Respiratory mechanics behavior after heart surgery: an experimental study

Changes in ventilatory mechanics and their consequent pulmonary complications are common after surgical procedures, particularly in cardiac surgery (CS), and may be associated with both preoperative history and surgical circumstances. This study aims to compare ventilatory mechanics in the moments before and after cardiac surgery (CS), describing how pulmonary complications occurred. An experimental, uncontrolled study was conducted, of the before-and-after type, and with a descriptive and analytical character. It was carried out in a private hospital in the city of Salvador, Bahia, Brazil, and involved 30 adult patients subjected to CS. In addition to clinical and epidemiological variables, minute volume (VE), respiratory rate (RR), tidal volume (VT), forced vital capacity (FVC), maximum inspiratory pressure (MIP), and peak expiratory flow (PEF) were also recorded. Data were collected in the following moments: preoperative (PRE-OP) period, immediate postoperative (IPO) period, and 1st postoperative day (1st POD). The sample was aged 48.1 ± 11.8 years old and had a body mass index of 25.5 ± 4.9 kg m-2; 60% of the patients remained on mechanical ventilation for less than 24 hours (17.5 [8.7-22.9] hours). There was a significant reduction in VT, FVC, MIP and PEF when PRE-OP versus IPO, and PRE-OP versus 1st POD were compared (p < 0.05). There were no significant changes between IPO and the 1st POD. The highest incidence of pulmonary complications involved pleural effusion (50% of the patients). This study showed that patients subjected to CS present significant damage to ventilatory parameters after the surgery, especially in the IPO period and on the 1st POD. It is possible that the extension of this ventilatory impairment has led to the onset of postoperative pulmonary complications.

Two‐Thumb Technique Is Superior to Two‐Finger Technique in Cardiopulmonary Resuscitation of Simulated Out‐of‐Hospital Cardiac Arrest in Infants

Background To compare the 2‐finger and 2‐thumb chest compression techniques on infant manikins in an out‐of‐hospital setting regarding efficiency of compressions, ventilation, and rescuer pain and fatigue. Methods and Results In a randomized crossover design, 78 medical students performed 2 minutes of cardiopulmonary resuscitation with mouth‐to‐nose ventilation at a 30:2 rate on a Resusci Baby QCPR infant manikin (Laerdal, Stavanger, Norway), using a barrier device and the 2‐finger and 2‐thumb compression techniques. Frequency and depth of chest compressions, proper hand position, complete chest recoil at each compression, hands‐off time, tidal volume, and number of ventilations were evaluated through manikin‐embedded SkillReporting software. After the interventions, standard Likert questionnaires and analog scales for pain and fatigue were applied. The variables were compared by a paired t ‐test or Wilcoxon test as suitable. Seventy‐eight students participated in the study and performed 156 complete interventions. The 2‐thumb technique resulted in a greater depth of chest compressions (42 versus 39.7 mm; P <0.01), and a higher percentage of chest compressions with adequate depth (89.5% versus 77%; P <0.01). There were no differences in ventilatory parameters or hands‐off time between techniques. Pain and fatigue scores were higher for the 2‐finger technique (5.2 versus 1.8 and 3.8 versus 2.6, respectively; P <0.01). Conclusions In a simulation of out‐of‐hospital, single‐rescuer infant cardiopulmonary resuscitation, the 2‐thumb technique achieves better quality of chest compressions without interfering with ventilation and causes less rescuer pain and fatigue.

