- 1 Abstract
- 2 Introduction
- 3 Weaning of mechanical ventilation
- 4 Hemodynamic effects of mechanical ventilation
- 5 Diagnose methods to detect cardiovascular dysfunction in patients with difficult weaning
- 6 Failure Criteria of spontaneous breathing trials
- 7 Discussion
- 8 Bibliography
Incluido en la revista Ocronos. Vol. VI. Nº 11–Noviembre 2023. Pág. Inicial: Vol. VI; nº 11: 148.4
Autor principal (primer firmante): Jenifer Monserrat Langarica López
Fecha recepción: 03/11/2023
Fecha aceptación: 15/11/2023
Ref.: Ocronos. 2023;6(11): 148.4
Jenifer Monserrat Langarica Lopez 1 M.D.
Ingrid Ailyn Gonzalez Lozano 2 M.D.
Elvia Berenice Gómez Rodriguez 3 M.D.
Assen Ognianov Iantchoulev 4 M.D.
Rocío Anahí Silva Martinez 5 M.D.
José de Jesús Valdivia-Nuno 5 M.D.
1 “Instituto Mexicano del Seguro Social, Hospital General Regional 110” Internal Medicine division Guadalajara, Jal, México.
2 “Instituto Mexicano del Seguro Social, Hospital General Regional 45” Internal Medicine division Guadalajara, Jal, México.
3 “Instituto Mexicano del Seguro Social, Hospital General Regional 180” Family Physicians division Guadalajara, Jal, México.
4 “Instituto de Seguridad y Servicios Sociales de los Trabajadores del Estado, Hospital Regional Valentín Gómez Farias” Cardiology division Guadalajara, Jal, México.
5 “Instituto Mexicano del Seguro Social, Centro Médico Nacional de Occidente” Cardio-Neumology Division, Cardiology Department, Guadalajara, Jal, México.
To my friends for all their support. To all patients for allowing me to learn.
Weaning failure from mechanical ventilation is defined as the inability to successfully release a patient from the ventilator. The term “weaning failure” can therefore also be applied to a failed spontaneous breathing test (SBT) or the need to resume mechanical ventilation within 2 to 7 days from when the patient was extubated. (12)
Up to one third cases of cases of mechanical ventilation weaning failure can be attributed partially to the development of heart failure, including both systolic and diastolic alterations.
Understanding physiological, pathophysiological, and hemodynamic changes which occur during mechanical ventilation and the weaning process, will enable a greater understanding for candidate selection which would in turn help decrease the probability of weaning failure.
Mechanical ventilation, Weaning failure, heart failure.
Mechanical ventilation (MV) is a temporary replacement of the normal respiratory function which can be applied in several pathological situations in which the individual is unable to meet their own physiological requirements. (1)
Pulmonary ventilation is produced when a pressure gradient is created, either by the contraction of the respiratory muscles or using mechanical ventilation, resulting in gas flow to the alveoli and enabling gas exchange.
The main difference between spontaneous physiological ventilation and MV is that physiological respiration occurs through the creation of a negative pressure gradient caused by the contraction of inspiratory muscles, which enables air to then fill the lungs, while MV generates a positive pressure which forces air into the lungs.
Weaning of mechanical ventilation
Weaning is the withdrawal of invasive mechanical ventilation, until the patient is fully able to perform spontaneous ventilation by themselves. Mechanical ventilation shutdown is synonymous with weaning, but not extubation. Extubation is the act of removing the orotracheal tube, while weaning is a much broader process, which can be broken down into several phases. (2)
The importance of the mechanical ventilation withdrawal is fundamental in patients in intensive care unit on mechanical ventilation, since the time used for this represents 40-50% of the total time in mechanical ventilation (3). It has also been shown that the longer the time in mechanical ventilation, the greater the mortality, morbidity and stay in the ICU (4). Unnecessary mechanical ventilation increases the risk of complications related to mechanical ventilation and increases mortality (5).
Therefore, it is a priority objective to shorten the mechanical ventilation time, if possible, to improve the chances of survival, to avoid associated iatrogenic practices, decrease the stay in ICU, minimize the discomfort of our patients and reduce the costs; starting their withdrawal as soon as possible. On the other hand, if we rush the removal of mechanical ventilation, we can also inflict damage to the patient, by increasing muscle fatigue, airway protection loss, as well as an increased risk of mortality (6). So, the timing of the decision to start weaning is decisive.
