Effect of leak around the endotracheal tube on measurements of pulmonary compliance and resistance during mechanical ventilation: a lung model study

Normal saline and lung recruitment with paediatric endotracheal suction (NARES): A pilot, factorial, randomised controlled trial

BACKGROUND/OBJECTIVE

Endotracheal suction is one of the most common and harmful procuedres performed on mechanically ventilated children. The aim of the study was to establish the feasibility of a randomised controlled trial (RCT) examining the effectiveness of normal saline instillation (NSI) and a positive end-expiratory pressure recruitment manoeuvre (RM) with endotracheal suction in the paediatric intensive care unit.

METHODS

Pilot 2 × 2 factorial RCT. The study was conducted at a 36-bed tertiary paediatric intensive care unit in Australia. Fifty-eight children aged less than 16 years undergoing tracheal intubation and invasive mechanical ventilation. (i) NSI or no NSI and (ii) RM or no RM with endotracheal suction . The primary outcome was feasibility; secondary outcomes were ventilator-associated pneumonia (VAP), change in end-expiratory lung volume assessed by electrical impedance tomography, dynamic compliance, and oxygen saturation-to-fraction of inspired oxygen (SpO₂/FiO₂) ratio.

RESULTS/FINDINGS

Recruitment, retention, and missing data feasibility criteria were achieved. Eligibility and protocol adherence criteria were not achieved, with 818 patients eligible and 58 enrolled; cardiac surgery was the primary reason for exclusion. Approximately 30% of patients had at least one episode of nonadherence. Children who received NSI had a reduced incidence of VAP; however, this did not reach statistical significance (incidence rate ratio = 0.12, 95% confidence interval = 0.01-1.10; p = 0.06). NSI was associated with a significantly reduced SpO₂/FiO₂ ratio up to 10 min after suction. RMs were not associated with a reduced VAP incidence (incidence rate ratio = 0.31, 95% confidence interval = 0.05-1.88), but did significantly improve end-expiratory lung volume at 2 and 5 min after suction, dynamic compliance, and SpO₂/FiO₂ ratio.

CONCLUSION

RMs provided short-term improvements in end-expiratory lung volume and oxygenation. NSI with suction led to a reduced incidence of VAP; however, a definitive RCT is needed to test statistical differences. A RCT of study interventions is worthwhile and may be feasible with protocol modifications including the widening of participant eligibility.

Use of a Mechanical Ventilator with Respiratory Function Monitoring Provides More Consistent Ventilation during Simulated Neonatal Resuscitation

INTRODUCTION

Positive pressure ventilation (PPV) with T-Piece and self-inflating bag (SIB) during neonatal resuscitation after birth is associated with variability in ventilation. The use of a ventilator with respiratory function monitoring (RFM) for PPV, however, has not been evaluated.

OBJECTIVE

To determine if ventilator + RFM can reduce ventilation variability compared to T-Piece and SIB in a preterm manikin at different combinations of target tidal volume (VT) and lung compliance (CL).

METHODS

Twenty clinicians provided PPV via mask and endotracheal tube (ETT) using SIB, T-Piece, T-Piece + RFM and Ventilator + RFM to a manikin with adjustable lung CL. Three combinations of CL and target VT: Low CL-Low VT, Low CL-High VT and High CL-Low VT were used in a random order.

RESULTS

The use of ventilator + RFM for PPV via ETT during High CL-Low VT period reduced the proportion of breaths with expiratory VT above target when compared to the other 3 devices (56 ± 35%, 85 ± 20%, 90 ± 25%, 92 ± 12% for ventilator + RFM, T-Piece + RFM, T-Piece, SIB, respectively; p < 0.05). During PPV via both mask and ETT, ventilator + RFM maintained the set Ti and rate, whereas SIB and T-Piece use resulted in higher rates, and T-Piece in higher proportion of breaths with prolonged Ti. During PPV via mask, ventilator + RFM reduced gas leakage compared to other devices.

