Diaphragm Ultrasound in Cardiac Surgery: State of the Art

In cardiac surgery, patients are at risk of phrenic nerve injury, which leads to diaphragm dysfunction and acute respiratory failure. Diaphragm dysfunction (DD) is relatively frequent in cardiac surgery and particularly affects patients after coronary artery bypass graft. The onset of DD affects patients’ prognosis in term of weaning from mechanical ventilation and hospital length of stay. The authors present a narrative review about diaphragm physiology, techniques used to assess diaphragm function, and the clinical application of diaphragm ultrasound in patients undergoing cardiac surgery.

Circulating Skeletal Troponin During Weaning From Mechanical Ventilation and Their Association to Diaphragmatic Function: A Pilot Study

Background: Patients with acute respiratory failure (ARF) may need mechanical ventilation (MV), which can lead to diaphragmatic dysfunction and muscle wasting, thus making difficult the weaning from the ventilator. Currently, there are no biomarkers specific for respiratory muscle and their function can only be assessed trough ultrasound or other invasive methods. Previously, the fast and slow isoform of the skeletal troponin I (fsTnI and ssTnI, respectively) have shown to be specific markers of muscle damage in healthy volunteers. We aimed therefore at describing the trend of skeletal troponin in mixed population of ICU patients undergoing weaning from mechanical ventilation and compared the value of fsTnI and ssTnI with diaphragmatic ultrasound derived parameters.Methods: In this prospective observational study we enrolled consecutive patients recovering from acute hypoxemic respiratory failure (AHRF) within 24 h from the start of weaning. Every day an arterial blood sample was collected to measure fsTnI, ssTnI, and global markers of muscle damage, such as ALT, AST, and CPK. Moreover, thickening fraction (TF) and diaphragmatic displacement (DE) were assessed by diaphragmatic ultrasound. The trend of fsTnI and ssTnI was evaluated during the first 3 days of weaning.Results: We enrolled 62 consecutive patients in the study, with a mean age of 67 ± 13 years and 43 of them (69%) were male. We did not find significant variations in the ssTnI trend (p = 0.623), but fsTnI significantly decreased over time by 30% from Day 1 to Day 2 and by 20% from Day 2 to Day 3 (p < 0.05). There was a significant interaction effect between baseline ssTnI and DE [F(2) = 4.396, p = 0.015], with high basal levels of ssTnI being associated to a higher decrease in DE. On the contrary, the high basal levels of fsTnI at day 1 were characterized by significant higher DE at each time point.Conclusions: Skeletal muscle proteins have a distinctive pattern of variation during weaning from mechanical ventilation. At day 1, a high basal value of ssTnI were associated to a higher decrease over time of diaphragmatic function while high values of fsTnI were associated to a higher displacement at each time point.

Pressure Support Versus T-Piece Trial For Weaning From Mechanical Ventilation

Aim: To compare pressure support versus T-piece trial for weaning from mechanical ventilation Methodology: Randomized clinical trial in Surgical ICU, Khyber Teaching hospital Peshawar. 48 patients who had been mechanically ventilated for at least 24 hours and were deemed suitable for weaning took part in the study. SBT with pressure support ventilation of 8cm of H2O was performed on one group of patients for two hours while the other group received a 30-minute SBT with pressure support ventilation. It was successful when extubation process is completed, (being able to go 72 hours without mechanical ventilation after the first SBT). Results: Extubation was successful in 83.3% who received pressure support ventilation and in 75% who employed a T-piece. The patients who required reintubation were 12% with support pressure and 16.7% with T piece ventilation. Mortality rate in support pressure group is 16.7% while 25% in T piece ventilation group. Conclusion: Pressure support ventilation for 30 minutes had a much higher success rate when it came to extubation. For spontaneous breathing trials, a shorter, less taxing ventilation approach should be used rather than the traditional one. Keywords: Extubation, Support pressure, T piece

Correlation between Handgrip Strength and Rapid Shallow Breathing Index for Assessment of Weaning from Mechanical Ventilation

