Diaphragm ultrasound for predicting weaning success in post-cardiac surgery acute respiratory distress syndrome patients: a prospective observational study in China

Yuan-Qin Huang; Pei Yu; Dou-Dou Xiang; Quan Gan

doi:10.4266/acc.004320

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Original Article Cardiology Diaphragm ultrasound for predicting weaning success in post-cardiac surgery acute respiratory distress syndrome patients: a prospective observational study in China: Acute and Critical Care 2025;40(3):435-443.
DOI: https://doi.org/10.4266/acc.004320
Published online: August 21, 2025

Yuan-Qin Huang¹

, Pei Yu²

, Dou-Dou Xiang³

, Quan Gan¹

¹Department of Intensive Care Unit, Maternal and Child Health Hospital of Hubei Province, Wuhan, China

²Department of Intensive Care Unit, Wuhan Asia Heart Hospital, Wuhan, China

³Department of Internal Medicine, Maternal and Child Health Hospital of Hubei Province, Wuhan, China

Corresponding author: Quan Gan Department of Intensive Care Unit, Maternal and Child Health Hospital of Hubei Province, Wuhan 430070, China Tel: +86-8716-8002 Email: micuganquan@126.com

• Received: November 3, 2024 • Revised: May 17, 2025 • Accepted: May 28, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Abstract
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
KEY MESSAGES
NOTES
REFERENCES

Abstract

Background
To explore the value of the diaphragm thickness fraction (TF) and diaphragm mobility (DM) measured by ultrasound for predicting ventilator withdrawal success in patients with acute respiratory distress syndrome (ARDS) after cardiac surgery.
Methods
This study included 246 patients undergoing the spontaneous breathing trial. Diaphragmatic function was evaluated by ultrasound, including the diaphragm thickness at the end of calm breathing (thickness of the diaphragm at functional residual capacity [TdiFRC]) and the maximum diaphragm thickness at the end of inspiration (thickness of the diaphragm at full vital capacity [TdiFVC]); TF=(TdiFVC–TdiFRC)/TdiFRC×100%. DM, the oxygenation index (the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen), and the rapid shallow breathing index (RSBI) were measured.
Results
Successful liberation from mechanical ventilation was observed in 209 patients. There were no significant differences in the TdiFRC (0.3±0.1 cm vs. 0.3±0.1 cm) or TdiFVC (0.3±0.1 cm vs. 0.2±0.1 cm) between the ventilator withdrawal success group and the ventilator withdrawal failure group (P>0.05). The TF was greater in the ventilator withdrawal success group than in the ventilator withdrawal failure group (40.8%±15.8% vs. 37.7%±9.2%, P<0.01). DM in the ventilator withdrawal success group was greater than that in the ventilator withdrawal failure group (1.5±0.5 cm vs. 1.2±0.4 cm, P=0.040). The RSBI was lower in the ventilator withdrawal success group than in the ventilator withdrawal failure group (74.3±25.6 breaths•min^–1•L^–1 vs. 89.9±34.5 breaths•min^–1•L^–1, P<0.01).
Conclusions
Diaphragmatic ultrasound can be used to predict the success of ventilator withdrawal in patients with ARDS.
Key Words: diaphragm; respiratory distress syndrome; ultrasonography; ventilator weaning

INTRODUCTION

Timely liberation from mechanical ventilation is crucial for patients with acute respiratory distress syndrome (ARDS) after cardiac surgery. Reasonable liberation from mechanical ventilation can reduce complications, shorten the hospitalization time and reduce hospitalization costs. However, the improper timing of weaning will lead to reintubation and increase the risk of a series of complications (such as infection, gastrointestinal bleeding and deep vein thrombosis) [1]. One-fifth of mechanically ventilated patients have respiratory muscle dependence [2]. The diaphragm, as an effective respiratory muscle for maintaining spontaneous breathing, is often dysfunctional during mechanical ventilation. Ultrasound is a noninvasive and effective tool for evaluating diaphragm function. This study aimed to explore the change rates of the diaphragm activity and diaphragm thickness, as evaluated by bedside ultrasound, and to evaluate the prediction of successful weaning among ARDS patients using the rapid shallow breathing index (RSBI). Recent studies, such as Inoue et al [3], have emphasized the critical role of diaphragmatic function in post-cardiac surgery patients, highlighting the potential of diaphragm ultrasound as a weaning predictor.