CONCLUSION

In this simulation study, use of a mechanical ventilator with RFM led to an overall improvement in volume targeting at different settings of CL and reduced the gas leak during mask ventilation. The efficacy and safety of using this strategy to neonatal resuscitation in the delivery room needs to be evaluated.

Adaptive control of a pressure-controlled artificial ventilator: a simulator-based evaluation using real COPD patient data

The paper discusses the application of a direct adaptive controller to a pressure controlled artificial ventilation problem. In pressure controlled ventilators, the manipulated variable is the maximum flow applied to the patient during the active phase (inspiration), and the regulated variable is the peak pressure at end-inspiration. This simulation case study focuses on patients diagnosed with Chronic Obstructive Pulmonary Disease (COPD), which require artificial/mechanical ventilation. An adaptive PID controller ensures peak pressures below critical values, by manipulating the flow delivered by the ventilator. The simulation study is performed on fractional-order models of the respiratory impedance identified from lung function data obtained from 21 COPD patients. Additional simulation studies show the robustness of the controller in presence of varying model parameters from the respiratory impedance of the patient. Possibilities to implement the control strategy as an online adaptive algorithm are also explored. The results show that the design of the control is suitable for this kind of application and provides useful insight on realistic scenarios.

Tracheal tube airleak in clinical practice and impact on tidal volume measurement in ventilated neonates

OBJECTIVE

To determine the prevalence, size, and factors affecting tracheal tube (TT) leak in clinical practice and their influence on the displayed tidal volume (Vt) in ventilated newborn infants using uncuffed TTs. Monitoring of Vt is important for implementation of lung-protective ventilation strategies but becomes meaningless in the presence of large TT airleaks.

DESIGN

Retrospective clinical study.

SETTING

Neonatal intensive care unit.

PATIENTS

Patient records of 163 neonates ventilated with Babylog 8000 for ≥ 5 hrs with a median (range) gestation age of 31.1 wks (23.3-41.9 wks) and a median birth weight of 1470 g (410-4475 g) were evaluated.

INTERVENTIONS

: Ventilatory settings, TT leak, and Vt were recorded every 3 hrs. The lowest, median, and highest TT leaks were noted on the day the first TT leak (>5%) occurred, the day on which TT leak peaked, and the day of extubation.

MEASUREMENTS AND MAIN RESULTS

A TT leak of >5% was seen in 122 (75%) infants. Neonates with TT leak, compared with those without TT leak, had a longer duration of mechanical ventilation (p < .001), a lower gestational age (p = .004), a reduced birth weight (p = .005), and a higher prevalence of reintubation (p = .003). The greatest TT leak was seen in infants ventilated with a TT of <3-mm diameter. During the entire duration of mechanical ventilation, 42.3% of all neonates experienced at least one TT leak of >40% commonly seen on the third day of mechanical ventilation. Regression analysis showed that a TT leak of 40% indicated that the displayed Vt was underestimated by 1.2 mL/kg (about 24% of target Vt).

CONCLUSIONS

TT leak is highly variable, and TT leak of >40% with clinically relevant Vt errors occurred in nearly half of all ventilated neonates. Preterm infants of low birth weight and with small-diameter TTs ventilated for a long period were at greater risk of TT leak.

Relationship between endotracheal tube leakage and under-reading of tidal volume in neonatal ventilators

AIM

Protective ventilation in neonates requires careful volume monitoring to prevent ventilator-induced lung injury caused by baro/volutrauma and hence chronic lung disease. This study investigated the effect of endotracheal tube (ET) leakage on the displayed tidal volume using an in vitro model.

METHODS

A neonatal lung model was ventilated via a 3 mm ET using three ventilators [Babylog 8000 (BL), Leoni (LE) and Stephanie (ST)]. Tidal volume was measured by each ventilator at the Y-piece and by a pneumotach (CO(2)SMO(+)) in the model. ET leaks were simulated by open tubes of different lengths. PIP (20 cmH(2)O) and PEEP (5 cmH(2)O) were kept constant, and the respiratory rate (RR) was varied between 20/min and 70/min (Ti:Te = 1:1).

