Breath-to-breath variability in displayed tidal volume:Real or artifact?
http://www.100md.com
《中华医药杂志》英文版 2006年第3期
Correspondence to Shabih Manzar, MD,Division of Neonatology,Rockford Memorial Hospital,2400 North Rockton Avenue,Rockford,Illinois 61103,US
Tel:+815- 971- 6500Fax:+815-968-5742E-mail: shabihman@hotmail.com
[Abstract]ObjectiveTo study the breath to breath variability in the exhaled tidal volume (Vte) measurements in surfactant treated mechanically ventilated premature neonates. MethodsA group of surfactant treated extremely low birth weight infants (birth weight less than 1 000 grams) were selected. They were all mechanically ventilated using AVEATM ventilator. The Vte was measured by the low dead space, single-use pneumotachometer placed between the endotracheal tube and Y-piece of the respiratory circuit. Computer-assisted recordings were used to study the variation in Vte measurements. The mean, median, range, variance, standard error of the mean (SEM), standard deviation (SD) and 95% confidence interval (CI) were calculated for a given five-minute epoch. ResultsThe mean Vte for all mandatory breath was noted to be (6.3 ± 1.3) ml/kg while for spontaneous breath was (4.3 ± 2) ml/kg,P= 0.32. A low variance, low SD, low range, low 95% CI and low SEM was noted for the five minutes epoch of Vte measurements. ConclusionsBedside tidal volume measurements vary widely on the second to second display. However, reliable measurements could be obtained by taking the average Vte of five minutes period.
[Key words]exhaled tidal volume;neonates;ventilator;variation
INTRODUCTION
With the advent of new generation computer-assisted ventilators, pulmonary mechanics monitoring (PMM) is being increasingly used in the neonatal intensive care units [1,2].Among the variety of PMM provided as a built-in feature, tidal volume is most often used parameter to assess the ventilation adequacy and to monitor pulmonary dynamics [3~7]. Tidal volume (Vt) is defined as the volume of each breath for the entire respiratory cycle [4]. In clinical settings, exhaled tidal volume (Vte) is generally used as a substitute of Vt. In neonates, Vte is preferred over the measurements of inhaled tidal volume (Vti) due to the fact that leak around the uncuffed endotracheal tube (used exclusively in neonates) is recognized to occur predominantly during inspiration [5,6].
Despite the potential importance of Vt in the management of ventilated neonate, controversies exist regarding the accuracy and clinical application of tidal volume measurements [6,7].Investigators have raised concerns regarding the wide variation in the measured and displayed tidal volume [8,9]. Several factors have been implicated for the imprecise measurement viz. the variability in the physical property of breathing gases [10](humidification, heat and FiO2 affect the physical characteristics of the inspired and expired gas), potential air leaks (use of uncuffed endotracheal tubes in neonates), increase in dead space by attaching the flow sensor to the respiratory circuit and finally moisture and mucus occluding the device causing risks to the neonates and faults in the pulmonary function measurements . However, evolution in engineering technology has resulted in the development of better flow sensors and new generation ventilators (e.g. AVEATM ventilator) with the target to rectify some of these flaws and maximize the precision in Vt measurements. The clinical studies on the variability in the bedside Vte measurement among the mechanically ventilated premature neonates are scanty. We conducted this pilot study to look at the breath to breath variation in Vte in such infants in a clinical setting.
METHODS
The study was conducted at John Stroger Hospital of Cook County, Chicago. The protocol was presented to Scientific Committee of the Institutional Review Board
and was exempted from review. The requirement for parental consent was waived in view of the observational nature of the study with no intervention on the infants. Also HIPAA (Health Insurance Portability and Accountability Act) waiver was obtained as the study did not require any link to the identification of the patients.
Patients
A group of extremely low birth weight (ELBW) infants defined as birth weight less than 1 000 grams were selected. These infants had clinical and radiological evidence of respiratory distress syndrome. They were treated with natural surfactant (Survanta, 4 ml/kg) and were mechanically ventilated. All infants were studied during the first 72 hours of admission. The data on the ventilator settings and pulmonary mechanics were collected directly from the AVEATM ventilator.
