According to World Health Organization estimates, 17.9 million people died from cardiovascular diseases in 2016, representing 31% of all global deaths (1). A significant number of these diseases require surgical treatments, with myocardial revascularization surgeries and correction of valvular diseases, followed by surgeries to correct aortic diseases and congenital heart defects, being the most common in adults and the elderly (2). Therefore, cardiac surgery is a complex procedure that has important organic repercussions, altering the physiological mechanisms of patients in different ways, leading to a critical postoperative state that implies the need for intensive care in order to establish a good recovery of the patients (3). Despite advances in cardiac surgery and perioperative care, postoperative complications remain frequent, leading to a substantial increase in mortality in patients undergoing these surgical procedures (4). Patients undergoing heart surgery undergo a series of pre-operative examinations and tests, so that surprises and complications do not occur. The procedure presents high morbidity and has its complications related to the preoperative situation and the cardiopulmonary bypass (CPB) used during the operation, making it necessary for patients undergoing these procedures to be well prepared hemodynamic ally and psychologically for the postoperative period (5) (6). The immediate postoperative period is the time of critical recovery that implies the need for intensive care in order to establish a good recovery for patients (7). Morbidity and mortality in the postoperative period of cardiac surgery is of great interest, motivating several postoperative management protocols (8)(9). Asymptomatic ischemic episodes are very common and seem to imply a worse prognosis (10) (11). The main risk factors for the emergence of organic changes in the postoperative period of cardiac surgeries are associated with: patient age, sex, previous medical history (existing underlying diseases), type of medication used preoperatively and risk factors. Intra-operative risk (type of surgery, length of stay on cardiopulmonary bypass, length of stay in hospital and use of specific medication) (12). Infectious processes have a high incidence, being one of the biggest causes of morbidity and mortality in surgical patients (13). When changes appear post-operatively, they must be identified and corrected as soon as possible, in order to guarantee the success of the surgery. Efforts need to be continuous to ensure good results from cardiac surgery (14). It is believed that the description and characterization of these complications through studies favor the construction of evaluation and intervention guides in this critical period of surgical recovery (15). The presence of lactate in human blood was described for the first time in 1843 by Joseph Scherer, a German chemist and physicist, after studying seven women who died after a febrile event during the postpartum period. In 1851, in a patient who died of leukemia, the German chemist once again identified the presence of this metabolite. Years later, Fletcher identified the production of lactic acid in skeletal muscle under anaerobic conditions. These observations, corroborated by other physiologists, were the basis for understanding the meaning of the elevation of this metabolite in critically ill patients (16)(17). Biomarkers have been defined as indicators of biological and pathological processes or indicators of response to pharmacological interventions, which attempt to separate what is normal from what is altered (18). Serum lactate, over recent years, has become an important and sensitive biomarker used as a prognostic tool in patients. Several metabolic changes contribute to the increase in lactate concentration in the body, including: catecholamines that promote the stimulation of the sodium/potassium pump; increased glycolysis; changes in the activity of the enzyme pyruvate dehydrogenase and decreased clearance, particularly through the liver (19). Recent studies have demonstrated that the increase or maintenance of lactate at high levels worsens the prognosis of patients (20). Under normal clinical conditions, the serum lactate concentration is less than 2 mmol/L and expresses the balance between production and lactate clearance (21). Oxygen delivery to tissues depends on hemoglobin levels, arterial oxygen saturation, and cardiac output. Decreasing any of these parameters results in a decrease in oxygen consumption when a critical level is reached. Significant reductions in oxygen delivery result in a decrease in oxygen consumption and, consequently, a sharp increase in lactate levels (22). Postoperative complications have a huge impact on morbidity and mortality, whether short or long term. According to Deng QW ET. al., a decrease in serum lactate is associated with a reduction in postoperative complications and, consequently, a reduction in morbidity (23). Therefore, correction of tissue hypoxia is extremely important to improve the prognosis of patients undergoing surgery.

