LETTERS Lung Reaeration and Reventilation after Aspiration of Pleural Effusions: a Study Using Electrical Impedance Tomography To the Editor: I read with interest the observations on changes in lung aeration and ventilation after thoracentesis reported by Alves and colleagues (1). It is intriguing to note the temporal differences between lung reaeration and reventilation after withdrawal of fluid. They have noted that reventilation of the lungs could not be predicted from changes in lung aeration. They put forward three possible explanations: (1) possible reexpansion pulmonary edema not seen on the post-thoracentesis chest radiographs; (2) expiratory small airway collapse resulting in air entrapment without effective ventilation; and (3) ipsilateral diaphragm dysfunction resulting from prolonged compression by a large effusion. There could be another possible explanation to this phenomenon. Post-thoracentesis ventilation may have been diminished for some patients by reduced compliance associated with parenchymal infiltration by primary metastatic cancer. These explanations could possibly explain the observed ventilatory changes in the ipsilateral lung noted after evacuation of the effusion, but it would be hard to imagine how they could lead to decrease in ventilation of the contralateral lung in 9 out of the 22 patients. Perhaps the decrease in contralateral lung reventilation is a normal physiological response. Prior to thoracentesis, ventilation of the normal lung may have been supranormal in compensation for diminished ventilation of the diseased lung. Restoration to normal ventilation of the contralateral lung might
Reply: Hypotheses for the Decrease in the Ipsilateral and Contralateral Lung Ventilation after a Pleural Aspiration We thank Dr. Biswas for his comments regarding our article (1). Dr. Biswas offered two interesting hypotheses regarding the decrease in the ventilation of the ipsilateral and contralateral lung after the pleural aspiration. We agree with both hypotheses. The first hypothesis offered by Dr. Biswas was that the decrease in the ipsilateral ventilation was due to a parenchymal infiltration. However, we believe that the hypothesis is not applicable to our study because all patients had a recent thoracic tomography and none had pulmonary lymphangitic carcinomatosis, extensive neoplastic parenchymal infiltration, or invasion of the visceral pleura. Above all, we measured the pleural pressure after removal of 500 ml of pleural effusion, and the calculated pleural elastance (data not shown) was under 19 cm H2O in all patients (mean value = 6 6 5 cm H2O), indicating a low probability of entrapped lung (2). The second hypothesis offered by Dr. Biswas was that the decrease in the contralateral lung ventilation after the aspiration 466
then have been an appropriate response to improved functioning of the diseased lung after thoracentesis. Additional insights into these possible mechanisms might be revealed by performing the same experiment on subjects who have a unilateral transudative pleural effusion and otherwise disease-free lungs. Irrespective of the limitations of the study, electrical impedance tomography appears to be a useful tool to identify changes in regional lung ventilation and a reproducible tool to identify those who would derive the most benefit in symptoms after drainage of their pleural effusion (2, 3). Author disclosures are available with the text of this letter at www.atsjournals.org. Abhishek Biswas, M.D. University of Pittsburgh Medical Center East Monroeville, Pennsylvania
References 1 Alves SH, Amato MB, Terra RM, Vargas FS, Caruso P. Lung reaeration and reventilation after aspiration of pleural effusions: a study using electrical impedance tomography. Ann Am Thorac Soc 2014;11: 186–191. 2 Frerichs I, Schmitz G, Pulletz S, Schadler ¨ D, Zick G, Scholz J, Weiler N. Reproducibility of regional lung ventilation distribution determined by electrical impedance tomography during mechanical ventilation. Physiol Meas 2007;28:S261–S267. 3 Marquis F, Coulombe N, Costa R, Gagnon H, Guardo R, Skrobik Y. Electrical impedance tomography’s correlation to lung volume is not influenced by anthropometric parameters. J Clin Monit Comput 2006;20:201–207. Copyright © 2014 by the American Thoracic Society
was a normal physiological response, because the contralateral kept an above-normal ventilation to compensate for the decreased ventilation of the ipsilateral lung that was encircled by the effusion. Forty-one percent of our patients presented that decrease, and we believe that the hypothesis offered by Dr. Biswas is a plausible one. In our study, we used electrical impedance tomography to evaluate the lung reaeration and reventilation after the aspiration of malignant pleural effusions. The study was designed to describe the lung reaeration and reventilation, but not to elucidate their causes, so we were only able to offer what we believed were plausible explanations to the phenomenon observed. We thank Dr. Biswas for his collaboration widening the hypotheses field. Author disclosures are available with the text of this letter at www.atsjournals.org. Pedro Caruso, M.D. Hospital das Cl´ınicas da Faculdade de Medicina da Universidade de Sa˜o Paulo Sa˜o Paulo, Brasil and Hospital A C Camargo Sa˜o Paulo, Brasil
AnnalsATS Volume 11 Number 3 | March 2014
LETTERS References 1 Alves SH, Amato MB, Terra RM, Vargas FS, Caruso P. Lung reaeration and reventilation after aspiration of pleural effusions: a study using electrical impedance tomography. Ann Am Thorac Soc 2014;11:186–191.
