Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine: Brussels, Belgium. 15-18 March 2016

[This corrects the article DOI: 10.1186/s13054-016-1208-6.].

Level of asthma control and healthcare utilization in Latin America

The purpose of this study was to investigate whether uncontrolled asthma was associated with healthcare outcomes among Latin American patients with asthma. We used data from 2168 patients with asthma who participated in the 2011 Latin America Asthma Insights and Management (AIM) survey. Using Global Initiative for Asthma (GINA) guidelines, patients were categorized as having asthma that was well-controlled, partly controlled, or uncontrolled. Overall, 7% of the patients surveyed had asthma that was classified as well-controlled. Patients whose asthma was not well-controlled were significantly more likely to report use of asthma medications (ORs ranging from 1.6-41) and to have had emergency healthcare visits or hospitalizations for their asthma in the previous year (ORs ranging from 2.1 to 5.9). They also reported decreases in their productivity compared to patients with well-controlled asthma. These associations suggest that emphasis on improving asthma control could have substantial effects on patient productivity and utilization of healthcare resources.

The 6-min walk distance in healthy subjects: reference standards from seven countries

The 6-min walk distance (6MWD) predicted values have been derived from small cohorts mostly from single countries. The aim of the present study was to investigate differences between countries and identify new reference values to improve 6MWD interpretation. We studied 444 subjects (238 males) from seven countries (10 centres) ranging 40-80 yrs of age. We measured 6MWD, height, weight, spirometry, heart rate (HR), maximum HR (HR(max)) during the 6-min walk test/the predicted maximum HR (HR(max) % pred), Borg dyspnoea score and oxygen saturation. The mean ± sd 6MWD was 571 ± 90 m (range 380-782 m). Males walked 30 m more than females (p < 0.001). A multiple regression model for the 6MWD included age, sex, height, weight and HR(max) % pred (adjusted r² = 0.38; p < 0.001), but there was variability across centres (adjusted r² = 0.09-0.73) and its routine use is not recommended. Age had a great impact in 6MWD independent of the centres, declining significantly in the older population (p < 0.001). Age-specific reference standards of 6MWD were constructed for male and female adults. In healthy subjects, there were geographic variations in 6MWD and caution must be taken when using existing predictive equations. The present study provides new 6MWD standard curves that could be useful in the care of adult patients with chronic diseases.

[Postoperative lung complications and mortality in patients with mild-to-moderate COPD undergoing elective general surgery]

OBJECTIVE

To verify the incidence of postoperative pulmonary complications (PPC) and mortality inpatients with mild-to-moderate chronic obstructive pulmonary disease(COPD) who undergo elective general surgery. Incidence of PPC and mortality were studied in relation to sex, age, anesthesia,surgical incision, duration of surgery, smoking, respiratory symptoms, comorbidity, nutritional status, lung examination, abnormal electrocardiogram,and PaO2, PaCO2, FEV1 and FEV1/FVC.

DESIGN

Prospective, open study.

MATERIAL AND METHODS

Fifty-nine COPD patients were enrolled (FEV1/FVC< 88% of reference for women and < 89% for men) and studied at a tertiary care university hospital. The patients were examined during the pre-operative period and followed until discharge.

RESULTS

Twenty patients (33.9%) experienced PPC and 6 died, two (3.4%) from lung-related causes. Thirty-five PPC events occurred: pneumonia (37.2%), bronchospasm(22.9%), atelectasis (11.4%), acute respiratory insufficiency(11.4%), prolonged mechanical ventilation (11.4%) and bronchial infection (5.7%). Risk factors for PPC were male gender, duration of surgery over 270 minutes, low FEV1/FVC (71.9 +/-10.9%) and surgical incision in the chest or upper abdomen. No significant difference between patients with or without PPC were found for age, presence of respiratory symptoms, comorbidity,abnormal lung examination, nutritional status, smoking, abnormal electrocardiogram, PaO2, PaCO2, FEV1 or duration of pre-operative hospitalization. The rate of PPC was higher in patients smoking more than a mean 40 packs of cigarettes per year. Patients with PPC had longer hospital stays (16.6 +/-15.0 vs. 7.5 +/- 5.7 days) and stayed longer in intensive care units (7.0 +/- 5.9 vs. 1.7 +/- 0.7 days) than did those with no complications (p < 0.05).

CONCLUSIONS

The incidence of PPC was 33.9% and lung-related mortality was 3.4%. Risk factors were male gender, amount of smoking, duration of surgery over 270 minutes, low FEV1/FVC, and chest or upper abdominal incision. No risk factor was found to predict mortality in this group.

