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ORIGINAL ARTICLE
Year : 2017  |  Volume : 30  |  Issue : 1  |  Page : 305-309

A comp arative study between successful weaning and weaning failure from mechanical ventilation by using transthoracic echocardiography


1 Department of Anaesthesia and Intensive Care Medicine, Menoufia University, Menoufia, Egypt
2 Department of Cardiology, Menoufia University, Menoufia, Egypt

Date of Submission31-Jan-2016
Date of Acceptance04-Apr-2016
Date of Web Publication25-Jul-2017

Correspondence Address:
Mohammed F Abd El Aziz
Shibin El-Kom, Menoufia, 32511
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_57_16

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  Abstract 


Background
Cardiogenic pulmonary edema has been recognized as a frequent cause of weaning failure. A spontaneous breathing trial (SBT) induced an elevation in the left ventricular filling pressure, which plays a key role in weaning failure. Transthoracic echocardiography (TTE) should be used to identify the cardiac origin of respiratory weaning failure. Tissue Doppler is a technique that directly measures myocardial velocities. The early diastolic mitral annulus velocity (Ea), pulsed Doppler mitral flow in early diastole E, and the resulting E/Earatio closely correlated with the measured invasive left ventricular filling pressure.
Objective
The aim of this study was to compare the success of weaning from mechanical ventilation (MV) and failure of weaning using TTE.
Patients and methods
The study included 30 patients who were divided into two groups: group I (the weaned group) (eight patients) included patients who fulfilled the criteria for weaning and the patients were not reintubated within 48 h following extubation, and group II (the weaning group) (22 patients) included patients with failed SBT or those who were reintubated within 48 h following extubation. The following parameters were recorded: demographic data (age, sex, and cause of MV), mean arterial blood and serum creatinine, the left ventricular ejection fraction, the E wave velocity by means of pulsed-wave Doppler analysis of mitral inflow, and the myocardial velocity recorded using the digital trunk interface technique. Eawas measured and E/Eawas calculated. The mean of three measurements was used for calculation.
Results
The success rate of weaning from MV was 26.7% and the mortality rate was 6.75%. The comorbidities associated with weaning failure were evident in the failure group. TTE parameters before SBT were as follows: left ventricular ejection fraction was comparable between the two groups, whereas E wave and E/Earatio were significantly decreased in the successful group. However, Eawave was significantly decreased in the failure group.
Conclusion
Measurement of the E/Earatio with TTE could predict weaning failure. Diastolic dysfunction with relaxation impairment is strongly associated with weaning failure.

Keywords: mechanical ventilation, spontaneous breathing trials, transthoracic echocardiography


How to cite this article:
Afifi MH, El-Feky EM, Abd El Aziz MF, Abdo W. A comp arative study between successful weaning and weaning failure from mechanical ventilation by using transthoracic echocardiography. Menoufia Med J 2017;30:305-9

How to cite this URL:
Afifi MH, El-Feky EM, Abd El Aziz MF, Abdo W. A comp arative study between successful weaning and weaning failure from mechanical ventilation by using transthoracic echocardiography. Menoufia Med J [serial online] 2017 [cited 2019 Apr 21];30:305-9. Available from: http://www.mmj.eg.net/text.asp?2017/30/1/305/211524




  Introduction Top


Weaning is the process of decreasing the amount of support that the patient receives from the mechanical ventilator, so the patient assumes a greater proportion of the ventilatory effort. The purpose is to assess whether mechanical ventilation (MV) can be successfully discontinued. Weaning may involve either an immediate shift from full ventilatory support to a period of breathing without assistance from the ventilator or a gradual reduction in the amount of ventilator support [1].

Traditional methods of weaning include spontaneous breathing trials (SBTs), progressive decreases in the level of pressure support during pressure support ventilation, and progressive decreases in the number of ventilator-assisted breaths during intermittent mandatory ventilation [2].

The best way to determine suitability for discontinuation of MV is to perform a SBT. There are three ways to determine this: putting the patient on a minimum pressure support and Positive end-expiratory pressure (PEEP) (e.g. 5–7 cmH2O pressure support/5 cmH2O PEEP performing mechanics and extubating), using CPAP alone, or using a T-piece [3].

