The diaphragm is the main respiratory muscle, which plays an important role in the respiratory movement, and its dysfunction predisposes to prolonged duration of mechanical ventilation and respiratory complications. Sonographic evaluation has recently started to become popular in the intensive care unit (ICU) for assessing diaphragmatic function [9]. In comparing the control COPD cases with others who suffered from MV with failed weaning experience, regarding US parameters during tidal breathing, both of inspiratory, expiratory DT, DE, and DTF % were significantly higher in the COPD group (control) than in the failed weaning group (B) (p < 0.001). Furthermore, during deep breathing techniques, all DT parameters were significantly higher in the COPD group than in the weaning failure group (p < 0.001). In our knowledge, this is the first study that compared pulmonary diseases and COPD as regards the diaphragmatic ultrasound parameter (Table 3).
Diaphragmatic thickness during tidal breathing (Fig. 3)
In the present study, DT at end inspiration in the successful group was 24 mm (23.25–26), versus failed group 18 mm (17–19.15), p < 0.001, with a cutoff point > 21mm, 95% sensitivity, 100% specificity, 100% PPV, 99% NPV, and an AUC 95% (Tables 1 and 2). Similarly, Farghaly and Hasan [3] found DT at end inspiration in a successful group was 24 mm (22–28), versus failed group 18 mm (15–20), with a cutoff point ≥ 21 mm, 77.5% sensitivity, 86.6% specificity, and an AUC of 83.1%. In the present study, DT (FRC) at end expiration in a successful group was 17 mm (15–18), versus failed group 14 mm (12.3–15), p = 0.001, with a cutoff point >15.5%, 62% sensitivity, 100% specificity, 100% PPV, 92% NPV, and an AUC 85% (Tables 1 and 2) (Fig. 3). Similarly, Farghaly and Hasan found that DT at end expiration in a successful group was 16 mm (11.2–18.7), versus failed group 11 mm (10–15), with a cutoff point ≥ 10.5 mm, 80% sensitivity, 50% specificity, and an AUC 68.8% [3]. In the present study, DTF% in a successful group was 44.41% (35.07–67.12), versus failed group 30.38% (23.34–38.07), with a cutoff point > 32.82%, 90% sensitivity, 75% specificity, 44% PPV, 97% NPV, and an AUC 77% (Tables 1 and 2) (Fig. 3). This result is consistent with studies by Farghally and Hasan [3] and Dinino et al. [10] which demonstrated that DTFs with a cutoff point more than 34 and 30, respectively, were associated with weaning success and better ICU outcomes. In contrast with Umbrello et al. [4], who observed patients after major elective surgery and first weaning failure, they reported that a cutoff point of DTF more than 20% was associated with weaning success, and this may be explained by the absence of surgical patients in this study. In the present study, DE in a successful group is 1.9 cm (1.53–2.75), versus failed group 1.66 cm (1.09–1.94), p = 0.001, with a cutoff point > 1.7 cm, 68% sensitivity, 65% specificity, 30% PPV, 90% NPV, and an AUC 0.73 (Tables 1 and 2 ) (Fig. 3). This result is consistent with the studies done by Matamis et al. [9] and Palkar et al. [11] who confirmed that DE at a cutoff point of more than 1.65 cm and 1.64 cm, respectively, was associated with weaning success and better ICU outcomes. Also, Gursel et al. [12] reported that tidal diaphragmatic excursion using standard ultrasound devices (SD) is 1.76 ± 0.69 cm (0.58–3.30) and using pocket-sized ultrasound devices (PSDs) 1.62 ± 0.70 cm (0.50–3.00). In the present study, the AUC of the DT Insp (95) was more than that of DTF (77), while AUC of DT Exp (FRC) (85) was more than that of DTF (77). In contrast, Farghaly and Hasan stated that AUC of DT (83.1) at end inspiration was more than DT (68.8) at the end expiration and AUC of DT (68.8) at the end expiration was less than DTF (70. 8). Also, it was found that AUC of DT (61) at the end expiration was less than that of DTF (79) alone [3]. In the present study, the DE was less (68%) sensitive than that DT Insp (95%), and the specificity of DT Insp (100%) was more than that of DE (30%) (Table 2). Similarly, Farghaly and Hasan observed that diaphragm excursion should not be used in the assessment of diaphragmatic contractile activity, whereas diaphragm thickening is a good indicator of respiratory effort [3]. Also, Umbrello et al. observed that during pressure support ventilation, diaphragm thickening was more accurate than diaphragm excursion and suggested that the use of diaphragm excursion is of little help during PSV and should not be used in the assessment of diaphragmatic contractile activity [4]. In contrast, Hayat et al. [13] reported that diaphragmatic excursion is a good method for predicting the weaning outcome.
