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Positive intrapulmonary oncotic pressure enhances short-term lung growth acceleration after fetal tracheal occlusion
Positive Intrapulmonary Oncotic Pressure Enhances Short-Term Lung Growth Acceleration After Fetal Tracheal Occlusion By Alexander Dzakovic, Amir Kaviani, Russell W. Jennings, Jay M. Wilson, and Dario O. Fauza Boston, Massachusetts
Purpose: This study was aimed at determining whether positive oncotic pressure induced in the fetal lung liquid could safely maximize accelerated lung growth after tracheal occlusion. Methods: Fetal lambs (n ⫽ 21) were divided into 4 groups: group I (n ⫽ 5) consisted of sham-operated controls; group II (n ⫽ 5) underwent simple tracheal occlusion (TO); group III (n ⫽ 5) received TO and 60 mL of saline injected into the trachea; and group IV (n ⫽ 6) underwent TO and intratracheal infusion of 60 mL of iso-osmotic, 6% Dextran 70. All fetuses were delivered near term, at a mean of 15.9 ⫾ 1 days postoperatively. Their lungs were studied by standard morphometric techniques, and the basic chemical profile of the lung liquid was analyzed. Statistical comparisons were by 1-way analysis of variance (ANOVA) and post-hoc analyses by the Bonferroni correction for multiple comparisons, with P values less than .05 considered significant.
T
HE ACCELERATION of pulmonary growth observed after fetal tracheal occlusion depends on sustained intrapulmonary distension by retained lung liquid, which is secreted actively by the alveolar-capillary membrane.1-3 Fetal tracheal occlusion, however, does not always lead to accelerated lung growth. Reasons for an adverse outcome include a short window between fetal intervention and the ever-present postoperative premature labor, the physiologic decrease in lung liquid secretion observed in the latter stages of gestation, and, possibly, fetal stress.4-6 We hypothesized that the intrapulmonary administration of an oncotic agent after fetal tracheal occlusion would lead to a short-term expansion of the lung liquid volume, even if carried out late in gestation. As a result, lung growth acceleration would be maximized. In the current study, an isosmotic solution was chosen as the oncotic agent in an attempt to avoid damage to the lung parenchyma.
Results: The lung volume-to-body-weight ratio (LV:BW) was significantly different among groups. Pairwise comparisons of LV:BW showed that it was higher in group IV than in all other groups, but there was no difference between groups II and III. Airspace fraction was not significantly different among groups, and histologic appearance was normal in all lung samples. There were no differences in lung liquid osmolarity, pH level, and electrolyte concentrations. Conclusion: Positive intrapulmonary oncotic pressure by an isosmotic agent boosts short-term lung growth acceleration after fetal tracheal occlusion with no evidence of cell damage. J Pediatr Surg 37:1007-1010. Copyright 2002, Elsevier Science (USA). All rights reserved. INDEX WORDS: Congenital diaphragmatic hernia, pulmonary hypoplasia, tracheal occlusion, lung development, fetus, dextran.
Fetal Surgical Manipulation and Delivery Time-dated pregnant ewes at 121 to 129 days gestation (mean, 125 ⫾ 2.7 days) were anesthetized with 2% to 4% halothane (Halocarbon Laboratories, River Edge, NJ) and received 1 g of cefazolin (BMH, Philadelphia, PA) intravenously before surgical manipulation. The bicornuate uterus was exposed through a midline laparotomy. Fetal lambs (n ⫽ 21) then were divided into 4 groups: group I (n ⫽ 5) consisted of sham-operated controls; group II (n ⫽ 5) underwent simple tracheal occlusion (TO) as previously described1; group III (n ⫽ 5) received TO and 60 mL of saline injected into the trachea; and group IV (n ⫽ 6) underwent TO and intratracheal infusion of 60 mL of pH-adjusted, isosmotic 6% Dextran 70 in 0.9% NaCl (B. Braun Medical, Irvine, CA). The amniotic fluid, which had been removed previously and kept at 37°C, was reinfused into the amniotic cavity, together with 500 mg of cefazolin. The gestational membranes and uterine wall were closed in one layer with a TA 90-mm Titanium surgical stapler (United States Surgical Corp [USSC], Norwalk, CT).
