Intensive care unit length of stay in OPCABG and ONCABG
Our study found that ICU LOS was significantly longer in OPCABG patients than in ONCABG patients. The result shows a gap between recent theories and practices in the authors' study centre. Some information regarding the issue was collected to explain the phenomenon. The authors found some problems arise following the CABG procedure, regardless of the technique; the problems are transient left ventricular dysfunction, capillary leak, warming from hypothermia, and emergence from anaesthesia. These problems contribute to the course of treatment in the intensive cardiac care unit. 
Although improvements in surgical procedures, cardioplegia delivery, and other myocardial protective characteristics over the last decade, the observed prevalence of transient left ventricular systolic failure (90%) did not vary between the late 1970s and the early 1990s. Transient myocardial depression has been linked by some authors to a lack of myocardial protection or the effects of cold cardioplegia. However, the majority of data points to cardiopulmonary bypass’s (CPB) inflammatory condition as the primary causal component. OPCABG is expected to prevent myocardial harm by lowering the inflammatory response, whether the lowered ventricular function is caused by oxygen free radicals or myocardial ischemia associated with cardioplegia. OPCABG significantly reduces the inflammatory response. However, it is essential to note that OPCABG does not entirely reduce the inflammatory response, as other factors such as surgical trauma and anaesthetic drugs have a role. While systemic vascular resistance does not arise immediately after surgery, it does rise as ventricular function deteriorates. This increase in systemic vascular resistance is most likely a result of decreased ventricular function and the need to maintain systemic blood pressure rather than being a primary cause of decreased cardiac contractility. It is essential to notice the confusing effect of vasopressor medicines to raise systemic blood pressure. Endothelial cells are also damaged by the inflammation-induced generation of oxygen free radicals and the release of proteolytic enzymes by neutrophils.  The endothelium's "gatekeeper" function is disrupted, and capillary permeability rises, resulting in oedema. Depending on the degree of CPB duration, the capillary leak syndrome might continue anywhere from a few hours to 1 to 2 days. Intravascular volume overload is a risk when the capillary leak stops and the interstitial oedema fluid is mobilized. . Hypothermia raises systemic vascular resistance, causes shaking (which increases O consumption and CO generation), and affects coagulation.  Severe postoperative bleeding (more than 10 U of blood transfused) is common after heart surgery, with an incidence of 3-5%. 
Advantages of OPCABG over ONCABG demonstrate that transient left ventricular dysfunction and capillary leak are minimal since the inflammatory effect of CPB usage is avoided; moreover, warming from hypothermia seems not to be a significant problem. We believe that issues with the anaesthetic strategy may cause the longer intensive care treatment course in OPCABG patients based on that description.  The provision of safe induction and maintenance of anaesthesia using a technique that offers maximum cardiac protection, maintenance of hemodynamic stability throughout surgery with the help of adequate monitoring and pharmacological support, and early emergence and ambulation in conjunction with excellent postoperative analgesia are among the anaesthetic goals of management of OPCABG surgery.  Hemmerling et al.  discuss the anaesthetic technique utilized for OPCABG to fulfil the goals. Hemmerling et al. state that the heart rate should be kept between 70 and 80 beats per minute, MAP > 70 mmHg, and SvO2 > 70%, and that clinicians should ensure adequate preload and apply for Trendelenburg position, repositioning the heart in the holding device, and vasopressors and/or inotropes (phenylephrine, dopamine, or norepinephrine) administration to treat hypotension. Fast extubation is a difficult decision for OPCABG patients due to hemodynamic instability caused by ischemia prevention and heart position throughout the operation. Anesthesiologists will utilize a lot of intravenous fluid and vasoconstrictor agents if there is hypotension during the surgery. This might result in volume overload and later interstitial oedema, which must be addressed during postoperative care, extending the treatment course by inadvertently delaying extubation. However, our data never mention any information about hypotension, vasoconstrictor agent use, volume overload, or duration of intubation in OPCABG patients.
In many studies, there has been mentioned that OPCABG shortens hospital of ICU LOS. Studies that support the statement are those conducted by Islam et al.  and Brewer et al. .Both studies mention that the off-pump technique shortens the course of treatment in hospitals and ICUs. Nonetheless, the study never discusses why off-pump can shorten the length of stay. In contrast, our study found that the length of stay in OPCABG patients was longer than in ONCABG patients. Unfortunately, information regarding the possibility of prolonged hospital and ICU length of stay in OPCABG was never demonstrated in other articles. The authors reflect on the results and found that the application of OPCABG still relies on clinicians' preparation, operators, and other supporting clinicians like anesthesiologists and cardiologists in dealing with the technique to get the desired outcome, especially to shorten the length of stay. The above explanation about post-CABG problems that usually arise and anaesthetic consideration for extubation in OPCABG might explain prolonged ICU LOS in OPCABG patients; despite many results in other centres, OPCABG can shorten the length of stay. However, the data from the authors' centre to support the explanation was still unclear.
Mortality in OPCABG and ONCABG
The degree to which a patient tolerates the CABG treatment, the natural course of the disease, the procedural complexity, and the postoperative recovery are all factors that influence mortality.  In this scenario, post-CABG mortality is linked to complications following the surgery, and ONCABG is the most common cause of these issues. It explains why ONCABG was found to have a lower death rate than OPCABG. However, there was no significant difference in mortality between the two groups in this study.
