Agitated Saline Bubble-Enhanced Ultrasound for Assessing Appropriate Position of Hemodialysis Central Venous Catheter in Critically Ill Patients.

To the Editor:

Renal replacement therapy is recommended to be initiated immediately in patients with life-threatening acute kidney injury (AKI)−related symptoms. Ultrasound-guided insertion of hemodialysis catheter is recommended for vascular access.1, 2, 3 Agitated saline bubble−enhanced ultrasound is efficient and rapid to ensure the correct positioning of central venous cateter in critically ill patients. Delayed appearance of microbubbles in the right atrium indicates inadequate positioning. A recent retrospective study performed in 202 patients admitted in a dialysis center and undergoing internal jugular catheterization for hemodialysis or medication administration reported that 2 catheter malpositions were detected immediately by agitated saline bubble−enhanced ultrasound.

The primary aim of this prospective study, which was performed in ventilated, critically ill patients with AKI, was to compare agitated saline bubble−enhanced ultrasound with bedside chest radiography for the confirmation of appropriate positioning of hemodialysis catheter. The secondary aim was to compare agitated saline bubble−enhanced ultrasound and bedside chest radiography completion times.

Results

As shown in Figure 1, a total of 99 patients were screened, and 91 were included. Clinical characteristics are shown in Table 1. Vascular accesses were jugular (28 right and 4 left) and subclavian veins (45 right and 14 left). Previous venous cannulation before patients’ intensive care unit (ICU) admission, obesity, and proximity of infected abdominal and/or vascular incisions made femoral access impracticable.

Figure 1

Study flow chart.

Table 1

Patient characteristics

Characteristics	All patients, n = 91	Jugular vein, n = 32	Subclavian vein, n = 59	P
Physiological characteristics
Sex male/female (%)	57/43	63/37	54/46	0.44
Age, yr, mean ± SD	59 ± 13	60 ± 13	58 ± 12	0.45
Body mass index, kg/cm	25 ± 4	25 ± 4	25 ± 4	0.91
SOFA score mean ± SD	11 ± 2	11 ± 2	11 ± 3	0.4
APACHE II mean ± SD	21 ± 6	21 ± 6	19 ± 5	0232
Charlson Comorbidity Index (mean ± SD)	3.7 ± 1.3	3.6 ± 1.3	3.8 ± 1.3	0.55
Outcome dead/alive (%)	15/85	15/85	14/86	0.78
Support of organ failure
Invasive mechanical ventilation (%)	85	71	83	0.5
Vasopressor support with norepinephrine (%)	82	75	69	0.28
Admission for medical/surgical disease (%)	62/38	65/35	59/41	0.55
Length of ICU stay (d, mean ± SD)	12 ± 3	11 ± 3	6 ± 3	0.6
Cause of acute kidney injury
Ischemia (%)	12	19	9	0.14
Nephrotoxicity (%)	11	9	12	0.7
Sepsis (%)	32	41	27	0.18
Multifactorial (%)	45	31	52	0.05
Renal replacement characteristics
Urea level (mmol/l, mean ± SD)	174 ± 13	174 ± 1.1	174 ± 1.9	0.8
Sustained low-efficiency dialysis (%)	43	31	69	0.44
Conventional intermittent hemodialysis (%)	24	45	55	0.24
Continuous venous hemodiafiltration	33	40	60	0.49
Maximal dialysis blood flow (ml/min mean ± SD)	228 ± 18	227 ± 19	228 ± 18	0.92
Insertion catheter attempts	1.5 (0.7)	1.5 (0.82)	1.5 (0.71)	0.89

APACHE, Acute Physiology and Chronic Health Evaluation; ICU, intensive care unit; SOFA, Sequential Organ Failure Assessment.

Among 84 hemodialysis catheters adequately positioned, 82 were identified by agitated saline bubble−enhanced ultrasound (Figures 2 and 3). All malpositioned hemodialysis catheters were identified by agitated saline bubble−enhanced ultrasound (Figures 4 and 5). The malpositions involved 5 ipsilateral internal jugular veins, 1 axillary vein, and 1 innominate vein. Two hemodialysis catheters adequately positioned were not identified by bubble-enhanced ultrasound. In the first patient, a partial vena cava thrombosis was suspected to interfere with microbubble appearance. In the second patient, a pulmonary artery catheter and a central venous catheter were already present in the superior vena cava, and likely partially obstructed the holes of the hemodialysis catheter.

Figure 2

(a) Bedside chest radiograph showing the adequate positioning of the hemodialysis catheter in the superior vena cava (black arrow) after insertion in the left internal jugular vein. (b) Ultrasound subxiphoid view showing right atrium (RA) and ventricle (RV) before the administration of microbubbles through the distal lumen of the catheter. (c) Ultrasound subxiphoid view showing the irruption of microbubbles in the RA and RV 1.5 seconds after their flush through the distal lumen of the catheter. Dynamic views can be visualized in Figure 3.

Figure 3

Ultrasound showing irruption of microbubbles in the right atrium and ventricle 1.5 seconds after the injection of saline air mixture (red arrow), attesting to the appropriate position of the hemodialysis catheter (black arrow on frontal chest x-ray).

Figure 4

(a) Bedside chest radiograph showing the inadequate positioning of the hemodialysis catheter in the ipsilateral right internal jugular vein after catheter insertion in the right subclavian vein (black arrow). (b) Ultrasound subxiphoid view showing right atrium (RA) and ventricle (RV) before the administration of microbubbles through the distal lumen of the catheter. (c) Ultrasound subxiphoid view showing the absence of microbubbles in RA and RV 4 seconds after their flush through the distal lumen of the catheter. Dynamic views can be visualized in Figure 5.

