An Evidence-Based Approach to Non-Invasive Ventilation in Cardiac Rehabilitation after Coronary Artery Bypass Grafting (CABG)

Abstract

Pulmonary impairment and decreased functional capacity are significant concerns following cardiovascular surgery, leading to extended hospital stays and mortality. Non-invasive ventilation (NIV) can provide significant prophylactic and therapeutic benefits in pre-operative and postoperative respiratory failure following coronary artery bypass grafting (CABG) surgery. Despite scant data, non-invasive ventilation outcomes are promising in phase I cardiac rehabilitation. There exists evidence that validates the utilization of non-invasive ventilation in the acute phase of cardiac rehabilitation and its application in patients following CABG; this context continues to be a subject of controversy within the existing body of literature. The purpose of this chapter is to demonstrate the efficacy of non-invasive ventilation as a prophylactic and therapeutic intervention for patients undergoing coronary artery bypass grafting (CABG) surgery, with the obvious aim of mitigating the occurrence of postoperative pulmonary dysfunction and decreased functional capacity.

1. Introduction

According to the World Health Organization (WHO), cardiovascular illnesses are responsible for a total of 17.9 million deaths annually. This figure is equivalent to around 32% of the overall world mortality rate. It is anticipated that coronary artery disease (CAD) will be the dominant contributor to morbidity and death in the realm of cardiovascular illness by the year 2030, resulting in about 23 million people losing their lives as a direct consequence of the condition [1]. Coronary artery bypass grafting (CABG) is a surgical procedure that has been found to enhance lifelong longevity and improve the overall individual’s standards of life afflicted with moderate to severe coronary artery disease. In contrast to the transient respiratory and functional capacity impairment experienced in the immediate aftermath of CABG surgery, the enduring advantages of CABG confer a lifelong benefit that enhances functional mobility and facilitates independent engagement in daily living activities. Almost all individuals who had CABG surgery experienced transient acute postoperative pulmonary complications (PPC). Nevertheless, when suitable preventive measures are implemented in the acute phase of cardiac rehabilitation, these short-time acute respiratory and functional abnormalities often exhibit favorable responses. The severity of PPC encompasses a spectrum of manifestations, including pain, weakness of the respiratory muscles, atelectasis, collapse of the lungs, reduced lung volume, profound hypoxia, and skeletal muscle weakness. In more severe cases, PPC may cause respiratory compromise and acute respiratory distress syndrome (ARDS), both of which are linked to escalated healthcare costs and excessive utilization of resources [2]. CABG’s mechanism often causes transient, acute postoperative pulmonary impairment. Many aspects must be considered during intraoperative procedures. These parameters include median sternotomy, anesthesia, surgery time, cardiopulmonary bypass (CPB), administration of blood-related substances, local hypothermia for heart protection, and harvesting of the internal mammary artery. Postoperative mechanisms encompass various factors that contribute to heightened pain resulting from the median sternotomy, intercostal drainage tubes, phrenic nerve impairment, augmented respiratory effort, compromised cough reflex, hypoxemia, and skeletal muscle weakness associated with diminished functional mobility. Additionally, specific preoperative variables exert an influence on postoperative pulmonary dysfunction, encompassing pre-existing lung diseases, smoking habits, advanced age, obesity, obstructive sleep apnea (OSA), heart failure, and inadequate nutritional status. During the process of rehabilitation, a notable proportion of patients who undergo heart surgery, specifically 10%, experience considerable pulmonary dysfunction. The occurrence of this condition is subject to variation, contingent upon the severity of the pulmonary complications that arise after the surgical procedure. During the initial days following cardiac surgery, three prevalent postoperative pulmonary complications that may endure are atelectasis, pleural effusion, and pneumonia [3, 4]. Furthermore, it is worth noting that hypoxia is observed in approximately 79% of cases, while hypercapnia is observed in approximately 38% of cases, typically within the first 24 h following the transition from the critical care unit. Despite the utilization of modern surgical techniques and improved postoperative care, postoperative pulmonary complications following CABG continue to exist and remain a significant cause of both mortality and morbidity. For the past two decades, NIV has been the commonly employed initial treatment for acute respiratory failure characterized by hypoxia or hypercapnia, which is often observed during chronic obstructive pulmonary disease exacerbations, cardiogenic pulmonary edema, and pneumonia. Due to the positive outcome observed with non-invasive ventilation, there has been a decrease in the necessity for endotracheal intubation. Nevertheless, there is a limited body of scientific research that has investigated therapeutic approaches aimed at preventing or mitigating pulmonary complications after cardiac surgery. Historically, chest physical therapy and the utilization of an incentive spirometer have been employed as methods to mitigate and manage postoperative pulmonary complications. While reintubation and mechanical ventilation are frequently utilized in the therapeutic care of patients experiencing respiratory failure and they are accompanied by various adverse outcomes including pneumonia, infections, increased expenses, morbidity, and mortality. Numerous modern clinical research has examined NIV efficacy in the prevention or reduction of postoperative complications in the acute phase of cardiac rehabilitation among individuals undergoing cardiac surgery. However, it is worth noting that there is limited research available on the potential benefits of non-invasive ventilation in reducing pulmonary complications and increasing functional capacity after extubation following CABG surgery.