The Harvard Medical School animal management program is sanctioned by the American Association for the accreditation of Laboratory Animal Care (AAALAC, file #000009) and meets National Institutes of Health Standards as set forth in the Guide for the Care and Use of Laboratory Animals (National Research Council Publication, revised 1996).
From the Departments of Surgery, Children’s Hospital and Harvard Medical School, and Harvard Center for Minimally Invasive Surgery, Boston, MA. Presented at the 53rd Annual Meeting of the Section on Surgery of the American Academy of Pediatrics, San Francisco, California, October 19-21, 2001. Supported by grants from the United States Surgical Corporation and The Children’s Hospital Surgical Foundation. Address reprint requests to Dario O. Fauza, MD, Children’s Hospital, 300 Longwood Ave, Fegan 3, Boston, MA 02115. Copyright 2002, Elsevier Science (USA). All rights reserved. 0022-3468/02/3707-0013$35.00/0 doi:10.1053/jpsu.2002.33830
Journal of Pediatric Surgery, Vol 37, No 7 (July), 2002: pp 1007-1010
1007
MATERIALS AND METHODS
1008
DZAKOVIC ET AL
Lung Preparation and Morphometric Analysis Each lamb was weighed and had its chest opened through a median sternotomy. Lung liquid was aspirated through the trachea and analyzed on a Stat Profile Ultra blood gas and electrolyte analyzer (Nova Biomedical, Waltham, MA). Both lungs then were removed en bloc and inflated with saline at 20 cm H2O pressure. Lung volumes were determined by water displacement of the inflated lung. Samples of lung tissue then were taken from standard positions on the periphery of the right and left apical and diaphragmatic lobes and fixed in 10% neutral buffered formalin (Sigma, St Louis, MO). Morphometric analysis within the intra-acinar region of the lung was performed using a Zeiss laboratory microscope (Carl Zeiss, Jena, Germany) with a projection head engraved with a 42-point coherent test lattice7 at a magnification of 200⫻. Airspace fraction analysis consisted of counting test points falling on airspace and alveolar wall tissue. Lung tissue was fixed and embedded for electron microscopy analysis as previously described.2 Silver sections were cut with a LKB ultramicrotome (LKB, Sweden), collected on 200-mesh copper grids and stained with uranyl acetate and lead citrate. All samples were viewed and micrographs obtained with a Zeiss EM10 transmission electron microscope (Carl Zeiss).
Statistical Analysis
Fig 1. The lung volume-to-body weight ratio was significantly higher in the group that underwent tracheal occlusion plus intrapulmonary delivery of Dextran 70 (TO/DX) than in all other groups (*) and significantly lower in the sham operated group (NL) than in all other groups. However, there was no difference between the group that underwent simple tracheal occlusion (TO) and the group that had tracheal occlusion plus intrapulmonary delivery of saline (TO/SL) (‡).
Statistical analysis was performed by 1-way ANOVA with post-hoc analyses by the Bonferroni correction for multiple comparisons as a means to compare individual groups. Significance was set at P values of less than .05.
The mother’s abdomen was closed in layers. On the first postoperative day, all ewes received 1.2 million units of benzathine penicillin intramuscularly (Wyeth Laboratories, Philadelphia, PA). All fetuses were delivered by cesarean section near full term, 14 to 18 days postoperatively (mean, 15.9 ⫾ 1 days) immediately after maternal euthanasia with a lethal dose of Somlethal (J. A. Webster, Sterling, MA). There was no difference in the duration of the postoperative period among groups by repeated measures analysis of variance (ANOVA).
Lung volume-to-body weight ratios (LV:BW) differed significantly among groups (P ⬍ .001). Pair-wise comparisons of LV:BW by the Bonferroni method showed that it was higher in group IV than in all other groups (P ⫽ .006 when compared with group III and P ⬍ .001 for comparisons with groups I and II) and lower in group I than in all other groups (P ⬍ .001 for all comparisons;
RESULTS
Fig 2. Transmission electron micrographs of the lung (A) Tracheal occlusion and (B) tracheal occlusion plus Dextran 70. There are no signs of cellular edema nor ultrastructural damage of the alveolar-capillary membrane (original magnification ⴛ2,200).
