Original Article
23
Volume Guarantee Ventilation during Surgical Closure of Patent Ductus Arteriosus Martin Keszler, MD1
Kabir Abubakar, MD2
1 Department of Pediatrics, Women and Infants Hospital of Rhode
Island, Brown University, Providence, Rhode Island 2 Department of Pediatrics, Georgetown University Hospital, Washington, District of Columbia
Address for correspondence Martin Keszler, MD, Department of Pediatrics, Women and Infants Hospital of Rhode Island, 101 Dudley Street, Providence, RI 02905 (e-mail: [email protected]).
Abstract
Keywords
► patent ductus arteriosus ► surgical closure ► volume guarantee ventilation
Background Surgical closure of patent ductus arteriosus (PDA) is associated with adverse outcomes. Surgical exposure requires retraction of the lung, resulting in decreased aeration and compliance. Optimal respiratory support for PDA surgery is unknown. Experience with volume guarantee (VG) ventilation at our institution led us to hypothesize that surgery would be better tolerated with automatic adjustment of pressure by VG to maintain tidal volume (V T) during retraction. Objective The objective of this study was to describe ventilator support, V T, and oxygenation of infants supported with VG during PDA surgery. Design/Methods Ventilator variables, oxygen saturation, and heart rate were recorded during PDA surgery in a convenience sample of infants during PDA closure on VG. Pressure limit increased 11% and set V T was 26% lower during lung retraction. Fentanyl and pancuronium/vecuronium were used for anesthesia/muscle relaxation. Longitudinal data were analyzed by analysis of variance for repeated measures. Results Seven infants, 25.4 1.5 weeks and 723 141 g, underwent closure of PDA on VG at a mean age 29.9 days. No air leak, bradycardia, or death occurred. Target V T was maintained with a modest increase in inflation pressure. Oxygenation remained adequate. Conclusions VG avoided hypoxemia and maintained adequate V T with only a modest increase in peak inflation pressure and thus may be a useful mode during PDA surgery.
Surgical closure of patent ductus arteriosus (PDA) remains one of the most common surgical procedures in newborn infants.1 Because of concerns about the potential adverse effects of the surgery,2–4 PDA is typically closed surgically only in infants with significant cardiorespiratory compromise attributed to a large left to right ductal shunt. Consequently, infants undergoing PDA closure are often unstable and have limited cardiopulmonary reserve. To obtain adequate surgical exposure, the surgical team must retract the left lung out of the operative field. Compression of the left lung leads to decreased lung compliance and inevitably results in some
degree of respiratory compromise with falling oxygen saturation (SpO2) and sometimes bradycardia, despite increasing inflation pressure. When severe, this decompensation may require temporary release of the lung compression to allow the patient to recover before proceeding. The limited respiratory reserve of these critically ill infants places a premium on surgical speed, which could potentially lead to errors or complications. The best approach to respiratory support during PDA surgery has not been studied. It is unknown whether compromised gas exchange intraoperatively contributes to the increased rate of neurodevelopmental
received January 29, 2014 accepted January 30, 2014 published online April 4, 2014
Copyright © 2015 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
DOI http://dx.doi.org/ 10.1055/s-0034-1371713. ISSN 0735-1631.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Am J Perinatol 2015;32:23–26.
Volume Guarantee Ventilation for PDA Surgery
Keszler, Abubakar
impairment reported to occur in infants after surgical PDA closure,2–4 but any technique that minimizes cardiopulmonary complications during PDA surgery would be desirable. Volume guarantee (VG) is a technique of volume-targeted ventilation available on the Babylog 8000þ and VN 500 neonatal ventilators (Draeger Medical, Lubeck, Germany). With VG, the microprocessor of the device automatically adjusts inflation pressure up to a set pressure limit to maintain a target tidal volume (V T) based on the exhaled V T of the previous inflation.5 VG has been shown to maintain more stable V T, reduce hypocapnia, and lead to shorter duration of mechanical ventilation.6,7 We therefore hypothesized that the use of VG with a lower target V T during PDA surgery would deliver an adequate and stable V T, decrease the severity of hypoxemia, and reduce or eliminate bradycardia.
