of Paediatrics, Royal Hobart Hospital, Hobart, Tasmania, Australia
  4. 4
    Department of Paediatrics, University of Melbourne, Victoria, Australia
  1. Dr A B Hoellering, Department of Neonatology, Royal Children’s Hospital, Flemington Road, Parkville, 3052 Victoria, Australia; abhoellering{at}doctors.org.uk

Abstract

Objectives: To compare change in lung volume (ΔVL), using respiratory inductive plethysmography, time to recover pre-suction lung volume (trec) and the cardiorespiratory disturbances associated with open suction (OS) and closed suction (CS) in ventilated infants.

Design: Randomised blinded crossover trial.

Setting: Neonatal intensive care unit.

Patients: Thirty neonates, 20 receiving synchronised intermittent mandatory ventilation (SIMV) and 10 high-frequency oscillatory ventilation (HFOV, four receiving muscle relaxant).

Interventions: OS and CS were performed, in random order, on each infant using a 6FG catheter at −19 kPa for 6 seconds and repeated after 1 minute.

Outcome measures: ΔVL, oxygen saturation (Spo2) and heart rate were continuously recorded from 2 minutes before until 5 minutes after suction. Lowest values were identified during the 60 seconds after suction.

Results: Variations in all measures were seen during CS and OS. During SIMV no differences were found between OS and CS for maximum ΔVL or trec; mean (95% CI) difference of 3.5 ml/kg (−2.8 to 9.7) and 4 seconds (−5 to 13), respectively. During HFOV trec was longer during OS by 13 seconds (0 to 27) but there was no difference in the maximum ΔVL of 0.1 mV (−0.02 to 0.22). A small reduction in SpO2 with CS in the SIMV group mean difference 6% (2.1 to 9.8) was the only significant difference in physiological measurements.

Conclusions: Both OS and CS produced transient variable reductions in heart rate and Spo2. During SIMV there was no difference between OS and CS in ΔVL or trec. During HFOV there was no difference in ΔVL but a slightly longer trec after OS.

https://doi.org/10.1136/adc.2007.132076

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    Respiratory failure is the commonest cause for admission to a neonatal intensive care unit. Many affected newborn infants require mechanical ventilation through an endotracheal tube (ETT).1 2 The presence of an ETT inhibits the infant’s intrinsic ability to remove endogenous lung secretions, and thus regular suctioning of the ETT is required.3

    ETT suction has adverse consequences such as transient hypoxia, loss of lung volume and cardiovascular instability.4 Neonatal ETT suction uses either open or closed suction devices. Open suction (OS) necessitates disconnection of the ETT from the ventilator, whereas closed suction (CS) is performed with the ventilator circuit intact. CS has been advocated as a technique that may preserve lung volume5 and limit cardiorespiratory instability.6 In muscle-relaxed adults and children, CS causes less loss of lung volume and cardiorespiratory instability than OS.6–8 These benefits have not been fully assessed in ventilated infants.3

    Reliable, non-invasive measurement of change in lung volume (ΔVL) is difficult in ventilated infants, especially during high-frequency oscillatory ventilation (HFOV). This has limited the ability to study lung volume changes in ventilated infants. Respiratory inductive plethysmography (RIP) is a validated method of measuring ΔVL during both conventional ventilation and HFOV.5 9–12

    The aims of this study were to compare ΔVL and time to recover to pre-suction lung volume after OS or CS in ventilated newborn infants, and to compare the immediate cardiorespiratory disturbances associated with each suction method.

    METHODS

    This study was performed in the neonatal unit of the Royal Children’s Hospital, Melbourne, from October 2004 to May 2006. The study was approved by the hospital’s Human Research Ethics Committee, and informed parental consent obtained for each infant. Ventilated infants <10 weeks old were eligible for the study if they were receiving ETT suction as part of routine care at least twice a day. Infants were not enrolled if they had a major congenital anomaly of the heart or lung, refractory hypotension or required an inspired oxygen concentration (FIo2) of ⩾0.9.

    Enrolled infants were grouped by their mode of ventilation: synchronised intermittent mandatory ventilation (SIMV) or HFOV. SIMV was delivered using the VIP Bird Gold ventilator (VIASYS, Yorba Linda, California, USA). HFOV was delivered by the Sensormedics 3100A high-frequency oscillator (Sensormedics, Yorba Linda). Ventilation settings were determined by the treating clinical team and were not adjusted during the study.

