Does High Ultrafiltration Volume Correlate to Occurrence of Desaturation in Patients Undergoing Hemodialysis?

Background: Hemodialysis is a metabolically stressful condition for patients that leads to reduced oxygen saturation and tissue perfusion. One of the identified drivers is a high ultrafiltration volume (UFV). Concurrently, central venous oxygen saturation (ScvO2) is a marker for global tissue hypoxia that has been used in cases of sepsis and trauma to guide fluid therapy. In dialysis patients with a central venous catheter (CVC) access ScvO2 is accessible. Here we intend to delineate the relationship of UFV to desaturation during dialysis through the measurement of ScvO2. Methods: PICO was formulated from a clinical case, and a literature search was conducted in Pubmed, Embase, Scopus, and Cochrane. Selected studies were then critically appraised using harm/etiology worksheet from CEBM1 for validity, importance, and applicability. Results: Studies by Harrison, et al., Zhang, et al. and Rotondi, et al. were chosen for answering our PICO. Harrison, et al. reported a relation of r: -0.680, p:0.015 between UFV and ScvO2. While, Zhang, et al. utilized retrospective data of Critline Monitor (CLM) reading of dialysis patients and reported a negative 0.3% slope of ScvO2 over corrected UFV (cUFV). Whilst, Rotondi, et al. demonstrated that in 20 patients separated equally to exclusively dialysis or ultrafiltration and both caused lowering of ScvO2, but only the former was statistically significant. Discussion: The mechanism of relationship may include incapability of plasma refill rate to compensate for the fluid shift during ultrafiltration, resulting in lower cardiac preload and stroke volume which is detrimental in patients who are natively prone to suffer from reflex bradycardia and intradialytic hypotension. Studies have shown that episodes of hypoxemia in dialysis patients translate to worse prognosis. Conclusion: ScvO2 is inversely proportional to UFV. As such, monitoring for ScvO2 in dialysis patients will be beneficial to prevent end-organ ischemia.