Despite its importance, the weaning process has not been rigorously defined or established. With the aim of review the subject and unify terms, a Weaning Consensus Conference on Mechanical Ventilation was held in Budapest in 2007, where the concept of weaning failure was established as the presence of any of the following: 1) Failure of spontaneous breathing test. 2) Reintubation and/or need for ventilatory support within 48 hours of extubation. 3) Death within 48 hours of extubation. (7)
Spontaneous breathing test (SBT) refers to a patient’s ventilation test through the endotracheal tube without ventilator support (through a T-piece that provides oxygen) or with a minimum assistance that can be performed by support pressure of 8 or less with or without PEEP, CPAP or automatic tube-ATC compensation. Using this method, it has been demonstrated the need to establish a weaning protocol in each unit in which the possibility of starting the process of removal of mechanical ventilation is evaluated daily, with the intention of not prolonging it. (8)
SBT is a simple, effective, and safe test and is considered the best indicator for evaluating a patient’s ability to disconnect from mechanical ventilation. (9)
It has been shown that about 60% of patients will tolerate the first spontaneous breathing test and may be extubated on the first attempt. The remaining 40% will not tolerate it and should be reconnected to the respirator. (10)
Reintubation usually occurs in the first 24 hours after extubation and is related to the following risk factors (11): poor secretion management requiring frequent aspiration, non-productive cough, positive fluid balance, heart failure, pneumonia, prolonged duration of mechanical ventilation, poor neurological level (score on the Glasgow Coma Scale less than 8 points) and severe chronic respiratory pathology. Reintubation is associated with increased in-hospital mortality, longer ICU stay, longer hospitalization, and nosocomial pneumonia. (6)
In 2002, the term «weaning-induced heart failure» was introduced. (12)
Weaning failure on mechanical ventilation is defined as the inability to release a patient from the ventilator. Therefore, the term «weaning failure» includes failure of a spontaneous breathing test (SBT) or the need to resume mechanical ventilation after extubation within 48 h to seven days. (12)
Investigating the causes of ventilation weaning failure is crucial because the duration of mechanical ventilation for those who fail SBT and reintubation for those who are needed, have both been associated with worse outcomes. (12)
Epstein et al. found that up to one third of ventilation weaning failures resulted only or partially from «congestive heart failure». An even higher prevalence of weaning-induced cardiovascular dysfunction has been reported in experienced centers where weaning is systematically examined. (13)
Cardiovascular dysfunction during weaning may involve both systolic and diastolic alterations. Systolic dysfunction is an already widely recognized risk factor for extubation failure. (14)
Current evidence suggests that diastolic left ventricular dysfunction is involved in weaning failure on mechanical ventilation, both in patients with systolic dysfunction (which alone is already a risk factor for weaning failure) as well as in patients with preserved left ventricular systolic function.
Hemodynamic effects of mechanical ventilation
During ventilation with positive pressure in the airway, intrathoracic pressure increases with inspiration, this increase produces compression of the right cavities, and decreases the preload in first instance of the right ventricle, thus decreasing the systolic volume of the right ventricle and consequently the preload of the left ventricle.
Likewise, positive pressure conditions an increase alveolar pressure increase, conditioning it to the increase in the resistance of the pulmonary vasculature, leading to an increase in the afterload of the right ventricle.
However, in the left ventricle afterload tends to decrease during ventilation with positive pressure (contrary in the right ventricle) due to increased intrathoracic pressure producing an increase in intrapericardial pressure, resulting in the left ventricle requiring less intraventricular pressure to achieve ejection to the systemic circulation.
That is why during the transition from positive pressure ventilation to spontaneous ventilation, through the weaning process, hemodynamic changes occur contrary to those previously described, such as: increased systemic venous return, increased preload of the right ventricle and left ventricle, increased afterload of the left ventricle and decrease in that of the right ventricle, increase in respiratory work and increased sympathetic tone.