The objective of this chapter is to demonstrate the efficacy of NIV as a prophylactic and therapeutic intervention for patients undergoing CABG surgery, with the specific aim of mitigating the occurrence of postoperative pulmonary dysfunction and decreased functional capacity. Additionally, this chapter aims to provide insights into the potential benefits of utilizing NIV in the acute phase of cardiac rehabilitation as an alternative therapeutic approach in the post-CABG population. Specifically, it will explore the potential effects of NIV on various aspects such as atelectasis, functional capacity, tissue perfusion, pulmonary function, reintubation rates, length of hospitalization, and overall functional capacity. The objective of this chapter is to furnish physiotherapists and healthcare providers with a comprehensive outline of NIV in the subsequent headings. These aspects must be taken into account in the management of inpatient clinical settings to guarantee the safety and efficacy of NIV therapy.

1. Physiology of non-invasive ventilation

2. The physiological mechanisms underlying respiratory failures after cardiac surgery

3. The application of non-invasive ventilation in prophylactic and therapeutic settings in cardiac surgery

4. Modalities of non-invasive ventilation (NIV)

5. Failure of non-invasive ventilation (NIV)

6. NIV interfaces and start-up

7. Untapped opportunities in the non-invasive ventilation (NIV)

8. Non-invasive ventilation (NIV) as an aid to cardiac rehabilitation (phase-I)

9. Future research

2. Physiology of non-invasive ventilation

NIV refers to a respiratory life support device that utilizes positive pressure and mask interfaces, eliminating the need for invasive ventilation methods such as the use of an endotracheal breathing tube. The primary importance of non-invasive ventilation (NIV) lies in its ability to alleviate the workload on the respiratory muscles and uphold adequate levels of arterial blood oxygen (PO₂) and carbon dioxide (PCO₂). The physiological effects of non-invasive ventilation (NIV) bear a resemblance to those of invasive ventilation, which involves the use of an artificial airway. However, several physiological effects distinguish non-invasive ventilation (NIV). Firstly, it is crucial to acknowledge that while there are advanced leak compensation NIV machines available, only a limited number of NIV machines are capable of delivering complete pre-determined pressure and volumes that are comparable to invasive ventilation. These leaks can have an impact on the sensitivity of triggering during flow delivery and the breath cycle, consequently affecting the synchrony between the patient and the ventilator. Non-invasive ventilation (NIV) is administered to the oronasal pharynx, which serves as connection between the esophagus and the trachea. Although gastroesophageal sphincters are present, the occurrence of elevated positive pressures in the esophagus can result in the expansion of the stomach. Hence, there is a notable risk of aspiration for the trachea when it is not adequately protected. The effectiveness of pulmonary hygiene techniques, such as pulmonary toilets and airway suctioning, is impeded. To mitigate exhalation leaks, the utilization of a single-limb circuit can potentially result in heightened carbon dioxide (CO₂) retention, commonly referred to as re-breathing, particularly when flow delivery settings are set at lower levels. Non-invasive ventilation (NIV) also offers notable benefits in comparison to invasive ventilation. The maintenance of glottic function in NIV results in a minimal risk of aspiration. The potential for non-invasive ventilation (NIV) breaks to enable patients to engage in speech and swallowing is a noteworthy aspect to consider. Furthermore, the level of irritation experienced by the airway due to trans-laryngeal intervention is relatively low, which could enhance patient comfort and potentially reduce the requirement for sedation when compared to invasive ventilation. NIV has been shown to effectively maintain upper respiratory tract patency in individuals diagnosed with obstructive sleep apnea. Additionally, in patients suffering from congestive heart failure, NIV has demonstrated the potential to mitigate the occurrence of pulmonary edema and reduce venous return. Improper administration of NIV can result in lung damage, similar to the adverse effects observed with invasive ventilation. The application of non-invasive ventilation (NIV) exerts a positive pressure, thereby alleviating the strain on the inspiratory muscles. It enhances pulmonary compliance by facilitating the dilation of obstructed alveoli, thereby enabling enhanced efficiency in the exchange of gases within the lungs, specifically oxygenation, and ventilation. Consequently, there is an enhancement in respiratory mechanics, potentially leading to the prevention of reintubation. The application of NIV during the acute phase of cardiac rehabilitation in post-cardiac surgery patients has been found to yield several direct advantages, such as the prevention of atelectasis and pneumonia, enhancement of functional capacity and pulmonary function, improvement in tissue perfusion, reduction in hospitalization duration, as well as decreased morbidity and mortality rates. One notable advantage of NIV in the context of post-cardiac surgery is its ability to prevent the need for reintubation. Reintubation carries various risks, involving prolonged invasive ventilation, pneumonia, infection, shock, ICU and hospital stays, and death. Non-invasive ventilation (NIV) has been found to optimize heart function after extubation by reducing inspiratory effort and left ventricular (LV) afterload. Moreover, NIV can be administered both as a prophylactic and as a therapeutic intervention. Additionally, it has the effect of normalizing or reducing the stress response and discomfort experienced after surgery, while also minimizing the occurrence of complications and enhancing the overall outcomes associated with cardiac surgical procedures [5, 6, 7].

