Respiratory Care

To determine the prevalence of confirmatory use of spirometry in patients admitted to a tertiary-care facility with the diagnosis of chronic obstructive pulmonary disease (COPD), including those with respiratory failure, and compare that to the use of confirmatory 2-dimensional echocardiography (2-D echo) in patients admitted with the diagnosis of congestive heart failure (CHF), to determine preferential confirmatory testing practices.

Academic tertiary-care hospital.

A 6-month retrospective review of charts of patients with a primary or secondary discharge diagnosis of COPD, respiratory failure, and CHF, using the appropriate International Classification of Diseases, Ninth Revision, Clinical Modification codes. Pulmonary function and echocardiography laboratory databases were reviewed to determine if the patients had had spirometry or 2-D echo performed during the 8 years prior to the study period.

Five hundred fifty-three patients were discharged with the diagnosis of COPD, and 173 patients (31%) had had spirometry. In contrast, 789 patients had the diagnosis of CHF, and a larger proportion of them (619 patients, 78%) had had 2-D echo (p < 0.001). Only 35% of the patients with respiratory failure and COPD had spirometry performed. There were a total of 219 patients with concomitant diagnoses of COPD and CHF. A majority of them (48%) had a 2-D echo as the only confirmatory test, 74 (34%) had both tests performed, 4 (2%) had spirometry only, and 36 (16%) had neither test performed. Of the patients with a diagnosis of COPD who had spirometry, 30% had spirometry findings consistent with restrictive or normal physiology.

A large proportion of patients hospitalized with the diagnosis of COPD have never had a confirmatory test, including those with presumably advanced disease. Compared to patients with CHF, patients with COPD are less likely to have had the confirmatory test performed, even when both conditions coexist. Many patients with the clinical diagnosis of COPD have an inconsistent physiologic diagnosis. To impact the increasingly important problem of COPD, we must raise awareness of the need to confirm its diagnosis and severity with spirometry.

Airway inflammation in acute and chronic respiratory diseases is characterized in part by abnormal pH in airway-lining fluid. The pH of exhaled-breath condensate (EBC) is low (acidic) in various pulmonary inflammatory diseases, including asthma, chronic obstructive pulmonary disease, cystic fibrosis, pneumonia, and acute respiratory distress syndrome. Because the time course of pH changes in the airway is not yet clear, we aimed to develop a method for frequent and intensive EBC pH data collection in mechanically ventilated patients.

We examined the collection, gas-standardizing (CO₂ removal), and continuous monitoring of pH of EBC from the expiratory port of a Servo-i ventilator with mechanically ventilated patients. We developed a condensing device that attaches to the exhaust port and is chilled by an electric cooling system. We built a 2-chamber gas-standardization and pH-measuring device that attaches to the condensing system and records pH every 6 s. After safety testing, we enrolled mechanically ventilated patients (with diverse reasons for requiring ventilatory support) for up to 96 h of continuous EBC pH condensimetry.

The pressure, volume, and flow of the ventilator attached to a test lung were unchanged by application of the condensimeter, at various flows (2-120 L/min) and ventilator settings. We monitored 19 pediatric patients for 6-96 h. The pH of the accumulated EBC in the storage container correlated with the geometric mean of all the pH data points from the condensimeter during the recording period (r² - 0.95, p < 0.001), which internally validated that the condensimetry system provides accurate, well gas-standardized readings for up to 96 h. The EBC pH values were similar to published reports of single samples. The EBC pH became more acidic during clinical deterioration and normalized with recovery.

Continuous monitoring of EBC pH from the ventilator exhaust port is safely achievable and reliably provides data that may become useful in monitoring critically ill patients.

To assess the ability of a decremental trial of positive end-expiratory pressure (PEEP) to identify an optimal PEEP level that maintains oxygenation after a lung-recruitment maneuver.

Prospective clinical trial.

Surgical intensive care unit of a university hospital.

Twenty sedated patients with acute lung injury and/or acute respiratory distress syndrome, ventilated for 1.2 ± 0.4 d.

Each patient received up to 3 lung-recruitment maneuvers with continuous positive airway pressure of 40 cm H₂O sustained for 40 s to increase the ratio of P_aO2 to F_IO2 by > 20%. Following the lung-recruitment maneuver, PEEP was set at 20 cm H₂O and then the F_IO2 was decreased until the oxygen saturation (measured via pulse oximetry [S_pO2 ]) was 90–94%. PEEP was then decreased in 2-cm H₂O steps until the S_pO2 dropped below 90%. The step preceding the drop to below 90% was considered the optimal PEEP. The lung was then re-recruited and PEEP and F_IO2 were set at the identified levels. The patients were followed for 4 h after the PEEP trial and the setting of PEEP and F_IO2 .

