1,721,004 research outputs found
Respiratory acidosis: is the correction with bicarbonate worth?
No full textBicarbonate infusion is traditionally used to increase pH during metabolic acidosis, but it has been also suggested to increase the pH during permissive hypercapnia. in this paper we will discuss the physicochemical effect of adding (Na+ HCO3-), first in a closed system (venous blood) and then in an open system (the blood after the lung). According to Stewart model, in the closed system two independent variables are changed (CO2 and strong ion difference). As a first result changes in pH are negligible. If the CO2 is cleared by the lung and the PCO2 is maintained as before the infusion, the rise in pH is due to the SID increase caused by the (Na+) rise. The effect is independent on (HCO3-) infusion and equivalent to adding (Na+OH-) instead of (Na+HCO3-)
Gastric tonometry
No full textGastric tonometry was originally proposed to assess the splanchnic perfusion. Several technological improvements have been introduced over the years and, to date, the preferred way to estimate the splanchnic perfusion is to rely on the arterial-gastric PCO2 gap. In this brief review we will discuss the value of the gastric tonometry, its physiological background and the clinical results observed so far
Prone position in acute Respiratory Distress Syndrome : Rationale, Indications and Limits
No full textIn the prone position, CT-scan densities redistribute from dorsal to ventral as the dorsal region tends to re-expand while the ventral zone tends to collapse. Although gravitational influence is similar in both positions, dorsal recruitment usually prevails over ventral de-recruitment, due to the need for the lung and its confining chest wall to conform to the same volume. The final result of proning is that the overall lung inflation is more homogeneous from dorsal to ventral than in the supine position with more homogeneously distributed stress and strain. As the distribution of perfusion remains nearly constant in both postures, proning usually improves oxygenation. Animal experiments clearly show that prone positioning delays or prevents ventilation-induced lung injury, likely due in large part to more homogeneously distributed stress and strain. Over the last 15 years, five major trials have been conducted to compare prone and supine position in ARDS regarding survival advantage. The sequence of trials enrolled patients who were progressively more hypoxemic, exposure to prone position was extended from 8 to 17 hours/day, and lung protective ventilation was more rigorously applied. Single patient and meta-analyses drawing from the four major trials showed significant survival benefit in patients with PaO2/FiO2 lower than 100. The latest PROSEVA trial confirmed these benefits in a formal randomized study. The bulk of data indicates that in severe ARDS, carefully performed prone positioning offers an absolute survival advantage of 10-17%, making this intervention highly recommended in this specific population subset
Continuous positive airway pressure delivered with a "helmet" : effects on carbon dioxide rebreathing
No full textOBJECTIVE: The "helmet" has been used as a novel interface to deliver noninvasive ventilation without applying direct pressure on the face. However, due to its large volume, the helmet may predispose to CO2 rebreathing. We hypothesized that breathing with the helmet is similar to breathing in a semiclosed environment, and therefore the PCO2 inside the helmet is primarily a function of the subject's CO2 production and the flow of fresh gas through the helmet. DESIGN: Human volunteer study. SETTING: Laboratory in a university teaching hospital. SUBJECTS: Eight healthy volunteers. INTERVENTIONS: We delivered continuous positive airway pressure (CPAP) with the helmet under a variety of ventilatory conditions in a lung model and in volunteers. MEASUREMENTS AND MAIN RESULTS: Gas flow and CO2 concentration at the airway were measured continuously. End-tidal PCO2, CO2 production, and ventilatory variables were subsequently computed. We found that a) when CPAP was delivered with a ventilator, the inspired CO2 of the volunteers was high (12.4 +/- 3.2 torr [1.7 +/- 0.4 kPa]); b) when CPAP was delivered with a continuous high flow system, inspired CO2 of the volunteers was low (2.5 +/- 1.2 torr [0.3 +/- 0.2 kPa]); and c) the inspired CO2 calculated mathematically for a semiclosed system model of CO2 rebreathing was highly correlated with the values measured in a lung model (r = .97, slope = 0.92, intercept = -1.17, p < .001) and in the volunteers (r = .94, slope = 0.96, intercept = 0.90, p < .001). CONCLUSIONS: a) The helmet predisposes to CO2 rebreathing and should not be used to deliver CPAP with a ventilator; b) continuous high flow minimizes CO2 rebreathing during CPAP with the helmet; and c) minute ventilation and Pco2 should be monitored during CPAP with the helmet
Effects of a new rotational device on complication rate during prone ventilation in patients with acute respiratory distress syndrome : a retrospective analysis
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Sepsis: state of the art
No full textIn recent years, we have considerably widened our knowledge of the pathophysiology of sepsis and some procedures, aiming both to relieve symptoms and control the inflammation/coagulation reaction, have proven to be effective in increasing survival. This improves when mechanical ventilation is applied with low tidal volumes, fluid replacement and the use of cardioactive drugs are titrated on the oxygen saturation of hemoglobin in the central venous system and blood glucose does not exceed certain limits. It is also evident that inflammation and coagulation are closely related to each other. The inhibition of only one pathway, such as the inhibition of inflammation with high dosage steroids or the inhibition of coagulation with antithrombin, does not produce a survival improvement. The only molecule which has proven to be notably effective in reducing mortality is Activated Protein C interacting on coagulation/fibrinolysis, as well as on inflammation processes. Multinodal modulation of several interdependent processes may be the probable reason for the proven effectiveness of this treatment
Physiologic rationale for ventilator setting in acute lung injury/acute respiratory distress syndrome patients
No full textOBJECTIVES: To review the physiologic approach to setting mechanical ventilation in acute lung injury/acute respiratory distress syndrome.
DATA SOURCES: MEDLINE search from 1979 to the present.
DATA SELECTION: Personal selection of some articles we believe relevant for understanding acute lung injury/acute respiratory distress syndrome physiopathology and its physiologic management.
DATA SUMMARY: Knowing the underlying pathology is key to estimating the potential for recruitment. The potential for recruitment is rather low when the consolidation of pulmonary units exceeds collapse, as in diffuse pneumonia. In contrast, when pulmonary unit collapse exceeds consolidation, as in acute lung injury/acute respiratory distress syndrome from extrapulmonary origin, the potential for recruitment may be high. To exploit the potential for recruitment, a transpulmonary pressure greater than the opening pressure must be applied to the lung. To do so, chest wall elastance must be measured or estimated. To avoid collapse after recruitment, a positive end-expiratory pressure greater than the compressive forces operating on the lung and an alveolar ventilation sufficient to prevent absorption atelectasis must be provided. Indeed, avoidance of stretch (low airway plateau pressure) and prevention of cyclic collapse and reopening (adequate positive end-expiratory pressure and alveolar ventilation) are the physiologic cornerstones of mechanical ventilation in acute lung injury/acute respiratory distress syndrome. When considering all the randomized clinical trials reported so far, it is tempting to speculate that transpulmonary pressure and stresses, rather than tidal volume per se, are the key factors that may have an impact on mortality.
CONCLUSIONS: The majority of physiologic, experimental, and clinical trial data converge on one simple concept: treat the lung gently
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