    Study protocol

    A randomised crossover trial was performed with each infant acting as its own control. The order of ETT suctioning was randomly determined and the allocation concealed in an opaque sealed envelope. The bedside nurse opened the envelope just before the first suction episode. The investigators were masked to suction technique by placing a screen between them and the patient, and the data reader was unaware of the suction technique during data analysis.

    At least 1 hour before collecting data, a TrachCare neonatal closed tracheal suction system (Ballard Medical Products, Draper, Utah, USA) was connected to the end of the ETT. Suction was performed, when clinically indicated, in the order determined at randomisation. CS was performed using the TrachCare system according to the manufacturer’s recommendations. OS was performed using a premeasured Mallinckrodt suction catheter (Mallinckrodt, Rowville, Australia). Apart from the method of suction all other aspects of the suction procedure were standardised. A size 6FG suction catheter was used, irrespective of ETT size. The suction catheter was passed to the ETT tip and suction applied for 6 seconds at −19 kPa. No changes in ventilator settings were made during each study, saline was not instilled and no recruitment manoeuvres were performed before or after suction. Two passes of the catheter were made 1 minute apart (a suction couplet). No changes to FIo2 were permitted between 2 minutes before and 5 minutes after each suction couplet. The alternative suction method was used when the bedside nurse thought the infant next required ETT suction. If the Spo2 fell to <80% or a heart rate (HR) of <100 bpm persisted for 2 minutes, the study was stopped and an alveolar recruitment procedure applied.13

    Measurements

    HR and oxygen saturation (Spo2) were measured and displayed continuously using the bedside monitor (Philips IntelliVue MP70 Monitor, Eindhoven, Netherlands). Proximal airway pressure, flow and tidal volume were measured at the proximal end of the ETT using a Florian respiratory function monitor (Acutronic Medical Systems, Zug, Switzerland).

    ΔVL was measured with a low-pass filtered, DC-coupled, respiratory inductive plethysmograph (Respitrace 200, Non-invasive Monitoring Systems, North Bay Village, Florida, USA) sampling at 200 Hz using the method we have described previously.9 10 During SIMV the RIP voltage output was calibrated to the tidal volume measured by the Florian monitor. Calibration was performed during 10 stable consecutive ventilator inflations before ETT suction. Coincidence of the onset of the pressure and flow signals was used to distinguish ventilator inflations from spontaneous breaths. A volume signal was derived from the sum of the chest and abdominal RIP voltages, allowing changes in lung volume to be quantified from the changes in RIP voltage. During HFOV the ΔVL could not be calibrated so an uncalibrated volume signal, in millivolts, was derived from the sum of chest and abdominal RIP voltages and used to assess ΔVL.

    Data collection and analysis

    Data were recorded from 2 minutes before each suction couplet until 5 minutes after. Flow, ventilator pressure and ΔVL were digitised and recorded using a programme built in LabVIEW (National Instruments, Austin, Texas, USA). ΔVL was expressed in either ml/kg (SIMV) or mV (HFOV).

    Each RIP recording was reviewed manually by the same investigator (ABH) and, in the case of spontaneously breathing infants, movement artefact discarded. Baseline end-expiratory lung volume was determined from the last stable RIP signal preceding each suction episode, defined as a level end-expiratory lung volume signal of at least 10 seconds’ duration (fig 1). The point of maximal negative ΔVL from baseline was identified during each suction pass and the point of greatest volume loss (ΔVLmax) determined. Time to recover to baseline lung volume (trec) was determined for each suction event. Figure 1 illustrates a recording and the principles of the analysis. In addition, the minimum HR and Spo2 (HRmin and Spo2min), and the time these occurred, were identified during the 60 seconds after each suction event. HR and Spo2 were recorded from the Philips IntelliVue Monitor at 12-second intervals.

    Figure 1
    Figure 1 Representative 60 second respiratory inductive plethysmography recording from infant 5 of the cohort receiving high-frequency oscillatory ventilation. It shows ventilator- generated tidal ventilation and spontaneous breaths (A; open diamonds). (B) The last stable 10-second period of ventilation before the first suction episode, from which baseline end-expiratory lung volume was derived. (C) The first suction episode with the maximum change in lung volume (ΔVL) indicated by the vertical arrow.

    Based on our pilot data 20 infants receiving SIMV and 10 receiving HFOV were required to detect a difference in ΔVL of 10% between suction methods (power 0.9, two-sided α error 0.05) for each mode of ventilation.

