Medicina pulmonar y respiratoria

Assessment of Hemodynamic Changes during Mechanical and Spontaneous Ventilation by Variations in Pulse Oximetry Waveform in Critically Ill Patients Undergoing Hemodialysis: A Pilot Study to Evaluate Reliability of a Noninvasive Technique

Abstract

Stern K, Pillai R, Chowdhury S and Baydur A

Background: Pulse oximetry (SpO2) waveform analysis has recently been compared to intraarterial waveform analysis in assessing intravascular volume in various conditions. Its usefulness during and following ultrafiltration (UF) has not been evaluated. The aim of this pilot study was to assess the relationship of volume removal during UF to SpO2 waveform fluctuations in spontaneously breathing (SB) patients and compare it to patients receiving mechanical ventilation (MV).
Hypothesis: Volume removal during UF increases the amplitude and peak-to-peak variability of the SpO2 waveform (ΔP and ΔS, respectively).
Methods: Pulse oximetry waveform analysis was conducted in thirty-eight critically ill patients (total: 81 encounters) undergoing UF. SpO2 was recorded at the fingertip in 36 of 38 patients.
Results: Fifty-seven encounters were in patients receiving MV, 24 in SB patients. Sepsis was the most common diagnosis in 13 of 38 (29%) patients, with septic shock in 12. Intravascular volume removed during UF ranged between 0.2 L and 4.2 L. Relative to pre-UF, median ΔS increased by 35% by the end of UF (p=0.001). In 57 encounters in MV patients, median ΔS increased by 35%, but did not reach significance (p=0.081), and in 24 encounters in SB patients, it decreased by 5.6% (p=0.001). The mean (± SD) phase angle, φ, between the intraarterial and pulse oximetry waveforms in 12 patients was 79 ± 22 degrees.
Conclusions: This hypothesis-generating study support a potential clinical application of SpO2 waveform variability in evaluating intravascular volume status in patients undergoing ultrafiltration. In general, ultrafiltration results in an increase in ΔS, findings attributable to the reduction in intravascular volume. However, this relationship may depend on respiratory status, which requires further studies to clarify. Prospective studies utilizing methods that accurately estimate baseline intravascular volume and examine how the rate of volume removal over time are related to changes in ΔS and ΔP are needed.