Anesthesia Progress Blog - Part 6

Cardiorespiratory Effects of Pressure Controlled Inverse Ratio Ventilation in Severe Respiratory Failure: ResultsData Analysis
Derived cardiorespiratory variables, systemic vascular resistance, pulmonary vascular resistance, arterial and mixed venous oxygen content, oxygen delivery, oxygen consumption, and oxygen extraction ratio were calculated using standard and previously described formulae. Where appropriate, cardiorespiratory and hemodynamic variables were normalized, using the calculated body surface area for each patient. Mean ± standard error of the mean was calculated for each of the cardiorespiratory variables, both before and after institution of PC-IRV. Comparison between values before and after initiation of PC-IRV was performed by a paired Students f-test. Differences were considered to be significant for p<0.05. read Read the rest of this entry »

Nine patients (Table 1) with severe ARDS, as manifested by diffuse pulmonary infiltrates on chest roentgenograms, arterial hypoxemia with widened A-a gradients despite supplemental oxygen, pulmonary capillary wedge pressures (WP) less than 20 mm Hg, and decreased static and dynamic thoracic compliance were entered in the study. In each case, the patient was placed on PC-IRV at the request of the attending physician, who judged the patient to be failing conventional volume contrblled ventilation with conventional ratios (VC-CRV). In all cases, a flow-directed pulmonary artery (Swan-Ganz) catheter with a fiberoptic channel for continuous measurement of mixed venous oxygen saturation had been placed previously for hemodynamic and cardiorespiratory monitoring. The mixed venous oxygen saturation determination from the pulmonary artery catheter was calibrated and verified by using a mixed venous blood sample in which the oxygen saturation was measured by COoximetry. All patients had indwelling arterial catheters and pulse oximeters. All patients previously had been placed on a Servo-controlled ventilator, operating in the volume controlled ventilation mode. Prior to initiation of the PC-IRV trial, all patients were sedated with appropriate doses of benzodiazepines and paralyzed with vecuronium or atracurium by continuous intravenous infusion, after an initial bolus dose. More info Read the rest of this entry »

Cardiorespiratory Effects of Pressure Controlled Inverse Ratio Ventilation in Severe Respiratory FailurePressure controlled inverse ratio ventilation is a recently described-2 ventilatory modality, in which the conventional inspiratory to expiratory (I:E) ratio is reversed, with the inspiratory phase becoming two to four times as long as the expiratory period. The PC-IRV has been reported to achieve improved oxygenation at lower peak airway pressures. Other advantages include lower minute volume and decreased levels of positive end expiratory pressure. In PC-IRY pressure control is used to change the inspiratory flow pattern so that each breath is initiated before expiratory flow from the previous breath reaches zero. A physiologic result of this ventilatory pattern is maintenance of end-expiratory pressures. The prolonged inspiratory phase, coupled with positive end-expiratory pressure, usually results in decreased peak inspiratory and increased mean airway pressures in patients receiving PC-IRV. Read the rest of this entry »

Hemodynamic Disturbances and Va/Q Matching in Hypoxemic Cirrhotic Patients: ConclusionThese results are consistent with those of Daoud et al; however, two comments on Pv02, which was not measured in the previously cited study, should be made: (1) since a fall in Pv02 appears to contribute significantly to the HPV response magnitude, the hyperkinetic heart syndrome restoring normal Pv02 may have played a role in the impairment of the HPV mechanism even in the presence of hypoxemia; and (2) although many factors led to a raised cardiac output, the rise was exactly adjusted to maintain a normal Pv02. Read the rest of this entry »

Another possibility for the reduced Pa02 in cirrhotic patients with portal hypertension is the presence of anastomoses between the portal venous system and the low pressure pulmonary veins.- Unfortunately, this portopulmonary bypass could not be evaluated by the multiple inert gas method used in the present study. In addition, a significant difference between the measured Pa02 and the Pa02 predicted from the values of Va/Q distribution, Ve, and Q may stem from an anatomic shunt (bronchial, thebesian veins . . .), which is not assessed by the inert gas elimination technique, or a defect in diffusion. Read the rest of this entry »

Hemodynamic Disturbances and Va/Q Matching in Hypoxemic Cirrhotic Patients: Pulmonary microcirculationOur results raised the problem of the mechanism of the impairment in gas exchange. Since the inert gas solution was always infused into a vein of the superior vena caval system, only intrathoracic shunt (iey an intracardiac or intrapulmonary shunt) could be evaluated. An extrathoracic origin of these Va/Q alterations could not be estimated. An atrial right-to-left shunt, by reopening of the foramen ovale, was improbable due to the low pulmonary pressures. The measured percentage of shunt in these patients was thus attributed to perfusion of unventilated areas. Three possibilities could account for this abnormal true shunt. Read the rest of this entry »

A low Pa02 may result from an incomplete diffusion equilibrium, hypoventilation, or other alterations of Va/Q relationships, including intrapulmonary, extra-pulmonary, or postpulmonary shunt. The oxygen diffusion capacity has been found to be normal in patients with cirrhosis of the liver. Our patients also presented with hyperventilation leading to respiratory alkalosis, which is consistently observed in cirrhosis. The increased ventilation and the almost normal dead space effectively ruled out hypoventilation as a source of the Va/Q inequality. buy glucophage Read the rest of this entry »

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