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Ann Thorac Surg 1996;61:1377-1380
© 1996 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Pooled Air in Open Heart Operations Examined by Transesophageal Echocardiography

First Department of Surgery, Hiroshima University School of Medicine, Hiroshima, Japan

Accepted for publication January 15, 1996.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background.The clinical significance of pooled air detected by transesophageal echocardiography during open heart operations is not clear.

Methods.Thirty-eight consecutive patients undergoing an open heart operation or an operation on the ascending aorta were divided into two groups on the basis of the absence (group 1, n = 14) or presence (group 2, n = 24) of pooled air. They were examined for intramyocardial echo contrast, ST segment elevation, conduction disturbances, and regional wall motion abnormalities.

Results.Echo contrast was found in no patient in group 1 and 66.7% of group 2 patients (p < 0.001). New regional wall motion abnormalities were detected in no patient in group 1 versus 33.3% of group 2 patients (p < 0.05), and ST segment elevation was seen in 33.3% of group 2 patients versus no group 1 patients (p < 0.05). Intramyocardial echo contrast was newly detected after the appearance of pooled air more frequently in patients with ST segment elevation (p < 0.001). Atrioventricular block and sinus arrest appeared in 3 patients and 2 patients, respectively. Postoperative regional wall motion abnormalities were found in 25.0% of patients and were not closely related to intraoperative echo contrast findings.

Conclusions.Pooled air, which is often detected in open heart operation by means of transesophageal echocardiography, is related to several cardiac events, including ST segment elevation, conduction disturbances, and regional wall motion abnormalities, although most of these are transient.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
In 1993, we [1] reported pooling of intracardiac air, which is often detected during open heart operations, especially at weaning from bypass, by transesophageal echocardiography. The pooled air is distinctly depicted as strongly echogenic, is often accompanied by an acoustic shadow and side lobes, and can move rapidly or stay at the highest position in each cardiac chamber. Bubbles, on the other hand, are depicted as small echogenic dots in the cardiac chamber that have no acoustic shadow and that move rapidly along in the bloodstream. Although several authors [2, 3] have reported the clinical sequelae of retained air during cardiac operations, they examined only bubbles. The clinical implication of pooled air, which was shown to amount to several milliliters [1], is not clear. In this study, we examined the clinical significance of pooled air.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
The cases of 38 consecutive patients undergoing an open heart operation or an operation on the ascending aorta from May 1994 to August 1995 were reviewed. There were 23 male and 15 female patients ranging from 15 to 79 years old. The left cardiac chamber was opened to the air in these patients, and the procedures were as follows: aortic valve replacement in 11 patients; mitral valve replacement or valvuloplasty in 12 (double-valve replacement in 1); closure of an atrial septal defect in 6; maze operation in 12 (maze procedure alone in 3); replacement of the ascending aorta in 3 (Bentall operation in 1); cryoablation in the left ventricle in 1; resection of a left atrial myxoma in 1; left atrial thrombectomy in 1; and closure of a patent ductus arteriosus combined with a maze procedure in 1.

All operations were performed by a single surgeon with the same perfusionist, and the methods of cardiopulmonary bypass and cardioplegia were not changed during this period. Hypothermia (rectal temperature of around 28°C) and hemodilution were used in every operation, as were a membrane oxygenator and an arterial line filter. Cardioplegic solution was administered antegrade and in the case of aortic valve procedures and operations on the ascending aorta, also in retrograde fashion.

The observations in this study were done with a 5 MHz transesophageal echocardiographic (TEE) system (EUP-ES322 or EUB-555; Hitachi Co Inc, Tokyo, Japan) as part of the intraoperative monitoring. The frequency of emitted ultrasound was changed to 3.5 MHz when needed. The electrocardiogram was monitored in lead II.

After the cardiotomy was closed, pooled air was examined in the coronary sinus of Valsalva, left ventricular (LV) apex, left atrium (LA), and right upper pulmonary vein (RUPV), as previously described [1]. The TEE findings were provided to the surgeon, who performed additional procedures with TEE guidance to eliminate air. Air in the RUPV was expelled toward the LA and left ventricle by inflating the lung and tilting the patient's right side downward or was aspirated with a fine needle. Air in the LA was moved to the LV apex and then was aspirated either through an LV vent tube or with a fine needle through the apex or was moved to the aorta by shaking the heart and then eliminated through the venting line.

