Pulse oximeters' reliability in detecting hypoxemia and bradycardia: Comparison between a conventional and two new generation oximeters

Objective: Pulse oximeters are increasingly used for patient monitoring; ho wever, they are traditionally very prone to motion artifact. Newly develope d instruments have lower false alarm rates. We wanted to know whether this is achieved at the expense of an increased proportion of false negative ala rms such as missed or delayed identification of hypoxemia and/or bradycardi a. Design: Observational study. Setting: Neonatal intensive care unit. Patients: A total of 17 unsedated preterm infants (median gestational age a t birth, 25 wks; range, 24-30 wks). Intervention: Long-term recordings of transcutaneous partial pressure of ox ygen (P-ToO2), heart rate, pulse oximeter saturation (Sp(O2)), and pulse ra te from a conventional oximeter and two new generation oximeters. Measurements: Recordings were analyzed for episodes with P-TcO2 < 40 torr o r with heart rate <80 beats/min for >5 sees. Hypoxemia was considered ident ified if Sp(O2) had fallen to <85% within 2 mins of P-TcO2 reaching 40 torr , and bradycardia was considered identified if pulse rate had fallen to <80 beats/min within 2 mins of the heart rate reaching this threshold. Main Results: A total of 202 falls in P-TcO2 to <40 torr occurred; 174 (86% ) were identified by all three oximeters. Of the remaining episodes, manual analysis of red and infrared absorption signals confirmed that Sp(O2) had indeed been <85% for greater than or equal to 10 sees in 11 episodes; there fore, these episodes should have been identified by all three oximeters. No ne of these had been missed by the conventional oximeter, but 10 (5.4% of t he total) were missed by one of the new generation instruments (Nellcor), a nd one (0.5%) was missed by the other (Masimo). Of 54 bradycardias, only 14 were identified by all three oximeters; 17 (32%) were missed by the conven tional, 37 (69%) by the Nellcor, and 4 (7%) by the Masimo instrument. Conclusion: One of the two new generation instruments investigated in this study missed 5.4% of hypoxemic episodes and 69% of bradycardias. It thus ap pears that this instrument's reduced false alarm rate is achieved at the ex pense of an unreliable and/or delayed identification of hypoxemia and brady cardia. The other instrument identified both conditions equally as or more reliably than a conventional pulse oximeter.