The study is retrospective, descriptive, bibliographic and documentary, carried out through the analysis of medical records of 194 individuals aged between 25 and 82 years who underwent cardiovascular surgery, attended by Hospital São Lucas in the city of Cascavel/PR, in the years 2022 and 2023. Serum lactate levels were associated with total length of stay, length of stay in the ICU and intra- or post-operative complications, thus analyzing the importance of lactate for the clinical outcome.Data collection was carried out through the Hospital Medical Archive System (SAME), without the need for a Free and Informed Consent Form (TCLE), as the study analyzed electronic medical records of around 200 hospital patients without direct contact with the participants. . The exemption from informed consent was requested and approved by the ethics committee on 05/04/20223, under protocol: 68441023.5.0000.5219.

194 medical records were analyzed to study the complications that occurred in patients. Based on these complications, the patients were divided into three groups: A- had no complications and were subsequently discharged, B- had some complications and were also discharged later, and C- had an event that resulted in death.

In the first group, A, composed of 92 uneventful patients, representing 47.4% of the total, the average length of stay was 10 days, with 3.9 days of ICU stay (86 patients). The mean preoperative lactate level was 1.4 mmol/dl (72 samples), increasing to 2.64 mmol/dl postoperatively (91 samples), which represents an increase of 88%. The second postoperative sample collected had an average of 2.57 mmol/dl (87 samples), showing a 3% decrease compared to the first sample, and this downward trend continued until the patient's discharge. In the second group, B, composed of 80 patients who had some complications, representing 41.2% of the total, the average hospitalization increased to 17 days, that is, 70% longer than the group without complications, with an average of 7.2 days of ICU stay. The mean preoperative lactate level was 1.72 mmol/dl (67 samples), increasing to 3.3 mmol/dl postoperatively (78 samples), which represents an increase of 97%. As in the first group, a progressive decrease was observed in subsequent samples until the patient's discharge. In the last group, C, which had complications resulting in death, 22 patients were included, representing 11.3% of the total. The length of stay and duration in the ICU were shorter compared to the second group, with averages of 15 days and 10 days, respectively. The mean preoperative lactate level was 1.61 mmol/dl (21 samples). Postoperative lactate showed an average of 3.63 mmol/dl (22 samples), representing an increase of 125% compared too preoperatively. In subsequent samples, there was an increase of 44%, with an average of 5.24 mmol/dl (19 samples), and subsequently an increase of 4%, with an average of 6.57 mmol/dl (17 samples).

Table 1: Correlation between length of stay, ICU length of stay, serum lactate and 2nd serum lactate sample.

Increased serum lactate levels are a sensitive, non-specific and universal biomarker of adverse conditions in the body. A rapid decrease in this value indicates the correct path in stabilizing and treating the critically ill patient. However, the use of this biomarker is not easy and opinions about its value are still very different in the current literature (24). Blood lactate levels have been used in several situations, including as a marker of tissue hypoperfusion in patients with shock, an indicator of adequate resuscitation after shock, a post-resuscitation prognostic index, a prognostic factor in situations of serious illness (25) and as an etiological diagnosis (26)(27). The results of this research were compatible with other studies that analyzed serum lactate as a marker of morbidity and mortality, which, when elevated, was shown to be related to clinical worsening of patients and even death. We found that in patients where lactate remained at normal values, the patients did not experience any complications, associated with the length of hospital stay, which was also shorter than the others. Previous studies demonstrate that a lower lactate level was considered a predictor of survival and is associated with a better neurological outcome and a higher level was related to increased mortality (28)(29). Furthermore, a level of 3 mmol/L at six hours after admission to intensive care and a level of 2 mmol/L after twelve hours, identifies a group of patients, after cardiac surgery, with a worse prognosis and a mortality rate of 30 days higher. A lactate level greater than 3 mmol/L six hours after cardiac surgery is independently associated with a 3.3 times higher risk of major post-surgical complications, including death (30). In our study, it was seen that hyperlactatemia has been found in seriously ill patients, and numerous clinical investigations have demonstrated an association between its levels and the type of evolution, being higher in those who progress to death (31). In the research carried out, the average blood lactate of the group of patients who died was higher than that of the group that survived. In the study carried out by Andersen LW et. al., having found a difference between the groups in oxygen consumption, but no difference in lactate levels, may indicate that the increase in lactate, in this context, is not only related to oxygen consumption, it can occur in the absence of hypoperfusion and may reflect other mechanisms such as decreased hepatic clearance or excessive adrenergic stimulation (30). Furthermore, Smith et al. suggest that hyperlactatemia identifies patients at risk of mortality and can also be used as an indicator of ICU admission.

