Identifying and treating intrinsic PEEP in infants with severe bronchopulmonary dysplasia.

RATIONALE: Infants with severe bronchopulmonary dysplasia (sBPD) and airway obstruction may develop dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEPi ), which impairs patient/ventilator synchrony. OBJECTIVES: To determine if PEEPi is present in infants with sBPD during spontaneous breathing and if adjusting ventilator PEEP improves patient/ventilator synchrony and comfort. METHODS: Interventional study in infants with sBPD. PEEPi measured by esophageal pressure (Pes) and pneumotachometer, during pressure-supported breaths. PEEP i defined as the difference between Pes at start of the inspiratory effort minus Pes at onset of inspiratory flow. The set PEEP was adjusted to minimize PEEP i . "Best PEEP" was the setting with minimal wasted efforts (WE), an inspiratory effort seen on the Pes waveform without a corresponding ventilator breath. FiO 2 and SpO 2 measured pre- and post-PEEP adjustment. Sedation requirements evaluated 72 hours preprocedure and postprocedure. RESULTS: Twelve infants were assessed (gestational age, 24.9 ± 1.4 weeks; study age, 48.8 ± 1.5 weeks, postmenstrual age). Mean baseline ventilator PEEP was 16.4 cm H2 O (14-20 cm H 2 O). Eight infants required an increase, one, a reduction, and three, no change in the set PEEP. For the eight infants requiring an increase in set PEEP, there was an 18.9% reduction in WE and a reduction in FiO 2 (0.084 ± 0.058) requirements in the subsequent 24 hours. Conditional sedation was reduced in five infants postprocedure. No adverse events occurred during testing. CONCLUSION: PEEPi is measurable in infants with sBPD with concurrent esophageal manometry and flow-time tracings without the need for pharmacological paralysis. In those with PEEP i , increasing ventilator PEEP to offset PEEP i improves synchrony.

Ventilator Strategies for Chronic Obstructive Pulmonary Disease and Acute Respiratory Distress Syndrome.

The management of the ventilator in patients with chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS) has a dramatic effect on the overall outcome. The incidence of COPD is increasing as the US population grows older. The most effective means to deal with pulmonary complications is to avoid them, but both COPD and ARDS have evidence-based interventions that have been shown to improve outcomes. Pulmonary complications affect up to 40% of patients, and their occurrence is associated with an increased duration of hospital stay, and an increased mortality.

Optimization of Mechanical Ventilation in a 31-Year-Old Morbidly Obese Man With Refractory Hypoxemia.

Morbidly obese, critically ill patients are prone to develop hypoxemic respiratory failure and ventilator dependency. The best method for recruiting the lungs of these patients and keeping alveoli open without causing injury remains unclear. We present the case of a 31-year-old patient with severe refractory hypoxemia reversed by lung recruitment maneuvers and subsequent application of positive end-expiratory pressure (PEEP) at a level determined by a decremental PEEP trial. The patient was extubated at a high PEEP level of 22 cm H2O followed by noninvasive ventilatory support after extubation. This case suggests that a recruitment maneuver followed by PEEP titration is necessary in obese patients for optimizing mechanical ventilation. Extubation to noninvasive ventilatory support with the identified optimal PEEP may decrease an inappropriate increased work of breathing and the risk of reintubation.

An open-source software for automatic calculation of respiratory parameters based on esophageal pressure.

PURPOSE: We have developed a software that automatically calculates respiratory effort indices, including intrinsic end expiratory pressure (PEEPi) and esophageal pressure-time product (PTPeso). MATERIALS AND METHODS: The software first identifies respiratory periods. Clean signals are averaged to provide a reference mean cycle from which respiratory parameters are extracted. The onset of the inspiratory effort is detected automatically by looking backward from the onset of inspiratory flow to the first point where the esophageal pressure derivative is equal to zero (inflection point). PEEPi is derived from this point. Twenty-three recordings from 16 patients were analyzed with the algorithm and compared with experts' manual analysis of signals: 15 recordings were performed during spontaneous breathing, 1 during non-invasive mechanical ventilation, and 7 under both conditions. RESULTS: For all values, the coefficients of determinations (r(2)) exceeded 0.94 (p<0.001). The bias (mean difference) between PEEPi calculated by hand and automatically was -0.26±0.52cmH2O during spontaneous breathing and the precisions (standard deviations of the differences) was 0.52cmH2O with limits of agreement of 0.78 and -1.30cmH2O. The mean difference between PTPeso calculated by hand and automatically was -0.38±1.42cmH2Os/cycle with limits of agreement of 2.46 and -3.22cmH2Os/cycle. CONCLUSIONS: Our program provides a reliable method for the automatic calculation of PEEPi and respiratory effort indices, which may facilitate the use of these variables in clinical practice. The software is open source and can be improved with the development and validation of new respiratory parameters.