After recovery of sinus rhythm, intramyocardial echo contrast [4], depicted as echogenic dots in the myocardium, was examined in the interventricular septum (IVS), posteromedial papillary muscle, and inferior LV wall. The result was considered positive only when contrast newly appeared after cardiopulmonary bypass; if contrast was present in the TEE images obtained before bypass, the result was considered negative. The patients were classified into two groups according to the absence or presence of pooled air: group 1 = no pooled air and group 2 = pooled air.

The following variables were compared in the two groups: (1) sex, age, and operative procedures; (2) operation time and duration of both cardiopulmonary bypass and aortic cross-clamping; (3) incidence of newly found intramyocardial echo contrast; (4) incidence of new regional wall motion abnormalities (RWMAs) in the period after bypass compared with wall motion in the period before bypass as diagnosed by a single observer; (5) incidence of ST segment elevation by more than 0.1 mV in lead II and conduction disturbances in the postbypass period; (6) incidence of spontaneous recovery of sinus rhythm from ventricular fibrillation without cardioversion; (7) incidence of recurrent ventricular fibrillation soon after spontaneous recovery of sinus rhythm or cardioversion; and (8) the highest serum levels of glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, lactate dehydrogenase, creatinine, creatine kinase, the myocardial-specific isoenzyme of creatine kinase, and amylase within 7 days of operation. In addition, RWMAs were examined postoperatively using transthoracic echocardiography by the cardiologists in our institution, who were blinded to the intraoperative TEE findings.

Data are shown as the mean ± the standard deviation. Statistical analysis was carried out by means of a ² test to examine the differences in incidence between the two groups and by means of Student's t test to examine the differences in mean values between the two groups. Differences in means of serum levels of enzymes were examined by means of a logarithm of each value. Significance was determined when the p value was less than 0.05.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Preoperative and operative group data are shown in Table 1. Age was significantly higher in group 2. There were no significant differences in sex, operative procedures, operation time, duration of cardiopulmonary bypass, or duration of aortic cross-clamping. There was no perioperative mortality in this series.

ST segment elevation in lead II was seen in 2 patients (14.3%) and 10 patients (41.7%) in groups 1 and 2, respectively (p = not significant). However, in 2 patients in each group, ST segment elevation had already been seen after cardioversion but before the appearance of air around the orifice of the right coronary artery. Thus, ST segment elevation newly developed after the appearance of air in 8 patients (33.3%) in group 2 versus none in group 1 (p < 0.05). The ST segment gradually returned to normal within 30 minutes in most patients. In 2 of these 8 patients, a new, small Q wave was found in lead II postoperatively. Intramyocardial echo contrast was found in all 8 patients with new ST segment elevation and in only 8 (26.7%) of 30 patients without new ST segment elevation (p < 0.001).

Conduction disturbances were analyzed in the 26 patients who did not have a maze operation. Atrioventricular block appeared in 3 patients and sinus arrest in 2. Pooled air was found in the LV apex or RUPV in all 5 patients, and every event occurred after the appearance of air bubbles in the coronary sinus of Valsalva, which were caused by the stirring up of air by ventilation, cardiac contraction, or both. In all 5 patients there was improvement within 30 minutes.

Patient 35 showed abrupt sinus arrest after entry of bubbles into the right coronary artery (Fig 1, top row). This event was associated with the appearance of intramyocardial echo contrast in the IVS (Fig 2) and the posteromedial papillary muscle (Fig 3). After atrial pacing for several minutes (see Fig 1, second row), pacing was captured (see Fig 1, third row), and then sinus rhythm recovered (see Fig 1, bottom row).

View larger version (148K): [in this window] [in a new window]   Fig 1. . (Patient 35.) Changes in electrocardiogram in lead II. Top row: abrupt sinus arrest after entry of bubbles into right coronary artery (arrow). Second row: start of atrial pacing (arrow). Third row: capture of atrial pacing (arrow). Bottom row: recovery of sinus rhythm (arrow). Calibration on left corresponds to 1 mV.

View larger version (88K): [in this window] [in a new window]   Fig 2. . Transesophageal echocardiogram showing intramyocardial echo contrast (EC) in interventricular septum. Contrast appeared after entry of air into right coronary artery. (LA = left atrium; LV = left ventricle; RA = right atrium; RV = right ventricle; RVPV = right ventricular pulmonary vein; T = transverse scan.)

View larger version (106K): [in this window] [in a new window]   Fig 3. . Transesophageal echocardiogram showing intramyocardial echo contrast (EC) at posteromedial papillary muscle. (LV = left ventricle; RV = right ventricle; RVPV = right ventricular pulmonary vein; T = transverse scan.).

