Part I of this thesis revolved around various aspects of lung ultrasound in a critical care setting. Given the high prevalence of pulmonary pathology on the Intensive Care Unit (ICU), diagnostic tools to assess the lungs are of great importance. While tools such as chest X-ray, CT or indwelling catheters (pulmonary artery catheter and pulse contour cardiac output catheter) play an important role, they come with drawbacks of invasive- ness, high patient burden, risk of complications and necessity for patient transport. As POCUS (Point Of Care UltraSound) suffers significantly less from these limitations, it was quickly adopted on the ICU after it had been shown to be an accurate diagnostic tool on the emergency ward. While this seemed like an ideal continuation of its use in lung pathology, fundamental issues limited simple translation: epidemiological characteris- tics differ, normal pulmonary physiology is disturbed by positive pressure ventilation and location of pathology is influenced by gravity and differs between ambulatory and in-hospital patients. In Part II of this thesis, the focus shifted from the lung towards the diaphragm. Force generating capacity of the diaphragm was recognized to play a prominent role in lib- erating patients from mechanical ventilation. As such, tools to quantify function were deemed of importance. POCUS was being hypothesized to be a viable tool in this regard, but evidence was still scarce. As such, this part was started with a literature review of the available evidence in chapter 5. The result was a concise overview with recommen- dations for applications in clinical practice. Interestingly, important variability between study methodology was observed, ranging from choice and positioning of transducer, to caliper placement for thickness measurements. In essence, Part III was the synthesis of the knowledge acquired in the previous parts of this thesis. Integration of information about various components of the respiratory system, allows for a much more detailed and targeted response to questions of respira- tory pathology. Especially in a critical care setting, where clinical problems are rarely unifactorial, the diagnostic and therapeutic approach should match their multifaceted aspects. POCUS offers flexibility as required by the situation and the clinical context. The question whether a patient has pneumonia can be answered with a simple and swift examination of only a few pulmonary areas, while elucidating the causes of extubation failure can be done through focused assessment of various contributing components, including heart, lungs, diaphragm and abdominal processes.