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NEUROSURGICAL ANESTHESIA

Accurate Placement of the Right Atrial Air Aspiration Catheter: A Descriptive Study and Prospective Trial of Intravascular Electrocardiography

Diplomat of the American Board of Anesthesiology.

Address correspondence and reprint requests to Randall H. E. Kerr, MD, Department of Anesthesiology, Loma Linda University Medical Center, 11234 Anderson St., Loma Linda, CA 92354. Address e-mail to kerr.randall{at}gmail.com.

	Abstract

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Appropriate positioning of the right atrial air aspiration catheter is critical to successful aspiration of air. The intravascular electrocardiography patterns currently used to position the right atrial air aspiration catheter have not been validated by echocardiography. In 10 patients, using simultaneous transesophageal echocardiography and intravascular electrocardiography, we found that the largest monophasic P wave without a biphasic component correlated with the right atrial-superior vena cava junction. Using this pattern, we performed a prospective trial on 10 subjects and demonstrated appropriate positioning in only 8. This preliminary study suggests that intravascular electrocardiography may not yield appropriate positioning in all patients.

	Introduction

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The multiorifice right atrial air aspiration catheter (RAAAC) is for diagnosis and treatment of venous air embolism. In vitro modeling (1) has shown that air aspiration is most effective when the catheter tip is positioned at the right atrial-superior vena cava junction (RA-SVCJx). The catheter is traditionally positioned using intravascular electrocardiography (IVECG). However, IVECG patterns were originally described using radiography or fluoroscopy (2), which delineate only external cardiac structures. Transesophageal echocardiography (TEE) provides accurate positioning by allowing direct visualization of the catheter in relation to the RA-SVCJx (3,4). TEE also permits presurgery screening for intracardiac pathology (5).

Using TEE, several studies have focused on the ability of IVECG to correctly position single-orifice central venous catheters (6,7). We found no study using TEE to validate IVECG-guided placement of a multiorifice RAAAC. Our goal was to first define the IVECG pattern correlating with the TEE-determined RA-SVC Jx then to perform a prospective trial of the IVECG pattern against TEE.

	METHODS

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After IRB approval and written informed consent, 20 adults undergoing general anesthesia for craniotomy, radical neck dissection, or posterior spinal instrumentation were studied. Exclusion criteria included rhythm other than sinus, inability to cannulate antecubital veins, and gastroesophageal pathology. The studies were performed after induction of general anesthesia before skin incision. Baseline comprehensive multiplane TEE images were obtained using a Hewlett Packard® 5500 M2424A (Andover, MA). The midesophageal bicaval view was used in catheter positioning. One echocardiographer with more than 15 yr TEE experience performed all studies. Location of the catheter tip at the RA-SVCJx was documented by 2-dimensional echocardiography and verified by performing an injection of agitated saline contrast. The RA-SVC Jx was defined as the superior edge of the crista terminalis (Fig. 1).

View larger version (93K): [in this window] [in a new window]   Figure 1. Arrow Product AK-0450 with sterile alligator clip attached directly to J-wire in fully engaged position.

The first part of the study was descriptive. In 10 patients (group A), the RAAAC was positioned using TEE with continuous IVECG recording. The morphologic P wave changes were noted as the catheter was advanced toward and then beyond the RA-SVCJx. The IVECG pattern representing the RA-SVCJx determined by TEE was identified.

The second part was a prospective trial of the pattern defined in the first part. In 10 patients (group B), the RAAAC was positioned by IVECG and the catheter depth was marked at the skin. The J-wire was removed. The catheter was subsequently adjusted as necessary under TEE visualization and the distance using both methods was recorded.

All catheters were placed via antecubital veins, using the Arrow International® (Reading, PA) Antecubital Central Venous Catheterization Kit (product AK-04250). This kit contains a single-lumen, multiorifice catheter with a pre-installed 0.89-mm J-shaped spring-wire guide (Fig. 2). The IVECG tracings were generated on a Philips® M1177A (Boeblingen, Germany) monitor using Einthoven's lead II. The right arm and left arm electrodes were in standard locations and the left leg electrode was attached by alligator clip directly to the preinstalled J-wire in its fully engaged position (with "J" protruding from the catheter tip).

View larger version (99K): [in this window] [in a new window]   Figure 2. Catheter positioned at the right atrial-superior vena cava junction. RAAAC, right atrial air aspirations catheter; SVC, superior vena cava.

	RESULTS

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Continuously recorded IVECG in group A demonstrated changing IVECG P wave morphology during insertion. While advancing the RAAAC from the arms, initial IVECG morphology was small amplitude P, QRS, and T waves. As the catheter was advanced the P wave became larger, gradually becoming very large and negative, often of equal or greater amplitude as the QRS. As the RAAAC was advanced beyond the TEE-identified RA-SVCJx, the P wave gradually became biphasic, equally biphasic, and, finally, positive in most patients. In several patients, the location at which an equally biphasic P wave was obtained was beyond the right atrium as far as the inferior vena cava or hepatic vein, and a positive P wave was not obtained. The IVECG P wave morphology that correlated with the RA-SVCJx identified by TEE was the largest monophasic negative P wave without any biphasic component (Fig. 3). In the upper strip, the P wave amplitude varies with respiration. In the lower strip there is a small initial positive deflection that is intermittently present with ventilation.

