Respiratory drive: a journey from health to disease.

Respiratory drive is defined as the intensity of respiratory centers output during the breath and is primarily affected by cortical and chemical feedback mechanisms. During the involuntary act of breathing, chemical feedback, primarily mediated through CO2, is the main determinant of respiratory drive. Respiratory drive travels through neural pathways to respiratory muscles, which execute the breathing process and generate inspiratory flow (inspiratory flow-generation pathway). In a healthy state, inspiratory flow-generation pathway is intact, and thus respiratory drive is satisfied by the rate of volume increase, expressed by mean inspiratory flow, which in turn determines tidal volume. In this review, we will explain the pathophysiology of altered respiratory drive by analyzing the respiratory centers response to arterial partial pressure of CO2 (PaCO2) changes. Both high and low respiratory drive have been associated with several adverse effects in critically ill patients. Hence, it is crucial to understand what alters the respiratory drive. Changes in respiratory drive can be explained by simultaneously considering the (1) ventilatory demands, as dictated by respiratory centers activity to CO2 (brain curve); (2) actual ventilatory response to CO2 (ventilation curve); and (3) metabolic hyperbola. During critical illness, multiple mechanisms affect the brain and ventilation curves, as well as metabolic hyperbola, leading to considerable alterations in respiratory drive. In critically ill patients the inspiratory flow-generation pathway is invariably compromised at various levels. Consequently, mean inspiratory flow and tidal volume do not correspond to respiratory drive, and at a given PaCO2, the actual ventilation is less than ventilatory demands, creating a dissociation between brain and ventilation curves. Since the metabolic hyperbola is one of the two variables that determine PaCO2 (the other being the ventilation curve), its upward or downward movements increase or decrease respiratory drive, respectively. Mechanical ventilation indirectly influences respiratory drive by modifying PaCO2 levels through alterations in various parameters of the ventilation curve and metabolic hyperbola. Understanding the diverse factors that modulate respiratory drive at the bedside could enhance clinical assessment and the management of both the patient and the ventilator.

A combination of mild-moderate hypoxemia and low compliance is highly prevalent in persistent ARDS: a retrospective study.

BACKGROUND: The Acute Respiratory Distress Syndrome (ARDS) is characterized by lung inflammation and edema, impairing both oxygenation and lung compliance. Recent studies reported a dissociation between oxygenation and compliance (severe hypoxemia with preserved compliance) in early ARDS and COVID-19-related-ARDS (CARDS). During the pandemic, in patients requiring prolonged mechanical ventilation, we observed the opposite combination (mild-moderate hypoxemia but significantly impaired compliance). The purpose of our study was to investigate the prevalence of this combination of mild-moderate hypoxemia and impaired compliance in persistent ARDS and CARDS. METHODS: For this retrospective study, we used individual patient-level data from two independent cohorts of ARDS patients. The ARDSNet cohort included patients from four ARDS Network randomized controlled trials. The CARDS cohort included patients with ARDS due to COVID-19 hospitalized in two intensive care units in Greece. We used a threshold of 150 for PaO2/FiO2 and 30 ml/cmH2O for compliance, estimated the prevalence of each of the four combinations of oxygenation and compliance at baseline, and examined the change in its prevalence from baseline to day 21 in the ARDSNet and CARDS cohorts. RESULTS: The ARDSNet cohort included 2909 patients and the CARDS cohort included 349 patients. The prevalence of the combination of mild-moderate hypoxemia and low compliance increased from baseline to day 21 both in the ARDSNet cohort (from 22.2 to 42.7%) and in the CARDS cohort (from 3.1 to 33.3%). Among surviving patients with low compliance, oxygenation improved over time. The 60-day mortality rate was higher for patients who had mild-moderate hypoxemia and low compliance on day 21 (28% and 56% in ARDSNet and CARDS), compared to those who had mild-moderate hypoxemia and high compliance (20% and 50%, respectively). CONCLUSIONS: Among patients with ARDS who require prolonged controlled mechanical ventilation, regardless of ARDS etiology, a dissociation between oxygenation and compliance characterized by mild-moderate hypoxemia but low compliance becomes increasingly prevalent. The findings of this study highlight the importance of monitoring mechanics in patients with persistent ARDS.

Sleep Architecture Patterns in Critically Ill Patients and Survivors of Critical Illness: A Retrospective Study.

