Effect of the size of evacuated blood collection tubes on total carbon dioxide concentration in equine plasma

Impact of blood collection devices and mode of transportation on peripheral venous blood gas parameters

BACKGROUND

Peripheral venous blood (PVB) gas analysis has become an alternative to arterial blood gas (BG) analysis in assessing acid-base balance. This study aimed to compare the effects of blood collection devices and modes of transportation on peripheral venous BG parameters.

METHODS

PVB-paired specimens were collected from 40 healthy volunteers into blood gas syringes (BGS) and blood collection tubes (BCT), transported by either a pneumatic tube system (PTS) or human courier (HC) to the clinical laboratory, and compared using a two-way ANOVA or Wilcoxon signed-rank test. To determine clinical significance, the PTS and HC-transported BGS and BCT biases were compared to the total allowable error (TEA).

RESULTS

PVB partial pressure of oxygen (pO2), fractional oxyhemoglobin (FO2Hb), fractional deoxyhemoglobin (FHHb), and oxygen saturation (sO2) showed statistically significant differences between BGS and BCT (p < 0.0001). Compared to HC-transported BGS and BCT, statistically significant increases in pO2, FO2Hb, sO2, oxygen content (only in BCT) (all p < 0.0001), and base excess extracellular (only in BCT; p < 0.0014) concentrations and a statistically significant decrease in FHHb concentration (p < 0.0001) were found in BGS and BCT delivered by PTS. The biases between PTS- and HC-transported BGS and BCT exceeded the TEA for many BG parameters.

CONCLUSIONS

Collecting PVB in BCT is unsuitable for pO2, sO2, FO2Hb, FHHb, and oxygen content determinations.

Acid-base disorders in sick goats and their association with mortality: A simplified strong ion difference approach

OBJECTIVES

To investigate the acid-base status of sick goats using the simplified strong ion difference (sSID) approach, to establish the quantitative contribution of sSID variables to changes in blood pH and HCO3 - and to determine whether clinical, acid-base, and biochemical variables on admission are associated with the mortality of sick goats.

ANIMALS

One hundred forty-three sick goats.

METHODS

Retrospective study. Calculated sSID variables included SID using 6 electrolytes unmeasured strong ions (USI) and the total nonvolatile buffer ion concentration in plasma (Atot ). The relationship between measured blood pH and HCO3 - , and the sSID variables was examined using forward stepwise linear regression. Cox proportional hazard models were constructed to assess associations between potential predictor variables and mortality of goats during hospitalization.

RESULTS

Hypocapnia, hypokalemia, hyperchloremia, hyperlactatemia, and hyperproteinemia were common abnormalities identified in sick goats. Respiratory alkalosis, strong ion acidosis, and Atot acidosis were acid-base disorders frequently encountered in sick goats. In sick goats, the sSID variables explained 97% and 100% of the changes in blood pH and HCO3 - , respectively. The results indicated that changes in the respiratory rate (<16 respirations per minute), USI, and pH at admission were associated with increased hazard of hospital mortality in sick goats.

CONCLUSIONS AND CLINICAL IMPORTANCE

The sSID approach is a useful methodology to quantify acid-base disorders in goats and to determine the mechanisms of their development. Clinicians should consider calculation of USI in sick goats as part of the battery of information required to establish prognosis.

Acid-base assessment: when and how to apply the Henderson-Hasselbalch equation and strong ion difference theory

The Henderson-Hasselbalch equation is probably the most famous equation in biology but is more descriptive than mechanistic. The traditional approach to acid-base assessment using the Henderson-Hasselbalch equation provides a clinically useful and accurate method when plasma protein concentrations are within the reference range. The simplified strong ion approach is a mechanistic acid-base model that can provide new insight into complicated acid-base disturbances. The simplified strong ion approach should be used to evaluate acid-base balance whenever plasma protein concentrations are abnormal.

Comparison of two analyzers for measurement of plasma total carbon dioxide concentration in horses

OBJECTIVE

To determine the degree of agreement between 2 analyzers for measurement of total CO₂ concentration (ctCO₂) in equine plasma.

ANIMALS

6 healthy untrained horses, 6 trained Standardbreds undergoing a simulated race protocol, and 135 trained Standardbreds at a racetrack.

PROCEDURES

Jugular venous blood samples were obtained from all horses. Two analyzers (commonly used analyzer A and less expensive analyzer B) were used to measure plasma ctCO₂ in each sample. Validation of both analyzers was conducted in accordance with guidelines established by the Clinical and Laboratory Standards Institute and involved characterization of linearity, total analytic error, and bias estimation.

RESULTS

Total analytic error (instrument SD) was 0.58 mmol/L (coefficient of variation, 1.6%) and 0.49 mmol/L (coefficient of variation, 1.4%) for analyzers A and B, respectively, when measuring an aqueous standard containing 36.0 mmol of CO₂/L. A 1 g/L decrease in plasma protein concentration corresponded to an increase in ctCO₂ measured with analyzer B of 0.065 mmol/L. A difference plot indicated that analyzer B produced values 2.7% higher than analyzer A for 103 samples from the 6 trained and exercised Standardbreds (mean plasma protein concentration, 67 g/L).

CONCLUSIONS AND CLINICAL RELEVANCE

Analyzer B provided adequate precision and linearity for measurement of ctCO₂ from 5 to 40 mmol/L and was therefore suitable for measuring ctCO₂ in equine plasma, provided allowances are made for changes in plasma protein concentration.

Effect of sample handling and storage time on the stability of total CO2 in equine plasma

REASONS FOR PERFORMING STUDY

The stability of total CO2 concentration (ctCO2) in plasma is influenced by storage temperature and handling during sample processing. Conflicting information exists regarding the stability of ctCO2 in equine plasma over time, and the effect of centrifugation on the measured value for plasma ctCO2 is unclear.

OBJECTIVES

To determine plasma ctCO2 stability over 5 days when equine blood is collected into Vacutainer tubes, centrifuged within 30 min of collection, and stored at 4 degrees C; and to determine whether a delay in centrifugation increases the rate at which plasma ctCO2 decreases over time.

METHODS

Blood was collected from 6 adult horses into 3 ml plastic Vacutainer tubes and randomly assigned to be centrifuged immediately, or after, storage. Plasma ctCO2 was measured in triplicate at 0, 24, 48, 72 and 96 h after collection using a NOVA-4 analyser Data were analysed using multivariable linear regression, with P < 0.05 being defined as significant.

RESULTS

Plasma ctCO2 decreased linearly over time during storage at 4 degrees C. The measured value for ctCO2 decreased at a faster rate (-0.28 mmol/l/day; P < 0.0001) when centrifugation was delayed, compared with immediate centrifugation (-0.10 mmol/l/day). There was a significant effect of sequence of sample analysis on the ctCO2 value when measured in triplicate: the second and third measurements were 0.31 and 0.41 mmol/l lower than the first measurement, respectively.

CONCLUSIONS

Blood samples collected from horses into Vacutainer tubes should be centrifuged immediately after collection and analysed as soon as possible to ensure accurate values for plasma ctCO2.

POTENTIAL RELEVANCE

Failure to centrifuge, or excessive delay in measuring ctCO2 after centrifugation, produces values significantly lower than the true value.