Asian Cardiovasc Thorac Ann 2006;14:223-226
© 2006 Asia Publishing EXchange Ltd
Experimental Assessment of the Drainage Capacity of Small Silastic Chest Drains
Hiroshi Niinami, MD,
Mimiko Tabata, MD,
Yasuo Takeuchi, MD1,
Mitsuo Umezu, PhD2
Department of Cardiovascular Surgery Juntendo University School of Medicine
1 Department of Cardiovascular Surgery, Daini Hospital, Tokyo Women’s Medical University
2 Department of Mechanical Engineering, Waseda University, Tokyo, Japan
For reprint information contact: Hiroshi Niinami, MD Tel: 81 3 3813 3111 Fax: 81 3 5800 0281 Email: hniinami{at}med.juntendo.ac.jp, Department of Cardiovascular Surgery, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan.
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ABSTRACT
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Recently, flexible fluted small silicone drains have been used widely as chest drains after cardiac surgery. Despite the clinical advantages of using smaller silastic chest drains over conventional chest tubes, an experimental comparison of the drainage capacity between these two drain tubes has not yet been performed. The drainage capacity of 19F silicone drains and 28F conventional tubes was tested. In an in vitro study, both tubes were set in a water bath and drained at a pressure of 10 mm Hg. In an in vivo study, the drains were inserted into the hemithorax in 8 adult pigs. Blood was infused at 20 mL·min–1 into both chest cavities and the tubes were drained at 15 cm H2O for 30 min. In the in vitro study, the drainage capacity of the conventional chest tube was 9-times higher than that of the smaller silicone drain (103.8 vs. 11.6 L·hr –1). However, in the in vivo study, there was no difference in drainage capacity between the two different tubes over time. This experiment demonstrated that the smaller silastic chest drain has sufficient drainage capacity, almost identical to the conventional chest tube, in the clinical setting.
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INTRODUCTION
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Drainage and decompression of the mediastinum, pericardial, and/or pleural spaces is necessary following cardiac surgery. This procedure is traditionally accomplished in many centers with multiple rigid wide-bore (28F to 36F) plastic tubes.1 However, because of the large diameter of these thoracic tubes, patients often experience pain at the entry site through the skin and fascia. In addition to pain, these large rigid tubes can limit ambulation postoperatively. If smaller silastic drains are used, then certain patients, such as those undergoing off-pump coronary artery revascularization procedures, can achieve mobility more rapidly. With the advent of less invasive methods of cardiac surgery, efforts have focused on limiting postoperative pain and hastening recovery. Recently, small flexible fluted silastic drains have been introduced clinically after cardiac operations, to minimize postoperative pain and encourage earlier ambulation. Some clinical reports have revealed the superiority of these new drains over conventional rigid chest tubes, in terms of reducing postoperative pain without compromising drainage capacity.2–4 Despite the clinical advantages of these new drains, the drainage capacity of the two types of tube has not been compared experimentally.
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MATERIALS AND METHODS
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The drainage capacity of the 19F silicone fluted drain (round Blake hubless silicone drain; Johnson & Johnson, Somerville, NJ, USA) and the 28F conventional rigid chest tube (Thoracic UK Catheter; Unitika, Tokyo, Japan) was tested in both in vitro and in vivo settings. The external appearance and cross section of both tubes is shown in Figure 1
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Figure 1. (A) External appearance and (B) cross section of the conventional and small silastic chest drains.
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In the in vitro study, both tubes were set in a water bath containing glycerin solution with a viscosity equivalent to blood (3.8 cP) and drained at a pressure of 10 mm Hg (Figure 2). The length of both drains in the water bath was 200 mm. The conventional chest tube was set without trimming, but the silicone drain was cut so that the entire fluted portion was completely submerged in the water bath. This study was performed in two settings: in the water bath alone, and in the water bath with the tubes embedded in a sponge. The drainage pattern was also visualized with both drain tubes embedded in sponges stained red, and drained at a pressure of 10 mm Hg.