Rationale: Sleep abnormalities are very frequent in critically ill patients during and after intensive care unit (ICU) stays. Their mechanisms are poorly understood. The odds ratio product (ORP) is a continuous metric (range, 0.0-2.5) of sleep depth measured in 3-second intervals and derived from the relationship of powers of different electroencephalographic frequencies to one another. When expressed as the percentage of epochs within 10 ORP deciles covering the entire ORP range, it provides information about the mechanism(s) of abnormal sleep. Objectives: To determine ORP architecture types in critically ill patients and survivors of critical illness who had previously undergone sleep studies. Methods: Nocturnal polysomnograms from 47 unsedated critically ill patients and 23 survivors of critical illness at hospital discharge were analyzed. Twelve critically ill patients were monitored also during the day, and 15 survivors underwent subsequent polysomnography 6 months after hospital discharge. In all polysomnograms, each 30-second epoch was characterized by the mean ORP of the 10 3-second epochs. The number of 30-second epochs with mean ORP within each of 10 ORP deciles covering the entire ORP range (0.0-2.5) was calculated and expressed as a percentage of total recording time. Thereafter, each polysomnogram was characterized using a two-digit ORP type, with the first digit (range, 1-3) reflecting increasing degrees of deep sleep (ORP < 0.5, deciles 1 and 2) and the second digit (range, 1-3) reflecting increasing degrees of full wakefulness (ORP > 2.25, decile 10). Results from patients were compared with those from 831 age- and gender-matched community dwellers free of sleep disorders. Results: In critically ill patients, types 1,1 and 1,2 (little deep sleep and little or average full wakefulness) dominated (46% of patients). In the community, these types are uncommon (<15%) and seen primarily in disorders that preclude progression to deep sleep (e.g., very severe obstructive sleep apnea). Next in frequency (22%) was type 1,3, consistent with hyperarousal. Day ORP sleep architecture was similar to night results. Survivors had similar patterns, with little improvement after 6 months. Conclusions: Sleep abnormalities in critically ill patients and survivors of critical illness result primarily from stimuli that preclude progression to deep sleep or from the presence of a hyperarousal state.

Hiccup-like Contractions in Mechanically Ventilated Patients: Individualized Treatment Guided by Transpulmonary Pressure.

Hiccups-like contractions, including hiccups, respiratory myoclonus, and diaphragmatic tremor, refer to involuntary, spasmodic, and inspiratory muscle contractions. They have been repeatedly described in mechanically ventilated patients, especially those with central nervous damage. Nevertheless, their effects on patient-ventilator interaction are largely unknown, and even more overlooked is their contribution to lung and diaphragm injury. We describe, for the first time, how the management of hiccup-like contractions was individualized based on esophageal and transpulmonary pressure measurements in three mechanically ventilated patients. The necessity or not of intervention was determined by the effects of these contractions on arterial blood gases, patient-ventilator synchrony, and lung stress. In addition, esophageal pressure permitted the titration of ventilator settings in a patient with hypoxemia and atelectasis secondary to hiccups and in whom sedatives failed to eliminate the contractions and muscle relaxants were contraindicated. This report highlights the importance of esophageal pressure monitoring in the clinical decision making of hiccup-like contractions in mechanically ventilated patients.

Respiratory system as the main determinant of dyspnea in patients with pulmonary hypertension.

Dyspnea on exertion is a devastating symptom, commonly observed in patients with pulmonary hypertension (PH). The pathophysiology of dyspnea in these patients has been mainly attributed to cardiovascular determinants and isolated abnormalities of the respiratory system during exercise, neglecting the contribution of the control of the breathing system. The aim of this review is to provide a novel approach to the interpretation of dyspnea in patients with PH, focused on the impact of the control of the breathing system during exercise. Exercise through multiple mechanisms affects the (1) ventilatory demands, as dictated by respiratory center activity, (2) actual ventilation, and (3) metabolic hyperbola. In patients with PH, exertional dyspnea can be explained by exercise-induced alterations in these variables. Compared to healthy subjects, at a given CO2 production during exercise, ventilatory demands in patients with PH are higher due to metabolic acidosis (early reaching the anaerobic threshold), hypoxemia, and excessive upward movement of metabolic hyperbola owing to abnormal exercise response of dead space to tidal volume ratio. Simultaneously, dynamic hyperinflation and respiratory muscles weakness decreases the actual ventilation for a given respiratory center activity, creating a dissociation between demands and ventilation. Consequently, a progressive increase in ventilatory demands and respiratory center activity occurs during exercise. The forebrain projection of high respiratory center activity causes exertional dyspnea despite the relatively low ventilation and significant ventilatory reserve. This type of analysis suggests that the respiratory system is the main determinant of exertional dyspnea in patients with PH, with the cardiovascular system being an indirect contributor.

