Page 14 - ANZCP Gazette April 2021

PAEDIATRIC CARDIOPULMONARY BYPASS PRIME:
ALREADY SWEET ENOUGH?
Hannah Lea CCP, FANZCP
Sydney Children’s Hospital Network Winner of the ANZCP Meritorious Award 2019
Abstract
Background: Paediatric patients, particularly neonates, are extremely vulnerable to hypoglycaemia. The effects of hypoglycaemia include cognitive dysfunction, seizures, and permanent brain damage. Commencement of cardiopulmonary bypass (CPB) with a hypoglycaemic prime could put the paediatric patient at increased risk of hypoglycaemia with its detrimental effects. The addition of glucose to the prime could ameliorate these effects however, the implications of this practice on the quality of the prime remains unclear. The aim of this study is to investigate the impact of glucose on the quality of a blood-primed circuit. Markers of quality were levels of extracellular potassium (K+), glucose, lactate and levels of plasma-free haemoglobin (pfHb). Method: A comparative in-vitro study was performed analysing the quality of 10 blood primed cardiopulmonary bypass circuits both with and without the addition of glucose over a four-hour period. Samples were stored in a water bath at 37oC to mimic the circulating CPB circuit, and assayed at baseline, then every hour for four hours. Results: There was a significant difference (P<0.05) in the amount of lactate produced between the two treatment groups. Higher levels of lactate were observed in the samples containing glucose at each time point. There was a slight decrease in K+ concentration in glucose containing samples, however this was not statistically significant (p>0.05). There was a significant decline in glucose concentration in the glucose containing samples over the test period. No significant difference in pfHb was observed between the two groups (p>0.05). Conclusion: The addition of glucose to a blood primed CPB circuit results in a higher production of lactate over a four-hour period. The omission of glucose resulted in lower extracellular K+ concentration, although this did not reach statistical significance. These findings would suggest that the addition of glucose provides a substrate for continued RBC metabolism as demonstrated by increasing levels of lactate coupled with inversely proportional decreases in glucose concentration in the sample group with glucose added. Larger scale studies investigating enzymatic and morphologic changes within the RBC would provide further insight into the impact of the omission of glucose to the quality of the blood primed CPB circuit.
Introduction
Cardiac surgery requiring cardiopulmonary bypass (CPB), in the neonatal and infant population remains one of the most challenging areas in modern medicine. This is primarily due to their diminutive circulating volume (Caneo et. al., 2019), making this patient demographic particularly susceptible to the volume and constituents of the solution used to prime the CPB circuit (Darling et. al., 2000).
In order to ameliorate the impact of the CPB prime upon this vulnerable patient group, the paediatric perfusionist should aim to ensure the CPB prime is as physiological as possible.
Whilst particularly susceptible to electrolyte disturbances and hypoglycaemia the infant is also at risk of anaemia as a result of excessive haemodilution once the CPB prime solution combines with the patients circulating blood volume (Osthaus et. al., 2008).
Relatively straightforward mathematical calculations are carried out preoperatively to predict the degree of haemodilution that the prime solution will inflict upon the patients haemoglobin (Hb) (Erpicum et. al., 2016). If the predicted degree of haemodilution is deemed unacceptable, the perfusionist will add a set volume of packed red blood cells (pRBC’s) to the prime in order to achieve the desired Hb, and thus prevent anaemia and maintain the oxygen-carrying capacity of the blood (Garcia-Roa et. al., 2017). However, as is well documented, the transfusion of pRBC’s is not without risk. Such transfusions have been linked to infectious diseases (Rawn, 2008). Other potential risks include ABO- mismatch haemolytic reactions, transfusion related acute lung injury (TRALI) and mortality (Vamvakas & Blajchman, 2009).
ThestoragelesionofpRBC’scanalsohavenegativeeffectsuponthe patient at the metabolic and biochemical levels (Garcia-Roa et. al., 2017). Haemolysis occurs during the storage of pRBCs, resulting in increased extracellular concentrations of potassium and plasma- free haemoglobin (pfHb) (Keidan, et. al., 2004). Subsequent to the accumulation of pfHb is nitric oxide (NO) scavenging leading to a decrease in NO availability and consequently endothelial dysfunction (Garcia-Roa et. al., 2017; Keidan, et. al., 2004). Moreover, a variety of morphological changes occur during storage, such as the accumulation of lactic acid which decreases the pH of the blood, below 6.5 having detrimental implications on pH-dependent enzymatic reactions of RBC’s (Keidan, et. al., 2004) and a decrease in levels of 2,3-diphosphoglycerate (2,3 DPG) which affects the affinity of Hb for oxygen and affects its ability to offload oxygen at this tissues (Leal-Noval et.al., 2008; Scott et. al., 2016). Another important component of the storage lesion is the depletion of reduced NADH, responsible for converting methaemoglobin, the form of haemoglobin unable to bind oxygen, back to oxyhaemoglobin (Leal-Noval et. al., 2008). This oxidative stress is exacerbated in the presences of acidosis. The combination of these changes have the potential to lead to serious clinical consequences such as arrhythmias, ischemia, renal failure, multi-organ failure, as well as an increased risk of morbidity and mortality (Leal-Noval et. al., 2008).
In order to reduce the adverse effects of the storage lesion, pRBCs can be washed in a cell processor prior to the addition to the CPB prime (Caneo et. al., 2019). Use of such devices has been found to decrease the potassium, lactate and other storage lesions such as plasma free- haemoglobin (pfHb) within the donor blood that may be detrimental to the neonatal or infant patient during the rapid onset of CPB (Swindell et. al., 2007).
The washing of pRBCs in a cell processor results in red blood cells suspended in whatever solution is chosen to wash them with (Caneo
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