MATERIALS AND METHODS

This study was conducted in accordance with the principles of the Declaration of Helsinki, and approval was obtained from the Ethics Committee of the Maternal and Child Health Hospital of Hubei Province (No. [2023]IEC(104)). Written informed consent was obtained from all patients included in the study.

Patient Population

In this prospective observational study, 246 hospitalized patients in the intensive care unit (ICU) (Figure 1), including 198 males (80.5%) and 48 females (19.5%) with an average age of 63±11 years, were selected from March 2020 to May 2023. There were 103 patients who underwent macrovascular surgery, 83 who underwent valve replacement, 54 who underwent bypass surgery and 6 who underwent other surgeries. According to the extubation results, 209 patients were in the successful weaning group, and 37 patients were in the failed weaning group. The inclusion criteria were as follows: (1) age ≥18 years; (2) met the Berlin criteria for ARDS; (3) the primary cause had improved, and the mind was clear, thus enabling adherence to mandatory actions; (4) had a stable heart rate of 60–120 beats/min and a stable systolic blood pressure of 90–150 mm Hg; and (5) had reduced ventilator conditions, including an inhaled oxygen concentration (fraction of inspired O₂, FiO₂) ≤50%, positive end-expiratory pressure (5 cm H₂O; 1 cm H₂O=0.098 kPa), and an oxygenation index, defined as the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO₂/FiO₂ ratio) ≥150 mm Hg (1 mm Hg=0.133 kPa). The exclusion criteria were as follows: (1) age <18 years; (2) complications of the central nervous system; (3) a history of thoracoabdominal surgery or the presence of a thoracostomy tube; (4) severe liver and kidney function damage, severe infection, or septic shock; and (5) ICU weakness syndrome. The ventilators used were ARZN-0113 (Draeger) and ASBC-0402 (Draeger).

The following data were collected from patients who met the inclusion criteria: age, body mass index, Acute Physiology and Chronic Health Evaluation (APACHE) II score, Sequential Organ Failure Assessment (SOFA) score, mechanical ventilation time, heart rate, mean arterial pressure, tidal volume, minute ventilation volume and other parameters. The spontaneous breathing trial (SBT) was performed for 30 minutes. The SBT adopted a low-level pressure support mode, a pressure support of 8 cm H₂O (1 cm H₂O=0.098 kPa), and a positive end expiratory pressure of 3 cm H₂O. Radial artery blood gas analysis was performed to calculate the oxygenation index (arterial oxygen partial pressure/inhaled oxygen concentration) and the RSBI. Diaphragm ultrasonography was performed 30 minutes after the completion of the SBT, consistent with prior studies [4] on diaphragmatic function assessment in mechanically ventilated patients.

Patients were placed at a head height of 30° in the supine position. Using a Philips CX50 ultrasonic instrument, a 3.5-MHz convex array probe and a 10-MHz [1] linear array probe were used. The probe was placed along the rib gap between the 7th and 9th ribs of the right armpit front (Figure 2). The diaphragm to be measured was found in two-dimensional (2D) mode, and the M mode was selected. The sampling line was perpendicular to the diaphragm, and the diaphragm thickness at full inspiration (thickness of the diaphragm at full vital capacity [TdiFVC]) and at end-expiration (thickness of the diaphragm at functional residual capacity [TdiFRC]) were measured. The thickness fraction (TF), defined as the change in diaphragm thickness from end-expiration to end-inspiration, was calculated as TF=(TdiFVC−TdiFRC)/TdiFRC×100%. The convex array probe was replaced and placed at the junction of the anterior armpit line with the rib edge (Figure 3). The probe direction was outward and downward. The diaphragm to be measured was found in 2D mode. The M mode was selected, and the sampling line was perpendicular to the diaphragm to measure diaphragm mobility (DM). Ultrasound measurements were performed by ICU doctors with bedside ultrasound qualifications.