Performance of Lung Ultrasound for Monitoring Interstitial Lung Disease.

OBJECTIVES: In this study, we sought to assess the validity of lung ultrasound (LUS) during the follow-up of patients with a wide spectrum of interstitial lung diseases (ILDs). METHODS: Twenty-four patients (13 males, 11 females; mean age ± SD, 65.4 ± 14.3 years; age range, 40-84 years) with a diagnosis of ILDs who were admitted to the Interstitial Lung Disease Unit were prospectively enrolled. Patients were examined with a 56-lung intercostal space LUS protocol in lateral decubitus position, at baseline, 6-months, and 1-year. The LUS score was defined as the sum of B-lines counted in each intercostal space. All patients underwent complete pulmonary function tests at baseline and follow-up time-points. High-resolution computed tomography (HRCT) was performed at baseline and during follow-up, according to personalized patients' needs. All HRCT studies were graded according to the Warrick scoring system (WS). RESULTS: Pooled data analysis showed a significant correlation between WS and LUS scores (P < .001). For separate time-point analysis, a significant correlation between LUS scores and WS was found at baseline (P < .001) and 1 year (P = .005). LUS scores negatively correlated with alveolar volume (VA) (P < .046) and diffusing capacity for carbon monoxide (DLCO) (P < .001) at 6 months and with transfer coefficient of the lung for carbon monoxide (KCO) (P < .031) and DLCO (P = .002) at 12-months. A multivariate regression model showed DLCO to be an independent predictor of LUS score at 1 year (P = .026). CONCLUSIONS: Our results highlight the validity and potential applicability of LUS for disease monitoring in a wide spectrum of ILDs.

Real-life Cretan asthma registry focused on severe asthma: On behalf of 'The Cretan registry of the use of Biologics in Severe Asthma'.

Asthma diagnosis and management remains a challenging task for the medical community. The aim of the present study was to present the functional and inflammatory profiles of patients with difficult-to-treat asthma in a real-life clinical setting referred to the specialized asthma clinic at the University Hospital of Heraklion. The registry included a cohort of 267 patients who were referred to the severe asthma clinic. Patients were assessed with emphasis on the history of allergies, nasal polyposis or other comorbidities. Blood testing for eosinophils counts and total and specific IgE, and pulmonary function tests were performed at baseline. The median age of patients with asthma was 55 years old, 68.5% were women and 58.3% were never smokers. The vast majority presented with late onset asthma (75.7%), whereas eight (3%) patients were on oral corticosteroids. The median number of exacerbations during the last 12 months was 1 (0-3). Furthermore, 50.7% of patients had a positive serum allergy test, the median eosinophil count was 300 (188-508.5) cells/µl of blood and median total IgE level was 117.5 (29.4-360.5) IU/ml. Patients were retrospectively grouped in the following categories: Group 1, mild-moderate asthma; group 2, patients prescribed a step 4 or 5 asthma therapy according to Global Initiative for Asthma; and group 3, patients on biologic agents. Group 1 had significantly higher FEV1% than groups 2 and 3 (93.4 vs. 79.9 and 79.4%, respectively; P<0.001). Finally, the median Asthma Control Questionnaire 7 (ACQ7) score was 1.14, with patients from groups 2 and 3 presenting higher ACQ7 scores compared with group 1 patients as expected (1.1 and 2.1 vs. 0.7, respectively; P<0.001). To the best of our knowledge, this was the first real-life asthma study in Crete that demonstrated that severe asthmatics predominantly have late-onset asthma with airflow obstruction and uncontrolled symptoms.

Ventilatory Ratio Threshold for Unassisted Breathing: A Retrospective Exploratory Analysis.

