Month: August 2020

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Can IVC collapsibility predict fluid responsiveness in non-ventilated patients?

ivc ultrasound

Background

Fluid responsiveness is key in guiding the resuscitation of critically ill patients, and both under and over resuscitation can lead to poor clinical outcomes. Vitals and physical exam are not always reliable in determining fluid responsiveness. The search for a quick, easy and accurate diagnostic test to determine fluid responsiveness is ongoing. IVC collapsibility (cIVC) has been proposed as a helpful measure, and in ventilated patients this measurement has been validated. However, spontaneously breathing patients have different physiology, so it is unclear if cIVC is an accurate predictor of fluid responsiveness in this cohort. Previous studies have recommended a cIVC cutoff of 40-42% as a reliable predictor of fluid responsiveness in spontaneously breathing patients (1,2). This study sought to validate those findings. 

 

Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients

Clinical Question

Can the collapsibility of the inferior vena cava differentiate between fluid responders and fluid non-responders in non-ventilated critically ill patients?

Methods & Study Design

• Design 

This was a prospective observational trial.

• Population 

Inclusion: spontaneously breathing patients with signs of acute circulatory failure in the ED and ICU of 2 academic hospitals in the US.

Exclusion: primary traumatic, cardiogenic, obstructive, or neurogenic shock; age < 18 years old; incarceration; pregnancy; and/or hospitalization for >36 h; NIPPV; if the clinical team felt that they had active pulmonary edema; or that believed that further IVFs might pose a clinical risk.

• Intervention 

A NICOM device monitored cardiac index at 1 minute intervals for the duration of the study. Patients had initial cardiac index measurements and IVC videos recorded. Then, after a 3 minute passive leg raise, an additional IVC video was recorded. Lastly, patients received a 500ml normal saline bolus and immediately had a final IVC video recorded. Images were reviewed after the study to determine the cIVC.  

• Outcomes  

The primary outcome was fluid responsiveness, defined as a ≥ 10% increase in cardiac index.

Results

A cIVC of 25% provided maximum sensitivity (87%) and specificity (81%) in identifying fluid responders. However, as you can see in the figure below, there were several patients with cIVC below 25% who were fluid responders, and several patients with cIVC above 25% who were not fluid responders. 

IVC fluid responder
Corl et al.

Strength & Limitations

Strengths: The prospective study design reduces bias and confounding factors. Few studies have examined fluid responsiveness in non-ventilated patients, and this adds to the growing body of evidence in this population. 

Limitations: This study primarily included patients with severe sepsis/septic shock and DKA/HHS. This limits the generalizability of the findings to other forms of acute circulatory failure. Furthermore, fluid responsiveness was measured once immediately following the bolus. Monitoring the patients’ clinical status over several hours or for the duration of the ICU admission may have provided additional, clinically relevant data regarding fluid resuscitation.

Authors Conclusion

“cIVC, as measured by POCUS, is able to detect fluid responsiveness and may be used to guide IVF resuscitation among spontaneously breathing critically-ill patients.”

Our Conclusion

In spontaneously breathing patients with distributive shock, cIVC can be a useful tool in identifying fluid responsiveness, with the caveat that a minority of patients with minimal IVC collapsibility may still be fluid responders and those with significant IVC collapsibility may not be fluid responders. There is certainly a trend toward a collapsible IVC identifying fluid responders, but the outliers in this study should be taken into account. IVC, along with history, exam and bedside echo, can be used to identify which patients may need more IV fluid resuscitation. 

The Bottom Line 

IVC collapsibility >25% predicts fluid responsiveness in spontaneously breathing patients with distributive shock most of the time, but should not be solely relied upon.

Authors

This post was written by Aaser Ali, MS4 at UCSD School of Medicine, Charles Murchison, MD and Amir Aminlari, MD. 

References

  1. Corl KA, George NR, Romanoff J, et al. Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients. J Crit Care. 2017;41:130-137.

  2. Machare-Delgado E, Decaro M, Marik PE. Inferior vena cava variation compared to
    pulse contour analysis as predictors of fluid responsiveness: a prospective cohort
    study. Intensive Care Med 2011;26(2):116–24.

  3. Muller L, Bobbia X, Toumi M, et al. Respiratory variations of inferior vena cava diam-
    eter to predict fluid responsiveness in spontaneously breathing patients with acute
    circulatory failure: need for a cautious use. Crit Care 2012;16(5):R188.

