CLINICAL STUDY | Carotid Ultrasound in Assessing Fluid Responsiveness in Patients with Hypotension and Suspected Sepsis

INTRODUCTION

Fluid resuscitation in sepsis and septic shock is the mainstay of treatment to restore intravascular volume, increase oxygen delivery, and reverse hypoperfusion and organ dysfunction. Since over-and under-resuscitation are associated with adverse outcome, it is important to identify those patients who would benefit from additional fluid administration after initial intravenous fluid (IVF) bolus.

In hypotensive patients, it is challenging to distinguish between patients who will respond to fluid administration, defined by an increased cardiac output, and those who will not. Clinicians have been using ultrasound (US) to assess important parameters in resuscitation of critically ill patients for decades.

US assessment of blood flow through the carotid arteries is a novel tool for real-time assessment of fluid responsiveness. They are easily visualized by US and are a good candidate for a surrogate measure of cardiac output. Corrected carotid flow time (CFTc) is the duration (ms) of systole in a cardiac cycle adjusted for the heart rate. Carotid blood flow (CBF) is the average flow (L/min) of blood through a carotid artery.

The authors hypothesized that absolute measures and dynamic changes in carotid flow parameters (CFTc and CBF) with passive leg raise (PLR) maneuver and administration of an IVF bolus would correlate with fluid responsiveness in hypotensive patients with sepsis, defined as normalization of blood pressure without persistent hypotension or need for vasopressor therapy within the first 12 hours of treatment.

MATERIALS AND METHODS

This was a prospective observational cross-sectional study of patients with hypotension and suspected sepsis admitted to a tertiary academic ED. Patients 18 and older with suspected sepsis and SBP < 10 mmHg were considered for enrollment. Exclusion criteria included age younger than 18 years, pregnant, did not have a regular rhythm on EKG, or were unable to tolerate a PLR maneuver.

Interventions

The initial carotid ultrasound was performed within 6 hours of the patient’s arrival, and as close to ED arrival as possible. The ultrasound was repeated after initial fluid resuscitation of 30 mL/kg IVF bolus, or at the 2-hour mark from the initial US, whichever came first. CFTc and CBF were sequentially measured at two distinct timepoints pre- and post-IVF bolus.

Ultrasound Measurements

For CFTc parameters, systolic time was measured from the beginning of the upstroke of the Doppler signal to the dicrotic notch of each cardiac cycle. Cycle time was measured from the onset of systole from one beat to the next. CFT was then corrected for HR. To improve precision, three cycles were measured, and the mean was used for calculations. CFTc was calculated by the formula CFTc = systolic time/√cycle time, with all times expressed in seconds.

CBF was calculated based on the maximum transverse diameter of the carotid artery at the level of the thyroid. The cross-sectional area of the vessel was calculated using the transverse maximal diameter in systole below the carotid bulb at the upper level of the thyroid or 3 cm blow the carotid bulb if no thyroid was visualized. Pulsed wave Doppler was used in a long-axis view of the vessel at the same location as the diameter measurement. The angle of insonation was standardized at 60°. CBF was calculated based on the maximum transverse diameter of the carotid artery at the level of the thyroid and an automatic Pulsed wave Doppler tracing of the time average mean velocity (TAMEAN) of a minimum of 3 cycles CBF was calculated using the formula: CBF (mL/min) = Area (cm2) x TAMEAN (cm/s) x 60 (sec/min).

Outcome Measures

The primary outcome was clinical fluid responsiveness, defined as normalization of blood pressure without episodes of SBP<90 within 12 hours after IVF resuscitation and without administration of vasopressors within 12 hours of ED arrival. The secondary outcome was sonographic fluid responsiveness, defined as the delta change in the CFTc and CBF before and after PLR, and before and after IVF. Tertiary clinical outcomes included in-hospital mortality, and the need for admission to the ICU.

RESULTS

Sixty-nine patients had complete datasets available and were included in the final analysis. Demographic information and baseline vital signs were similar between the two groups.

36 (52%) of the 69 enrolled patients were fluid responders and 48% were fluid non-responders, meaning they had persistent hypotension or required vasopressors after the prescribed fluid bolus. The clinical non-responder group received a larger volume of IVF prior to enrollment (993 mL vs. 333 mL, p=.003). The non-responder group also had a higher rate of need for vasopressors at 2 hours (28% vs 0%, p= 0.001) and ICU admission (33% vs. 6%, p=0.005).

CONCLUSIONS

The authors concluded that among patients presenting to the ED with suspected sepsis, CFTc and CBF as measured by carotid ultrasound did not predict fluid responsiveness, in-hospital mortality, or need for ICU admission.