Cardiogenic pulmonary edema has been recognized as a frequent cause of weaning failure. The definitive diagnosis remains difficult; in this situation right heart catheterization was proposed as the reference tool. A SBT induced an elevation in the left ventricular filling pressure (LVFP), which plays a key role in weaning failure. As the introduction of a pulmonary artery catheter remains an invasive and potentially harmful procedure, there is growing evidence to suggest that transthoracic echocardiography (TTE) should be used to identify the cardiac origin of respiratory weaning failure [4],[5],[6].

Tissue Doppler is a technique that directly measures myocardial velocities. The early diastolic mitral annulus velocity (Ea) has been shown to be a relatively load-independent measure of myocardial relaxation. When Ea is combined with pulsed Doppler mitral flow in early diastole E, the resulting E/Ea ratio closely correlated with the measured invasive LVFP [7].

This study aimed to compare the success of weaning from MV and failure of weaning by using TTE.


  Patients and Methods Top


This study was approved by the local Clinical Research Ethics Committee of Menoufia hospital and written informed consent was obtained from their families. The sample included patients on MV for over 48 h before they were considered ready to undergo an initial SBT. Criteria for weaning were as follows: Glaskow coma scale above 8, hemodynamically stable, adequate oxygenation and ventilation, and the ability to protect his or her own airway with good cough reflex.

The exclusion criteria were as follows: being on tracheostomy, active neuromuscular disease, pregnancy, poor echocardiography window, heart rate faster than 140 beats per minute at baseline, and presence of atrioventricular conduction abnormalities; patients with severe mitral regurgitation, mitral stenosis, or a prosthetic mitral valve were also excluded because E/Ea had not been validated in such patients for the evaluation of LVFP.

A complete echocardiography was performed by one evaluator just before the SBT defined by a left ventricle ejection fraction (LVEF) under 50% and relaxation impairment by a protodiastolic annulus mitral velocity Ea under or equal to 8 cm/s.

All patients underwent the SBT, which lasted 1 h and consisted of a low pressure support trial at 7 cmH2O. Patients were considered to have failed the SBT if they developed any of the following signs during the 1-h SBT: respiratory frequency greater than 35 breaths per minute, arterial oxygen saturation less than 90%, heart rate greater than 140 beats per minute or sustained increase or decrease in blood pressure with systolic arterial pressure greater than 200 or less than 80 mmHg, diaphoresis, and signs of distress. The time of occurrence of these signs after starting the SBT was noted. Patients who successfully completed the SBT were extubated. The attending physician in charge of the patient had no access to the TTE findings.

Failure of the weaning process was defined as a failed SBT or the need for reintubation within 48 h following extubation.

During assisted MV, the level of pressure support (PS), PEEP, the patient's respiratory rate (RR), tidal volume, and the RR/tidal volume ratio were recorded just before initiation of the SBT. Arterial blood gas analysis was performed just before and at the end of the SBT. Heart rate, RR, blood pressure, pulsed oximetry, and consciousness were monitored throughout the SBT. TTE was performed just before the SBT.

Thereafter, the patients were divided into two groups: group I (the weaned group) (eight patients), which included patients who fulfilled the criteria for weaning and the patients were not reintubated within 48 h following extubation, and group II (the weaning failure group) (22 patients), which included patients who failed SBT or those who were reintubated within 48 h following extubation.

The following parameters were recorded: demographic data (age, sex, and cause of MV), mean arterial blood, serum creatinine, the LVEF, measurement of the E wave velocity using pulsed-wave Doppler analysis of mitral inflow, and the myocardial velocity using the DTI technique. The sample volume was placed at the junction of the left ventricular wall with the mitral annulus of the lateral myocardial segments from apical four-chamber views. Ea was measured and E/Ea was calculated. The mean of three measurements was used for calculation.

Results were collected, tabulated, and statistically analyzed using an IBM compatible personal computer with statistical package for the social sciences, version 20 (IBM, Chicago, USA). Two types of statistics were used.

Descriptive statistics were presented as number and percent for qualitative data and as mean, SD, and range for quantitative data.

Statistical analysis

The Mann–Whitney test (nonparametric test) is a test of significance used for comparison between two groups not normally distributed having quantitative variables. Paired samples t test was applied for comparison between the normally distributed quantitative data at interval for the same group. The Wilcoxon signed test was applied for comparison between the not normally distributed quantitative data at interval for the same group. A P value of greater than 0.05 was considered statistically nonsignificant.