Trials of bilevel positive airway pressure - spontaneous in patients with complex sleep apnoea.

INTRODUCTION: Patients with complex sleep apnoea (CompSAS) have obstructive sleep apnoea and experience persistent central apnoeas when exposed to positive airway pressure. Elevated loop gain is one of the postulated mechanisms of CompSAS. We speculated that bilevel positive airway pressure - spontaneous (BPAP-S), by producing relative hyperventilation, may more readily produce CompSAS activity than continuous positive airway pressure (CPAP). If found to do so, a trial of BPAP-S might be a simple way of identifying patients with elevated loop gain who are at risk for CompSAS. MATERIALS AND METHODS: Thirty-nine patients with complex sleep apnoea were included in the study. Segments of NREM sleep on CPAP and BPAP-S matched for body position and expiratory airway pressure (comparison pressure) were retrospectively analysed. Correlations between clinical and demographic variables and polysomnographic response to CPAP and BPAP-S were sought. RESULTS: There was no difference in any of the polysomnographic indices on CPAP and BPAP-S. In 19 patients the use of CPAP was associated with lower AHI at the comparison pressure; in 20 patients the opposite was true. No clinical variables correlated to the differential response to CPAP vs. BPAP-S. CONCLUSIONS: BPAP-S was not more effective than CPAP in stimulating complex sleep apnoea activity.

Auto-PEEP in respiratory failure.

Intrinsic positive end-expiratory pressure (auto-PEEP) is a common occurrence in patients with acute respiratory failure requiring mechanical ventilation. Auto-PEEP can cause severe respiratory and hemodynamic compromise. The presence of auto-PEEP should be suspected when airflow at end-exhalation is not zero. In patients receiving controlled mechanical ventilation, auto-PEEP can be estimated measuring the rise in airway pressure during an end-expiratory occlusion maneuver. In patients who trigger the ventilator or who are not connected to a ventilator, auto-PEEP can be estimated by simultaneous recordings of airflow and airway and esophageal pressure, respectively. The best technique to accurately measure auto-PEEP in patients who actively recruit their expiratory muscle remains controversial. Strategies that may reduce auto-PEEP include reduction of minute ventilation, use of small tidal volumes and prolongation of the time available for exhalation. In patients in whom auto-PEEP is caused by expiratory flow limitation, the application of low-levels of external PEEP can reduce dyspnea, reduce work of breathing, improve patient-ventilator interaction and cardiac function, all without worsening hyperinflation. Neurally adjusted ventilatory assist, a novel strategy of ventilatory assist, may improve patient-ventilator interaction in patients with auto-PEEP.

Aumento de presión en la vía aérea durante la ventilación mecánica: más allá del broncoespasmo / No disponible

No disponible

Ineffective triggering predicts increased duration of mechanical ventilation.