Methods To obtain a preliminary assessment of the potential utility of the intraoperative use of VG, we recorded ventilator variables, V T, and SpO2 and heart rate (HR) of infants during surgical closure of PDA in a convenience sample of infants undergoing surgical PDA closure while supported with VG at Georgetown University Hospital over a 5-year period. Infants who required PDA surgery based on the judgment of the clinical team were studied when the investigator was available and verbal parental consent could be obtained. Only patients without substantial leak (> 20%) around the endotracheal tube were studied, to ensure accurate measurement of V T. Surgery was performed in the neonatal intensive care unit (NICU) and was reserved for severely symptomatic infants who failed multiple medical closure attempts. Because VG had been the standard mode of ventilator support for many years at Georgetown University Hospital and PDA surgery was routinely performed in a special surgical bay of the NICU, it became standard practice in most infants to continue the same mode of support during surgery for PDA closure, as well as other procedures. Thus, the use of the VG during PDA closure was considered standard care and only the recording of the respiratory variables was being done for the purpose of the study. Consequently, only verbal parental consent was required for the use of the de-identified data. Patients were transferred to an open warmer in the surgical bay of the NICU and positioned in the right lateral decubitus position for appropriate surgical exposure. Infants remained on the ventilator settings and mode selected by the clinicians (assist control þ VG or pressure support þ VG). Set and measured V T, pressure limit, measured peak inflation pressure (PIP), ventilator rate, and fraction of inspired oxygen (FIO2) were recorded at 10-second intervals from the RS232 port of the Babylog 8000 þ ventilator using the Babyview software (Draeger Medical). HR and SpO2 were manually recorded from the bedside monitor, noting the lowest values. Surgical anesthesia was induced with high-dose fentanyl and muscle relaxation with pancuronium or vecuronium. Anesthesia was induced, maintained, and monitored by one of the staff anesthesiologists, while respiratory support was managed by one of the authors (M.K.). Baseline ventilation American Journal of Perinatology
Vol. 32
No. 1/2015
variables, HR, and SpO2 were recorded before induction of anesthesia. Following induction of anesthesia and muscle relaxation, the ventilator rate was increased to 50 inflations/min to compensate for the lack of spontaneous breathing and a second set of baseline values were obtained. Intraoperatively, the PIP limit was increased by 3 to 5 cm H2O as needed just before and during lung retraction and the target V T was reduced by 20 to 25% from baseline, recognizing that maintaining a normal V T during lung retraction would require excessive inflation pressure and likely result in volutrauma as the V T would be redistributed to the opposite lung. The ventilator rate was increased to 60/min during lung retraction to partially compensate for the smaller V T. FIO2 was initially increased by approximately 0.1 to 0.2 and subsequently adjusted as needed to avoid desaturation that would inevitably occur because of some degree of compression atelectasis leading to worsening ventilation/perfusion (V/Q) matching. The ventilator settings and monitored values were again recorded at the time of maximum lung retraction and again after completion of the operation and skin closure. Following release of the lung, the V T setting and PIP limit were returned to the preoperative value and the positive endexpiratory pressure was increased by 2 cm H2O for 5 minutes to help re-recruit any atelectatic portion of the lung, then returned to baseline. Demographic data were obtained from the medical record of each infant and all data were subsequently de-identified. The 10-second interval ventilator data recorded from the Babyview software onto a laptop were exported into an Excel (Microsoft Corporation, Redmond, WA) spreadsheet and mean values for each patient for each time period were calculated. Descriptive statistics were used to evaluate the patient population. Analysis of variance for repeated measures was used to compare the mean values for each patient for each time period.