BACKGROUND: The ventilatory ratio (VR) is a simple index of ventilatory efficiency and dead space. Because increased dead space and high ventilatory demands impose a limitation to unassisted ventilation, and may predispose patients to injurious strong efforts during assisted ventilation, evaluation of the VR could provide helpful information during weaning. We hypothesize that there is a threshold of VR associated with tolerance of unassisted breathing. METHODS: In a retrospective analysis, we included subjects ventilated in a control mode for at least 24 h, who were successfully liberated from mechanical ventilation, without use of noninvasive ventilation, and discharged alive from the ICU. We focused on the successful weaning attempts (the last, if more than one was performed) and evaluated the VR at the beginning and at the end of the assisted ventilation period. RESULTS: We examined 2,000 medical records and included in our analysis 572 subjects (age: 68 y, R5-95 = 25-85, 68% male) with main admission diagnosis of respiratory failure (23%), sepsis (11%), brain injury (34%), and postoperative (14%). The VR at the beginning and the end of the assisted ventilation period was 1.5 (R5-95 = 1-2.1) and 1.4 (R5-95 = 1-2), respectively. The median duration of assisted ventilation in subjects with a VR ≥ 2 at the beginning of the assisted ventilation period was 3 d (R5-95 = 0-14 d), significantly longer than in those with a VR < 2, 0.5 d (R5-95 = 0-8 d, P < .001). CONCLUSIONS: Successful liberation from assisted ventilation was associated with a VR < 2. A VR > 2 was associated with longer duration of weaning. The VR could be used as an additional tool to facilitate the decision-making process during weaning.

Case Report: Diagnosis of Myelodysplastic Syndrome in a 72-Year-Old Female With Interstitial Lung Disease.

Acute fibrinous and organizing pneumonia (AFOP) is an entity that can be secondary to various conditions leading to lung injury, such as infections, malignancies, and various autoimmune conditions or idiopathic interstitial lung disease, when no obvious underlying cause is identified. Myelodysplastic syndromes (MDS), on the other hand, are a spectrum of clonal myeloid disorders, with a higher risk of acute leukemia, characterized by ineffective bone marrow (BM) hematopoiesis and, thus, peripheral blood (PB) cytopenias. Immune deregulation is thought to take part in the pathophysiology of the disease, including abnormal T and/or B cell responses, innate immunity, and cytokine expression. In the literature, there are a few case reports of patients with MDS that have presented pulmonary infiltrates and were diagnosed as having AFOP or organizing pneumonia (OP). It is rare, though, to have isolated pulmonary infiltrates without Sweet's syndrome or even the pulmonary infiltrates to precede the diagnosis and treatment of MDS, which was our case. We present a 72-year-old female developing new lung infiltrates refractory to antibiotic treatment that responded well to corticosteroids and was histologically described as having OP. The treatment was gradually successfully switched to mycophenolate mofetil (MMF). The patient was later diagnosed with MDS. This interesting case report suggests firstly that a diagnosis of AFOP or OP should alert the clinician to search for an underlying cause including MDS and vice versa, the use of systemic steroids should not be postponed, and, finally, that MMF can successfully be used in these patients.

[COMMENT] Respiratory diseases in the era of COVID-19: Pearls and pitfalls.

Coronavirus disease 2019, a respiratory tract infection that has evolved into a pandemic, is expected to affect patients with underlying respiratory disease in a greater number and greater severity than patients with other underlying disorders. Whether this is true is an interesting question. However, the challenge both for the doctors and patients is to keep the respiratory disease in remission and prevent any exacerbations. Proper recommendations have been proposed for a wide range of respiratory disorders including chronic obstructive pulmonary disease (COPD), asthma and interstitial lung diseases, regarding the continuation or not of the treatment during this period and ways to maintain stability.

Obstructive sleep apnea in pulmonary fibrosis.

PURPOSE OF REVIEW: In previous years, there was limited research related to the role of sleep in interstitial lung diseases (ILDs). Physicians treating ILD patients tended to focus mainly on the daily disabling symptoms overlooking the possible significant role of coexisting sleep disorders, such as obstructive sleep apnea (OSA). However, recently, there has been a growing interest in OSA in ILDs, as well as OSA effect on sleep, life quality and outcome in these patients with emphasis on idiopathic pulmonary fibrosis (IPF). RECENT FINDINGS: OSA has been recognized as an important, high-prevalence comorbidity for the diagnosis and management of IPF. This publication provides a summary of the most relevant recent evidence with regard to OSA in various ILDs and especially IPF, including prevalence, clinical presentation, complications, screening and diagnosis. It also provides updated evidence on the role of OSA therapy in improving sleep, quality of life and disease outcome. SUMMARY: It is too early to characterize OSA and ILDs association as an 'overlap' syndrome. In depth research is needed, including studies with large numbers of ILDs and IPF patients. The main priority is to increase the awareness among physicians for early diagnosis of OSA in ILDs patients.

[Comment] Treatment strategies to fight the new coronavirus SARS-CoV-2: A challenge for a Rubik's Cube solver.

