Evaluation of pulse co-oximetry to determine haemoglobin saturation with oxygen and haemoglobin concentration in anaesthetized horses: a retrospective study.

The research studied the effectiveness of pulse co-oximetry in measuring oxygen saturation and haemoglobin concentration in anaesthetized horses and found it to have low biases but wide limits of agreement, suggesting it is not a suitable substitute for direct measurements.

Background and Methods

• The study aimed to evaluate the ability of pulse co-oximetry (specifically the Masimo Radical 7 device) to accurately measure haemoglobin concentration (tHb, g L) and the percentage of haemoglobin saturation with oxygen (SaO2) in anaesthetized horses.
• This was compared with measurements obtained from a co-oximeter-enabled blood gas analyser, the Siemens Rapid-point 500.
• 30 horses were anaesthetized and 47 heparinized arterial blood samples were collected for blood gas analysis.
• The Masimo SpO device was used to non-invasively measure arterial haemoglobin saturation with oxygen. It also provided arterial haemoglobin concentration (SpHb) and arterial oxygen content (SpCaO2).

Data Analysis

• Data from the two devices were compared using Bland-Altman analysis, correlation tests, accuracy root mean square (ARMS) statistics, and total allowable error where possible.
• The Bland-Altman analysis measures the agreement between two different methods of measurements. This allows the researchers to identify any systematic bias between measures from two different methods.

Results

• The results showed a low bias, but wide limits of agreement (LoA) between the Masimo SpO and SaO2 measures (bias = -1.4%, LoA = -4.0 to 1.3%), which means there was a small average difference, but a large range of differences between the methods.
• When comparing the device’s measurements of haemoglobin concentration to the standard, there was also a low bias but a wide LoA, however, the percentage bias was within the 7% limits recommended by the Clinical Laboratory Improvement Amendments (CLIA) for humans.
• The bias and LoA between SpCaO2 and CaO were -0.2 mL dL and -6.7 to 6.2 mL dL respectively.

Conclusion

• Overall, the study concluded that while the Masimo SpO device did meet current ARMS standards and CLIA limits, the wide LoA suggests that it is not recommended as a substitute for direct measurements in horses.
• It was also noted that as pulse oximeters and co-oximeters use algorithms based on human haemoglobin, there is no true gold standard exists for determining levels in horses.