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Case # 22: Abdominal Aortic Aneurysm

abdominal aortic aneurysm

 

A 72 year old male with known abdominal aortic aneurysm (5.7 cm s/p fem-tib bypass, L AKA) presents for 3 weeks with diarrhea and mild LLQ pain. No nausea, vomiting, fever, back pain, urinary symptoms, or blood in stool. He has no localizing abdominal exam & no peritoneal signs, strong even radial pulses, and normal cardiopulmonary exam. On further chart review, patient is noted to have a 5+ cm aorta for the past 2 years, with the most recent CT scan a few weeks ago showing growth from 5.5 cm to 5.7 cm. An abdominal ultrasound is performed with the following findings.

Vitals: 

T 98.7 HR 64 BP 167/80 RR 18 O2 100%

What are we concerned about for this patient and why? What is the interpretation of the abdominal ultrasound? What are the next steps for management in the ED?

 

Courtesy of The Pocus Atlas

Answer and Learning Points

Answer:

The patient’s presenting complaints (diarrhea, mild abdominal pain) do not coincide with the classic triad of ruptured AAA (hypotension, back pain, pulsatile abdominal mass). In addition, this patient is hemodynamically stable and comfortable, which is reassuring. However, ruptured AAA can have a wide variety of presentations and should always be considered in patients with known large AAA. In addition, this patient had a known AAA >5 cm for the past two years with poor vascular surgery follow-up, and the risk for rupture for AAA’s 5.0-5.9cm increases by 5-10% each year. (1)

As this patient recently had a CT scan a few weeks ago revealing large, stable AAA, the decision was made to investigate via ultrasound rather than undergo more radiation from CT. Ultrasound is also highly sensitive and specific for detecting AAA. (2) The above images show the AAA has a large intramural thrombus with no evidence of leaking fluid nor dissection flap. The AAA is stable, measuring a similar width of 5.7 cm. The clinician can investigate further by doing a RUSH exam to reassure against intraperitoneal bleeding and other types of shock. Elective aortic surgery is recommended for patients with AAA >5.5 cm, because at this threshold the risk of rupture is greater than risk of surgery, therefore it is reasonable to consult vascular surgery for this patient in the ED. (1)

 

Learning Points

  • Ruptured AAA being a surgical emergency and nearly uniformly fatal. Risk of rupture is proportional to size of AAA:AAA rupture risk
  • Elective aortic surgery is the most effective management, however, is not recommended until the aneurysm exceeds 5.5 cm diameter. In the ED setting, it is reasonable to consult vascular surgery for an asymptomatic patient with an incidental finding of aneurysm >5.5 cm. (1)
  • A systematic review of seven studies (n=655) evaluated operating characteristics of emergency department ultrasonography for AAA. With AAA defined as >3cm dilation of aorta, the review showed that ultrasound yielded excellent diagnostic performance. (2)

  • An effective abdominal aortic ultrasound requires:

(1) Evaluation of the entire aorta from the subxiphoid area to the iliac branch bifurcation. Most abdominal aortic aneurysms lie in the infrarenal aorta.

(2) Moving bowel gas out of the way with the probe with either graded compression or curvilinear probe with larger footprint

(3) Careful differentiation aorta from IVC. The aorta will be anterior to the vertebrae and the left of the IVC.

(4) Measuring outer to outer wall. Clot can create can second inner wall and falsely decrease aortic width measurement.

References

(1) Abdominal Aortic Aneurysms (AAA) - Cardiovascular Disorders. Merck Manuals Professional Edition. Accessed July 9, 2020. https://www.merckmanuals.com/professional/cardiovascular-disorders/diseases-of-the-aorta-and-its-branches/abdominal-aortic-aneurysms-aaa

(2) Rubano E, Mehta N, Caputo W, Paladino L, Sinert R. Systematic review: emergency department bedside ultrasonography for diagnosing suspected abdominal aortic aneurysm. Acad Emerg Med. 2013;20(2):128-138. doi:10.1111/acem.12080

(3) Michelle H-B. Tips and Tricks: Big Red - The Aorta and How to Improve Your Image. ACEP Emergency Ultrasound. Accessed July 9, 2020. https://www.acep.org/how-we-serve/sections/emergency-ultrasound/news/february-2016/tips-and-tricks-big-red---the-aorta-and-how-to-improve-your-image/

This post was written by Caresse Vuong, MS4, Charles Murchison, MD and Amir Aminlari MD

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