Page 15 - ANZCP Gazette April 2021

et. al., 2019). These solutions, such as saline or Plasmalyte-148® do not generally contain glucose. If the paediatric CPB prime does not contain glucose two potential issues may present. The first issue being, a lack of substrate for RBC metabolism and, the second issue is the risk of transient patient hypoglycaemia on the initiation of CPB.
Transient hypoglycaemia during CPB in infants has been found to be associated with neurologic injury (de Ferranti et. al., 2004). In order to prevent this occurrence, and assist in creating a physiological prime, glucose may be added to the prime solution. Such a practice will also provide a metabolic substrate for any washed red blood cells that have been added.
Erythrocytes do not possess mitochondria and are therefore unable to produce energy by aerobic metabolism. Instead they rely on the anaerobic metabolism of glucose via the Embden- Meyerhof pathway, also known as glycolysis, to produce ATP for maintenance of cellular processes (Brown, 1996). Each unit of pRBCs that comes direct from the blood bank will therefore contain a set amount of glucose to facilitate this process during storage (Hess, 2006). The Australian Red Cross Blood Service suspends RBCs in a saline adenine glucose and mannitol (SAG-M), which contains 0.9 g/L of dextrose.
This study aims to investigate the impact of the addition of glucose on the quality of the blood primed CPB circuit. This will be achieved by comparing the quality of a blood primed CPB circuit containing glucose against a blood primed CPB circuit without glucose. The measured markers of quality will be lactate production, extracellular potassium and glucose concentration, as well as the degree of haemolysis, as determined by measuring plasma free haemoglobin (pfHb).
Materials and Method
Study design
This study was a controlled in-vitro comparative study. Ten CPB circuits requiring a blood prime were chosen. After blood priming of the circuit, a 5 mL sample of the blood prime was taken from each circuit before the addition of glucose (no glucose group). Glucose was then added to the prime and another 5 mL sample of blood was taken from each circuit (glucose group). The number of samples in each group was 10 (n=10).
pRBC processing
Prior to the addition to the CPB circuit, each unit of pRBCs was washed in the Fresenius Kabi C.A.T.S®plus Continuous AutoTransfusion System. Once added to the collection reservoir the donor blood, which had an average volume of 267 mL, and an average age of six days, was diluted with 1 litre of Plasmalyte-148®. Plasmalyte-148® was also used as the wash solution. Each unit of blood was processed using the ‘high quality’ wash program. Once the final processing was complete, the washed red blood cells were added to the CPB circuit.
CPB circuit prime
Each CPB circuit prime solution consisted of Plasmalyte-148®, sodium bicarbonate, water for injections, heparin, calcium chloride and 20% human albumin. Each circuit was warmed and circulated at 37 degrees Celsius (oC). Following the addition of washed red blood cells ultrafiltration was commenced in order to haemoconcentrate the prime. Once ultrafiltration was complete the circuit was left to circulate for three min at high pressure (in excess of 100 mmHg) to ensure a homogeneous solution. The
‘no glucose’ sample was then taken. 50% glucose was then added to the prime to obtain a circulating glucose level of 3.0–4.0 mmol/L. Following circulation for another three minutes, the ‘glucose’ sample was taken.
Sample incubation
Once obtained, all blood samples were gently syringed into BD Vacutainer® blood tubes, gently agitated and then placed immediately into a Grant Y28 © Jepson Bolton International, water bath set at 37oC. This temperature was chosen to reflect the circulating prime solution of the circuit prior to the initiation of CPB. The temperature of the water bath was verified using a NATA accredited thermometer.
Extracellular electrolyte/metabolite concentrations
Blood samples were analysed using the Siemens RAPIDLab® 1265 blood gas analyser every hour for four hours (time points 0, 1, 2, 3, and 4). A four-hour period was chosen to reflect the transfusion guidelines of the National Blood Authority Australia, which state that once a blood product is spiked, it has an expiry of four hours. The variables of interest were extracellular potassium (K+), lactate and glucose concentrations.
Haemolysis
To determine the degree of haemolysis, blood was centrifuged and the plasma component analysed using the HemoCue© Plasma/Low Hb photometer system. This device quantitatively determines the amount of low-level haemoglobin within the plasma as a marker of the amount of haemolysis expressed in grams per litre (g/L). A plasma free haemoglobin (pfHb) test was completed at time point 0, 2 and 4 (h).
Statistical analysis
Data was analysed using SAS software for windows, version 9. A Pearson’s Chi squared test was used to assess the difference in the mean measured values over time between the two treatment groups with a p-value of equal to or less than 0.05 (p≤0.05) used as an indicator of statistical significance
Results
Lactate concentration
There was a significant difference (p=0.046) between these two sample groups. In both ‘No Glucose’ and ‘Glucose’ groups the concentration of lactate rose over time (Figure 1). However, there was significantly higher production of lactate in the glucose containing samples at each time point, with a mean difference of 3.96 mmol/L at the end of the four hour period (Table 1).
APRIL 2021 | www.anzcp.org 12