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Ann Thorac Surg 2004;78:613-619
© 2004 The Society of Thoracic Surgeons
a Department of Pharmacology, University of Melbourne, Melbourne, Australia
d Department of Anesthesia, The Royal Melbourne Hospital, Melbourne, Australia
b Department of Pain Management, The Royal Melbourne Hospital, Melbourne, Australia
c Department of Cardiothoracic Surgery, The Royal Melbourne Hospital, Melbourne, Australia
e Department of Anesthesia, Westmead Hospital, Westmead, Australia
f Department of Anesthesia, Royal Perth Hospital, Perth, Australia
Accepted for publication February 18, 2004.
* Address reprint requests to Dr Royse, PO Box 1022, Research, Victoria, Australia, 3095
e-mail: colin.royse{at}mh.org.au
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Abstract |
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METHODS: Forty-six patients undergoing cardiac surgery from two institutions were evaluated, and an examination sequence was developed.
RESULTS: An 11-view examination is presented as a consensus between the two institutions. In clinical usage, there were no major complications attributable to use of the device. Minor air leaks occurred in 6 patients, and 2 cases of sternal wound infection occurring in a cluster of infections are reported, but causation was not attributed to use of the device. There were no significant differences in measurements of the aortic valve area, pulmonary artery diameter, left ventricular outflow tract dimension, or the sinotubular junction between substernal and transesophageal examinations. All 16 wall-motion segments were well visualized in most patients with substernal epicardial echocardiography.
CONCLUSIONS: Substernal epicardial echocardiography is a safe device for use in the postoperative environment.
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Introduction |
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Substernal epicardial echocardiography (SEE) is a novel echocardiography window allowing excellent imaging of the heart in the intensive care unit environment [3, 4]. The Medtronic SEEIT cannula (Medtronic, Minneapolis, MN) is a 9-mm mediastinal drain that incorporates a blind-ended sterile 11-mm or 16-mm silicon sleeve into which a TEE probe is inserted (Fig 1). The potential benefits of this approach are that high-quality echocardiography images can be obtained in awake and extubated patients, and that the probe can be left in situ for continuous monitoring. Postoperatively, awake and extubated patients described dull pressure type pain as the probe is advanced through the rectus sheath, but no discomfort during the examination [4]. The image quality is reported to be excellent and at least equal to that obtained with TEE [3, 4].
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The aims of this study were to produce a standardized examination protocol and to compare anatomical accuracy with TEE. The study represents a collaboration between the Royal Melbourne Hospital and Westmead Hospital investigator groups.
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Material and methods |
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Anesthetic procedure
Patients were anesthetized with a combined regional and general anesthetic technique at the Royal Melbourne site and by general anesthetisia at the Westmead site. All patients were still sedated at the time the study was performed.
Operative procedures
The chest was opened through median sternotomy. Before chest wall closure, a 2.5-cm to 3-cm horizontal incision was made through the center of the left rectus sheath to allow insertion of a 16-mm SEE drain (SEEIT 19616 cannula). The drain rests over the pericardium so that its blind end is positioned over the aortic arch and right brachiocephalic artery (Fig 1).
Echocardiography
Before sternal closure, a standard intraoperative TEE examination using an adult multiplane probe was conducted according to published guidelines (Royal Melbourne site only) [5]. The probe was then removed and disinfected before use in the SEE cannula.
After application of the sternal wound dressings, 20 mL 0.9% saline was injected through the Luer connector of the SEE cannula. The TEE probe was then inserted into the SEE cannula and advanced until the first view was obtained. We developed a sequence of 11 views based on collaborative experience between the Westmead Hospital and Royal Melbourne Hospital research groups. The SEE drain was left in situ postoperatively and removed on the second postoperative day. The SEEIT cannula is about twice the size of a standard 24-gauge chest drain. It is compressible, but returns to the origional shape after the deforming pressure is removed.
