Changes in metabolism and blood flow in peripheral tissue (skeletal muscle) during cardiac surgery with cardiopulmonary bypass: the biochemical microdialysis study

Symptom progression following on-pump versus off-pump coronary artery bypass graft surgery in patients with peripheral arterial disease

OBJECTIVE

This study aims to examine whether cardiac surgery leads to symptom progression in the early postoperative period in patients with the peripheral arterial disease (PAD) and evaluate the difference between on-pump (OPCAB) and off-pump (ONCAB) coronary artery bypass graft surgery with regard to the symptom progression.

METHODS

This retrospective study included one hundred consecutive adult patients with PAD at Fontaine stage 2b (pain-free walking distance less than 100 m) undergoing ONCAB and one hundred consecutive adult patients with PAD at Fontaine stage 2b (pain-free walking distance less than 100 m) undergoing OPCAB. Symptom progression was defined as the development of ischemic rest pain (Fontaine stage 3).

RESULTS

In the first week after surgery, 12 patients in the OPCAB group and 53 patients in the ONCAB group had postoperative symptom progression (p < 0.001). Rest pain resolved in most of these patients on the 15th postoperative day. At the end of the second month, rest pain resolved in all patients. Logistic regression analysis revealed that cardiac surgery with CPB, ABI < 0.5, postoperative nadir hct levels ≤ 25%, and intraoperative tissue hypoxia were independently associated with postoperative symptom progression.

CONCLUSIONS

In summary, we found that cardiac surgery may lead to symptom progression in patients with severe claudication in the early postoperative period. Our results suggest that OPCAB may lead to lower rates of symptom progression compared to ONCAB.

Malignant Hyperthermia During Cardiac Surgery Successfully Treated by Deep Hypothermia Using Cardiopulmonary Bypass: A Case Report

Malignant hyperthermia (MH) is a life-threatening hypermetabolic disorder triggered by volatile anesthetics and/or succinylcholine. We report a case of a 58-year-old patient with a type-A aortic dissection. After induction of general anesthesia, a hypermetabolic reaction was successfully treated by deep hypothermia using cardiopulmonary bypass. Dantrolene became available in theater after the hypermetabolism was already treated successfully by hypothermia. Because of a low suspicion of MH, dantrolene was not administered when it became available. The patient fully recovered, and MH susceptibility was confirmed. Cardiopulmonary bypass should be considered to treat MH in case dantrolene and conservative therapy are unavailable or insufficient.

Lactate Elevation During and After Major Cardiac Surgery in Adults: A Review of Etiology, Prognostic Value, and Management

Elevated lactate is a common occurrence after cardiac surgery. This review summarizes the literature on the complex etiology of lactate elevation during and after cardiac surgery, including considerations of oxygen delivery, oxygen utilization, increased metabolism, lactate clearance, medications and fluids, and postoperative complications. Second, the association between lactate and a variety of outcomes are described, and the prognostic role of lactate is critically assessed. Despite the fact that elevated lactate is strongly associated with many important outcomes, including postoperative complications, length of stay, and mortality, little is known about the optimal management of postoperative patients with lactate elevations. This review ends with an assessment of the limited literature on this subject.

Tissue and plasma concentrations of cephuroxime during cardiac surgery in cardiopulmonary bypass — a microdialysis study

Aim: Wound and mediastinal infections are still very serious complications of open-heart surgery, in spite of the use of prophylactic antibiotics. The use of cardiopulmonary bypass (CPB) is associated with profound physiological changes affecting the pharmacokinetic behaviour of antibiotics.

The aim of this pilot study was to monitor the tissue concentrations of cephuroxime (prophylactic antibiotic) in skeletal muscle during cardiac surgery using CPB by interstitial microdialysis. These concentrations were compared with plasma concentrations of cephuroxime.

Material and methods: Nine adult patients operated on using CPB were enrolled in this study. Cephuroxime was used as a prophylactic antibiotic (1st dose — 3 g of cefuroxime i.v. with anesthesia induction, 2nd dose — 1.5 g i.v. after CPB with protamine sulphate, 3rd dose — 1.5 g i.v. 8 hours after the surgery).

Interstitial microdialysis was performed by probe CMA 60 (CMA Microdialysis AB, Sweden) inserted into the patient's deltoid muscle. Concentrations of cephuroxime in dialysates and in plasma were determined by the modified fluid chromatography method. The unbound cephuroxime fraction in plasma was obtained by using an ultrafiltration method. Samples of dialysates were collected at the following intervals: before CPB, each 30 minutes of CPB, at the end of CPB. Samples of blood were collected at these intervals: incision, start of CPB, each 30 minutes of CPB, at the end of CPB, at the end of surgery. Concentrations of cephuroxime in tissue were corrected by in vivo recoveries of the microdialysis probes.

