Functional Residual Capacity In Patients Research Articles

Postural changes in lung volumes in patients with heart failure and Cheyne-Stokes respiration: Relationship with sleep apnea severity

Background and aimIt has been proposed that the increased severity of sleep apnea frequently observed in heart failure (HF) patients with Cheyne-Stokes respiration (CSR) when sleeping in the supine compared to the lateral position, may be caused by the concomitant reduction in functional residual capacity (FRC). We assessed positional changes in FRC in patients with CSR and investigated the relationship between these changes in the laboratory and corresponding changes in CSR severity during sleep. MethodsAfter a diagnostic polysomnography, 18 HF patients with dominant CSR and an apnea-hypopnea index (AHI)≥15 events/h underwent a standard pulmonary function test in the sitting position. Measurements were repeated in the supine, left lateral and right lateral. The latter two measurements were averaged to obtain a single lateral measurement. ResultsThe FRC in the seated position was 3.0 ± 0.5 L (85 ± 13% of predicted), decreased to 2.3 ± 0.3 L (−21 ± 8%, p < 0.0001) in the supine position, and increased to 2.8 ± 0.4 L (+21 ± 12%, p < 0.0001) from the supine to the lateral position (−5±8% vs seated, p = 0.013). During sleep, the AHI and the apnea index (AI) decreased from 47 ± 15 events/h to 26 ± 12 events/h (−46 ± 20%, p < 0.0001) and from 29 ± 21 events/h to 12 ± 10 events/h (−61 ± 40%, p < 0.001) from the supine to the lateral position. Changes in the AI were significantly correlated with corresponding changes in FRC (ρ = −0.55, p = 0.032). ConclusionIn patients with HF and CSR, lying in the supine position causes a significant reduction in FRC in the context of a chronically reduced FRC. The negative correlation between postural changes in FRC and AI supports the hypothesis that the reduction in lung gas stores in the supine position may promote/exacerbate respiratory control instability.

This Month in Anesthesiology

This Month in Anesthesiology

Correlation between functional residual capacity and trans-pulmonary pressure in acute respiratory distress syndrome patients and their prognostic value

To analyze the application of functional residual capacity (FRC)-guided optimal positive end-expiratory pressure (PEEP) in pulmonary retention in patients with acute respiratory distress syndrome (ARDS), and to explore the correlation between FRC and trans-pulmonary pressure and their predictive value for prognosis. Seventy-eight ARDS patients on mechanical ventilation admitted to department of critical care medicine of the First Affiliated Hospital of Jinzhou Medical University from March 2018 to May 2019 were enrolled. According to random number table method, the patients were divided into experimental group and the control group. PEEP of all patients were gradually increased in recruitment after fully sedation and analgesia. The best PEEP was set by monitoring FRC in the experimental group, and by monitoring maximum oxygen in the control group set. The differences before and after 30 minutes and 2 hours recruitment manoeuvres in dynamic compliance (Cdyn), oxygenation index (PaO2/FiO2), and mechanical power (MP) were compared between the two groups. Pearson method was used to analyze the correlation between FRC and trans-pulmonary pressure. The predictive value of FRC and trans-pulmonary pressure for 28-day mortality in patients with ARDS was analyzed by receiver operating characteristic (ROC) curve. The optimal PEEP was (16.24±1.57) cmH2O (1 cmH2O = 0.098 kPa) in the experimental group and (14.11±1.15) cmH2O in the control group in recruitment maneuvres, with statistically significant difference between the two groups (t = 5.678, P = 0.000). Pearson correlation analysis showed that there was a significant correlation between FRC and trans-pulmonary pressure in ARDS patients (r = 0.759, P = 0.000). Cdyn and PaO2/FiO2 in the experimental group were higher than the control group at 30 minutes and 2 hours after recruitment maneuvres [Cdyn (mL/cmH2O): 61.16±3.55 vs. 58.54±5.25, 58.59±2.82 vs. 56.86±3.40; PaO2/FiO2 (mmHg, 1 mmHg = 0.133 kPa): 245.27±14.86 vs. 239.00±5.34, 192.25±5.11 vs. 188.86±5.07], MP was lower than the control group (J/min: 16.32±1.11 vs. 17.05±1.22, 15.22±1.25 vs. 17.03±1.50), the difference was statistically significant (all P < 0.05). The ROC curve analysis showed that both FRC and trans-pulmonary pressure had predictive value for the 28-day mortality of ARDS patients, and the area under the ROC curve (AUC) was 0.868, and 0.828 respectively (both P < 0.01). Measuring FRC in patients with ARDS during recruitment maneuvres can guide optimal PEEP. FRC was significantly correlated with trans-pulmonary pressure, and both of them had predictive value for 28-day mortality in ARDS patients.