Diaphragmatic thickness during deep breathing
In the current study, diaphragm thickness at TLC in a successful group was 36 mm (33–39.75), versus failed group 26 mm (23.25–29.75) with a cutoff point 28.5, 100% sensitivity, 65% specificity, 39% PPV, 100% NPV, and an AUC 0.87, while diaphragm thickness at RV in the successful group was 25 mm (22–27), versus failed group 20.5 mm (18–22.75) with a cutoff point 22.5 mm, 73% sensitivity, 75% specificity, 39% PPV, 93% NPV, and an AUC 0.75 (Tables 1 and 2) (Fig. 4). Similarly, Ferrari et al. stated that diaphragm thickness (DT) at TLC in a successful group was 38 mm (29–45), versus failed group 30 mm (20–40) [1], while DT at RV in a succeeded group was 25 mm (19–28), versus failed group 24 mm (17–30). Moreover, Gursel et al. found that the maximal inspiratory thickness was SD 47 ± 16mm (23–68) and PSDs 45 ± 12mm (24–91). In contrast, Pirompanich and Romsaiyut noted that DT at TLC in a succeeded group was 35 ± 13 and 38 mm (IQR 29–45), versus failed group 31 ± 13 mm and 30 mm (IQR 20–40) [12], while diaphragm thickness at RV in a successful group was 22 ± 09 mm and 25 mm (IQR 19–28), versus failed group 25 ± 11 mm and 24 mm (IQR 17–30).There were higher values about RV in the failed group more than the successful group, and these variables can be explained by different causes for mechanical ventilation as well as different ventilation periods and different ethnic groups which may affect the thickness of the diaphragm. In the present study, DTF in a successful group was 50% (43.05–58.20), versus failed group 25% (23.80–26.99), with a cutoff point of 37%, 97% sensitivity, 100% specificity, 97% PPV, 100% NPV, and an AUC 1 (Tables 1 and 2) (Fig. 4). These results are consistent with studies done by Ferrari et al. [1] which demonstrated that DTFs of more than 36% were associated with weaning success and better ICU outcomes. Our study found that DE in a successful group was 3.6 cm (3–5.4), versus failed group 2.95 cm (1.73–4.05), with a cutoff point DE 3.1 cm, 75% sensitivity, 55% specificity, 27% PPV, 91% NPV, and an AUC 0.68 (Tables 1 and 2) (Fig. 4). Similarly, Carrie et al. found that DE in the successful group was 4.1 ±2. 1cm, versus failed group 3 ± 1.8cm with a cutoff point DE 2.7cm [14]. Also, Gursel et al. found in their study DE (±SD) was 2.97 ± 1.18cm (1.33–5.40) and PSDs 2.67 ± 0.90cm (1.30–4.70) [12]. Moreover, Lerolle et al. reported that DE less than 2.5 cm was a predictor of weaning failure, in post-cardiac patients connected to mechanical ventilation [15]. In the present study, the DTF was more specific and sensitive with a higher AUC (100%, 97%, 1) than DE (55%, 75%, 0.91) (Table 2) (Fig. 4). This result is consistent with the studies by Samanta et al. [16] and Ferrari et al. [1] who reported that the DTF is more accurate than DE in the prediction of successful weaning. In the present study, DT Insp (TLC) is more sensitive and specific (100%, 65%) than DE (75%, 55%). The AUC of DT Insp (TLC) was more than that of DT Exp (RV) (0.87 and 0.75, respectively). The AUC of DTF was more than the AUC of DT Insp (TLC) (100 and 87, respectively) (Table 2) (Fig. 4). In contrast, Farghaly and Hasan observed that the AUC of DT at end inspiration was more than DT at end expiration (83.1 and 68. 