RESULTS

Tidal volume displayed by a ventilator decreased independently of RR with increasing leakage up to 21% (BL), 30% (LE) and 33% (ST). However, the volume delivered to the lung was nearly constant. The displayed leakage varied between 0 and 78% and was dependent on RR and leakage resistance. There were distinct differences between the three ventilators in the relationship between displayed leakage and volume error. Accepting a volume error <10% for RR between 20 and 70/min, ET leakage of up to 20% for BL, 12% for LE, but only <5% for ST, was acceptable.

CONCLUSION

Tidal volume underestimation arising from ET leakage depends on ventilator pressures, timing parameters and ventilator-specific algorithms for signal processing. Therefore, neonatologists should be aware of these issues to prevent lung over-inflation when adjusting target volume in the presence of ET leakage.

Ventilator assessment of respiratory mechanics in paediatric intensive care

Many modern "paediatric" mechanical ventilators have in-built features for estimation of respiratory mechanics which could be useful in the management of ventilated infants and children. The aim of this study was to determine if such measurements were reproducible and accurate. Ventilator (Draeger Evita 4) displayed compliance (Cvent) and resistance (Rvent) values were assessed and compared to the results of respiratory system mechanics (respiratory system compliance (Crs) and resistance (Rrs)) measurements obtained using a single breath occlusion technique. Seventeen children (median age 5.1; range 0.3 to 16 yrs) were studied on 24 occasions. The mean coefficients of variations for the techniques were similar (Cvent 13%; Crs 11%; Rvent 16%; Rrs 14%). The mean (SD) Crs (22.8 (12.3) ml/cmH2O) did not differ significantly from Cvent (22.1 (12.7) ml/cm H2O) but the mean Rrs 21.0 (12.7) cmH2O/l/s was significantly higher than the mean Rvent 32.0 (32.0) cmH2O/l/s (p = 0.03). Bland and Altman analysis demonstrated a mean difference of -10.94 cmH2O/l/s (SD 24.1) between Rrs and Rvent; the agreement between Rrs and Rvent decreased as Rrs increased (p = 0.008).

CONCLUSIONS

Ventilator assessment of compliance, but not resistance, using the Evita 4 is reproducible and reliable.

Limitation of measurements of expiratory tidal volume and expiratory compliance under conditions of endotracheal tube leaks

OBJECTIVE

Endotracheal tube leaks (ETTLs) occur in neonates ventilated with uncuffed tubes. Assuming that the influence of ETTLs might be neglected during expiration, only expiratory tidal volume is measured for calculation of expiratory compliance in cases of large ETTLs. However, expiratory ETTL might be substantial. Therefore, we evaluated the effect of ETTL size on expiratory tidal volume and compliance.

DESIGN

Prospective laboratory study and retrospective clinical study.

SETTING

University research laboratory and neonatal intensive care unit.

PATIENTS

Sixty ventilated neonates (weight 640-2160 g, gestational age 25-33 wks) were investigated.

INTERVENTIONS

The impact of increasing ETTLs on inspiratory and expiratory measured tidal volume (Vm), corrected tidal volume (Vc), and leak volume (Vl) was investigated in a ventilated neonatal lung model. The range of ETTLs (1% to 95%) was subdivided into five groups of 12 infants each. Furthermore, the relationships between standard ETTL size and inspiratory and expiratory ETTLs were evaluated using nonlinear regression. Standard ETTL size was defined as the difference between measured inspiratory and expiratory tidal volume (Vm) related to inspiratory Vm.

MEASUREMENTS AND MAIN RESULTS

The size of a standard ETTL was 40% when expiratory ETTL reached 10% and was 12% when the inspiratory ETTL reached 10%. In infants, the differences between Vm and Vc were statistically significant during inspiration in the group beginning at a standard ETTL of 41% and during expiration in the group beginning at a standard ETTL of 69% (p < .05). Results of nonlinear regression showed that the standard ETTL was 33% (95% confidence interval, 28% to 36%) when expiratory ETTL reached 10% and was 13% (95% confidence interval, 12% to 15%) when inspiratory ETTL reached 10%.