A competent physician and respiratory therapist jointly assessed whether tracheal intubation should be removed. The criterion for successful weaning was defined as no requirement for invasive mechanical ventilation for at least 72 hours after extubation. Weaning failure was defined as re-intubation within 48 hours, the need for tracheostomy, or hemodynamic instability (respiratory rate >40 breaths/min; systolic blood pressure >180 mm Hg or <90 mm Hg; arrhythmia; rapid atrial fibrillation; multisource frequent premature ventricular tachycardia and short-term ventricular tachycardia; sweating; three concave signs; poor airway clearance ability) requiring non-invasive ventilation or reintubation, consistent with previous studies [5]. Patients were recruited at their first SBT attempt. Patients who had previously failed an SBT were excluded from this study to ensure uniformity in the study population. The weaning results were recorded for each patient.

Statistical Analysis

The IBM SPSS statistics version 26.0 statistical software (IBM Corp.) was used for statistical analysis. Normally distributed data are expressed as the mean±standard deviation. The following variables were compared between the groups using a t-test: age, body mass index, APACHE II score, SOFA score, mechanical ventilation time, heart rate, mean arterial pressure, tidal volume, minute ventilation volume, oxygenation index, thickness of the quiet end-expiratory diaphragm, thickness of the maximum end-inspiratory diaphragm, change rate of the diaphragm thickness, DM, and shallow-fast respiratory index. The receiver operating characteristic (ROC) curve was used to predict the successful weaning threshold, and P<0.05 indicated a statistically significant difference. This study follows the STROBE guidelines for observational research.

RESULTS

Comparison of Physiological Indices between the Two Groups

There were no significant differences in the general indicators (age, body mass index, APACHE II score, SOFA score, mechanical assistance time, heart rate, mean arterial pressure, tidal volume, minute ventilation volume, carbon dioxide partial pressure, etc.) between the two groups before weaning (P>0.05), as shown in Table 1.

Comparison of the Diaphragm Ultrasound, PaO₂/FiO₂ and RSBI Results between the Groups

There was no significant difference in the TdiFRC or TdiFVC between the two groups (P>0.05), while the differences in the PaO₂/FiO₂ ratio, TF, RSBI and DM between the groups were significant (P<0.05), as shown in Table 2.

ROC Curve Analysis of the Diaphragm Ultrasound Results Combined with the RSBI for Predicting Successful Weaning

ROC curve analysis was used to determine the best cutoff values for the TF and RSBI to indicate successful weaning. A TF >27.9% was determined to be the threshold for predicting successful weaning; this cutoff value yielded a sensitivity of 85.00%, a specificity of 89.03%, and an area under the curve (AUC) of 0.809 (95% CI, 0.749–0.869) (Table 3, Figure 4). The optimal cutoff for the RSBI was determined to be <105 breaths•min^–1•L^–1 [6]; this cutoff value yielded a sensitivity of 91.34%, a specificity of 32.98%, and an AUC of 0.745 (95% CI, 0.659–0.848) (Table 3, Figure 5).

DISCUSSION

The diaphragm is the main respiratory muscle of the human body and the main respiratory muscle that drives respiratory movement [7]. Diaphragm dysfunction is common in ICU patients after receiving mechanical ventilation treatment, and various studies have been performed at this stage. A total of 20%–30% of patients on mechanical ventilation will have ventilator dependence [8], and premature or delayed weaning will lead to weaning failure, resulting in serious adverse consequences. According to previous literature, the risk of patient mortality may increase by 40%–50% [9,10] .Therefore, the choice of the withdrawal time is crucial. Selecting correct and effective guidance indicators for mechanical ventilation weaning in clinical practice is important for improving the success rate of mechanical ventilation weaning and ensuring the efficacy of treatment and healing of patients [11].