3. The physiological mechanisms underlying respiratory failure after cardiac surgery

Acute respiratory failure, characterized by hypoxic and/or hypercapnic respiratory failure, can manifest in a significant proportion of individuals who have undergone cardiac surgery. This occurrence can be attributed to various factors, including pre-existing comorbidities such as advanced age, restrictive or obstructive lung disease, and heart failure, as well as perioperative and postoperative influences such as general anesthesia, duration of surgery, atelectasis, pleural effusion, and incisional pain. Hypoxemic respiratory failure can manifest following cardiac surgery due to postoperative pulmonary dysfunction, which encompasses various conditions such as aspiration, atelectasis, pneumonia, pulmonary edema, and acute respiratory distress syndrome. These aforementioned conditions collectively hinder the efficient transfer of oxygen across the alveolar-capillary membrane in the pulmonary system, resulting in a partial pressure of oxygen (PaO₂) below the threshold of 60 mmHg. In the context of clinical environments, the established approach to managing hypoxemic respiratory failure involves the administration of oxygen therapy in conjunction with chest physical therapy. Similar to what was mentioned earlier, hypercarbia respiratory failure (hypoventilation) can occur after cardiac surgery when there is insufficient removal of carbon dioxide from the distal alveoli. This leads to respiratory acidosis, characterized by an elevation in the partial pressure of carbon dioxide (PaCO₂) above 45 mmHg, along with concurrent hypoxemia. Nevertheless, the primary factors contributing to hypercarbia encompass prolonged neuromuscular blockade after cardiac surgery, excessive sedation, and respiratory exhaustion [8, 9, 10].

4. The application of non-invasive ventilation in prophylactic and therapeutic settings in cardiac surgery

As mentioned earlier, individuals who undergo cardiac surgery face an increased susceptibility to experiencing pulmonary complications and decreased functional capacity following the procedure. Despite the limited availability of data, the use of NIV in the acute phase of cardiac rehabilitation as a preventive and therapeutic intervention has the potential to reduce or prevent postoperative pulmonary complications, including atelectasis, reintubation rates, impaired tissue perfusion, and skeletal muscle weakness associated with decreased functional capacity.

4.1 Atelectasis

Atelectasis is a medical condition distinguished by the partial or complete collapse of a lung or a specific segment of a lung. Atelectasis frequently occurs following cardiac surgery and is a prevalent contributor to hypoxia and impaired gas exchange. Atelectasis is a common finding in postoperative chest radiographs following cardiac surgery, with a prevalence ranging from 30% to 72%. It is considered a significant factor in the development of respiratory dysfunction after surgery [11, 12]. Specifically, basal atelectasis is observed in 94% of patients within the initial 48-hour period after CABG surgery. Irrespective of the administration method, be it intravenous or inhalational, it is observed that the majority of patients undergoing general anesthesia encounter atelectasis during both spontaneous respiration and following the administration of muscle paralytics [13]. CABG surgery induces changes in respiratory mechanics, leading to diminished expiratory flow, reduced ciliary rate, and impaired cough reflex, ultimately resulting in atelectasis and pneumonia. These complications can subsequently contribute to heightened respiratory effort and diminished lung capacity. Failure to appropriately treat and manage atelectasis may result in compromised pulmonary function, the development of pneumonia hospital-acquired, and an extended duration of hospitalization. Typically, conventional postoperative physiotherapy after CABG involves the integration of an incentive spirometer and respiratory exercises. In a randomized controlled study comprising 26 patients who underwent CABG, the control group (CG) exhibited an atelectasis rate of 61.5%, while the NIV group demonstrated a rate of 54% (P = 0.691). Following the surgical procedure, it was observed that the group receiving NIV exhibited a significantly greater vital capacity (P 0.015). This study demonstrates that NIV is highly favored by patients who experience heightened discomfort as a result of pain perception [14]. In a study conducted by Matte et al. [15], it was observed that 30% of patients who underwent treatment with incentive spirometry and 15% of patients who received treatment with CPAP or BIPAP exhibited mild or moderate atelectasis on the second day following their surgery. The study sample consisted of 96 patients. Nevertheless, there was a notable enhancement in oxygenation and a decreased decline in lung volumes. According to Pasquina et al. [16]. A study found that 60% of patients who underwent non-invasive ventilation (NIV) with BIPAP experienced an improvement in their radiological atelectasis score, while only 40% of patients who underwent NIV with CPAP showed a similar improvement. Similarly, the application of continuous positive airway pressure (CPAP) to individuals who encountered postoperative atelectasis after cardiac procedures (as indicated by radiographic evidence) resulted in a notable enhancement of the condition, as assessed through radiological scoring. According to a study conducted by researchers [16], it has been observed that atelectatic lung zones have the potential to reduce functional residual capacity and elevate pulmonary shunt, even in cases where heart surgery has been performed successfully without any complications. The presence of unventilated atelectatic lung zones can contribute to nearly 20% of the overall lung capacity, resulting in hypoxemia following CABG [17]. According to this perspective, the initiation of NIV serves to prevent the collapse of alveoli and facilitate improved recruitment of alveoli, thereby mitigating the occurrence of atelectasis and augmenting functional residual capacity.