OBJECTIVES: To determine whether high rates of ineffective triggering within the first 24 hrs of mechanical ventilation (MV) are associated with longer MV duration and shorter ventilator-free survival (VFS). DESIGN: Prospective cohort study. SETTING: Medical intensive care unit (ICU) at an academic medical center. PATIENTS: Sixty patients requiring invasive MV. INTERVENTIONS: None. MEASUREMENTS: Patients had pressure-time and flow-time waveforms recorded for 10 mins within the first 24 hrs of MV initiation. Ineffective triggering index (ITI) was calculated by dividing the number of ineffectively triggered breaths by the total number of breaths (triggered and ineffectively triggered). A priori, patients were classified into ITI >or=10% or ITI <10%. Patient demographics, MV reason, codiagnosis of chronic obstructive pulmonary disease (COPD), sedation levels, and ventilator parameters were recorded. MEASUREMENTS AND MAIN RESULTS: Sixteen of 60 patients had ITI >or=10%. The two groups had similar characteristics, including COPD frequency and ventilation parameters, except that patients with ITI >or=10% were more likely to have pressured triggered breaths (56% vs. 16%, p = .003) and had a higher intrinsic respiratory rate (22 breaths/min vs. 18, p = .03), but the set ventilator rate was the same in both groups (9 breaths/min vs. 9, p = .78). Multivariable analyses adjusting for pressure triggering also demonstrated that ITI >or=10% was an independent predictor of longer MV duration (10 days vs. 4, p = .0004) and shorter VFS (14 days vs. 21, p = .03). Patients with ITI >or=10% had a longer ICU length of stay (8 days vs. 4, p = .01) and hospital length of stay (21 days vs. 8, p = .03). Mortality was the same in the two groups, but patients with ITI >or=10% were less likely to be discharged home (44% vs. 73%, p = .04). CONCLUSIONS: Ineffective triggering is a common problem early in the course of MV and is associated with increased morbidity, including longer MV duration, shorter VFS, longer length of stay, and lower likelihood of home discharge.

The evaluation of a pulmonary display to detect adverse respiratory events using high resolution human simulator.

OBJECTIVE: Authors developed a picture-graphics display for pulmonary function to present typical respiratory data used in perioperative and intensive care environments. The display utilizes color, shape and emergent alerting to highlight abnormal pulmonary physiology. The display serves as an adjunct to traditional operating room displays and monitors. DESIGN: To evaluate the prototype, nineteen clinician volunteers each managed four adverse respiratory events and one normal event using a high-resolution patient simulator which included the new displays (intervention subjects) and traditional displays (control subjects). Between-group comparisons included (i) time to diagnosis and treatment for each adverse respiratory event; (ii) the number of unnecessary treatments during the normal scenario; and (iii) self-reported workload estimates while managing study events. MEASUREMENTS: Two expert anesthesiologists reviewed video-taped transcriptions of the volunteers to determine time to treat and time to diagnosis. Time values were then compared between groups using a Mann-Whitney-U Test. Estimated workload for both groups was assessed using the NASA-TLX and compared between groups using an ANOVA. P-values < 0.05 were considered significant. RESULTS: Clinician volunteers detected and treated obstructed endotracheal tubes and intrinsic PEEP problems faster with graphical rather than conventional displays (p < 0.05). During the normal scenario simulation, 3 clinicians using the graphical display, and 5 clinicians using the conventional display gave unnecessary treatments. Clinician-volunteers reported significantly lower subjective workloads using the graphical display for the obstructed endotracheal tube scenario (p < 0.001) and the intrinsic PEEP scenario (p < 0.03). CONCLUSION: Authors conclude that the graphical pulmonary display may serve as a useful adjunct to traditional displays in identifying adverse respiratory events.

Auto-PEEP: how to detect and how to prevent--a review.

Auto-positive end expiratory pressure (auto-PEEP) is a physiologic event that is common to mechanically ventilated patients. Auto-PEEP is commonly found in acute severe asthma, chronic obstructive pulmonary disease, or patients receiving inverse ratio ventilation. Factors predisposing to auto-PEEP include a reduction in expiratory time by increasing the respiratory rate, tidal volume or inspiratory time. Auto-PEEP predisposes the patient to increased work of breathing, barotrauma, hemodynamic instability and difficulty in triggering the ventilator. Failure to recognize the hemodynamic consequences of auto-PEEP may lead to inappropriate fluid restriction or unnecessary vasopressor therapy. Auto-PEEP can potentially interfere with weaning from mechanical ventilation. Many methods have been described to measure the Auto-PEEP. Although not apparent during normal ventilator operation, the auto-PEEP effect can be detected and quantified by a simple bedside maneuver: expiratory port occlusion at the end of the set exhalation period. The measurement of static and dynamic auto-PEEP differs and depends upon the heterogeneity of the airways. The work of breathing can be decreased by providing external PEEP to 75-80% of auto-PEEP in patients who are spontaneously breathing during mechanical ventilation but there is no evidence such external PEEP would be useful during controlled mechanical ventilation when there is no patient inspiratory effort. Ventilator setting should aim for a prolonged expiratory time by reducing the respiratory rate rather than increasing inspiratory flow. Routine monitoring for auto-PEEP in patients receiving controlled ventilation is recommended.