AVEA Ventilator System
The AVEATMventilator (Model No.16184, VIASYS Healthcare, Palm Spring, CA) [11]was used exclusively to obtain the Vte measurements. The ventilator was operated by certified respiratory therapists (RT). The calibration and equipment check was done periodically as routine and for potential problems. At admission, the time, weight and endotracheal tube (ETT) size and length were logged in by the RTs by using the ‘Setup’ menu of the ventilator. The AVEA ventilator has the feature of measuring and displaying up to 34 parameters on the 24-hour trend form recorded as one minute averaged value. The time is displayed in yellow while event values are displayed in green with asterisk at the time. Up to 10 parameters could be seen at one time. The AVEA ventilator also has the feature of recording minute by minute spontaneous breath and mandatory breath separately and displaying these values separately as well as simultaneously with the averaged Vte/kg value for that minute. The ventilator is also capable of recording the events. The time of any intervention e.g. endotracheal suctioning or blood sampling is recorded by selecting the ‘Event’ drop down menu and selecting the intervention (suctioning or blood gas). The computer-assisted processor stored all the values, including Vte, for that time in yellow color with the time marked with an asterisk. This information could be retrieved and reviewed by using the ‘Trend’ menu.
Vte Measurements
All the babies enrolled in the study were breathing spontaneously at the time of the study and were ventilated using the synchronized intermittent mandatory ventilation (SIMV) mode. No paralysis, sedation or pressure support was used during the study period. The babies were excluded if they received any of these interventions or were on assist-control (A/C) mode of ventilation. The Vte was measured by a low dead space pneumotachometer (VarFlex) attached between the proximal end of the endotracheal tube and Y-piece. This technique has shown to give a better Vte measurement in infants [12]. The principle is based on measuring the flow from resistance. The flow (V′) is being measured in a tube with a small fixed resistance (R). The pressure drop (P1-P2) across the resistance relates linearly to flow (P1 - P2 = R. V′). A single-use pneumotachometer (PNT) was used for each neonate. The PNT was precalibrated and was checked periodically by the nurse and RT for occlusion by mucus or secretions. By using the trend touch button (see below), the Vte, for both spontaneous and mandatory breaths were selected to be displayed as well as to be shown in the 24-hours recordings. To eliminate the chance of error in Vte/ kg recordings, a manual check for the current weight was performed.
In clinical setting, no ‘gold standard’ is available to estimate the accuracy of tidal volume. We used the textbook range to look for the accuracy [4]. Precision was defined as the nearly similar reproducible measurements. A five minute epoch (short-term variation) was used to study the variability in the Vte measurements. The five minute block readings were obtained from the stored recording using the frozen screen technique on the ventilator (touch Screen, touch Trend, touch Freeze, scroll down/up by using the knob). Only one investigator (SM) looked at all the readings. The five obtained Vte values were entered into the computer data sheet and later analyzed using the descriptive statistics of SPSS version 7.5. The range, mean, median, variance, standard error, standard deviation and 95% confidence interval were calculated for the given 5 values. A wide range, high variance, high standard error and standard deviation and wide 95% confidence interval were taken as indicators of increased variability.
A total of 126 observations (63 spontaneous Vte and 63 mandatory Vte for the same epoch) were made on seven ELBW infants, with 3 readings per day on each, 8∶00, 12∶00 and 16∶00 (long-term variation) respectively.
RESULTS
A narrow range, low variance, low standard error, low standard deviation and narrow 95% confidence interval were noted for the mean of five-minute epoch Vte values (individual data not shown). A high precision was noted for the measured Vte values. The mean Vte for all mandatory breath was noted to be (6.3 ± 1.3) ml/kg (Figure 1) while for spontaneous breath was (4.3 ± 2) ml/kg, P=0.32.
Figure 1 Exhaled tidal volume(Vte) (ml/kg)
DISCUSSION
The study demonstrated that bedside tidal volume (Vte) measurements are reliable discarding the notion of GIGO (garbage in,garbage out) [6]. We attributed the precision in Vte measurements to the use of the low dead space pneumotachometer (PNT) [12] along with the modified approach of using a trend or epoch rather than a single displayed value. During the study period, a single-use PNT was used with periodical check for moisture and clogging by mucus. Similarly, the respiratory circuit was regularly monitored for humidity and heat, as these may alter the physical characteristics of the exhaled gases and could potentially lead to erroneous Vte readings.
