Sufentanil

Study objectives: To evaluate the placement and complications of a coronary sinus (CS) catheter in human subjects.

Design: Sixty-two CS catheters inserted in patients scheduled for coronary artery bypass graft surgery (CABG).

Setting: University hospital, anesthesia and cardiothoracic surgery departments.

Patients: Sixty-two patients without valvular of concomitant diseases undergoing CABG.

Interventions: CS fluoroscopy, measurements of CS flow, CS oxygen saturation, and CS distal tip pressure before incision, after incision, 20 min after aortic cross-clamp release (X-oft), 50 min after X-off, 2 h after X-off, 4 h after X-off, and 6 h after X-off.

Results: In 57 patients (92%), we achieved successful CS catheter placement. In five patients (8%), CS catheter positioning was not possible. Of the 57 CS catheters placed, dislocation occurred during the operation in six patients (11%) and postoperatively in three patients (6%). Cardiac complications of CS catheter placement occurred in nine patients (15%). Four patients (6%) acquired hemopericardium. Three of these patients had a small hematoma in the right ventriele. In two other patients, contrast medium appeared in the right ventricular wall during catheterization. No hemodynamic signs of these complications were detected clinically. Irregular heart rhythm was observed in only three patients. CS blood oxygen saturation ranged from 40 to 60%. CS flow amounted to 3% of cardiac output. Variations in CS flow paralleled changes in cardiac output.

Conclusions: A CS catheter is a useful tool for clinical human cardiac research; however, the placement of a CS catheter can cause minor myocardial damage in > 10% of patients. Importantly, this damage may not be clinically evident, but only observed after thoracotomy. CS oxygen saturation, CS flow, distal tip pressure, and fluorosecopy are reliable tools to assess a safe and correct positioning of the CS catheter.

Key words: coronary artery bypass graft surgery; coronary sinus catheterization; coronary sinus flow: myocardial damage

Abbreviations: CABG = coronary artery bypass graft surgery; CS = coronary sinus; CVP = central venous pressure; ECC = extracorporeal circulation; Finj = flow rate of injection; Tb = blood temperature; Ti = temperature of the infused saline solution; Tm = temperature of the saline solution and blood mixture: X-off = aortic cross-clamp release

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The coronary sinus (CS) drains 95% of the venous blood of the myocardial muscle into the right atrium, while the remaining 5% of myocardial venous flow drains through the thebesian vessels. (1,2) In 1971, Ganz et al (3) described a thermodilution technique to measure total CS blood flow. In human metabolic studies of the heart, it is necessary to obtain myocardial venous blood samples, which is only possible via cannulation of the CS. Substrate concentrations in arterial and CS blood, in combination with the measured CS flow, yield information about the myocardial use of substrates and oxygen.(4) The measured CS temperature during cardiac surgery provides another monitoring tool for determination of hypothermic protection in combination with cardioplegic solutions. The flow in the CS correlates with cardiac output, mean arterial pressure, and the flow through the coronary arteries, and varies with the myocardial requirement for oxygen (5,6); therefore, the technique of CS cannulation is useful, and at times essential, in studies of the cardiovascular system in humans.

Information about this technique is important, because the coronary venous system is increasingly used for left ventricular or biventricular pacing in patients with severe heart failure, (7) and for ablating posteroseptal accessory neural pathways by means of a venous approach and radiofrequency energy. (8) According to the literature to date, most complications occur during insertion of the CS catheter via the internal jugular vein. (9) They include placement in a false route, accidental arterial puncture, and perforation of the upper lung. (10) During insertion of the catheter into the heart, dysrrhythmias and perforation of the atrium and/or right ventricle are possible, which may result in a cardiac tamponade (11) and pericardial effusion. (8) Little is known about the incidence of these cardiac complications, since they may be clinically silent.

Measurements of CS flow may be influenced by catheter position (12); therefore, verification of correct placement is essential. A number of criteria (CS oxygen saturation, CS flow, distal tip pressure, and fluoroscopy) have been suggested, but not verified, as indicators of adequate placement. Criteria for correct placement of the catheter are important, as they will improve the safety of the procedure and the quality (accuracy and reproducibility) of the metabolic data.