CONCLUSIONS

Expiratory Vl has a relevant impact if a certain ETTL size is reached.

The effect of inhaled nitric oxide on pulmonary function in preterm infants

OBJECTIVE

Bronchopulmonary dysplasia (BPD) in preterm infants is associated with impaired alveolar growth, inflammation and airway hyperreactivity. In animal models of BPD, inhaled nitric oxide (NO) improves alveolar growth and inhibits airway smooth muscle proliferation. This study was designed to assess the effect of inhaled NO on resistance and compliance in ventilated preterm infants with evolving BPD.

STUDY DESIGN

Expiratory resistance and compliance of the respiratory system were measured in 71 ventilated preterm infants, < or = 32 weeks gestation, randomized to NO (n=34) versus placebo (n=37) for > or = 24 days at 7 to 21 days of life.

RESULT

At baseline expiratory resistance (231+/-71 versus 215+/-76 cm H(2)O l(-1) s(-1)) and compliance (0.49+/-0.14 versus 0.53+/-0.13 ml cm H(2)O(-1) kg(-1)) were comparable between placebo and NO groups, respectively. There was no effect of NO on expiratory resistance or compliance at 1 h, 1 week or 2 weeks of study gas administration.

CONCLUSION

NO had no short- or medium-term effect on expiratory resistance or compliance in ventilated preterm infants.

A recruitment manoeuvre performed after endotracheal suction does not increase dynamic compliance in ventilated paediatric patients: a randomised controlled trial

QUESTION

Does a recruitment manoeuvre after suctioning have any immediate or short-term effect on ventilation and gas exchange in mechanically-ventilated paediatric patients?

DESIGN

Randomised controlled trial with concealed allocation, assessor blinding, and intention-to-treat analysis.

PARTICIPANTS

Forty-eight paediatric patients with heterogeneous lung pathology. Fourteen patients were subsequently excluded from analysis due to large leaks around the endotracheal tube.

INTERVENTION

The experimental group received a single standardised suctioning procedure followed five minutes later by a standardised recruitment manoeuvre. The control group received only the single suctioning procedure.

OUTCOME MEASURES

Measurements of ventilation (dynamic lung compliance, expiratory airway resistance, mechanical and spontaneous expired tidal volume, respiratory rate) and gas exchange (transcutaneous oxygen saturation) were recorded, on three occasions before and on two occasions after the recruitment manoeuvre, using a respiratory profile monitor.

RESULTS

There was no difference between the experimental and the control group in dynamic compliance, expired airway resistance, or oxygen saturation either immediately after the recruitment manoeuvre, or after 25 minutes. The experimental group decreased mechanical expired tidal volume by 0.3 ml/kg (95% CI 0.1 to 0.6), increased spontaneous expired tidal volume by 0.3 ml/kg (95% CI 0.0 to 0.6), and increased total respiratory rate by 3 bpm (95% CI 1 to 4) immediately after the recruitment manoeuvre compared with the control group, but these differences disappeared after 25 minutes.

CONCLUSION

There is insufficient evidence to support performing recruitment manoeuvres after suctioning infants and children.

Continuous Monitoring of Dynamic Pulmonary Compliance Enables Detection of Endobronchial Intubation in Infants and Children

BACKGROUND

Auscultation of breath sounds is used routinely to confirm tracheal placement of endotracheal tubes (ETT). In infants and children, this method is limited by the conduction of breath sounds bilaterally, despite endobronchial intubation. Although several methods of detecting endobronchial intubation have been described, none is both simple and reliable. In this investigation, we determined whether changes in pulmonary compliance and airway pressures, measured using continuous side stream spirometry, can reliably detect endobronchial intubation in pediatric patients.

METHODS

Forty patients aged 1 month to 6 years were included. After endotracheal intubation the ETT was incrementally advanced as two observers monitored breath sounds and spirometry (Pressure-Volume Loops). Changes in pulmonary compliance, peak inspiratory pressure, or auscultation were reported, at which point ETT position was confirmed by fiberoptic bronchoscopy.