ONCOTIC ACCELERATION OF FETAL LUNG GROWTH
1009
Table 1. Osmolarity, pH, and Electrolyte Concentrations
Normal TO TO/SL TO/DX
Osmolarity (mOsm/L)
pH (mEq/L)
Na⫹ (mEq/L)
K⫹ (mEq/L)
Cl⫺ (mEq/L)
285.2 ⫾ 2.0 283.4 ⫾ 1.5 284.6 ⫾ 1.8 284.5 ⫾ 1.9
6.2 ⫾ .03 6.3 ⫾ .03 6.2 ⫾ .02 6.3 ⫾ .03
147 ⫾ .9 146 ⫾ 1.2 146 ⫾ 1.4 145 ⫾ .7
6.1 ⫾ .1 5.8 ⫾ .1 5.8 ⫾ .2 5.7 ⫾ .2
149 ⫾ 1 148 ⫾ 2 150 ⫾ 2 146 ⫾ 3
NOTE. Values are expressed as mean ⫾ standard error of the mean. Abbreviations: TO, tracheal occlusion; TO/SL, tracheal occlusion plus intrapulmonary delivery of saline; TO/DX, tracheal occlusion plus intrapulmonary delivery of Dextran 70. There were no significant differences among groups.
Fig 1). However, there was no difference between groups II and III (P ⫽ .99; Fig 1). Airspace fraction showed no significant difference between groups I (0.62 ⫾ 0.02), II (0.65 ⫾ 0.04), III (0.64 ⫾ 0.03), and IV (0.66 ⫾ 0.01). Histologic appearance was normal in all lung samples studied. This observation, combined with the airspace fraction data, shows a preserved maturation pattern and absence of emphysematous changes in all groups. Electron microscopy found no signs of cellular edema nor ultrastructural damage of the alveolar-capillary membrane in any sample (Fig 2). There were no differences in lung liquid osmolarity, pH level, and electrolyte (Na⫹, K⫹, and Cl⫺) concentrations among groups (Table 1). DISCUSSION
In addition to premature labor, erratic postoperative lung liquid production has been one of the reasons clinical application of fetal tracheal occlusion has met with limited success.8 In the current study, we have shown that positive intrapulmonary oncotic pressure by an isosmotic agent can maximize the short-term effects of fetal tracheal occlusion late in gestation, probably by expanding lung liquid volume, without any evidence of cell damage. We purposely chose to occlude the fetal trachea late in gestation because it has been shown that lung liquid secretion decreases sharply at the latter stages of pregnancy.4,5 Yet, our data show that this physiologic decrease in lung liquid production can be overcome by simple positive oncotic pressure inside the alveoli, at least for up to 2 weeks postoperatively. Given the facts that clinical fetal tracheal occlusion usually is performed
in the third trimester of gestation (because of fetal viability) and postoperative preterm labor results frequently in a short window between surgery and delivery, it is reasonable to speculate that delivery of an oncotic agent into the fetal lung at the time of tracheal occlusion could improve the currently disappointing results. More studies are needed before clinical application of this concept. For instance, the pharmacokinetics of Dextran 70 in the fetal lung remains to be determined. Dextran 70 is a very large polysaccharide normally metabolized by plasma amylases, dextranases, and the reticuloendothelial system (RES).9,10 It is likely to be eliminated at a much slower rate from the alveolar lumen than after intravenous application.9 Moreover, significant functional impairment of the RES has been described after extensive intravenous Dextran therapy.10 Given that type II pneumocytes compose the pulmonary component of the RES, the response of those cells to Dextran delivery into the fetal lung liquid after tracheal occlusion also must be determined. Finally, the use of hyperosmotic agents should be explored as well. Although the abovementioned studies should be pursued before clinical application, the current data suggest that the administration of an oncotic agent into the fetal lungs can be an effective and practical way to enhance control over lung growth acceleration after fetal tracheal occlusion. ACKNOWLEDGMENT The authors thank Jeffrey Pettit for his excellence in laboratory assistance.
