Long-term effects of spontaneous breathing during ventilatory support in patients with acute lung injury.

Improved gas exchange has been observed during spontaneous breathing with airway pressure release ventilation (APRV) as compared with controlled mechanical ventilation. This study was designed to determine whether use of APRV with spontaneous breathing as a primary ventilatory support modality better prevents deterioration of cardiopulmonary function than does initial controlled mechanical ventilation in patients at risk for acute respiratory distress syndrome (ARDS). Thirty patients with multiple trauma were randomly assigned to either breathe spontaneously with APRV (APRV Group) (n = 15) or to receive pressure-controlled, time-cycled mechanical ventilation (PCV) for 72 h followed by weaning with APRV (PCV Group) (n = 15). Patients maintained spontaneous breathing during APRV with continuous infusion of sufentanil and midazolam (Ramsay sedation score [RSS] of 3). Absence of spontaneous breathing (PCV Group) was induced with sufentanil and midazolam (RSS of 5) and neuromuscular blockade. Primary use of APRV was associated with increases (p < 0.05) in respiratory system compliance (CRS), arterial oxygen tension (PaO2), cardiac index (CI), and oxygen delivery (DO2), and with reductions (p < 0.05) in venous admixture (QVA/QT), and oxygen extraction. In contrast, patients who received 72 h of PCV had lower CRS, PaO2, CI, DO2, and Q VA/Q T values (p < 0.05) and required higher doses of sufentanil (p < 0.05), midazolam (p < 0.05), noradrenalin (p < 0.05), and dobutamine (p < 0.05). CRS, PaO2), CI and DO2 were lowest (p < 0.05) and Q VA/Q T was highest (p < 0.05) during PCV. Primary use of APRV was consistently associated with a shorter duration of ventilatory support (APRV Group: 15 +/- 2 d [mean +/- SEM]; PCV Group: 21 +/- 2 d) (p < 0.05) and length of intensive care unit (ICU) stay (APRV Group: 23 +/- 2 d; PCV Group: 30 +/- 2 d) (p < 0.05). These findings indicate that maintaining spontaneous breathing during APRV requires less sedation and improves cardiopulmonary function, presumably by recruiting nonventilated lung units, requiring a shorter duration of ventilatory support and ICU stay.     

Combination antibiotic therapy with macrolides improves survival in intubated patients with community-acquired pneumonia

Objective  

To assess the effect on survival of macrolides or fluoroquinolones in intubated patients admitted to the intensive care unit (ICU) with severe community-acquired pneumonia (severe CAP).     

Airway pressure release ventilation versus assist-control ventilation: a comparative propensity score and international cohort study

Purpose

To compare characteristics and clinical outcomes of patients receiving airway pressure release ventilation (APRV) or biphasic positive airway pressure (BIPAP) to assist-control ventilation (A/C) as their primary mode of ventilatory support. The objective was to estimate if patients ventilated with APRV/BIPAP have a lower mortality.

Methods

Secondary analysis of an observational study in 349 intensive care units from 23 countries. A total of 234 patients were included who were ventilated only with APRV/BIPAP and 1,228 patients who were ventilated only with A/C. A case-matched analysis according to a propensity score was used to make comparisons between groups.

Results

In logistic regression analysis, the most important factor associated with the use of APRV/BIPAP was the country (196 of 234 patients were from German units). Patients with coma or congestive heart failure as the reason to start mechanical ventilation, pH <7.15 prior to mechanical ventilation, and patients who developed respiratory failure (SOFA score >2) after intubation with or without criteria of acute respiratory distress syndrome were less likely to be ventilated with APRV/BIPAP. In the case-matched analysis there were no differences in outcomes, including mortality in the intensive care unit, days of mechanical ventilation or weaning, rate of reintubation, length of stay in the intensive care unit or hospital, and mortality in the hospital.

Conclusions

In this study, the APRV/BIPAP ventilation mode is being used widely across many causes of respiratory failure, but only in selected geographic areas. In our patient population we could not demonstrate any improvement in outcomes with APRV/BIPAP compared with assist-control ventilation.     

