Bubble Time – A New, Simple Way to Detect RV Dysfunction

September 27, 2024

Post correction 27 Sept 2024, 0915: Bubble time is the duration from injection to clearance of bubbles from the RV, not first appearance of bubbles in the RV. ~Clay Smith

Written by Jonathan Brewer

Spoon Feed
By agitating and injecting a saline flush into an IV catheter, right ventricular (RV) dysfunction was identified when bubbles were cleared from the RV at a time of ≥ 40 seconds with high sensitivity. It was ruled out as well with good specificity, with a bubble time < 40 seconds.

It’s “bubble time”
This was a prospective cohort study with 196 hemodynamically stable patients in a single quaternary care emergency department in which an advanced emergency medicine ultrasound (AEMUS) fellowship-trained emergency physician or current fellow conducted a point-of-care echo and then injected a 10-mL agitated saline solution flush into the patient’s IV catheter. They then calculated the time it took for the “bubbles” to clear from the RV. After identifying the presence or absence of RV dysfunction based on this time, patients underwent a comprehensive echocardiogram within the next 36 hours that was read by a board-certified cardiologist for confirmation.

Patients with RV dysfunction had a median bubble time of 62 seconds, whereas patients without RV dysfunction had a median bubble time of 21 seconds (p < .0001). After further analysis with a Wilcoxon rank sum test, receiver operator characteristic (ROC) curve analysis determined an optimal cutoff value of RV bubble time of 40 seconds with a sensitivity of 0.97 (95%CI 0.93-1.00) and specificity of 0.87 (95%CI 0.82-0.93). 

While this was very interesting study, there were several limitations that must be noted. The sample size was low, with only 196 patients, and there were no unstable patients included in the study. As hemodynamic instability is common with acute RV dysfunction, it is unclear if this study is applicable to patients with clinical signs of shock. In addition, all ultrasounds were conducted by emergency physicians that were in the process of completing or had fellowship training, which may lead to a lack of generalizability. Finally, all IV (18g and 20g) catheters in this study were placed within 2 cm of the antecubital fossa, which could have an effect on timing.

How will this change my practice?
As an AEMUS faculty myself, I look forward to seeing more data on this, but I do not think that this can be solely utilized to identify RV dysfunction at this time – and the authors also note this as well. More studies will need to occur with a cohort of patients that are not hemodynamically stable and with other non-fellowship-trained emergency physicians to ensure that this is ready for primetime. In the meantime, there are many other ways to assess for RV dysfunction (i.e. tricuspid annular planar systolic excursion) that we can utilize in the interim. However, I’m excited to see if this easy-to-perform technique continues to gain traction.

Editor’s note: Kind of bummed Jonathan doesn’t think this is ready for prime time. I feel like I could probably spot the return and clearance of agitated saline bubbles from the RV, and I know I can use a stopwatch. Even if not the full picture of RV function, I will likely add this technique as part of my rudimentary assessment of RV function at the bedside. ~Clay Smith

Source
Right Ventricular “Bubble Time” to Identify Patients With Right Ventricular Dysfunction. Ann Emerg Med. 2024 Aug;84(2):182-194. doi: 10.1016/j.annemergmed.2024.02.005. Epub 2024 Apr 10. PMID: 38597847.