Results: Plasma concentrations of cephuroxime were 163.5 ± 40.1, 79.3 ± 17.4, 73.7 ± 16.8, 66.1 ± 18.3, 57.0 ± 10.9, 120.7 ± 29.9 (mg . L—1) and concentrations of free plasma fraction of cephuroxime were 119.5 ± 35.2, 67.8 ± 15.5, 66.0 ± 12.5, 54.8 ± 12.2, 49.6 ± 9.8, 102.6 ± 26.0 (mg . L—1).

The concentrations of cephuroxime in dialysates were 44.3 ± 15.7, 36.1 ± 11.6, 31.9 ± 9.3, 34.6 ± 12.3, 27.6 ± 12.9, 56.7 ± 17.6 (mg . L—1).

The mean in vivo recovery of cephuroxime in this study was 30%.

Corrected concentrations (calculated by in vivo recovery) of cephuroxime in skeletal muscle were 148, 120, 106, 115, 92, 189 (mg . L—1).

Conclusion: Our preliminary results show that CPB can modify the time course of cephuroxime plasma and tissue concentrations. A decrease in plasma drug concentrations occurred at the start of CPB and lasted until CPB ended. An increase in plasma concentrations corresponds to the second drug dose after CPB. The concentrations of cephuroxime in skeletal muscle (corrected by recovery) during CPB are higher than plasma concentrations. It is influenced by important changes during CPB; closely associated with hemodilution, a shift of intravascular volume, solutes and albumin to the extravascular space and inconstant protein binding of cephuroxime during operation. Perfusion (2007) 22, 129—136.

Microdialysis of paraspinal muscle in healthy volunteers and patients underwent posterior lumbar fusion surgery

Paraspinal muscle damage is inevitable during conventional posterior lumbar fusion surgery. Minimal invasive surgery is postulated to result in less muscle damage and better outcome. The aim of this study was to monitor metabolic changes of the paraspinal muscle and to evaluate paraspinal muscle damage during surgery using microdialysis (MD). The basic interstitial metabolisms of the paraspinal muscle and the deltoid muscle were monitored using the MD technique in eight patients, who underwent posterior lumbar fusion surgery (six male and two female, median age 57.7 years, range 37-74) and eight healthy individuals for different positions (five male and three female, age 24.1 +/- 0.8 years). Concentrations of glucose, glycerol, and lactate pyruvate ratio (L/P) in both tissues were compared. In the healthy group, the glucose and glycerol concentrations and L/P were unchanged in the paraspinal muscle when the body position changed from prone to supine. The glucose concentration and L/P were stable in the paraspinal muscle during the surgery. Glycerol concentrations increased significantly to 243.0 +/- 144.1 microM in the paraspinal muscle and 118.9 +/- 79.8 microM in the deltoid muscle in the surgery group. Mean glycerol concentration difference (GCD) between the paraspinal muscle and the deltoid tissue was 124.1 microM (P = 0.003, with 95% confidence interval 83.4-164.9 microM). The key metabolism of paraspinal muscle can be monitored by MD during the conventional posterior lumbar fusion surgery. The glycerol concentration in the paraspinal muscle is markedly increased compared with the deltoid muscle during the surgery. It is proposed that GCD can be used to evaluate surgery related paraspinal muscle damage. Changing body position did not affect the paraspinal muscle metabolism in the healthy subjects.

Impact of cardiopulmonary bypass on peripheral tissue metabolism and microvascular blood flow

The aim of this study was to monitor and compare the changes in metabolism and blood flow in the skeletal muscles during cardiac operations performed with cardiopulmonary bypass (CPB) and operations without CPB (off-pump) by means of interstitial microdialysis (Figure 1). Surgical revascularization, coronary artery bypass grafting (CABG), was performed in 40 patients randomized to two groups. Twenty patients (On-Pump Group) were operated on using CPB, 20 patients (Off-Pump Group) were operated on without CPB. Interstitial microdialysis was performed by 2 probes of a CMA 60 (CMA Microdialysis AB, Solna, Sweden) inserted into the patient's deltoid muscle. Microdialysis measurements were performed at 30-minute intervals. Glucose, lactate, pyruvate and glycerol as markers of basic metabolism and tissue perfusion were measured in samples from the first probe, using a CMA 600 Analyzer (CMA Microdialysis AB). Blood flow through the interstitium was monitored by means of dynamic microdialysis of ethanol as a flow-marker in the dialysates taken from the second probe (ethanol dilution technique). Results in both the groups were statistically processed and compared. Both the groups were similar in respect of preoperative characteristics. Dynamic changes of interstitial concentrations of the measured analytes were found in both the patient groups (on-pump vs. off-pump) during the operation. There was no significant difference in dialysate concentrations of glucose and lactate between the groups. Significant differences were detected in pyruvate and glycerol interstitial concentrations, lactate/pyruvate ratio and lactate/glucose ratio between the on-pump vs. off-pump patients. In the Off-Pump Group, pyruvate concentrations were higher and the values of concentrations of glycerol lower. The lactate/pyruvate ratio and the lactate/glucose ratio, indicating the aerobic and anaerobic tissue metabolism status, were lower in the Off-Pump Group. There was no significant difference in dialysate concentrations of ethanol as a flow-marker during the surgery in either of the groups. There was no statistically significant difference between the groups (On-Pump Group vs. Off-Pump Group) comparing the postoperative clinical outcome (ICU stay, ventilation duration, length of hospital stay). The dynamic changes in the interstitial concentrations of the glucose, glycerol, pyruvate and lactate were found in both the groups of patients (On-Pump Group and Off-Pump Group), but there was no difference in local blood flow when the ethanol dilution technique was used. These results showed significantly higher aerobic metabolic activity of the peripheral tissue of patients in the Off-Pump Group vs. the On-Pump Group during the course of cardiac revascularization surgery. Results suggest that extracorporeal circulation, cardiopulmonary bypass, compromises peripheral tissue (skeletal muscles) energy metabolism. These changes have no impact on the postoperative clinical outcome; no significant difference between the groups was found.