Results Seven infants receiving moderately high baseline ventilator support underwent closure of PDA on VG between September 2004 and June 2010 and had all data available for analysis. The mean gestational age was 25.4 1.5 weeks and mean birth weight was 723 141 g. Ten other infants underwent PDA ligation during this period but did not have physiologic recording during the procedure and one did not have a complete set of data available. The mean gestational age of 24.5 0.8 weeks, mean birth weight of 673 164 g, and survival rate (83.3%) of the entire cohort of surgical PDA closure patients were similar to the patients who were studied. Postnatal age at surgery was 29.9 16.1 days and mean weight at surgery was 995 303 g. All infants failed 2 attempts at medical closure with ibuprofen or indomethacin and were ventilator dependent at the time of surgery. The time course of the respiratory variables and HR are shown in ►Table 1. All infants survived, no air leak was noted, and no infant experienced bradycardia (defined as HR < 100). After anesthesia/muscle relaxation, the inflation pressure rose modestly in response to lack of patient effort with no change
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
24
Volume Guarantee Ventilation for PDA Surgery
Keszler, Abubakar
25
Table 1 Time course of the respiratory variables and heart rate Anesthesia
Retraction
Completion a
Pressure limit (cm H2O)
26.5 4.2
27.1 3.8
30.6 3.8
Observed PIP (cm H2O)
22.9 4.2
25.2 4.0
29.1 4.4a
27.6 5.0 25.1 4.7
V T set (mL/kg)
6.24 1.0
6.30 1.0
4.65 0.8
a
6.30 1.0
V T observed (mL/kg)
6.53 0.9
6.26 1.0
4.58 0.6
a
6.31 0.9
FIO2
0.50 0.17
0.49 0.18
0.88 0.09a
0.48 0.20
SpO2 nadir (%)
91.8 3.0
94.6 2.3
89.5 5.9
92.4 2.5
Heart rate (beats/min)
163 9
165 11
138 12
147 8a
a,b
Abbreviations: FIO2, fraction of inspired oxygen; PIP, peak inflation pressure; SpO2, oxygen saturation; V T, tidal volume. Note: Data are mean SD. a p < 0.05 compared with baseline. b Lowest observed value.
in the measured V T. Inflation pressure rose further during retraction but the device was able to maintain the new, lower target V T in all patients. Only a moderate increase in FIO2 was required in most infants, suggesting adequate lung volume was maintained during retraction. Following completion of the procedure, FIO2, V T, and inflation pressure returned to preoperative values.
Discussion This study provides encouraging preliminary data supporting the utility of volume-targeted ventilation during surgical closure of PDA in sick preterm infants requiring moderately high level of ventilator support. For many years, PDA surgery and other procedures have been commonly performed in NICUs, rather than operating rooms to avoid the risk associated with transport of these critically ill patients.8–10 Consequently, it has become feasible to continue support with neonatal ventilators, as opposed to anesthesia machines or manual ventilation, which may be less optimal forms of support of these unstable infants. Our findings are consistent with published data on VG and with the known operating principles of the Babylog ventilator.11 The relatively large baseline V T of slightly more than 6 mL/kg in these 4-week-old infants with evolving chronic lung disease is similar to our earlier observations of V T requirements at 3 weeks of age.12 This V T requirement reflects the increased alveolar dead space due to heterogeneity of lung aeration and increased anatomic dead space resulting from acquired tracheomegaly.13 It can be seen in ►Table 1 that before induction of anesthesia and muscle relaxation, the mean observed V T was slightly larger than the set value and observed inflation pressure was well below PIP limit, reflecting the fact that at least some infants were spontaneously generating V T above the set value. Once spontaneous breathing was stopped, set and observed V T became nearly equal and the inflation pressure rose as the ventilator now needed to compensate for the lack of spontaneous effort of the infant. Modestly higher inflation pressures and a moderate increase in FIO2 were needed during lung retraction, but mean SpO2 remained close to
90%, despite the intentional reduction in V T. The substantial increase in FIO2 is most likely due to some degree of atelectasis of the retracted lung, which will inevitably lead to some intrapulmonary right to left shunting. The recorded HR decreased significantly during lung retraction, but this may be in part the result of recording the lowest, rather than typical HR value during retraction. Although the decrease is statistically significant, the decrease is probably not clinically important as the HR never dropped below 120/min. The HR was relatively high at baseline, presumably reflecting the hemodynamic effect of the PDA. Following clipping of the ductus, HR remained lower than baseline, likely due to the redistribution of circulating blood volume and abolition of the left to right shunt. This pilot observational study has some obvious limitations. The number of subjects is quite small because surgical PDA closure is now done infrequently. Adequacy of ventilation was not monitored by arterial blood gases or transcutaneous CO2, so we cannot comment on whether any degree of respiratory acidosis or