In clinical practice, some models and strategies of mechanical ventilation are used to assist in the weaning process, and some indicators are used to help determine weaning timing and predict weaning results. At present, the known weaning indicators for mechanical ventilation include the respiratory rate, airway closure pressure, and SBT [12], but the reference thresholds for these indicators have not been unified in clinical practice at this stage. Traditional offline screening indicators cannot accurately and comprehensively predict the possibility of offline success. The RSBI is one of the best predictors, and it is also the most commonly used indicator in clinical practice. The RBSI, as a prediction index for withdrawal, has a high sensitivity but low specificity. In this study, the sensitivity of using the RBSI to predict successful withdrawal was 91.34%, while the specificity was only 32.98%. Thus, it is difficult to determine the optimal time for weaning. Therefore, it is very important to explore more accurate and better weaning indicators for the treatment of patients with ARDS [13].

To compensate for the deficiency of the RSBI, it is necessary to combine it with indicators that have high specificity. In recent years, with the promotion of bedside ultrasound technology in the ICU [14], ultrasound has received increasing attention in the evaluation of diaphragm function in patients on mechanical ventilation. Ultrasound is a simple, noninvasive and highly repeatable method. Patients with a long duration of mechanical ventilation—especially patients with ARDS due to surgical operation [15], a systemic inflammatory response, malnutrition, oxidative stress, acute ischemia and hypoxia, and multiple organ failure—can experience diaphragm thinning, decreased activity, and reduced contractility, which results in diaphragm dysfunction. Mechanical ventilation itself can also affect diaphragmatic function and may result in ventilator-associated diaphragmatic dysfunction. Traditional methods for evaluating diaphragmatic function, such as diaphragmatic electrical activity, have not been widely used in clinical practice because of traumatic injury or ionizing radiation, and the results of fluoroscopy and other clinical methods are poor, which is not convenient for repeated examinations. In recent years, with the popularization of bedside ultrasound technology in the ICU, ultrasound examination has received increasing attention for evaluating the diaphragmatic function of patients on mechanical ventilation [16,17]. In May 2015, more than 20 medical experts on critical illnesses from across the country formed a consensus group on bedside ultrasound, and in 2016, the Chinese Expert Consensus on Critical Care Ultrasound was promulgated. The guidelines clearly indicate that critical ultrasound plays an important role in the clinical diagnosis of ARDS, is an important means of bedside assessment of diaphragm function and is helpful for accurate offline implementation. The methods of evaluating diaphragmatic function by critical ultrasound include measuring the diaphragm thickness change and diaphragm activity. Diaphragm activity is strongly affected by the respiratory depth, functional residual volume, intra-abdominal pressure and other factors. The index is not as strong as the diaphragm thickness. The thickness of the quiet end-expiratory diaphragm and the thickness of the maximum end-inspiratory diaphragm cannot truly reflect the diaphragm function, and the absolute values of the normal diaphragm thickness are quite different. Only dynamic diaphragm thickness can reflect diaphragm function. Goligher et al. [18] confirmed that it was feasible, repeatable and effective to measure the thickness of the diaphragm by observing the shape and change in the diaphragm in patients by using critical ultrasound. Changes in the diaphragm thickness are strongly correlated with diaphragm electrical activity, diaphragm pressure and other diaphragm function indices, which can be used to evaluate diaphragm function and assess the autonomous respiratory ability of patients.

The diaphragm thickness variation index was used as the diaphragm function index, which had a good predictive value for weaning. In this study, the TF was used as a predictor of successful weaning, with a sensitivity of 85% and a specificity of 89.03%. When the TF was combined with the shallow fast breathing index, the specificity of the weaning success was significantly improved [19]. This is mainly due to the fact that the dynamic indicators of the diaphragm thickness reflect the real diaphragm functional state, and the shallow fast breathing index reflects all the inspiratory muscle capacity indicators. Patients with acute respiratory distress after cardiac surgery often use the auxiliary respiratory muscles, which are accessory muscles for respiratory activity, to compensate for ventilation insufficiency and prevent diaphragmatic dysfunction. However, the auxiliary respiratory muscle as an accessory muscle of respiration is more prone to fatigue than the diaphragm and lacks the endurance. Even patients with a normal RSBI before weaning may need mechanical ventilation again because of respiratory failure after weaning. Therefore, the diaphragmatic function of such patients needs to be further assessed to prepare for successful weaning. Our findings align with prior research, including Inoue et al. [3], demonstrating the relevance of diaphragmatic function assessment in this specific patient population.