Lung protective ventilation - protective effect of adequate supported spontaneous breathing

Based on available data, it can be suggested that spontaneous breathing during ventilator support has not to be suppressed even in patients with severe pulmonary dysfunction if no contraindications are present. Experimental data do not support the contention that spontaneous breathing aggravates ventilator-induced lung injury. During spontaneous breathing increase in PTP is maximal in the depended lung areas in adjunct to the diaphragm and causes recruitment of initially atelectatic lung areas thereby avoiding cyclic alveolar collapse and reopening. This should result in a lung protective effect of adequate supported spontaneous breathing. Clinical data supported this belief demonstrating improvement in pulmonary gas exchange, systemic blood flow, and oxygen supply to the tissue and a decrease in days on ventilator support and duration of stay in the intensive care unit.     

Should we breathe quiet or noisy?

External noise is introduced by computer-generated random levels of pressure assistance during noisy pressure support ventilation (PSV). In patients, noisy PSV was associated with higher tidal volume variability but not improved cardio-pulmonary function compared with conventional PSV. The potential role of noisy PSV in the management of critically ill patients requiring ventilatory support has to be explored further.Although introduced as weaning techniques, modes providing mechanical support of spontaneous breathing have become standard in primary mechanical ventilator support in critically ill patients. In Critical Care, Spieth and colleagues [1] report for the first time the use of noisy pressure support ventilation (PSV) in patients with acute hypoxemic respiratory failure.Normal breathing shows considerable variation in tidal volume (V_T), flow rate, and respiratory rate, which is lost during mechanical ventilation (MV). In addition to elevation of intrathoracic and intrapulmonary pressures, MV causes a non-physiological uniform breathing pattern. Based on the concept that MV should mimic physiologically noisy breathing patterns, biologically variable or noisy MV was introduced, which attempted to mimic spontaneous breath-to-breath variability during volume-controlled MV [2]. Experimental and small clinical trials suggest that biologically variable or noisy MV may improve pulmonary gas exchange, compliance and dead space by preventing de-recruitment when compared to conventional MV [2,3]. These findings support the concept that alveolar recruitment achieved by large V_T exceeds the de-recruitment by small V_T. Other mechanisms claimed to explain improved lung function during biologically variable or noisy MV include stochastic resonance [4], increased respiratory sinus arrhythmia [5], endogenous surfactant release [6,7], and dynamic effects on the pressure-volume curve [7].Nowadays, modes providing assisted support of spontaneous breathing should not only assure adequate gas exchange and unloading of the patient’s work of breathing but should provide patient-ventilator synchrony, optimized diaphragmatic unloading, lung-protective ventilation, and the preservation of physiological respiratory patterns and variability. To accomplish all these tasks ventilatory assistance can no longer be constant but has to continuously adapt to changes in ventilatory demand and respiratory mechanics. To adapt to the continuously changing respiratory demand, pressure assistance is proportional to the instantaneous flow and volume, reflecting the inspiratory muscles’ pressure during proportional assist ventilation (PAV) [8] or proportional to the electrical activity of the diaphragm during neurally adjusted ventilator assist (NAVA) [9]. Thus, PAV and NAVA try to amplify the patient''s respiratory center output. Several experimental investigations and clinical trials in small groups of critically ill patients have demonstrated that PAV and NAVA, when compared to conventional PSV, enhance patient-ventilator interaction and synchrony, which translates into better comfort and sleep quality and preserves V_T variability, which has been associated with improvements in gas exchange and lung mechanics [10,11].In patients with mechanically assisted spontaneous breathing, the noise can be introduced externally or can come directly from the respiratory center. In contrast to PAV and NAVA, which amplify the noise coming from the respiratory center, external noise is introduced by computer-generated random levels of pressure assistance during noisy PSV [12]. Experimental investigations in induced lung injury showed that noisy PSV, when compared with conventional PSV and pressure-controlled MV, was associated with a significantly higher coefficient of variation of V_T and airway pressure, and resulted in better pulmonary gas exchange, reduced alveolar edema in overall lung as well as reduced inflammation in the nondependent parts of the lungs [13]. In a porcine model with induced lung injury an external source of noise (noisy PSV) and noise derived from amplification of the respiratory center (PAV) improved gas exchange and produced higher V_T variability, whereas the pulmonary inflammatory response and diffuse alveolar damage score did not differ when compared to conventional PSV lungs [14].Spieth and colleagues [1] investigated the short-term effects of conventional and noisy PSV in patients with acute hypoxemic respiratory failure. Noisy PSV was associated with higher V_T variability and a lower number of asynchrony events. In contrast to experimental findings, cardio-pulmonary function and spatial distribution of ventilation were comparable between conventional and noisy PSV [1]. During conventional and noisy PSV, however, V_T significantly higher than 8 ml/kg predicted body weight was frequently noticed. By design noisy PSV applies V_T as high as 16 ml/kg and as low as 1.6 ml/kg once every 20 to 30 minutes [12]. Although short-term experiments demonstrate that this mixture of ultra-protective and non-protective V_T during noisy PSV does not add to lung injury based on histological examinations, long-term investigations have to clarify the relevance of periodic non-protective V_T ventilation in critically ill patients.     