alkalosis occurred. The faster cycling rate of the ventilator was intended to maintain adequate minute ventilation, though such compensation could only be partially effective, due to the proportionally larger drop in alveolar V T relative to the modest increase in ventilator rate. Each patient served as their own control, but there was no comparison group supported on a different mode because VG support had become the standard of care in our NICU. The ventilator adjustments described in this report were based on our best estimate and experience, but were not experimentally validated as the best possible choice. Surgical PDA closure is now such an uncommon procedure that no single institution can mount an adequately powered controlled trial. The best approach to respiratory support during PDA surgery has not been adequately studied. One report described the use of high-frequency oscillatory ventilation during surgery, but the report only contained three patients.14 A larger study of 40 pediatric patients aged approximately 3.5 years and weighing close to 11 kg compared selective right lung ventilation with a slow rate of 20 to 24 inflations/min and moderate V T of 8 mL/kg to bilateral ventilation with a reduced V T of 5 mL/kg and a faster rate American Journal of Perinatology
Vol. 32
No. 1/2015
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Baseline
Volume Guarantee Ventilation for PDA Surgery
Keszler, Abubakar
of 32 to 40. The authors noted better oxygenation with the more rapid rate and smaller V T approach.15 Our observational study for the first time provides descriptive data on the course of ventilation variables during surgical closure of the PDA. The automatic adjustment of working pressure by VG maintained adequate V T and prevented hypoxemia and bradycardia. It is likely that the microprocessor-controlled adjustment in inflation pressure using VG results in more consistent V T delivery while avoiding excessively high inflation pressure that can easily occur when ventilation is provided manually with an anesthesia bag. Thus, volume-targeted ventilation may be a useful mode during surgical closure of the PDA. These preliminary observations could serve as a basis for larger controlled studies that are needed to confirm our findings.
Note Dr. Keszler has been a consultant to Draeger Medical, Inc. No person from the company had any input into any aspect of the work. No financial or other support was received.
4 Clyman R, Cassady G, Kirklin JK, Collins M, Philips JB 3rd. The role
5
6
7
8
9
10
11
References 1 Laughon M, Bose C, Clark R. Treatment strategies to prevent or
close a patent ductus arteriosus in preterm infants and outcomes. J Perinatol 2007;27(3):164–170 2 Kabra NS, Schmidt B, Roberts RS, Doyle LW, Papile L, Fanaroff A. Neurosensory impairment after surgical closure of patent ductus arteriosus in extremely low birth weight infants: results from the Trial of Indomethacin Prophylaxis in Preterms. J Pediatr 2007; 150(3):229–234, 234. e1 3 Chorne N, Leonard C, Piecuch R, Clyman RI. Patent ductus arteriosus and its treatment as risk factors for neonatal and neurodevelopmental morbidity. Pediatrics 2007;119(6):1165–1174
American Journal of Perinatology
Vol. 32
No. 1/2015
12
13 14 15
of patent ductus arteriosus ligation in bronchopulmonary dysplasia: reexamining a randomized controlled trial. J Pediatr 2009; 154(6):873–876 Abubakar KM, Keszler M. Patient-ventilator interactions in new modes of patient triggered ventilation. Pediatr Pulmonol 2001; 32(1):71–75 Keszler M, Abubakar K. Volume guarantee: stability of tidal volume and incidence of hypocarbia. Pediatr Pulmonol 2004;38(3): 240–245 Wheeler K, Klingenberg C, McCallion N, Morley CJ, Davis PG. Volume-targeted versus pressure-limited ventilation in the neonate. Cochrane Database Syst Rev 2010;(11):CD003666 Shenassa H, Sankaran K, Duncan W, Tyrrell M, Bharadwaj B. Surgical ligation of patent ductus arteriosus in a neonatal intensive care unit is safe and cost effective. Can J Cardiol 1986;2(6): 353–355 Taylor RL, Grover FL, Harmon PK, Escobedo MK, Ramamurthy RS, Trinkle JK. Operative closure of patent ductus arteriosus in premature infants in the neonatal intensive care unit. Am J Surg 1986; 152(6):704–708 Gould DS, Montenegro LM, Gaynor JW, et al. A comparison of onsite and off-site patent ductus arteriosus ligation in premature infants. Pediatrics 2003;112(6 Pt 1):1298–1301 Keszler M, Abubakar KM. Volume guarantee ventilation. In: Donn SM, Wiswell T, eds. Clinics in Perinatology: Update on Surfactant and Mechanical Ventilation. Vol. 34. Philadelphia, PA: Elsevier Press; 2007:107–116 Keszler M, Nassabeh-Montazami S, Abubakar K. Evolution of tidal volume requirement during the first three weeks of life in infants
23
Volume Guarantee Ventilation during Surgical Closure of Patent Ductus Arteriosus Martin Keszler, MD1
Kabir Abubakar, MD2
1 Department of Pediatrics, Women and Infants Hospital of Rhode
Island, Brown University, Providence, Rhode Island 2 Department of Pediatrics, Georgetown University Hospital, Washington, District of Columbia
Address for correspondence Martin Keszler, MD, Department of Pediatrics, Women and Infants Hospital of Rhode Island, 101 Dudley Street, Providence, RI 02905 (e-mail: [email protected]).