RESULTS

Endobronchial intubation decreased measured pulmonary compliance by 45 +/- 11% (mean +/- sd; P < 0.001, Range 26%-66%) and increased peak airway pressures by 26 +/- 17% (mean +/- sd; P < 0.001, Range 0-87). Changes in peak airway pressures were smaller and more variable when compared to changes in compliance. Breath-sound auscultation failed to detect endobronchial intubation in 7.5% of cases.

CONCLUSIONS

Pulmonary compliance changes are a sensitive and an accurate indicator of endobronchial intubation in infants and children. Both increased peak airway pressures and changes in breath sounds are less sensitive indicators of endobronchial intubation.

Calculation of intratracheal airway pressure in ventilated neonatal piglets with endotracheal tube leaks

OBJECTIVE

In ventilated neonates, only the applied pressure of the ventilator is adjusted and monitored. When an endotracheal tube leaks, intratracheal pressure decreases depending on the size of the endotracheal tube and of the leak. Furthermore, an increase in resistance and/or compliance might delay the increase of intratracheal pressure during inspiration and its decline during expiration. Short inspiratory time can cause insufficient ventilation, because intratracheal pressure peak might not be reached. Short expiratory time may lead to air trapping, because intratracheal pressure could not return to baseline. The aim of this study was to develop a mathematical algorithm to calculate intratracheal pressure continuously during ventilation and to evaluate the accuracy of this method.

DESIGN

Prospective, animal study.

SETTING

University research laboratory.

SUBJECTS

To verify the mathematical algorithm, eight neonatal piglets (1600-2600 g) were studied under different endotracheal tube leak conditions (45% to 98%). The median compliance and resistance were 1.06 mL/cm H2O/kg and 123 cm H2O/L/sec, respectively.

INTERVENTIONS

Pressure decreases caused by the different endotracheal tubes were measured in a model while air flow was increased stepwise. Based on these results, a mathematical method was developed to calculate intratracheal pressure under leak conditions continuously in relation to the flow through the endotracheal tube as well as to calculate the values of resistance, compliance, and applied pressure of the ventilator.

MEASUREMENTS AND MAIN RESULTS

The intratracheal pressure calculated was compared with the measured intratracheal pressure over time. The differences between measured and calculated intratracheal pressure related to peak applied pressure of the ventilator did not exceed 10%. The medians of absolute amounts of differences between measured and calculated intratracheal pressure were <1 cm H2O.

CONCLUSIONS

The accuracy of the calculation of intratracheal pressure ensures adequate monitoring of artificial ventilation, even in the presence of endotracheal tube leaks. This might decrease the risk of barotrauma and improve the effectiveness of ventilation.

Correction of compliance and resistance altered by endotracheal tube leaks and non-linear pressure/volume-relationships

Measurements of lung compliance (C) and resistance (R) are influenced by endotracheal tube leaks (ETTL) as well as non-linear pressure/volume relationships (P/V relationship). To keep C and R reliable, we developed an algorithm to mathematically correct inspiratory and expiratory volume (V) and flow. In this study, a ventilated lung model for non-linear P/V relationship with adjustment of an increasing ETTL was studied. In addition, the recordings (airway pressure, flow, and volume) of 21 infants (median weight: 1,220 g, range: 640-2,160 g, with a median leak size of 32%, range: 24-56%) were investigated. C and R were calculated continuously from the recordings of flow, volume, and airway pressure over time according to the changing volume. A method especially developed for the analysis of non-linear pressure-volume-relationship (APVNL) was employed. C and R affected by leaks were corrected applying the newly developed mathematical algorithm and compared with measurements without leakage. C could be corrected up to a leak of 80% and R up to 55% leak at half tidal V for the model with non-linear P/V-R. C and R without leak and after leak correction did not differ significantly in all infants where the APVNL method was applied (P > 0.05).

