Manual ventilation and open suction procedures contribute to negative pressures in a mechanical lung model.

INTRODUCTION: Removal of pulmonary secretions in mechanically ventilated patients usually requires suction with closed catheter systems or flexible bronchoscopes. Manual ventilation is occasionally performed during such procedures if clinicians suspect inadequate ventilation. Suctioning can also be performed with the ventilator entirely disconnected from the endotracheal tube (ETT). The aim of this study was to investigate if these two procedures generate negative airway pressures, which may contribute to atelectasis. METHODS: The effects of device insertion and suctioning in ETTs were examined in a mechanical lung model with a pressure transducer inserted distal to ETTs of 9 mm, 8 mm and 7 mm internal diameter (ID). A 16 Fr bronchoscope and 12, 14 and 16 Fr suction catheters were used at two different vacuum levels during manual ventilation and with the ETTs disconnected. RESULTS: During manual ventilation with ETTs of 9 mm, 8 mm and 7 mm ID, and bronchoscopic suctioning at moderate suction level, peak pressure (PPEAK) dropped from 23, 22 and 24.5 cm H2O to 16, 16 and 15 cm H2O, respectively. Maximum suction reduced PPEAK to 20, 17 and 11 cm H2O, respectively, and the end-expiratory pressure fell from 5, 5.5 and 4.5 cm H2O to -2, -6 and -17 cm H2O. Suctioning through disconnected ETTs (open suction procedure) gave negative model airway pressures throughout the duration of the procedures. CONCLUSIONS: Manual ventilation and open suction procedures induce negative end-expiratory pressure during endotracheal suctioning, which may have clinical implications in patients who need high PEEP (positive end-expiratory pressure).

Can ventilator settings reduce the negative effects of endotracheal suctioning? Investigations in a mechanical lung model.

BACKGROUND: The insertion of suction devices through endotracheal tubes (ETTs) increases airway resistance and the subsequent suctioning may reduce airway pressures and facilitate atelectasis. The aim of this study was to investigate how airway pressures and tidal volumes change when different combinations of suction equipment and ETT sizes are used, and to what extent unfavorable effects can be ameliorated by choice of ventilator settings. METHODS: A mechanical ventilator was connected to a lung model by ETTs of 9 mm, 8 mm or 7 mm internal diameter (ID) with a pressure transducer inserted distal to the ETT. The effects of suction procedures with bronchoscope and closed catheter systems were investigated during pressure controlled ventilation (PCV) and volume controlled ventilation (VCV). In each mode, the effects of changes in inspiration:expiration (I:E) ratio, trigger sensitivity and suction pressure were examined. RESULTS: The variables that contributed most to negative model airway pressures and loss of tidal volume during suctioning were (in descending order); 1) Small-size ETTs (7-8 mm ID) combined with large diameter suction devices (14-16 Fr); 2) inverse I:E ratio ventilation (in VCV); 3) negative ventilator trigger sensitivity; and 4) strong suction pressure. The pressure changes observed distal to the ETTs were not identical to those detected by the ventilator. CONCLUSIONS: Negative model airway pressure was induced by suctioning through small-size ETTs. The most extreme pressure and volume changes were ameliorated when conventional ventilator settings were used, such as PCV mode with short inspiration time and a trigger function sensitive to flow changes.

Specific allergen immunotherapy: effect on IgE, IgG4 and chemokines in patients with allergic rhinitis.

BACKGROUND: Allergen-specific immunotherapy (SIT) is considered as the most effective treatment for Immunoglobulin E (IgE)-mediated allergies. However, how specific immunotherapy attenuates allergic responses is still not clear, but could potentially involve cytokines as well as IgG4-mediated responses. Based on the role of chemokines in IgE-mediated inflammation, we examined the SIT-induced chemokine response in patients with allergic rhinitis. METHODS: We included 35 patients with allergic rhinitis; 20 patients received SIT and 15 patients were not treated with specific immunotherapy. The patients were followed for 3 years. Blood samples were collected before SIT and 3, 5, 7 and 21 weeks and 1, 2 and 3 years after the start of therapy. Total IgE, specific IgE, IgG4 and chemokine levels were assessed. RESULTS: Our main findings were: (i) SIT was associated with an early increase in total and specific IgE during the first 7 weeks, with a subsequent decline, accompanied by a marked increase in specific IgG4 when IgE started to decline; (ii) these SIT-induced responses were accompanied by and in some degree correlated with increased plasma concentrations of the chemokines, monocyte chemoattractant protein (MCP)-1, and eotaxin; and (iii) within the SIT group, these correlations with chemokines were restricted to IgE and IgG4 against birch tree pollen. CONCLUSION: Our findings further support a role for IgG4-mediated mechanisms in the beneficial effects of SIT in patients with allergic rhinitis (AR) and that increased levels of certain chemokines also could be of importance for the effect of such therapy.

Reduction in cardiorespiratory fitness after lung resection is not related to the number of lung segments removed.