Abstract
Keywords
► patent ductus arteriosus ► surgical closure ► volume guarantee ventilation
Background Surgical closure of patent ductus arteriosus (PDA) is associated with adverse outcomes. Surgical exposure requires retraction of the lung, resulting in decreased aeration and compliance. Optimal respiratory support for PDA surgery is unknown. Experience with volume guarantee (VG) ventilation at our institution led us to hypothesize that surgery would be better tolerated with automatic adjustment of pressure by VG to maintain tidal volume (V T) during retraction. Objective The objective of this study was to describe ventilator support, V T, and oxygenation of infants supported with VG during PDA surgery. Design/Methods Ventilator variables, oxygen saturation, and heart rate were recorded during PDA surgery in a convenience sample of infants during PDA closure on VG. Pressure limit increased 11% and set V T was 26% lower during lung retraction. Fentanyl and pancuronium/vecuronium were used for anesthesia/muscle relaxation. Longitudinal data were analyzed by analysis of variance for repeated measures. Results Seven infants, 25.4 1.5 weeks and 723 141 g, underwent closure of PDA on VG at a mean age 29.9 days. No air leak, bradycardia, or death occurred. Target V T was maintained with a modest increase in inflation pressure. Oxygenation remained adequate. Conclusions VG avoided hypoxemia and maintained adequate V T with only a modest increase in peak inflation pressure and thus may be a useful mode during PDA surgery.
Surgical closure of patent ductus arteriosus (PDA) remains one of the most common surgical procedures in newborn infants.1 Because of concerns about the potential adverse effects of the surgery,2–4 PDA is typically closed surgically only in infants with significant cardiorespiratory compromise attributed to a large left to right ductal shunt. Consequently, infants undergoing PDA closure are often unstable and have limited cardiopulmonary reserve. To obtain adequate surgical exposure, the surgical team must retract the left lung out of the operative field. Compression of the left lung leads to decreased lung compliance and inevitably results in some
degree of respiratory compromise with falling oxygen saturation (SpO2) and sometimes bradycardia, despite increasing inflation pressure. When severe, this decompensation may require temporary release of the lung compression to allow the patient to recover before proceeding. The limited respiratory reserve of these critically ill infants places a premium on surgical speed, which could potentially lead to errors or complications. The best approach to respiratory support during PDA surgery has not been studied. It is unknown whether compromised gas exchange intraoperatively contributes to the increased rate of neurodevelopmental
received January 29, 2014 accepted January 30, 2014 published online April 4, 2014
Copyright © 2015 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
DOI http://dx.doi.org/ 10.1055/s-0034-1371713. ISSN 0735-1631.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Am J Perinatol 2015;32:23–26.
Volume Guarantee Ventilation for PDA Surgery
Keszler, Abubakar
impairment reported to occur in infants after surgical PDA closure,2–4 but any technique that minimizes cardiopulmonary complications during PDA surgery would be desirable. Volume guarantee (VG) is a technique of volume-targeted ventilation available on the Babylog 8000þ and VN 500 neonatal ventilators (Draeger Medical, Lubeck, Germany). With VG, the microprocessor of the device automatically adjusts inflation pressure up to a set pressure limit to maintain a target tidal volume (V T) based on the exhaled V T of the previous inflation.5 VG has been shown to maintain more stable V T, reduce hypocapnia, and lead to shorter duration of mechanical ventilation.6,7 We therefore hypothesized that the use of VG with a lower target V T during PDA surgery would deliver an adequate and stable V T, decrease the severity of hypoxemia, and reduce or eliminate bradycardia.