All these factors, to a greater or lesser extent, tend to increase the filling pressures of the left ventricle and consequently in some patients, this could culminate in the development of pulmonary edema, one of the main recognized causes of failure in weaning. (15)
Roche-Campo, in a prospective, randomized, multicenter trial, found out 39% of patients with mechanical ventilation and prolonged weaning (>7 days) had isolated diastolic dysfunction, compared with 22% of patients with systolic dysfunction by transthoracic echocardiographic evaluation.
Thus, positing diastolic dysfunction as a risk factor and probable predictor of weaning failure; Isolated Diastolic dysfunction in this study was defined as LVEF greater than or equal to 50%, BNP greater than 35 and diastolic dysfunction parameters such as E/e’ radius greater than or equal to 13 or a maximum and lower velocity at 9, as indicators of increased left ventricular filling pressures and alteration in left ventricular relaxation respectively. (16)
Similar results were found by Konomi in 2016, they found a significant relation between diastolic dysfunction and failure in weaning, documenting it as the best independent risk factor associated with weaning failure in patients with or without concomitant systolic dysfunction. (17)
Identification of patients at high risk of weaning failure secondary to cardiovascular disfunction is crucial for the care of critically ill patients. Systolic dysfunction has been previously and widely identified as a risk factor for weaning, however in recent years, Increased evidence of diastolic dysfunction has been obtained in patients with depressed systolic function or preserved systolic function, as a major contributor to weaning failure in patients with mechanical ventilation.
Diagnose methods to detect cardiovascular dysfunction in patients with difficult weaning
With the intention of objectively quantifying the lung ultrasound findings, a study (18) that proposed the «LUS score» tool emerged in 2010 to assess the lung aeration pattern in patients with pneumonia undergoing antibiotic treatment. This scale was used to assess the degree of alveolar recruitment with the different ventilatory maneuvers (19), and as a predictor of success in extubation (20). It seems a good tool to assess the lung pattern, it allows to simplify with a number how aerated our patient’s lungs are and allows evolutionary comparisons of the same patient or others. It is a technique that may be done by the patient’s bed in 5 or 10 minutes, and easy to learn.
This numerical score scale evaluates the twelve regions of the two hemithorax according to the ultrasound findings. The anterior and posterior axillary line define the anterior, lateral and posterior regions of the lung; and a transverse line at the level of the pulmonary hilus (sternal middle) divide the upper and lower areas. Therefore, the 6 regions to be evaluated for each hemithorax are delimited: antero-superior, antero-inferior, latero-superior, latero-inferior, postero-superior and postero-inferior.
Four air lung patterns are defined: Normal pattern: presence of «lung-sliding» with A lines, occasionally or some isolated line B (2 or less). Moderate loss of the airway: multiple (more than 2) well-defined and irregularly separated lines B (comets) leaving the pleural line or a small subpleural consolidation. Severe airfoil loss: multiple confluent B lines leaving the pleural line or a small subpleural consolidation. Lung consolidation pattern: tissue pattern with pinpoint or hyperechoic images representing the aerial broncogram (it may be pneumonia or atelectasis).
The adapted scoring system distinguishes four ventilation patterns as follows: normal aeration (N; presence of pulmonary slip with A lines and less than two isolated B lines), moderate loss of pulmonary ventilation (B1; more than two well-defined lines) severe loss of pulmonary ventilation (B2; multiple coalescing B lines) and pulmonary consolidation C; presence of a tissue pattern). Scores of 0-3 were attributed respectively to the four categories (0 points for N, 1 point for B1, 2 points for B2 and 3 points for C), and for each region the worst visible pattern was recorded, all scores of both lungs will be added, Obtaining a score of 0 to 36 points, If LUS is greater than 16 points, the patient has a high risk of failure of mechanical ventilation withdrawal.
Instead of using the original LUS score, a modified procedure (LUSm), evaluating four lung regions on each side instead of the six standards. Evaluating four areas: anterior-superior, anterior-inferior, lateral and basal postero. The basal posterior area is where most of the critical patient pathology occurs according to Lichtenstein. The total LUSm score for all areas ranged from 0 to 24 points. If LUSm is greater than 7 points, the patient has a high risk of mechanical ventilation removal failure. (20)
Evaluation of diastolic function with echocardiography
In terms of diastolic evaluation, there are several parameters that reflect the filling period of the left ventricle, among them the most used and studied in these contexts are: maximum velocity of the E wave of the transmitral flow, maximum wave velocity e of mitral ring movement, ratio E/A and ratio E/e’.
