Annals of Cardiac Anaesthesia 2005; 8: 39–44
ORIGINAL Shinde et al. Blood Lactate LevelsARTICLES during CPB 39
Blood Lactate Levels During Cardiopulmonary Bypass for Valvular Heart Surgery Santosh B Shinde, Kumud K Golam, Pawan Kumar, Neela D Patil Departments of Biochemistry, Anaesthesiology, and Cardiovascular and Thoracic Surgery, Lokmanya Tilak Municipal Medical College and Hospital, Sion, Mumbai
Cardiopulmonary bypass (CPB) is widely used to maintain systemic perfusion and oxygenation during open-heart surgery. Tissue hypoperfusion with resultant lactic acidosis during CPB, may occur during hypothermia, extreme haemodilution, low flow CPB, and excessive neurohormonal activation. There has been no documentation of the correlation between blood lactate level elevations in the perioperative period, and its relation to preoperative New York Heart Association (NYHA) classification and the use of ionotropic support during weaning from CPB, duration of postoperative ventilatory support and perioperative mortality. We studied the perioperative blood lactate levels in 82 patients undergoing valvular heart surgery. Arterial blood samples were collected at different stages of CPB. The observed mean baseline lactate levels were 1.9±0.8 mmol/L (normal range of 0.9 to 1.7 mmol/L). The mean circulating lactate levels at 15 min and 45 min after institution of CPB increased to 7.01±2.6 mmol/L and 9.92±3.5 mmol/L. A progressive decline in the mean lactate level, was seen during rewarming (at 35°C), immediately off-bypass, 24 hours and 48 hours postoperatively with mean lactate levels being 7.01±3.2 mmol/L, 4.75±1.01 mmol/L, 3.06±1.1 mmol/L, and 2.10±1.05 mmol/L respectively. Comparison of mean lactate levels in NYHA class I, II, III, and IV patients showed that in the intraoperative period and immediately after CPB, the elevation in lactate levels were statistically significant (p< 0.001) in patients in NYHA Class IV. However the values, in all classes, were similar at 24 and 48 hours after CPB. Also, patients with lactate levels >4 mmol/ L required prolonged inotropic and ventilatory support. (Annals of Cardiac Anaesthesia 2005; 8: 39–44) Key words:- Lactic acidosis, CPB, Hyperlactataemia, NYHA classification
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ardiopulmonary bypass (CPB) is instituted, during various cardiac operations, to allow adequate systemic perfusion. Presently there are no definitive biochemical markers of prognostic value in patients undergoing valvular heart surgery under CPB. Tissue perfusion is at risk during CPB and in the immediate postoperative period.1 The duration of CPB, degree of hypothermia, duration of cooling and rewarming, pH management strategy and the haematocrit value are all potential factors that may contribute to tissue hypoperfusion during CPB.1 In addition, factors like impaired venous drainage or Address for Correspondence: Dr. K. K. Golam, D2/10 KINARA, 358, Municipal Tenements, A.G. Road, Worli Seaface, Mumbai 400 018 Email:
[email protected]
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anatomic lesions characterised by reduced splanchnic flow or excessive systemic runoff may limit perfusion. Finally the systemic inflammatory response to CPB may also impair tissue oxygenation and perhaps more specifically, tissue oxygen extraction.1 Improvements in CPB and overall haemodynamic management have reduced the incidence of severe perioperative tissue hypoperfusion.2 It is an established fact that tissue hypoperfusion is associated with lactic acidosis secondary to anaerobic metabolism. Measurement of blood lactate levels can, hence be used as a marker to assess the adequacy of tissue perfusion.2 Glycolysis is the first step of glucose metabolism and occurs in the cytoplasm of virtually all cells.
