Corrected Carotid Artery Flow Time and Volume Responsiveness
The Article: Carotid Flow Time Changes With Volume Status in Acute Blood Loss. David C. Mackenzie, MD et al. American College of Emergency Physicians, September 2015, Vol. 66, Issue 3, Pages 277–282.
The Goal: To determine the effect of acute blood loss and the passive leg raise maneuver on corrected carotid artery flow time. Also, to identify if corrected carotid artery flow time is a predictor of volume responsiveness.
The Study: A prospective, observational study using a convenience sample of healthy, adult volunteer whole blood donors aged 18-55 and without history of atrial fibrillation or aortic disease. Pre and post blood donation US fellowship trained Emergency Physicians obtained images and calculated a patient’s corrected carotid artery flow time both supine and following a passive leg raise maneuver. A blinded, US fellowship trained Emergency Physician then also calculated the corrected carotid artery flow time.
Mean supine corrected carotid artery flow times before and after phlebotomy were 320ms (95% CI 315-325ms) and 299ms (95% CI 294-304ms).
Mean increase in corrected carotid artery flow time after passive leg raise before and after phlebotomy were 4ms (95% CI -1 to 9ms) and 23ms (95% CI 18-28).
Using pre-phlebotomy supine position as standard for euvolemia, a corrected carotid artery flow time cutoff of 310ms was 75% sensitive (95% CI 64-84%) and 69% specific (95% CI 58-79%) for identifying hypovolemia.
A change in corrected carotid artery flow time of 5% was 66% sensitive (95% CI 55-77%) and 77% specific (95% CI 67%-87%) for hypovolemia.
Takeaway: Even though the absolute value and changes in corrected carotid artery flow times were found to be poorly sensitive and specific to assess for volume responsiveness, it is a promising avenue for further research. It is important to have a non-invasive, reliable way to assess for volume responsiveness in the ED. It is possible that this technique will be useful in the assessment septic patients, trauma patients with a more severe hypovolemia, or any other number of ED patients.