REFERENCES 1. Wilson JM, DiFiore JW, Peters CA: Experimental fetal tracheal ligation prevents the pulmonary hypoplasia associated with fetal nephrectomy: Possible application for congenital diaphragmatic hernia. J Pediatr Surg 28:1433-9; discussion 1439-40, 1993 2. DiFiore JW, Fauza DO, Slavin R, et al: Experimental fetal tracheal ligation reverses the structural and physiological effects of pulmonary hypoplasia in congenital diaphragmatic hernia. J Pediatr Surg 29:248-56; discussion 256-7, 1994 3. DiFiore JW, Fauza DO, Slavin R, et al: Experimental fetal tracheal ligation and congenital diaphragmatic hernia: A pulmonary vascular morphometric analysis. J Pediatr Surg 30:917-23; discussion 923-4, 1995
4. Mescher EJ, Platzker AC, Ballard PL, et al: Ontogeny of tracheal fluid, pulmonary surfactant, and plasma corticoids in the fetal lamb. J Appl Physiol 39:1017-1021, 1975 5. Kitterman JA, Ballard PL, Clements JA, et al: Tracheal fluid in fetal lambs: Spontaneous decrease prior to birth. J Appl Physiol 47:985-989, 1979 6. Brown MJ, Olver RE, Ramsden CA, et al: Effects of adrenaline and of spontaneous labour on the secretion and absorption of lung liquid in the fetal lamb. J Physiol 344:137-152, 1983 7. Weibel ER: Stereologic Methods, in Weibel ER (ed): Practical Methods for Biological Morphometry (vol I). San Diego, CA, Academic Press, 1989, pp 63-236
1010
DZAKOVIC ET AL
8. Harrison MR, Mychaliska GB, Albanese CT, et al: Correction of congenital diaphragmatic hernia in utero IX: Fetuses with poor prognosis (liver herniation and low lung-to-head ratio) can be saved by fetoscopic temporary tracheal occlusion. J Pediatr Surg 33:1017-1022; discussion 1022-1023, 1998
9. Klotz U, Kroemer H: Clinical pharmacokinetic considerations in the use of plasma expanders. Clin Pharmacokinet 12:123-135, 1987 10. Ginz HF, Gottschall V, Schwarzkopf G, et al: [Excessive tissue storage of colloids in the reticuloendothelial system]. Anaesthesist 47:330-334, 1998
Discussion Dr Stolar (New York, NY): One of the problems with the trachea occlusion model is that the target cell seems to be the type II pneumocyte, and it contributes to some loss of surfactant. Have you had a chance to look for lamellar bodies or surfactant protein in your lung liquids? A. Dzakovik (response): That is a very good question.
We currently are looking at what happens to dextran after we inject it, and there has been an interesting paper published in Germany that told us that type II pneumocytes or reticular endothelial system cells are involved in degradation, and there actually might be some effect on these type II pneumocytes. We are currently investigating that in our next protocol.
Purpose: This study was aimed at determining whether positive oncotic pressure induced in the fetal lung liquid could safely maximize accelerated lung growth after tracheal occlusion. Methods: Fetal lambs (n ⫽ 21) were divided into 4 groups: group I (n ⫽ 5) consisted of sham-operated controls; group II (n ⫽ 5) underwent simple tracheal occlusion (TO); group III (n ⫽ 5) received TO and 60 mL of saline injected into the trachea; and group IV (n ⫽ 6) underwent TO and intratracheal infusion of 60 mL of iso-osmotic, 6% Dextran 70. All fetuses were delivered near term, at a mean of 15.9 ⫾ 1 days postoperatively. Their lungs were studied by standard morphometric techniques, and the basic chemical profile of the lung liquid was analyzed. Statistical comparisons were by 1-way analysis of variance (ANOVA) and post-hoc analyses by the Bonferroni correction for multiple comparisons, with P values less than .05 considered significant.
T
HE ACCELERATION of pulmonary growth observed after fetal tracheal occlusion depends on sustained intrapulmonary distension by retained lung liquid, which is secreted actively by the alveolar-capillary membrane.1-3 Fetal tracheal occlusion, however, does not always lead to accelerated lung growth. Reasons for an adverse outcome include a short window between fetal intervention and the ever-present postoperative premature labor, the physiologic decrease in lung liquid secretion observed in the latter stages of gestation, and, possibly, fetal stress.4-6 We hypothesized that the intrapulmonary administration of an oncotic agent after fetal tracheal occlusion would lead to a short-term expansion of the lung liquid volume, even if carried out late in gestation. As a result, lung growth acceleration would be maximized. In the current study, an isosmotic solution was chosen as the oncotic agent in an attempt to avoid damage to the lung parenchyma.