Both the incidence of cardiac complications and the verification of placement can only be assessed by thoracotomy; therefore, we studied these issues in patients undergoing thoracotomy for coronary artery bypass graft surgery (CABG). Our findings indicate that small cardiac complications may be more common than believed, and that placement accuracy can be achieved by using the suggested criteria.

MATERIALS AND METHODS

The study was performed as a part of a metabolic study for which written informed consent of the patients and approval by the local Human Investigation Committee were obtained. Sixty-two patients with two-vessel or three-vessel coronary artery disease documented by coronary arteriography (New York Heart Association class III-IV), scheduled for CABG with the use of extracorporeal circulation (ECC), were included. All patients had a left ventricular ejection fraction > 50%. Cardiac medications, including [beta]-blockers, calcium entry blockers, nitrates, and anti-hypertensive agents, were continued and administered on the morning of the operation. The patients were premedicated with 0.03 to 0.06 mg/kg lorazepam 30 min prior to transportation to the operating theater.

After induction of anesthesia with midazolam (60 to 80 g[micro]/kg), sufentanil (1 to 1.5 g[micro]/kg), etomidate (0.2 to 0.3 mg/kg), and pancuronium bromide (0.1 mg/kg), (13) two 7F Arrow introducers (AK-09701-A; Arrow International; Reading, PA) were inserted in the right internal jugular vein, punctured at the level of the cricoid just lateral of the right carotid artery. A pulmonary artery catheter (Baxter; Irvin, CA) was inserted through the first introducer. The bend of this catheter through the heart, visualized by radiograph examination, was used as a marker to position the CS catheter. The CS catheter (Baim CS Flow Thermal Dilution Catheter; Elecath; Rahway, NJ) was inserted through the second introducer, positioned cephalad of the first introducer, under continuous pressure measurement at the distal tip, and with interval radiographic examination. Using anteroposterior fluoroscopy (Fig 1), the CS catheter was manipulated so that its position was horizontal and slightly cranial from the position of the pulmonary artery catheter, with the tip pointing toward the left shoulder. Simultaneously, distal tip pressures were recorded. If the distal tip pressure of the CS catheter increased > l0 mm Hg above central venous pressure (CVP). and no ventricular pressure curve could be distinguished, the catheter was assumed to have impacted on the trabecular ventricular wall and the catheter was drawn back into the superior vena cava. Increased resistance to insertion of the CS catheter, and distal tip pressures 2 to 3 mm Hg greater than CVP indicated positioning in the CS ostium. Fluoroscopy was then again performed, and the tip was positioned approximately 4 cm into the CS lumen. Administration of contrast medium via the distal and proximal opening of the CS catheter visualized the CS as a tube, with a retrograde bloodstream disappearing along the catheter into the right atrium (Fig 2).

[FIGURES 1-2 OMITTED]

CS oxygen saturation and CS flow were measured. Ganz et al (3) developed a retrograde thermodilution technique for the measurement of CS, which can be used in humans. (4, 14) A catheter with a temperature sensitive thermistor is positioned in the CS, CS flow measurements were performed with a continuous infusion of NaCl (0.9%) at room temperature for a period of 30 s with a constant flow rate of injection (Finj) of 50 mL/min (Mark V infusion pump; Metrad) through the distal lumen of the CS catheter. The saline solution mixes with the blood (which has a higher and known temperature).

The temperature of the saline solution and blood mixture (Tm) depends on blood flow, infusion rate, blood temperature (Tb), the temperature of the infused saline solution (Ti), the Finj, and a constant value (C). This results in the following formula: CS flow = (Tm--Ti/Tb--Tm) X Finj X C (Fig 2).

The use of the CS catheter for blood sampling and flow measurements has several limitations. The CS is a venous sinus collecting blood from many tributaries. This implies that the position of the catheter tip determines the par of the heart that is represented in the measurements. Consequently, a shift in catheter position causes a change in measured flow. The catheter position will therefore hamper the comparison of flow measurements between patients because it is impossible to achieve identical catheter positions in different patients; however, if catheter position remains stable, proportional changes of the flow over time within one patient can be measured accurately. Another source of error consists of the influx of atrial blood into the CS. (15) Influx of atrial blood during the measurement dilutes the saline solution that is infused and causes an overestimation of the CS flow. To prevent such flow measurement errors, the tip of the CS catheter has to be inserted 4 cm into the CS. Data were analyzed with a CS flow analyzer (Baim model 7 L-C2000; Elecath) and Baim CS flow calculator (Elecath).