4.2 Pulmonary function assessment

The presence of a limited capacity to produce autonomous deep inhalations leads to the manifestation of restrictive breathing patterns, and the etiology of this restrictive breathing pattern is characterized by multiple contributing factors. While CABG surgery has proven to be a successful method for coronary revascularization, it is frequently linked to a restrictive breathing pattern and declined pulmonary function, which in turn may result in adverse health outcomes and even death. The etiology of impaired pulmonary function after CABG surgery is multifactorial, encompassing various factors such as a reduced expansion of the rib cage and disorganized movement of the chest wall, dysfunction of the diaphragmatic dysfunction due to phrenic nerve injury, accumulation of pleural fluid, and the occurrence of basal atelectasis. Nevertheless, it is worth noting that a decrease in pulmonary function can also be attributed to respiratory muscle dysfunction, characterized by a reduction in both functional residual capacity (FRC) and vital capacity (VC). In the initial week following coronary artery bypass graft (CABG) surgery, there is a notable decline of 30–60% in slow vital capacity. This reduction persists at a diminished level of 12% even after a duration of up to 1 year. A significant decrease in preoperative functional residual capacity (FRC) values, amounting to 70%, is observed for a duration of at least 7–10 days. Additionally, there is a reduction of 40–50% in vital capacity (VC) compared to preoperative levels, which persists for a period of 10–14 days. Nevertheless, in the context of postoperative cardiac surgery, the occurrence of a restrictive breathing pattern and hypoxemia is predominantly inevitable, although subject to potential modification [14]. According to Stell et al. [18], the utilization of NIV in the postoperative acute phase of cardiac rehabilitation has been found to enhance vital capacity, a critical metric for assessing the likelihood of reintubation. Additionally, NIV can decrease the load on the respiratory system and enhance pulmonary functions through the activation of closed alveoli, thereby opening up the atelectasis lung. Consequently, NIV demonstrates superiority over alternative techniques in facilitating deep breaths, leading to enhanced lung volume and capacities among patients who exhibit uncooperative behavior, excessive sedation, or an inability to engage in deep breathing due to pain, particularly in the immediate postoperative phase following cardiac surgery [18, 19]. Franco et al. [14] discovered notable disparities in vital capacities among two cohorts of patients who underwent heart surgery. The measured values in the NIV group were 2.64, 0.99, 1.53, and 1.94 before the operation, immediately after extubation, and 24 and 48 hours after extubation, respectively. In contrast, the control group had values of 2.11, 0.90, 0.90, and 0.97 [20]. The NIV group exhibited superior performance as a result of the patient’s active engagement in generating deep breaths, thereby mitigating discomfort experienced during physical exertion. Furthermore, this intervention is advantageous for patients who exhibit reluctance in performing deep inhalations after cardiac surgery.

4.3 Reintubation rate

Reintubation may occur in critically ill postoperative cardiac surgery patients, despite adherence to the recommended weaning protocols. The rates of reintubation in a critical care unit following general surgical procedures vary between 1% and 13%, while the rate after cardiac surgery is approximately 6.6%. The act of reintubation has been found to increase the duration of mechanical ventilation, which in turn leads to an extension of both the length of stay in the intensive care unit (ICU) and the overall hospital stay. Reintubation has been widely recognized as an independent factor contributing to elevated mortality rates. Therefore, it can be inferred that patients who necessitate reintubation exhibit an unfavorable prognosis, as evidenced by a mortality rate ranging from 30% to 40%. A cohort of 1640 patients admitted to the intensive care unit (ICU) underwent a retrospective analysis and revealed a reintubation rate of 7.3% (n = 119), with 36 patients (30.3%) undergoing CABG surgery. The majority of patients undergoing cardiovascular surgery exhibit a range of medical conditions, including hypertension, diabetes, hyperlipidemia, as well as comorbidities such as pneumonia and renal failure. Additionally, there is an increased likelihood for these individuals to necessitate re-intubation, as well as exhibit inferior scores in terms of SOFA, APACHE II, and Euro SCORE. Remarkably, the cohort that did not undergo non-invasive ventilation before reintubation exhibited a greater mortality rate. Consequently, a multitude of studies advocates for the prompt implementation of non-invasive ventilation (NIV) following extubation as a proactive approach to mitigate the risk of extubation failure, mitigate complications, and reduce the duration of hospitalization. Based on a recent extensive analysis, the utilization of NIV after cardiothoracic surgery has been shown to enhance individuals’ oxygenation levels, decrease the likelihood of postoperative complications, and diminish the need for endotracheal intubation [21, 22].