The diagnosis of diastolic dysfunction in patients with weaning failure according to a systematic review with meta-analysis conducted by Meirelles Almeida was performed mainly with the E/e’ relation and the E/A relation, other measures of diastolic function, such as E wave deceleration time, left ventricular isovolumetric relaxation time and left atrial volume could not be used for analysis due to the low number of articles in which this association was reported. (21)
The maximum velocity of the transmitral wave E evaluates the period of rapid filling of the left ventricle at the beginning of diastole, reflecting the pressure gradient between the ventricle and the left atrium in the diastole proto. It is affected by changes in preload, changes in left atrial pressure, and alterations in left ventricular relaxation. (21)
The maximum velocity of the e’ wave of the excursion of the mitral ring during diastole, reflects the left ventricle relaxation, so alterations, will produce changes in the speed of this wave. That’s why it’s a measure used to correct the influence of left ventricular relaxation that it has on the maximum speed of the E wave, Thus, attempting to isolate the effect of filling pressures at the maximum speed of wave E. So according to this has been established to the ratio E/e’ as a reliable and specific measure in the evaluation of filling pressures of the left ventricle. Values of E/e’ below 8 usually translate normal LV filling pressures, while values above 14 reflect with high specificity an increase in left ventricular filling pressures. (22)
Papanikolaua in 2011, found the E/e’ ratio during the spontaneous ventilation test has the highest diagnostic performance in predicting weaning failure, compared to other parameters for diastolic evaluation such as deceleration time, the E/A ratio, propagation velocity, maximum wave velocity A and maximum e’ wave velocity, also observed that during weaning diastolic function tends to deteriorate regardless of its previous state at the beginning of weaning. (23)
The mitral E/A ratio is generally used to identify left ventricular filling patterns that may correspond to a normal pattern (E/A <0.8), alteration in relaxation (E<A), pseudonormalized (E/A 0.8-2) and a restrictive filling (E/A >2). However, using E/A radio in isolation makes it more difficult to estimate diastolic function and estimate filling pressures, because even though it is used to classify filling patterns, there is a significant number of other variables affect this relationship, regardless of diastolic function, such as heart rate, rhythm, PR interval and cardiac output among others. (21)
Therefore, the E/e’ radius is better echocardiographic parameter than the E/A radius to detect an increase in the filling pressures of the left ventricle, at least in patients with systolic dysfunction. (17)
Mechanical ventilation-induced diaphragmatic dysfunction (MVIDD).
MVIDD is defined as a progressive decrease in diaphragmatic muscle strength that occurs early after the onset of MV, affecting up to 65% of ventilated patients (18). Although respiratory muscle weakness may be included within the overall muscle involvement of the critical patient, the MVIDD concept refers to diaphragmatic dysfunction secondary to the negative effect of MV and which may occur in parallel or not to affect the rest of the musculature.
The term was introduced by Vassilakopoulos in 2004 (19), based on observations previously made in patients undergoing controlled MV, in which a progressive and rapid loss of diaphragmatic function was observed, from the first 12-18 hours after the start of mechanical ventilation (20). Structural alterations (atrophy and muscle damage) and functional alterations (decreased strength and resistance to fatigue) occur which result in decreased ability to generate strength and resistance to fatigue, which results in a lower inspiratory capacity.
It has been shown that MVIDD worsens the prognosis and is associated with failure in extubation (18), with an increase in MV days and mortality (9). Despite the deleterious effects of MVIDD, routine monitoring of diaphragmatic function is not performed, so this entity is probably underdiagnosed (21).
we include the evaluation of the diaphragm in our evaluations to get more information of possible causes in the weaning of mechanical ventilation.
Diaphragm thickness at end of expiration (TEE) and the inspiratory peak (TEI). The fraction of diaphragm thickening (FDT) results from the difference between TEI and TEE, divided by TEE. FDT correlates with transdiaphragmatic pressure, an estimator of diaphragm function (12).
The FDT is different in people subjected to MV compared to those who breathe spontaneously, FDT is around 54% in not ventilated patients (42-78%) (25) carried out with deep inspiration. In the case of MV this value is lower and figures below 20-30% have been related to failure in the removal of mechanical ventilation. This index has been proposed as an indicator of diaphragmatic efficiency in breathing (26) and as a predictor of success in weaning (27).
