Bubble Time to diagnose Right Ventricular Failure

Oct 24, 2024

Right Ventricular(RV) failure presents a significant challenge in the emergency department. It can affect our resuscitative efforts. The only way to diagnose it is with echocardiography. That may not be an option in many emergency departments and POCUS skills may not be adequate to give us the necessary information we need.

This study proposed "a novel method of identifying RV dysfunction using RV “bubble time,” which is the duration of time bubbles from a saline solution flush are visualized in the RV on POCUS echocardiography."

"We hypothesize that it is possible to identify a cutoff value for RV bubble time that has high sensitivity and specificity in identifying patients with and without RV dysfunction, compared with comprehensive echocardiography."

What They Did

This was a prospective diagnostic cohort study(1) of a convenience sample, where patients were included by emergency ultrasound fellowship-trained faculty members and advanced emergency medicine ultrasound fell...

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What They Did

Patients were eligible if:

18 years or older,
had an 18G or 20G intravenous catheter in place within 2 cm of the antecubital fossa and
had comprehensive echocardiography ordered by the emergency physician.

Patients were excluded if:

they had a pacemaker or defibrillator in place,
were pregnant,
a prisoner,
were unable to provide informed consent
they had evidence of shock
they had an initial ECG with ST elevations

The sonographer was blinded to the clinical information and performed the POCUS prior to the patient receiving the comprehensive echocardiogram. The treating clinicians were blinded to the POCUS results.

The patient was placed in a supine position. A phased array transducer with cardiac presettings was used with an initial parasternal long view axis echocardiographic view. This was followed by a subxiphoid view and the view providing optimal visualization of the RV was used for the study.

Once the view was established, a member of the study team would vigorously shake a 10-mL saline solution flush for 5 seconds, then rapidly administer the 10-mL saline solution flush within 5 seconds into the patient’s intravenous catheter.

Ultrasound clips were taken for the entire duration of the study and 18 seconds post the saline solution no longer being seen in the right ventricle. The times measured were, time from the saline solution being pushed into the catheter, the time the bubbles from the saline solution flush were first seen within the RV, and the time the saline solution bubbles were no longer seen within the RV.

The bubble time was the total duration of time from the appearance of saline solution bubbles in the RV to the disappearance of bubbles from the RV.

RV enlargement was assessed. The RV was considered enlarged on POCUS if it was greater than or equal to the diameter of the LV on the apical 4-chamber view.

Primary Outcomes: The optimal cutoff value of RV bubble time within the RV that identifies patients with and without RV dysfunction"(RV enlargement or evidence of strain,depressed RV function, low tricuspid annular planar systolic excursion, decreased free wall movement, or evidence of RV free wall longitudinal strain on the comprehensive echocardiogram.)"

What They Found

206 patients were approached, and data from 196 patients were analyzed, where the top 5 indications for echocardiography were:

chest pain (27.0%),
abnormal ECG (15.8%),
dyspnea (15.3%),
heart failure (7.1%), and
syncope/collapse (6.1%).

In the 127 patients without RV dysfunction, the median RV bubble time was 21 seconds (IQR 12 to 32) compared to the 69 patients patients with RV dysfunction , which was 62 seconds (IQR 52 to 93).

Limitations of this Study

The sample size was small.
There is a possibility of selection bias due to a convenience sample being used.
There was no blinding of sonographers to the patient’s appearance, which could also introduce biasin terms of bubble time estimation.
All the POCUS studies were performed by ultrasound fellowship-trained physicians, which may not extend to all emergency physicians,
This study had a large number of patients with RV impairment.
The bubble time of 40 seconds or more is associated with RV dysfunction on either view however, the bubble time between subxiphoid and parasternal long views were not directly compared.
Haemodynamically unstable patients were not included in this study.
All IV cannulas were placed within 2 cm of the cubital fossa.

My Take on This

This study showed that a "RV bubble time of 40 seconds or longer had a high sensitivity of 0.97 in identifying patients with RV dysfunction and a high specificity of 0.87 in identifying patients without RV dysfunction...."

I'm not sure how this will change practice. Just looking at the possibility of being able to predict RV failure, is a crucial part of our patient management approach. Our current approach of giving small volumes of fluid and assessing response along with perfoming ultrasound to look for a 'D' Sign, or RV bulge into the Left Ventricle, is a little hit and miss. I'm excited about the potential to perform a simple test such as injecting agitated saline into a cubital fossa vein.

It's application to haemodynamically unstable patients is uncertain, as they were not included in this study. Could injecting patients when they come in unstable and then comparing the improvement or otherwise with pressors or fluids may be helpful. Right now, without the study in unstable patients, it becomes conjecture.