4.4 Tissue perfusion

Tissue perfusion refers to the process by which blood is delivered to and circulated within the various tissues of the body. Blood lactate and central-venous oxygen saturation (ScvO₂) have been identified as important and separate factors that can predict the occurrence of complications and death after cardiac surgery, especially in patients with left ventricular failure. Nevertheless, there exists a correlation between tissue hypoxia and negative postoperative outcomes, including skeletal muscle weakness, systemic acute inflammation, septic shock, and acute renal failure. Postoperative complications are often exacerbated by low ScvO₂ levels and elevated blood lactate values, leading to prolonged hospitalization and heightened rates of morbidity and mortality. A deviation from normal ScvO₂ levels, such as a lower value of 68% or a higher value exceeding 80%, may suggest an augmented rate of oxygen extraction to fulfill the metabolic requirements of organs. Additionally, this condition may be accompanied by an elevation in anaerobic energy production and the accumulation of blood lactate. The potential benefits observed after the implementation of NIV in individuals with left ventricular (LV) dysfunction can be attributed to its ability to improve cardiac function by reducing inspiratory effort and LV afterload. There is empirical evidence suggesting that NIV can potentially improve cardiac function through the modification of cardiac morphology. Elevated pleural pressure, subsequently leading to a decrease in transmural pressure, results in a reduction in both left-ventricle preload and afterload. This phenomenon induces an instantaneous impact on cardiac function in response to positive pressure. As a result of this observation, a proposition has been put forth suggesting that the application of positive pressure could potentially augment cardiac function and myocardial contractility. The utilization of bi-level positive airway pressure is advised due to the findings of a randomized controlled trial, which indicated that it yielded a greater improvement in left ventricular ejection fraction compared to continuous positive airway pressure in individuals diagnosed with systolic dysfunction [23]. According to Ranucci et al., blood lactate levels exhibited an increase of over threefold when the central venous oxygen saturation (CvO₂) reached a value of 68%. The combined assessment of blood lactate levels and ScvO₂ has the possibility to serve as a valuable clinical tool in distinguishing the etiology of elevated lactate levels, specifically whether they are attributed to hypoperfusion or other causative factors. In comparison to the cessation of mechanical ventilation (extubation), the initiation of NIV resulted in an increase in ScvO₂. Conversely, the termination of mechanical ventilation (extubation) led to a decrease in ScvO₂ [24]. Nevertheless, there was no alteration observed in arterial blood oxygenation (SaO₂). The findings indicate that enhanced distribution of blood flow, resulting in improved tissue perfusion, has a positive impact on heart function. Furthermore, the utilization of NIV contributes to a reduction in the effort required for respiration, primarily due to its assistance in supporting the function of the inspiratory muscles [25]. The occurrence of dyspnea in the early stages of heart failure can be ascribed to a redistribution of blood circulation toward the peripheral muscles during periods of physical exertion. Even during periods of inactivity, the reduced capacity of the respiratory and peripheral muscles to undergo oxidation processes may result in an elevation in oxygen consumption and an inadequate provision of oxygen to meet the body’s demands. NIV utilization has been demonstrated to decrease the effort required for respiration, leading to enhanced blood flow distribution and subsequent improvement in the perfusion of tissues and improved skeletal muscle weakness [26]. The application of non-invasive ventilation (NIV) in different clinical scenarios resulted in a significant decrease in blood lactate levels and an increase in central venous oxygen saturation (ScvO₂). The utilization of NIV in the acute phase of cardiac rehabilitation following CABG surgery can effectively promote tissue perfusion.

4.5 Functional capacity

Functional capacity refers to an individual’s capability for executing tasks and engaging in activities in an approach that aligns with functional objectives. The occurrence of a significant decrease in functional capacity after undergoing heart surgery is well-documented in the literature. Several factors have been identified as contributors to this decline in functional capacity, including respiratory compromise, tissue perfusion, peripheral muscle dysfunction, and reduced cardiac function. Consequently, the utilization of non-invasive ventilation (NIV) in the acute phase of cardiac rehabilitation shortly after the removal of an endotracheal tube can effectively enhance pulmonary function and oxygenation. This, in turn, facilitates the peripheral muscle’s blood flow, ultimately resulting in enhanced physical functional performance [27]. Additionally, the use of non-invasive ventilation (NIV) reduces the elevated workload on the respiratory system and enhances the delivery of blood to tissues by augmenting the left ventricular afterload function, ultimately leading to optimal cardiac output. In their study, Cordeiro et al. [28] demonstrated that the immediate implementation of NIV in the acute phase of cardiac rehabilitation following extubation yields a significant enhancement in pulmonary function. However, it is worth noting that an enhancement in circulatory function and peripheral muscle perfusion has been shown to have a positive impact on walking and physical exercise performance [28]. Based on data obtained from the Brazilian Registry of Clinical Trials, the 6-minute walk test showed that the control group averaged 264.34 m and the experimental group 334.07 m. Three NIV sessions with a positive pressure of 10 cmH₂O for 1 h within 26 h after extubation yielded these outcomes. A 0.002 p-value showed a significant difference between the groups [29].