There were no significant differences in serum levels of glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, lactate dehydrogenase, creatine kinase, myocardial-specific isoenzyme of creatine kinase, amylase, pancreas-specific amylase, and creatinine (Table 3).

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
This study demonstrates that the presence of pooled air is closely related to the appearance of intramyocardial echo contrast, ST segment elevation, conduction disturbances, or RWMAs in the early postbypass period. In this study, the majority of these events were transient and had resolved by the end of the operation, and no deaths resulted. Our findings suggest that many events that had been diagnosed simply as ``unusual events of unknown cause'' could have been due to air embolism caused by pooled intracardiac air.

We thought that multiple bubbles might cause air embolism in various organs including the brain [5, 6] and examined the biochemical variables. However, there were no significant differences in the serum levels of these variables between the two groups.

This study has an obvious limitation. The sequelae observed are those that occurred after intensive attempts to eliminate air with TEE guidance, and consequently they have been underestimated. We provided the surgeon with TEE findings of air in real time because we considered it ethically unacceptable to simply observe the events and not try to eliminate air just for the sake of the study.

Numerous bubbles entered the right coronary artery, and this was followed by the appearance of intramyocardial echo contrast and other events, despite intensive air-eliminating procedures. It seems that the intramyocardial echo contrast indicates air that has not been eliminated. To examine the importance of air, it would be better to compare the cardiac-related events with the total amount of air that escaped the air-removal procedures. However, this was not feasible because quantitative analysis of air was not available.

Despite a few bubbles in the LA and left ventricle, transesophageal echocardiography clearly revealed the pooled air in the RUPV. Neither lung inflation nor bed tilting was adequate to remove all the air from the RUPV. Aspiration with a fine needle was of limited use. Air in the RUPV began to move toward the LA after ventricular contraction and pulmonary circulation resumed. However, once the air appeared in the LA, its elimination became difficult because it kept moving. The air moved along the left atrial wall toward the LV apex. Aspiration of air at the LV apex was often inadequate. With LV contraction, air at the apex was suddenly ejected into the sinus of Valsalva and entered the right coronary artery, often followed by conduction disturbances and ST segment elevation. The head-down position places the right coronary sinus at the highest level and potentially can cause air to enter the right coronary artery.

The majority of events resolved soon after an increase in systemic blood pressure with catecholamine support, temporary ventricular pacing, or both. The bubbles appeared to be gradually squeezed out of the myocardium by LV contractions. In a few patients, however, the echo contrast was gross and diffuse and remained so for a longer time, possibly because the air embolus was too large to be washed away or absorbed.

In conclusion, pooled air is linked to several cardiac events including ST segment elevation, conduction disturbances, and RWMAs, although most are transient. Whatever the event, the hemodynamics can become unstable in the early postbypass period. Transesophageal echocardiography appears to be advantageous for monitoring air-eliminating procedures.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Address reprint requests to Dr Orihashi, First Department of Surgery, Hiroshima University School of Medicine, Kasumi 1-2-3, Minami-ku, Hiroshima 734, Japan.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

1. Orihashi K, Matsuura Y, Hamanaka Y, et al. Retained intracardiac air in open heart operations examined by transesophageal echocardiography. Ann Thorac Surg 1993;55:1467–71.
2. Topol EJ, Humphrey LS, Borkon AM, et al. Value of intraoperative left ventricular microbubbles detected by transesophageal two-dimensional echocardiography in predicting neurologic outcome after cardiac operations. Am J Cardiol 1985;56:773–5.[Medline]
3. Oka Y, Moriwaki KM, Hong Y, et al. Detection of air emboli in the left heart by M-mode transesophageal echocardiography following cardiopulmonary bypass. Anesthesiology 1985;63:109–13.[Medline]
4. Oka Y. Intracardiac air. In: Oka Y, Goldiner PL, eds. Transesophageal echocardiography. Philadelphia: Lippincott, 1992:277–90.
5. Johnston WE, Stump DA, DeWitt DS, et al. Significance of gaseous microemboli in the cerebral circulation during cardiopulmonary bypass in dogs. Circulation 1993;88(5 Suppl 2): 319–29.[Free Full Text]
6. Fessatidis T, Prapas S, Hevas A, et al. Prevention of perioperative neurological dysfunction. A six year perspective of cardiac surgery. J Cardiovasc Surg (Torino) 1991;32:570–4.[Medline]

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Kazumasa Orihashi Yuichiro Matsuura Norimasa Mitsui Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Orihashi, K. Articles by Sueshiro, M. Search for Related Content PubMed PubMed Citation Articles by Orihashi, K. Articles by Sueshiro, M.