8, respectively) [3]. Also, Di Nino et al. observed that the AUC for DT end expiration was less than that for DTF% alone (0.79 and 0.61, respectively) [10]. However, they determined DT, DTF, and DE during tidal breathing, while in the current study, DT, DTF, and DE were assessed during tidal and deep breathing. In the present study, the AUC of DTF during deep breathing was more than DT Insp during tidal breathing (100 and 95, respectively), while the AUC of DT Insp was more than DT Insp (TLC) (95 and 87, respectively) (Table 2). In the present study, the RSBI in the successful group was 58 (52–63) breath/min/L, versus failed group 46 (41–51) breath/min/L, p < 0.005, and a cutoff value for RSBI was 35.5 b/min with 47% sensitivity, 90% specificity, 51% PPV, 188% NPV, and the AUC of 71% in predicting extubation failure (Tables 1 and 2) (Fig. 5). Similarly, Farghaly and Hasan observed that the RSBI in a successful group was 51.5 (44–79), versus failed group 50 (40–65), p <0.005 [3]. Also, Pirompanich and Romsaiyut found that the average RSBI in a successful group was 54. 3 ± 22.8, versus failed group 47.7 ± 14.8, p < 0.012 [14]. In contrast, Ferrari et al. observed that the RSBI in a successful group was 70 (57–83), versus failed group 120 (110–148), p < 0.0001 [1]. This variation can be explained by different causes for mechanical ventilation as well as different ventilation periods, which may affect the outcome of the weaning process. During tidal breathing, the specificity of RSBI was less than DT at insp and DT Exp (FRC) at end expiration (90, 100, and 100). But the specificity of RSBI is more than DTF and DE (90, 75, and 65). But the AUC of RSBI is less than DT Insp, DT Exp (FRC), DTF, DE, TLC, RV, and DTF (71, 95, 85, 77, 73, 87, 75, and 100, respectively). The AUC of RSBI during forced expiration and inspiration is more than DE (71 and 68, respectively) (Table 2) (Figs. 3, 4, and 5). Similarly, DiNino et al. reported that the diaphragmatic thickness and diaphragmatic thickness fraction are more accurate than RSBI, for predicting successful weaning [10]. Also, Pirompanich and Romsaiyut observed that integration of DTF (right) (AUC 95%) and RSBI (AUC 70%) are more accurate than RSBI (AUC 70%), for foretelling of successful extubation [17]. Similarly, Farghaly and Hasan reported that the diaphragm thickness, DTF, and DE during tidal breathing are more accurate than RSBI [3]. They recommended to consider the use of these parameters with RSBI to improve weaning outcome. In addition, Hayat et al. reported that the DE during tidal breathing is more accurate than RSBI, but they did not use DT and DTF in the comparison [13]. Ramakrishnan and Siddiqui reported that the diaphragmatic excursion is probably better in predicting extubation success than RSBI [18].
Fate of the studied patients
In the present study, as regards group A, the number of patients with successful weaning was 31 (77.5%) versus 9 (22.5%) of weaning failure, while in group B, the number of patients with successful weaning was 29 (72.5%) versus 11 (27.5%) of weaning failure. This is consistent with Esteban et al. [8], 27%. This is in contrast with Ferrari et al. [1] who reported a 63% failure rate. This variation can be explained by different causes for mechanical ventilation as well as different ventilation periods before starting the weaning process, which may affect the outcome of the weaning process.
Study limitations
The measurements of the diaphragm were not supplemented with direct measurements (such as the maximal expiratory pressure, maximal inspiratory pressure, and transdiaphragmatic pressure). This study was done in the respiratory care unit, and there were no surgical treated patients. While the (reference) thickness of the diaphragm in many diseases, e.g., COPD, pneumonia, and DM, is still unknown, the golden standard of measuring the diaphragmatic strength is phrenic nerve stimulation, and comparing it with sonographic findings was not done in this study. This study did not target a certain chest disease in its assessment of the diaphragm. The right hemidiaphragm was used in the diaphragmatic assessment being easier in imaging than the left hemidiaphragm which is often impeded by intestinal and gastric gas.