# Small Ani. Med- Clinical Manifestation of Respiratory Disease 5

wilsbach's version from 2015-12-05 03:12

## Calculations-- know A-a and BLOOD GAS

Question Answer
easy way to remember how to calc blood gas
what is the A-a gradient formula??? EXPLAINPAO2 – PaO2.....ok so we're talking room air. PAO2 is 150 minus PaCO2(given value) divided by 0.8 (constant value also- this is "R").....Then of course you take this and subtract the PaO2...another given value.
**what is NORMAL A-a gradient?Normal < 15 mmHg on room air....if >15, you can say they have abnormal pulmonary dysfunction (impairment of O2 exchange)
Do this equation: Room air. normal dog. PaO2 of 95mmHg, PaCO2 40mmHg....calculate the A-a gradient. is it normal?So, it is PAO2 minus PaO2..... PAO2 is 150-PaCO2/0.8 so 150-40/0.8... (dont forget PEMDAS!) = 100. So PAO2 is 100, minus the PaO2 of 95= 5. which is less than 15 so we are normal. So A-a (exchange between alveoli and arteries) is normal so VQ gradient is normal.
Do this equation: Room air. Dyspneic dog after anesthesia. PaO2= 72 mmHg, PaCO2= 56 mmHg. Calculate the A-a gradient.ok so equation is PAO2-PaO2. PAO2 is 150-PaCO2/0.8. So 150-56/0.8= 80. Then it's PAO2-PaO2 so 80-72= 8. Eight is still less than 15, which is in normal range, so the dog has adequate exchange and is NOT HYPOXIC.
BLOOD GAS: NORMALS: pH (7.351-7.463), PCO2 (31-43), HCO3- (18-26). RESULTS of VBG: pH-7.011, PCO2 -25, HCO3 - 12, PO2 -53.6....what do you think this is?metabolic acidosis with appropriate compensation
BLOOD GAS: NORMALS: pH (7.351-7.463), PCO2 (31-43), HCO3- (18-26). RESULTS of VBG: pH 7.21 pCO2 53 mmHg HCO3- 27.5 mmol/L ...what do you think this is?Acute respiratory acidosis with appropriate metabolic compensation(there is at least a 1.5 mmol/L increase in HCO3- for every 10mmHg increase in PCO2)
BLOOD GAS: NORMALS: pH 7.35-­‐7.45, PaCO2 35-­‐45, HCO3 22-­‐26. RESULTS: pH=7.42 pH=7.42, PaCO2=30mmHg. HCO3=19 what do you think it is?compensated respiratory alkalaemia ((pH normal bc compensated, know its alka bc the CO2 is down...think of CO2 as an acid)
BLOOD GAS AND A-a---CALC BOTH: NORMALS: pH 7.35-­‐7.45, PaCO2 35-­‐45, HCO3 22-­‐26. RESULTS: pH 7.48, pCO2 26.1, HCO3- 19.6, paO2 78.3A-a: PAO2-PaO2..... so 150-26.1/0.8= 117.4-78.3= 39.1 (TOO HIGH, >15!). Blood GAS: resp alkalosis
How to tell if a blood gas is compensated?You are gonna get a chart- first recog what the prob is. EX) NORMALS: pH (7.35 – 7.46). pCO2 (32-43). HCO3- (18-26). Your patient is pH 7.26, pCO2 28 mmHg, HCO3- 12 mmol/L. So you figured out it was Metabolic Acidosis. Then, there is a chart. They should (i hope ) be giving us the chart. Ok cool. So the chart is like a ratio. In this example, The HCO3- dec 6 down from the normal range. For every 1 is 0.7, so if there is 6, it's 6x0.7=4.2 so if it WAS compensated, the pCO2 would be dropped 4.2 from normal range to totally compensate. The pCO2 is 4 under the normal range-- not 4.2, so it is technically NOT compensated but it sure is close.