Effect of endotracheal suction on lung dynamics in mechanically-ventilated paediatric patients

Endotracheal suctioning is performed regularly in ventilated infants and children to remove obstructive secretions. The effect of suctioning on respiratory mechanics is not known. This study aimed to determine the immediate effect of endotracheal suctioning on dynamic lung compliance, tidal volume, and airway resistance in mechanically-ventilated paediatric patients by means of a prospective observational clinical study. Lung mechanics were recorded for five minutes before and five minutes after a standardised suctioning procedure in 78 patients intubated with endotracheal tubes < or = 4.0 mm internal diameter. Twenty-four patients with endotracheal tube leaks > or = 20% were excluded from analysis. There was a significant overall decrease in dynamic compliance (p < 0.001) and mechanical expired tidal volume (p = 0.03) following suctioning with no change in the percentage endotracheal tube leak (p = 0.41). The change in dynamic compliance was directly related to both endotracheal tube and catheter sizes. There was no significant change in expiratory or inspiratory airway resistance following suctioning (p > 0.05). Although the majority of patients (68.5%) experienced a drop in dynamic compliance following suctioning, dynamic compliance increased in 31.5% of patients after the procedure. This study demonstrates that endotracheal suctioning frequently causes an immediate drop in dynamic compliance and expired tidal volume in ventilated children with variable lung pathology, intubated with small endotracheal tubes, probably indicating loss of lung volume caused by the suctioning procedure. There is no evidence that suctioning reduces airway resistance.

Respiratory physiotherapy vs. suction: the effects on respiratory function in ventilated infants and children

OBJECTIVE

To assess and compare the effects of physiotherapy and suction on expired tidal volume (V(TE)), respiratory compliance (C(rs)), resistance (R(rs)) and arterial blood gases.

DESIGN

Randomised cross-over study comparing outcomes after both treatments on the same day.

SETTING

Intensive tertiary care units, Great Ormond Street Hospital, London.

PATIENTS

One hundred children on full ventilatory support requiring physiotherapy. Paired measurements were obtained in 90 participants, and 7 others were excluded because of tracheal tube leak.

INTERVENTIONS

Respiratory physiotherapy and suction.

MEASUREMENTS AND RESULTS

Physiotherapy lasted longer and required more saline and catheters per treatment. There were no significant group changes in V(TE) or C(rs) after either treatment, but a tendency for R(rs )to fall following physiotherapy which reached significance in patients on volume-preset ventilation. There were also small but statistically significant reductions in HCO(3)(-), base excess and SaO(2) after physiotherapy. V(TE) and C(rs) increased and R(rs) decreased in excess of their 95% limits of agreement for normal variability in approximately twice as many subjects following physiotherapy than suction, these differences being significant for V(TE) and approaching significance for C(rs) and R(rs).

CONCLUSIONS

Physiotherapy appeared to have an advantage in reducing R(rs )in some patients, but also produced changes in derived blood gas parameters. Within individuals, physiotherapy treatments were also more likely to produce improvements in V(TE), C(rs) and R(rs) than suction. Further research should identify sensitive patient selection criteria and assess longer-term effects of such treatments.

Correction of compliance and resistance altered by endotracheal tube leaks

OBJECTIVE

Measurements of lung compliance and resistance are influenced by endotracheal tube leaks. To keep compliance and resistance reliable, we developed an algorithm to correct inspiratory and expiratory volume and flow mathematically.

DESIGN

Prospective, clinical study.

SETTING

University research laboratory and neonatal intensive care unit.

MODEL

A ventilated lung model with a linear pressure-volume relationship and with adjustment of an increasing endotracheal tube leak was investigated.

PATIENTS

A total of 21 ventilated premature neonates (median weight, 1220 g; range, 640-2160 g; median leak, 32%; range, 24-56%) were studied.

MEASUREMENTS AND MAIN RESULTS

Compliance and resistance were calculated from the recordings of flow, volume, and airway pressure over time employing linear regression of the equation of motion to obtain compliance and resistance. Compliance and resistance altered by leaks were corrected and compared with measurements without leak. Compliance and resistance of the lung model could be corrected up to an endotracheal tube leak size of 86%. Compliance and resistance without leak and after leak correction did not differ significantly for all infants using the linear regression method (p >.05). For the correction of compliance in 15 and for the correction of resistance in 12 of the 21 infants, the coefficients of variation of ten measured breaths without leak were greater or equal to the differences of the values of compliance and resistance between conditions of no leak and corrected leak, respectively.

