Answer
A PEEP level of less than 10 cm water rarely causes hemodynamic problems in the absence of intravascular volume depletion. The cardiodepressant effects of PEEP are often minimized with judicious intravascular volume support or cardiac inotropic support. Although peak pressure is related to the development of barotrauma, arterial hypotension is related to the mean airway pressure that may decrease venous return to the heart or decrease right ventricular function.
A PEEP level greater than 10 cm water is generally an accepted indication to monitor cardiac output by using a Swan-Ganz catheter. However, if the patient remains clinically stable with an adequate urine output, then hemodynamic monitoring may not be necessary. When PEEP greater than 10 cm water is necessary, the left atrial filling pressure can be estimated after an adjustment is made for the effect of the PEEP on the transducer of the catheter. The equation commonly used is LAP = PCWP - (PEEP/3), where LAP is left atrial pressure and PCWP is pulmonary capillary wedge pressure.
Withdrawal of PEEP from a patient should not be attempted in most clinical situations until the patient has achieved satisfactory oxygenation with an FIO2 of 40% or less. Formal weaning from PEEP is then undertaken by reducing the PEEP in 3- to 5-cm of water decrements while the hemoglobin-oxygen saturations are monitored. An unacceptable decrease in the hemoglobin-oxygen saturation should prompt the clinician to immediately reinstitute the last PEEP level that provided good hemoglobin-oxygen saturation.
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An example of the Drinker and Shaw negative-pressure ventilator (iron lung).
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The pressure, volume, and flow to time waveforms for assist-control ventilation.
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The pressure, volume, and flow to time waveforms for controlled ventilation.
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The components of mechanical ventilation inflation pressures. Paw is airway pressure, PIP is peak airway pressure, Pplat is plateau pressure.
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The effects of decreased respiratory system compliance (A) and increased airway resistance (B) on the pressure-time waveform.
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Determination of the lower inflection point to estimate the best (optimal) positive end-expiratory pressure (PEEP) from the pressure-volume hysteresis curve.
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The effect of positive end-expiratory pressure (PEEP) on the pressure-time inflation curve.
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The pressure, volume, and flow to time waveforms for synchronized intermittent mandatory ventilation (SIMV).
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The pressure, volume, and flow to time waveforms for synchronized intermittent mandatory ventilation (SIMV) with pressure-support ventilation.
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The flow to time waveform demonstrating auto–positive end-expiratory pressure (auto-PEEP).
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The pressure, volume, and flow to time waveforms for pressure-regulated volume-controlled ventilation.
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The pressure, volume, and flow to time waveforms for proportional-assist ventilation.
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The pressure, volume, and flow to time waveforms for airway pressure–release ventilation.
