CARDIOVASCULAR JOURNAL OF AFRICA • Volume 35, No 3, September – October 2024 174 AFRICA was longer than six hours (p = 0.001; p < 0.01). However, L0 and L1 lactate values did not differ significantly (p > 0.05) (Table 2). In predicting extubation time, a statistically significant correlation was found between the cut-off value of 1.7 for L2; 1.9 for L3; 2.2 for L4; 2.1 for L5; 1.7 for L6 and 1.8 for ΔL (p < 0.01) (Table 3). ROC curve graphs of lactate levels and ΔL values are presented in Figs 2 and 3. The area under the curve of ΔL levels was more acceptable than the others (0.742). Discussion In this research, we examined the distribution of serum lactate levels in samples taken at different peri-operative times and their relationship with early extubation in patients undergoing isolated CABG surgery. It was observed that serum lactate levels reached peak levels after the ACC was removed. We concluded that lactate values from the onset of CPB to the postoperative period, as well as the difference between pre-operative and maximum lactate values (ΔL), measured in the peri-operative period, were high in late-extubated patients. However, among the variables we examined, only the duration of CPB and ACCT was longer in patients who were extubated late. Mechanical ventilation duration exceeding 24 hours after cardiac surgery is defined as prolonged ventilation and is seen in approximately 10% of patients.11,12 Prolonged mechanical ventilation increases the length of stay in the ICU and the cost of treatment. Therefore, prolonged mechanical ventilation is considered to be as serious a complication as stroke and acute renal failure.13 The negative outcomes of prolonged ventilation increase the need for early extubation protocols. Studies have shown that early extubation does not increase postoperative morbidity and mortality rates, even in high-risk patients.14 In addition, early extubation did not increase the risk of postoperative re-intubation.15 However, Richey et al.7 observed that the early extubation protocol shortened the ventilation time in cardiac surgery, but extended the length of stay in the ICU. In this study, the length of hospital stay did not affect other primary Table 2. Comparison of serum lactate levels, mmol/l Sampling times Extubation time p-value < 6 hours (n = 129) ≥ 6 hours (n = 78) L0, mean ± SD 1.11 ± 0.32 1.12 ± 0.28 0.798d median (min–max) 1.1 (0.5–1.9) 1.2 (0.6–1.7) L1, mean ± SD 1.32 ± 0.34 1.33 ± 0.39 0.830c median (min–max) 1.3 (0.5–2.1) 1.3 (0.7–3) L2, mean ± SD 1.58 ± 0.53 1.87 ± 0.75 0.001c* median (min–max) 1.5 (0.6–4.5) 1.9 (0.9–5.6) L3, mean ± SD 1.78 ± 0.55 2.11 ± 0.78 0.001c* median (min–max) 1.7 (0.7–3.6) 2 (0.7–5.3) L4, mean ± SD 2.28 ± 0.74 2.91 ± 1.14 0.001c* median (min–max) 2.1 (0.9–4.8) 2.6 (1.2–6.2) L5, mean ± SD 1.96 ± 0.87 2.61 ± 1.37 0.001c* median (min–max) 1.7 (0.8–5.2) 2.3 (0.9–6.5) L6, mean ± SD 1.67 ± 0.74 2.23 ± 1.10 0.001c* median (min–max) 1.5 (0.8–4.1) 2.2 (0.8–6.6) ΔL, mean ± SD 1.37 ± 0.69 2.39 ± 1.29 0.001c* median (min–max) 1.2 (0.3–3.7) 2.2 (0.4–5.6) cMann–Whitney U-test, dStudent’s t-test, *p < 0.01. Table 3. Diagnostic scans and ROC curve analyses for lactate levels in predicting extubation time Sampling times Diagnostic scan ROC curve p-value Cut-off value Sensitivity Specificity Positive predictive value Negative predictive value Area 95% CI L2 ≥ 1.7 69.23 60.47 51.40 76.50 0.641 0.563–0.720 0.001* L3 ≥ 1.9 66.67 64.34 53.10 76.10 0.648 0.572–0.724 0.001* L4 ≥ 2.2 75.64 53.49 49.60 78.40 0.667 0.590–0.743 0.001* L5 ≥ 2.1 58.97 65.89 51.10 72.60 0.629 0.547–0.711 0.002* L6 ≥ 1.7 58.97 64.34 50.00 72.20 0.657 0.578–0.737 0.001* ∆L ≥ 1.8 65.38 75.97 62.20 78.40 0.742 0.668–0.816 0.001* 1 – Specificity 0.0 0.2 0.4 0.6 0.8 1.0 Sensitivity 1.0 0.8 0.6 0.4 0.2 0.0 Fig. 3. ROC curve for ∆L. 1 – Specificity 0.0 0.2 0.4 0.6 0.8 1.0 Sensitivity 1.0 0.8 0.6 0.4 0.2 0.0 L2 L5 L3 L6 L4 Reference line Fig. 2. ROC curve for lactate levels.
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