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INTRODUCTION

Acute respiratory failure (ARF) accounts for a substantial portion of intensive care unit (ICU) admissions. Patients receiving invasive mechanical ventilation, as well as those receiving noninvasive respiratory support, such as high-flow nasal cannula and noninvasive positive-pressure ventilation, are at risk for hemodynamic and further respiratory decompensation. Therefore, close monitoring is necessary to identify early signs of instability and to allow for prompt intervention to prevent morbidity and mortality.

The primary goals of monitoring include ensuring adequate circulatory function, ensuring adequate ventilation and oxygenation, detecting the mechanisms of circulatory or respiratory decompensation when they occur, providing surveillance for common complications associated with noninvasive and invasive respiratory support, evaluating hemodynamic and respiratory responses to therapeutic interventions, and watching the trajectories of hemodynamic and respiratory disorders over time to gain insight into a patient’s prognosis.

Given the myriad forms of physiologic monitoring available to the modern clinician, many considerations should be taken into account when deciding which monitoring parameter and system to use. First, clinicians should select parameters and systems that have proven accuracy for the specific patient and clinical scenario. Second, clinicians should take into consideration the level of comfort and expertise that the entire clinical team has with the chosen monitoring system. Even the most precise and advanced monitoring system can lead clinical teams astray if they lack the expertise to appropriately interpret and act upon the data it provides. Third, and most important, physiologic monitoring data should not be evaluated in isolation, as reliable interpretation of data necessitates review of multiple data sources in a collective fashion at a single time point, as well as review of trends in data over time.

This chapter reviews the various parameters and methods available for hemodynamic and respiratory monitoring in patients with ARF.

HEMODYNAMIC MONITORING

In this section, we review noninvasive and invasive methods for hemodynamic monitoring in patients with ARF. Respiratory monitoring is detailed in a subsequent section of this chapter.

Hemodynamic assessment is a vital component of caring for critically ill patients. In addition to alerting clinicians to early signs of hemodynamic decompensation, it can provide important diagnostic information on the cause of the patient’s respiratory failure, including differentiation between cardiogenic and noncardiogenic pulmonary edema—a distinction that has clear therapeutic implications.

Hemodynamic monitoring is also vital in identifying untoward effects of positive-pressure ventilation on the cardiovascular system. Positive-pressure ventilation increases intrathoracic pressure, decreases venous return, and increases pulmonary vascular resistance, thereby potentially reducing right ventricular cardiac output and causing right ventricular dilatation. In certain patients, these effects can impair left ventricular filling if the impaired right ventricular function and cavity dilatation cause the interventricular septum to impinge on the left ventricle due to ventricular interdependence. Positive-pressure ventilation may lead to an overall summative reduction in cardiac output and, in rare circumstances, such as in patients with severe pre-existing right ...

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