Diaphragmatic function as a predictor of weaning failure, have a lower FDT compared to patients with successful weaning. From several studies, the optimal FDT cut to successfully predict weaning ranges from 20% to 36% depending on the fan support provided during the measurement; the higher the support, the lower the FDT, a 29% FDT cut is an optimal value for identifying diaphragm dysfunction (12).
Diaphragmatic displacement (DD) during breathing. The height of the curve is the diaphragmatic displacement or excursion, which in spontaneous breathing is approximately 18+3 mm in men and 16+3 mm in women (25). Some authors consider that a displacement of less than 10-15mm predicts failure in extubation and that it defines the presence of diaphragmatic dysfunction (28), although for others it has shown poor results as a predictor of weaning (29).
In MV patients diaphragmatic displacement may not measure diaphragmatic functionality and the effect of MV on the diaphragm (30), so it does not seem the most appropriate variable to assess the diaphragm in patients connected to the ventilator.
Failure Criteria of spontaneous breathing trials
Clinical and subjective: Agitation and anxiety, depressed mental status, diaphoresis, cyanosis, increased accessory muscle activity, facial signs of distréss.
Objectives measurements: PaO2 ≤50-60 mmHg on FiO2 ≥0.5 or SaO2 ≤90%; PaCO2 ≥50 or and increase in PaC02 ≥8 mmHg; pH ,7.32 or a decrease in pH ≥0.07 pH units; fR/VT ≥105 breaths/min/L; fR ≥35 breaths/min or increased by ≥50%; fC ≥140 beats/min or increased by ≥20%; Systolic BP ≥180 mmHg or increased by ≥20%; Systolic BP ≤90 mmHg (35)
A leak test (air leaks around the endotracheal tube after deflation of the cuff) of ≥110 ml or ≥15% Vt is positive. (35)
Mechanical ventilation weaning algorithm to reduce re-intubation. (Fig1)
There is no validated algorithm, and no cabinet or laboratory study parameter exceeding the physician’s clinical criteria. We use the information from various sources and try to keep as much information as possible to reduce the risk of reintubation of our patients.
Figure 1. Mechanical ventilation weaning algorithm to reduce re-intubation.
There are no official clinical practice guidelines addressing the treatment of confirmed weaning-induced cardiovascular dysfunction. (13)
Cardiovascular causes are among the main causes of weaning failure, cardiac dysfunction during weaning can be both systolic and diastolic. Cohorts have been reported where isolated diastolic dysfunction is even more prevalent than systolic dysfunction in cases of prolonged weaning. (17)
As for the parameters of the evaluation of diastolic function, elevation of the E/e’ radius has been found to be associated with an increased risk of failure at weaning. This increase of the E/e’ radio, driven by a reduction in the speed of the e’ wave. (17)
The E/A ratio according to various revisions (21-23) have not shown utility as a predictor of failure or success at weaning. Other diastolic function parameters, such as E wave deceleration time, isovolumetric relaxation time, left atrial volume, do not have enough evidence to evaluate their usefulness in this scenario. However, there is no current consensus to determine the best approach for evaluating diastolic function in the mechanical ventilation weaning process.
In the pulmonary ultrasound trials with LUS measurement to predict successful weaning of mechanical ventilation, we observed that they also present a good sensitivity and specificity, but with highly variable results, which indicates a lot of inaccuracy.
The main echocardiography limitation is that it is operator dependent observational technique and require proper training, another limitation is that it needs an adecuate window and cannot be performed in obese patients, individuals with pulmonary emphysema or pleural drainage, or patients with wounds and dressings in the measuring area.
In both cases pulmonary ultrasound and in the evaluation of diastolic function, we can conclude that studies are scarce, with low quality and heterogeneity, so that more studies are required with criteria that are refined in the inclusion and exclusion of patients.
There is a dilemma of finding the right time to progress in the withdrawal of mechanical ventilation and the emergence of new non-invasive ultrasound methods predictors of success in weaning mechanical ventilation, we question its true usefulness as true predictors of success. There are still few papers, with very variable results, and a little known and standardized technique, which requires a meta-analysis to find out its true usefulness.
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