External Fixation of a Subglottic Tracheal Silicone Stent To the Editor: We read with interest the case of subglottic tracheal stenosis discussed by Keshava and colleagues (1). The patient had a stricture just 1.5 cm below the vocal cords (VC). We agree with the authors that placing a silicone stent in such a scenario carries a high risk of stent migration. To prevent displacement, we use an inexpensive method of externally fixing the stent. Although first described in 1994, the basic technique is uncommonly used in patient management (2). A 19-year-old girl presented to our chest clinic with breathlessness and stridor. She gave a history of endotracheal intubation and prolonged mechanical ventilation. Flexible bronchoscopy revealed a 2-cm-long complex tracheal stenosis starting 3 cm below the VC, causing 80% luminal narrowing. As the patient declined surgery, we proceeded with rigid bronchoscopy. Dilatation of the stenosed segment was performed according to standard procedure practiced at our center using a rigid tracheoscope (3). A 7-cm-long silicone stent of external diameter 16 mm was placed 2 cm below the VC using a previously described technique (3). After the procedure, the patient remained asymptomatic for 14 months, at which time dyspnea recurred. Fiberoptic bronchoscopy
2 Lan RS, Lo SK, Chuang ML, Yang CT, Tsao TC, Lee CH. Elastance of the pleural space: a predictor for the outcome of pleurodesis in patients with malignant pleural effusion. Ann Intern Med 1997;126:768–774. Copyright © 2014 by the American Thoracic Society
showed downward displacement of the stent. Using rigid bronchoscopy, the narrowed segment was dilated and the stent was repositioned. However, on this occasion, the stent migrated within 2 weeks. To prevent recurrent migration, we planned to externally fix the stent in the following manner. After repositioning, the optical telescope was advanced into the deployed stent to transilluminate a suitable area on the neck at least 1 cm above the sternal notch and 2 cm below the upper edge of the stent. Under full aseptic precautions, two 16-guage intravenous cannulas were inserted 1.5 cm apart from the anterior aspect of the neck to enter the anterior tracheal wall (in the space between two tracheal rings) and the silicone stent. The cannulas were visualized piercing the stent in real time through the rigid bronchoscope (Figure 1A). Needles were removed, and a 1-0 Ethilon thread (thread 1) was introduced through one cannula and a loop fashioned from another thread (thread 2) through the other cannula. Both the loop and the loose end of thread 1 could be seen inside the trachea through the bronchoscope (Figure 1B). Next, the loose end of thread 1 was drawn into the loop using grasping forceps (Figures 1C and 1D). The loop was then pulled from outside so that thread 1 came out from the second cannula (Figure 1E). Finally, both cannulas were removed, leaving thread 1 in place (Figure 1F), which was then tied into a knot onto the skin of the neck. Fiberoptic bronchoscopy performed
Figure 1. Bronchoscopic view of the suturing technique used. (A) First cannula with thread 1 in place. (B) Both cannulas along with thread 1 and the loop made from thread 2 in place. (C, D) Loose end of thread 1 being drawn into the loop. (E) Loop being pulled from outside drawing thread 1 with it. (F) Thread 1 in place with both the ends outside onto the neck skin.
Letters
467
Reply: Hypotheses for the Decrease in the Ipsilateral and Contralateral Lung Ventilation after a Pleural Aspiration We thank Dr. Biswas for his comments regarding our article (1). Dr. Biswas offered two interesting hypotheses regarding the decrease in the ventilation of the ipsilateral and contralateral lung after the pleural aspiration. We agree with both hypotheses. The first hypothesis offered by Dr. Biswas was that the decrease in the ipsilateral ventilation was due to a parenchymal infiltration. However, we believe that the hypothesis is not applicable to our study because all patients had a recent thoracic tomography and none had pulmonary lymphangitic carcinomatosis, extensive neoplastic parenchymal infiltration, or invasion of the visceral pleura. Above all, we measured the pleural pressure after removal of 500 ml of pleural effusion, and the calculated pleural elastance (data not shown) was under 19 cm H2O in all patients (mean value = 6 6 5 cm H2O), indicating a low probability of entrapped lung (2). The second hypothesis offered by Dr. Biswas was that the decrease in the contralateral lung ventilation after the aspiration 466
then have been an appropriate response to improved functioning of the diseased lung after thoracentesis. Additional insights into these possible mechanisms might be revealed by performing the same experiment on subjects who have a unilateral transudative pleural effusion and otherwise disease-free lungs. Irrespective of the limitations of the study, electrical impedance tomography appears to be a useful tool to identify changes in regional lung ventilation and a reproducible tool to identify those who would derive the most benefit in symptoms after drainage of their pleural effusion (2, 3). Author disclosures are available with the text of this letter at www.atsjournals.org. Abhishek Biswas, M.D. University of Pittsburgh Medical Center East Monroeville, Pennsylvania
