The impact of intensivist-performed, examination extended ultrasound in intensive care medicine

Abstract

Intensivist-performed ultrasound, including transthoracic echocardiography (TTE) and to a lesser extent lung ultrasound, has been integrated into clinical practice in ICU. However, it is only used when indicated as a goal-directed test to answer a specific clinical question posed by the treating intensivist. The impact of such practice has been shown to be clinically useful and may be associated with better outcome.

In contrast, routine practice of ultrasound in critical care is plausible and has a good rationale with diagnostic, monitoring and sometimes therapeutic advantages. In addition to its non-invasive nature, safety and reproducibility, routine use of ultrasound as an extended bedside examination – irrespective of indications – may be clinically useful in various phases during the course of ICU admission. Nonetheless, there are gaps in the literature surrounding this approach.

In our literature review, we aim to investigate the role of intensivist-performed critical care ultrasound (TTE and lung with or without diaphragm) on clinical outcomes when performed routinely as an adjunct to clinical assessment during the first 24 hours of admission and during the peri-extubation period as a predicting factor of extubation outcome.

The thesis includes three prospective observational studies, where different applications of ultrasound are investigated. Each study is preceded by literature review relevant to the study topic.

The first study investigated the feasibility and impact of routine combined limited transthoracic echocardiography and lung ultrasound on diagnosis and management of patients admitted to ICU. Objectives: routine combined limited TTE and lung ultrasound performed within 24 hours of admission to ICU is feasible and changes diagnosis and management in a high proportion of patients.

Design: Prospective observational study. Setting: Tertiary ICU. Participants: 93 critically ill participants within 24 hours of admission to ICU.

Methods: A treating intensivist documented a clinical diagnosis and management plan before and after combined limited TTE and lung ultrasound. Ultrasound was performed by an independent intensivist and checked for accuracy off-line by a second reviewer.

Results: Ultrasound images were interpretable in 99% of cases, with good interobserver agreement. The haemodynamic diagnosis was altered in 66% of participants, comprising new (14%) and altered (25%) abnormal states and exclusion of clinically diagnosed abnormal state (27%). Valve pathology of at least moderate severity was diagnosed for mitral regurgitation (7%), aortic stenosis (1%), aortic stenosis and mitral regurgitation (1%) and tricuspid regurgitation (3%). One case of mitral regurgitation was excluded. Lung pathology diagnosis was changed in 58% of participants, comprising consolidation (13%), interstitial syndrome (4%) and pleural effusion (23%) and exclusion of clinically diagnosed consolidation (6%), interstitial syndrome (3%) and pleural effusion (9%). Management changed in 65% of participants, comprising increased (12%) or decreased (23%) fluid therapy; initiation (10%), change (6%) or cessation (9%) of inotropic, vasoactive or diuretic drugs; non-invasive ventilation (3%); and pleural drainage (2%).

Conclusion: Routine screening of patients with combined limited TTE and lung ultrasound on admission to ICU is feasible and frequently alters diagnosis and management.

The second study is titled ‘Diaphragmatic regional displacement assessed by ultrasound and correlated to subphrenic organ movement in the critically ill patients - an observational study’.

Objectives: The objectives of the study were to identify the most reliably imaged regions of the diaphragm, to evaluate the correlation of movement between different parts of each hemidiaphragm and to assess the agreement between liver or spleen displacement and movement of the ipsilateral hemidiaphragm.

Design: Prospective observational study. Setting: Tertiary ICU. Participants: 90 participants

Methods: Images of the diaphragm, liver and spleen were obtained using 2-dimensional ultrasound. Acceptable agreement between regions of the diaphragm, liver and spleen was defined as an absence of fixed or proportional bias using Deming regression analysis. Limits of agreement of two standard deviations of the difference less than 30% of the mean value was considered acceptable.

Results: We included 90 critically ill participants. The medial (87%) and middle (73%) regions of the right hemidiaphragm, liver (87.7%), medial (71%) and middle (51%) regions of the left hemidiaphragm and spleen (81%) were most frequently imaged. In non-intubated group, acceptable agreement was present between the movements of the middle and medial regions of the right hemidiaphragm, middle and medial regions of the left hemidiaphragm and between the movement of the middle region of the left hemidiaphragm and displacement of the spleen. In the intubated group and in all participants when combined, acceptable agreement was only present between the movements of the middle and medial regions of the right hemidiaphragm and middle and medial regions of the left hemidiaphragm. Acceptable agreement was not present between the diaphragm movement and the liver or spleen displacement in the intubated group or in all participants.

Conclusion: The diaphragm medial part is visualised in the majority of studied participants. The medial and middle regions of the hemidiaphragm may be used interchangeably to assess the hemidiaphragm movement. Acceptable agreement does not exist for the diaphragm and solid organ movement, other than for the left middle region and the spleen in non-intubated participants only.

The third study is titled ‘The impact of heart, lung and diaphragmatic ultrasound on prediction of failed extubation from mechanical ventilation in critically ill patients: a prospective observational pilot study’. Objectives: Failed extubation from mechanical ventilation in critically ill patients is multifactorial, complex and not well understood. We aimed to identify whether combined TTE, lung and diaphragmatic ultrasound can predict extubation failure in critically ill patients.

Design: Prospective observational study. Setting: Tertiary ICU. Participants: 53 participants who were intubated >48 hours and deemed by the treating intensivist ready for extubation.

Methods: A 60-minute pre-extubation weaning trial (pressure support <10 cmH2O and positive end expiratory pressure 5 cmH2O) was performed. Prior to extubation, data collected included ultrasound assessment of left ventricular ejection fraction, left atrial area, early diastolic trans-mitral flow velocity wave (E), E/A, E/E', interatrial septal motion, lung loss of aeration score and diaphragm movement. At the end of the weaning trial the rapid shallow breathing index and serum B-type natriuretic peptide concentration were measured. Success and failure of weaning was assessed by defined criteria. Decision to extubate was at the discretion of the treating intensivist. Failure of extubation was defined as re-intubation or non-invasive ventilation within 48 hours after extubation.

Results: Of 53 extubated participants, 11 failed extubation. Failed extubation was associated with diabetes, ischaemic heart disease, higher E/E' (OR 1.27, 95% CI 1.05-1.54), left atrial area (OR 1.14, CI 1.02-1.28), fixed rightward curvature of the interatrial septum (OR 12.95, CI 2.73-61.41) and higher loss of aeration score of anterior and lateral regions of the lungs (OR 1.41, CI 1.01-1.82).

Conclusion: Failed extubation in mechanically ventilated patients is more prevalent if markers of left ventricular diastolic dysfunction and loss of lung aeration are present.

There are encouraging signs that support the use of multiple ultrasound modalities routinely as an adjunct to clinical evaluation of critically ill patients with a strong signal for the use of combined TTE and lung ultrasound. Adding lung ultrasound to TTE is complementary, and enhances the information obtained from TTE. It may also predict outcomes of weaning from mechanical ventilation.