The evaluation of the diaphragmatic contraction and movement amplitude by bedside ultrasound is helpful for the etiological diagnosis of respiratory insufficiency [20], it helps evaluate lung function and guides clinical weaning treatment. Unlike previous studies, for patients post-cardiac surgery, the placement method of the transducer differs due to constraints in positioning and drainage tubes. Traditional methods involve placing the transducer above the umbilicus and sliding it to observe diaphragmatic movement, whereas this study employs a fixed-point placement for observation [21]. For patients with symmetrical diaphragmatic function changes, unilateral (right) diaphragmatic function can reflect overall diaphragmatic function. For patients with asymmetrical diaphragmatic function changes, it is necessary to evaluate bilateral diaphragmatic function. In view of the influence of positive pressure ventilation on diaphragmatic movement, it may be more reasonable to evaluate diaphragmatic function by the contraction amplitude in patients with mechanical ventilation. This improves the accuracy of the prediction results and improves their heterogeneity. Studies have confirmed that the number and quality of the diaphragm and skeletal muscles assessed by critical ultrasound are related to the muscle strength and function and are effective means of early detection and evaluation of therapeutic effects.

In this study, the sample size was not calculated because it was derived from clinical experience and the number of cases was small, which has several limitations. Owing to the feasibility of the operation, we only observed the right diaphragm and the left diaphragm because most of the chest tube, dressing cover, and imaging difficulties were not included in the study. Therefore, for a few patients with unilateral diaphragmatic dysfunction, the reference value of the research results was reduce [22]. In this study, we found that the proportion of patients with ARDS after major vascular surgery was significantly greater than that of patients with ARDS after major vascular surgery [23]. We did not exclude the possibility of weaning failure caused by factors such as lung injury, combined infection, septic shock or traumatic stress. Therefore, this study did not stratify patients by different causes of ARDS, resulting in certain limitations in the evaluation of the significance of the TF in patients with various diseases or different types of surface acute respiratory distress. Additional in-depth and detailed studies are needed [24].

In conclusion, diaphragmatic ultrasound can be used as an additional adjunct procedure in the decision-making process for weaning patients with ARDS from ventilators and improving the success rate of withdrawal after cardiac surgery. This approach is worthy of widespread clinical application.

KEY MESSAGES

▪ Diaphragmatic ultrasound can effectively predict the success rate of withdrawal in patients with acute respiratory distress syndrome after cardiac surgery.

▪ It can play a significant role in guiding the safe clinical removal of ventilators.

NOTES

CONFLICT OF INTEREST

No potential conflict of interest relevant to this article was reported.

FUNDING

This work was supported by the Wuhan Health Research Fund (WX21Z27).

ACKNOWLEDGMENTS

None.

AUTHOR CONTRIBUTIONS

Conceptualization: YQH. Data curation: PY. Project administration: QG. Funding acquisition: YQH . Writing - original draft: YQH. Writing - review & editing: DDX. All authors read and agreed to the published version of the manuscript.

Figure 1.

Study flowchart.

Figure 2.

Diaphragm thickness. (A) A 10-MHz linear array probe was placed along the rib gap between the 7th and 9th ribs of the front of the right armpit. (B) B mode was used to measure the thicknesses of diaphragm. (C) The M mode was selected to measure the thicknesses of the diaphragm at end-inspiration and end-expiration.

Figure 3.

Diaphragm activity. (A) A 3.5-MHz convex array probe was placed at the junction of the anterior armpit line or the middle clavicle line with the rib edge. (B) B mode was used to measure the diaphragm. (C) The M mode was selected, and diaphragm mobility was measured using a sampling line that is perpendicular to the diaphragm.

Figure 4.

Receiver operating characteristic (ROC) curve for using the thickening fraction to predict successful weaning.

Figure 5.

Receiver operating characteristic (ROC) curve for using the rapid shallow breathing index to predict successful weaning.

Table 1.