Effects of heliox and non-invasive neurally adjusted ventilatory assist (NIV-NAVA) in preterm infants

Due to its unique properties, helium–oxygen (heliox) mixtures may provide benefits during non-invasive ventilation, however, knowledge regarding the effects of such therapy in premature infants is limited. This is the first report of heliox non-invasive neurally adjusted ventilatory assist (NIV-NAVA) ventilation applied in neonates born ≤ 32 weeks gestational age. After baseline NIV-NAVA ventilation with a standard mixture of air and oxygen, heliox was introduced for 3 h, followed by 3 h of air-oxygen. Heart rate, peripheral capillary oxygen saturation, cerebral oxygenation, electrical activity of the diaphragm (Edi) and selected ventilatory parameters (e.g., respiratory rate, peak inspiratory pressure) were continuously monitored. We found that application of heliox NIV-NAVA in preterm infants was feasible and associated with a prompt and significant decrease of Edi suggesting reduced respiratory effort, while all other parameters were stable throughout the study, and had similar values during heliox and air-oxygen ventilation. This therapy may potentially enhance the efficacy of non-invasive respiratory support in preterm neonates and reduce the number of infants progressing to ventilatory failure.

Personalized mechanical ventilation in acute respiratory distress syndrome

A personalized mechanical ventilation approach for patients with adult respiratory distress syndrome (ARDS) based on lung physiology and morphology, ARDS etiology, lung imaging, and biological phenotypes may improve ventilation practice and outcome. However, additional research is warranted before personalized mechanical ventilation strategies can be applied at the bedside. Ventilatory parameters should be titrated based on close monitoring of targeted physiologic variables and individualized goals. Although low tidal volume (VT) is a standard of care, further individualization of VT may necessitate the evaluation of lung volume reserve (e.g., inspiratory capacity). Low driving pressures provide a target for clinicians to adjust VT and possibly to optimize positive end-expiratory pressure (PEEP), while maintaining plateau pressures below safety thresholds. Esophageal pressure monitoring allows estimation of transpulmonary pressure, but its use requires technical skill and correct physiologic interpretation for clinical application at the bedside. Mechanical power considers ventilatory parameters as a whole in the optimization of ventilation setting, but further studies are necessary to assess its clinical relevance. The identification of recruitability in patients with ARDS is essential to titrate and individualize PEEP. To define gas-exchange targets for individual patients, clinicians should consider issues related to oxygen transport and dead space. In this review, we discuss the rationale for personalized approaches to mechanical ventilation for patients with ARDS, the role of lung imaging, phenotype identification, physiologically based individualized approaches to ventilation, and a future research agenda.

Mirtazapine Reduces Susceptibility to Hypocapnic Central Sleep Apnea in Males with Sleep Disordered Breathing - A Pilot Study

Studies in those with spinal cord injury (SCI) have demonstrated that medications targeting serotonin receptors may decrease the susceptibility to central sleep-disordered breathing (SDB). We hypothesized that mirtazapine would decrease the propensity to develop hypocapnic central sleep apnea (CSA) during sleep. We performed a single-blind pilot study on a total of 10 men with SDB (seven with chronic SCI and three non-injured) aged 52.0±11.2 years. Participants were randomly assigned to either mirtazapine (15mg) or a placebo for at least one week followed by a seven-day washout period before crossing over to the other intervention. Study nights included polysomnography and induction of hypocapnic CSA using a non-invasive ventilation (NIV) protocol. The primary outcome was CO2 reserve, defined as the difference between eupneic and end of NIV PETCO2 preceding induced hypocapneic CSA. Secondary outcomes included controller gain (CG), other ventilatory parameters, and SDB severity. CG was defined as the ratio of change in minute ventilation (V̇e) between control and hypopnea to the change in CO2 during sleep. CO2 reserve was significantly widened on mirtazapine compared to placebo (-3.8±1.2 vs. -2.0±1.5mmHg; p=0.015). CG was significantly decreased on mirtazapine compared to placebo (2.2±0.7 vs. 3.5±1.9L/(mmHg*min); p=0.023). There were no significant differences for other ventilatory parameters assessed or SDB severity between mirtazapine and placebo trials. These findings suggest that the administration of mirtazapine can decrease the susceptibility to central apnea by reducing chemosensitivity and increasing CO2 reserve, however considering the lack of changes in AHI, further research is required to understand this finding's significance.

