Methods for determination of individual PEEP for intraoperative mechanical ventilation using a decremental PEEP trial

(1) Background: Individual PEEP settings (PEEP(IND)) may improve intraoperative oxygenation and optimize lung mechanics. However, there is uncertainty concerning the optimal procedure to determine PEEP(IND). In this secondary analysis of a randomized controlled clinical trial, we compared different methods for PEEP(IND) determination. (2) Methods: Offline analysis of decremental PEEP trials was performed and PEEP(IND) was retrospectively determined according to five different methods (EIT-based: RVD(I) method, Global Inhomogeneity Index [GI], distribution of tidal ventilation [EIT VT]; global dynamic and quasi-static compliance). (3) Results: In the 45 obese and non-obese patients included, PEEP(IND) using the RVD(I) method (PEEP(RVD)) was 16.3 ± 4.5 cm H(2)O. Determination of PEEP(IND) using the GI and EIT VT resulted in a mean difference of −2.4 cm H(2)O (95%CI: −1.2;−3.6 cm H(2)O, p = 0.01) and −2.3 cm H(2)O (95% CI: −0.9;3.7 cm H(2)O, p = 0.01) to PEEP(RVD), respectively. PEEP(IND) selection according to quasi-static compliance showed the highest agreement with PEEP(RVD) (p = 0.67), with deviations > 4 cm H(2)O in 3/42 patients. PEEP(RVD) and PEEP(IND) according to dynamic compliance also showed a high level of agreement, with deviations > 4 cm H(2)O in 5/42 patients (p = 0.57). (4) Conclusions: High agreement of PEEP(IND) determined by the RVD(I) method and compliance-based methods suggests that, for routine clinical practice, PEEP selection based on best quasi-static or dynamic compliance is favorable

Control of positive end-expiratory pressure (PEEP) for small animal ventilators

<p>Abstract</p> <p>Background</p> <p>The positive end-expiratory pressure (PEEP) for the mechanical ventilation of small animals is frequently obtained with water seals or by using ventilators developed for human use. An alternative mechanism is the use of an on-off expiratory valve closing at the moment when the alveolar pressure is equal to the target PEEP. In this paper, a novel PEEP controller (PEEP-new) and the PEEP system of a commercial small-animal ventilator, both based on switching an on-off valve, are evaluated.</p> <p>Methods</p> <p>The proposed PEEP controller is a discrete integrator monitoring the error between the target PEEP and the airways opening pressure prior to the onset of an inspiratory cycle. In vitro as well as in vivo experiments with rats were carried out and the PEEP accuracy, settling time and under/overshoot were considered as a measure of performance.</p> <p>Results</p> <p>The commercial PEEP controller did not pass the tests since it ignores the airways resistive pressure drop, resulting in a PEEP 5 cmH₂O greater than the target in most conditions. The PEEP-new presented steady-state errors smaller than 0.5 cmH₂O, with settling times below 10 s and under/overshoot smaller than 2 cmH₂O.</p> <p>Conclusion</p> <p>The PEEP-new presented acceptable performance, considering accuracy and temporal response. This novel PEEP generator may prove useful in many applications for small animal ventilators.</p

Effects of descending positive end-expiratory pressure on lung mechanics and aeration in healthy anaesthetized piglets

INTRODUCTION: Atelectasis and distal airway closure are common clinical entities of general anaesthesia. These two phenomena are expected to reduce the ventilation of dependent lung regions and represent major causes of arterial oxygenation impairment in anaesthetic conditions. The behaviour of the elastance of the respiratory system (E(rs)), as well as the lung aeration assessed by computed tomography (CT) scan, was evaluated during a descendent positive end-expiratory pressure (PEEP) titration. This work sought to evaluate the potential usefulness of E(rs )monitoring to set the PEEP in order to prevent tidal recruitment and hyperinflation of healthy lungs under general anaesthesia. METHODS: PEEP titration (from 16 to 0 cmH(2)O, tidal volume of 8 ml/kg) was performed, and at each PEEP, CT scans were obtained during end-expiratory and end-inspiratory pauses in six healthy, anaesthetized and paralyzed piglets. The distribution of lung aeration was determined and the tidal re-aeration was calculated as the difference between end-expiratory and end-inspiratory poorly aerated and normally aerated areas. Similarly, tidal hyperinflation was obtained as the difference between end-inspiratory and end-expiratory hyperinflated areas. E(rs )was estimated from the equation of motion of the respiratory system during all PEEP titration with the least-squares method. RESULTS: Hyperinflated areas decreased from PEEP 16 to 0 cmH(2)O (ranges decreased from 24–62% to 1–7% at end-expiratory pauses and from 44–73% to 4–17% at end-inspiratory pauses) whereas normally aerated areas increased (from 30–66% to 72–83% at end-expiratory pauses and from 19–48% to 73–77% at end-inspiratory pauses). From 16 to 8 cmH(2)O, E(rs )decreased with a corresponding reduction in tidal hyperinflation. A flat minimum of E(rs )was observed from 8 to 4 cmH(2)O. For PEEP below 4 cmH(2)O, E(rs )increased in association with a rise in tidal re-aeration and a flat maximum of the normally aerated areas. CONCLUSION: In healthy piglets under a descending PEEP protocol, the PEEP at minimum E(rs )presented a compromise between maximizing normally aerated areas and minimizing tidal re-aeration and hyperinflation. High levels of PEEP, greater than 8 cmH(2)O, reduced tidal re-aeration but increased hyperinflation with a concomitant decrease in normally aerated areas

Gas exchange during exercise in different evolutional stages of chronic Chagas' heart disease

OBJECTIVE: To compare gas exchange at rest and during exercise in patients with chronic Chagas' heart disease grouped according to the Los Andes clinical/hemodynamic classification. METHODS: We studied 15 healthy volunteers and 52 patients grouped according to the Los Andes clinical/hemodynamic classification as follows: 17 patients in group IA (normal electrocardiogram/echocardiogram), 9 patients in group IB (normal electrocardiogram and abnormal echocardiogram), 14 patients in group II (abnormal electrocardiogram/echocardiogram, without congestive heart failure), and 12 patients in group III (abnormal electrocardiogram/echocardiogram with congestive heart failure). The following variables were analyzed: oxygen consumption (V O2), carbon dioxide production (V CO2), gas exchange rate (R), inspiratory current volume (V IC), expiratory current volume (V EC), respiratory frequency, minute volume (V E), heart rate (HR), maximum load, O2 pulse, and ventilatory anaerobic threshold (AT). RESULTS: When compared with the healthy group, patients in groups II and III showed significant changes in the following variables: V O2peak, V CO2peak, V ICpeak, V ECpeak, E, HR, and maximum load. Group IA showed significantly better results for these same variables as compared with group III. CONCLUSION: The functional capacity of patients in the initial phase of chronic Chagas' heart disease is higher than that of patients in an advanced phase and shows a decrease that follows the loss in cardiac-hemodynamic performance