An effective pressure-flow characterization of respiratory asynchronies in mechanical ventilation.

Ineffective effort during expiration (IEE) occurs when there is a mismatch between the demand of a mechanically ventilated patient and the support delivered by a Mechanical ventilator during the expiration. This work presents a pressure-flow characterization for respiratory asynchronies and validates a machine-learning method, based on the presented characterization, to identify IEEs. 1500 breaths produced by 8 mechanically-ventilated patients were considered: 500 of them were included into the training set and the remaining 1000 into the test set. Each of them was evaluated by 3 experts and classified as either normal, artefact, or containing inspiratory, expiratory, or cycling-off asynchronies. A software implementing the proposed method was trained by using the experts' evaluations of the training set and used to identify IEEs in the test set. The outcomes were compared with a consensus of three expert evaluations. The software classified IEEs with sensitivity 0.904, specificity 0.995, accuracy 0.983, positive and negative predictive value 0.963 and 0.986, respectively. The Cohen's kappa is 0.983 (with 95% confidence interval (CI): [0.884, 0.962]). The pressure-flow characterization of respiratory cycles and the monitoring technique proposed in this work automatically identified IEEs in real-time in close agreement with the experts.

On some factors determining the pressure drop across tracheal tubes during high-frequency percussive ventilation: a flow-independent model.

To provide an in vitro estimation of the pressure drop across tracheal tubes (ΔPTT) in the face of given pulsatile frequencies and peak pressures (Pwork) delivered by a high-frequency percussive ventilator (HFPV) applied to a lung model. Tracheal tubes (TT) 6.5, 7.5 and 8.0 were connected to a test lung simulating the respiratory system resistive (R = 5, 20, 50 cmH2O/L/s) and elastic (C = 10, 20, and 50 mL/cmH2O) loads. The model was ventilated by HFPV with a pulse inspiratory peak pressure (work pressure Pwork) augmented in 5-cmH2O steps from 20 to 45 cmH2O, yielding 6 diverse airflows. The percussive frequency (f) was set to 300, 500 and 700 cycles/min, respectively. Pressure (Paw and Ptr) and flow (V') measurements were performed for all 162 possible combinations of loads, frequencies, and work pressures for each TT size, thus yielding 486 determinations. For each respiratory cycle ΔPTT was calculated by subtracting each peak Ptr from its corresponding peak Paw. A non-linear model was constructed to assess the relationships between single parameters. Performance of the produced model was measured in terms of root mean square error (RMSE) and the coefficient of determination (r2). ΔPTT was predicted by Pwork (exponential Gaussian relationship), resistance (quadratic and linear terms), frequency (quadratic and linear terms) and tube diameter (linear term), but not by compliance. RMSE of the model on the testing dataset was 1.17 cmH2O, r2 was 0.79 and estimation error was lower than 1 cmH2O in 68% of cases. As a result, even without a flow value, the physician would be able to evaluate ΔPTT pressure. If the present results of our bench study could be clinically confirmed, the use of a nonconventional ventilatory strategy as HFPV, would be safer and easier.

End-tidal versus manually-controlled low-flow anaesthesia.

During low-flow manually-controlled anaesthesia (MCA) the anaesthetist needs constantly adjust end-tidal oxygen (EtO2) and anaesthetic concentrations (EtAA) to assure an adequate and safe anaesthesia. Recently introduced anaesthetic machines can automatically maintain those variables at target values, avoiding the burden on the anaesthetist. End-tidal-controlled anaesthesia (EtCA) and MCA provided by the same anaesthetic machine under the same fresh gas flow were compared. Eighty patients were prospectively observed: in MCA group (n = 40) target end-tidal sevoflurane (1%) and EtO2 concentrations (≥ 35%) were manually controlled by the anaesthetist. In EtCA group (n = 40) the same anaesthetic machine with an additional end-tidal control feature was used to reach the same targets, rendering automatic the achievement and maintenance of those targets. Anaesthetic machine characteristics, amount of consumed gases, oxygen and sevoflurane efficiencies, and the amount of interventions by the anaesthetist were recorded. In EtCA group EtAA was achieved later (145 s) than in MCA (71 s) and remained controlled thereafter. Even though the target expired gas fractions were achieved faster in MCA, manual adjustments were required throughout anaesthesia for both oxygen and sevoflurane. In MCA patients the number of manual adjustments to stabilize EtAA and EtO2 were 137 and 107, respectively; no adjustment was required in EtCA. Low-flow anaesthesia delivered with an anaesthetic machine able to automatically control EtAA and EtO2 provided the same clinical stability and avoided the continuous manual adjustment of delivered sevoflurane and oxygen concentrations. Hence, the anaesthetist could dedicate more time to the patient and operating room activities.