4.6 Acute respiratory failure (ARF)

Acute respiratory failure (ARF) is a medical condition categorized by the insufficient ability of the respiratory system to effectively oxygenate the blood and eliminate carbon dioxide. ARF is a commonly observed condition that occurs after cardiac surgery, particularly among individuals with pre-existing lung disease and undergoing major heart surgery. The study revealed that individuals who underwent cardiac surgical procedures that involved a combination of factors such as low ejection fraction and severe SAPS II scores were identified as being at the greatest susceptibility for the development of ARF following the surgery. In a study conducted by Filsoufi et al. [30], a cohort of 5798 individuals who underwent heart surgery within a six-year timeframe was examined. The researchers found that the incidence of acute renal failure (ARF) reached its peak at 9.1%, with a total of 529 cases [30]. ARF is predominantly observed in patients undergoing both valve and CABG procedures, with a prevalence rate of 14.8%. In a study conducted over a span of 4 years, Kilger et al. [31] examined a cohort of 2261 individuals who underwent cardiac surgery. The findings of the study revealed that 35% of the patient population experienced post-extubation ARF. Furthermore, it was observed that intermittent NIV treatment proved beneficial for 33% of these patients. ARF following extubation is a significant complication that has the possibility to elevate both morbidity and mortality rates [31]. The administration of early NIV therapy in the acute phase of cardiac rehabilitation after extubation demonstrated efficacy in mitigating the occurrence of respiratory compromise following extubation in a population at high risk. Patients diagnosed with hypoxemic ARF have the potential to successfully circumvent the need for endotracheal intubation. In a clinical study involving 94 patients with ARF, it was observed that 89 individuals (94%) were able to successfully avoid the need for endotracheal intubation through the implementation of NIV. Notably, initiating NIV within a timeframe of 3 h following a minor decline in the proportion of arterial oxygen partial pressure to fractional inspired oxygen (PaO₂/FIO₂) was found to be advantageous for patients with moderate hypoxemic respiratory failure after cardiovascular surgery. This finding holds a significant interest. Nevertheless, it is imperative to prioritize early intubation and exercise caution when selecting patients for NIV. Additionally, it is important to note that a 24-h interval between extubation and NIV initiation poses a substantial risk for NIV failure [32, 33]. In a randomized controlled trial, it was determined that a score exceeding 20 on the Acute Physiologic Assessment and Chronic Health Evaluation (APACHE) II is an independent risk factor for NIV failure in patients who undergo extubation for acute respiratory failure (ARF) [34]. Nevertheless, the occurrence of reintubation ranges from 6% to 52% among patients who undergo NIV following cardiac surgery [17]. After undergoing cardiothoracic surgery, the implementation of NIV therapies demonstrated enhanced oxygenation and a decreased necessity for reintubation. The use of NIV proved to be a secure and effective strategy for managing postoperative ARF in a cohort of 83 patients. These individuals were discharged to their homes after receiving NIV to treat respiratory failure after heart surgery, which took place outside of the critical care department [35]. According to the available evidence, individuals diagnosed with hypoxemic ARF have the possibility to successfully circumvent the need for endotracheal intubation. In a clinical study involving a cohort of 94 patients diagnosed with ARF, it was observed that 89 individuals (94%) were able to successfully avoid the need for endotracheal intubation through the implementation of NIV. NIV in the acute phase of cardiac rehabilitation has been identified as a secure and feasible alternative for managing cases of postoperative ARF in settings outside of the critical care department, provided that careful monitoring is maintained.

5. Modalities of non-invasive ventilation

Non-invasive positive pressure ventilation (NIPPV) refers to oxygen delivery through a face mask, utilizing either constant or variable pressures. Examples of NIPPV include bi-level positive airway pressure (BiPAP) and constant positive airway pressure (CPAP). A significant proportion of medical practitioners opt for uncomplicated and easily transportable NIV devices. BiPAP (IPAP and EPAP) devices have been specifically engineered to provide two adjustable pressure levels. There are two types of positive airway pressure: inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP). CPAP is administered exclusively through the use of expiratory positive airway pressure (EPAP). A limited number of machines possess time modes that allow for the delivery of pressure support (PS) at pre-established intervals [36]. In addition to their primary function, invasive ventilators can deliver NIV. However, it should be noted that older models of ventilators may generate frequent alarms related to “air leaks” when used for NIV ventilation. This is primarily because these older models cannot adequately adjust for changes in airflow. The more recent iterations of ventilators have addressed the issue of leakage in the ventilator circuit through the implementation of microprocessors. These microprocessors are responsible for monitoring the variations in inspiratory and expiratory tidal volumes during the initial breath cycle. Consequently, the peak inspiratory flow experiences an increase without a concomitant increase in the inspiratory time. CPAP modes are frequently employed in conventional ventilators to deliver NIV. Currently, the chosen CPAP and PS levels align with the IPAP and EPAP configurations of the conventional portable NIV. It is advisable to consider that the PS setting on the conventional ventilator provides an additional level of PS beyond the specified CPAP level. In contrast, the pressure support of the IPAP in a typical portable NIV machine incorporates the configured EPAP. Therefore, the PS provided by a portable device, measured at 14 and 8 cm H₂O, is equivalent to the delivery of 6 and 8 cm H₂O by a standard ventilator. If the patient requires supplementary breaths, the utilization of the synchronized intermittent mandatory ventilation (SIMV)-pressure control mode may be considered. The inclusion of non-invasive ventilation pressure support (NIV PS) has become prevalent in contemporary ventilators. In the present scenario, the inspiratory pressure and positive end-expiratory pressure (PEEP) are adjusted to meet the required breaths, while the PS and CPAP are adjusted to regulate the patient’s ventilation during spontaneous breaths.