Background. Assessment of weaning from mechanical ventilation (MV) is an important process. Rapid shallow breathing index (RSBI) is a standard tool to evaluate a patient’s readiness before the spontaneous breathing trial (SBT). Handgrip strength (HGS) is an alternative method for assessment of respiratory muscle strength. Relationship between HGS and RSBI has not been explored. This study aimed to determine the correlation between HGS and RSBI to predict successful extubation in mechanically ventilated patients. Methods. A prospective study was conducted in screened 120 patients requiring MV with tracheal intubation >48 h. HGS was performed at 48 h after intubation, 10 min before and 30 min after SBT, and 1 h after extubation. RSBI was performed at 10 min before SBT. Results. A total of 93 patients (58% men) were included in the final analysis. Mean age was 71.6 ± 15.2 years. Patients admitted in general medical wards were 84.9%. APACHE II score was 13.5 ± 4.7. Most patients were intubated from pneumonia (39.8%). Weaning failure was 6.5%. The main result shows that HGS was negatively correlated with RSBI (regression coefficient −0.571, P < 0.001 ). The equation for predicting RSBI, derived from the linear regression model, was predicted RSBI (breaths/min/L) = 39.285 + (age ∗ 0.138)–(HGS ∗ 0.571). Conclusions. HGS had significantly negative correlation with RSBI for assessment of weaning from MV. A prospective study of the HGS cutoff value is needed to investigate the difference between patients who succeeded and those who failed extubation. This trial is registered with TCTR20180323004.

Lung Ultrasound to Monitor Disease Severity and Aid Prognostication in COVID-19 Pneumonia: A Retrospective Analysis of Serial Lung Ultrasound Assessments

Background: The aim of this retrospective analysis was to assess if serial lung ultrasound assessments in patients with COVID-19 pneumonia, including a novel simplified scoring system, correlate with PaO2:FiO2 ratio, as a marker of disease severity, and patient outcomes. Methods: Patients treated for COVID-19 pneumonia in a tertiary intensive care unit who had a lung ultrasound assessment were included. Standardised assessments of anterior and lateral lung regions were prospectively recorded. A validated lung ultrasound score-of-aeration and a simplified scoring system based on the number of disease-free lung regions were correlated with: PaO2:FiO2 ratio, successful weaning from mechanical ventilation, and status (alive or dead) at discharge. MedCalc© statistical software was used for statistical analysis. Results: 28 patients (109 assessments) were included. Correlation was seen between score-of-aeration and PaO2:FiO2 ratio (r = -0.61, p<0.0001) and between the simplified scoring system and PaO2:FiO2 ratio (r = 0.52 p<0.0001). Achieving a score-of-aeration of ≤9/24 or ≥2 disease-free regions was associated with successful weaning from mechanical ventilation and survival to ICU discharge (accuracy of 94% and 97% respectively). Conclusion: Retrospective analysis from this small cohort of patients demonstrates that scores-of-aeration and a simplified scoring system based on the number of disease-free antero-lateral regions from serial LUS assessments correlate with PaO2:FiO2 ratio as a marker of disease severity in patients with COVID-19 pneumonia. In addition, lung ultrasound may help identify patients who will have favourable outcomes.

Weaning from Mechanical Ventilation

Weaning off mechanical ventilation (MV) is a process that ultimately ends with a patient’s liberation from the ventilator. As extubation failure worsens prognosis, every effort should be made to safely extubate the patient when the clinical condition allows it. There are several methods and techniques to assess whether a patient is ready for weaning. The clinician should choose the proper method for each patient to minimalize the risk of extubation failure. When liberation from MV is not possible, tracheostomy and transferring the patient to a long-term rehabilitation ward may be required. If this is not feasible, palliative care should be considered.

Role of Capnograghy during weaning from mechanical ventilation in patients with chronic obstructive pulmonary disease

Background Chronic obstructive pulmonary disease (COPD) is characterized by persistent airflow limitation associated with an enhanced chronic inflammatory response in the airway, acute exacerbations of COPD can lead to progressive respiratory failure necessitating mechanical ventilation. Weaning of these patients may prove difficult and a spontaneous breath trial should be provided before the decision of extubation. Aim To evaluate the role of capnograghy in COPD patients during weaning from mechanical ventilation. Subject and methods This was a cross sectional prospective study conducted on 50 patients who were admitted at the Respiratory Intensive Care Unit of Abbassia Chest hospital and diagnosed as COPD and on mechanical ventilation. During the weaning trial, the role of capnography device evaluated considering the ability of Pet CO2 parameter in predicting hypercapnia and subsequently weaning outcome Results The changes in ABG reading before and after the SBT, PaCO2 and Pet CO2 showed significant elevation at the end of SBT,P=0.001 for both, while O2 saturation was significantly decrease at the end of SBT, P0.001. Conclusion The study found that Pa CO2 and PetCO2 are correlated to each other before, during and after SBT. Most of the studies that was found reported that PetCO2 is highly correlated with Paco2 and that PetCO2 may be a rapid and reliable predictor of arterial PaCO2 in respiratory distress.