Comparison of the general characteristics between the successful weaning group and the failure group

Variable	Weaning success group (n=209)	Weaning failure group (n=37)	t-value	P-value
Age (yr)	62±8	63±11	0.292	0.771
BMI (kg/m²)	22.7±3.1	22.4±3.3	0.391	0.687
APACHE II score	17.2±5.3	18.7±6.9	0.716	0.487
SOFA score	3.7±2.1	4.2±2.2	0.813	0.512
Mechanical assist time (day)	18.3±5.5	20.8±4.2	1.209	0.234
Heart rate (beats/min)	91.3±15.5	89.9±18.2	0.457	0.643
Mean arterial pressure (mm Hg)	92.4±15.5	88.9±19.3	1.049	0.301
Tidal volume (ml)	458.0±40.0	413.0±65.0	0.811	0.421
MV (L/min)	8.6±1.8	9.1±1.7	0.723	0.489

Values are presented as mean±standard deviation.

BMI: body mass index; APACHE: Acute Physiology and Chronic Health Evaluation; SOFA: Sequential Organ Failure Assessment; MV: mechanical ventilation.

Table 2.

Comparison of the diaphragm ultrasound results, PaO₂/FiO₂ ratios and RSBI values between the groups

Variable	Weaning success group	Weaning failure group	t-value	P-value
PaO₂/FiO₂ ratio	199.7±69.3	153.8±77.2	−2.068	0.046
TdiFRC (cm)	0.3±0.1	0.3±0.1	–1.230	0.225
TdiFVC (cm)	0.3±0.1	0.2±0.1	0.032	0.977
TF (%)	40.8±15.8	37.7±9.2	4.401	<0.01
DM (cm)	1.5±0.5	1.2±0.4	–1.346	0.040
RSBI (breaths·min^–1·L^–1)	74.3±25.6	89.9±34.5	3.876	<0.01

Values are presented as mean±standard deviation.

PaO₂/FiO₂ ratio: the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen; RSBI: rapid shallow breathing index; TdiFRC: thickness of the diaphragm at functional residual capacity; TdiFVC: thickness of the diaphragm at full vital capacity; TF: thickness fraction; rate; DM: diaphragm mobility.

Table 3.

Predictive values of the TF and RSBI for successful weaning

Parameter	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	AUC	95% CI
TF (%)	85.00	89.03	81.43	79.56	0.809	0.749–0.869
RSBI (breaths·min^–1·L^–1)	91.34	32.98	65.76	78.37	0.745	0.659–0.848

TF: thickness fraction; RSBI: rapid shallow breathing index; PPV: positive predictive value; NPV: negative predictive value; AUC: area under the curve.