Effect of caffeine on skeletal muscle function before and after fatigue

We studied the effect of caffeine on voluntary and electrically stimulated contractions of the adductor pollicis muscle in five adult volunteers. Caffeine (500 mg) was administered orally in a double-blind fashion. Electrical stimulation of the ulnar nerve was performed at 10, 20, 30, 50, and 100 Hz before and after a sustained voluntary contraction held at 50% of the maximal voluntary contraction (MVC). A brief tetanus at 30 Hz was also performed to calculate relaxation rate in the fresh muscle. Contractile properties, relaxation rate, and endurance were then assessed after caffeine and placebo, as well as the response of the fatigued muscle to different frequencies of stimulation. There was no difference in the maximal tension obtained with electrical stimulation (T100) or in the MVC between placebo and caffeine. The tensions developed with electrical stimulation at lower frequencies increased significantly with caffeine ingestion, shifting the frequency-force curve to the left, both before and after fatigue. Mean plasma caffeine concentration associated with these responses was 12.2 +/- 4.9 mg/l. We conclude that caffeine has a direct effect on skeletal muscle contractile properties both before and after fatigue as demonstrated by electrical stimulation.

Factors influencing pulsus paradoxus in asthma

In five normal subjects with pulsus paradoxus (change in systolic blood pressure greater than 10 mm Hg) induced by breathing through external inspiratory resistance, the change in systolic blood pressure was related to swings in esophageal pressure (change in intrapleural pressure [PpI]). Effects of hyperinflation (to 75 to 85 percent of vital capacity) were examined by adding expiratory resistances, and the influence of the configuration of the chest wall was studied by using "intercostal" and "abdominal" breathing patterns. There was a curvilinear relationship between the change in systolic blood pressure and the change in PpI, and hyperinflation was not necessary for the production of pulsus paradoxus. At the same change in PpI, there was no significant difference between "intercostal" and "abdominal" breathing, suggesting that pulmonary overdistention with tensing of the mediastinum is not an important etiologic mechanism. Analysis of sustained Muller's maneuvers suggested that the temporal breathing pattern may be important in determining the degree of paradox and may account for its variability in patients with a given degree of obstruction of air flow.

The failing inspiratory muscles under normoxic and hypoxic conditions

The effects of hypoxemia on inspiratory muscle fatigue were assessed in 4 normal subjects. They breathed to exhaustion through high inspiratory resistances producing an inspiratory mouth pressure (Pm) of about 80% of maximal mouth pressure. The endurance time (tlim) during hypoxia (13% O2) was found to be shorter than that while breathing room air at equal inspiratory mouth pressures. Endurance time during hypoxia was also compared with that while breathing room air at equal rates of energy consumption (C), assuming that C is proportional to: Formula: (See Text). At these equal rates, endurance time during hypoxia still remained shorter than that during normoxia. Fatigue was also assessed by measuring the electromyographic power spectrum of the diaphragm and the parasternal intercostals. The power spectrum shifted towards low frequencies during fatigue and a greater rate of shift was observed under hypoxic conditions. The rate of lactate production during hypoxemia was greater than that during normoxia; however, blood lactate concentrations at the end of the tests were similar under both conditions. It was concluded that respiratory muscles, working against high inspiratory resistances, fall as pressure generators sooner during low oxygen breathing. The effect of low oxygen breathing on inspiratory muscle fatigue resulted in a shorter endurance time, a faster rate in the shift of the electromyographic power spectrum, and a greater rate of increase in blood lactate concentrations.

Relation between flow, curvilinearity, and density dependence of pulmonary pressure-flow curves

In nine normal subjects we measured pulmonary pressure-flow curves by ensemble averaging over 20 breaths and solving the equation P = K'V alpha where P is flow-resistive pressure, K' is slope, 5 V is flow, and alpha is curvilinearity. The study was performed at four lung volumes from 37 to 73% of total lung capacity, with the subjects breathing air or HeO2. K' was lower at every lung volume during HeO2 breathing, whereas the exponent alpha was uninfluenced by either lung volume or HeO2 breathing. Although alpha increased with flow rate, comparison of air and HeO2 curves revealed that alpha was not uniquely related to Reynolds' number. Furthermore there was no correlation between curvilinearity and the density dependence of K'. These observations are inconsistent with the general equation P = KV alpha rho alpha-1 mu 2-alpha, where K is a constant related to airway geometry, rho is density and mu is viscosity. (Wood et al., J. Appl. Physiol. 41: 234-244, 1976). The reasons for this discrepancy are unclear, but do not appear to be related to effects of oscillatory flow because alpha was similar from 20 to 90 breaths/min in four subjects. We conclude that the curvilinearity of pulmonary pressure-flow curves is related to flow but independent of gas density and is not explicable solely on the basis of Reynolds' number.

Pulmonary pressure-flow curves measured by a data-averaging circuit

We measured pulmonary pressure-flow curves in nine normal nonsmoking subjects using a data-averaging circuit. With this method we obtained mean pressure flow curves of 20 consecutive breaths free of cardiac artifacts. Within-observer and within-subject-within-day reproducibility were good especially for the inspiratory limb of the curve. Within-subject-between-day variability in curvilinearity was substantial. In most subjects there was a continuous increase in resistance throughout the course of expiration even though the airways did not become dynamically compressed. This resulted in a mean value of expiratory resistance that was greater than during inspiration. Resistance early in expiration, however, was identical to that during inspiration. The data-averaging circuit allows for a more accurate assessment of the slope and the curvilinearity of pulmonary pressure-flow curves than other methods described before.