abg - DM SEMINAR DM SEMINAR APRIL 02, 2004 APRIL 02, 2004...

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Unformatted text preview: DM SEMINAR DM SEMINAR APRIL 02, 2004 APRIL 02, 2004 ARTERIAL BLOOD GAS: INTERPRETATION AND CLINICAL IMPLICATIONS NAVNEET SINGH DEPARTMENT OF PULMONARY AND CRITICAL CARE MEDICINE PGIMER CHANDIGARH Conditions Invalidating or Conditions Invalidating or Modifying ABG Results Modifying ABG Results DELAYED ANALYSIS Consumptiom of O2 & Production of CO2 continues after blood drawn into syringe Iced Sample maintains values for 1-2 hours Uniced sample quickly becomes invalid PaCO2 ↑ 3-10 mmHg/hour PaO2 ↓ at a rate related to initial value & dependant on Hb Sat Parameter 37 C (Change every 10 min) 4 C (Change every 10 min) ↓ pH 0.01 0.001 ↑ PCO2 1 mm Hg 0.1 mm Hg ↓ PO2 0.1 vol % 0.01 vol % EFFECT OF TEMP ON RATE OF CHANGE IN ABG VALUES EXCESSIVE HEPARIN Dilutional effect on results ↓ HCO 3- & PaCO2 Syringe be emptied of heparin after flushing Risk of alteration of results ↑ with: 1 . ↑ size of syringe/needle 2 . ↓ vol of sample 25% lower values if 1ml sample taken in 10 ml syringe (0.25 ml heparin in needle) Syringes must be > 50% full with blood sample HYPERVENTILATION OR BREATH HOLDING May lead to erroneous lab results AIR BUBBLES 1. PO2 ∼ 150 mmHg & PCO2 ∼ 0 mm Hg in air bubble(R.A.) 2. Mixing with sample lead to ↑ PaO2 & ↓ PaCO2 3. Mixing/Agitation ↑ S.A. for diffusion more erroneous results 4. Discard sample if excessive air bubbles 5. Seal with cork/cap imm after taking sample FEVER OR HYPOTHERMIA 1. Most ABG analyzers report data at N body temp 2. If severe hyper/hypothermia, values of pH & PCO2 at 37 C can be significantly diff from pt’s actual values 3. Changes in PO2 values with temp predictable 4. No significant change of HCO3-, O2 Sat, O2 capacity/content, CO2 content values with temp 5. No consensus regarding reporting of ABG values esp pH & PCO2 after doing ‘temp correction’ 6. ? Interpret values measured at 37 C: Most clinicians do not remember normal values of pH & PCO2 at temp other than 37C In pts with hypo/hyperthermia, body temp usually changes with time (per se/effect of rewarming/cooling strategies) – hence if all calculations done at 37 C easier to compare Values other than pH & PCO2 do not change with temp Hansen JE, Clinics in Chest Med 10(2), 1989 227-237 7. ? Use Nomogram to convert values at 37C to pt’s temp 8. Some analysers calculate values at both 37C and pt’s temp automatically if entered 9. Pt’s temp should be mentioned while sending sample & lab should mention whether values being given in report at 37 C/pts actual temp WBC COUNT 0.1 ml of O2 consumed/dL of blood in 10 min in pts with N TLC Marked increase in pts with very high TLC/plt counts – hence imm chilling/analysis essential TYPE OF SYRINGE 1. pH & PCO2 values unaffected 2. PO2 values drop more rapidly in plastic syringes (ONLY if PO2 > 400 mm Hg) 3. Other adv of glass syringes: Min friction of barrel with syringe wall Usually no need to ‘pull back’ barrel – less chance of air bubbles entering syringe...
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This note was uploaded on 12/03/2011 for the course MEDICINE 350 taught by Professor Dr.aslam during the Winter '07 term at Medical College.

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abg - DM SEMINAR DM SEMINAR APRIL 02, 2004 APRIL 02, 2004...

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