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

OBJECTIVE: This study compared the values of variables measured by pulse co-oximetry (Masimo Radical 7; Masimo Europe Limited, UK) with those measured by a co-oximeter-enabled blood gas analyser (Siemens Rapid-point 500; Siemens Healthcare Limited, UK) in anaesthetized horses. STUDY DESIGN: Retrospective study. ANIMALS: A total of 30 anaesthetized horses. METHODS: In total, 47 heparinized arterial blood samples were collected for blood gas analysis to determine haemoglobin concentration (tHb, g L-1) and percentage of haemoglobin saturation with oxygen (SaO2). Arterial haemoglobin saturation with oxygen was determined noninvasively by pulse co-oximetry (Masimo SpO2). Pulse co-oximetry also provided arterial haemoglobin concentration (SpHb) and arterial oxygen content (SpCaO2). Arterial oxygen content was calculated (CaO2) in 39 samples using SaO2 and the value of Hüfner's constant used by Masimo Radical 7 (1.3 mL g-1). Data were compared using Bland-Altman analysis, correlation tests, accuracy root mean square (ARMS) statistics and total allowable error, where available. RESULTS: Low bias but wide limits of agreement (LoA) were found between Masimo SpO2 and SaO2 (bias = -1.4%, LoA = -4.0 to 1.3%), with an ARMS of 3%. Compared with tHb, SpHb showed low bias (6.2 g L-1) but wide LoA (-39.6 to 52.6 g L-1); its % bias (5.2%) was still within the 7% limits recommended by the Clinical Laboratory Improvement Amendments (CLIA) for humans. When comparing SpCaO2 and CaO2, the bias and LoA were -0.2 mL dL-1 and -6.7 to 6.2 mL dL-1, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Masimo SpO2 was acceptable for current ARMS standards, and SpHb measurements also met CLIA limits. The wide LoA in this study, however, suggest that the Masimo Radical 7 cannot be recommended as a substitute for direct measurements. As blood gas machines, pulse oximeters and co-oximeters use algorithms based on human haemoglobin, no true gold standard exists for horses.

Comparison of the spread of two different volumes of contrast medium when performing ultrasound-guided transversus abdominis plane injection in dog cadavers.

OBJECTIVES: To compare, via CT imaging, the spread of different volumes of diluted iodinated contrast medium in the transversus abdominis muscle plane of dog cadavers. METHODS: Prospective, randomised study. An electro stimulation or a SonoTAP needle was inserted in plane with the ultrasound beam in the fascia between the internal oblique and transversus abdominis muscles. A test dose of 1 ml of diluted contrast (30 mg/mL iohexol) was injected to confirm positioning, followed by 0 · 5 mL/kg (n=14) or 1 mL/kg (n=12) and the distribution of the fluid compared. RESULTS: Contrast medium was identified exclusively in the transversus abdominis plane in 19 of 26 dogs. In one dog, the contrast lay between the external and internal oblique muscles and partially in three dogs. Intraperitoneal contrast was detected in 6 of 26 dogs (23%). No significant differences were found in the dorso-ventral or cranio-caudal spread or area of distribution but a significant difference was found in the transverse spread. There was an association between poor ultrasound visualisation of the tip of the needle and intraperitoneal injection. CLINICAL SIGNIFICANCE: Injection of 1 mL/kg of diluted contrast did not result in wider cranio-caudal spread in the transversus abdominis muscle plane of dog cadavers when compared with 0 · 5 mL/kg. Intraperitoneal injection is a risk and might be reduced with good needle visualisation.