Early short-term application of high-frequency percussive ventilation improves gas exchange in hypoxemic patients.

BACKGROUND: Hypoxemia in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) patients represents a common finding in the intensive care unit (ICU) and frequently does not respond to standard ventilatory techniques. OBJECTIVE: To study whether the early short-term application of high-frequency percussive ventilation (HFPV) can improve gas exchange in hypoxemic patients with ALI/ARDS or many other conditions in comparison to conventional ventilation (CV) using the same mean airway pressure (P(aw)), representing the main determinant of oxygenation and hemodynamics, irrespective of the mode of ventilation. METHODS: Thirty-five patients not responding to CV were studied. During the first 12 h after admission to the ICU the patients underwent CV. Thereafter HFPV was applied for 12 h with P(aw) kept constant. They were then returned to CV. Gas exchange was measured at: 12 h after admission, every 4 h during the HFPV trial, 1 h after the end of HFPV, and 12 h after HFPV. Thirty-five matched patients ventilated with CV served as the control group (CTRL). RESULTS: PaO(2)/FiO(2) and the arterial alveolar ratio (a/A PO(2)) increased during HFPV treatment and a PaO(2)/FiO(2) steady state was reached during the last 12 h of CV, whereas both did not change in CTRL. PaCO(2) decreased during the first 4 h of HFPV, but thereafter it remained unaltered; PaCO(2) did not vary in CTRL. Respiratory system compliance increased after HFPV. CONCLUSIONS: HFPV improved gas exchange in patients who did not respond to conventional treatment. This improvement remained unaltered until 12 h after the end of HFPV.

Comparison of noninvasive ventilation by sequential use of mask and helmet versus mask in acute exacerbation of chronic obstructive pulmonary disease: a preliminary study.

BACKGROUND: Noninvasive positive pressure ventilation (NPPV) using a face mask is the ventilatory mode of choice in selected patients experiencing acute exacerbation of chronic obstructive pulmonary disease (COPD). A high incidence of intolerance limits the use of this approach. OBJECTIVE: To evaluate the sequential use of mask and helmet during NPPV in patients with severe exacerbation of COPD in order to reduce the intolerance to these devices. METHODS: Fifty-three patients ventilated for the first 2 h with NPPV by mask were studied. If gas exchange and clinical status improved, they were randomized to continue on NPPV by mask or helmet. Physiological parameters were measured at admission, after the first 2 h on NPPV by mask, 4 h after randomization and at discharge. Need for intubation, ventilatory assistance, length of stay (LOS) and complications were recorded. RESULTS: After the first 2 h of NPPV, gas exchange and clinical parameters improved in 40 patients. Four hours after randomization, PaCO(2) was lower in the mask group than in the helmet group. Nine patients in the mask group and 2 in the helmet group failed NPPV, 8 and 1, respectively, owing to intolerance. Time of noninvasive ventilation and LOS were lower in the mask than in the helmet group. CONCLUSIONS: In patients with acute exacerbation of COPD and undergoing NPPV, the sequential use of a mask and helmet diminished the incidence of failure. Under the present experimental conditions, the use of a helmet increased LOS and the duration of artificial ventilation.

High-frequency percussive ventilation improves perioperatively clinical evolution in pulmonary resection.

OBJECTIVE: During thoracotomy, positive end-expiratory pressure is applied to the dependent lung and continuous positive airway pressure (CPAP) inflates the nondependent lung to avoid hypoxemia. These methods do not allow the removal of produced secretions. We hypothesized that high-frequency percussive ventilation(HFPV) can improve both conditions and reduce hospital length of stay in these patients. DESIGN: Randomized prospective study. SETTING: University Hospital. PATIENTS: Fifty-three consecutive patients undergoing elective pulmonary partial resection were enrolled. Nine were excluded because of surgical reasons. INTERVENTIONS: The nondependent lung was ventilated with HFPV in 22 patients and other 22 received CPAP. In both groups,the dependent lung was ventilated with continuous mechanical ventilation. MEASUREMENT AND MAIN RESULTS: Cardiocirculatory variables and blood gas analysis were measured during surgery. Postoperatively,all patients underwent chest physiotherapy, and SpO2,body temperature, the amount of sputum produced, and chest radiography were recorded. Before nondependent lung re-expansion,HFPV patients presented higher PaO2 than CPAP group (p = 0.020). The amount of secretions was higher in chronic obstructive pulmonary disease patients treated with HFPV than in those who received CPAP (199 and 64 mL, respectively, p = 0.028). HFPV increased by 5.28 times the chance of sputum production by chronic obstructive pulmonary disease patients (chi(2) = 46.66, p < 0.0001; odds ratio = 5.28). A patient treated with HFPV had a 3.14-fold larger chance of being discharged earlier than a CPAP-treated subject (likelihood ratio = 11.5, p = 0.0007). CONCLUSIONS: Under the present settings, HFPV improved oxygenation in one-lung ventilation during pulmonary resection. Postoperatively, it decreased the length of stay and increased the removal of secretions in comparison with CPAP.