  Results Top


The results of 30 patients admitted in Menoufia Critical Care Unit on MV are presented. Eight patients were successfully weaned from MV. However, two from the failure group died before 28 days.

[Table 1] shows the demographic data. Age, sex, and causes of ICU admission were comparable between the two groups, whereas associated comorbidities were significantly more evident in the failure group [Figure 1].
Table 1 Demographic data

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Figure 1: Prognosis among the studied patients.

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[Figure 2] shows the indications of mean velocity (MV), DCL (36.7%), hypoxia (36.7), hypercapnia (23.3%), and respiratory failure (3.3%). The two groups were comparable as regards these results.
Figure 2: Indications of mechanical ventilation.

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[Table 2] shows mean arterial pressure (MAP) and serum creatinine. MAP was significantly increased in the successful group, whereas serum creatinine was significantly elevated in the failure group.
Table 2 Comparison between successful weaning and weaning failure as regards MAP and serum creatinine

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[Table 3] shows TTE parameters before SBT. LVEF was comparable between the two groups, whereas E wave and E/Ea ratio were significantly decreased in the successful group. However, Ea wave was significantly decreased in the failure group.
Table 3: Table 3 Comparison between successful weaning and weaning failure as regards transthoracic echocardiography parameters before spontaneous breathing trial

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  Discussion Top


In the present study, the successful weaning rate was 26.7% and failure rate was 73.7% and the mortality rate was 6.7%. Two patients died in the failure group.

The demographic data (age, sex, cause of ICU admission, and the cause of MV) were comparable between the studied groups.

As regards the concomitant diseases between the two groups, there was a significant increase in diabetic, hypertensive, and chronic renal patients in the failure weaning group.

This result is in agreement with the study by Siddiqui et al. [8], who studied the risk factors for prolonged postoperative MV after open heart surgery and concluded that diabetes mellitus is one of the risk factors.

Moreover, Gumus et al. studied the risk factors associated with prolongation of MV after coronary artery bypass graft, and they concluded that chronic renal dysfunction is one of the risk factors [9].

The MAP showed a significant increase in the successful group, whereas serum creatinine showed a significant decrease in the successful group.

Vieira et al. [10] conducted a study on 140 patients on MV, and they concluded that renal dysfunction has serious consequences in the duration of MV, weaning from MV, and mortality in critically ill cancer patients.

Moreover, Chao et al. [11] compared patients on MV who developed acute kidney injury (AKI) and other patients without AKI in the Taiwan's National Health Insurance during 1998–2007 and concluded that patients with AKI-dialysis had significantly longer MV.

In the present study, the systolic function assessed using LVEF was not associated with weaning outcome. This is in accordance with previous studies. Mekontso-Dessap et al. [12] showed in a subgroup of patients who underwent TTE that the LVEF did not differ between patients in the failed or in the successful group. Similar data were obtained by Lamia et al. [13], Zapata et al. [14], and by Moschietto et al. [15].

The diagnosis of diastolic abnormalities can be confirmed when Doppler with tissue imaging provides evidence of impaired myocardial relaxation [16],[17],[18]. The Ea velocity constitutes a noninvasive and relatively load-independent index of left ventricular relaxation and diastolic function. Relaxation impairment is defined by an Ea velocity below or equal to 8 cm/s [16].

In the present study, in comparison with the successful group, patients in the failed group had a lower Ea velocity and exhibited more frequent impairment in relaxation.

Abnormal relaxation resulted in a prolongation of the isovolumic relaxation time with an upward shift and to the left of the diastolic pressure/volume curve [19].

This is in agreement with the study by Moschietto et al. [15], who studied the role of TTE in the prediction of weaning progress from MV and concluded that Ea was lower in the failed group. Ea increased during SBT in the successful group, whereas no change occurred in the failed group [15].

In our study, the E/Ea ratio was significantly increased in the failure group.

E/Ea closely correlated with the measured invasive LVFP, even in patients under MV [20].

Caille et al. [4] and Moschietto et al. [15] found a significantly higher E/Ea before SBT in patients with weaning failure.


  Conclusion Top


Measurement of the E/Ea ratio with TTE could predict weaning failure. Diastolic dysfunction with relaxation impairment is strongly associated with weaning failure.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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