After thoracotomy, the cardiac surgeon inspected the heart and palpated the CS region and, when possible, inspected the CS. Placement was regarded as successful when fluoroscopy indicated the catheter was in the CS, when the mean CS oxygen saturations were in the range of 40 to 60%, when CS flow was approximately 2 to 3% of the measured cardiac output, and when the distal pressure was slightly greater than CVP. The catheter was considered to be dislocated, during operation and postoperatively, it CS oxygen saturation was similar to mixed venous oxygen saturation, if CS flow could not be measured, or if distal tip pressure was the same as CVP or showed a ventricular pressure curve. Samples were obtained and measurements performed before incision, after incision, 20 min and 50 min after aortic cross-clamp release (X-off), and 2 h, 4 h, and 6 h after X-off (Table 1).

ECC was performed at a flow of 2.4 L/[m.sub.2] body surface area, while maintaining a mean BP between 60 mm Hg and 80 mm Hg, Patients were cooled to a Tb of 28 to 30[degrees]C. Statistical analysis was performed by paired Student t test. Values were considered to be significantly different at p < 0.05.

RESULTS

The study group consisted of 62 subjects: 49 men and 13 women. Patient demographics are outlined in Table 2.

Catheter Placement

In 57 patients (92%), catheters were placed correctly; in 5 patients (8%), correct placement in the CS could not be achieved (Table 3). In one patient, early in the study, the catheter was inserted into a liver vein that under fluoroscopy projected on the same place as the CS. In another patient, placement was impossible because the CS was angled too sharply backwards and upwards. During the operation, dislocation occurred in six patients (11%). In three patients (6%), the CS catheter dislocated postoperatively. In 62 attempts of CS catheter placement, 48 attempts (77%) were successful and without any problems in the postoperative period. In all patients with a dislocated catheter, CS oxygen saturations were similar to mixed venous oxygen saturations, and CS flow was not measurable. In two patients, a ventricular pressure curve was observed after CS dislocation.

Myocardial Complications

After thoracotomy and inspection of the myocardium, four patients (6%) showed blood in the pericardium (Table 4). Of these, three patients (5%) showed small bleeding spots in the right ventricular wall. Two patients (3%) showed contrast medium in the right ventricular wall. During catheter placement, three patients (5%) showed an irregular heart rhythm, all without hemodynamic consequences.

CS Parameters

After X-off, cardiac output increased as compared with preoperative values (Table 5). The variations in cardiac output paralleled variations in CS flow (Fig 3). CS flow varied between 2% and 3% of cardiac output (Table 5). The oxygen saturation of CS blood varied between 30% and 60%, and was at every sample point significantly different from mixed venous oxygen saturations. CS pressure was 1- to 2-mm Hg greater than CVP. No hemodynamic changes could be detected during catheter placement. CS resistance was decreased after X-off, and CS flow increased (Fig 4).

[FIGURES 3-4 OMITTED]

DISCUSSION

Placement of a CS catheter can cause minor myocardial damage without evident clinical hemodynamic signs. Dhala et al(8) reported the occurrence of cardiac tamponade in three patients, and a pericardial effusion without hemodynamic consequences in one patient during transcatheter ablation of posteroseptal accessory neural pathways.

In the setting of our study, CABG permitted inspection of the heart and confirmation of the correct placement of the CS catheter. In the absence of thoracotomy, the reported complications would have remained unnoticed. The CABG operation allowed inspection of the heart and confirmation of the correct placement of the CS catheter. The study also demonstrated the reliability of CS flow, distal tip pressure, CS saturation, and fluoroscopy as parameters for judging correct placement.

We chose not to use an approach via the groin, in case it was needed for cannulation for ECC. We also did not approach the CS via the subclavian veins, as the extra curve in the subclavian veins can make manipulation of the catheter more difficult. The cranial approach via the right jugular vein is more direct, and in most patients there is sufficient space for the introduction of two 7F introducers.