Our observation contradicted the previous reports questioning the accuracy of tidal volume measurements [6~9]. Chow et al [7] studied the Vte accuracy by using calibrated syringes as the ‘gold standard’. It was a bench research using the standard pulmonary settings. In contrast, Castle et al [8] supplemented there data by in vivo recordings. They attributed the inaccuracy in tidal volume measurement to the site of measurement. The present study was unique as it was performed in total clinical setting.
The SIMV mode of ventilation was used with no paralysis or sedation. The infants were allowed to breathe spontaneously during the mechanical ventilation. In this way, we were able to obtain separate tidal volumes for mechanical and spontaneous breaths. The average Vte for spontaneous breath (4.3 ml/kg) were relatively lower than the average Vte for the machine generated mandatory breath (6.3 ml/kg). The difference could be explained by a relatively weaker respiratory effort during the spontaneous breathing as compared to higher tidal volumes generated by machine breath. However, minimal intra-subject variability was noted between these Vte measurements.
As we did not measure the dead space (DS), argument could be raised about the accuracy of Vte measurements. In clinical non-standardized settings, it is very difficult to control for or measure the anatomical, alveolar or physiological dead space, especially in infants with relatively dynamic pulmonary compliance. Bohr method could be used to calculate the DS (anatomical DS = Alveolar CO2 - Expired CO2 / Alveolar CO2 or physiological DS = Arterial PCO2 - Expired CO2 / Arterial PCO2) but it requires technical perfection [13]. As we took all Vte measurement from surfactant treated infants we expect the DS/ Vt ratio to be minimal. Use of surfactant has shown to decrease the dead space to tidal volume ratio considerably [14].The other alternative described to obtain dead space free ventilation is the use of correction algorithm and dead space free flow-through technique but the former is possible in vitro and the latter has shown to have a very high inter-subject variability [15,16].
The other limitation of this pilot study is the small sample size and repeated measurements on the same infants. Thus, our findings may not be applicable to neonates with varying severity and pathology of their respiratory illnesses especially the term infants [17]. We are planning to duplicate our findings by a larger study including a heterogeneous group of term and preterm infants with wide spectrum of respiratory pathology.
The data presented in the study is exclusively obtained from a single brand of ventilator. As the basic technology used for obtaining Vte measurements is essentially the same in other in-use brands of ventilators, we do not expect a wide variation. However, multi-center studies that use the other brands of ventilators are warranted to further validate our findings.
In summary, variation in the bedside tidal volume (Vt) measurements is minimal and by using the low dead space pneumotachometer and following a trend of Vte values over a specified time, reliable Vt measurements could be obtained.
ACKNOWLEDGEMENTS
I would like to thank Dr. Suma Pyati, Chairman of Neonatal Division, John H Stroger, Jr. Hospital of Cook County, Chicago for her continuous support during the study.
REFERENCES
1. Schibler A, Frey U. Role of lung function testing in the management of mechanically ventilated infants. Arch Dis Child Fetal Neonatal Ed, 2002,87:F7-F10.
2. Numa AH, Newth CJ. Assessment of lung function in the intensive care unit. Pediatr Pulmonol,1995,19:118-128.
3. Cheema IU, Ahluwalia JS. Feasibility of tidal volume -guided ventilation in newborn infants: a randomized, crossover trial using volume guarantee modality. Pediatrics,2001,107:1323-1328.
4. Bhutani VK, Sivieri EM. Pulmonary function and graphics. In : Goldsmith JP, Karotkin EH (Eds). Assisted ventilation of the Neonates, 4th edition.Saunders, PA, 2003, 293-309.
5. Kondo T, Matsumoto I, Lanteri CJ, Sly PD. Respiratory mechanics during mechanical ventilation:A model study on the effects of leak around a tracheal tube. Pediatr Pulmonol ,1997,24:423-428.
