Objective: Arterial oxygen saturation (Sao(2)) and arterial carbon dioxide partial pressure (Paco(2)) are 2 of the most important respiratory parameters in the treatment of critically ill neonates. Noninvasive monitoring of these parameters is desirable for continuous estimating of the respiratory status and reducing blood loss because of repeated blood gas analyses. Transcutaneous measurement of Pco(2) (Ptcco(2)) represents a simple and noninvasive technique for continuous monitoring of ventilation. However, sensor preparation, positioning, taping, and repeated changes of the sensor location make the handling difficult and complicate its use in the neonatal care unit. Recently, a new sensor for combined assessment of pulse oximetry oxygen saturation (Spo(2)) and Ptcco(2) has been introduced (TOSCA Monitor; Linde Medical Sensors, Basel, Switzerland). The monitor combines pulse oximetry and Ptcco(2) measurement in a single ear sensor, which works at 42 degrees C to enhance blood flow in capillaries below the sensor.
Methods: In a prospective, open, nonrandomized study of 60 ill neonates, the new ear sensor for combined assessment of Spo(2) and Ptcco(2) at 42 degrees C was tested. The sensor was adapted to the ear of a neonate with a Varihesive layer (Conva Tec; Princeton, NJ). Data obtained from the ear sensor were compared with Spo(2 Finger/Heel), Sao(2), and Paco(2) obtained from arterial blood gas in 30 patients and with a capillary blood gas in an additional 30 patients using Bland Altman bias analysis. Data are presented as median (range).
Results: The postconceptional age of the patients was 38.3 weeks (range: 28 5/7-40 5/7) in the arterial group and 37.9 weeks (range: 29 6/7-41 0/7) in the capillary group. Age of the newborns studied was 3.5 days (range: 1-28) in the arterial blood sample group (n = 30) and 6 days (range: 2-28) in the capillary blood sample group (n = 30). Patient weight was 3.02 kg (range: 1.5-4.5) in the arterial group and 2.76 kg (range: 1.0-3.71) in the other group. Three patients had weights of <1500 g. Twenty-one of 60 patients were conventionally ventilated, 4 patients received high-frequency oscillation, and 35 were not ventilated. Mean difference (bias) and precision (2 SD of the mean difference) between Ptcco(2 TOSCA) and Paco(2) were -0.44 kPa (-3.21 mm Hg) and 0.82 kPa (6.02 mm Hg) and between Ptcco(2 TOSCA) and Pcapco(2) were -0.09 kPa (-0.67 mm Hg) and 1.11 kPa (8.07 mm Hg), respectively. Spo(2) assessment by the TOSCA revealed slightly higher values compared with Sao(2) (bias: -0.48%), whereas Spo(2) (Finger/Heel) values were slightly lower than Sao(2) (bias: 0.52%).
Conclusion: The TOSCA monitor with the ear sensor adapted to ears of neonates allows reliable estimation of Sao(2) and Paco(2). A potential benefit is the reduction in motion artifacts because of less head movement in newborns and that only a single cable leads form the patient to the monitor. In addition, the sensor is not removed for chest radiograph or for nursing the infant on his or her parent's lap. Long-term studies in a large population with continuous measurements are required to confirm these preliminary findings and to elucidate the benefits in detection of respiratory deterioration and the potential side effects of this sensor.