Constant Positive End-expiratory Pressure Research Articles

The effect of mode, inspiratory time, and positive end-expiratory pressure on partial liquid ventilation.

Partial liquid ventilation (PLV) has been shown to be an effective means of improving oxygenation in the injured lung. However, little is known about how approach to ventilation during PLV affects gas exchange and pulmonary mechanics. We hypothesized that gas exchange and pulmonary mechanics would be best with positive end-expiratory pressure (PEEP) set above the lower inflection point (LIP) of the pressure-volume (P-V) curve regardless of mode of ventilation or inspiratory to expiratory time (I:E) ratio and that the efficiency of ventilation would be greatest with volume-controlled ventilation (VCV) compared with pressure-controlled ventilation (PCV) and with long inspiratory time as compared with short inspiratory time. Lung injury was induced in 14 sheep by lavage, 10 of which were studied. Sheep were then assigned to high-PEEP (Group H, n = 5) and low-PEEP (Group L, n = 5) groups. In Group H applied PEEP was set at the LIP and in Group L applied PEEP was set at 5 cm H2O after the lung was filled with perflubron (PFB). We randomly compared VCV and PCV with I:E ratios of 1:2, 1:1, and 2:1. Peak inspiratory pressure and VT were adjusted to maintain a constant end-inspiratory plateau pressure (Pplat) of about 25 cm H2O in both groups and a constant total PEEP of about 5 cm H2O in Group L and about 12 cm H2O in Group H. There were no differences in oxygenation among modes in Group H. In Group L VCV 2:1 and all of the PCV modes in Group L had a lower PaO2 than VCV 1:1 (p < 0.05). PaCO2 and VD/VT were significantly different (p < 0.05) among modes. VD/VT was highest during PCV 1:2 with PEEP of 5 cm H2O (p < 0.05). Quasi-static compliance in Group H was higher than in Group L (p < 0.05). We conclude that during low PEEP gas exchange deteriorated in VCV with long inspiratory time and in PCV. Oxygenation was enhanced during VCV 1:1 when compared with VCV at longer I:E ratios or PCV at any I:E ratio. With PEEP set at the LIP, adequate gas exchange and improved lung mechanics could be obtained in all modes assessed.

Nasal continuous positive airway pressure in the treatment of obstructive sleep apnea

Nasal continuous positive airway pressure (CPAP) effectively treats obstructive sleep apnea by providing a pneumatic splint in the supraglottic airway. This treatment involves administration of a constant positive end-expiratory pressure (PEEP) within the range of 2.5 to 17.5 cm H 2 O. The optimal PEEP not only eliminates apneas and hypopneas, but also consolidates sleep. Establishing the optimal PEEP requires Polysomnographic monitoring of the patient during REM and NREM states as well as all sleep positions. The most common adverse effects are nasal dryness, nasal congestion, rhinorrhea, and sneezing. Room air humidification reduces nasal irritation and dryness; some models of CPAP equipment are adaptable to allow placement of a humidifier in the system. Long-term compliance with CPAP was studied in a survey of 121 patients who underwent a CPAP trial. After 6 months, 74.4% were compliant; after 18 months 66.6% reported compliance. Patients tended toward greater compliance when they received regular follow-up care by a physician with significant experience with this treatment modality.

Tidal Volume Reduction in ARDS: Effect on Cardiac Output and Arterial Oxygenation

During continuous positive pressure ventilation (CPPV), mean airway pressure and lung volume will be influenced both by the tidal volume (VT) employed and the amount of positive end-expiratory pressure (PEEP). The effect of varying levels of CPPV on PaO2 and cardiac output (Q) has been previously assessed by adjusting the level of PEEP at constant VT. This study examined the influence of a 200-ml reduction in VT, at a constant PEEP of 15 cm H2O, on the PaO2 and Q of 21 patients with adult respiratory distress syndrome (ARDS). The relationship between change in Q and change in total respiratory system compliance (Cst) after VT reduction was also examined. VT reduction from 14.1 +/- 0.8 ml/kg to 11.2 +/- 0.9 ml/kg yielded an increase in Q (+ 15 +/- 12 percent, p less than 0.01) without a significant change in PaO2 (-6.3 +/- 15.0 mm Hg, p = 0.08). Cst increased with VT reduction (+ 3.1 +/- 1.8 ml/cm H2O). There was only a modest correlation (r = +0.42, p = 0.06) between delta Q percent and delta Cst following VT reduction. VT reduction at high level PEEP may yield a significant improvement in Q and net O2 delivery, but the degree of hemodynamic improvement is variable and is not reliably predicted noninvasively by measurement of Cst.

The effects of tidal-volume change with positive end-expiratory pressure in pulmonary edema.

The effects of variation in tidal volume were studied in 14 dogs with pulmonary edema during mechanical ventilation with a constant positive end-expiratory pressure (PEEP) of 10 cm H2O. Tidal volumes (VT) of 5 ml/kg with PEEP improved PEEP over that seen with a VT of 15 ml/kg without PEEP. Oxygenation improved with PEEP as VT was increased stepwise from 5 to 25 ml/kg. The greatest improvement in oxygenation and ventilation with PEEP occurred when VT was increased from 5 to 10 ml/kg. Thereafter, as VT was increased, improvement in oxygenation was small and was accompanied by a gradual decline in cardiac output. A tidal volume of 10 ml/kg and a positive end-expiratory pressure of 10 cm H2O produced the most effective gas exchange with the least impairment of cardiac output.