6. Mammel MC. Bedside tidal volume measurements: GIGO? Crit Care Med,2002,30:2606.
7. Chow LC, Vanderhal A, Raber J,et al. Are tidal volume measurement in neonatal pressure-controlled ventilation accurate? Pediatr Pulmonol,2002,34: 196-202.
8. Castle RA, Dunne CJ, Mok Q, et al. Accuracy of displayed values of tidal volume in pediatric intensive care unit. Crit Care Med,2002,30:2566-2574.
9. Roske K, Foitzik B, Wauer RR,et al. Accuracy of volume measurements in mechanically ventilated newborns: A comparative study of commercial devices. J Clin Monit Comput,1998,14: 413-420.
10. Snepvangers Y, de Winter P, Burger J, et al. Correction factors for oxygen and flow-rate effects on neonatal Fleisch and Lilly pneumotachometers. Pediatr Crit Care Med,2003,4:227-232.
11. Operator’s Manual AVEA Ventilator Systems, March,2003.
12. Cannon ML, Cornell J, Tripp-Hamel DS, et al. Tidal volume for ventilated infants should be determined with a pneumotachometer placed at the endotracheal tube. Am J Respir Crit Care Med,2000,162: 2109-2112.
13. Bhutani V, Abbasi S. Evaluation of pulmonary functions in the neonate. In: Polin RA, Fox WW,Eds.Fetal and Neonatal Physiology, W B Saunders, PA, 1992,853- 871.
14. Chung EH, Ko SY, Chang YS,et al.Changes in dead space/tidal volume ratio and pulmonary mechanics after surfactant replacement therapy in respiratory distress syndrome of the newborn infants. J Korean Med Sci,2001,16:51-56.
15. Foitzik B, Schmidt M, Proquitte H,et al.Deadspace free ventilatory measurements in newborns during mechanical ventilation. Crit Care Med,2001,29:413-419.
16. Paetow U, Windstetter D, Schmalisch G. Variability of tidal breathing flow-volume loops in healthy and sick newborns. Am J Perinatol,1999,16:549-559.
17. Hjalmarson O, Sandberg K. Abnormal lung function in healthy preterm infants.Am J Respire Crit Care Med,2002,165:83-87.
Division of Neonatology,Rockford Memorial Hospital,2400 North Rockton Avenue,Rockford,Illinois 61103,US
(Editor Jaque)(Shabih Manzar)
Tel:+815- 971- 6500Fax:+815-968-5742E-mail: shabihman@hotmail.com
[Abstract]ObjectiveTo study the breath to breath variability in the exhaled tidal volume (Vte) measurements in surfactant treated mechanically ventilated premature neonates. MethodsA group of surfactant treated extremely low birth weight infants (birth weight less than 1 000 grams) were selected. They were all mechanically ventilated using AVEATM ventilator. The Vte was measured by the low dead space, single-use pneumotachometer placed between the endotracheal tube and Y-piece of the respiratory circuit. Computer-assisted recordings were used to study the variation in Vte measurements. The mean, median, range, variance, standard error of the mean (SEM), standard deviation (SD) and 95% confidence interval (CI) were calculated for a given five-minute epoch. ResultsThe mean Vte for all mandatory breath was noted to be (6.3 ± 1.3) ml/kg while for spontaneous breath was (4.3 ± 2) ml/kg,P= 0.32. A low variance, low SD, low range, low 95% CI and low SEM was noted for the five minutes epoch of Vte measurements. ConclusionsBedside tidal volume measurements vary widely on the second to second display. However, reliable measurements could be obtained by taking the average Vte of five minutes period.
[Key words]exhaled tidal volume;neonates;ventilator;variation
INTRODUCTION
With the advent of new generation computer-assisted ventilators, pulmonary mechanics monitoring (PMM) is being increasingly used in the neonatal intensive care units [1,2].Among the variety of PMM provided as a built-in feature, tidal volume is most often used parameter to assess the ventilation adequacy and to monitor pulmonary dynamics [3~7]. Tidal volume (Vt) is defined as the volume of each breath for the entire respiratory cycle [4]. In clinical settings, exhaled tidal volume (Vte) is generally used as a substitute of Vt. In neonates, Vte is preferred over the measurements of inhaled tidal volume (Vti) due to the fact that leak around the uncuffed endotracheal tube (used exclusively in neonates) is recognized to occur predominantly during inspiration [5,6].