References 1 Alves SH, Amato MB, Terra RM, Vargas FS, Caruso P. Lung reaeration and reventilation after aspiration of pleural effusions: a study using electrical impedance tomography. Ann Am Thorac Soc 2014;11: 186–191. 2 Frerichs I, Schmitz G, Pulletz S, Schadler ¨ D, Zick G, Scholz J, Weiler N. Reproducibility of regional lung ventilation distribution determined by electrical impedance tomography during mechanical ventilation. Physiol Meas 2007;28:S261–S267. 3 Marquis F, Coulombe N, Costa R, Gagnon H, Guardo R, Skrobik Y. Electrical impedance tomography’s correlation to lung volume is not influenced by anthropometric parameters. J Clin Monit Comput 2006;20:201–207. Copyright © 2014 by the American Thoracic Society
was a normal physiological response, because the contralateral kept an above-normal ventilation to compensate for the decreased ventilation of the ipsilateral lung that was encircled by the effusion. Forty-one percent of our patients presented that decrease, and we believe that the hypothesis offered by Dr. Biswas is a plausible one. In our study, we used electrical impedance tomography to evaluate the lung reaeration and reventilation after the aspiration of malignant pleural effusions. The study was designed to describe the lung reaeration and reventilation, but not to elucidate their causes, so we were only able to offer what we believed were plausible explanations to the phenomenon observed. We thank Dr. Biswas for his collaboration widening the hypotheses field. Author disclosures are available with the text of this letter at www.atsjournals.org. Pedro Caruso, M.D. Hospital das Cl´ınicas da Faculdade de Medicina da Universidade de Sa˜o Paulo Sa˜o Paulo, Brasil and Hospital A C Camargo Sa˜o Paulo, Brasil
AnnalsATS Volume 11 Number 3 | March 2014
LETTERS References 1 Alves SH, Amato MB, Terra RM, Vargas FS, Caruso P. Lung reaeration and reventilation after aspiration of pleural effusions: a study using electrical impedance tomography. Ann Am Thorac Soc 2014;11:186–191.
External Fixation of a Subglottic Tracheal Silicone Stent To the Editor: We read with interest the case of subglottic tracheal stenosis discussed by Keshava and colleagues (1). The patient had a stricture just 1.5 cm below the vocal cords (VC). We agree with the authors that placing a silicone stent in such a scenario carries a high risk of stent migration. To prevent displacement, we use an inexpensive method of externally fixing the stent. Although first described in 1994, the basic technique is uncommonly used in patient management (2). A 19-year-old girl presented to our chest clinic with breathlessness and stridor. She gave a history of endotracheal intubation and prolonged mechanical ventilation. Flexible bronchoscopy revealed a 2-cm-long complex tracheal stenosis starting 3 cm below the VC, causing 80% luminal narrowing. As the patient declined surgery, we proceeded with rigid bronchoscopy. Dilatation of the stenosed segment was performed according to standard procedure practiced at our center using a rigid tracheoscope (3). A 7-cm-long silicone stent of external diameter 16 mm was placed 2 cm below the VC using a previously described technique (3). After the procedure, the patient remained asymptomatic for 14 months, at which time dyspnea recurred. Fiberoptic bronchoscopy
2 Lan RS, Lo SK, Chuang ML, Yang CT, Tsao TC, Lee CH. Elastance of the pleural space: a predictor for the outcome of pleurodesis in patients with malignant pleural effusion. Ann Intern Med 1997;126:768–774. Copyright © 2014 by the American Thoracic Society
showed downward displacement of the stent. Using rigid bronchoscopy, the narrowed segment was dilated and the stent was repositioned. However, on this occasion, the stent migrated within 2 weeks. To prevent recurrent migration, we planned to externally fix the stent in the following manner. After repositioning, the optical telescope was advanced into the deployed stent to transilluminate a suitable area on the neck at least 1 cm above the sternal notch and 2 cm below the upper edge of the stent. Under full aseptic precautions, two 16-guage intravenous cannulas were inserted 1.5 cm apart from the anterior aspect of the neck to enter the anterior tracheal wall (in the space between two tracheal rings) and the silicone stent. The cannulas were visualized piercing the stent in real time through the rigid bronchoscope (Figure 1A). Needles were removed, and a 1-0 Ethilon thread (thread 1) was introduced through one cannula and a loop fashioned from another thread (thread 2) through the other cannula. Both the loop and the loose end of thread 1 could be seen inside the trachea through the bronchoscope (Figure 1B). Next, the loose end of thread 1 was drawn into the loop using grasping forceps (Figures 1C and 1D). The loop was then pulled from outside so that thread 1 came out from the second cannula (Figure 1E). Finally, both cannulas were removed, leaving thread 1 in place (Figure 1F), which was then tied into a knot onto the skin of the neck. Fiberoptic bronchoscopy performed
Figure 1. Bronchoscopic view of the suturing technique used. (A) First cannula with thread 1 in place. (B) Both cannulas along with thread 1 and the loop made from thread 2 in place. (C, D) Loose end of thread 1 being drawn into the loop. (E) Loop being pulled from outside drawing thread 1 with it. (F) Thread 1 in place with both the ends outside onto the neck skin.
Letters
467