Methods To obtain a preliminary assessment of the potential utility of the intraoperative use of VG, we recorded ventilator variables, V T, and SpO2 and heart rate (HR) of infants during surgical closure of PDA in a convenience sample of infants undergoing surgical PDA closure while supported with VG at Georgetown University Hospital over a 5-year period. Infants who required PDA surgery based on the judgment of the clinical team were studied when the investigator was available and verbal parental consent could be obtained. Only patients without substantial leak (> 20%) around the endotracheal tube were studied, to ensure accurate measurement of V T. Surgery was performed in the neonatal intensive care unit (NICU) and was reserved for severely symptomatic infants who failed multiple medical closure attempts. Because VG had been the standard mode of ventilator support for many years at Georgetown University Hospital and PDA surgery was routinely performed in a special surgical bay of the NICU, it became standard practice in most infants to continue the same mode of support during surgery for PDA closure, as well as other procedures. Thus, the use of the VG during PDA closure was considered standard care and only the recording of the respiratory variables was being done for the purpose of the study. Consequently, only verbal parental consent was required for the use of the de-identified data. Patients were transferred to an open warmer in the surgical bay of the NICU and positioned in the right lateral decubitus position for appropriate surgical exposure. Infants remained on the ventilator settings and mode selected by the clinicians (assist control þ VG or pressure support þ VG). Set and measured V T, pressure limit, measured peak inflation pressure (PIP), ventilator rate, and fraction of inspired oxygen (FIO2) were recorded at 10-second intervals from the RS232 port of the Babylog 8000 þ ventilator using the Babyview software (Draeger Medical). HR and SpO2 were manually recorded from the bedside monitor, noting the lowest values. Surgical anesthesia was induced with high-dose fentanyl and muscle relaxation with pancuronium or vecuronium. Anesthesia was induced, maintained, and monitored by one of the staff anesthesiologists, while respiratory support was managed by one of the authors (M.K.). Baseline ventilation American Journal of Perinatology
Vol. 32
No. 1/2015
variables, HR, and SpO2 were recorded before induction of anesthesia. Following induction of anesthesia and muscle relaxation, the ventilator rate was increased to 50 inflations/min to compensate for the lack of spontaneous breathing and a second set of baseline values were obtained. Intraoperatively, the PIP limit was increased by 3 to 5 cm H2O as needed just before and during lung retraction and the target V T was reduced by 20 to 25% from baseline, recognizing that maintaining a normal V T during lung retraction would require excessive inflation pressure and likely result in volutrauma as the V T would be redistributed to the opposite lung. The ventilator rate was increased to 60/min during lung retraction to partially compensate for the smaller V T. FIO2 was initially increased by approximately 0.1 to 0.2 and subsequently adjusted as needed to avoid desaturation that would inevitably occur because of some degree of compression atelectasis leading to worsening ventilation/perfusion (V/Q) matching. The ventilator settings and monitored values were again recorded at the time of maximum lung retraction and again after completion of the operation and skin closure. Following release of the lung, the V T setting and PIP limit were returned to the preoperative value and the positive endexpiratory pressure was increased by 2 cm H2O for 5 minutes to help re-recruit any atelectatic portion of the lung, then returned to baseline. Demographic data were obtained from the medical record of each infant and all data were subsequently de-identified. The 10-second interval ventilator data recorded from the Babyview software onto a laptop were exported into an Excel (Microsoft Corporation, Redmond, WA) spreadsheet and mean values for each patient for each time period were calculated. Descriptive statistics were used to evaluate the patient population. Analysis of variance for repeated measures was used to compare the mean values for each patient for each time period.