Results: The lung volume-to-body-weight ratio (LV:BW) was significantly different among groups. Pairwise comparisons of LV:BW showed that it was higher in group IV than in all other groups, but there was no difference between groups II and III. Airspace fraction was not significantly different among groups, and histologic appearance was normal in all lung samples. There were no differences in lung liquid osmolarity, pH level, and electrolyte concentrations. Conclusion: Positive intrapulmonary oncotic pressure by an isosmotic agent boosts short-term lung growth acceleration after fetal tracheal occlusion with no evidence of cell damage. J Pediatr Surg 37:1007-1010. Copyright 2002, Elsevier Science (USA). All rights reserved. INDEX WORDS: Congenital diaphragmatic hernia, pulmonary hypoplasia, tracheal occlusion, lung development, fetus, dextran.
Fetal Surgical Manipulation and Delivery Time-dated pregnant ewes at 121 to 129 days gestation (mean, 125 ⫾ 2.7 days) were anesthetized with 2% to 4% halothane (Halocarbon Laboratories, River Edge, NJ) and received 1 g of cefazolin (BMH, Philadelphia, PA) intravenously before surgical manipulation. The bicornuate uterus was exposed through a midline laparotomy. Fetal lambs (n ⫽ 21) then were divided into 4 groups: group I (n ⫽ 5) consisted of sham-operated controls; group II (n ⫽ 5) underwent simple tracheal occlusion (TO) as previously described1; group III (n ⫽ 5) received TO and 60 mL of saline injected into the trachea; and group IV (n ⫽ 6) underwent TO and intratracheal infusion of 60 mL of pH-adjusted, isosmotic 6% Dextran 70 in 0.9% NaCl (B. Braun Medical, Irvine, CA). The amniotic fluid, which had been removed previously and kept at 37°C, was reinfused into the amniotic cavity, together with 500 mg of cefazolin. The gestational membranes and uterine wall were closed in one layer with a TA 90-mm Titanium surgical stapler (United States Surgical Corp [USSC], Norwalk, CT).
The Harvard Medical School animal management program is sanctioned by the American Association for the accreditation of Laboratory Animal Care (AAALAC, file #000009) and meets National Institutes of Health Standards as set forth in the Guide for the Care and Use of Laboratory Animals (National Research Council Publication, revised 1996).
From the Departments of Surgery, Children’s Hospital and Harvard Medical School, and Harvard Center for Minimally Invasive Surgery, Boston, MA. Presented at the 53rd Annual Meeting of the Section on Surgery of the American Academy of Pediatrics, San Francisco, California, October 19-21, 2001. Supported by grants from the United States Surgical Corporation and The Children’s Hospital Surgical Foundation. Address reprint requests to Dario O. Fauza, MD, Children’s Hospital, 300 Longwood Ave, Fegan 3, Boston, MA 02115. Copyright 2002, Elsevier Science (USA). All rights reserved. 0022-3468/02/3707-0013$35.00/0 doi:10.1053/jpsu.2002.33830
Journal of Pediatric Surgery, Vol 37, No 7 (July), 2002: pp 1007-1010
1007
MATERIALS AND METHODS
1008
DZAKOVIC ET AL
Lung Preparation and Morphometric Analysis Each lamb was weighed and had its chest opened through a median sternotomy. Lung liquid was aspirated through the trachea and analyzed on a Stat Profile Ultra blood gas and electrolyte analyzer (Nova Biomedical, Waltham, MA). Both lungs then were removed en bloc and inflated with saline at 20 cm H2O pressure. Lung volumes were determined by water displacement of the inflated lung. Samples of lung tissue then were taken from standard positions on the periphery of the right and left apical and diaphragmatic lobes and fixed in 10% neutral buffered formalin (Sigma, St Louis, MO). Morphometric analysis within the intra-acinar region of the lung was performed using a Zeiss laboratory microscope (Carl Zeiss, Jena, Germany) with a projection head engraved with a 42-point coherent test lattice7 at a magnification of 200⫻. Airspace fraction analysis consisted of counting test points falling on airspace and alveolar wall tissue. Lung tissue was fixed and embedded for electron microscopy analysis as previously described.2 Silver sections were cut with a LKB ultramicrotome (LKB, Sweden), collected on 200-mesh copper grids and stained with uranyl acetate and lead citrate. All samples were viewed and micrographs obtained with a Zeiss EM10 transmission electron microscope (Carl Zeiss).