Comprehensive SEE examination
An important phase in the study was development of a standard SEE examination. Initially, we attempted to replicate the standardized TEE views. However, the axis of the drain is oblique to the axis of the esophagus. Short-axis (SAX) views of the heart had the same left-right orientation as TEE images; the right side of the patient is seen on the left of screen. However, long-axis (LAX) views of the heart had the opposite left-right orientation to TEE views. The SEE views presented anterior structures on the apex of the sector whereas the TEE views presented them on the bottom of the sector. Based on the primary requirement of SEE to monitor postoperative ventricular function, we decided that it was important that SAX views of the ventricles resemble that of transesophageal and transthoracic echocardiographies. Hence the views were not left-right inverted. Most other views require a degree of reorientation for the surgeon or echocardiographer familiar with TEE. The development of images involved recording the angle at which a view was obtained, and the mean angle is presented (the angle may vary 20 to 30 degrees between subjects). This information was used to determine the typical angle required to obtain a good quality view. We recommend that tip of the probe should not be angulated with the flexion or lateral movement controls in order to minimize the possibility of compression of cardiac structures by the probe.
The 11 SEE views are shown in Figure 2, and an example of the mid-SAX view is shown in Figure 3 to illustrate the fidelity of image obtained. Comparable views for TEE and SEE are shown in Table 1. The views are classified according to probe position within the cannula sleeve and transducer angulation. The recommended sequence is in order 1 to 11. The order of the sequence is based on obtaining anatomical information, followed by left ventricular function information, and finally assessment of the aorta. Assessment of the aorta is performed last because pathology in this area is less likely to be a cause of hemodynamic compromise, compared with the valves or ventricles. There are major probe manipulations within the sheath: first, advancing the probe to the mid position; second, withdrawl to the proximal position, and third, advancement to the distal position. At each position, different views are obtained by altering the angle of insonation with minimal probe manipulation.
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Regional wall-motion segments
Images were used to identify the 16 standard regional wall-motion segments [5]. A positive identification was recorded if an individual wall-motion segment could be tracked from end-diastole to end-systole. The transgastric mid-SAX, transgastric basal SAX, midesophageal four-chamber, midesophageal two-chamber, and midesophageal LAX views were used for TEE; and the basal SAX, mid-SAX, and apical SAX views were used to identify the segments for SEE.
Accuracy of two-dimensional measurements
Statistical analysis
Paired-samples Student's t test was used for comparisons of anatomical dimensions. The correlation coefficient (r) was Pearson's product-moment. A Bland-Altman plot was then constructed to illustrate the limits of agreement, using their formula for small sample size [7]. Significance was defined as p less than 0.05. Analysis was done using SPSS V11.0 (SPSS, Chicago, IL).
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Results |
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In the Westmead Hospital experience, 25 patients completed SEE examinations. Twenty-one patients had CABG, 3 patients had aortic valve replacement, and 1 patient had combined aortic valve replacement and mitral valve repair. In 2 patients, the TEE was unable to be passed through the SEE sleeve. Removal and inspection of the cannula revealed no fault or physical blockage of the cannula in either case, and the cause was considered most likely due to inadequate size of the incision (the SEE cannula is thick silicon, but is compressible). There were no major complications reported, but minor air leaks were noted in 6 patients.
In both hospitals, the SEE cannula was removed within the first 48 hours after surgery, and there were no cases of tube perforation or blockage.
Regional wall-motion segments
A description of adequate imaging of left ventricular regional wall-motion segments for SEE and TEE is shown in Table 2. All 16 wall-motion segments were adequately viewed in most patients with both examination methods. The basal septal wall was most likely to be missed by SEE, whereas the apical segments are most likely to be missed with TEE.
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Comment |
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TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
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Role of SEE
The potential therapeutic impact of echocardiography in the intensive care unit is considerable. In patients with abnormal hemodynamics, the use of echocardiography can lead to a change in management in both cardiac and noncardiac intensive care patients in 40% to 70% of diagnostic occasions [2, 8–11]. Echocardiography provides superior diagnostic information to that obtained from pulmonary artery catheter monitoring, allowing anatomical and functional assessment of the hemodynamic status. Additionally, echocardiography allows direct assessment of ventricular volume as opposed to indirect assessment obtained from a pressure-based monitoring system. Although noninvasive echocardiography is preferable to TEE, the image quality during transthoracic imaging may be inadequate to obtain sufficient diagnostic information. However, TEE is at least semi-invasive and also requires sedation in order to perform it, having the potential problem of exacerbating an already unstable hemodynamic state. Colreavy and associates [2] reported the complication rate of 1.6% in critically ill patients undergoing TEE examinations, including hypotension pulmonary aspiration and oropharyngeal bleeding, none of which cause long-term morbidity.