All animal procedures were in strict accordance with the National Institute of Health Guidelines for the Care and Use of Laboratory Animals (National Institutes of Health publication no. 86-23, revised 1985) and were approved by the Institutional Animal Care Committee of our university. Eight adult pigs (38 to 42 kg) were anesthetized with halothane. In all animals, a silastic drain was inserted into either the right or left hemithorax, with a conventional drain tube in the other side. Blood was collected from different pigs in blood collecting bags (Terumo, Tokyo, Japan) and infused at 20 mL·min–1 into both chest cavities; both tubes were drained at 15 cm H2O using an underwater sealed drainage apparatus (MS-008; Senko Ika Co. Ltd., Tokyo, Japan) for up to 30 min (Figure 3).
Statistical analysis was performed using the StatView (version 5.0) software package (SAS Institute Inc., Cary, NC, USA). Values are expressed as means with standard deviations. The significance of the differences in the data was assessed by the unpaired Student t test. A statistical probability of less than 0.05 was considered as indicating significance.
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RESULTS
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In the in vitro study, the drainage of the conventional chest tube was 103.8 L·hr –1 and that of the fluted silicone drain was 11.6 L·hr –1 in the water bath alone, which meant that the drainage capacity of the conventional chest tube was 9-times higher than that of the smaller silicone drain. However, when both drain tubes were embedded in the sponge, this rate was reduced by 11% in the conventional tube and unchanged in the silastic drain (Figure 4). A flow visualization test revealed different drainage patterns in the two tubes (Figure 5). The most effective portions were the most proximal slits of the silicone drain and the side hole of the conventional chest tube. In the in vivo study, the relationship between time and suction volume and that between infusion and suction volume were linear in all animals and in both tubes (R2 > 0.9). There was no difference in drainage capacity between the two different tubes over time (Figure 6).
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Figure 4. Drainage capacity of the two different drain tubes with and without a sponge; solid bars = 19F silicone drain tube, open bars = 28F conventional chest tube. Note that when both drain tubes were embedded in the sponge, the flow rate was reduced by 11% in the conventional tube but unchanged in the silicone drain.
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Figure 5. Comparison of flow visualization test results using two different drain tubes. Note that the most effective portions were the most proximal slits of the silicone drain and the side hole of the conventional chest tube.
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Figure 6. Mean drainage in all 8 animals at each time point; closed circle = 19F silicone drain tube, open circle = 28F conventional chest tube.
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DISCUSSION
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Since the beginning of open heart surgery, rigid chest tubes of polyvinyl chloride have been used routinely to decompress the mediastinal and pleural spaces of fluid and air to prevent hemodynamic compromise from cardiac tamponade or tension pneumothorax, and to monitor the bleeding rate postoperatively.1 Although complications associated with the use of these tubes are rare, they do have several undesirable aspects. Due to their rigidity, there is the potential for compression of intrathoracic structures, such as coronary bypass conduits, with resultant myocardial ischemia.5 Bypass grafts may also be drawn into the large side holes of the tubes, which can also create myocardial ischemia.6 Cardiogenic shock caused by compression of the right ventricle by a large rigid chest tube has been also reported.7 Thrombus formation within the drain tube may hinder further drainage and promote residual collection of blood within the pericardial cavity, which can have significant acute or chronic consequences. These undesirable features can be eliminated by the introduction of flexible fluted small silicone drains.
Blake silicone drains are small-bore (19F), round, flexible, fluted drains that exert constant suction over the entire length of the fluted portion of the drain. With non-collapsible tubing and long channels for drainage, they are theoretically resistant to occlusion with thrombi. Obney and colleagues2 compared two different chest tubes clinically after cardiac procedures in a retrospective study. They concluded that conventional chest tubes were not necessarily better when it came to draining the mediastinum. Lancey and colleagues3 also demonstrated the safety and efficacy of 19F Blake silicone drains in patients undergoing open heart surgery. However, their study was not a comparative one, and in fact they pointed out the importance of a randomized prospective trial comparing the silicone drains to conventional large-bore tubes to evaluate their true advantage. Recently, Akowuah and colleagues4 designed a prospective randomized trial to compare the 19F Blake silicone drain and the 28F conventional chest drain in 70 patients undergoing elective coronary artery bypass grafting. They concluded that 19F Blake drains were as effective as traditional chest tubes in terms of an increase in pleural or pericardial effusions or re-exploration for tamponade or bleeding, and furthermore, they caused less pain. Although their study was prospective and randomized, it focused mainly on the degree of pain before and during removal of the drain. To utilize this new drain tube in all types of open heart surgery, it is important to know the drainage ability of the tubes and precisely compare the drainage capacity in experimental models.