Method of delivering constant nitric oxide concentrations during full and partial ventilatory support

Objective. The objective of our study was to evaluate the precision and safety of administering nitric oxide (NO) during full and partial ventilatory support.Methods. NO was administered either using a microprocessor-controlled servo ventilator, substituting an NO-N₂ mixture for the ventilator's usual air supply or by adding an NO-N₂ mixture with a constant flow at the proximal end of the tracheal tube. NO, nitrogen dioxide (NO₂), and nitrous and nitric acid (HNO_x) was quantified selectively with a sequential, selective, hollow tube preconcentration and chemiluminescence analysis in a respiratory system model during various modes of full and partial ventilatory support.Results. The servo valve system of the ventilator provided accurate NO concentrations during full and partial ventilatory support. Interaction of spontaneous and mechanical ventilation during partial ventilatory support resulted in irregular inspiratory flow patterns and a difference of 3.6% to 44.1% between the desired and measured inspiratory NO concentrations when NO was administered at a constant flow to the proximal end of the tracheal tube. NO₂ was not detected. Small amounts of 0.6 to 0.8 ppm HNO_x were detected when 80 ppm NO was administered in a humid gas mixture of 37°C in the presence of 90% oxygen.Conclusions. NO can be administered accurately without formation of NO₂ during full and partial ventilatory support with the electronically controlled valve system of the ventilator. Formation of HNO_x is a potential problem at high NO and O₂ concentrations in the presence of moisture.Christian Putensen, MD, was supported by the Erwin Schroedinger Foundation, grant no. J0637-MED.The investigators thank Chris A. Jackson and Christine D.Geraghty for their excellent technical help, and Maura LeCroy for editorial assistance.     

Kinetic and reversibility of mechanical ventilation-associated pulmonary and systemic inflammatory response in patients with acute lung injury

Abstract Objective. To investigate the kinetic and reversibility of mechanical ventilation-associated pulmonary and systemic inflammatory response in patients with acute lung injury (ALI). Design. Prospective observational cross-over study. Setting. Intensive care unit of a university hospital. Patients. Twelve mechanically ventilated patients with ALI. Interventions. Mechanical ventilation was transiently changed from a lung protective setting with PEEP of 15 cmH₂O and a V_T of 5 ml/kg predicted body weight to a more conventional ventilatory setting with PEEP of 5 cmH₂O and V_T of 12 ml/kg predicted body weight for a period of 6 h. Measurements and results. We examined the profile of interleukin (IL)-1#, IL-1 receptor antagonist, IL-6, IL-10, and tumor necrosis factor in the plasma of all patients, and in the bronchoalveolar lavage (mini-BAL) fluid of six of these patients. Measurements were performed at baseline, 1 h, and 6 h after each change of the ventilatory setting. Switching to conventional mechanical ventilation was associated with a higher PaO₂ (P <0.05) and a marked increase (P <0.05) of measured plasma cytokines in patients with and without mini-BAL with a maximum after 1 h. Similarly, intraalveolar cytokine concentrations increased with conventional mechanical ventilation. While plasma cytokine levels returned to baseline values, intraalveolar cytokine concentrations further increased when lung protective mechanical ventilation was reestablished. Conclusions. In patients with ALI, initiation of low PEEP and high V_T mechanical ventilation is associated with cytokine release into circulation which occurred within 1 h. It is independent from BAL procedures and can be reversed by reinstitution of lung protective mechanical ventilation.