REFERENCES

1. Eskandar N, Apostolakos MJ. Weaning from mechanical ventilation. Crit Care Clin 2007;23:263-74.Article PubMed
2. Zambon M, Greco M, Bocchino S, Cabrini L, Beccaria PF, Zangrillo A. Assessment of diaphragmatic dysfunction in the critically ill patient with ultrasound: a systematic review. Intensive Care Med 2017;43:29-38.Article PubMed PDF
3. Inoue R, Nagamine Y, Ohtsuka M, Goto T. Association between diaphragmatic dysfunction after adult cardiovascular surgery and prognosis of mechanical ventilation: a retrospective cohort study. J Intensive Care 2023;11:39.Article PubMed PMC PDF
4. De Jong A, Capdevila M, Chanques G, Cazenave L, Jaber S. What is the most appropriate spontaneous breathing trial before extubation in ICU ventilated patients? Anaesth Crit Care Pain Med 2019;38:429-30.Article PubMed
5. Parada-Gereda HM, Tibaduiza AL, Rico-Mendoza A, Molano-Franco D, Nieto VH, Arias-Ortiz WA, et al. Effectiveness of diaphragmatic ultrasound as a predictor of successful weaning from mechanical ventilation: a systematic review and meta-analysis. Crit Care 2023;27:174.Article PubMed PMC PDF
6. Tobin MJ, Perez W, Guenther SM, Semmes BJ, Mador MJ, Allen SJ, et al. The pattern of breathing during successful and unsuccessful trials of weaning from mechanical ventilation. Am Rev Respir Dis 1986;134:1111-8.Article PubMed
7. Xiao A, Song J, Gong S, Wang M, Hu W, Lu H. Clinical study of diaphragm ultrasound in predicting extubation outcomes for ICU patients undergoing mechanical ventilation. Chin J Crit Care Med 2019;12:250-5.
8. Barbariol F, Deana C, Guadagnin GM, Cammarota G, Vetrugno L, Bassi F. Ultrasound diaphragmatic excursion during non-invasive ventilation in ICU: a prospective observational study. Acta Biomed 2021;92:e2021269. Article PubMed PMC
9. Zhihua L, Qiuping X, Yuehua Y. Clinical study of diaphragmatic thickening score guiding weaning of patients with mechanical ventilation in chronic obstructive pulmonary disease. Chin J Emerg Med 2016;25:491-4.
10. Vivier E, Haudebourg AF, Le Corvoisier P, Mekontso Dessap A, Carteaux G. Diagnostic accuracy of diaphragm ultrasound in detecting and characterizing patient-ventilator asynchronies during noninvasive ventilation. Anesthesiology 2020;132:1494-502.Article PubMed PDF
11. Wang X, Huang S, Xia Z, Yao S, Xia H. Application progress of ultrasound monitoring of diaphragm function in clinic. Zhonghua Wei Zhong Bing Ji Jiu Yi Xue 2021;33:638-40.Article PubMed
12. Agusti A, Soriano JB. COPD as a systemic disease. COPD 2008;5:133-8.Article PubMed
13. McCool FD, Oyieng'o DO, Koo P. The utility of diaphragm ultrasound in reducing time to extubation. Lung 2020;198:499-505.Article PubMed PMC PDF
14. Jiang JR, Tsai TH, Jerng JS, Yu CJ, Wu HD, Yang PC. Ultrasonographic evaluation of liver/spleen movements and extubation outcome. Chest 2004;126:179-85.Article PubMed
15. Matamis D, Soilemezi E, Tsagourias M, Akoumianaki E, Dimassi S, Boroli F, et al. Sonographic evaluation of the diaphragm in critically ill patients: technique and clinical applications. Intensive Care Med 2013;39:801-10.Article PubMed
16. Xiaoting W, Dawei L, Kaijiang Y. Expert consensus on severe ultrasound in China. Chin J Intern Med 2016;55:900-12.
17. Spiesshoefer J, Herkenrath S, Henke C, Langenbruch L, Schneppe M, Randerath W, et al. Evaluation of respiratory muscle strength and diaphragm ultrasound: normative values, theoretical considerations, and practical recommendations. Respiration 2020;99:369-81.Article PubMed PDF
18. Goligher EC, Laghi F, Detsky ME, Farias P, Murray A, Brace D, et al. Measuring diaphragm thickness with ultrasound in mechanically ventilated patients: feasibility, reproducibility and validity. Intensive Care Med 2015;41:642-9.Article PubMed PDF
19. Maynard-Paquette AC, Poirier C, Chartrand-Lefebvre C, Dubé BP. Ultrasound evaluation of the quadriceps muscle contractile index in patients with stable chronic obstructive pulmonary disease: relationships with clinical symptoms, disease severity and diaphragm contractility. Int J Chron Obstruct Pulmon Dis 2020;15:79-88.Article PubMed PMC
20. Rittayamai N, Chuaychoo B, Tscheikuna J, Dres M, Goligher EC, Brochard L. Ultrasound evaluation of diaphragm force reserve in patients with chronic obstructive pulmonary disease. Ann Am Thorac Soc 2020;17:1222-30.Article PubMed
21. Tuinman PR, Jonkman AH, Dres M, Shi ZH, Goligher EC, Goffi A, et al. Respiratory muscle ultrasonography: methodology, basic and advanced principles and clinical applications in ICU and ED patients-a narrative review. Intensive Care Med 2020;46:594-605.Article PubMed PMC PDF
22. Nekludova GV, Avdeev SN. Possibilities of ultrasound research of the diaphragm. Ter Arkh 2019;91:86-92.Article PDF
23. Whebell S, Sane S, Naidu S, White H. Use of ultrasound to determine changes in diaphragm mechanics during a spontaneous breathing trial. J Intensive Care Med 2021;36:1044-52.Article PubMed PDF
24. Vetrugno L, Guadagnin GM, Barbariol F, Langiano N, Zangrillo A, Bove T. Ultrasound imaging for diaphragm dysfunction: a narrative literature review. J Cardiothorac Vasc Anesth 2019;33:2525-36.Article PubMed