This experiment demonstrated that the drainage capacity of the smaller silastic tube was less than that of the conventional chest tube, simply due to its different diameter. However, this silastic drain is capable of draining more than 10 L·hr –1, which is sufficient drainage capacity to judge the amount of bleeding necessary for re-exploration. Furthermore, in the in vivo study, we designed a hemothorax model that continuously bled at a rate of 1,200 mL·hr –1, thereby revealing identical drainage ability of the two different drain tubes. This in vivo study confirmed that the 9-times higher drainage ability observed in vitro could be ignored in the clinical setting. We chose the hemothorax model rather than the mediastinal or pericardial bleeding model because the different tubes could be compared in the same animal to eliminate bias in positioning the tubes and in the distance between each tube and the bleeding point. However, the disadvantage of this model is that for pleural drainage it is placed in the chest cavity, and the drains sit between the chest wall and lung, so that other structures or tissue cannot obstruct the side holes of the conventional chest tube and the slits of the Blake drain tube. In the in vitro study, an interesting phenomenon was that the drainage capacity of the conventional chest tube was reduced by 11% when it was embedded in a sponge, whereas the sponge had no effect on the capacity of the Blake drain. It can be hypothesized that the silastic fluted drain tube can drain more efficiently than the conventional chest tube when it sits in spaces surrounded by tissue, fat, or clots. This difference can be explained by the unique design of the Blake drain which allows fluid to be drained by a capillary phenomenon along the long slit.
Another important finding was obtained by the visualization study, which was that the most effective portions were the most proximal slits of the silastic drain and the side hole of the conventional tube (Figure 5
). This indicates that when the Blake silicone drain is placed, its most proximal slit should be situated where the most effective drainage is required. For instance, when the pericardial drain is inserted, the slits should be placed completely into the pericardial cavity. Also, when the substernal drain is inserted, the most proximal slits should be placed in the middle or two thirds of the way down from the sternal notch. In other words, the slits should not be placed in the area around the diaphragm, to avoid undesirable suction.
It is well documented that one of the greatest advantages of utilizing the Blake drain rather than the conventional rigid chest tube is that the patient suffers less pain both before and during the procedure of drain removal.4 In our clinical practice, we have gained the same impression since the introduction of the Blake drain after cardiac and vascular surgery. As long as the drainage capacity is identical between the two different tubes, we believe that the flexible fluted silicone drains are superior in terms of patient pain to the conventional rigid chest tubes. Furthermore, the silastic fluted drain may have a better drainage capacity in spaces surrounded by tissue, because of its specific design. We believe that this system can replace conventional rigid chest tubes.
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REFERENCES
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- Munnell ER, Thomas EK. Current concepts in thoracic drainage systems. Ann Thorac Surg 1975;19:261–8.[Abstract]
- Obney JA, Barnes MJ, Lisagor PG, Cohen DJ. A method for mediastinal drainage after cardiac procedures using small silastic drains. Ann Thorac Surg 2000;70:1109–10.[Abstract/Free Full Text]
- Lancey RA, Gaca C, Vander Salm TJ. The use of smaller, more flexible chest drains following open heart surgery: an initial evaluation. Chest 2001;119:19–24.[Medline]
- Akowuah E, Ho EC, George R, Brennan K, Tennant S, Braidley P, et al. Less pain with flexible fluted silicone chest drains than with conventional rigid chest tubes after cardiac surgery. J Thorac Cardiovasc Surg 2002;124:1027–8.[Free Full Text]
- Svedjeholm R, Hakanson E. Postoperative myocardial ischemia caused by chest tube compression of vein graft. Ann Thorac Surg 1997;64:1806–8.[Free Full Text]
- Chapin JW, Kahre J, Newland M. Acute myocardial ischemia caused by mediastinal chest tube suction. Anesth Analg 1980;59:386–7.[Free Full Text]
- Kollef MH, Dothager DW. Reversible cardiogenic shock due to chest tube compression of the right ventricle. Chest 1991;99:976–80.[Medline]
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ABSTRACT
INTRODUCTION