AIM: To evaluate the effect of lung cancer surgery on cardiorespiratory fitness (CRF), and to assess the agreement between the predicted postoperative (ppo) V̇O2peak and actually measured postoperative peak oxygen uptake (V̇O2peak). METHODS: Before and 4-6 weeks after lung cancer surgery, 70 patients (35 women) underwent measurements of pulmonary function and CRF via a cardiopulmonary exercise test. In addition, the 23 non-exercising patients underwent measurements after 6 months. The ppo V̇O2peak calculated from the number of functional segments removed was compared with the actually measured postoperative values of V̇O2peak for accuracy and precision. RESULTS: After surgery, the V̇O2peak decreased from 23.9±5.8 to 19.2±5.5 mL/kg/min (-19.6±15.7%) (p<0.001). The breathing reserve increased by 5% (p=0.001); the oxygen saturation remained unchanged (p=0.30); the oxygen pulse decreased by -1.9 mL/beat (p<0.001); the haemoglobin concentration decreased by 0.7 g/dL (p=0.001). The oxygen pulse was the strongest predictor for change in V̇O2peak; adjusted linear squared: r2=0.77. Six months after surgery, the V̇O2peak remained unchanged (-3±15%, p=0.27). The ppo V̇O2peak (mL/kg/min) was 18.6±5.4, and the actually measured V̇O2peak was 19.2±5.5 (p=0.24). However, the limits of agreement were large (CI -7.4 to 8.2). The segment method miscalculated the ppo V̇O2peak by more than ±10 and ±20% in 54% and 25% of the patients, respectively. CONCLUSIONS: The reduction in V̇O2peak and lack of improvement 6 months after lung cancer surgery cannot be explained by the loss of functional lung tissue. Predicting postoperative V̇O2peak based on the amount of lung tissue removed is not recommendable due to poor precision. TRIAL REGISTRATION NUMBER: NCT01748981.

Lung function and dyspnea in patients with permanent atrial fibrillation.

BACKGROUND: Reduced forced expiratory volume in one second (FEV(1)) has been associated with new-onset atrial fibrillation (AF), and AF patients often complain of dyspnea. We hypothesized that patients with permanent AF had reduced lung function compared to subjects in sinus rhythm. METHODS: The participants were 75year-olds from the general population. FEV(1), forced vital capacity (FVC), maximal voluntary ventilation (MVV), total lung capacity by single breath (TLC(SB)), single-breath diffusing capacity of the lung for carbon monoxide (DLCO(SB)) and exercise testing with peak oxygen uptake (VO(2) peak) were assessed. The slope of minute ventilation over carbon dioxide output defined ventilatory efficiency. The Symptom Checklist-frequency and severity questionnaire assessed dyspnea. RESULTS: AF patients had significantly higher number (%) of subjects below the 5th percentile of predicted FEV(1) (7 (27) versus 3 (4), p=0.005), FVC (6 (23) versus 2 (3), p=0.006) and TLC(SB) (11 (42) versus 12 (18), p=0.014) compared to control subjects, also after adjustment for smoking and obesity, or if disregarding subjects with chronic heart failure. The dyspnea frequency and severity scores correlated with VO(2) peak (r=-0.6, p<0.01) in AF patients, and in control subjects with % predicted FEV(1), MVV and TLC(SB) (r=-0.3, p<0.05). CONCLUSION: More patients with permanent AF had lung function below normal range than control subjects in sinus rhythm, irrespective of smoking, obesity or chronic heart failure. Dyspnea, however, was related to exercise capacity rather than to lung function in AF patients.

Respiratory gas exchange indices for estimating the anaerobic threshold.

Several methods are used for estimating the anaerobic threshold (AT) during exercise. The aim of the present study was to compare AT values based on blood lactate measurements with those obtained from computerised calculations of different respiratory gas indices. Twelve healthy, well-trained men performed a stepwise incremental test on both treadmill and cycle ergometer. Respiratory gases were measured continuously, and blood samples were drawn every third minute. AT was determined, based on 1) blood lactate concentrations (Lactate-AT), 2) respiratory exchange ratio (RER-AT), 3) V- slope method (Vslope-AT), and 4) ventilatory equivalent for VO2 (EqO2-AT). Lactate-AT and RER-AT values showed similar values, both on treadmill and on cycle ergometer. EqO2-AT showed a trend towards lower values for AT, while Vslope-AT gave significantly lower values for AT for both exercise modes. Bland-Altman plots showed an even distribution of data for RER-AT, while a more scattered and skewed distribution of data was observed when EqO2-AT and Vslope-AT were compared with Lactate-AT. The study demonstrates that RER-based estimates of AT correlate well with the blood lactate-based AT determination. The RER method is non-invasive and simple to perform, and, in the present study, seemed to be the best respiratory index for estimation of AT. Key PointsAnaerobic threshold can reliably be estimated by respiratory gas indices in well fit subjects.Sophisticated computerassisted equations are not superior to the use of a simple cut-off value of Respiratory Exchange Ratio in estimating the anaerobic threshold.Estimation of anaerobic threshold, by using a pre-defined cut-off value for Respiratory Exchange Ratio, is non- invasive and simple to perform in a respiratory laboratory.