ResUS Pearl: IVC Ultrasound & Volume Assessment

                 

Background:
Determining when to give intravascular volume to hypotensive patients is an imperfect science. Commonly used methods to assess volume status include urine output, passive leg raise, arterial pulse pressure variation, jugular venous pressure, fluid challenge as well as IVC collapsibility.  US-guided assessment of the IVC is an attractive option because it is rapid, reproducible, noninvasive and does not require specialized monitoring equipment. Of note, studies have varying results about the accuracy of IVC ultrasound to predict fluid responsiveness.

Key Physiology:
The IVC serves as a high-capacity intravascular reservoir for the circulatory system.
In spontaneous ventilation the ambient pressure in the thoracic cavity is slightly negative, becoming more negative during inspiration.  With inspiration blood is driven from the IVC into the right heart, which reduces IVC volume and can result in collapse.With positive pressure mechanical ventilation the ambient pressure is positive (i.e., PEEP) and becomes more positive during inspiration. During expiration this pressure is reduced and the IVC can collapse.
The theory behind IVC ultrasound is that if the IVC collapses more or if its baseline diameter is smaller, this represents lower intravascular volume and may predict volume responsiveness. There are several conditions that will enlarge the IVC diameter, confounding such measurements, including:

Cardiac: tamponade, right heart failure
Pulmonary: tension pneumothorax, pulmonary embolism, pulmonary hypertension, status asthmaticus

The bottom line:
Despite the sweet sweet physiology behind IVC ultrasound, the myriad studies don’t give us reason to rely on it to titrate resuscitation of our hypotensive patients, although the data is promising at the extremes of the IVC diameter. LifeInTheFastLane has a great summary.

A very collapsible or very small IVC is likely fluid responsive
Spontaneously breathing patients: IVC diameter <0.9cm
Ventilated patients: IVC diameter <1.2 cm or 18%+ collapse

A very large or non-collapsible IVC isn’t fluid responsive
Ventilated patients: IVC diameter >2.5cm

References

Submitted by: K Tiemeier, MD

ResUS in the Literature: Echo Integrated ACLS

Journal:  Chinese Journal of Traumatology

Title: Echocardiography integrated ACLS protocol versus conventional cardiopulmonary resuscitation in patients with pulseless electrical activity cardiac arrest.

Authors: Chardoli M, Heidari F, Rabiee H, Sharif-Alhoseini M, Shokoohi H, Rahimi-Movaghar V.

Date: 2012

Design: Prospective interventional study, patients presenting with PEA arrest were randomized into two groups.

• Group A, trained emergency physicians performed echocardiography.
• Group B underwent ACLS protocol without echocardiography

Measures: Evaluated cardiac activity, right ventricle dilation, left ventricle function, pericardial effusion/tamponade and IVC size. The presence or absence of mechanical ventricular activity (MVA) and evidence of PEA reversible causes were recorded. The return of spontaneous circulation (ROSC) and death were evaluated in both groups.

Results:

100 patients enrolled (50 in Group A, 50 in Group B)

The resuscitation outcomes for PEA arrest patients with/without cardiac activity on ResUS are described in Table 1

Importantly: The presence of  ventricular activity had 43% positive predictive value for ROSC. The absence of ventricular activity had 100% positive predictive value for death

The authors noted:
"ROSC was recorded in 17 (34%) and 14 (28%) patients in Groups A and B, respectively. However, resuscitation results did not indicate any significant difference between the two groups (P=0.52, power=0.06)"

Commentary: 

The only randomized trial of ResUS cited by AHA 2015 guidelines in support of ResUS during CPR.  ResUS "may be considered during the management of cardiac arrest, although its usefulness has not been well established (Class IIb, LOE C-EO)".

• This study demonstrates no survival benefit in patients receiving ResUS. 
• A qualified sonographer needs to be present 
• ResUS should not interfere with the standard treatment.
• No cardiac activity = death

Small number of cases, single center, More (large scale) studies are needed!

Posted by: A Adedipe, MD

ResUS Pearl: Confirmation of ETT Placement

POCUS can be used as an adjunct method for verification of proper endotracheal tube (ETT) placement, and can be used in real-time during or immediately following laryngoscopy.

Advantages

Helpful for emergency intubations where ETCO₂ has a higher error rate:

• Cardiac Arrest 
• Status Asthmaticus
• Pulmonary Edema
• Pulmonary Embolism 

Additionally, unlike ETCO₂ detectors, ultrasound can help confirm appropriate ETT depth.

Technique
Place a high frequency linear probe in the transverse position just cephalad to the suprasternal notch.

US Findings

Several different confirmatory findings have been described to determine ETT location, primarily relying on the exclusion of esophageal intubation. To date, there is no sonographic finding that is widely accepted amongst investigators.

References

American College of Emergency Physicians Board of Directors. Verification of Endotracheal Tube Placement. policy statement. Revised April 2009.

Favot, M. Ultrasound for Verification of Endotracheal Tube Location. Academic Life in Emergency Medicine.  March 2015.

Submitted by: A Hughes, MD