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Abstract

Introduction: Advancements in critical care have extended the use of point of care ultrasound (POCUS) exponentially in the hands of the experienced Intensivist. Current methods for measuring the cardiac output (CO) in the Intensive Care Unit (ICU) require invasive devices such as the Pulmonary Artery (PA) catheter or the arterial waveform pulse contour analysis (PCA). Each of these methods is an invasive technique with some inherent risks. This study was designed to test the accuracy and feasibility of carotid artery Doppler Flow Volume measurements and compare it to other existing invasive CO measurement modalities. Methods: A prospective observational cohort study conducted in an urban, academic tertiary care center. An IRB approval was obtained for the study. Patients were selected from the surgical or cardiothoracic ICU when invasive monitoring was already initiated via either a PA catheter or PCA. Patients with possible cerebral and carotid pathology were excluded. Physicians performing the Doppler study were experts in POCUS. Patients were placed in the semi-fowler position at 30 degrees with head rotated away from the site of measurement. Using the Sonosite edge with linear 38xi transducer 5-10MHz (Seattle, WA) images of the common carotid artery were obtained at the level of the thyroid gland. The Doppler flow volume was measured in different cycles (beats) and an average of 3 cycles was taken. Concurrent vital signs and measured cardiac output via invasive devices was recorded. Results: Patient cohort comprised 39 patients; 52% were females. Average age was 59+/- 13 years, and 66% were monitored by PCA device and 33% by PA. Intra class correlation (ICC) analysis was used to analyze the data. A perfect agreement was defined as ICC of 0.81–1.00 and substantial agreement was 0.61–0.80. The results demonstrated almost perfect correlation (0.8152) between measurements of CO by ultrasound versus invasive modalities. The ICC was 0.84 when compared to measurements by the PCA and 0.74 when compared to PA Catheter, showing substantial agreement between ultrasound and the invasive modalities. Conclusions: Using POCUS, Carotid Doppler flow volume can help estimate the CO in ICU patients with no carotid disease or apparent change in the cerebral circulation, and may limit the need for invasive monitoring for CO estimation.