Hold your breath and we will know if Covid will pass without leaving damage or on the contrary it will lead to respiratory complications. Beyond the oversimplification, a group of Italian researchers has developed a “risk test” that is based precisely on the examination of voluntary apneas to try to identify patients with Covid-19 most at risk of developing respiratory failure and having, therefore, need to be admitted to intensive care. The study has just been published in the journal Respirology.
Because it is important to understand who is most at risk
Since the start of the pandemic, a major challenge for doctors has been to understand in time which patients with Covid-19 are most likely to have future respiratory failure and which patients are likely to recover with minimal intervention. Two years after the start of the pandemic, almost 10% of those who fall ill with Covid-19 and are not vaccinated are hospitalized. Of these, half subsequently develop respiratory failure and require intensive care.
These are particularly worrying data, especially for those geographic areas that have low vaccination rates and few ICU beds. In addition, doctors are asked to decide which patients are at greatest risk of respiratory failure for early administration of new therapies that are available in limited quantities. For this reason, practicable triage strategies are sought to facilitate the recognition of cases at higher risk of severe prognosis.
The study on Respirology is based on a discovery made on a pilot population. “In patients suffering from Covid-19 who are hospitalized and who are preliminarily subjected to voluntary apnea – he explains Ludovico Messineoan expert on sleep and respiratory disorders at Harvard Medical School and Brigham and Women’s Hospital – a longer duration of apnea and oxyhemoglobin desaturation, which is a drop in oxygen that binds to hemoglobin in the tissues, post-apnea more deep are associated with a high risk of respiratory failure, a factor that requires non-invasive ventilation or with oral-tracheal intubation, and which is often associated with death “.
Silent hypoxemia
The idea arises from the fact that many Covid patients do not experience dyspnea (the ‘breathlessness’) following collapses in hemoglobin saturation (the so-called silent hypoxemia). This means that the course of many Covid patients is unpredictable, with some initially presenting few clinical manifestations but then quickly ending up in intensive care.
To quantify the risk of ventilatory failure associated with Covid-19 in the individual patient, the researchers created a specific prediction score, i.e. a predictive scale which, following the compilation of specific parameters detected with the execution of voluntary apneas (i.e. duration of ‘maximal apnea and mean oxyhemoglobin desaturation post-voluntary apnea) and in combination with patient-related characteristics (such as Body Mass Index, presence of previous cardiac pathologies and oxyhemoglobin saturation at rest), returns the probabilities (in percentage) of ending in ventilatory support as a consequence of Covid-19. This first study was conducted on four centers and in collaboration with three continents (Europe, United States, Australia).
The validation study
In the most recent work released on Respirology, the researchers conducted a validation study of the previous discovery on a new court of patients affected by Covid-19, more numerous than the previous one (110 patients, recruited from 3 Italian centers: Brescia, Pavia and Chiari). “Validation studies – continues Messineo – are fundamental because they allow us to confirm the ‘generalizability’ of the discoveries. In practice, without a validation study, a discovery could be conditioned by multiple confounding factors inherent in the original population”. Furthermore, in the previous study, doctors had recorded the parameters derived from voluntary apneas with sophisticated and specialized equipment, while in this most recent study they used only a stopwatch (to measure the duration of maximal apnea) and a pulse oximeter (to measure desaturation. post-apnea). All this to favor the clinical ‘feasibility’ of voluntary apneas. Finally, chest x-rays and CT were performed in a large number of patients in the study.
In this new research, the discovery of the pilot study was confirmed: a high prediction score (which rises if the Covid patient, at the time of admission, has a long duration of maximal apnea and a profound post-apnea oxyhemoglobin desaturation) is associated with a risk of ventilatory failure 5 times higher than in the patient with a low prediction score. “The lion’s share – explains the Italian researcher – in the increase in the risk of ventilatory insufficiency is played above all by the extent of the desaturation: the deeper the oxyhemoglobin desaturation, the higher the risk. Furthermore, we have shown that the prediction score is rises simultaneously with the worsening of the radiological picture: again, the main vector that carries this association is the extent of the desaturation “.
Translate the risk into real numbers
This discovery is fundamental because it translates the patient’s risk (on admission to the hospital, therefore first) in numbers. In practice, a Covid patient with a high risk of developing respiratory failure, when subjected to voluntary apneas, would have a high prediction score, but also a compromised picture on a radiological level, visible on X-ray and CT of the chest. “In many centers, especially those characterized by a high influx of patients or a lack of machinery such as CT scan or radiologists on duty – continues Messineo – hospital triage is often complicated, with many Covid-19 patients not receiving risk stratification adequate and / or sufficiently prioritized therapy. By performing our maximal apnea procedure which takes a total of less than 15 minutes and filling in our prediction score, you can receive a precise risk description that is highly correlated with radiological severity. “