CARDIOVASCULAR JOURNAL OF AFRICA • Volume 35, No 3, September – October 2024 AFRICA 173 intra-operative variables, such as cardiopulmonary bypass time (CPBT) and aortic cross-clamp time (ACCT), were recorded. The serum lactate levels at seven different times were recorded: pre-operative (L0), at the start of CPB (L1), after aortic-cross clamping (L2), after aortic cross-clamp removal (L3), after CPB (L4), at ICU admission (L5), and postoperative first hour in ICU (L6). The difference between L0 and the peak level of lactate in the peri-operative period was indicated as ΔL. After the patients were taken to the operating room and monitored, anaesthesia induction was performed with intravenous fentanyl (1–5 µ/kg), midazolam (0.5 mg/kg), propofol (1–1.5 mg/kg), and rocuronium (0.6 mg/kg), according to haemodynamic stability. Anaesthesia was then maintained with an inhalation anaesthetic (sevoflurane, at one minimum alveolar concentration), and infusion of remifentanil (0.25 µ/kg/ min). Muscle relaxation was provided with rocuronium (0.2 mg/ kg) at intervals of 20–25 minutes. Surgical procedures were started with a median sternotomy. CPB was used for all isolated coronary artery bypass grafts (CABGs). During CPB, moderate systemic hypothermia was applied. During CPB, the flow rate was maintained between 2.2 and 2.5 l/min/m2, a perfusion pressure of 50–80 mmHg, and haematocrit between 20 and 25%. Following the surgery, the patient was extubated, determined by decisions based on clinical appearance, laboratory tests and lung imaging. Clinically, patients had to be awake and they had to be haemodynamically stabilised, moving the limbs, and without excessive bleeding (< 50 ml/h) or neurological deficit. Pneumothorax, atelectasis and severe pleural effusion should be excluded on the chest X-ray. Arterial blood gas analysis should show pH > 7.35, PaO2 > 70 mmHg and PaCO2 < 40 mmHg. Statistical analysis The Number Cruncher Statistical System (NCSS) 2007 (Kaysville, Utah, USA) program was used for statistical analysis. Descriptive statistical methods (mean, standard deviation, median, frequency, percentage, minimum and maximum) were used for evaluating the study data. The conformity of the quantitative data to the normal distribution was tested with the Shapiro–Wilk test and graphical examinations. The independent groups t-test was used for comparison of normally distributed quantitative variables between two groups, and the Mann– Whitney U-test was used for comparisons between two groups of non-normally distributed quantitative variables. Pearson’s chi-squared test and the Fisher–Freeman–Halton exact test were used to compare qualitative data. Diagnostic screening tests (sensitivity, specificity, positive and negative predictive values) and receiver operating characteristic (ROC) curve analysis were used to determine the cut-off value for the parameters. Statistical significance was accepted as p < 0.05. Results Data from 207 patients who underwent isolated CABG were obtained after excluding those who had had emergency and valve surgery as seen from scanning the files. There were 170 (82.1%) males and 37 (17.9%) females. The patients’ mean age was 59.60 ± 10.46 years and the mean BMI was 28.68 ± 4.76 kg/ m2. The extubation time of most of the cases (62.3%, n = 129) was less than six hours. There were no statistically significant differences between the subjects’ gender, age, BMI, the number of vessels worked on, EF, incidence of AF, DM, HT, COPD and heart failure (HF), use of inotropic drugs or IABP, and blood transfusion status according to extubation times (p > 0.05) (Table 1). However, it was observed that ACCT, CPBT and ∆L values were significantly different between the two groups (p = 0.001; p < 0.01), but pre-operative Hb values did not differ (p > 0.05) (Table 1). The distribution of peri-operative serum lactate levels is presented in Fig. 1. Mean lactate levels were observed to peak in L4. The lactate values of L2, L3, L4, L5 and L6 were found to be statistically significantly higher in cases where extubation time Table 1. Comparison of individual features, co-existing diseases and peri-operative data Variables Extubation time p-value < 6 hours (n = 129) ≥ 6 hours (n = 78) Gender: M/F, n 107/22 63/15 0.711a Age, mean ± SD 58.81 ± 10.32 60.91 ± 10.64 0.211c BMI, mean ± SD 28.70 ± 4.92 28.66 ± 4.52 0.948d Vessels, n (%) 6 (4.7) 2 (2.6) 0.537b 1 55 (42.6) 27 (34.6) 2 45 (34.9) 31 (39.7) 3 23 (17.8) 18 (23.1) 4 50.23 ± 9.52 48.21 ± 9.36 0.114c ACCT, mean ± SD 59.11 ± 22.04 70.68 ± 24.88 0.001c* CPBT, mean ± SD 96.57 ± 32.15 115.62 ± 31.23 0.001c* Pre-operative Hb, mean ± SD 13.25 ± 1.76 13.53 ± 1.53 0.232c DM, n (%) 39 (30.2) 18 (23.1) 0.264a HT, n (%) 55 (42.6) 36 (46.2) 0.621a COPD, n (%) 16 (12.4) 5 (6.4) 0.166a Heart failure, n (%) 19 (14.7) 11 (14.1) 0.901a Inotropes, n (%) 33 (25.6) 24 (30.8) 0.418a IABP, n (%) 18 (14) 13 (16.7) 0.596a AF, n (%) 20 (15.5) 9 (11.5) 0.426a Blood transfusion, n (%) 75 (58.1) 39 (50) 0.264a aPearson’s chi-squared test, bFisher–Freeman–Halton test, cMann–Whitney U-test, dStudent’s t-test, *p < 0.01. BMI: body mass index, Hb: haemoglobin, DM: diabetes mellitus, HT: hypertension, COPD: chronic obstructive pulmonary disease, IABP: intra-aortic ballon pump, AF: atrial fibrillation, ACCT: aortic cross-clamping time, CPBT: cardiopulmonary bypass time. Sampling times L0 L1 L2 L3 L4 L5 L6 Mean lactate values 3 2.25 1.5 0.75 0 Fig. 1. Distribution of lactate measurements. Red line: extubation time ≥ 6 hours; blue line: extubation time < 6 hours.
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