Continuing Education Activity

Mechanical ventilation is an established supportive treatment for patients with various forms of respiratory failure. Despite the widespread use and clear benefits of mechanical ventilation, it is not a risk-free intervention. Prolonged mechanical ventilation increases the risk of pneumonia, barotrauma, tracheal injuries, and musculoskeletal deconditioning. At the same time, delayed weaning is associated with increased morbidity, mortality, hospital stay, and risk of long-term care facility discharge. The weaning process comprises almost 42% of the total duration of the ventilation. This activity describes the methods used to wean from the mechanical ventilator and highlights the interprofessional team's role in managing these patients.

Objectives:

• Identify the etiology of respiratory failure that lead to the need for ventilation.
• Outline the assessment of a patient being weaned from the ventilator.
• Summarize the approaches to weaning a patient from a ventilator.
• Explain interprofessional team strategies for improving care and outcomes in patients being weaned from the ventilator.

Introduction

Mechanical ventilation is an established supportive treatment for patients with various forms of respiratory failure. Despite the widespread use and clear benefits of mechanical ventilation, it is not a risk-free intervention. Prolonged mechanical ventilation increases the risk of pneumonia, barotrauma, tracheal injuries, and musculoskeletal deconditioning. At the same time, delayed weaning is associated with increased morbidity, mortality, hospital stay, and risk of long-term care facility discharge.[1][2]

For most patients (70%), weaning from mechanical ventilation is a straightforward process. That usually entails extubation after the passage of the first spontaneous breathing trial (SBT). The remaining 30% of patients represent a challenge for ICU physicians. Difficulties usually arise in patients with chronic obstructive and restrictive pulmonary disease, heart failure, and neuromuscular disorders, among other potential causes.

The weaning process comprises almost 42% of the total duration of the ventilation.[3] In our discussion, we review the most common barriers to successful ventilator weaning and the various extubation readiness assessment tools.[4][5][6]

Etiology

Respiratory Insufficiency

Arguably the most common mechanism underlying failure to wean patients off the ventilator. In its simplest form, the problem stems from an imbalance between respiratory pump capacity and demands.

Reduced Ventilatory Capacity  

The prolonged duration of mechanical ventilation, especially when accompanied by the use of passive modes of ventilation, can lead to diaphragmatic weakness and atrophy. Other factors contributing to respiratory muscle weakness include excessive steroids, sedatives, paralytic agent use, critical illness myopathy, a systemic inflammatory response associated with sepsis, malnutrition, and immobility. All of these factors are inherent to the ICU patient population; together, they trap the patient in a vicious circle where more weakness leads to more difficulty in weaning off the vent, leading to prolonged ICU stay and so forth.

Cardiovascular Insufficiency

Heart failure is another risk factor that can compound the ventilator weaning process. Important physiological changes occur during the process of transition from mechanical ventilation to spontaneous breathing. The most notable of which is a loss of positive intra-thoracic pressure. That results in an increase in venous return to the right ventricle and an increase in both preload and afterload. This is particularly relevant in the ICU patient population, most of whom have variable degrees of positive fluid balance. That increase in cardiac work can raise myocardial oxygen demand and precipitate ischemia in patients with coronary artery disease. 

Evaluation

There are many barriers to safe liberation from mechanical ventilation.[7] The aim is to accomplish opportune weaning (weaning within 24 hours of fulfilling the required criteria) while preventing premature or delayed weaning.[8]

Critical Steps in the Weaning and Extubation Process

1. Induction of Intermittent Mandatory Ventilation (IMV) after confirming the patient's readiness.
2. Spontaneous breathing trial (SBT) for at least 30 minutes.
3. Cuff-leak test. [9]

The most critical component in the weaning process is appropriately determining the patient's readiness to initiate the weaning process.[10]

Examining Readiness to Wean From Mechanical Ventilation

Despite the known hazards associated with prolonged mechanical ventilation, many patients remain unnecessarily intubated for more extended periods than needed. This knowledge stems from the fact that patients who accidentally self-extubate have a 31-78% risk of reintubation. That means the same patient population has a 22-69% chance of successfully weaning off mechanical ventilation. Even the most experienced clinicians may underestimate a patient's readiness for ventilator weaning.

This is why major critical care societies strongly encourage the implementation of protocols for daily sedation interruption and spontaneous breathing trials. However, before a patient is considered for ventilator weaning, the following questions are well worth considering to ensure maximum chances of successful ventilator weaning:

• Has the disease process that led to mechanical ventilation resolved or improved?
• Is the patient hemodynamically stable? Absence of shock or requirement for pressors or significant arrhythmias
• Is the patient adequately oxygenated? (Fraction of inspired oxygen <50% and/or low PEEP requirements)
• Is the patient adequately awake and communicative? (absence of encephalopathy, agitation, or overtly altered mental status)

Note that the presence of any of the above parameters doesn't guarantee weaning failure. The opposite also holds true. Because clinical judgment may sometimes over or underestimate a patient's readiness, a need for objective measures exists. Those indices should ideally be easily measurable and widely applicable.