Despite the potential importance of Vt in the management of ventilated neonate, controversies exist regarding the accuracy and clinical application of tidal volume measurements [6,7].Investigators have raised concerns regarding the wide variation in the measured and displayed tidal volume [8,9]. Several factors have been implicated for the imprecise measurement viz. the variability in the physical property of breathing gases [10](humidification, heat and FiO2 affect the physical characteristics of the inspired and expired gas), potential air leaks (use of uncuffed endotracheal tubes in neonates), increase in dead space by attaching the flow sensor to the respiratory circuit and finally moisture and mucus occluding the device causing risks to the neonates and faults in the pulmonary function measurements . However, evolution in engineering technology has resulted in the development of better flow sensors and new generation ventilators (e.g. AVEATM ventilator) with the target to rectify some of these flaws and maximize the precision in Vt measurements. The clinical studies on the variability in the bedside Vte measurement among the mechanically ventilated premature neonates are scanty. We conducted this pilot study to look at the breath to breath variation in Vte in such infants in a clinical setting.
METHODS
The study was conducted at John Stroger Hospital of Cook County, Chicago. The protocol was presented to Scientific Committee of the Institutional Review Board
and was exempted from review. The requirement for parental consent was waived in view of the observational nature of the study with no intervention on the infants. Also HIPAA (Health Insurance Portability and Accountability Act) waiver was obtained as the study did not require any link to the identification of the patients.
Patients
A group of extremely low birth weight (ELBW) infants defined as birth weight less than 1 000 grams were selected. These infants had clinical and radiological evidence of respiratory distress syndrome. They were treated with natural surfactant (Survanta, 4 ml/kg) and were mechanically ventilated. All infants were studied during the first 72 hours of admission. The data on the ventilator settings and pulmonary mechanics were collected directly from the AVEATM ventilator.
AVEA Ventilator System
The AVEATMventilator (Model No.16184, VIASYS Healthcare, Palm Spring, CA) [11]was used exclusively to obtain the Vte measurements. The ventilator was operated by certified respiratory therapists (RT). The calibration and equipment check was done periodically as routine and for potential problems. At admission, the time, weight and endotracheal tube (ETT) size and length were logged in by the RTs by using the ‘Setup’ menu of the ventilator. The AVEA ventilator has the feature of measuring and displaying up to 34 parameters on the 24-hour trend form recorded as one minute averaged value. The time is displayed in yellow while event values are displayed in green with asterisk at the time. Up to 10 parameters could be seen at one time. The AVEA ventilator also has the feature of recording minute by minute spontaneous breath and mandatory breath separately and displaying these values separately as well as simultaneously with the averaged Vte/kg value for that minute. The ventilator is also capable of recording the events. The time of any intervention e.g. endotracheal suctioning or blood sampling is recorded by selecting the ‘Event’ drop down menu and selecting the intervention (suctioning or blood gas). The computer-assisted processor stored all the values, including Vte, for that time in yellow color with the time marked with an asterisk. This information could be retrieved and reviewed by using the ‘Trend’ menu.
Vte Measurements
All the babies enrolled in the study were breathing spontaneously at the time of the study and were ventilated using the synchronized intermittent mandatory ventilation (SIMV) mode. No paralysis, sedation or pressure support was used during the study period. The babies were excluded if they received any of these interventions or were on assist-control (A/C) mode of ventilation. The Vte was measured by a low dead space pneumotachometer (VarFlex) attached between the proximal end of the endotracheal tube and Y-piece. This technique has shown to give a better Vte measurement in infants [12]. The principle is based on measuring the flow from resistance. The flow (V′) is being measured in a tube with a small fixed resistance (R). The pressure drop (P1-P2) across the resistance relates linearly to flow (P1 - P2 = R. V′). A single-use pneumotachometer (PNT) was used for each neonate. The PNT was precalibrated and was checked periodically by the nurse and RT for occlusion by mucus or secretions. By using the trend touch button (see below), the Vte, for both spontaneous and mandatory breaths were selected to be displayed as well as to be shown in the 24-hours recordings. To eliminate the chance of error in Vte/ kg recordings, a manual check for the current weight was performed.