Determinants of dynamic hyperinflation in a bench model.

BACKGROUND: Previous in vivo data suggest that high airway resistance (R(aw)) promotes dynamic hyperinflation, especially when coupled to high minute ventilation (V(E)). However, no studies have systematically examined the relative effects of various mechanical parameters on dynamic hyperinflation. METHODS: Intrinsic positive end-expiratory pressure (PEEPi) was measured with a ventilator-lung model, over a range and various permutations of R(aw), V(E), respiratory system compliance (C(RS)), and duty cycles/flow regimes. RESULTS: Substantial dynamic hyperinflation (PEEPi > 5 cm H(2)O occurred at various V(E), even when R(aw) was low (4 cm H(2)O/L/s) or just above normal (18 cm H(2)O/L/s). A V(E) > or = 15 L/min was associated with increasing PEEPi in this model, across a broad range of mechanical permutations. PEEPi was significantly higher in all models during descending ramp flow than during constant flow, at equivalent peak flows (wherein duty cycle during descending ramp flow was twice that of constant flow). PEEPi was equivalent when duty cycles (and all other mechanical parameters) were equal. PEEPi was significantly greater, irrespective of duty cycle, R(aw), and C(RS), when delivered with lower tidal volume (0.6 L vs 1.0 L). The change in peak airway pressure associated with development of dynamic hyperinflation was consistently greater than the observed PEEPi. Higher V(E), resistance, compliance, and duty cycles were all independently associated with dynamic hyperinflation. CONCLUSIONS: In this bench model, dynamic hyperinflation occurred with high V(E), even at low R(aw). Since moderate R(aw) and V(E) frequently occur in vivo, even without obstructive lung disease, occult dynamic hyperinflation is likely to occur commonly. PEEPi was greater with high frequency and small tidal volume (0.6 L) than with equal V(E) of lower frequency and larger tidal volume (1.0 L).

[Hemodynamic and ventilatory complications of mechanical ventilation with high intrinsic positive end-expiratory pressure]. / Hemodynamische en ventilatoire complicaties van beademing met hoge intrinsieke positieve eindexpiratoire druk.

In three mechanically ventilated patients ventilatory and circulatory complications resulted from high levels of intrinsic positive end-expiratory pressure (PEEPi): progressive pulmonary hyperinflation due to impairment of the expiration. PEEPi was initially not considered as the cause of shock and low tidal volumes and/or high inflation pressures. In a 74-year-old man the circulation deteriorated further when hand bagging was started in an attempt to improve his ventilatory condition; after reduction of the respiration rate, he recovered well. In a 40-year-old woman with relapsing polychondritis sedation helped to reduce the respiratory rate so as to restore sufficient expiratory time. A 59-year-old woman developed acute exacerbation of severe chronic obstructive pulmonary disease, and went into shock during interhospital ambulance transport; she was stabilized after recognition of PEEPi and adjustment of the setting of the ventilator. Detection of PEEPi (e.g. by the finding of a deep inflation level on physical examination) is more important than exact measurement of PEEPi. If PEEPi is detected, the ventilator should be set at PEEP at 80-90% of PEEPi, low frequency (e.g. 8/min) and a long expiratory time, and high inspiratory flow.

Comparison of four methods for measuring elevation of FRC in mechanically ventilated infants.