Results Seven infants receiving moderately high baseline ventilator support underwent closure of PDA on VG between September 2004 and June 2010 and had all data available for analysis. The mean gestational age was 25.4 1.5 weeks and mean birth weight was 723 141 g. Ten other infants underwent PDA ligation during this period but did not have physiologic recording during the procedure and one did not have a complete set of data available. The mean gestational age of 24.5 0.8 weeks, mean birth weight of 673 164 g, and survival rate (83.3%) of the entire cohort of surgical PDA closure patients were similar to the patients who were studied. Postnatal age at surgery was 29.9 16.1 days and mean weight at surgery was 995 303 g. All infants failed 2 attempts at medical closure with ibuprofen or indomethacin and were ventilator dependent at the time of surgery. The time course of the respiratory variables and HR are shown in ►Table 1. All infants survived, no air leak was noted, and no infant experienced bradycardia (defined as HR < 100). After anesthesia/muscle relaxation, the inflation pressure rose modestly in response to lack of patient effort with no change
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
24
Volume Guarantee Ventilation for PDA Surgery
Keszler, Abubakar
25
Table 1 Time course of the respiratory variables and heart rate Anesthesia
Retraction
Completion a
Pressure limit (cm H2O)
26.5 4.2
27.1 3.8
30.6 3.8
Observed PIP (cm H2O)
22.9 4.2
25.2 4.0
29.1 4.4a
27.6 5.0 25.1 4.7
V T set (mL/kg)
6.24 1.0
6.30 1.0
4.65 0.8
a
6.30 1.0
V T observed (mL/kg)
6.53 0.9
6.26 1.0
4.58 0.6
a
6.31 0.9
FIO2
0.50 0.17
0.49 0.18
0.88 0.09a
0.48 0.20
SpO2 nadir (%)
91.8 3.0
94.6 2.3
89.5 5.9
92.4 2.5
Heart rate (beats/min)
163 9
165 11
138 12
147 8a
a,b
Abbreviations: FIO2, fraction of inspired oxygen; PIP, peak inflation pressure; SpO2, oxygen saturation; V T, tidal volume. Note: Data are mean SD. a p < 0.05 compared with baseline. b Lowest observed value.
in the measured V T. Inflation pressure rose further during retraction but the device was able to maintain the new, lower target V T in all patients. Only a moderate increase in FIO2 was required in most infants, suggesting adequate lung volume was maintained during retraction. Following completion of the procedure, FIO2, V T, and inflation pressure returned to preoperative values.
Discussion This study provides encouraging preliminary data supporting the utility of volume-targeted ventilation during surgical closure of PDA in sick preterm infants requiring moderately high level of ventilator support. For many years, PDA surgery and other procedures have been commonly performed in NICUs, rather than operating rooms to avoid the risk associated with transport of these critically ill patients.8–10 Consequently, it has become feasible to continue support with neonatal ventilators, as opposed to anesthesia machines or manual ventilation, which may be less optimal forms of support of these unstable infants. Our findings are consistent with published data on VG and with the known operating principles of the Babylog ventilator.11 The relatively large baseline V T of slightly more than 6 mL/kg in these 4-week-old infants with evolving chronic lung disease is similar to our earlier observations of V T requirements at 3 weeks of age.12 This V T requirement reflects the increased alveolar dead space due to heterogeneity of lung aeration and increased anatomic dead space resulting from acquired tracheomegaly.13 It can be seen in ►Table 1 that before induction of anesthesia and muscle relaxation, the mean observed V T was slightly larger than the set value and observed inflation pressure was well below PIP limit, reflecting the fact that at least some infants were spontaneously generating V T above the set value. Once spontaneous breathing was stopped, set and observed V T became nearly equal and the inflation pressure rose as the ventilator now needed to compensate for the lack of spontaneous effort of the infant. Modestly higher inflation pressures and a moderate increase in FIO2 were needed during lung retraction, but mean SpO2 remained close to
90%, despite the intentional reduction in V T. The substantial increase in FIO2 is most likely due to some degree of atelectasis of the retracted lung, which will inevitably lead to some intrapulmonary right to left shunting. The recorded HR decreased significantly during lung retraction, but this may be in part the result of recording the lowest, rather than typical HR value during retraction. Although the decrease is statistically significant, the decrease is probably not clinically important as the HR never dropped below 120/min. The HR was relatively high at baseline, presumably reflecting the hemodynamic effect of the PDA. Following clipping of the ductus, HR remained lower than baseline, likely due to the redistribution of circulating blood volume and abolition of the left to right shunt. This pilot observational study has some obvious limitations. The number of subjects is quite small