After the lung-recruitment maneuver, all the patients' P_aO2 /F_IO2 increased > 50%. The mean ± SD P_aO2 /F_IO2 on the optimal decremental trial PEEP was 211 ± 79 mm Hg, versus 135 ± 37 mm Hg at baseline (p < 0.001), and was sustained at that level for the 4-h study period (227 ± 81 mm Hg at 4 h). F_IO2 at baseline was 0.54 ± 0.12 versus 0.38 ± 0.12 (p < 0.001) at 4 h. PEEP was 11.9 ± 3.0 cm H₂O at baseline and 9.1 ± 4.7 cm H₂O (p = 0.011) at 4 h.

A decremental PEEP trial identifies a PEEP setting that sustains for 4 h the oxygenation benefit of a 40-cm H₂O, 40-s lung-recruitment maneuver.

Lung-protective ventilation using tidal volume (V_T) of 4–6 mL/kg (predicted body weight) reduces mortality (compared with traditional V_T) in patients with acute respiratory distress syndrome and acute lung injury. Standardized use of lower V_T can result in respiratory acidosis and has raised new concerns about the appropriate configuration of the ventilator circuit, especially in regard to the dead space (V_D) of the apparatus. We hypothesized that, with a patient receiving lung-protective ventilation, the removal of all apparatus dead space from the circuit would reduce P_aCO2 and allow a reduction in minute ventilation.

All the studied patients met the American-European consensus-conference criteria for acute respiratory distress syndrome/acute lung injury, were receiving a lung-protective ventilation strategy, were > 18 years of age, and were hemodynamically stable. We prospectively tested 3 different ventilator-circuit configurations, in random sequence, for 15 min each: (1) standard hygroscopic heat-and-moisture exchanger (HME) with 15-cm flexible tubing, (2) 15-cm flexible tubing only, (3) no HME or flexible tubing. V_T, respiratory rate, positive end-expiratory pressure, and fraction of inspired oxygen were maintained constant throughout the study, and exhaled CO₂ was measured continuously. Physiologic dead space (V_D/V_T) was calculated using the Enghoff modification of the Bohr equation.

Seven patients were studied. Removal of the HME from the circuit significantly decreased V_D/V_T (by approximately 6%) and P_aCO2 (by approximately 5 mm Hg). Removal of both the HME and flexible tubing from the circuit reduced V_D/V_T by an additional 5%, and P_aCO2 by an additional 6 mm Hg. With both circuit-configuration changes, minute ventilation fell from a mean of 11.51 L/min to 10.35 L/min, and pH increased from 7.30 to 7.38. Carbondioxide production did not change significantly.

In patients receiving lower-V_T ventilation, removing all the apparatus V_D from the ventilator circuit reduces P_aCO2 and increases pH, at a lower minute ventilation. This information will help guide ventilator-circuit configuration for patients receiving lungprotective ventilation.

The periodic administration of positive airway pressure combined with directed cough could aid mucus clearance in patients with cystic fibrosis (CF) and severe airway obstruction.

To compare the short-term effect of positive expiratory pressure (PEP) physiotherapy via mask (mask PEP), continuous positive airway pressure (CPAP), and noninvasive positive-pressure ventilation (NPPV) physiotherapies on amount of sputum collected.

Directed cough was standardized for each patient and used as the control treatment. We studied 17 patients with CF (mean ± SD age 28 ± 7 y) and severe airway obstruction (forced expiratory volume in the first second 25 ± 6% of predicted) admitted for pulmonary exacerbation. Mask PEP, CPAP, NPPV, and the control treatment (directed cough) were administered in a random sequence. Each patient received each treatment twice a day (in 70-min sessions) for 2 consecutive days. We measured the wet and dry weight of sputum collected and the number of directed and spontaneous coughs during each session. Spirometry and pulse oximetry were conducted before and after each session. For mask PEP, CPAP, and NPPV, each patient gave a subjective score for the efficacy and tolerability of the treatment, compared to the control treatment.