    Differences between OS and CS for ΔVL, trec and Spo2 were analysed using repeated measures analysis of variance, with a Tukey post hoc test, or a paired t test where appropriate. A p value <0.05 was considered significant. Statistical analysis used Graph Pad Prism version 4.02 for Windows (Graphpad software, San Diego, California, USA).

    RESULTS

    Thirty infants were studied, 20 receiving SIMV and 10 HFOV, and completed each study without complications, including prolonged desaturation or bradycardia. Table 1 summarises their clinical details. The HFOV group generally had a higher gestational age at delivery, but were younger and had worse lung disease at the time of study. They were also more likely to be sedated and four were receiving muscle relaxant at the time of study. Within the SIMV group eight infants were ventilated to treat respiratory distress syndrome (RDS). Six were ventilated immediately after surgery (two with concomitant RDS). One infant each had chronic lung disease of the newborn, meconium aspiration syndrome, central apnoea, persistent pulmonary hypertension of the newborn, tracheomalacia and cardiac failure secondary to vein of Galen aneurysmal malformation. In the HFOV group five had meconium aspiration syndrome (four also received muscle relaxant), three RDS, one pneumonia and one infant had recently had surgery. Four infants in the HFOV group also had persistent pulmonary hypertension of the newborn and were receiving inhaled nitric oxide. Thirteen infants were male in the SIMV group and nine in HFOV group.

    View this table:
    Table 1 Ventilator group characteristics

    Loss of lung volume

    Lung volume loss was not significantly influenced by suction method. During SIMV the mean (SD) ΔVLmax was 15.8 (14.1) ml/kg and 19.3 (16.5) ml/kg for CS and OS, respectively (fig 2A), with a mean difference between suction methods of 3.5 (95% CI −2.8 to 9.7) ml/kg. During HFOV there was a trend toward greater loss of lung volume with OS than with CS. Maximum ΔVL for CS and OS was 0.20 (0.13) mV and 0.30 (0.14) mV, respectively (fig 2B) with a mean difference of 0.1 (95% CI −0.02 to 0.22) mV. In all cases ΔVLmax occurred during the suction or within 60 seconds of the start of suction.

    Figure 2
    Figure 2 Maximum change in lung volume (ΔVL) during open and closed suction in 20 infants receiving synchronised intermittent mandatory ventilation (A), expressed in ml/kg, and 10 infants receiving high-frequency oscillatory ventilation (HFOV) (B), in mV. Dashed lines represent the mean for each variable and error bars are standard deviation of the mean. The data for the four infants in the HFOV group receiving muscle relaxants (B) are shown in grey.

    Time to recover lung volume

    Figure 3 shows the time to recover to baseline lung volume. This was significantly longer after OS than CS during HFOV but not during SIMV; mean (95% CI) difference between OS and CS 13 (0 to 27) seconds and 4 (−5 to 130) seconds, respectively. During CS, trec was similar in the SIMV and HFOV groups at a mean (SD) of 19 (14) and 19 (15) seconds, respectively. During OS, the mean (SD) trec was 23 (16) seconds in the SIMV group and 33 (16) seconds in the HFOV group, this difference was not significant. It appeared that during OS trec was increased by the use of muscle relaxant, although this cohort was too small for subgroup analysis.

    Figure 3
    Figure 3 Time to recover baseline lung volume (VL) after endotracheal tube suction during closed (CS) and open (OS) suction in infants receiving synchronised intermittent mandatory ventilation (SIMV) and high-frequency oscillatory ventilation (HFOV). MR represents the cohort of four infants in the HFOV group who were also receiving muscle relaxant. Bars represent mean and error bars standard deviation of the mean. *Indicates a significant difference between CS and OS (p = 0.047; paired t test).

    Oxygen saturation

    Both methods of suction resulted in a variable desaturation from baseline (figs 4A and B). Spo2 quickly recovered after ETT suction and had returned to baseline values by 2 minutes after the second suction pass, irrespective of suction method or mode of ventilation. Table 2 shows baseline and Spo2min values for both groups. During SIMV the mean Spo2min with OS was 6.0% (95% CI 2.1% to 9.8%) less than with CS. During HFOV there was no significant difference in Spo2min with a mean difference between suction methods of 2.7% (95% CI −1.6% to 7.0%). Oxygen desaturation during CS was small but significantly greater in infants receiving HFOV than in those receiving SIMV with a mean difference of 3.0% (95% CI 0.3% to 8.5%). Change in Spo2 appeared greater during the second pass of the suction catheter than the first, for both modes of ventilation and both methods of suction, but this difference was not statistically significant.

