Anesthesia General » Critical Care
Acute Lung Injury and ARDS
The European—American Consensus Conference in 1993 provided working definitions of Acute Lung Injury and ARDS to improve diagnostic consistency and interpretation of the results of clinical and epidemiological studies. 4 Both Acute Lung Injury and ARDS are characterized by the presence of hypoxaemia and pulmonary infiltrates without elevated left atrial pressure. The two conditions are distinguished by severity of pulmonary gas exchange impairment: A Pao2—Fio, ratio of 300 or less defines acute lung injury, and a ratio of 200 or less defines ARDS regardless of the amount of positive end-expiratory pressure (PEEP) needed to support oxygenation. The lung in Acute Lung Injury and ARDS is characterized by a major change in the elastic property of the alveoli. Surface tension plays an important role in determining the lung elasticity. The forces created … Read entire article »
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Most common causes of acute respiratory distress syndrome ARDS
Most common causes of acute respiratory distress syndrome ARDS are the clinical condition first described by Ashbaugh in 1967, to describe a group of patients with acute inflammation of the lungs resulting in severe hypoxia that is not amenable for correction by oxygen therapy. The reported incidence of ARDS is about 1.5—13.5% per 100,000 population with a mortality of 2760%.2 A variety of aetiological factors — pneumonia, aspiration, mechanical trauma, pulmonary embolism, and systemic sepsis — are the most common causes of acute respiratory distress syndrome ARDS Histologically, the most common causes of acute respiratory distress syndrome ARDS is characterized by diffuse damage to both the endothelial and epithelial surfaces of the alveoli that disrupts the lung’s barrier function, flooding alveolar spaces with fluid, inactivating surfactant, causing inflammation, and producing severe gas … Read entire article »
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Oxygen Partial Pressure
About one-fifth (20.9%) of air contains oxygen. In the inspired air, oxygen has partial pressure at 1/5 of the atmospheric pressure, i.e., 159 mm Hg. Oxygen partial pressure decreases to 100 mm Hg up to alveoli. Oxygen tension in venous blood is 40 mm Hg. The larger the O2 or CO2 tension difference between the gas phase in the alveolus and plasma in the capillary, the greater the diffusion. The mixed venous blood entering the pulmonary capillary has a Oxygen Partial Pressure of 40 mm Hg (5.3 kPa), and alveolar Oxygen Partial Pressure is approximately 100 mm Hg (13.3 kPa), thus creating a driving pressure of 60 mm Hg (8 kPa). When blood flows through the capillary, it takes up oxygen (and delivers CO2), but because oxygen pressure builds up in capillary blood, … Read entire article »
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Chronic oxygen deficiency
Chronic oxygen deficiency is defined as a prolonged lack of oxygen to the body as that occurs in living in high altitudes or by having severe chronic lung disease. Chronic oxygen deficiency have the following effects : There is decreased mental efficiency due the prolonged deficiency of oxygen Sleepiness, headache, lassitude and fatigubility are also common Euphoria is also sometimes seen. Increased ventilation or hyperventilation is occurs as a compensatory mechanism in Chronic oxygen deficiency to maintain the oxygen saturation and normal bodily functions. Persistent increased ventilation results in reduction in the alveolar ventilation and carbon dioxide tension. Respiratory alkalosis, is the end result of prolonged hyperventilation as that occurs in Chronic oxygen deficiency. Metabolic acidosis, is a compensatory phenomenon to maintain the acid base balance. Interference with oxygen transport mechanism also occurs in the long run, as a final attempt to proper oxygenation inspite of … Read entire article »
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4 Types of Hypoxia
There are 4 types of Hypoxia . The 4 types of Hypoxia are as follows: 1. Anoxic hypoxia or Diffusion hypoxia Anoxic hypoxia also called as diffusion hypoxia is essentially due to the deficency of oxygen being absorbed by the lungs. This is either due to a decrease in the inspired concentration of oxygen in the air which can result in suffocation. Another reason is due to a defect in the absorption of oxygen by the lungs due to some pathology or defect at the alveolo cappilary membrane of the lungs, where the real gas exchange takes place. 2. Anaemic hypoxia Another among the 4 Types of Hypoxia is the Anemic hypoxia. This is due to decreases oxygen binding capacity of the lungs, most commonly due to a decrease in the hemoglobin concentration. Hemoglobin is the main carrier of oxygen in the circulation throughout the body. Hence, … Read entire article »