The present study showed that serum lactate has a relationship with the prognosis of patients in the postoperative period of cardiovascular surgery, in both sexes, different ages and ethnicities. Evaluating the quantification of serum lactate, it is noted that the higher the mean and progression of the biomarker in critically ill patients, the more numerous and severe the postoperative complications, also associated with worse clinical outcomes over time. As values considered in the predicted average, they are associated with a lower risk of these same events. Thus, the importance of the role of serum lactate as a prognostic biomarker in postoperative cardiovascular surgery patients is seen, being capable of improving patient management and thus avoiding adverse events that may occur.In conclusion, this study showed that the majority of patients who died had higher blood lactate levels than patients in the group who survived, and that, to predict death, serial monitoring is superior to isolated determination. Thus, becoming a guide for daily clinical risk management, making it possible to optimize care for patients in the postoperative period of cardiovascular surgery.

1. Of World Health Organization. Cardiovascular Diseases. Recuperado 28 de junho de 2019. De Cardiovascular Diseases.
2. jesus Bmde, Silva Srda, Carreiro Dl, Coutinho Ltm, Santos Ca and COUTINHO WLM. Relationship between Burnout Syndrome and health conditions among Army Military. Tempus Actas de Saúde Coletiva. 2016; 10: 11-28.
3. taniguchi Fp, Souza Ar, Martins As. Tempo de circulação extracorpórea como fator risco para insuficiência renal aguda. Rev Bras Cir Cardiovasc. 2007; 22: 201-5.
4. zheng Z, Jayaram R, Jiang L, Jzhao Ey, Li Q And Casadei B. Perioperative Rosuvastatin in Cardiac Surgery. New England Journal of Medicine. 2016; 374.
5. fernandes Ams, Mansur Aj, Canêo Lf, Lourenço Dd, Piccioni Ma And Franchi Sm. et al. Redução do período de internação e de despesas no atendimento de portadores de cardiopatias congênitas submetidos à intervenção cirúrgica cardíaca no protocolo da via rápida. Arq Bras Cardiol. 2004; 83: 18-26.
6. virani Ss, Nambi V, Razavi M, Lee Vv, Elayda M, Wilson Jm, et al. Preoperative statin therapy is not associated with a decrease in the incidence of postoperative atrial fibrillation in patients undergoing cardiac surgery. Am Heart J. 2008; 15: 541-6.
7. Soares Gmt, Ferreira Dcds And Gonçalves Mpc. Complicações Em Cirurgia Cardíaca. 2011; 24: 139–146.
8. azzolin Ko, Castro I, Feier F, Pandolfo F, Oderich C. Valor prognóstico do índice de performance miocárdica no pósoperatório de cirurgia de revascularização miocárdica. Arq Bras Cardiol. 2006; 87: 456-61.
9. lobo Filho Jg, Leitão Mca, Lobo Filho Hg, Soares Jph, Magalhães Ga, Leão Filho Csc. et al. Cirurgia de revascularização coronariana esquerda sem CEC e sem manuseio da aorta em pacientes acima de 75 anos. Rev Bras Cir Cardiovasc. 2002; 17: 208-14.
10. costa Mb, Magalhães Ss, Caldas Lr, Barral Mm, Souza Mc, Paula Rb. Valor do teste ergométrico na detecção da isquemia miocárdica silenciosa em pacientes diabéticos. HU Revista. 2008; 34: 107-12.
