RESULTS: We initially found close correlations between ΔS and net ultrafiltrate volume removed (r=0.60, p<0.02). No significant change in ΔP was found. The number of respiratory cycles required to achieve a variation <10% for ΔS varied from 5 to 30 and was achieved in 9 of 10 samples for 30 cycles. For ΔP, a variation of <10% was only achieved in 4 of 10 encounters for 30 cycles. Upon reviewing the variability of the data, an additional sample of convenience of 15 ICU patients with renal failure in 34 encounters of hemodialysis was obtained, each encounter preceded within 24 hours by inferior vena cava ultrasound (IVC US) collapsibility index assessment of intravascular volume prior to ultrafiltration. The SpO2 waveform was digitized and is currently being analyzed.