because surgical PDA closure is now done infrequently. Adequacy of ventilation was not monitored by arterial blood gases or transcutaneous CO2, so we cannot comment on whether any degree of respiratory acidosis or alkalosis occurred. The faster cycling rate of the ventilator was intended to maintain adequate minute ventilation, though such compensation could only be partially effective, due to the proportionally larger drop in alveolar V T relative to the modest increase in ventilator rate. Each patient served as their own control, but there was no comparison group supported on a different mode because VG support had become the standard of care in our NICU. The ventilator adjustments described in this report were based on our best estimate and experience, but were not experimentally validated as the best possible choice. Surgical PDA closure is now such an uncommon procedure that no single institution can mount an adequately powered controlled trial. The best approach to respiratory support during PDA surgery has not been adequately studied. One report described the use of high-frequency oscillatory ventilation during surgery, but the report only contained three patients.14 A larger study of 40 pediatric patients aged approximately 3.5 years and weighing close to 11 kg compared selective right lung ventilation with a slow rate of 20 to 24 inflations/min and moderate V T of 8 mL/kg to bilateral ventilation with a reduced V T of 5 mL/kg and a faster rate American Journal of Perinatology
Vol. 32
No. 1/2015
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Baseline
Volume Guarantee Ventilation for PDA Surgery
Keszler, Abubakar
of 32 to 40. The authors noted better oxygenation with the more rapid rate and smaller V T approach.15 Our observational study for the first time provides descriptive data on the course of ventilation variables during surgical closure of the PDA. The automatic adjustment of working pressure by VG maintained adequate V T and prevented hypoxemia and bradycardia. It is likely that the microprocessor-controlled adjustment in inflation pressure using VG results in more consistent V T delivery while avoiding excessively high inflation pressure that can easily occur when ventilation is provided manually with an anesthesia bag. Thus, volume-targeted ventilation may be a useful mode during surgical closure of the PDA. These preliminary observations could serve as a basis for larger controlled studies that are needed to confirm our findings.
Note Dr. Keszler has been a consultant to Draeger Medical, Inc. No person from the company had any input into any aspect of the work. No financial or other support was received.
4 Clyman R, Cassady G, Kirklin JK, Collins M, Philips JB 3rd. The role
5
6
7
8
9
10
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References 1 Laughon M, Bose C, Clark R. Treatment strategies to prevent or
close a patent ductus arteriosus in preterm infants and outcomes. J Perinatol 2007;27(3):164–170 2 Kabra NS, Schmidt B, Roberts RS, Doyle LW, Papile L, Fanaroff A. Neurosensory impairment after surgical closure of patent ductus arteriosus in extremely low birth weight infants: results from the Trial of Indomethacin Prophylaxis in Preterms. J Pediatr 2007; 150(3):229–234, 234. e1 3 Chorne N, Leonard C, Piecuch R, Clyman RI. Patent ductus arteriosus and its treatment as risk factors for neonatal and neurodevelopmental morbidity. Pediatrics 2007;119(6):1165–1174
American Journal of Perinatology
Vol. 32
No. 1/2015
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of patent ductus arteriosus ligation in bronchopulmonary dysplasia: reexamining a randomized controlled trial. J Pediatr 2009; 154(6):873–876 Abubakar KM, Keszler M. Patient-ventilator interactions in new modes of patient triggered ventilation. Pediatr Pulmonol 2001; 32(1):71–75 Keszler M, Abubakar K. Volume guarantee: stability of tidal volume and incidence of hypocarbia. Pediatr Pulmonol 2004;38(3): 240–245 Wheeler K, Klingenberg C, McCallion N, Morley CJ, Davis PG. Volume-targeted versus pressure-limited ventilation in the neonate. Cochrane Database Syst Rev 2010;(11):CD003666 Shenassa H, Sankaran K, Duncan W, Tyrrell M, Bharadwaj B. Surgical ligation of patent ductus arteriosus in a neonatal intensive care unit is safe and cost effective. Can J Cardiol 1986;2(6): 353–355 Taylor RL, Grover FL, Harmon PK, Escobedo MK, Ramamurthy RS, Trinkle JK. Operative closure of patent ductus arteriosus in premature infants in the neonatal intensive care unit. Am J Surg 1986; 152(6):704–708 Gould DS, Montenegro LM, Gaynor JW, et al. A comparison of onsite and off-site patent ductus arteriosus ligation in premature infants. Pediatrics 2003;112(6 Pt 1):1298–1301 Keszler M, Abubakar KM. Volume guarantee ventilation. In: Donn SM, Wiswell T, eds. Clinics in Perinatology: Update on Surfactant and Mechanical Ventilation. Vol. 34. Philadelphia, PA: Elsevier Press; 2007:107–116 Keszler M, Nassabeh-Montazami S, Abubakar K. Evolution of tidal volume requirement during the first three weeks of life in infants