Figure 5

Ultrasound showing no irruption of microbubbles in the right atrium (RA) and ventricle (RV) after the injection of saline air mixture (red arrow), attesting to the innappropriate position of the hemodialysis catheter in the right internal jugular vein (white arrow on frontal chest x-ray).

A single intra-atrial position of the hemodialysis catheter was recognized by agitated saline bubble−enhanced ultrasound (Figures 6 and 7). A single pneumothorax was detected by lung ultrasound and confirmed by chest radiograhy. Agitated saline bubble−enhanced ultrasound had a high sensitivity, specificity, and diagnostic accuracy (Table 2), with a κ coeffcient of 0.84.

Figure 6

(a) Bedside chest radiography showing the inadequate positioning of the hemodialysis catheter in the right atrium (black arrow) after catheter insertion in the right internal jugular vein. (b) Ultrasound subxiphoid view showing right atrium (RA) and ventricle (RV) before the administration of microbubbles through the distal lumen of the catheter. (c) Ultrasound subxiphoid view showing the absence of microbubbles in RA and RV 4 seconds after their flush through the distal lumen of the catheter. Dynamic views can be visualized in Figure 7.

Figure 7

Ultrasound showing the presence of microbubbles immediately after the injection of saline air mixture, attesting to the intra-atrial position of the hemodialysis catheter (black arrow on frontal chest x-ray).

Table 2

Concordance between agitated saline bubble−enhanced ultrasound and chest radiography for identifying appropriate hemodialysis catheter tip positioning

		Chest x-ray+	Chest x-ray−
Agitated saline bubble−enhanced ultrasound+		82	0
Agitated saline bubble−enhanced ultrasound−		2	7
Sensitivitya = 98%	Specificityb = 100%	Diagnostic accuracyc = 98%

True positive result denotes correct placement of hemodialysis catheter according to bubble-enhanced ultrasound and chest radiography. True negative result = incorrect placement of hemodialysis catheter according to bubble-enhanced ultrasound and chest radiography. False positive result = correct placement of hemodialysis catheter according to bubble-enhanced ultrasound not confirmed by chest radiography. False negative result = incorrect placement of hemodialysis catheter according to bubble-enhanced ultrasound not confirmed by chest radiography.

Sensitivity = (true positive/[true positive + false negative]).

Specificity = (true negative/[true negative + false positive]).

Diagnostic accuracy = ([true positive + true negative]/[true positive + true negative + false positive + false negative).

The average time to confirmation of appropriate hemodialysis catheter placement was 10.5 minutes (95% confidence interval = 9.7–11.3 minutes) by bedside agitated saline bubble−enhanced ultrasound and 133.5 minutes (95% confidence interval = 124.1–142.8 minutes) by bedside chest radiography (P < 0.0001).

Discussion

In this prospective study performed in critically ill patients with AKI, agitated saline bubble−enhanced ultrasound was highly accurate in identifying adequate placement of hemodialysis cateter. It was significantly faster than bedside chest radiography.

The use of ultrasound guidance for the placement of central venous catheters in critically ill patients is recommended.2, 3, 6, 7 This recommendation applies to critically patients requiring placement of a hemodialysis catheter for grade 3 AKI. Given the presence of a sonographer during catheter insertion, it is logical to use ultrasound for assessing adequate positioning at the end of the procedure. There are 2 contrast-enhanced ultrasound methods for assessing correct positioning of central venous catheters. The first is based on the rapid flush of saline through the catheter. Correct positioning is detected as an immediate (≤2-second) echogenic turbulent flow pattern within the right atrium. Color Doppler imaging improves flow turbulence detection. Three prospective studies reported a sensitivity of 75% and a specificity of 100% for assessing inappropriate catheter positioning compared to bedside chest radiography.10, 11, 12 The second method, based on the rapid flush of a saline−air mixture through the inserted catheter, is more sensitive.4, 5 Correct catheter positioning is detected as the appearance within 2 seconds of multiple micobubbles in the right atrium. Incorrect positioning is detected as the lack of or delayed appearance of these microbubbles. The present study confirms the high sensitivity (99%) and specificity (100%) of the technique for assessing appropriate hemodialysis catheter placement.

In addition to easy implementation, agitated saline bubble−enhanced ultrasound avoids radiation exposure for patients and health care workers, and reduces time delay to catheter use. Adequate positioning is required to obtain an appropriate blood flow allowing efficient dialysis. In our study, the blood flow rate was considered adequate in every patient (>200 ml/min) after repositioning the 7 malpositioned catheters. Transthoracic lung ultrasound can also accurately detect pneumothorax complicating hemodialysis catheter insertion, questioning the use of routine postprocedure bedside chest radiography.

Our study has several limitations. First, it is an observational single-center study. Second, only hemodialysis catheter positioned in the right atrium could be directly visualized using the subxiphoid 4-chamber view. In fact, the majority of malpositioned catheters are located in the contralateral subclavian vein and/or ipsilateral internal jugular vein. The internal jugular vein can be visualized by ultrasound using short- and long-axis neck planes, whereas the subclavian vein can be visualized using short- and long-axis supra- and infraclavicular approaches.3, 14 Therefore, if, at the end of the procedure, agitated saline bubble−enhanced ultrasound results are negative without evidence of intra-atrial positioning of the catheter tip, then ultrasound examination of subclavian and internal jugular veins that were not punctured should be performed to detect the presence of the catheter.

In conclusion, the dynamic ultrasound visualization of microbubbles in the right atrium was highly accurate to identify adequate placement of hemodialysis central venous catheters and significantly faster than bedside chest radiography. It allowed the immediate start of renal replacement therapy, thereby expediting patient care.

Disclosure

All the authors declared no competing interests.