Abstract â–¡ 56

Objective: Pulse oximeters are increasingly used for patient monitoring but are very prone to motion artifact. Newly developed instruments have lower false alarm rates (Bohnhorst&Poets, Intensive Care Med 1998;24:277-278). We wanted to know whether this is achieved at the expense of a less reliable identification of hypoxaemia and/or bradycardia. This was with the underlying aim to test the suitability of these devices for use as home monitors.

Methods: 17 unsedated preterm infants (median GA at birth 25 wk, range 24-30) underwent long-term recordings of transcutaneous partial pressure of oxygen (PTcO2), heart rate, pulse oximeter saturation (SpO2) and pulse rate from 3 instruments (Nellcor N-200 and N-3000 (Oxismart), Nellcor Puritan Bennett, Pleasington, CA; Masimo SET, Masimo Corp., Irvine, CA). Recordings were analysed for episodes with PTcO2 <40 mmHg or with heart rate <80/min. for >5 s. Hypoxaemia was considered identified if SpO2 had fallen to <85% within 2 min. of PTcO2 reaching 40 mmHg, and bradycardia if pulse rate had fallen to <80 beats/min. within 2 min. of heart rate reaching this threshold.

Results: 202 falls in PTcO2 to <40 mmHg occurred; 174 (86%) were identified by all 3 oximeters. In 15 of these episodes, however, the N-200 only alarmed because it had zeroed out due to signal loss; the same happened 4 times with the N-3000, but only once with Masimo SET. Of the remaining episodes where at least 1 oximeter had not alarmed, manual analysis of red and infrared absorption signals confirmed that SpO2 had indeed been <85% for at least 10 s in 11 episodes, i.e. these episodes should have been identified by all 3 pulse oximeters. None of these had been missed by N-200, but 10 (5.4% of the total) by N-3000 and 1 (0.5%) by Masimo SET. Of 54 bradycardias, only 14 were identified by all 3 oximeters; 17 (32%) were missed by N-200, 37 (69%) by N-3000, and 4 (7%) by Masimo SET.

Conclusion: The Nellcor N-3000 missed 5.4% of hypoxaemic episodes and 69% of bradycardias. This instrument s reduced false alarm rate may thus be achieved at the expense of an unreliable and/or delayed identification of hypoxaemia and bradycardia. The other low-alarm-rate instrument (Masimo SET) identified both conditions equally or even more reliably than a conventional pulse oximeter.