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Hypoxia signs
Following are the Hypoxia signs Psychological Hypoxia signs – Higher centers are first impaired in hypoxia due to deficiency of oxygen to the brain tissue. Psychomotor and emotional judgement is poor in the absence of oxygen. The mechanisms mediating cerebral vasodilation during hypoxia are not fully understood but may include neurogenic effects initiated by peripheral and neuraxial chemoreceptors, as well as local humoral influences. At least part of the hyperemic response to hypoxia is mediated by NO of neuronal origin . Hypoxia-induced hyperpolarization of vascular smooth muscle by the opening of ATP-dependent K+ channels also leads to vasodilation. Recent studies have indicated that the rostral ventrolateral medulla (RVM) serves as an oxygen sensor within the brain. Stimulation of the RVM by hypoxia results in an increase in CBF (but not CMR), and lesions of the RVM suppress the … Read entire article »
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Preparation of carbon dioxide gas
The preparation of carbon dioxide gas is needed before it is actually stored in cylinders. The preparation of carbon dioxide gas is done though following steps : 1. From fermentation in the brewing of beer 2. By-product of manufacture of hydrogen in petroleum refining 3. Combustion of other fuels 4. By heating magnesium and calcium carbonate in the presence of their oxides. It is stored in gray cylinders at 50 bar. Solid CO2 is stored and transported in insulated containers. The filling ratio in cylinders is 0.75 in temperate climates and 0.67 in tropical regions. The liquid phase disappears when 83% of gas is exhausted. Oxygen-CO2 premixed cylinders are available, after the final preparation of carbon dioxide gas . These are black with white/white shoulder and filled to a pressure of 137 atmospheres. … Read entire article »
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Use of nitrogen
Nitrogen is present in the atmosphere and it constitutes 78.08% of total air. Moreover, the use of nitrogen is growing very rapidly these days. Use of nitrogen in medicine is helpful as it can be used as diluent of oxygen in order to avoid oxygen toxicity. It is stored in either compressed air or in liquid form. It has weak anaesthetic effect in hyperbaric conditions. It is not soluble but may be dissolved in blood and body tissues at increased pressure. On decomposition it can be released in the form of bubbles and results in decomposition sickness syndrome. It is treated with hyperbaric oxygenation. … Read entire article »
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Uses of carbon dioxide
There are numerous uses of carbon dioxide in modern anesthesia. It is used : • To increase depth of anaesthesia with volatile anaesthetic agents by stimulating respiration.- • To increase cerebral blood flow during carotid artery surgery. • To produce hyperventilation during blind nasal intubation. • To stimulate the respiration after artificial hyperventilation. • It may be of help in production of hypothermia due to vasodilatation. • To avoid hypocarbia during cardiopulmonary bypass. The other uses of carbon dioxide include the following : • In production of pneumoperitoneum during laparoscopy. • In cryoprobes. • In the production of Laser light for surgical procedures. … Read entire article »
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Effects of helium Inhalation
In the atmosphere it is present in the concentration of 0.003%. It is stored as high pressure gas in the cylinders. There are several effects of helium Inhalation . The medical diagnostic utility is secondary to its low density, insolubility and thermal conductivity. • Molecular weight is 4. • Specific gravity is 176. • It can diffuse through rubber. • It is non-inflammable and does not support combustion. • The cylinder is brown in colour and kept at pressure of 1987 psi. Premixed with oxygen can be administered via facemask. The other effects of helium Inhalation include: • It is helpful in pulmonary function testing as it is highly diffusible gas carried away by the pulmonary circulation, and so dilution in lungs can be measured. Helium breathing is helpful in large airway obstruction, apart from the other … Read entire article »
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