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Diaphragm ultrasound for predicting weaning success in post-cardiac surgery acute respiratory distress syndrome patients: a prospective observational study in China

Acute Crit Care. 2025;40(3):435-443. Published online August 21, 2025

DOI: https://doi.org/10.4266/acc.004320

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Diaphragm ultrasound for predicting weaning success in post-cardiac surgery acute respiratory distress syndrome patients: a prospective observational study in China

Figure 1. Study flowchart.

Figure 2. Diaphragm thickness. (A) A 10-MHz linear array probe was placed along the rib gap between the 7th and 9th ribs of the front of the right armpit. (B) B mode was used to measure the thicknesses of diaphragm. (C) The M mode was selected to measure the thicknesses of the diaphragm at end-inspiration and end-expiration.

Figure 3. Diaphragm activity. (A) A 3.5-MHz convex array probe was placed at the junction of the anterior armpit line or the middle clavicle line with the rib edge. (B) B mode was used to measure the diaphragm. (C) The M mode was selected, and diaphragm mobility was measured using a sampling line that is perpendicular to the diaphragm.

Figure 4. Receiver operating characteristic (ROC) curve for using the thickening fraction to predict successful weaning.

Figure 5. Receiver operating characteristic (ROC) curve for using the rapid shallow breathing index to predict successful weaning.

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Diaphragm ultrasound for predicting weaning success in post-cardiac surgery acute respiratory distress syndrome patients: a prospective observational study in China

Variable	Weaning success group (n=209)	Weaning failure group (n=37)	t-value	P-value
Age (yr)	62±8	63±11	0.292	0.771
BMI (kg/m²)	22.7±3.1	22.4±3.3	0.391	0.687
APACHE II score	17.2±5.3	18.7±6.9	0.716	0.487
SOFA score	3.7±2.1	4.2±2.2	0.813	0.512
Mechanical assist time (day)	18.3±5.5	20.8±4.2	1.209	0.234
Heart rate (beats/min)	91.3±15.5	89.9±18.2	0.457	0.643
Mean arterial pressure (mm Hg)	92.4±15.5	88.9±19.3	1.049	0.301
Tidal volume (ml)	458.0±40.0	413.0±65.0	0.811	0.421
MV (L/min)	8.6±1.8	9.1±1.7	0.723	0.489

Variable	Weaning success group	Weaning failure group	t-value	P-value
PaO₂/FiO₂ ratio	199.7±69.3	153.8±77.2	−2.068	0.046
TdiFRC (cm)	0.3±0.1	0.3±0.1	–1.230	0.225
TdiFVC (cm)	0.3±0.1	0.2±0.1	0.032	0.977
TF (%)	40.8±15.8	37.7±9.2	4.401	<0.01
DM (cm)	1.5±0.5	1.2±0.4	–1.346	0.040
RSBI (breaths·min^–1·L^–1)	74.3±25.6	89.9±34.5	3.876	<0.01

Parameter	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	AUC	95% CI
TF (%)	85.00	89.03	81.43	79.56	0.809	0.749–0.869
RSBI (breaths·min^–1·L^–1)	91.34	32.98	65.76	78.37	0.745	0.659–0.848

Table 1. Comparison of the general characteristics between the successful weaning group and the failure group

Values are presented as mean±standard deviation.

BMI: body mass index; APACHE: Acute Physiology and Chronic Health Evaluation; SOFA: Sequential Organ Failure Assessment; MV: mechanical ventilation.

Table 2. Comparison of the diaphragm ultrasound results, PaO2/FiO2 ratios and RSBI values between the groups

Values are presented as mean±standard deviation.

Table 3. Predictive values of the TF and RSBI for successful weaning

TF: thickness fraction; RSBI: rapid shallow breathing index; PPV: positive predictive value; NPV: negative predictive value; AUC: area under the curve.