Application of extracorporeal carbon dioxide removal combined with continuous blood purification therapy in ARDS with hypercapnia in patients with critical COVID-19.

INTRODUCTION: Coronavirus disease-19 (COVID-19) is a new type of epidemic pneumonia caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The population is generally susceptible to COVID-19, which mainly causes lung injury. Some cases may develop severe acute respiratory distress syndrome (ARDS). Currently, ARDS treatment is mainly mechanical ventilation, but mechanical ventilation often causes ventilator-induced lung injury (VILI) accompanied by hypercapnia in 14% of patients. Extracorporeal carbon dioxide removal (ECCO2R) can remove carbon dioxide from the blood of patients with ARDS, correct the respiratory acidosis, reduce the tidal volume and airway pressure, and reduce the incidence of VILI. CASE REPORT: Two patients with critical COVID-19 combined with multiple organ failure undertook mechanical ventilation and suffered from hypercapnia. ECCO2R, combined with continuous renal replacement therapy (CRRT), was conducted concomitantly. In both cases (No. 1 and 2), the tidal volume and positive end-expiratory pressure (PEEP) were down-regulated before the treatment and at 1.5 hours, one day, three days, five days, eight days, and ten days after the treatment, together with a noticeable decrease in PCO2 and clear increase in PO2, while FiO2 decreased to approximately 40%. In case No 2, compared with the condition before treatment, the PCO2 decreased significantly with down-regulation in the tidal volume and PEEP and improvement in the pulmonary edema and ARDS after the treatment. CONCLUSION: ECCO2R combined with continuous blood purification therapy in patients with COVID-19 who are criti-cally ill and have ARDS and hypercapnia might gain both time and opportunity in the treatment, down-regulate the ventilator parameters, reduce the incidence of VILI and achieve favorable therapeutic outcomes.

Lethal avian influenza A (H5N1) virus replicates in pontomedullary chemosensitive neurons and depresses hypercapnic ventilatory response in mice.

The highly pathogenic H5N1 (HK483) viral infection causes a depressed hypercapnic ventilatory response (dHCVR, 20%↓) at 2 days postinfection (dpi) and death at 7 dpi in mice, but the relevant mechanisms are not fully understood. Glomus cells in the carotid body and catecholaminergic neurons in locus coeruleus (LC), neurokinin 1 receptor (NK1R)-expressing neurons in the retrotrapezoid nucleus (RTN), and serotonergic neurons in the raphe are chemosensitive and responsible for HCVR. We asked whether the dHCVR became worse over the infection period with viral replication in these cells/neurons. Mice intranasally inoculated with saline or the HK483 virus were exposed to hypercapnia for 5 min at 0, 2, 4, or 6 dpi, followed by immunohistochemistry to determine the expression of nucleoprotein of H5N1 influenza A (NP) alone and coupled with 1) tyrosine hydroxylase (TH) in the carotid body and LC, 2) NK1R in the RTN, and 3) tryptophan hydroxylase (TPH) in the raphe. HK483 viral infection blunted HCVR by ∼20, 50, and 65% at 2, 4, and 6 dpi. The NP was observed in the pontomedullary respiratory-related nuclei (but not in the carotid body) at 4 and 6 dpi, especially in 20% of RTN NK1R, 35% of LC TH, and ∼10% raphe TPH neurons. The infection significantly reduced the local NK1R or TPH immunoreactivity and population of neurons expressing NK1R or TPH. We conclude that the HK483 virus infects the pontomedullary respiratory nuclei, particularly chemosensitive neurons in the RTN, LC, and raphe, contributing to the severe depression of HCVR and respiratory failure at 6 dpi. NEW & NOTEWORTHY The H5N1 virus infection is lethal due to respiratory failure, but the relevant mechanisms remain unclear. In this study, we demonstrated a gradual diminution of hypercapnic ventilatory response to a degree, leading to respiratory failure over a 6-day infection. Death was associated with viral replication in the pontomedullary respiratory-related nuclei, especially the central chemosensitive neurons. These results not only provide insight into the mechanisms of the lethality of H5N1 viral infection but also offer clues in the development of corresponding treatments to minimize and prevent respiratory failure.

Lethal avian influenza A (H5N1) virus induces ataxic breathing in mice with apoptosis of pre-Botzinger complex neurons expressing neurokinin-1 receptor.

Lethal influenza A (H5N1) induces respiratory failure in humans. Although it also causes death at 7 days postinfection (dpi) in mice, the development of the respiratory failure and the viral impact on pre-Botzinger complex (PBC) neurons expressing neurokinin 1 receptor (NK1R), which is the respiratory rhythm generator, have not been explored. Body temperature, weight, ventilation, and arterial blood pH and gases were measured at 0, 2, 4, and 6 dpi in control, lethal HK483, and nonlethal HK486 viral-infected mice. Immunoreactivities (IR) of PBC NK1R, H5N1 viral nucleoprotein (NP), and active caspase-3 (CASP3; a marker for apoptosis) were detected at 6 dpi. HK483, but not HK486, mice showed the following abnormalities: 1) gradual body weight loss and hypothermia; 2) tachypnea at 2-4 dpi and ataxic breathing with long-lasting apneas and hypercapnic hypoxemia at 6 dpi; and 3) viral replication in PBC NK1R neurons with NK1R-IR reduced by 75% and CASP3-IR colabeled at 6 dpi. Lethal H5N1 viral infection causes tachypnea at the early stage and ataxic breathing and apneas (hypercapnic hypoxemia) leading to death at the late stage. Its replication in the PBC induces apoptosis of local NK1R neurons, contributing to ataxic breathing and respiratory failure.

West Nile Meningoencephalitis Presenting as Isolated Bulbar Palsy With Hypercapnic Respiratory Failure: Case Report and Literature Review.

BACKGROUND: Since the outbreak of West Nile virus (WNV) in the United States in 1999, the WNV neuroinvasive disease has been increasingly reported with a wide spectrum of neuromuscular manifestations. CASE: We submit a case of a 46-year-old male with a history of alcohol abuse, diabetes, hypertension, and hepatitis C who presented with fever, nausea, shortness of breath, and dysphagia. The patient rapidly developed hypercapnic respiratory failure and was found to have WNV meningoencephalitis without obvious neuromuscular weakness. His hospital course was significant for repeated failures of extubation secondary to persistent bulbar weakness eventually requiring tracheotomy. CONCLUSION: This is a unique case of WNV meningoencephalitis with bulbar palsy without other neuromuscular manifestations resulting in recurrent hypercapnic respiratory failure.

Rescue hypothermia for refractory hypercapnia.

Hypothermia may reduce the CO(2) production by decreasing the metabolism of the cooled tissue. We describe the first clinical use of hypothermia to lower hypercarbia in a case of bronchiolitis related respiratory failure unresponsive to maximal respiratory support. In this case, hypothermia allowed sparing the use of extracorporeal life support. Conclusion Hypothermia might be useful for severe acute respiratory failure unresponsive to aggressive respiratory support.