Insulin and contraction increase nutritive blood flow in rat muscle in vivo determined by microdialysis of L-[14C]glucose

In the present study, a mathematical model using the microdialysis outflow: inflow (O/I) ratio of the novel analogue L-[14C]glucose has been developed which allows the calculation of the nutritive (and non-nutritive) flow in muscle as a proportion of total blood flow. Anaesthetized rats had microdialysis probes carrying L-[14C]glucose inserted through a calf muscle group (tibialis/plantaris/gastrocnemius). The nutritive fraction of total blood flow was determined under basal conditions and in response to contraction (electrical field stimulation), insulin (hyperinsulinaemic euglycaemic clamp with 10 mU min(-1) kg(-1) insulin) or saline control from limb blood flow and the microdialysis O/I ratio of L-[14C]glucose. Both contraction and insulin infusion decreased the O/I ratio of L-[14C]glucose and increased total limb blood flow. Calculations based on mathematical models using L-[14C]glucose O/I and limb blood flow revealed that during basal conditions, the nutritive fraction of total flow was 0.38 +/- 0.06, indicating that basal flow was predominantly non-nutritive. Contraction and insulin increased the nutritive fraction to 0.82 +/- 0.24 (P < 0.05) and 0.52 +/- 0.12 (P < 0.05). Thus the increase in limb blood flow from insulin was fully accommodated by nutritive flow, while contraction increased nutritive flow at the expense of non-nutritive flow. This novel method using microdialysis and the O/I ratio of L-[14C]glucose allows the determination of the nutritive fraction of total flow in muscle as well as the proportion of total flow that may be redistributed in response to contraction and insulin.

Intraoperative Management of Hyperglycemia in the Cardiac Surgical Patient

The stress response of cardiac surgery leads to hyperglycemia, and undergoing cardiopulmonary bypass magnifies this response greatly. Counter-regulatory hormones, the cytokine response, and the automatic nervous system are all part of the coordinated host response that can lead to hyperglycemia. Postoperative hyperglycemia is associated with worsened perioperative outcomes, and there are data demonstrating this to also be true for the intraoperative period. Many factors affect intraoperative glucose control, including cardiopulmonary pump (CPB) prime fluid composition, temperature while on CPB, and medications such as catecholamines and glucocorticoids. Intraoperative glucose control has a significant impact on postoperative outcomes. No optimal intraoperative insulin regimen has been identified, but continuous intravenous infusions appear to be superior to intermittent sliding scale dosing. In addition, the technique of hyperinsulinemic glucose clamp shows the greatest promise of achieving normoglycemia while on CPB.

Post-operative myocardial dysfunction does not affect the physiological response to early mobilization after coronary artery bypass grafting

BACKGROUND

An acute increase in oxygen demand can be compensated for either by increased cardiac index (CI) or increased oxygen extraction, resulting in reduced mixed venous oxygen saturation (SvO2). We tested the hypothesis that post-operative cardiac dysfunction may explain why oxygen extraction alone is increased during early mobilization after cardiac surgery.

METHODS

Twenty patients with a pre-operative ejection fraction > 50% were included in an open prospective observational study comparing the changes in SvO2 and hemodynamics during mobilizations immediately prior to surgery and on the first post-operative morning.

RESULTS

Mobilization induced an absolute reduction in SvO2 of 17.7 +/- 7.4% pre- and 19.0 +/- 5.5% post-operatively (NS). ANOVA for a series of measurements throughout the mobilization sequence identified no different effect on SvO2 between pre- and post-operative mobilizations (P = 0.567). The SvO2 level was reduced post-operatively resulting in a SvO2 during standing exercise of 55% before and 49% after the surgery (P < 0.01). Mobilization increased the heart rate (HR) and decreased the stroke volume index (SVI), leaving CI unchanged. This response was similar pre- and post-operatively (NS). Compared with pre-operative measurements, CI and HR increased post-operatively while SVI remained unchanged despite elevated cardiac filling pressures and reduced systemic vascular resistance. The left ventricular stroke work index was reduced, indicating reduced myocardial performance.

CONCLUSION

Myocardial function was reduced on the first morning after coronary artery bypass grafting (CABG), but during post-operative mobilization this reduction did not significantly influence the changes in CI or SvO2.