The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
Extrinsic positive end-expiratory pressure (PEEP) applied to the patient at the airway opening is used artificially to increase end-expiratory lung volume. Extrinsic PEEP is increased or decreased in small increments in ventilator-dependent patients because of its marked effects on cardiorespiratory status. Unintentional or unmeasured end-expiratory hyperinflation, called intrinsic or auto-PEEP, can...
The mechanisms generating intrinsic or auto-positive end-expiratory pressure (PEEP) during controlled mechanical ventilation in a relaxed patient also occur during spontaneous breathing or when the patient triggers the ventilator during an assisted mode [1, 2]. These include an increased time constant for passive exhalation of the respiratory system, a short expiratory time resulting from a relatively...
The main goal of mechanical ventilation is to help restore gas exchange and reduce the work of breathing (WOB) by assisting respiratory muscle activity. Knowing the determinants of WOB is essential for the effective use of mechanical ventilation and also to assess patient readiness for weaning. The active contraction of the respiratory muscles causes the thoracic compartment to expand, inducing pleural...
Most mechanical ventilators display tracings of airway pressure (Paw) volume (V) and flow (V·). In volume preset modes, Paw informs about the mechanical properties of the respiratory system and about the activity of respiratory muscles acting on the system. When monitoring ventilator waveforms, it is important to appropriately scale the tracing so that nuances in time profiles may be appreciated....
Background: The measurement of respiratory system resistance during mechanical ventilation is important to ascertain the causes of increase in airway pressure during volume-controlled ventilation, which may include airways resistance and decreased respiratory system compliance. Discussion: Separation of total resistance from compliance of the respiratory system can be assessed...
Wasted or ineffective efforts are inspiratory efforts that fail to trigger the ventilator [1]. Nearly 25% of mechanically ventilated patients exhibit ineffective efforts which are even more frequent in COPD patients [2]. The pathophysiology of wasted efforts can be illustratively presented using the Campbell diagram.
Dead space is that part of the tidal volume that does not participate in gas exchange. Although the concept of pulmonary dead space was introduced more than a hundred years ago, current knowledge and technical advances have only recently lead to the adoption of dead space measurement as a potentially useful bedside clinical tool.
This brief review centers on the multiple inert gas elimination technique (MIGET). This technique, developed in the 1970s, measures the pulmonary exchange of a set of six different inert gases dissolved together in saline (or dextrose) and infused intravenously. It then uses those measurements to compute the distribution of ventilation/perfusion ratios that best explains the exchange of the six gases...
Given a stable cardiac output (CO) and inspiratory oxygen concentration (FIO2), any gas exchange abnormality leading to hypoxia or hypercapnia may be explained solely on the basis of an altered distribution of the ventilation and perfusion (V·A/Q·) regardless of the underlying disease [1].
This research was supported by the Red Respira-ISCIII-RTIC-03/11 and the Comissionat per a Universitats i Recerca de la Generalitat de Catalunya (2001 SGR00386). R.R.-R. holds a career scientist award from the Generalitat de Catalunya.
Continuous monitoring of arterial blood saturation using pulse oximetry has become the standard of care in the ICU. With the proliferation of pulse oximeters, episodic hypoxemia is detected much more commonly than previously suspected. By alerting the clinician to the presence of hypoxemia, pulse oximeters can lead to a more rapid treatment of serious hypoxemia and possibly avoid serious complication...
Background: Changes in body temperature have important impact on measurements of blood gases. In blood gas analyzers the samples are always kept constant at a temperature of exactly 37°C during the measurements, and therefore results are not correct if body temperature differs from 37°C. Objective: Lack of knowledge of the effects of body temperature on results of blood gas monitoring may...
The primary physiological task of the cardiovascular system is to deliver enough oxygen (O2) to meet the metabolic demands of the body. Shock and tissue hypoxia occur when the cardiorespiratory system is unable to cover metabolic demand adequately. Sustained tissue hypoxia is one of the most important cofactors in the pathophysiology of organ dysfunction [1]. Therefore determining the adequacy of...
The acute respiratory distress syndrome (ARDS) is characterized by severe hypoxemia, a cornerstone element in its definition. Numerous indices have been used to describe this hypoxemia, such as the arterial to alveolar O2 difference, the intrapulmonary shunt fraction, the oxygen index and the PaO2/FIO2 ratio. Of these different indices the PaO2/FIO2 ratio has been adopted for routine use because of...
In the hypoxemic patient under mechanical ventilation, changes in cardiac output may influence the level of arterial oxygenation, with several and sometimes opposite effects. The purpose of this Physiological Note is to give the reader the physiological background to understand these effects, which are often highly relevant for the bedside management of patients with acute lung injury.
Almost 20 years ago, Adriaan Versprille published an editorial in this journal to explain why, in his opinion, the calculation of pulmonary vascular resistance (PVR) is meaningless [1]. The uncertainties of PVR were underscored a year later by McGregor and Sniderman in the American Journal of Cardiology [2]. Obviously, both papers failed to convince. A Medline search from 1985 to the end of 2002 reveals...
The bedside estimation of left ventricular (LV) performance of critically ill patients is an important aspect of the diagnosis and management of these patients. Ever since the introduction of the balloon flotation pulmonary catheterization, health care providers have used measurements of pulmonary artery occlusion pressure (Ppao) to estimate both pulmonary venous pressure and LV preload. However,...
Background: Ppao values are routinely used to assess pulmonary vascular status and LV performance. Regrettably, under many common clinically relevant conditions, even when Ppao values are measured accurately, Ppao values at baseline and in response to therapy often reflect an inaccurate measure of cardiovascular status. Results and conclusions: Thus, caution should be used...
Pulmonary capillary pressure is a primary determinant of fluid flux across the pulmonary capillary wall [1]. Increasing pulmonary capillary pressure increases fluid flux out of the capillaries into the interstitium and in the extreme induces pulmonary edema. Pulmonary capillary pressure is itself determined by the mean pulmonary artery pressure, pulmonary vascular resistance, and total blood flow...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.