In clinical setting, no ‘gold standard’ is available to estimate the accuracy of tidal volume. We used the textbook range to look for the accuracy [4]. Precision was defined as the nearly similar reproducible measurements. A five minute epoch (short-term variation) was used to study the variability in the Vte measurements. The five minute block readings were obtained from the stored recording using the frozen screen technique on the ventilator (touch Screen, touch Trend, touch Freeze, scroll down/up by using the knob). Only one investigator (SM) looked at all the readings. The five obtained Vte values were entered into the computer data sheet and later analyzed using the descriptive statistics of SPSS version 7.5. The range, mean, median, variance, standard error, standard deviation and 95% confidence interval were calculated for the given 5 values. A wide range, high variance, high standard error and standard deviation and wide 95% confidence interval were taken as indicators of increased variability.
A total of 126 observations (63 spontaneous Vte and 63 mandatory Vte for the same epoch) were made on seven ELBW infants, with 3 readings per day on each, 8∶00, 12∶00 and 16∶00 (long-term variation) respectively.
RESULTS
A narrow range, low variance, low standard error, low standard deviation and narrow 95% confidence interval were noted for the mean of five-minute epoch Vte values (individual data not shown). A high precision was noted for the measured Vte values. The mean Vte for all mandatory breath was noted to be (6.3 ± 1.3) ml/kg (Figure 1) while for spontaneous breath was (4.3 ± 2) ml/kg, P=0.32.
Figure 1 Exhaled tidal volume(Vte) (ml/kg)
DISCUSSION
The study demonstrated that bedside tidal volume (Vte) measurements are reliable discarding the notion of GIGO (garbage in,garbage out) [6]. We attributed the precision in Vte measurements to the use of the low dead space pneumotachometer (PNT) [12] along with the modified approach of using a trend or epoch rather than a single displayed value. During the study period, a single-use PNT was used with periodical check for moisture and clogging by mucus. Similarly, the respiratory circuit was regularly monitored for humidity and heat, as these may alter the physical characteristics of the exhaled gases and could potentially lead to erroneous Vte readings.
Our observation contradicted the previous reports questioning the accuracy of tidal volume measurements [6~9]. Chow et al [7] studied the Vte accuracy by using calibrated syringes as the ‘gold standard’. It was a bench research using the standard pulmonary settings. In contrast, Castle et al [8] supplemented there data by in vivo recordings. They attributed the inaccuracy in tidal volume measurement to the site of measurement. The present study was unique as it was performed in total clinical setting.
The SIMV mode of ventilation was used with no paralysis or sedation. The infants were allowed to breathe spontaneously during the mechanical ventilation. In this way, we were able to obtain separate tidal volumes for mechanical and spontaneous breaths. The average Vte for spontaneous breath (4.3 ml/kg) were relatively lower than the average Vte for the machine generated mandatory breath (6.3 ml/kg). The difference could be explained by a relatively weaker respiratory effort during the spontaneous breathing as compared to higher tidal volumes generated by machine breath. However, minimal intra-subject variability was noted between these Vte measurements.
As we did not measure the dead space (DS), argument could be raised about the accuracy of Vte measurements. In clinical non-standardized settings, it is very difficult to control for or measure the anatomical, alveolar or physiological dead space, especially in infants with relatively dynamic pulmonary compliance. Bohr method could be used to calculate the DS (anatomical DS = Alveolar CO2 - Expired CO2 / Alveolar CO2 or physiological DS = Arterial PCO2 - Expired CO2 / Arterial PCO2) but it requires technical perfection [13]. As we took all Vte measurement from surfactant treated infants we expect the DS/ Vt ratio to be minimal. Use of surfactant has shown to decrease the dead space to tidal volume ratio considerably [14].The other alternative described to obtain dead space free ventilation is the use of correction algorithm and dead space free flow-through technique but the former is possible in vitro and the latter has shown to have a very high inter-subject variability [15,16].
The other limitation of this pilot study is the small sample size and repeated measurements on the same infants. Thus, our findings may not be applicable to neonates with varying severity and pathology of their respiratory illnesses especially the term infants [17]. We are planning to duplicate our findings by a larger study including a heterogeneous group of term and preterm infants with wide spectrum of respiratory pathology.