    Figure 4
    Figure 4 Change in oxygen saturation (Spo2) and heart rate (HR) from baseline pre-suction values during and for 5 minutes after two passes of closed suction (CS) and open suction (OS) during synchronised intermittent mandatory ventilation (SIMV; A and C) and high-frequency oscillatory ventilation (HFOV; B and D). All data expressed as mean (SD).
    View this table:
    Table 2 Baseline and minimum oxygen saturation (Spo2) values during closed and open suction

    Heart rate

    Both suction methods resulted in a transient drop in HR during both suction passes which recovered by 2 minutes after the second pass (figs 4C and D). The mean difference in maximum HR change between OS and CS for the SIMV and HFOV groups respectively was 7.7 (95% CI −6.8 to 22.2) bpm and 8.0 (95% CI −0.5 to 16.6) bpm. In all cases loss of lung volume was followed by deterioration in Spo2 and HR. The magnitude of change in lung volume did not correlate with the magnitude of change in Spo2 or HR (Spearman correlation coefficients between 0.11 and 0.33) with either OS or CS.

    DISCUSSION

    This study is the first to compare the effects of OS and CS on lung volume, Spo2and HR exclusively in ventilated newborn infants. It showed little difference between suction technique in lung volume loss, Spo2 or HR changes. There was great variation in these measures for both OS and CS and negative effects were transient.

    Loss of lung volume occurred with both OS and CS. There was some volume sparing with CS, particularly in the HFOV group, but the difference was not statistically, or clinically, significant. These results differ from similar studies in adults and children.5 7 8 14 The only other study to compare loss of lung volume in children during ETT suction also used RIP. This study involved 14 conventionally ventilated muscle-relaxed children, only two of whom were neonates.5 OS caused more than double the loss of lung volume compared with CS (mean (SD) 133 (127) ml vs 50 (49) ml, respectively). The small sample size, heterogeneous population and universal use of muscle relaxant limit the relevance of this study to current neonatal ventilatory management.

    CS does not require disconnection of the ventilator circuit, which is often cited as an advantage, and may explain the minor volume sparing seen in our study.5 Circuit disconnection during OS was found to account for almost 75% of the total volume loss in a study of seven newborn infants receiving HFOV and muscle relaxant.10 In our study, the RIP tracings suggest that the spontaneously breathing infant can restore lung volume at or after ETT suction and even during the act of disconnection. Fernandez and colleagues also reported rapid recovery from lung derecruitment in spontaneously breathing ventilated adult patients receiving OS and CS.14 Furthermore, lung volume recovery times in our study were longer after OS than CS in the more sedated HFOV cohort and longest for OS in the muscle-relaxed infants receiving HFOV. This latter group of infants, in whom the capacity for re-recruitment by spontaneous breathing is ablated by muscle relaxant, inevitably take longer to restore pre-suction lung volume. Choong and coworkers noted a similar delay in lung volume recovery after open suction in muscle-relaxed children.5 Clearly such findings cannot be extrapolated to spontaneously breathing subjects, particularly those receiving SIMV, in whom we have found little difference in recovery times between OS and CS.

    What is already known on this topic

    • Endotracheal tube suction is associated with transient hypoxia, loss of lung volume, bradycardia and oxygen saturation.

    • In adult and paediatric patients receiving muscle-relaxants, suction methods that keep the ventilator circuit intact (closed suction) result in less volume loss than methods that involve disconnection from the ventilator (open suction).

    Previous trials have reported some improved stability in HR and oxygenation with CS. Meta-analysis suggested some short-term benefit from CS in preventing a change in HR after suction of >10% (relative risk = 0.56, 95% CI 0.32 to 0.99),3 although this only included two trials totalling 22 infants.15 16 The study by Mosca and coworkers reported fewer episodes of hypoxia (Spo2 <90%) for CS than OS (relative risk = 0.30, 95% CI 0.11 to 0.80).16 In a study of 200 ventilated infants comparing OS and CS, Kalyn et al found CS had significantly better short-term physiological stability than OS.6 However, the clinical significance of these results is debatable: Spo2 fell from a mean (SD) of 96 (3)% to 93 (5)% and 95 (4)% for OS and CS, respectively. Similar, clinically small, differences were reported for change in HR.6 In our study there was some protection against desaturation with CS compared with OS in the SIMV group. This difference was no longer apparent by 2 minutes and no difference was found for changes in HR.