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40 Shinde et al. Blood Lactate Levels during CPB
The end product of this pathway is pyruvate, which can then diffuse into mitochondria and get metabolised to carbon dioxide by the Kreb’s cycle.3 Increased blood lactate may occur with or without concomitant metabolic acidosis. Such hyperlactataemia is usually seen in subclinical tissue hypoperfusion, secondary to elevated blood catecholamine levels. This is either stress induced, due to administration of catecholamine or due to alkalosis where buffering systems are able to mitigate any fall in the pH.4 This study was conducted to establish blood lactate level, as a prognostic tool, in patients undergoing valvular heart surgery under CPB. The following were evaluated: - Lactate levels and its correlation with preoperative clinical condition (as per New York Heart Association). - The intra and postoperative outcomes, following CPB for valvular heart surgery. Methods Eighty two consecutive patients undergoing valvular heart surgery under CPB were included in this study. On the basis of history, the patients were allocated to their respective class as per the NYHA functional classification5 (Table 1). The departmental review board of Lokamanya Tilak Municipal Medical College and General Hospital approved the study. Diabetic patients on treatment with phenformin were excluded from the study. The reason being that in this group there is increased peripheral extrasplanchnic glucose utilisation by a shift from oxidative to anaerobic metabolism. As such they have been associated with development of lactic acidosis. Anaesthesia Technique On the day of surgery, the patient was premedicated with morphine (0.2 mg/kg) and promethazine (0.5 mg/kg) intramuscularly about 30-45 minutes prior to induction of anaesthesia. Anaesthesia was induced with thiopentone (5 mg/ kg) and vecuronium was used to accomplish endotracheal intubation with appropriate sized
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Annals of Cardiac Anaesthesia 2005; 8: 39–44
tube, (generally 9.0 mm for males and 7.5 mm for females). Anaesthesia was maintained with 50% oxygen (O2), 50% nitrous oxide (N2O) along with halothane 0.5% to 1%. Morphine (0.05 mg/kg) was given before incision and 0.15 mg/kg was added to the pump prime. Additional morphine (0.1 mg/kg) and vecuronium (0.1 mg/kg) were administered during rewarming. Post-CPB anaesthesia was maintained with 50% O2, 50% N2O, halothane 0.5 to 1%, and vecuronium (1/4th of induction dose). The bypass circuit was primed with a mixture of Ringer’s lactate and gelofusine to make the priming volume 1500 ml. Standard bypass techniques with systemic hypothermia of 28-32ºC were employed. Mean arterial pressure was continuously monitored and maintained between 50 and 60 mm Hg. The haemoglobin was maintained between 6 and 8 gm%. Urine output was monitored throughout the procedure. Blood sugar was monitored using a glucometer intraoperatively and the sugar levels were maintained between 180 and 240 mg%. After surgery was completed, CPB was discontinued and heparin was neutralised with protamine. Patients received ionotropic support in the form of dopamine (5-10 µg/Kg/min) and adrenaline (0.06-0.6 µg/Kg/min) was added if required to attain the desired haemodynamic stability. Before shifting the patient to cardiac intensive care unit, morphine 0.1 mg/kg was given intravenously. In the intensive care unit the patient was electively ventilated with continuous monitoring of haemodynamic parameters and arterial blood gas analysis. Blood lactate level measurement: For measuring lactate levels, arterial blood was collected through the intra-arterial catheter (inserted for blood pressure monitoring) immediately after induction of anaesthesia. This was termed as the baseline sample. Subsequent samples were collected at the following intervals. - 15 minutes after institution of CPB - 45 minutes after institution of CPB (if any) - Rewarming (at 35°C)
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Annals of Cardiac Anaesthesia 2005; 8: 39–44
Shinde et al. Blood Lactate Levels during CPB 41
- Immediately after terminating the CPB - 24 hours post-surgery, and - 48 hours post-surgery. The blood samples were collected in a sample tube containing 3 ml of 5% metaphosphoric acid. Samples were stored in ice carriers and transferred to the laboratory where they were immediately centrifuged. The protein free filtrate was then collected in another tube for the estimation of lactate (using the spectrophotometer method at 340 nm). 6 The endpoint of the study was predetermined with the last sample being collected at 48 hours after termination of CPB. The one-way ANOVA was used for statistical analysis. Results Demographic data showed average age of 35±10.2 years with weight of 50±12.4 kg. There were 43 males and 39 females. Table 1 shows distribution of patients according to their NYHA class. Maximum patients (34) belonged to NYHA class II. Table 2 shows the distribution of various surgical procedures. Most patients (37) underwent mitral valve replacement. Table 3 shows mean lactate levels during the perioperative period. Table 4 shows the mean lactate levels in different NYHA class patients. No statistically significant changes were seen in NYHA class I, II and III. However,
NYHA class IV patients showed significant (p