Some suggested indices correlate directly with ventilatory parameters, such as minute ventilation (VE) or vital capacity(VC). Other indices correlate with the degree of oxygen requirements, such as the ratio of arterial to alveolar oxygen ratio (Pao2/PAo2), the ratio of arterial oxygen to the fraction of inspired oxygen (PaO2/FiO2) ratio, or the alveolar-arterial oxygen gradient (A-a gradient). Also, some parameters examine respiratory muscle strength, such as maximal inspiratory pressure (MIP).

There are so many indices because none of them is perfect. There is a wide degree of variability in the performance of the above tests, and their predictive value is far from optimal. The reason being is that these indices only measure one aspect of the respiratory function, while the weaning process is complex and multifactorial.

Rapid Shallow Breathing Index (RSBI)

Defined as the ratio of respiratory rate (f) to tidal volume (VT), initially described by Yang and Tobin 1991. Their trial found that RSBI <105 correlated with weaning success, while a score >105 correlated with weaning failure.[11] The reported sensitivity, specificity, positive predictive value, and negative predictive values were  97, 64, 78, and 95 percent, respectively. Since the initial description, their results were confirmed in multiple subsequent trials, and their test has gained wide popularity and is integrated into ventilator liberation protocols in many ICUs.The test is ideally conducted over 30 minutes while the patient is on minimal pressure support ventilation (PSV) and/or a small PEEP value. 

Diaphragmatic rapid shallow breathing index comprising:

• Diaphragmatic excursion rapid shallow breathing index (DE-RSBI)
• Respiratory rate [RR]/DE) and the
• Diaphragm thickening fraction rapid shallow breathing index (DTF-RSBI, RR/DT showed a higher predictability value compared to RSBI alone.[12][13]

Adjuncts to Predict and Facilitate Safe Weaning

• Diaphragmatic ultrasound to assess Diaphragm thickening fraction (DTF).[14] A point-of-care ultrasound comprising of the lung, diaphragm (diaphragmatic thickness fraction), and cardiac dynamic assessment of changes to velocity time integral (VTI) following passive leg raise is also helpful in assessing the readiness for the weaning process.[15]
• Assessment of Airway occlusion pressure (P0.1), central venous-to-arterial pO2 gradient, and central venous oxygen saturation during SBT.[11]
• Daily sedation interruption (DSI) facilitates weaning.[16]
• An early rise in CVP after starting an SBT has a high risk of extubation failure.[17]
• The frailty index is also crucial.[18]
• Diaphragm EMG.[19]
• Extubation predictive score (ExPreS) score of ≥59 points has an OR of 23.07 for safe extubation.[9]
• Machine learning.[20]
• Brain natriuretic peptide (BNP).[21]
• Mechanical Ventilation-Respiratory Distress Observation Scale (MV-RDOS.)[22]

Treatment / Management

Spontaneous Breathing Trial (SBT)

Patients should be assessed daily for readiness to wean off mechanical ventilation. Trials are often part of an ICU protocol for ventilator liberation and usually start after the patient fulfills many of the criteria mentioned previously. Trials should be conducted with the patient off sedation, on minimal ventilator support (pressure support ventilation PSV of 5-8 mmHg or less and/or a small amount of PEEP. There is some data to suggest using zero PSV and zero PEEP (known as ZEEP trials), which seems to correlate with higher chances of successful ventilator weaning.

For a spontaneous breathing trial to be considered successful, a patient should be able to breathe for at least 30 minutes without signs of hemodynamic derangement (respiratory rate <35, no significant elevation or drop in blood pressure, oxygen saturation >90%), and with the absence of signs of distress or anxiety is usually combined with one of the readiness indices, such as the RSBI calculated at the beginning and end of each trial. Other factors to consider include respiratory secretions burden, the presence of a strong cough, and the ability to maintain adequate wakefulness. A successful trial is usually followed by a cuff leak test and removal of the endotracheal tube, and discontinuation of mechanical ventilation.

The cuff leak test is to ensure there is an adequate gas leak around the endotracheal tube after the cuff is deflated. This ensures the airway is patent without significant laryngeal edema. Failure to fulfill one or more of the aforementioned parameters usually correlates with higher chances of weaning failure and reintubation. Those patients should be placed back on comfortably, controlled mode with appropriate sedation. A careful work-up should be done to examine underlying barriers to a successful weaning process. It is worth mentioning that the clinician’s judgment is an important consideration when considering extubation. An experienced clinician can often combine all the data and see through an apparently failed weaning parameter.SBT duration (30–120 min) has almost an 80% chance of safe extubation.[3]

Extubation to Non-invasive Ventilation (NIV)