6. Failure of non-invasive ventilation

Endotracheal intubation (ETI) becomes necessary in situations where NIV proves ineffective, as the alternative outcome would be the patient’s demise. The study results specify that there is a distinct association between NIV failure and mortality specifically in patients with ARF. This observation suggests that the utilization of NIV applications should be approached cautiously. The primary factors contributing to the failure of NIV in the acute phase of cardiac rehabilitation of postoperative CABG patients are characterized by inadequate monitoring and a lack of attentiveness toward the patients’ response to NIV therapy. NIV failure can be categorized into three distinct time periods: immediate failure, which occurs within minutes to less than 1 hour; early failure, which transpires between one and 48 h; and late failure, which manifests after 48 h. Simultaneously, it is important to take into account additional factors such as the size of the mask, circuit leaks, and inadequate trigger levels. These aspects can be adjusted according to the patient’s comfort to achieve the most favorable outcome. Nevertheless, despite these interventions, if respiratory distress persists, it is advisable to contemplate discontinuing NIV and instead opt for elective intubation and mechanical ventilation. The ratio of arterial oxygen (PaO₂) to inspired oxygen (FiO₂), commonly referred to as the PaO₂/FiO₂ ratio, along with baseline indicators such as heart rate and respiratory rates, serve as prognostic factors for determining the success or failure of NIV in cases of acute respiratory failure [37, 38, 39]. In a separate investigation on acute postoperative respiratory insufficiency, it was observed that the PaO₂/FiO₂ ratio exhibited a decline after 1 hour of NIV therapy. Several randomized controlled trials (RCTs) conducted on patients in intensive critical care units have made predictions about the failure of NIV in cases of postoperative ARF. These predictions include factors such as the worsening of pre-existing diseases, high scores on the Simplified Acute Physiology Score (SAPS) II, scores on the Acute Physiology and Chronic Health Evaluation (APACHE) II, presence of multiple organ dysfunctions, acute respiratory distress syndrome (ARDS), community-acquired pneumonia, and shock [40, 41]. Evidence-based research insists on the cautious selection of patients or the avoidance of NIV therapies in CABG patients experiencing severe acute respiratory failure. Recent studies have indicated a correlation between delays in the intubation process and adverse outcomes, as well as heightened mortality rates in the affected population.

7. NIV Interfaces and start-up

The crucial factor contributing to the success of NIV in the acute phase of cardiac rehabilitation is purely based on the careful selection of an appropriate mask, encompassing considerations of patient comfort, optimal fit, and tolerance. Currently, there are various interfaces for NIV, including oronasal masks, nasal masks, nasal pillows, full-face masks, and helmets. However, there is not much actual data to show that one technique is better than the other. The utilization of a full-face mask has been observed to result in oronasal dryness and claustrophobic sensations. However, it effectively mitigates the occurrence of air leaks in the vicinity of the eyes and mouth, while also alleviating discomfort experienced above the nasal bridge. Oronasal masks, conversely, are frequently employed in clinical settings [42]. Proper monitoring of non-invasive ventilation (NIV) following extubation is essential. It is crucial to engage in preoperative discussions with the patient regarding the significance and procedural techniques associated with NIVs. This proactive approach is vital as it contributes to the patient’s postoperative comfort. It is recommended that patients receive an adequate dosage of analgesics and be positioned at an inclination of no less than 35 degrees before initiating non-invasive ventilation (NIV). The initiation of the NIV (CPAP Mode) involves the implementation of low-pressure support (PS) to facilitate the patient’s prompt adaptation to the administered pressure, thereby synchronizing with their respiratory pattern. Once the patient has achieved a satisfactory level of respiration comfort, progressively increase the pressure support (PS) and secure the head straps as necessary. The increment of the PSs should be tailored to the individual patient to achieve a reduction in breathing effort and ensure appropriate synchronization. To ascertain the veracity of clinical alterations, it is recommended to procure arterial blood gas measurements within a time frame of 1–2 h. The subsequent step involves the utilization of an inspiratory volume trigger, which can vary between 1 and 2 L/min, or an inspiratory pressure trigger, ranging from 1 to 2 cm of water. This trigger is implemented with a moderate to maximal slope. Typically, in the initial stages of utilizing the NIV mode known as BiPAP, it is common practice to apply minimal levels of expiratory positive airway pressure (EPAP) at 4 cm of water and inspiratory positive airway pressure (IPAP) at 8 cm of water, which is 4 cm higher than the EPAP level. The EPAP and IPAP levels can be incrementally increased by 1–2 cm of H₂O until reaching a maximum of 10 cm of H₂O for EPAP and 25 cm of H₂O for IPAP. If there is a need for increased pressure, it may be required to make adjustments to the interface, optimize the fit of the mask, or consider the option of intubation [43].