Pressure Measurement

CS catheter distal tip pressure measurements could not prevent the occurrence of right ventricular hematoma in three patients. This happened in spite of the fact that if even one of the four parameters used to check the right position of the CS catheter was out of range, we repeated the procedure to correct the positioning. CS catheter placement in a liver vein occurred in one patient early in the study. CS pressure was only slightly greater than CVP and therefore not an appropriate indicator for dislocation or correct position; however, elevated pressures helped to find the right position during insertion.

Fluoroscopy

Insertion of the CS catheter too deep in the CS or great cardiac vein may cause artificially low measurements of CS flow; therefore, we performed fluoroscopy with contrast medium through the proximal opening in the CS catheter at 4 cm of the tip. Fluoroscopy visualized the CS. After injection of contrast medium through the distal tip of the CS, the contrast medium could be seen to disappear along the catheter into the right atrium. Overinsertion also became visible.

Prior placement of the pulmonary artery catheter served as a useful landmark. The cranial curve of the pulmonary artery catheter in the heart as shown by fluoroscopy helped to locate the tricuspid value and the outlet of the CS into the right atrium. When the CS catheter was inserted into the introducer, manipulated horizontally, cranially and parallel to the pulmonary artery catheter, with the curve of the CS catheter pointed in a posterior direction, and with the tip pointing in the direction of the left shoulder, the CS could be cannulated.

CS Flow

CS flow measurements should be in the range of 2 to 3% of cardiac output. If the CS catheter was inserted > 4 to 5 cm into the CS, withdrawal of the CS catheter induced an increase in flow that was at a maximum when the catheter tip was introduced approximately 4 cm in the CS. (12) For this reason, radiograph examination was also performed at the postoperative ICUs to control the correct position again. Bagger (12) stated that due to differences in catheter positioning, CS flows of different patients should not be compared; therefore, we compared within-patient values. We conclude that this ratio may be another indication of correct placement.

Oxygen Saturation

Measuring CS oxygen saturation alone is not a reliable parameter for determining catheter placement, because venous oxygen saturation in other organs such as the liver, if they are in a low range, may approach the upper levels of CS oxygen saturation. CS oxygen saturation is significantly lower than the mixed venous oxygen saturation. When the CS catheter is dislocated, the CS oxygen saturations should equal the mixed venous oxygen saturation, which was indeed the case in all patients in whom dislocation occurred.

The use of a CS catheter is of great value in human cardiac clinical research; however, insertion and use of a CS catheter need careful attention. Fluoroscopy and measurements of CS flow, CS oxygen saturation, and distal tip pressure are necessary to control correct placement, and proved to be adequate. Yet, despite these precautions, minor myocardial damage could not be prevented in approximately 10% of patients. Importantly, these incidences went clinically unnoticed. This could be diminished by using less-stiff catheters that are maneuverable with a wire so that damage may be less.

Verifying the correct position of the CS catheter increases the safety of using this device and improves the reliability and quality of the obtained data. Most complications occurred in the first 10 patients who were studied. As time went on, our confidence in our assessment of correct catheter position grew. As a consequence, fewer episodes of catheter repositioning were necessary. Not unexpectedly, there appears to be a learning curve for achieving correct positioning of a CS catheter.

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Chris J. M. Langenberg, MD; Henk G. Pietersen, MD; Gijs Geskes, MD; Anton J. M. Wagenmakers, MD, PhD; Peter B. Soeters, MD, PhD; and Marcel Durieux, MD, PhD

* From the Department of Anesthesiology (Dr. Langenberg), Jeroen Bosch Ziekenhuis, Hertogenbosch; Departments of Surgery (Drs. Pietersen and Soeters), Thoracic Surgery (Dr. Geskes), and Human Biology (Dr. Wagenmakers), University Hospital Maastricht; and Department of Anesthesiology (Dr. Durieux), University of Maastricht, The Netherlands. Manuscript received April 23, 2002; revision accepted February 27, 2003.

Correspondence to: Chris J. M. Langenberg, MD, Jeroen Bosch Ziekenhuis, Department of Anesthesiology, Postbus 90153, 5200 ME's Hertogenbosch, The Netherlands; e-mail: clan@wish.net

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