Statistical Analysis
Fig 1. The lung volume-to-body weight ratio was significantly higher in the group that underwent tracheal occlusion plus intrapulmonary delivery of Dextran 70 (TO/DX) than in all other groups (*) and significantly lower in the sham operated group (NL) than in all other groups. However, there was no difference between the group that underwent simple tracheal occlusion (TO) and the group that had tracheal occlusion plus intrapulmonary delivery of saline (TO/SL) (‡).
Statistical analysis was performed by 1-way ANOVA with post-hoc analyses by the Bonferroni correction for multiple comparisons as a means to compare individual groups. Significance was set at P values of less than .05.
The mother’s abdomen was closed in layers. On the first postoperative day, all ewes received 1.2 million units of benzathine penicillin intramuscularly (Wyeth Laboratories, Philadelphia, PA). All fetuses were delivered by cesarean section near full term, 14 to 18 days postoperatively (mean, 15.9 ⫾ 1 days) immediately after maternal euthanasia with a lethal dose of Somlethal (J. A. Webster, Sterling, MA). There was no difference in the duration of the postoperative period among groups by repeated measures analysis of variance (ANOVA).
Lung volume-to-body weight ratios (LV:BW) differed significantly among groups (P ⬍ .001). Pair-wise comparisons of LV:BW by the Bonferroni method showed that it was higher in group IV than in all other groups (P ⫽ .006 when compared with group III and P ⬍ .001 for comparisons with groups I and II) and lower in group I than in all other groups (P ⬍ .001 for all comparisons;
RESULTS
Fig 2. Transmission electron micrographs of the lung (A) Tracheal occlusion and (B) tracheal occlusion plus Dextran 70. There are no signs of cellular edema nor ultrastructural damage of the alveolar-capillary membrane (original magnification ⴛ2,200).
ONCOTIC ACCELERATION OF FETAL LUNG GROWTH
1009
Table 1. Osmolarity, pH, and Electrolyte Concentrations
Normal TO TO/SL TO/DX
Osmolarity (mOsm/L)
pH (mEq/L)
Na⫹ (mEq/L)
K⫹ (mEq/L)
Cl⫺ (mEq/L)
285.2 ⫾ 2.0 283.4 ⫾ 1.5 284.6 ⫾ 1.8 284.5 ⫾ 1.9
6.2 ⫾ .03 6.3 ⫾ .03 6.2 ⫾ .02 6.3 ⫾ .03
147 ⫾ .9 146 ⫾ 1.2 146 ⫾ 1.4 145 ⫾ .7
6.1 ⫾ .1 5.8 ⫾ .1 5.8 ⫾ .2 5.7 ⫾ .2
149 ⫾ 1 148 ⫾ 2 150 ⫾ 2 146 ⫾ 3
NOTE. Values are expressed as mean ⫾ standard error of the mean. Abbreviations: TO, tracheal occlusion; TO/SL, tracheal occlusion plus intrapulmonary delivery of saline; TO/DX, tracheal occlusion plus intrapulmonary delivery of Dextran 70. There were no significant differences among groups.
Fig 1). However, there was no difference between groups II and III (P ⫽ .99; Fig 1). Airspace fraction showed no significant difference between groups I (0.62 ⫾ 0.02), II (0.65 ⫾ 0.04), III (0.64 ⫾ 0.03), and IV (0.66 ⫾ 0.01). Histologic appearance was normal in all lung samples studied. This observation, combined with the airspace fraction data, shows a preserved maturation pattern and absence of emphysematous changes in all groups. Electron microscopy found no signs of cellular edema nor ultrastructural damage of the alveolar-capillary membrane in any sample (Fig 2). There were no differences in lung liquid osmolarity, pH level, and electrolyte (Na⫹, K⫹, and Cl⫺) concentrations among groups (Table 1). DISCUSSION
In addition to premature labor, erratic postoperative lung liquid production has been one of the reasons clinical application of fetal tracheal occlusion has met with limited success.8 In the current study, we have shown that positive intrapulmonary oncotic pressure by an isosmotic agent can maximize the short-term effects of fetal tracheal occlusion late in gestation, probably by expanding lung liquid volume, without any evidence of cell damage. We purposely chose to occlude the fetal trachea late in gestation because it has been shown that lung liquid secretion decreases sharply at the latter stages of pregnancy.4,5 Yet, our data show that this physiologic decrease in lung liquid production can be overcome by simple positive oncotic pressure inside the alveoli, at least for up to 2 weeks postoperatively. Given the facts that clinical fetal tracheal occlusion usually is performed