There was no statistically significant difference in the dry weight of sputum collected: mask PEP 0.9 ± 0.6 g, CPAP 0.8 ± 0.4 g, NPPV 0.9 ± 0.6 g, control treatment 1.0 ± 0.8 g. There was a statistically significant difference in the wet weight of sputum collected: mask PEP 15.8 ± 5.5 g, CPAP 13.7 ± 5.5 g, NPPV 13.2 ± 5.0 g, control treatment 14.0 ± 5.0 g (p < 0.05), but that difference became nonsignificant when we took into account the number of spontaneous coughs. There were no statistically significant changes in the spirometry and pulse-oximetry values. The patients' subjective efficacy scores were similar for mask PEP, CPAP, and NPPV. Less fatigue was reported after NPPV and CPAP than after mask PEP.

There were no differences in sputum clearance or pulmonary-function measures between mask PEP and short-term administration of either CPAP or NPPV combined with directed cough. After mask PEP these patients felt more tired than after CPAP or NPPV secretion-clearance therapy.

To assess and compare immediate effects of chest physiotherapy with positive expiratory pressure (PEP) versus oscillating PEP on transcutaneously measured blood-gas tensions in patients with cystic fibrosis.

Fifteen patients (mean age 12.5 y, range 6.9–21.5 y) participated. The treatments were randomized and performed on 2 separate occasions, 8 weeks apart. Spirometry was conducted before and after each treatment. We transcutaneously measured oxygen tension (P_tO2 ) and carbon dioxide tension (P_tCO2 ) 20 min before, during, and 10 min after each treatment.

There were no changes in spirometry values. During PEP, different trends in blood-gas tension were seen, and there were no consistent changes. During oscillating PEP, P_tO2 increased and P_tCO2 decreased. During oscillating PEP, P_tCO2 was lower and the intra-individual change in P_tCO2 was more pronounced than during PEP. The results obtained immediately after oscillating PEP showed a higher P_tO2 and a lower P_tCO2 than with PEP.

PEP and oscillating PEP can both cause transitory effects on blood gases in patients with cystic fibrosis. However, oscillating PEP alters blood-gas tensions more than does PEP, and hyperventilation during oscillating PEP may reduce treatment time.

Since there is a growing use of analgesia and sedation in spontaneously breathing patients undergoing diagnostic or therapeutic interventions, recommendations by national societies of anesthesiologists call for the application of capnometry during all anesthetic procedures.

We compared readings from a transcutaneous capnometer (Tosca) and an end-tidal capnometer (Microcap Plus) to P_aCO2 measurements made via arterial-blood-gas analysis. We studied 30 spontaneously breathing patients who were recovering from general anesthesia, and we used Bland Altman analysis to compare the capnometry readings to the arterial-blood-gas values. Expiratory gas samples for end-tidal capnometry were taken either from a conventional face mask or an oral/nasal cannula.

The Tosca significantly overestimates P_aCO2 (mean ± SD difference 5.6 ± 3.4 mm Hg). The Microcap Plus significantly underestimates P_aCO2 (mean ± SD difference −14.1 ± 7.4 mm Hg). There was no significant difference between the face mask and oral/nasal cannula with regard to collecting end-tidal samples.

Both the Tosca and Microcap Plus provide just an approximate estimation of P_aCO2 . Clinical use of these monitors can not be proposed under actual conditions but will be advantageous after correction of the limiting errors.

We report the performance of an ultrasound-based portable spirometer (EasyOne) used in a population-based survey of the prevalence of chronic obstructive pulmonary disease, conducted in 5 Latin American cities: São Paulo, Brazil; México City, México; Montevideo, Uruguay; Santiago, Chile; and Caracas, Venezuela (the Latin American COPD Prevalence Study [PLATINO]).

During the survey period (which ranged from 3 months to 6 months in the various locations) we collected daily calibration data from the 70 EasyOne spirometers used in the 5 survey cities. The calibrations were conducted with a 3-L syringe, and the calibration data were stored in the spirometer's database.

Ninety-seven percent of the calibration volumes were within ± 64 mL (2.1%) of the 3-L calibration signal. Excluding data from the first city studied (São Paulo), where one calibration syringe had to be replaced, 98% of the calibration checks were within ± 50 mL (1.7%). The measured volume was affected only minimally by the syringe's peak flow or emptying time.

In these 70 EasyOne spirometers neither calibration nor linearity changed during the study. Such calibration stability is a valuable feature in spirometry surveys and in the clinical setting.