Right Ventricular Strain Is Common in Intubated COVID-19 Patients and Does Not Reflect Severity of Respiratory Illness

Background: Right ventricular (RV) dysfunction is common and associated with worse outcomes in patients with coronavirus disease 2019 (COVID-19). In non-COVID-19 acute respiratory distress syndrome, RV dysfunction develops due to pulmonary hypoxic vasoconstriction, inflammation, and alveolar overdistension or atelectasis. Although similar pathogenic mechanisms may induce RV dysfunction in COVID-19, other COVID-19-specific pathology, such as pulmonary endothelialitis, thrombosis, or myocarditis, may also affect RV function. We quantified RV dysfunction by echocardiographic strain analysis and investigated its correlation with disease severity, ventilatory parameters, biomarkers, and imaging findings in critically ill COVID-19 patients. Methods: We determined RV free wall longitudinal strain (FWLS) in 32 patients receiving mechanical ventilation for COVID-19-associated respiratory failure. Demographics, comorbid conditions, ventilatory parameters, medications, and laboratory findings were extracted from the medical record. Chest imaging was assessed to determine the severity of lung disease and the presence of pulmonary embolism. Results: Abnormal FWLS was present in 66% of mechanically ventilated COVID-19 patients and was associated with higher lung compliance (39.6 vs 29.4 mL/cmH2O, P = 0.016), lower airway plateau pressures (21 vs 24 cmH2O, P = 0.043), lower tidal volume ventilation (5.74 vs 6.17 cc/kg, P = 0.031), and reduced left ventricular function. FWLS correlated negatively with age (r = −0.414, P = 0.018) and with serum troponin (r = 0.402, P = 0.034). Patients with abnormal RV strain did not exhibit decreased oxygenation or increased disease severity based on inflammatory markers, vasopressor requirements, or chest imaging findings. Conclusions: RV dysfunction is common among critically ill COVID-19 patients and is not related to abnormal lung mechanics or ventilatory pressures. Instead, patients with abnormal FWLS had more favorable lung compliance. RV dysfunction may be secondary to diffuse intravascular micro- and macro-thrombosis or direct myocardial damage. Trial Registration: National Institutes of Health #NCT04306393. Registered 10 March 2020, https://clinicaltrials.gov/ct2/show/NCT04306393

Glutathione ethyl ester reverses the deleterious effects of fentanyl on ventilation and arterial blood-gas chemistry while prolonging fentanyl-induced analgesia

There is an urgent need to develop novel compounds that prevent the deleterious effects of opioids such as fentanyl on minute ventilation while, if possible, preserving the analgesic actions of the opioids. We report that L-glutathione ethyl ester (GSHee) may be such a novel compound. In this study, we measured tail flick latency (TFL), arterial blood gas (ABG) chemistry, Alveolar-arterial gradient, and ventilatory parameters by whole body plethysmography to determine the responses elicited by bolus injections of fentanyl (75 μg/kg, IV) in male adult Sprague–Dawley rats that had received a bolus injection of GSHee (100 μmol/kg, IV) 15 min previously. GSHee given alone had minimal effects on TFL, ABG chemistry and A-a gradient whereas it elicited changes in some ventilatory parameters such as an increase in breathing frequency. In vehicle-treated rats, fentanyl elicited (1) an increase in TFL, (2) decreases in pH, pO2 and sO2 and increases in pCO2 (all indicative of ventilatory depression), (3) an increase in Alveolar-arterial gradient (indicative of a mismatch in ventilation-perfusion in the lungs), and (4) changes in ventilatory parameters such as a reduction in tidal volume, that were indicative of pronounced ventilatory depression. In GSHee-pretreated rats, fentanyl elicited a more prolonged analgesia, relatively minor changes in ABG chemistry and Alveolar-arterial gradient, and a substantially milder depression of ventilation. GSHee may represent an effective member of a novel class of thiolester drugs that are able to prevent the ventilatory depressant effects elicited by powerful opioids such as fentanyl and their deleterious effects on gas-exchange in the lungs without compromising opioid analgesia.