Although previously thought of as a failed weaning attempt, it is currently endorsed by the American College of Chest Physicians (CHEST) and the American Thoracic Society (ATS) to extubate patients to preventive non-invasive ventilation. Multiple studies correlated extubation to NIV with shorter ICU length of stay and short-term mortality. Patients who should be considered for such intervention include high-risk intubated patients, including those who repeatedly fail their SBT, patients with advanced COPD or CHF, hypercapnic patients, and those >65 years of age. NIV is applied to patients with failed weaning from prolonged ventilation.[23] NIV had fewer days requiring IMV and a shorter antibiotic duration for respiratory infections.[24] This achieved de-cannulation in 43% of chronic ventilator-dependent patients.[25]

If the patient fails SBT, gradual reduction in pressure support (PS) or daily T-piece trials), or following ventilatory setup can be adopted:

• Synchronized intermittent mandatory ventilation (SIMV)
• Continuous positive airway pressure (CPAP)
• Adaptive support ventilation (ASV)
• Airway pressure release ventilation (APRV)
• Proportional assist ventilation (PAV) or
• Neurally adjusted ventilator assist (NAVA)[26]

The protocol-based approach is recommended for a safe and effective weaning process.[11][27] Dichotomizing the “right patients” and weaning these patients at the “right time” is fundamental in the weaning process.[11]

Differential Diagnosis

Common reasons for failed weaning include:

• Cardiac dysfunction
• Cognitive dysfunction
• Respiratory pump failure
• Respiratory muscle and diaphragmatic dysfunction
• Metabolic disorders

Prognosis

Timely and safe weaning is important.[11] Weaning protocol, driven either by the registered nurse or the respiratory therapist, has been effective.[28][29]

Protocol-based algorithmic weaning process helps prevent hyperoxia.[30] This also shortens the length of ventilation support and duration of ICU stay, as well as reduces the overall mortality.[31]

This process is dependent on the algorithmic approaches comprising of:

• Stringent screening for the readiness of the patient for weaning
• Weaning modes in ventilation
• SBT methods, and
• De-escalating sedation and facilitating the mobilization of the patients.[32]

Newer approaches to facilitate the process include:

• Early noninvasive ventilation
• Neurally-adjusted ventilatory setup, and
• Point of care ultrasound.[33]

Complications

One study showed premature weaning in 60.8% and delayed weaning in 23.6% of patients.[8]

Deterrence and Patient Education

Heterogeneity in implementing current guidelines and perceived benefits of the protocol-based weanings has been observed. A review of more than 2000 Asian intensive care specialists revealed :

• SBT was the most common method (80%) of weaning in 80%
• Weaning protocol was followed in 62%
• Sedation protocol followed in 72.5%, and
• Respiratory therapists were present in only 42% of the respondents.[34]

Pearls and Other Issues

The major variables governing the delayed weaning and extubation process have been observed to be related to the SBT timing and making the final call for extubation.[35]

Protocol-based weaning extubation algorithm needs to be followed.[9] The role of the nurse is critical in the weaning process.[36] The nurse-led weaning process is safe, effective, and economical.[37]

Critical Components During the Weaning Process

• Assessment of the readiness of the patients for extubation
• Safe tolerance of SBT
• Implementation of prophylactic NIV, and
• Monitoring of the patients after extubation.[38][39]

Various Clinical Parameters Governing the Safe Weaning Process

• Inspiratory muscle training (IMT) since respiratory pump failure has been observed in almost 60% of mechanically ventilated patients.[40]
• A cough peak flow between 55 and 65L/minute.[41]
• Glasgow Coma Scale (motor score ≤5), prolonged ventilation (≥7 days), and copious secretion have a high risk of weaning and extubation failure.[42]
• Elevated PaCO2 values during SBT have increased the odds of weaning failure.[43]
• Adequate nutrition for the patient is crucial.[44]
• Hypoalbuminemia and hypophosphatemia also delay the weaning process.[45]

Enhancing Healthcare Team Outcomes

Effective interprofessional team collaboration in the weaning process is of prime importance.[36][46] Nurse-driven weaning protocols have been observed to be safe and effective.[47] The concept of a specialized weaning center is also on the rise.[48] Weaning off mechanical ventilation can often become a daunting task for the clinician caring for critically ill patients. It requires a meticulous daily assessment and collaborative effort between the ICU care team. The ultimate decision should be based on a multitude of clinical factors, combined with predictive scores after careful clinician assessment that is often influenced by experience. Working as a team that includes a pulmonologist, intensivist, anesthesiologist, respiratory therapist, and an ICU when it comes to weaning is vital. No one person should decide to wean a patient; countless cases of solo weaning have gone bad. Every weaning that fails is associated with higher morbidity for the patient. It is important to know and understand that there are more mechanically ventilated patients at any given moment than should be. Finally, weaning from a mechanical ventilator should never be an emergency and preferably should be done during the daytime.[49][50]

A to Z Algorithm for Safe Weaning and Extubation