The data presented in the study is exclusively obtained from a single brand of ventilator. As the basic technology used for obtaining Vte measurements is essentially the same in other in-use brands of ventilators, we do not expect a wide variation. However, multi-center studies that use the other brands of ventilators are warranted to further validate our findings.
In summary, variation in the bedside tidal volume (Vt) measurements is minimal and by using the low dead space pneumotachometer and following a trend of Vte values over a specified time, reliable Vt measurements could be obtained.
ACKNOWLEDGEMENTS
I would like to thank Dr. Suma Pyati, Chairman of Neonatal Division, John H Stroger, Jr. Hospital of Cook County, Chicago for her continuous support during the study.
REFERENCES
1. Schibler A, Frey U. Role of lung function testing in the management of mechanically ventilated infants. Arch Dis Child Fetal Neonatal Ed, 2002,87:F7-F10.
2. Numa AH, Newth CJ. Assessment of lung function in the intensive care unit. Pediatr Pulmonol,1995,19:118-128.
3. Cheema IU, Ahluwalia JS. Feasibility of tidal volume -guided ventilation in newborn infants: a randomized, crossover trial using volume guarantee modality. Pediatrics,2001,107:1323-1328.
4. Bhutani VK, Sivieri EM. Pulmonary function and graphics. In : Goldsmith JP, Karotkin EH (Eds). Assisted ventilation of the Neonates, 4th edition.Saunders, PA, 2003, 293-309.
5. Kondo T, Matsumoto I, Lanteri CJ, Sly PD. Respiratory mechanics during mechanical ventilation:A model study on the effects of leak around a tracheal tube. Pediatr Pulmonol ,1997,24:423-428.
6. Mammel MC. Bedside tidal volume measurements: GIGO? Crit Care Med,2002,30:2606.
7. Chow LC, Vanderhal A, Raber J,et al. Are tidal volume measurement in neonatal pressure-controlled ventilation accurate? Pediatr Pulmonol,2002,34: 196-202.
8. Castle RA, Dunne CJ, Mok Q, et al. Accuracy of displayed values of tidal volume in pediatric intensive care unit. Crit Care Med,2002,30:2566-2574.
9. Roske K, Foitzik B, Wauer RR,et al. Accuracy of volume measurements in mechanically ventilated newborns: A comparative study of commercial devices. J Clin Monit Comput,1998,14: 413-420.
10. Snepvangers Y, de Winter P, Burger J, et al. Correction factors for oxygen and flow-rate effects on neonatal Fleisch and Lilly pneumotachometers. Pediatr Crit Care Med,2003,4:227-232.
11. Operator’s Manual AVEA Ventilator Systems, March,2003.
12. Cannon ML, Cornell J, Tripp-Hamel DS, et al. Tidal volume for ventilated infants should be determined with a pneumotachometer placed at the endotracheal tube. Am J Respir Crit Care Med,2000,162: 2109-2112.
13. Bhutani V, Abbasi S. Evaluation of pulmonary functions in the neonate. In: Polin RA, Fox WW,Eds.Fetal and Neonatal Physiology, W B Saunders, PA, 1992,853- 871.
14. Chung EH, Ko SY, Chang YS,et al.Changes in dead space/tidal volume ratio and pulmonary mechanics after surfactant replacement therapy in respiratory distress syndrome of the newborn infants. J Korean Med Sci,2001,16:51-56.
15. Foitzik B, Schmidt M, Proquitte H,et al.Deadspace free ventilatory measurements in newborns during mechanical ventilation. Crit Care Med,2001,29:413-419.
16. Paetow U, Windstetter D, Schmalisch G. Variability of tidal breathing flow-volume loops in healthy and sick newborns. Am J Perinatol,1999,16:549-559.
17. Hjalmarson O, Sandberg K. Abnormal lung function in healthy preterm infants.Am J Respire Crit Care Med,2002,165:83-87.
Division of Neonatology,Rockford Memorial Hospital,2400 North Rockton Avenue,Rockford,Illinois 61103,US
(Editor Jaque)(Shabih Manzar)