Extreme obesity-particular aspect of invasive and noninvasive ventilation

The obesity rate is increasing worldwide and the percentage of obese patients in the intensive care unit (ICU) is rising concomitantly. Ventilatory support strategies in obese patients must take into account the altered pathophysiological conditions. Unfortunately, prospective randomized multicenter trials on this subject are lacking. Therefore, current strategies are based on the individual experiences of ICU physicians and single-center studies. Noninvasive ventilation (NIV) in critically ill patients with acute respiratory failure and obesity hypoventilation syndrome (OHS) is an efficient treatment option and should be provided as early as possible is an effort to avoid intubation. Patient positioning is also crucial: half-sitting positions (>45°) improve lung compliance and functional residual capacity in patients with respiratory failure. Transpulmonary pressure measurements or the Acute Respiratory Distress Syndrome (ARDS) Network tables may help to adjust the optimal positive end-expiratory pressure (PEEP). The tidal volume should be adapted to the ideal and not the actual bodyweight (Vt= 6 ml/kg of ideal bodyweight) to avoid lung damage and (additional) right ventricular stress. Under particular conditions, inspiratory pressures>30 cmH2O may be tolerated for alimited duration. Early tracheostomy combined with termination/reduction of sedation and relaxation is controversy discussed in the literature as atherapeutic option during invasive ventilation of morbidly obese patients. However, data on early tracheotomy in obese respiratory failure patients are rare and this should be regarded as an individual treatment attempt only. In cases of refractory lung failure, venovenous extracorporeal membrane oxygenation (vv-ECMO) is an option despite anatomic changes in morbid obesity.

Functional residual capacity in beagle dogs with and without acute respiratory distress syndrome.

Traditionally, the choice of tidal volume for mechanical ventilation was based on body weight (BW) and usually, predicted BW was used to correct actual BW inter-individual variations in obesity and muscle weight. The method of selecting tidal volume depended on the fact that normal lung volumes, especially functional residual capacity (FRC), were mainly determined by height (indirectly by predicted BW), sex and age in healthy persons. However, FRCs in patients with acute respiratory distress syndrome (ARDS) might not abide by the same rule and be significantly different from each other in patients with the same height and sex. We hypothesized that FRC was determined by body length (surrogate for predicted BW) and age in healthy male beagle dogs but not in lung injured ones. A total of 24 dogs were recruited and ARDS model was induced by intravenous injection of oleic acid. FRC was measured by chest computer tomography. Blood gas analysis, extra vascular lung water and respiratory system mechanics were tested at baseline and post-lung injury. Age, body length and actual BW were also recorded before experiments. After lung injury, FRC decreased sharply from baseline (414±84) to (214±70) mL. For healthy lungs, FRC could be estimated by the following formula: FRC =21.86 × age (months) + 20.55 × body length (cm) - 1,337.98 (P<0.05), while for injured lungs, the formula of multiple linear regression was invalid (P=0.305). FRC was linearly related to body length in healthy dogs but not in lung injured ones. The traditional view of setting tidal volume based on predicted BW should be challenged cautiously.

Continuous negative extrathoracic pressure combined with high-frequency oscillation improves oxygenation with less impact on blood pressure than high-frequency oscillation alone in a rabbit model of surfactant depletion

BackgroundNegative air pressure ventilation has been used to maintain adequate functional residual capacity in patients with chronic muscular disease and to decrease transpulmonary pressure and improve cardiac output during right heart surgery. High-frequency oscillation (HFO) exerts beneficial effects on gas exchange in neonates with acute respiratory failure. We examined whether continuous negative extrathoracic pressure (CNEP) combined with HFO would be effective for treating acute respiratory failure in an animal model.MethodsThe effects of CNEP combined with HFO on pulmonary gas exchange and circulation were examined in a surfactant-depleted rabbit model. After induction of severe lung injury by repeated saline lung lavage, 18 adult white Japanese rabbits were randomly assigned to 3 groups: Group 1, CNEP (extra thoracic negative pressure, -10 cmH2O) with HFO (mean airway pressure (MAP), 10 cmH2O); Group 2, HFO (MAP, 10 cmH2O); and Group 3, HFO (MAP, 15 cmH2O). Physiological and blood gas data were compared among groups using analysis of variance.ResultsGroup 1 showed significantly higher oxygenation than Group 2, and the same oxygenation with significantly higher mean blood pressure compared to Group 3.ConclusionAdequate CNEP combined with HFO improves oxygenation with less impact on blood pressure than high-frequency oscillation alone in an animal model of respiratory failure.

Effect of positive end-expiratory pressure on lung mechanics during anaesthesia in dogs

We studied supine anaesthetized dogs to determine whether the use of positive end-expiratory pressure to increase functional residual capacity (FRC) could thereby prevent the small lung compliance values frequently reported during anaesthesia. We first made control measurements of FRC and of both static (CSTAT) and dynamic (CDYN) lung compliance. Continuous positive pressure ventilation (CPPV) with 5 cm H2O positive end-expiratory pressure was then commenced, and FRC and compliance measurements were repeated at 15-minute intervals during one hour of CPPV. We found that the positive end-expiratory pressure served to increase FRC to a level expected for unanaesthetized normally breathing dogs in the same posture (J. Appl. Physiol. 36: 93, 1974), and this FRC was well maintained during the one-hour observation period. Despite the volume preservation, we found a marked decline in lung compliance, equal in both CSTAT and CDYN; however, these changes were completely reversed to control values following hyperinflation of lung (artificial sighting). We conclude that diminution in lung compliance in our anaesthetized dogs was not dependent on low lung volume breathing but must have been due to another mechanism such as suppression of sighing or possibly regional hypoventilation. It might well be important to recognize that reversible reduction of compliance may occur despite increase of FRC in patients managed with positive end-expiratory pressure.

Effects of humidity in inspired air on airway resistance and functional residual capacity in patients with respiratory diseases.

Effects of humidity in inspired air on airway resistance and functional residual capacity in patients with respiratory diseases.

Functional residual capacity in patients with pulmonary emphysema. A comparative study using gas dilution and plethysmographic techniques for measurement.

Excerpt Many methods have been used to measure the functional residual capacity of the lung (FRC), some simple, others complicated and elaborate. Nevertheless, an accurate measurement of functional...