Resp Care
-
The aim of this article is to identify and interpret the data provided by modern ventilators that provide the greatest clinical help in evaluating respiratory mechanics during mechanical ventilation. In intensive care, respiratory mechanics can be assessed in dynamic conditions (no flow-interruption) or static conditions (occlusion techniques) to record compliance and resistance and to monitor pressure, flow, and volume. ⋯ Pressure-volume loops and flow-volume loops provide useful information on the dynamic trends of the respiratory system compliance and resistance, respectively. Modern ventilators provide complete monitoring of respiratory system mechanics, which is our guideline for optimizing ventilatory support and avoiding complications associated with mechanical ventilation.
-
Severe airflow obstruction is a common cause of acute respiratory failure. Dynamic hyperinflation affects tidal ventilation, increases airways resistance, and causes intrinsic positive end-expiratory pressure (auto-PEEP). Most patients with asthma and chronic obstructive pulmonary disease have dynamic hyperinflation and auto-PEEP during mechanical ventilation, which can cause hemodynamic compromise and barotrauma. ⋯ The ventilatory pattern should be directed toward minimizing dynamic hyperinflation and auto-PEEP by using small tidal volume and preserving expiratory time. With a spontaneously breathing patient, to reduce the work of breathing and improve patient-ventilator interaction, it is crucial to set an adequate inspiratory flow, inspiratory time, trigger sensitivity, and ventilator-applied PEEP. Ventilator graphics are invaluable for monitoring and treatment decisions at the bedside.
-
Review
Monitoring respiratory mechanics during mechanical ventilation: where do the signals come from?
Graphical patient data have become essential to the understanding and management of ventilator-dependent patients. These electronically generated data often reveal clues to subtle complications that, if corrected, could lead to improved patient-ventilator harmony. The apparent precision of the waveforms and the 3- or 4-place display of numeric data imply high accuracy. ⋯ The abundance of viewable information pertinent to the management of the ventilated patient can be traced to the availability of the many types of transducers combined with microprocessor electronics. The process of capturing a variable of interest (sensing and signal transduction), converting it to a digitized electronic signal (analog-to-digital-conversion), operating on that signal (such as for control of the breathing algorithm and checking for violation of alarm thresholds), and finally converting it back to an analog signal that appears on a monitor generally receives scant appreciation. The process, however, lies at the core of data management in modern ICU ventilators.
-
The measurement of esophageal and gastric pressures with balloon-tipped catheters has been used with great success over the past half century to delineate the physiology of the mechanical respiratory system. Pleural pressure and abdominal pressure values estimated from esophageal and gastric pressure measurements allow analysis of lung and chest wall compliance, as well as work of breathing, respiratory muscle function, and the presence of diaphragm paralysis. ⋯ In this article I review the historical background, physiology, placement techniques, and potential clinical applications of esophageal and gastric pressure measurements. In addition, I will briefly review the measurement of bladder pressure, which is a related topic.
-
The quasi-static pressure-volume (P-V) curve of the respiratory system describes the mechanical behavior of the lungs and chest wall during inflation and deflation. To eliminate resistive and convective acceleration effects, the measurement of volume and pressure must be performed during short periods of apnea or during very slow flow. ⋯ The P-V curve has been studied in many disease states, but it has been applied most extensively to patients with acute respiratory distress syndrome, in hopes that it might allow clinicians to customize ventilator settings according to a patient's individual respiratory mechanics and thus protect the patient from ventilator-induced lung injury. However, lack of standardization of the procedure used to acquire P-V curves, difficulties in measuring absolute lung volume, lack of knowledge regarding how to use the information, and a paucity of data showing a benefit in morbidity and mortality with the use of P-V curves have tempered early enthusiasm regarding the clinical usefulness of the quasi-static P-V curve.