MONITORING DURING MECHANICAL VENTILATION
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GAS EXCHANGE DURING MECHANICAL VENTILATION
The detrimental effects of hypoxemia have been recognized for centuries and dramatically summarized by Haldane who wrote, “anoxemia not only stops the machine but wrecks the machinery.” The adverse effect of hypoxemia on longevity was shown in long-term oxygen therapy trials, which showed that survival in patients who continuously had a Pa o2 below 55 mm Hg was decreased approximately 60% compared with patients who received oxygen therapy for most of the day. With the proliferation of pulse
Airway Occlusion Pressure
In routine critical care, respiratory center function rarely is measured at the bedside, although recent technologic developments have made it feasible. Measuring airway pressure 0.1 second after initiating an inspiratory effort against an occluded airway (P0.1) provides a measure of respiratory drive.113 Several investigators have examined the usefulness of P0.1 measurements in predicting a patient's ability to resume spontaneous ventilation following a period of mechanical ventilation. Three
Static Compliance
In a relaxed patient, effective static compliance of the total respiratory system (Crs,st) can be calculated as the volume delivered by the ventilator divided by the distending transthoracic pressure. Conditions of zero gas flow to permit measurement of Crs,st can be achieved by selecting the “inspiratory-hold” option on the ventilator or by occluding the expiratory port long enough to allow the airway pressure to reach a constant value (Fig. 9).13 The resulting plateau pressure represents the
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2016, Clinics in Chest MedicineCitation Excerpt :When this Pes or Paw is integrated over time it is the PTP and when integrated over volume it is the WOB for the patient and ventilator respectively. In mechanically ventilated patients, when PTP and WOB calculations using only Paw measurements (ventilator loads) are done during both a controlled and an assisted breath with similar flows and volumes, the difference in PTP or WOB between the two breath types reflects the patient loads during the assisted breaths.72,75 Importantly, the PTP and WOB both include the elastance and resistive loads in the equation of motion but, unlike WOB, PTP also includes the isometric load imposed by the assist triggering process.76–79
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2008, Emergency Medicine Clinics of North AmericaCitation Excerpt :Patients may have arterial oxygen saturations below 80% despite a normal reading on the pulse oximeter. This delay in response time occurs more often with finger probes [11]. Perhaps the greatest limitation to the use of pulse oximetry in the critically ill patient is that it provides no measure of ventilation or acid base status [4].
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Address reprint requests to Amal Jubran, MD, Division of Pulmonary and Critical Care Medicine, Veterans Administration Hospital, Route 111N, Hines, IL 60141
This article is supported by a grant from the Veterans Administration Merit Review.
All material in this article is in the public domain with the exception of any borrowed tables and figures.