The advantages of SEE over TEE relate to the ability to perform repeated examinations without requirement for sedation or intubation, and to allow prolonged examination for the continual assessment of hemodynamic variables such as left ventricular volume and systolic function. There are few data, however, on the use of this technology and whether it compares favorably with TEE [3, 4]. Hanlon and associates [3] described their results of 13 patients studied with the cannula prototype. They used a pediatric probe in most patients and found excellent imaging of the heart in most patients. Of concern, however, is that they reported an incident of sleeve perforation with the TEE probe. Furnary and associates [4] reported a series of 21 patients using the commercially available SEE IT 19611 cannula, which has an 11-mm sleeve suitable for a pediatric TEE probe. They compared images obtained with SEE against those obtained with TEE, and found SEE to be superior when imaging anterior and right ventricular structures, and TEE superior when imaging posterior structures such as the left atrium and pulmonary veins. Additionally, they found the probe easy to insert and did not report any complications. In our study, we used the SEEIT 19616 cannula, which incorporates a 16-mm sleeve suitable for use with a standard adult multiplane probe. The study concurs with that of Furnary and associates [4] in that the image quality is excellent in most patients, but the limitations of examination relate to posterior structures including the distal arch and descending aorta.
The most important benefit of SEE in the intensive care unit is to monitor ventricular function and volume, and to diagnose the cause of hemodynamic instability. The excellent view of the ventricles in cross section makes this echocardiographic window ideal for these purposes. In tamponade, for example, the right ventricle is well visualized, being an anterior structure, and compression by hematoma would be easily seen. Continual monitoring with SEE could lead to early detection of tamponade.
There will be variability in the exact orientation of the image, caused by variations in the orientation of the cannula to the heart. In our experience, the cannula was inserted through the left rectus sheath and positioned so that the tip usually lies over the aortic arch and right brachiocephalic artery. This orientation lies over the long axis of the heart and allows imaging of the ascending aorta and proximal arch. The views obtained are quite different in both orientation and positioned to those obtained with TEE. The 11-view examination that we describe allows examination of all valves, all wall-motion segments, the ascending aorta and proximal arch, and Doppler examination of all valves.
Safety
In the two parallel arms of the study, a total of 46 patients were evaluated with the SEE cannula. There were no problems related to the insertion of the cannula, although the qualitative opinion was that the cannula was large, and the incision required was considerably larger than that required for a standard mediastinal chest drain. In the Westmead Hospital experience, the TEE probe could not be inserted through a rectus sheath in 2 patients, which probably related to inadequate size of the incision (the cannula is compressible). In all other cases, the probe passed easily into the sleeve and was easy to manipulate within the sleeve. The design of the cannula is still in evolution, with the revised version having a rounder and smaller profile that is likely to overcome the problems of large insertion incisions and air leakage. There were no major complications directly attributable to the use of the cannula, or any perforations of the sleeve. Sleeve perforation was reported with the prototype cannula by Hanlon and associates [3], but with the commercially available version, this complication was considered very unlikely by the manufacturer. In our series, there were no reports of tube perforation after inspection of the removed device. Minor air leaks may be attributable to the larger incision required to insert the cannula. In the Royal Melbourne Hospital series, we reported 2 patients who had sternal wound infection. These cases, however, occurred with a cluster of sternal wound infections within our surgical unit, and we believe that the sternal wound infection was an association with the cannula rather than causation. There have been no other sternal wound infections reported in the literature to date with the cannula. We do believe, however, that is prudent to disinfect the TEE probe before use in order to minimize the risk of contamination of the cannula.
The study was designed to clinically evaluate the SEE cannula and was not designed to measure the therapeutic impact of it. Although we are confident that the device is easy to insert and to use, and that the information obtained from it is equivalent to that derived from TEE, we do not have data to comment on this clinical utility in the perioperative setting. It is likely, however, to facilitate high-quality echocardiography imaging, which will impact on clinical management. Further research is required to further evaluate the device in the intensive care environment.
In conclusion, the SEE cannula is easy to insert and use, and appears safe to use in the perioperative environment. Anatomical assessment is comparable with that obtained by TEE.
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Acknowledgments |
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TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
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References |
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TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
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This article has been cited by other articles:
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  A. A. Alsaddique Recognition of diastolic heart failure in the postoperative heart Eur. J. Cardiothorac. Surg., December 1, 2008; 34(6): 1141 - 1148. [Abstract] [Full Text] [PDF]
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