The use of a CPB machine in ONCABG, as well as the manipulation of the ascending aorta, has been linked to several perioperative complications, including myonecrosis during aortic occlusion, cerebrovascular accidents, generalized neurological deficits (e.g., stroke, coma, postoperative neurocognitive dysfunction), renal dysfunction (increased incidence of postoperative renal failure requiring dialysis), and the Systemic Inflammatory Response (SIRS). 
Many studies have attempted to propose strategies for dealing with such issues. Some researchers have utilized S100 beta serum concentrations to measure brain injury, and increased serum levels have been linked to the number of microemboli exiting the CPB circuit during CABG. On the other hand, others have observed a higher incidence of microemboli with on-pump CABG (as compared to off-pump CABG) but have not observed a comparable impairment in neurocognitive function one week to six months after surgery. Lipid material and particle matter have been highlighted as possible causes of postoperative neurocognitive dysfunction in blood collected from the operating field after on-pump CABG. 
After significant morbid events such as trauma, infection, or major surgery, SIRS manifests as a broad systemic inflammation.  Surgical trauma, contact of blood with nonphysiological surfaces (e.g., pump tubing, oxygenator surfaces), myocardial ischemia and reperfusion, and hypothermia all combine to cause a dramatic release of cytokines (e.g., interleukin (IL-6 and IL-8) and other inflammatory mediators after on-pump cardiac surgery. SIRS has been observed in patients undergoing CPB, prompting the development of measures to avoid or reduce its recurrence.  Increased serum concentrations of cytokines (e.g., IL-2R, IL-6, IL-8, tumour necrosis factor-alpha) and other inflammatory modulators (e.g., P-selectin, sE-selectin, soluble intercellular adhesion molecule-1, plasma endothelial cell adhesion molecule-1, and plasma malondialdehyde) that reflect leukocyte and platelet activation have been linked  A study found that patients who had a 50% increase in serum creatinine concentration after CPB had more elevation of neutrophil CD11b expression (a sign of leukocyte activation), indicating activated neutrophils in the pathogenesis of SIRS and the incidence of post-CPB renal impairment. The effects of modifying neutrophil activation to lessen the development of SIRS have been studied; however, the results have been mixed.  These cytokines had lower serum concentrations after CPB after preoperative intravenous methylprednisolone (10 mg/kg). This reduction, however, was not linked to improved hemodynamic indicators, reduced blood loss, less use of inotropic drugs, shorter ventilation times, or shorter ICU stays.  Similarly, intravenous immunoglobulin G has not been linked to lower rates of short-term morbidity or 28-day mortality in patients with post-CPB SIRS. Other strategies for preventing SIRS after CPB have been investigated, such as using CPB circuits (including oxygenators) coated with materials known to reduce complement and leukocyte activation, CPB tubing covalently bonded to heparin, and CPB tubing coated with polyethylene oxide polymer or Polyethylene oxide polymer (2-methoxyethyl acrylate).  After CPB, plasma concentrations of P-selectin, intercellular adhesion molecule-1, IL-8, plasma endothelial cell adhesion molecule-1, and plasma malondialdehyde were lower after leukocyte depletion via customized filters in the CPB circuits. Finally, closed CPB microcircuits have been designed to reduce blood–air interface and blood interaction with nonbiological surfaces, stimulating cytokine generation. However, whether these manoeuvres and procedures have a discernable impact on CABG outcomes is unknown. 
OPCABG, unlike ONCABG, is done on a beating heart utilizing stabilizing devices (which minimize cardiac motion). It also includes strategies to reduce myocardial ischemia and systemic hemodynamic instability. As a result, CPB is no longer required. This approach does not eliminate the requirement to manage the ascending aorta during the proximal anastomosis creation.  According to Head et al. , 25% of CABG procedures were conducted off-pump in 2001. The current rate of OPCABG procedures in the Western world is 20%, but in Asia, most treatments are performed off-pump. By avoiding cardiopulmonary bypass, which is linked with microemboli formation, increased blood-brain barrier permeability, and aortic manipulation during cross-clamping and cannulation, OPCABG could theoretically reduce morbidity, notably stroke and mortality. In that study, the off-pump method was superior to ONCABG in terms of mortality (OR = 0.69, 95 per cent CI 0.60-0.75, p = 0.0001). 
A study conducted by Brewer et al.  supports our findings. The study demonstrates no difference in operative mortality for OPCAB patients compared within ONCAB patients (ONCABG, 1.8%; OPCABG, 2.3%; p = 0.259). However, another study conducted by Islam et al.  mentions the risk of mortality increases with the ONCABG technique as it increases SIR's incidence, which can cause mortality from septic shock. Hillis et al.  mention in the ACCF/AHA Guideline for Coronary Artery Bypass Graft Surgery that around the year 2005, an AHA scientific statement comparing the two techniques concluded that regardless of some studies about the comparison of both procedures, both generally result in excellent outcomes and that neither technique should be considered superior to the other. Because CPB maintains systemic circulation, surgeons often favour ONCABG in patients with hemodynamic impairment. OPCABG, on the other hand, is favoured by some surgeons who have substantial experience with it and are therefore familiar with its technical aspects. According to the explanations, ONCABG was better for mortality than OPCABG because of the impacts of the CPB machine, SIRS, and cerebrovascular accidents. However, our study suggests that there is no significant difference in mortality in both techniques in the authors' centre.