The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

A COMPARISON OF REFLECTIVE AND TRANSMISSION OXIMETRY IN PATIENTS WITH POOR PERFUSION


Richard Branson RRT, Bradley Davis MD, Kenneth Davis MD, Chandra Singh RRT, Chris Blakeman RRT, Jay Johannigman MD. University of Cincinnati, Departments of Surgery and Respiratory Care.

Background: Pulse oximetry is ubiquitous to intensive care prompting the term the 5th vital sign. Post-operative patients with hypotension and/or hypothermia are often challenges for traditional digital transmission oximetry (DTO). We compared the accuracy and success of DTO to a new reflective forehead oximeter (RFO) in post-operative patients at risk for hypotension and or hypothermia. 

Methods
: Informed consent was obtained from 20 patients or next of kin, undergoing surgical procedures predicted to last > 4 hrs. Immediately post-op all patients were fitted with digital (Max-A) and forehead (Max Fast) sensors connected to Nellcor N-595 oximeters. The forehead sensor was placed above the eyebrow and secured with a headband. Digital disposable sensors were placed on either hand. During routine care heart rate and saturations from the two monitors were recorded at the time arterial blood gases and hemodynamics were determined. Monitoring lasted until a minimum of 8 samples were obtained from each subject. Oxygen saturation from arterial blood was measured using a co-oximeter. Mean ± SD was calculated for HR, SaO2, and SpO2. Both SpO2 values were compared using Pearson's Correlation Coefficient and underwent analysis using the method of Bland and Altman.

Results: During the immediate post-operative period, DTO failed to detect a pulsatile signal in 7 patients for a mean time of 8.8 ± 6.7 hrs , while RFO failed to register a signal in 3 patients for a mean time of 3.3 ± 0.9 hrs. The mean duration of monitoring was 26.2 ± 7 hrs. Mean heart rate was 99 ± 17 bpm and SaO2 was 91.9 ± 3.1%. DTO heart rate was 98 ± 24 (r=0.98) and SpO2 was 93.7 ± 3.2% (r=0.758). RFO heart rate was 99 ± 20 (r = 0.99) and SpO2 was 92 ± 3.4% (r = 0.906).The mean difference between SaO2 and Digital SpO2 was 1.53 ± 2.19% with a root mean square difference of 2.67% while the mean difference between SaO2 and SpO2 was 0.06 ± 1.45% with a root mean square difference of 1.45% (p<0.05 DTO vs. TFO). Ten of 20 patients had core temp < 35°C, 8 of 20 patients had a systolic blood pressure <90 mmHg at some point during the study.

CONCLUSION: 
In this group of post-operative surgical patients with a high incidence of hypotension and hypothermia, reflective forehead oximetry performs better than digital transmission oximetry with regard to obtaining a signal and ability of SpO2 to represent SaO2.

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