in the third trimester of gestation (because of fetal viability) and postoperative preterm labor results frequently in a short window between surgery and delivery, it is reasonable to speculate that delivery of an oncotic agent into the fetal lung at the time of tracheal occlusion could improve the currently disappointing results. More studies are needed before clinical application of this concept. For instance, the pharmacokinetics of Dextran 70 in the fetal lung remains to be determined. Dextran 70 is a very large polysaccharide normally metabolized by plasma amylases, dextranases, and the reticuloendothelial system (RES).9,10 It is likely to be eliminated at a much slower rate from the alveolar lumen than after intravenous application.9 Moreover, significant functional impairment of the RES has been described after extensive intravenous Dextran therapy.10 Given that type II pneumocytes compose the pulmonary component of the RES, the response of those cells to Dextran delivery into the fetal lung liquid after tracheal occlusion also must be determined. Finally, the use of hyperosmotic agents should be explored as well. Although the abovementioned studies should be pursued before clinical application, the current data suggest that the administration of an oncotic agent into the fetal lungs can be an effective and practical way to enhance control over lung growth acceleration after fetal tracheal occlusion. ACKNOWLEDGMENT The authors thank Jeffrey Pettit for his excellence in laboratory assistance.
REFERENCES 1. Wilson JM, DiFiore JW, Peters CA: Experimental fetal tracheal ligation prevents the pulmonary hypoplasia associated with fetal nephrectomy: Possible application for congenital diaphragmatic hernia. J Pediatr Surg 28:1433-9; discussion 1439-40, 1993 2. DiFiore JW, Fauza DO, Slavin R, et al: Experimental fetal tracheal ligation reverses the structural and physiological effects of pulmonary hypoplasia in congenital diaphragmatic hernia. J Pediatr Surg 29:248-56; discussion 256-7, 1994 3. DiFiore JW, Fauza DO, Slavin R, et al: Experimental fetal tracheal ligation and congenital diaphragmatic hernia: A pulmonary vascular morphometric analysis. J Pediatr Surg 30:917-23; discussion 923-4, 1995
4. Mescher EJ, Platzker AC, Ballard PL, et al: Ontogeny of tracheal fluid, pulmonary surfactant, and plasma corticoids in the fetal lamb. J Appl Physiol 39:1017-1021, 1975 5. Kitterman JA, Ballard PL, Clements JA, et al: Tracheal fluid in fetal lambs: Spontaneous decrease prior to birth. J Appl Physiol 47:985-989, 1979 6. Brown MJ, Olver RE, Ramsden CA, et al: Effects of adrenaline and of spontaneous labour on the secretion and absorption of lung liquid in the fetal lamb. J Physiol 344:137-152, 1983 7. Weibel ER: Stereologic Methods, in Weibel ER (ed): Practical Methods for Biological Morphometry (vol I). San Diego, CA, Academic Press, 1989, pp 63-236
1010
DZAKOVIC ET AL
8. Harrison MR, Mychaliska GB, Albanese CT, et al: Correction of congenital diaphragmatic hernia in utero IX: Fetuses with poor prognosis (liver herniation and low lung-to-head ratio) can be saved by fetoscopic temporary tracheal occlusion. J Pediatr Surg 33:1017-1022; discussion 1022-1023, 1998
9. Klotz U, Kroemer H: Clinical pharmacokinetic considerations in the use of plasma expanders. Clin Pharmacokinet 12:123-135, 1987 10. Ginz HF, Gottschall V, Schwarzkopf G, et al: [Excessive tissue storage of colloids in the reticuloendothelial system]. Anaesthesist 47:330-334, 1998
Discussion Dr Stolar (New York, NY): One of the problems with the trachea occlusion model is that the target cell seems to be the type II pneumocyte, and it contributes to some loss of surfactant. Have you had a chance to look for lamellar bodies or surfactant protein in your lung liquids? A. Dzakovik (response): That is a very good question.
We currently are looking at what happens to dextran after we inject it, and there has been an interesting paper published in Germany that told us that type II pneumocytes or reticular endothelial system cells are involved in degradation, and there actually might be some effect on these type II pneumocytes. We are currently investigating that in our next protocol.