Dead space in acute respiratory distress syndrome.

Dead space is the portion of each tidal volume that does not take part in gas exchange and represents a good global index of the efficiency of the lung function. Dead space is not routinely measured in critical care practice, because the difficulties in in interpreting capnograms and the different methods of calculations. Different dead space indices can provide useful information in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) patients, where changes in microvasculature are the main determinants for the increase in dead space and consequently a worsening of the outcome. Lung recruitment is a dynamic process that combines recruitment manoeuvres (RMs) with positive end expiratory pressure (PEEP) and low Vt to recruit collapsed alveoli. Dead space guided recruitment allows avoiding regional overdistension or reduction in cardiac output in critical care patients with ALI or ARDS. Different patterns of ventilation affect also CO2 elimination; in fact, end-inspiratory pause prolongation reduces dead space, increasing respiratory system compliance; plateau pressure and consequently driving pressure increase accordingly. Dead space measurement is a reliable method that provides important clinical and prognostic information. Different capnographic indices can be useful to evaluate therapeutic interventions or setting mechanical ventilation.

Uncommon Occurrences of Air Embolism: Description of Cases and Review of the Literature.

Many different risk factors have been associated with the occurrence of gas embolism making this potentially lethal complication easily avoidable. However, this condition can occur in circumstances not commonly reported. Three different and extremely uncommon cases of gas embolism are presented and discussed: the first was caused by the voluntary ingestion of hydrogen peroxide, the second occurred during a retrograde cholangiopancreatography, and the last followed the intrapleural injection of Urokinase. Whereas in the first patient the gas embolism was associated with only relatively mild digestive symptoms, in the remaining two it caused a massive cerebral ischemia and an extended myocardial infarction, respectively. Despite a hyperbaric oxygen therapy performed timely in each case, only the first patient survived. The classical risk factors associated with gas embolism like indwelling central venous catheters, diving accidents, etc. are rather well known and thus somewhat preventable; however, a number of less common and difficult-to-recognize causes can determine this condition, making the correct diagnosis elusive and delaying the hyperbaric oxygen therapy, whose window of opportunity is rather narrow. Thus, a gas embolism should be suspected in the presence of not otherwise explainable sudden neurologic and/or cardiovascular symptoms also in circumstances not typically considered at risk.

High-flow nasal interface improves oxygenation in patients undergoing bronchoscopy.

During bronchoscopy hypoxemia is commonly found and oxygen supply can be delivered by interfaces fed with high gas flows. Recently, the high-flow nasal cannula (HFNC) has been introduced for oxygen therapy in adults, but they have not been used so far during bronchoscopy in adults. Forty-five patients were randomly assigned to 3 groups receiving oxygen: 40 L/min through a Venturi mask (V40, N = 15), nasal cannula (N40, N = 15), and 60 L/min through a nasal cannula (N60, N = 15) during bronchoscopy. Gas exchange and circulatory variables were sampled before (FiO(2) = 0.21), at the end of bronchoscopy (FiO(2) = 0.5), and thereafter (V40, FiO(2) = 0.35). In 8 healthy volunteers oxygen was randomly delivered according to V40, N40, and N60 settings, and airway pressure was measured. At the end of bronchoscopy, N60 presented higher PaO(2), PaO(2)/FiO(2), and SpO(2) than V40 and N40 that did not differ between them. In the volunteers (N60) median airway pressure amounted to 3.6 cmH(2)O. Under a flow rate of 40 L/min both the Venturi mask and HFNC behaved similarly, but nasal cannula associated with a 60 L/min flow produced the better results, thus indicating its use in mild respiratory dysfunctions.

Respiratory mechanics in COPD patients who failed non-invasive ventilation: role of intrinsic PEEP.

Non-invasive positive pressure ventilation (NPPV) is the first choice to treat exacerbations in COPD patients. NPPV can fail owing to different causes related to gas exchange impairment (RF group) or intolerance (INT group). To assess if the respiratory mechanical properties and the ratio between the dynamic and static intrinsic positive end-expiratory pressure (PEEP(i),dyn/PEEP(i),stat), reflecting lung mechanical inequalities, were different between groups, 29 COPD patients who failed NPPV (15 RF and 14 INT) were studied, early after the application of invasive ventilation. Blood gas analysis, clinical status, and mechanical properties were measured. pH was higher in INT patients before intubation (p<0.001). PEEP(i),dyn/PEEP(i),stat was found higher in INT group with (p=0.021) and without PEEP (ZEEP, p<0.01). PEEP(i),dyn/PEEP(i),stat was exponentially associated with the duration of NPPV in INT group (p=0.011). INT and RF patients had similar impairment of respiratory system resistance and elastance.

