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Assessment of myocardial glutamate requirements early after coronary artery bypass surgery
I Vanhanen1, R Svedjeholm, E Håkanson
1Department of Cardiothoracic Surgery, University Hospital, Linköping, Sweden.
Insights
Determining the optimal glutamate dose post-coronary artery bypass grafting (CABG) is crucial. A specific infusion rate can maximize heart glutamate uptake without adverse effects, aiding recovery.
Area of Science:
- Cardiology
- Biochemistry
- Metabolic Research
Background:
- Glutamate is vital for cardiac metabolism, especially during ischemia.
- Myocardial glutamate uptake after coronary artery bypass surgery (CABG) may be limited by arterial glutamate levels.
- Elevated glutamate can have adverse effects, necessitating careful dosage determination.
Purpose of the Study:
- To identify the minimum effective dose of glutamate for myocardial supply after CABG.
- To investigate the relationship between glutamate infusion rates, arterial levels, and myocardial uptake.
- To establish a safe and effective glutamate infusion strategy for post-CABG patients.
Main Methods:
- Ten patients undergoing elective CABG received intravenous L-glutamic acid infusions at varying rates.
- Arterial glutamate levels and myocardial uptake were measured during two 30-minute periods post-surgery.
- Dose-dependent effects on glutamate levels and uptake were analyzed.
Main Results:
- Intravenous glutamate increased arterial levels and myocardial uptake in a dose-dependent manner.
- Maximal myocardial uptake occurred with an arterial glutamate increase of 172 +/- 34 mumol/L.
- Significant myocardial uptake increases were achieved with less than 100 mumol/L arterial glutamate elevation.
- An infusion rate of 30-40 mg glutamate/kg body weight/hour is suggested for maximal uptake.
Conclusions:
- A glutamate infusion rate of 30-40 mg/kg/h appears sufficient for near-maximal myocardial uptake post-CABG.
- Further studies are needed to confirm this dosage in high-risk patient populations.
- Careful monitoring of arterial glutamate levels is essential to balance efficacy and potential adverse effects.
Abstract:
Glutamate is an important substrate for the intermediary metabolism of the heart, particularly in association with ischemia. Early after coronary artery bypass surgery (CABG) myocardial uptake of glutamate seems to be limited by substrate availability (arterial levels). However, glutamate is not an innocuous substrate. As arterial levels of glutamate are important both for myocardial uptake and adverse effects, an attempt was made to determine a minimum dose of glutamate sufficient to supply the needs of the heart after CABG. Ten patients received and infusion of 220-240 ml of 0.1 M L-glutamic acid solution at varying rates during two 30-min periods, starting 2 h after uncomplicated elective CABG. Intravenous glutamate infusion caused a dose-dependent linear increase in arterial glutamate and an increased myocardial uptake of glutamate. However, myocardial uptake of glutamate correlated with arterial levels only at lower infusion rates. Although maximal peak uptake in individual patients (6.6 +/- 1.1 mumol/min) occurred at an average increase of arterial whole blood glutamate of 172 +/- 34 mumol/L, the greatest impact on myocardial glutamate uptake was achieved by increasing arterial whole blood glutamate by less than 100 mumol/L. This implies that an infusion rate of 30-40 mg glutamate/kg BW/h could suffice to achieve a maximal or near maximal myocardial glutamate uptake in most patients after CABG. The adequacy of this dosage remains to be confirmed in high-risk patients.