11. Dias Cmcc, Maiato Acca, Baqueiro Kmm, Figueiredo Amf, Rosa Fw, Pitanga Jo et al. Resposta circulatória à caminhada de 50 m na unidade coronariana na síndrome coronariana aguda. Arq Bras Cardiol. 2009; 92: 135-42.
12. abelha Fj, Botelho M, Fernandes V, Barros H. Outcome and quality of life after aorto-bifemoral bypass surgery. [Abstract]. BMC Cardiovasc Disord. 2010; 10: 15.
13. Hammermeister Ke, Burchfiel C, Johnson R, Grover Fl. Identification of patients at greatest risk for developing major complications at cardiac surgery. Circulation. 1990; 82: 380-9.
14. Soares, et al. Complicações em Cirurgias Cardíacas. Rev Bras Cardiol. 2011; 24: 139-146.
15. et al. Complicações do pós-operatório imediato de cirurgia cardíaca eletiva: estudo transversal. Revista de Enfermagem Referência, vol. IV núm. 22; 2019.
16. Okorie, O.N. And P. Dellinger, Lactate: Biomarker and Potential Therapeutic Target. Critical Care Clinics, 2011; 27: 299-326.
17. Vernon C. And Letourneau Jl. Lactic Acidosis: Recognition, Kinetics, and Associated Prognosis. Critical Care Clinics. 2010; 26: 255-283.
18. Lachmann, G. And K. Reinhart. The History of Biomarkers: How Far Have We Come? Critical Care Clinics. 2020. 36: 1-10.
19. vincent Jl. et al. The value blood lactate kinetics in critically ill patients: a systematic review. Crit Care, 2016; 20: 257.
20. mikkelsen, M. E.; Miltiades, A. N.; Gaieski, D. F. et al. Serum Lactato is associated with mortality in severe sepsis independent of organ failure and shock. Crit Care Med. 2009; 37: 1670-1677.
21. MATOS SIS. Nível de lactato como indicador prognóstico de mortalidade e morbilidade hospitalar. Instituto de Ciências Biomédicas Abel Salazar – Universidade do Porto. 2021.
22. Bakker Jr. Postelnicu And Mukherjee V. Lactate Where Are We Now? Critical Care Clinics 2020; 36: 115-124.
23. deng Qw. et al. Is goal-directed fluid therapy based on dynamic variables alone sufficient to improve clinical outcomes among patients undergoing surgery? A meta-analysis. Crit Care. 2018; 22: 298.
24. Bakker Jr. Postelnicu And Mukherjee V. Lactate: Where Are We Now? Critical Care Clinics. 2020; 36: 115-124.
25. Cruz Gf, Aviles-Rivera Dh, Fernandez-Sein A. Lactic acid levels as prognostic measure in acutely ill patients. Puerto Rico Health Sci J. 1991; 10: 9-13.
26. MIZOCK BA. Significance of hyperlactatemia without acidosis during hypermetabolic stress. Crit Care Med. 1997; 25: 1780-1.
27. kliegel A, Losert H, Sterz F, Holzer M, Zeiner A, Havel C et al. Serial lactate for prediction of outcome after cardiac arrest. Medicine (Baltimore). 2004; 83: 274-9.
28. Wang J et al. Predictors of survival and neurologic outcome for adults with extracorporeal cardiopulmonary resuscitation: A systemic review and meta-analysis. Medicine. 2018; 97: 4813257.
29. sumi Y. et al. Plasma Adenylate Levels are elevated in Cardiopulmonary Arrest Patients and May Predict Mortality. Shock. 2019; 51: 698-705.
30. hajjar La. et al. High lactate levels are predictors of major complications after cardiac surgery. J Thorac Cardiovasc Surg. 2013; 146: 455-60.
31. nguyen Hb, Rivers Ep, Knoblich Bp, Jacobsen G, Muzzin A, Ressler Ja. et al. Early lactate clearance is associated with improved outcome in severe sepsis and septic shock. Crit Care Med. 2004; 32: 1637-42.