The aim of the study was to compare measurements of the elevation of functional residual capacity (FRC) above the relaxation volume obtained in 34 mechanically ventilated infants (median weight 2.6 kg, range 1.2-9) from four different methods: (1) direct measurement of the complete exhalation volume after brief disconnection from the ventilator, (2) calculated measurement from total positive end-expiratory pressure (PEEP) measured by end-expiratory occlusion of the breathing circuit, (3) extrapolated evaluation from the mathematical model of Brody, (4) extrapolated evaluation from the passive expiration method. We considered the direct measurement (1) as the "gold standard". Measurements obtained by total PEEP (2) and by the Brody's mathematical model (3) provided similar results than the direct measurement. Conversely, graphical extrapolation from the passive expiration method (4) underestimated the elevation of FRC. In conclusion, we suggest using the mathematical extrapolation from the Brody's model to evaluate the elevation of FRC in mechanically ventilated infants: this method is non-invasive, does not require disruption of gas flow, can be easily performed with all the neonatal ventilators, and allows continuous breath-by-breath measurements.

Correcting static intrinsic positive end-expiratory pressure for expiratory muscle contraction. Validation of a new method.

We have recently shown (Eur. Respir. J. 1997;10:522-529) that in spontaneously breathing and actively expiring patients, static intrinsic positive end-expiratory pressure (PEEPi,st) can be corrected for expiratory muscle contraction by subtracting the average expiratory rise in gastric pressure (Pga,exp rise), calculated from three breaths just prior to an airway occlusion, from the end-expiratory airway pressure (Paw) of the first occluded inspiratory effort (PEEPi,st avg). However, since in some patients there is substantial variability in the intensity of expiratory muscle activity and hence in Pga,exp rise, this method may be inaccurate because the Pga,exp rise of breaths preceding airway occlusion may differ from that of the first postocclusion breath. In the present study, we introduced a new method consisting of synchronous subtraction of Pga,exp rise from Paw, both occurring during airway occlusion (PEEPi,st sub). PEEPi,st sub and PEEPi,st avg were each compared with the reference PEEPi,st (PEEPi,st ref), which was obtained during muscular paralysis and simulation of the spontaneous breathing pattern by the ventilator. We found that, in 25 critically ill patients, PEEPi,st sub (mean +/- SD, 5.3 +/- 2.6 cm H(2)O) was nearly identical to PEEPi,st ref (5.4 +/- 2.4 cm H(2)O). Their mean difference was -0.06 cm H(2)O with limits of agreement -0.96 to 0.84 cm H(2)O, indicating a strong agreement between these methods. In contrast, mean difference of PEEPi,st avg and PEEPi,st ref was 0.73 cm H(2)O with limits of agreement -3.97 to 5.43 cm H(2)O, indicating lack of agreement. Coefficient of variation of Pga,exp rise was 14.3 +/- 7.2% (range, 5.2 to 28.3%). There was a good correlation between the coefficient of variation of Pga,exp rise and the difference between PEEPi,st avg and PEEPi,st ref (r = 0.909; p < 0.001). We conclude that PEEPi,st can be accurately measured in spontaneously breathing patients by synchronous subtraction of Pga,exp rise from Paw during airway occlusion.

Static intrinsic PEEP in COPD patients during spontaneous breathing.

Intrinsic positive end-expiratory pressure (PEEPi) is routinely determined under static conditions by occluding the airway at end-expiration (PEEPi,st). This procedure may be difficult in patients with chronic obstructive pulmonary disease (COPD) during spontaneous breathing, as both expiratory muscle activity and increased respiratory frequency often occur. To overcome these problems, we tested the hypothesis that the difference between maximum airway opening (MIP) and maximum esophageal (Ppl max) pressures, obtained with a Mueller maneuver from the end-expiratory lung volume (EELV), can accurately measure PEEPi,st. Using this method, we found that, in eight ventilator-dependent tracheostomized COPD patients (age 71+/-7 yr), PEEPi,st averaged 13.0+/-2.9 cm H2O. That measurement was validated by comparison with a reference static PEEPi (PEEPi,st-Ref) taken at the same EELV adopted by patients during spontaneous breathing, and measured on the passive quasi-static pressure-volume (P/V) curve of the respiratory system, obtained during mechanical ventilation. PEEPi,st-Ref averaged 13.1+/-3.0 cm H2O, i.e., a value essentially equal to PEEPi,st measured by means of our technique. We conclude that PEEPi,st can be accurately assessed in spontaneous breathing COPD patients by the difference between MIP and Ppl max during the Mueller maneuver.