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49 Cards in this Set
- Front
- Back
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How can you calculate PaCO2?
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production of CO2/elimination of CO2=VCO2/(minute ventilation-dead space)
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What are the three determinants of PaCO2 and thus adequacy of ventilation?
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CO2 production, minute ventilation, and dead space
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What are causes of high CO2 production(VCO2)?
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fever, thyrotoxicosis, CNS trauma, overfeeding(TPN)
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What are causes of low CO2 production(VCO2)?
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hypothermia, hypothyroidism, drugs(barbs)
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What are causes of decreased minute ventilation(high PaCO2)?
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drugs, CNS disease, metabolic alkalosis, muscle weakness, sleep apnea, hypothyroidism, COPD
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What are causes of increased minute ventilation(low PaCO2)?
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anxiety, head trauma, metabolic acidosis, pregnancy, asthma, CHF
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What are causes of increased alveolar dead space(increased PaCO2)?
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pulmonary vascular disease, PE, vasculitis, COPD, ARDS, pulmonary fibrosis, shock
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How do you quantify physiologic dead space?
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(PaCO2-PeCO2)/PaCO2
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What is the relationship between alveolar ventilation and PaCO2 in a mechanically ventilated patient when displayed graphically?
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curvilinear(rectangular hyperbola)
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What is the most efficient way to increase oxygen content in the blood?
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increase hemoglobin
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What is the haldane effect?
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How oxygen determines the affinity of hemoglobin for CO2
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What are the normal values of mixed venous oxygen saturation and tension?
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mixed venous O2 sat: 65-75%
mixed venous O2 tension: 35-45mm Hg |
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What factors determine mixed venous oxygen tension(PvO2)?
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COAL: CO, Oxygen consumption, Amount of hemoglobin, Loading of hemoglobin(saturation of Hb)
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What is the equation for SvO2?
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SvO2=SaO2-(VO2/(COxHbx13))
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What is the normal V/Q ratio?
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0.8(nml ventilation is 4L/min, nml perfusion is 5L/min
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How do you calculate shunt fraction?
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(CcO2-CaO2)/(CcO2-CvO2); CcO2-content pulmonary capillary blood, CvO2 content mixed venous blood
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what is the normal shunt fraction?
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Qs/Qt=0.1
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What is the normal A-a gradient?
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10-20mmHg
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What is an approximate A-a gradient based on age?
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1/4 x the patients age
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Why do patient's under general anesthesia have a widened A-a gradient?
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increased V/Q mismatch due to altered lung and chest wall compliance
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What are causes of increased A-a gradient?
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V/Q mismatch, diffusion impairment, intracardiac(right to left) shunt
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How do FiO2 and hypoventilation affect the A-a gradient?
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normal A-a gradient
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How does hypercarbia affect PaO2 at a particular FiO2?
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limits PaO2 according to the alveolar gas equation
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What kind of syringes should be used for blood gas and why?
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glass syringes if possible because CO2 and O2 don't dissolve into the wall of the syringe and minimizes the risk of air bubbles in the syringe
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Why should heparin be used as the anticoagulant in ABG syringes?
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EDTA, citrates and oxalates alter the pH
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What variables are necessary for proper interpretation of blood gas?
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FiO2, temp, source, ventilator settings
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What electrode does the pH, PCO2, PO2 require for interpretation of ABG?
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pH-sanz electode
pCO2-Severinghaus electrode pO2-clark electrode |
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What factors influence blood gas values?
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age, sex, barometric pressure
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How do the kidneys and the lungs compensate for pH abnormalities?
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lungs: hyper or hypoventilation
kidneys: vary the reabsorption of filtered bicarb, add new bicarb to the plasma flowing through the kidneys |
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What is the henderson hasselbalch equation?
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pH=6.1+log(base/acid)=6.1+log(bicarb/(0.03xPaCO2))
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How is the pH affected by increases in arterial PaCO2?
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for every 10mm Hg increase in PaCO2 the pH decreases by 0.1
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What are some causes of respiratory acidosis?
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reduced minute ventilation, alveolar hypoventilation, increased alveolar dead space, increased CO2 production, increased mechanical dead space
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what are causes of nonanion gap acidosis?
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BADR: bicarb loss such as GI tract, acid loads, dilution of bicarb with saline, renal defects: poor bicarb reabsorption and acid secretion
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How can you determine if the reflex compensation response of the lungs in a metabolic acidosis is appropriate?
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the PCO2 should be equal to the last two digits of the pH
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What is the major problem with giving NaBicarb for lactic acidosis?
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bicarb reacts with hydrogen ions to form carbonic acid which then dissociates to CO2 and water which can worsen the acidosis
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If you are considering giving bicarb to a patient with a combined metabolic and respiratory acidosis what should you do first?
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treat the respiratory acidosis first
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How do you determine the dose of bicarb to give for metabolic acidosis?
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kg x deviation of bicarb from 24 x 0.2(0.4 if infant)
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Besides worsening a respiratory acidosis what other problems are associated with the use of bicarb?
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intraventricular hemorrhage, hypernatremia, hyperosmolarity, left shift of oxyhemoglobin dissociation curve due to rebound alkalosis
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How is the solubility of O2 and CO2 affected by temperature?
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at lower temperature the solubility of oxygen and CO2 is higher, there are less molecules in the gas phase and the partial pressure of both are decreased
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What is the alpha stat strategy of interpreting a blood gas?
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uncorrected arterial blood gas values, no attempt is made to correct for partial pressure of O2 and CO2 for changes in temperature
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What is the pH stat strategy for interpreting a blood gas?
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relies upon temperature corrected values and involves administering CO2 systemically to the patient to correct for lower partial CO2 pressure secondary to its increased solubility in solution
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what are criteria for intubation?
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RR>35/min, VC<15cc/kg, MIF<20cm H20, PaO2<70mmHg on FiO2 40%, A-a gradient >350 torr with FiO2 100%, PaCO2 > 55 unless chronically hypercarbic, Vd/Vt>0.6
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What are criteria for extubation?
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RR<30, stable BP and pulse, no inotropic support, patient afebrile, ABG good on 40% with PaO2>70 and PaCO2<55, MIF more negative than a negative 20cmH20, VC>15cc/kg
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What is the normal pH at birth in the umbilical vein, artery, and also what is this value at 60 min?
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umbilical vein: 7.35
umbilical artery: 7.28 60min: 7.30-7.35 |
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What is the normal pCO2 at birth in the umbilical vein, artery, also at 60 min and 24 hrs?
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umbilical vein: 40
umbilical artery: 50 60min: 30 24hrs: 30 |
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What is the normal pO2 at birth in the umbilical vein, artery, also at 60 min and 24 hrs?
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umbilical vein: 30
umbilical artery: 20 60min: 60 24hrs: 70 |
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How are amines affected by the solution becoming more acidic or basic?
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RNH3+<->RNH2 + H+; as system becomes more acidic they are more charged and less lipophilic; as the system becomes more basic they are less charged and more lipophilic
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How are carboxylic acids affect by acidic or basic solutions?
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R-COOH<-->RCOO- + H+; as the system becomes more acidic they are less charged and more lipophilic
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what is the pH and pKa of narcotics, local anesthetics, and thiopental?
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thiopental:pH 10.5, pKa 7.6
narcotics: pH 2.6-6.0, pKa 6.1 local anesthetics: pH 5-7, pKa 8-9 |