    What this study adds

    • The negative effects of suction on lung volume, heart rate and oxygen saturation are transient and highly variable with both open and closed suction methods in spontaneously breathing ventilated infants.

    • The ability of a spontaneously breathing ventilated infant to recruit its own lung volume may be more important than the suction method used.

    As far as we know, this study is the first to examine the relationship between lung volume and cardiorespiratory changes in ventilated infants during open and closed ETT suction. Hypoxaemia is a well-documented adverse consequence of ETT suctioning and may result from transient disconnection from the inspired oxygen or atelectasis and ventilation perfusion mismatch.17 18 In our study lung volume loss associated with ETT suctioning appeared to act as the stimulus for deoxygenation but did not correlate with its magnitude. This finding suggests that deoxygenation cannot be attributed solely to lung derecruitment, and may be influenced by other factors, such as pulmonary vasospasm and exacerbation of intrapulmonary shunts. Similarly the magnitude of HR change was found to correlate poorly with the magnitude of lung volume loss.

    The purpose of ETT suction is to remove secretions from the respiratory tree. Animal and bench-top data suggest that OS is more effective at removing secretions than CS.19 20 However, lung volume was preserved and time to recover baseline volume was shorter with CS in the HFOV group, and for muscle-relaxed infants in particular. Our study suggests that rather than adopting a single suction policy it is preferable to individualise the suction method according to the clinical situation, ideally, balancing the need to maximise secretion removal and the need to minimise complications.

    Most comparisons, including this study, of OS and CS in infants have focused on short-term outcomes6 15 16 and have not assessed possible long-term clinical differences such as the neurological implications and differences in rates of infection with OS and CS. In a systematic review of adult patients, CS resulted in greater airway colonisation than OS but there was no difference in the incidence of pneumonia or mortality.21 A final observation from our study is that while the protocol demanded that suction was performed when deemed clinically indicated, there was no tangible improvement in lung volume status, Spo2 or HR before and after suction. Further research is needed to determine when ETT suction is clinically indicated.

    This study has some limitations. The number in the HFOV group was small and the ΔVL data more variable than predicted. Possibly, a larger sample size would have shown a significant difference for ΔVL in this group, or the cohort receiving muscle relaxant. Increased respiratory illness severity may also influence the difference between OS and CS. The ETT diameter was not constant in this study. Future research should examine whether the cross-sectional area of the ETT relative to the suction catheter influences lung volume change, cardiorespiratory instability and, in the case of CS, delivered tidal volumes.

    RIP is an established and validated method of determining relative change in lung volume during SIMV and HFOV but it has limitations.9 11 12 The known sensitivity to thermal changes and baseline signal drift22 were minimised by allowing at least 40 minutes for signal stabilisation before data recording. RIP is exquisitely sensitive to movement artefact. Determining the difference between artefact and true changes in baseline lung volume is difficult. In this study all RIP recordings were manually reviewed by an investigator and potential artefact data discarded. Furthermore, controversy surrounds the reliability of calibration of voltage to volume changes, especially over long periods and for patients receiving HFOV.23 Consequently, in this study RIP data were recorded for ⩽10 minutes, and during SIMV, calibration was repeated before each recording. RIP data from the HFOV group were not calibrated to a known volume and were expressed as a relative change in mV rather than ml/kg, limiting any comparison between the two ventilation groups.

    CONCLUSION

    Both OS and CS caused transient, and highly variable, derecruitment of lung volume. The short-term volume-sparing benefits of CS compared with OS apparent in paediatric and adult patients were not replicated in this study of ventilated infants, many of whom, as in clinical practice, were breathing spontaneously. Differences in HR and Spo2 were transient and could not be explained simply by change in lung volume. These findings, together with emerging concerns about the relative efficacy of suction methods suggest that it may be time to reassess the role of OS in ventilated infants.

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    Footnotes

    • Competing interests: None.

    • Funding: This project was funded by an unconditional Murdoch Children’s Research Institute project grant (grant ID 05028). DGT is supported by a National Health and Medical Research Council Medical Postgraduate Research Scholarship. BC was partly supported by a National Health and Medical Research Council Programme grant (grant ID 384100).

    • Ethics approval: Approved by the hospital’s Human Research Ethics Committee.