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

Positive end expiratory pressure titration guided by plateau pressure in chronic obstructive pulmonary disease patients

BACKGROUND

PEEP decreases intrinsic PEEP (PEEPi) in COPD patients. However, the best PEEP for someone with COPD is unclear.

METHODS

Ten COPD patients who received invasive mechanical ventilation were enrolled. Before PEEP titration, subjects were sedated and received mandatory ventilation. PEEP increased from 0 to 15 cmH₂ O. At each PEEP, peak pressure (Ppeak), plateau pressure (Pplat), PEEPi, and other variables were recorded. Increment of Pplat (ΔPplat) and PEEPi were plotted against PEEP applied. The best PEEP was recorded at the cross of the two curves.

RESULTS

From PEEP = 0 cmH₂ O to best PEEP, Ppeak (37.4 ± 5.1 vs. 38.4 ± 4.9 cmH₂ O) and Pplat (18.7 ± 3.3 vs. 20.4 ± 3.2 cmH₂ O) increased slightly, resistance (28.1 ± 5.6 vs. 26.6 ± 5.0 cmH₂ O/l/s) decreased slightly, and PEEPi (7.9 ± 2.3 vs. 1.5 ± 0.4 cmH₂ O) decreased sharply. Compliance, heart rate, blood pressure, and SpO₂ did not change. However, from best PEEP to PEEP = 15 cmH₂ O, Ppeak (38.4 ± 4.9 vs. 44.9 ± 4.3 cmH₂ O) and Pplat (20.4 ± 3.2 vs. 27.6 ± 3.3 cmH₂ O) increased sharply, and systolic blood pressure (116 ± 13 vs. 99 ± 14 mmHg) and compliance (46.1 ± 18.1 vs. 37.7 ± 10.6 mL/cmH₂ O) decreased sharply. At the same time, PEEPi (1.5 ± 0.4 vs. 0.7 ± 0.8 cmH₂ O) decreased only slightly, and resistance, heart rate, and SpO₂ did not change.

CONCLUSIONS

It is feasible to use Pplat as a simple way of determining the best PEEP in COPD patients.

Comparison of respiratory mechanics measurements in the volume cycled ventilation (VCV) and pressure controlled ventilation (PCV)

Abstract Introduction Monitoring respiratory mechanics may provide important information for the intensivist, assisting in the early detection of pulmonary function changes of patients hospitalized in ICU. Objective: To compare measurements of respiratory mechanics in VCV and PCV modes, and correlate them with age and oxygenation index. Materials and methods: Cross-sectional study conducted in the adult ICU of the Hospital Nossa Senhora da Conceição, in Tubarão - SC. A hundred and twenty individuals were selected between March and August 2013. The respiratory mechanics measurements were evaluated using compliance and resistance static measures of the respiratory system in PCV and VCV modes between the 1st and 5th day of hospitalization. Simultaneously, the oxygenation index PaO2/FiO2 was collected. Results: The obtained results were: compliance (VCV) = 40.9 ± 12.8 mL/cmH2O, compliance (PCV) = 35.0 ± 10.0 mL/cmH2O, resistance (VCV) = 13.2 ± 4.9 cmH2O/L/s, resistance (PCV) = 27.3 ± 16.2 cmH2O/L/s and PaO2/FiO2 = 236.0 ± 97.6 mmHg. There was statistical difference (p < 0.001) between the compliance and resistance measures in VCV and PCV modes. The correlations between the oxygenation index and compliance in VCV and PCV modes and resistance in VCV and PCV modes were, respectively, r = 0.381 (p < 0.001), r = 0.398 (p < 0.001), r = -0.188 (p = 0.040), r = -0.343 (p < 0.001). Conclusion: Despite the differences between the respiratory mechanics measurements the monitoring using VCV and PCV modes seems to show complementary aspects.

Monitoring of total positive end-expiratory pressure during mechanical ventilation by artificial neural networks

Ventilation treatment of acute lung injury (ALI) requires the application of positive airway pressure at the end of expiration (PEEP_app) to avoid lung collapse. However, the total pressure exerted on the alveolar walls (PEEP_tot) is the sum of PEEP_app and intrinsic PEEP (PEEP_i), a hidden component. To measure PEEP_tot, ventilation must be discontinued with an end-expiratory hold maneuver (EEHM). We hypothesized that artificial neural networks (ANN) could estimate the PEEP_tot from flow and pressure tracings during ongoing mechanical ventilation. Ten pigs were mechanically ventilated, and the time constant of their respiratory system (τ_RS) was measured. We shortened their expiratory time (TE) according to multiples of τ_RS, obtaining different respiratory patterns (R_pat). Pressure (P_AW) and flow (V'_AW) at the airway opening during ongoing mechanical ventilation were simultaneously recorded, with and without the addition of external resistance. The last breath of each R_pat included an EEHM, which was used to compute the reference PEEP_tot. The entire protocol was repeated after the induction of ALI with i.v. injection of oleic acid, and 382 tracings were obtained. The ANN had to extract the PEEP_tot, from the tracings without an EEHM. ANN agreement with reference PEEP_tot was assessed with the Bland-Altman method. Bland Altman analysis of estimation error by ANN showed -0.40 ± 2.84 (expressed as bias ± precision) and ±5.58 as limits of agreement (data expressed as cmH₂O). The ANNs estimated the PEEP_tot well at different levels of PEEP_app under dynamic conditions, opening up new possibilities in monitoring PEEP_i in critically ill patients who require ventilator treatment.

Ventilator settings and monitoring parameter targets for initiation of continuous mandatory ventilation: a questionnaire study

PURPOSE

To inform development of educational tools, we sought to identify initial ventilator settings and monitoring targets for 3 scenarios.

METHOD

A survey was e-mailed to Canadian Society of Respiratory Therapists members with 2 reminders in March/April 2011.

RESULTS

Total evaluable surveys were 363. More participants selected pressure as opposed to volume ventilation for acute respiratory distress syndrome (ARDS; 77%) than for chronic obstructive pulmonary disease (COPD; 50%) and postoperative ventilation (32%; P < .001). Mean tidal volume was lower for ARDS than for COPD and postoperative ventilation (5.7, 6.9, and 7.2 mL/kg, respectively; P < .001). Maximum acceptable plateau pressures were highest for ARDS (30 cm H2O vs 29 cm H2O [COPD] and 27 cm H2O [postoperative], P < .001). Initial positive expiratory end pressure (12 cm H2O vs 7 cm H2O vs 5 cm H2O) and fraction of inspired oxygen (Fio2; 1.0 vs 0.5 vs 0.3) were also higher for ARDS (both P < .001); however, only 8% selected a positive expiratory end pressure/Fio2 combination as recommended by ARDSnet. Values of oxygen saturation as measured by pulse oximetry of 97% (ARDS) and 94% (COPD and postoperative) were considered appropriate for Fio2 reduction. The lowest pH was 7.28 vs 7.23 vs 7.26; the highest pH was 7.46 vs 7.44 vs 7.46 (P < .001). Partial pressure of carbon dioxide (arterial) of 51 mm Hg (postoperative) to 65 mm Hg (ARDS) was considered acceptable.

CONCLUSION

Lung protective ventilation was favored, yet distinct differences in ventilator settings were evident. Monitoring targets suggested relatively conservative practices for Fio2 reduction but an understanding of permissive hypercapnia.