8. Untapped opportunities in the non-invasive ventilation (NIV)

Irrespective of the benefits ascribed to the utilization of NIV in the acute phase of cardiac rehablitation, there exists considerable heterogeneity in the approaches employed for its implementation across different healthcare institutions worldwide. A significant proportion, specifically 30%, of medical practitioners/respiratory physiotherapists do not perform an initial blood gas analysis before initiating non-invasive ventilation (NIV). In a study involving a sample of 3000 physicians, it was found that 648 individuals, constituting 21.6% of the participants, reported utilizing NIV in the critical care unit setting. Among these respondents, 469 physicians, accounting for 72.4% of the NIV users, reported incorporating NIV into their clinical practice, representing approximately 68.4% of their overall patient care. Furthermore, it was observed that a significant proportion of physicians, specifically 71.4%, reported employing NIV frequently for managing chronic obstructive pulmonary disease (COPD) exacerbations [44]. The routine utilization of NIV for the prevention or treatment of respiratory failure after CABG surgery was not observed. According to a retrospective analysis spanning 6 years, it was observed that among patients with acute respiratory failure who satisfied the eligibility criteria for the NIV trial, only 34% received NIV, while a significant majority of 66% required endotracheal intubation [45]. One evident factor contributing to the underutilization of the NIV is the presence of inadequate comprehension and insufficient training among medical practitioners, including doctors and respiratory therapists. To optimize the results of NIV in the acute phase of cardiac rehabilitation, it is recommended to seek virtual tutoring and training as a means to mitigate failures and enhance the utilization of NIV during the postoperative period [46].

9. Non-invasive ventilation (NIV) as an aid to cardiac rehabilitation (phase-I)

In healthy elderly people, 10 days of bed rest reduces quadriceps strength by 20% [47]. After CABG surgery, pulmonary function and skeletal muscle weakness are the main factors reducing ADLs. Despite early mobilization and chest physiotherapy, cardiac surgery patients often develop pulmonary dysfunction and muscular weakness. This might worsen post-operative outcomes if preoperative variables such as loss of body tissue, physical inactivity, altered metabolism, multiple comorbidities, decreased LV functions and age were present. Generally, pulmonary dysfunction and muscular inactivity are caused by surgical stress and pain which is the most reversible component after cardiac surgery [48]. In this context, cardiac rehabilitation is an effective therapy for patients with cardiovascular disease that improves pulmonary, functional capacity, and quality of life, as well as reducing hospital admissions and health care costs. Cardiac rehabilitation consists of three phases: phase-1 (clinical phase), phase-2 (outpatient cardiac rehabilitation), and phase-3 (post-cardiac rehabilitation maintenance). Phase 1 cardiac rehabilitation starts in the critical care units (if the patient is stable). Rehabilitation intensity depends on the patient’s medical state and acute illness complications. Following CABG and after extubation NIV could be considered as a prophylactic and therapeutic tool to improve pulmonary gas exchange in postoperative patients. This, in turn, facilitates the peripheral muscle’s blood flow, ultimately resulting in enhanced physical mobility. The frequency and duration of non-invasive ventilation (NIV) treatment, regardless of its prophylactic or therapeutic nature, are exclusively determined by the patient’s medical condition and their level of participation.

Despite evidence of extensive research supporting the advantages of NIV associated with cardiac rehabilitation, the level of patient participation in such programs remains notably deficient. According to data obtained from Medicare and the Centers for Disease Control and Prevention (CDC), it has been shown that around 31% of patients who had coronary bypass grafting surgery participated in or were enrolled in cardiac rehabilitation or secondary prevention programs. Qualitative research done in 2017 on how patients felt about cardiac rehabilitation showed that the severity of the cardiovascular illness or incident, the presence of pre- and post-psychological obstacles, such as time constraints and exercise-related apprehension in phase I cardiac rehabilitation, and the patient’s future goals were some of the things that affected the patients’ feelings about cardiac rehabilitation and their participation in the program [49]. Hence, the cardiac rehabilitation team needs to consider NIV as prophylactic or therapeutic, based on the patient’s medical conditions and other factors, when formulating phase I cardiac rehabilitation programs for patients.

10. Future research

Previous research investigations have highlighted the potential advantages of NIV for individuals undergoing cardiovascular surgery, both before and after the procedure. However, there is a dearth of empirical evidence to substantiate this assertion. Further investigation is warranted to ascertain the appropriate recipients, timing, and methodologies for treatment. It is observed that individuals who undergo cardiac surgery have a higher propensity for developing pulmonary complications. Consequently, the timely administration of NIV in selected patients has the potential to substantially reduce the duration of hospitalization and demonstrate cost-effectiveness. Unfortunately, there is currently a lack of available data about the economic aspects of the subject matter. It would be beneficial to undertake additional comprehensive research to examine the complexities associated with non-invasive ventilation (NIV). Moreover, it is imperative to undergo training to ensure the efficacy and safety of NIV. To facilitate the implementation of non-invasive ventilation (NIV) interventions, the cardiac thoracic intensive care unit (CTICU) must establish a consistently available NIV service and employ a skilled team comprising of a physician and a respiratory physiotherapist who possess extensive knowledge and expertise in NIV techniques [50].

11. Conclusions

The use of established guidelines, evidence-based training, and practical application have together enhanced the efficacy of non-invasive ventilation (NIV) in phase-I of cardiac rehabilitation. The involvement of a healthcare practitioner, such as a physician or respiratory physiotherapist, who has the requisite knowledge and is ready to dedicate extra time to the initiation and execution of non-invasive ventilation (NIV) therapy is essential for the initiation of NIV therapy. Nevertheless, more research using randomization is required to demonstrate empirical support for the use of non-invasive ventilation (NIV) in patients who have had coronary artery bypass graft (CABG) surgery, particularly during the phase-I cardiac rehabilitation.