SARS-coronavirus-2 (SARS-CoV-2), the etiologic agent of the new lung disease COVID-19 is closely related to SARS-CoV, and together with MERS-CoV are three new human coronaviruses that emerged in the last 20 years. The COVID-19 outbreak is a rapidly evolving situation with higher transmissibility and infectivity compared with SARS and MERS. Clinical presentations range from asymptomatic or mild symptoms to severe illness. The prevalent cause of mortality is pneumonia that progresses to ARDS. The ongoing pandemic has already resulted in more than 135,000 deaths and an unprecedented burden on national health systems worldwide. Pending the availability of a vaccine, there is a critical need to identify effective treatments and a number of clinical trials have been implemented worldwide. Trials are based on repurposed drugs that are already approved for other infections, have acceptable safety profiles or have performed well in animal studies against the other two deadly coronaviruses. Supportive care remains the mainstay of therapy at present, as it is still unclear how well these data can be extrapolated to SARS-CoV-2. Most of those emerging re-introduced drugs are administered to patients in the context of clinical trials. In this review, we summarize the strategies currently employed in the treatment of COVID-19.

Combined Pulmonary Fibrosis and Emphysema.

Combined pulmonary fibrosis and emphysema (CPFE) is a clinical entity characterized by the combination of upper lobe emphysema and lower lobe fibrosis, the latter owing to various interstitial lung diseases. These patients have a characteristic lung function profile, with relatively preserved dynamic and static lung volumes, contrasting with a significant reduction of carbon monoxide transfer. The pathogenic mechanisms leading to the coexistence of emphysema with fibrosis remain unclear and different theories have been proposed. CPFE is frequently complicated by pulmonary hypertension, acute exacerbations, and lung cancer leading to poor natural history and prognosis. The syndrome of CPFE represents a distinct pulmonary manifestation in the spectrum of lung diseases associated with connective tissue diseases. Currently, there are no established recommendations regarding the management of patients with CPFE. We provide a review on the existing knowledge of CPFE regarding the epidemiology, pathogenesis, clinical manifestations, radiologic appearance, complications, prognosis, and possible treatment options.

New respiratory symptoms and lung imaging findings in a woman with polymyositis.

Can you identify the cause of the acute respiratory failure in this patient with a history of polymyositis? http://ow.ly/jeDO30jLX5R.

Paroxysmal cough and left sacroiliac joint pain in a 50-year-old Caucasian man.

Can you diagnose this patient with pulmonary symptoms, thoracic and laboratory test abnormalities and sacroiliac joint pain? http://ow.ly/LPyy30kaViz.

Effects of dexmedetomidine on sleep quality in critically ill patients: a pilot study.

BACKGROUND: Dexmedetomidine, a potent α-2-adrenergic agonist, is widely used as sedative in critically ill patients. This pilot study was designed to assess the effect of dexmedetomidine administration on sleep quality in critically ill patients. METHODS: Polysomnography was performed on hemodynamically stable critically ill patients for 57 consecutive hours, divided into three night-time (9:00 PM to 6:00 AM) and two daytime (6:00 AM to 9:00 PM) periods. On the second night, dexmedetomidine was given by a continuous infusion targeting a sedation level -1 to -2 on the Richmond Agitation Sedation Scale. Other sedatives were not permitted. RESULTS: Thirteen patients were studied. Dexmedetomidine was given in a dose of 0.6 µg kg(-1) h(-1) (0.4 to 0.7) (median [interquartile range]). Compared to first and third nights (without dexmedetomidine), sleep efficiency was significantly higher during the second night (first: 9.7% [1.6 to 45.1], second: 64.8% [51.4 to 79.9], third: 6.9% [0.0 to 17.1], P < 0.002). Without dexmedetomidine, night-time sleep fragmentation index (7.6 events per hour [4.8 to 14.2]) and stage 1 of sleep (48.0% [30.1 to 66.4]) were significantly higher (P = 0.023 and P = 0.006, respectively), and stage 2 (47.0% [27.5 to 61.2]) showed values lower (P = 0.006) than the corresponding values (2.7 events per hour [1.6 to 4.9], 13.1% [6.2 to 23.6], 80.2% [68.9 to 92.8]) observed with dexmedetomidine. Without sedation, sleep was equally distributed between day and night, a pattern that was modified significantly (P = 0.032) by night-time dexmedetomidine infusion, with more than three quarters of sleep occurring during the night (79% [66 to 87]). CONCLUSION: In highly selected critically ill patients, dexmedetomidine infusion during the night to achieve light sedation improves sleep by increasing sleep efficiency and stage 2 and modifies the 24-h sleep pattern by shifting sleep mainly to the night.