CONCLUSION

Pulmonary compliance and resistance can be reliably corrected even in the presence of a substantial endotracheal tube leak, which makes pulmonary function tests more reliable.

Effect of delayed sternal closure after cardiac surgery on respiratory function in ventilated infants

OBJECTIVE

Studies examining the effect of sternal closure on respiratory function have not been published, and currently there is little evidence to guide ventilation management immediately after closure. The aim of this study was to establish the impact of delayed sternal closure on expired tidal volume, respiratory system compliance, and CO2 elimination immediately after the procedure in infants who had undergone open heart surgery.

DESIGN

Prospective study of respiratory function before and after delayed sternal closure.

SETTING

Cardiac intensive care unit, Great Ormond Street Hospital, London.

PATIENTS

Seventeen infants (median age, 2 wks) with open median sternotomy incisions after cardiac surgery. Data were collected between August 1998 and March 2000.

INTERVENTIONS

Respiratory function was measured continuously for 30 mins before and after delayed sternal closure in paralyzed ventilated infants.

MEASUREMENTS AND RESULTS

Four babies were excluded from the study because they required either immediate increase in ventilation after delayed sternal closure (n = 3) or removal of pericardial blood collection (n = 1). In the remaining 13 infants, expired tidal volume and CO2 elimination decreased significantly (p < .005) by a mean of 17% and 29%, respectively, after sternal closure. In five of the remaining 13 patients, the magnitude of tracheal tube leak increased by > or = 10% after delayed sternal closure, thereby invalidating recorded changes in respiratory system compliance. Of the eight infants in whom there was a minimal change in leak, respiratory system compliance decreased significantly (p < .05) by a mean of 19%.

CONCLUSIONS

This study supports the hypothesis that respiratory function may be compromised after delayed sternal closure and that ventilatory support should be increased to counteract the anticipated decrease in tidal volume. Extra vigilance should be applied in monitoring blood gases after delayed sternal closure to assess clinical responses to sternal closure or changes in ventilatory support. Accurate assessment of change in respiratory system compliance after any therapeutic intervention may be precluded by changes in tracheal tube leak during the procedure.

Accuracy of volume measurements in mechanically ventilated newborns: a comparative study of commercial devices

OBJECTIVE

Ventilatory measurements in ventilated newborns are increasingly used to monitor and to optimize mechanical ventilation. The aim of this study was to compare the accuracy of volume measurements by different instruments using standardized laboratory conditions.

METHODS

The accuracy of displayed volume values of different commercial devices (Bicore CP-100, Ventrak 1500, Ventrak 1550, Babylog 8000, PEDS IV and SensorMedics 2600) was investigated using adjustable calibration syringes (volume range 2-60 ml, breathing rates 30/min-60/min) and humidified (>95%), heated (35 degrees C) breathing gas with adjustable FIO2 (0.21-1.0). The pneumotach and also the tubes were placed within an incubator (37 degrees C).

RESULTS

The relative volume error of all devices was in conformity with clinically allowed tolerances (Bicore CP-100 6.4+/-0.5% (mean +/- SD), Ventrak 1500 3.6+/-4.2%, Ventrak 1550 6.5+/-2.7%, Babylog 8000 -5.5+/-1.5%, PEDS IV -4.0+/-1.4%, SensorMedics 2600 3.5+/-1.75%) for the measuring range studied (10 ml < V < 60 ml, rate 30-60/min, FIO2 = 0.21). Unacceptable errors were obtained for volumes lower than 10 ml with Bicore CP-100 (-28.5+/-26%) and PEDS IV (-10.3+/-3.4%). Changes in FIO2 had an important influence on volume measurements and only the SensorMedics 2600 and the PEDS IV corrected properly for FIO2 changes.

CONCLUSION

Most of the currently available neonatal spirometry devices allow sufficiently accurate volume measurements in the range of 10-60 ml and at frequencies between 30-60/min provided that an increased FIO2 is taken into account.