View larger version (33K): [in this window] [in a new window]   Figure 3. Two examples of the intravascular electrocardiogram tracing obtained at the right atrial-superior vena cava junction.

Correct positioning was defined as within 1 cm of RA-SVC Jx as described by Chu et al. (6). In group B, IVECG yielded correct positioning in 8 of 10 subjects (Table 1, Fig. 4). There was no significant difference in right arm versus left arm placements.

View larger version (33K): [in this window] [in a new window]   Figure 4. Scatterplot of intravascular electrocardiography (IVECG) placements relative to the right atrial-superior vena cava junction (RA-SVC Jx). RA, right atrium; SVC, superior vena cava.

The RA-SVCJx was identified by TEE in all 20 patients. Location of the RAAAC tip at the RA-SVCJx was facilitated by the echogenicity of the RAAAC (Fig. 1) and verified by injection of agitated saline contrast in all patients. We were able to obtain all images of complete comprehensive intraoperative TEE studies in 18 subjects. Table 2 lists the findings from the preoperative TEE examinations.

	DISCUSSION

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Our study revealed the same pattern described by Chu et al. (6), who used single-orifice port-a-catheters and transduced by flushing the catheter with sodium bicarbonate. This is significant because the source of the intracardiac electrical potentials has been shown to vary between single and multiorifice catheters (8). A single-orifice catheter can sense electrical potentials only at the catheter tip, whereas the multiorifice catheter may sense at multiple sites.

We transduced directly on the fully engaged J-wire because it has been shown to produce superior IVECG tracings (9) and is more convenient than flushing the catheter. However, positioning via the J-wire could introduce error because the catheter becomes more pliable when the wire is removed and can follow vascular curves more closely. This may result in cephalad retraction after IVECG positioning. Variation of P wave morphology with ventilation was seen in all subjects. It is likely that positive pressure ventilation alters the anatomic relationship between the right atrium and the RAAAC, which is relatively fixed at the antecubital fossa, which could lead to alterations in P wave morphology. Despite these limitations, IVECG provided accurate placement in most patients.

Although TEE has not been validated for positioning the RAAAC, we assume that it is more accurate than radiographic methods because internal landmarks are visualized by TEE as opposed to radiographic images of external cardiac structures, including the pericardium and any pericardial fat. According to the in vitro model of Bunegin et al. (1), the RAAAC should be most effective for air aspiration when placed at the RA-SVC junction. We believe 2-dimensional echocardiographic visualization of the RAAAC allows very accurate localization of the catheter tip at nearly any point between the SVC and the IVC. A trial that involved direct anatomic visualization via atriotomy on cardiopulmonary bypass or autopsy could be used to validate TEE for this use. Schummer et al. (10) have done this in a canine model but not with TEE.

Despite the small size, the study did detect outliers from our defined goal of ±1 cm from the RA-SVCJx. IVECG was unable to correctly position the RAAAC in 2 of 10 subjects. In both of these cases, the IVECG tracing was atypical as the catheter was advanced toward the heart and the pattern defined in the first part of the study was difficult to obtain. We think this could have been the result of variations in either the gross anatomy or the electrical anatomy of the heart. Schummer's group (10,11) has proposed that tissue structures surrounding the lower SVC, such as the atrium and pericardium, help generate IVECG waveforms. Indeed, in one of the outliers (subject 19), TEE examination revealed marked right atrial appendage enlargement that extended cephalad around the SVC.

Variations in electrical anatomy could also lead to inaccurate catheter positioning. The atrial pacemaker complex has been shown to be widely spread throughout the atrium. The pacemaker is usually in a band 1.5 cm wide by 7.5 cm long along the RA-SVCJx but can also be found in extreme inferior and anterosuperior locations (12). We retrospectively reviewed preoperative surface 12-lead ECGs and found the other outlier (subject 13) to have an abnormal P wave axis (deviated to the right). The pattern described did place the catheter within 22 mm of the RA-SVCJx in this small group, which may be acceptable positioning in many clinical settings.

Our baseline TEE studies revealed previously undiagnosed findings in many subjects. These may be significant as new findings of a patent foramen ovale (22%), decreased left ventricular function (6%), or pulmonary hypertension (6%) may alter intraoperative management of patients undergoing major surgical procedures including those with a greater risk of air embolism. Several authors have proposed routine preoperative echocardiography in all patients undergoing procedures at high risk for air embolism (5,13–15).

Our small study showed that the largest monophasic negative P wave without a biphasic component is the J-wire IVECG pattern that correlates with the TEE-determined RA-SVC Jx when placing the multiorifice RAAAC. However, conditions such as atrial enlargement or variations in atrial electrophysiology could lead to inaccurate placement. For patients undergoing procedures with high risk for venous air embolism, the IVECG pattern described will allow positioning of the RAAAC tip fairly close to the RA-SVC junction. If greater certainty were needed, then TEE would likely be superior to IVECG. Furthermore, TEE may detect previously undiagnosed significant intracardiac pathology.

	Footnotes

 
Accepted for publication April 4, 2006.

Supported, in part, by the Department of Anesthesiology, Loma Linda University Medical Center.

	REFERENCES

Top Abstract Introduction METHODS RESULTS DISCUSSION REFERENCES

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Kerr, R. H. E. Articles by Applegate, R. L. Search for Related Content PubMed PubMed Citation Articles by Kerr, R. H. E. Articles by Applegate, R. L., II Related Collections Neuroanesthesia Monitoring (Non-cardiac)