This collaborative study with Masimo Corporation will involve 2 phases. In the first phase of this study, 25 subjects weighing 0.5 to 3.0 kg will be recruited and hemoglobin values will be obtained from the non-invasive probe at the same time as blood samples are routinely drawn for Hgb analysis using the cyanomethemoglobin method (ADVIA 2121). Masimo Corporation will use this data to calibrate or modify the hemoglobin reading (SpHb®) sensors and monitors. All results and conclusions from this phase will be discussed with the investigation team in order to determine if additional subjects are needed (at increments of 25 subjects at a time). Once the sensor designs have been optimized, another group of patients will be studied to document the accuracy and precision of the hemoglobin reading (SpHb®) measurements.