Relationship between the timing of administration of IgM and IgA enriched immunoglobulins in patients with severe sepsis and septic shock and the outcome: a retrospective analysis.

PURPOSE: Because the use of IgM and IgA enriched polyclonal intravenous immunoglobulins (eIg) is a standard of care in critically ill patients admitted to our intensive care unit (ICU) with the diagnosis of severe sepsis or septic shock, we investigated if the delay from the onset of severe sepsis and septic shock and their administration could influence the outcome. MATERIALS AND METHODS: The medical records of all patients with severe sepsis or septic shock admitted to our ICU from July 2004 through October 2009 and treated with eIg (Pentaglobin®; Biotest, Dreieich, Germany) were retrospectively examined. RESULTS: A total of 129 adult patients with severe sepsis or septic shock were considered eligible. Thirty-two percent of patients died during the ICU stay. Survivors were given eIg significantly earlier than nonsurvivors (23 vs 63 hours, P < .05). The delay in the administration of eIg and the Simplified Acute Physiology Score II were the only variables that entered stepwise a propensity score-adjusted logistic model. The delay in the administration of eIg was a significant predictor of the odds of dying during the ICU stay (odds ratio for 1 hour of delay, 1.007; P < .01; 99% confidence interval from 1.001 to 1.010) and proved to be independent from the Simplified Acute Physiology Score II and other variables. CONCLUSIONS: The efficacy of eIg, being maximal in early phases of severe sepsis and/or septic shock, is probably time dependent.

Gas distribution in a two-compartment model ventilated in high-frequency percussive and pressure-controlled modes.

PURPOSE: To demonstrate in a two-compartment heterogeneous mechanical model of the lung how different loads applied to one compartment, while the other is kept constant, would modify gas distribution between the two pathways under high-frequency percussive ventilation (HFPV). Additionally, these results were compared with those generated in the same model by pressure-controlled ventilation (PCV). METHODS: Analysis was based on a Siemens lung simulator, representing a fixed branch of the system with an elastance equal to 45 cmH(2)O/L and a resistance of 20 cmH(2)O/L/s, and a single-compartment lung simulator, representing a variable pathway of the model, presenting three elastic loads varying between 35 and 85 cmH(2)O/L and three resistive loads varying between 5 and 50 cmH(2)O/L/s. Each simulator represented one compartment of the model connected to a central airway that was ventilated with either a volumetric diffusive respirator (VDR-4; Percussionaire Corporation, Sandpoint, ID, USA) or a Siemens Servo 900c ventilator. Flow and pressures were measured in each branch of the model under nine conditions representing the combinations of three elastic and three resistive loads (variable branch) while the loads in the other pathway were kept constant. RESULTS: HFPV was able to avoid hyperinflation and reduce tidal volume in a bicompartmental heterogeneous lung model. Under HFPV, gas distribution between the two compartments was not constrained by their time constants. PCV yielded gas distribution as determined by the time constant of each compartment. CONCLUSIONS: HFPV accommodated volume distribution without overinflating compartments with low time constants, thus possibly presenting a potential protective behavior in mechanically heterogeneous lungs.

Gas distribution in a two-compartment model during volume or pressure ventilation: role of elastic elements.

The results of the studies on pulmonary gas distribution during constant-flow controlled-volume inflation (VCV) and inspiratory constant pressure inflation (PCV) in experimental studies are conflicting. In a mathematical model, with the characteristics of two lung compartments including tissue viscoelastic properties, pulmonary gas distribution was tested by simulating PCV and VCV at same inflation volumes. The compartmental distributions of the tidal volume were compared during CMV and PCV in different configurations obtained by changing the elastic and viscoelastic properties in each compartment, but maintaining the same total values of respiratory mechanics measured in patients. In all instances PCV resulted in a slightly higher air-trapping than in VCV mode. Heterogeneous elastic properties diverted most of the tidal volume towards the less compromised compartment. However, both ventilatory modes provided similar compartmental gas distribution, but during VCV compartmental peak pressures were higher in the sicker compartment respect to PCV. The use of PCV could grant a less remarkable pressure variability able to reduce the potential ventilator-associated lung injury. Moreover, the parameters measured during an end-inspiratory pause could not pinpoint unique characteristics for each configuration.