Pathophysiology of Oxygen Delivery in Respiratory Failure

Monitoring patients with acute respiratory failure during non-invasive respiratory support to minimize harm and identify treatment failure

Non-invasive respiratory support (NRS), including high flow nasal oxygen therapy, continuous positive airway pressure and non-invasive ventilation, is a cornerstone in the management of critically ill patients who develop acute respiratory failure (ARF). Overall, NRS reduces the work of breathing and relieves dyspnea in many patients with ARF, sometimes avoiding the need for intubation and invasive mechanical ventilation with variable efficacy across diverse clinical scenarios. Nonetheless, prolonged exposure to NRS in the presence of sustained high respiratory drive and effort can result in respiratory muscle fatigue, cardiovascular collapse, and impaired oxygen delivery to vital organs, leading to poor outcomes in patients who ultimately fail NRS and require intubation. Assessment of patients' baseline characteristics before starting NRS, close physiological monitoring to evaluate patients' response to respiratory support, adjustment of device settings and interface, and, most importantly, early identification of failure or of paramount importance to avoid the negative consequences of delayed intubation. This review highlights the role of respiratory monitoring across various modalities of NRS in patients with ARF including dyspnea, general respiratory parameters, measures of drive and effort, and lung imaging. It includes technical specificities related to the target population and emphasizes the importance of clinicians' physiological understanding and tailoring clinical decisions to individual patients' needs.

Role of SatO2, PaO2/FiO2 Ratio and PaO2 to Predict Adverse Outcome in COVID-19: A Retrospective, Cohort Study

COVID-19 respiratory failure is a life-threatening condition. Oxygenation targets were evaluated in a non-ICU setting. In this retrospective, observational study, we enrolled all patients admitted to the University Hospital of Genoa, Italy, between 1 February and 31 May 2020 with an RT-PCR positive for SARS-CoV-2. PaO2, PaO2/FiO2 and SatO2% were collected and analyzed at time 0 and in case of admission, patients who required or not C-PAP (groups A and B) were categorized. Each measurement was correlated to adverse outcome. A total of 483 patients were enrolled, and 369 were admitted to hospital. Of these, 153 required C-PAP and 266 had an adverse outcome. Patients with PaO2 <60 and >100 had a higher rate of adverse outcome at time 0, in groups A and B (OR 2.52, 3.45, 2.01, respectively). About the PaO2/FiO2 ratio, the OR for < 300 was 3.10 at time 0, 4.01 in group A and 4.79 in group B. Similar odds were found for < 200 in any groups and < 100 except for group B (OR 11.57). SatO2 < 94% showed OR 1.34, 3.52 and 19.12 at time 0, in groups A and B, respectively. PaO2 < 60 and >100, SatO2 < 94% and PaO2/FiO2 ratio < 300 showed at least two- to three-fold correlation to adverse outcome. This may provide simple but clear targets for clinicians facing COVID-19 respiratory failure in a non ICU-setting.

Erythropoietin and amyotrophic lateral sclerosis: Plasma level determination

In amyotrophic lateral sclerosis (ALS), respiratory muscle weakness causes ventilatory insufficiency and tissue hypoxia, which induces a number of metabolic pathways, and in particular increases erythropoietin (EPO) synthesis. EPO is a glycoprotein with neuroprotective properties that stimulates erythropoiesis. Here, EPO plasma level in a large population of ALS patients, with and without respiratory failure, was measured. Plasma EPO level of patients with ALS (n = 98), controls with other neuromuscular diseases (n = 58) and healthy controls (n = 20) has been quantified by ELISA. No significant difference was found between ALS patients and the two control groups. EPO level was not different between bulbar- and spinal-onset patients and was not correlated with disease duration or functional impairment. However, in the ALS group EPO level was higher in females (p = 0.0006) and correlated positively with age (p = 0.006). The subgroup of ALS patients with respiratory failure had higher plasma levels of EPO compared with ALS patients with preserved respiratory function (p = 0.016), but short-term non-invasive ventilation did not change EPO level. In conclusion, EPO levels were found to be significantly higher in ALS patients with respiratory impairment representing preservation of this homeostatic mechanism.

Pulmonary histopathology of Cytauxzoon felis infections in the cat

Cytauxzoonosis, caused by Cytauxzoon felis, is a regionally common, often fatal tick-borne disease primarily affecting the domestic cat. Retrospective analysis of case records from January 1995 to June 2005 identified 148 domestic cats diagnosed with cytauxzoonosis, having suitable archived lung sections. Lung sections were examined and graded on relevant parameters, the chief purpose of which was to characterize the pulmonary lesion of fatal feline cytauxzoonosis. Parameters were scored 0 to 3 for no lesion, mild, moderate, and severe, respectively. Evaluated parameters included the presence of interstitial pneumonia, increases in number of alveolar macrophages, degree of intra-alveolar hemorrhage, neutrophils infiltrating peribronchial and septal interstitium, and degree of vascular occlusion. Overall, interstitial pneumonia was moderate (1.72 +/- 0.65); alveolar macrophage numbers were mild (1.20 +/- 0.60); and intra-alveolar hemorrhage was mild (0.78 +/- 0.75). Neutrophil infiltrates were moderate (1.89 +/- 0.76), and vascular occlusion was moderate to severe (2.26 +/- 0.61). Pulmonary edema was common; its scoring was incorporated into the assessment for interstitial pneumonia. Interestingly, a thrombus was detected in the lung of 1 cat. The current understanding of the pathogenesis of cytauxzoonosis focuses on vascular occlusion by macrophages distended by megaschizont parasite stages within liver, spleen, and lung. These findings corroborate the current understanding yet shed light on the possibility that macrophage activation and inflammatory mediators lead to an interstitial pneumonic process characterized by neutrophilic infiltrates and pulmonary edema. These characterized lesions are likely correlative with the respiratory distress seen in affected cats.