PROCEDURE FOR DRAWING MIXED VENOUS BLOOD GASES
FROM A PULMONARY ARTERY CATHETER


Equipment Required:

1- heparinized blood gas syringe (premixed, powdered heparin)
1- syringe or vacutainer with red top tube for discharge sample
unsterile gauze square
1-Chlorhexidine 2% and 70% alcohol swab

PPE-non-sterile gloves and assess need for face shield

1 bag of ice.
A  functional pulmonary artery line


 

Procedure
 Rationale
1. Mixed venous blood gases must be drawn from the pulmonary artery port of the right heart catheter or a right ventricular lumen (provided that the right ventricular port is situated in the right ventricle)

Proceed to withdraw a discard sample as per procedure for withdrawal blood samples from an indwelling line. 

 1.
  • Mixed venous gases should reflect  the oxygen remaining from all areas of the body.  The sample should be obtained after blood returning from the superior and inferior vena cava and coronary sinus have been mixed and "averaged".   Blood in the right ventricle or pulmonary artery is fully mixed.
  • If blood is drawn from the right atrium, it may reflect the oxygen from only the superior vena cava (normal oxygen saturation is 70%), inferior vena cava (normally 80%) or coronary sinus (normal 56%) instead of an averaged pool (normal 60-80%).
  • The mixed venous sample should also be drawn prior to reoxygenation in the pulmonary capillary.

    •  
2. Ensure that stopcock is turned to 45o between syringe changes. 2. Forty five degrees is off in all 3 directions.  This will prevent any heparinized saline from entering the tubing between the stopcock and the patient catheter between syringe changes.
3. Evaluate pulmonary artery tracing to verity that the catheter is not wedged. 3. Aspiration from a catheter that is wedged can cause arterialized blood to be drawn into the syringe, falsely elevating the result.
4.
  • Gently aspirate a 3 mL discard sample and discard.
  • Gently aspirate a 1-2 mL blood gas sample into a heparinized syringe.
 4. Vigorous aspiration can cause arterialized blood from the pulmonary capillary to be drawn into the syringe, falsely elevating the result.
5. If the mixed venous oxygen saturation is > 80%, repeat the sample with careful attention to technique.  If a second sample produces an elevated oxygen saturation, have resident withdraw the catheter and repeat.

If the oxygen saturation remains elevated, the patient should be evaluated for possible ventricular septal defect or patent ductus arteriosa.

 5.
  • If a catheter is advanced too far distally, it may not be in far enough to produce a wedge tracing, but may lead to aspiration of arterialized blood from the pulmonary capillary.
  • A ventricular septal defect or patent ductus arteriosa would cause left sided blood to enter the pulmonary artery, elevated the oxygen saturation.
  • 6.
    		•  Label the syringe and place on ice. Either take sample to the point of care testing machine (GEM) or send sample to the lab on ice in a biohazardous bag . 6. Ice stops the cells from metabolizing.  If there is a delay before the sample is tested, a sample that is left at room temperature may have a false increase in carbon dioxide, decreased pH or lowered PaO2 due to continued cell metabolism.
    7. Flush the catheter, stopcock and clearlink cap of blood and replace cap as per blood drawing protocol.

    The pulmonary artery lumen requires manual flushing for at least one minute to clear the long narrow lumen.
    If blood remains in the lumen, gently flush with a 10 mL syringe of saline.

    		 7. To maintain catheter patency and reduce potential for bacterial colonization.

    Inadequate flushing will lead to loss of lumen patency. 
    Vigorous flushing can cause pulmonary vasoconstriction.
    Avoid syringes < 10 mL; smaller syringes lead to increased resistance during flushing.

     

     

     

    8.

    		 Remove non-sterile gloves and perform hand hygiene.

    8.

    In accordance with the MoHLTC 4 moments of hand hygiene and LHSC infection control policies in an effort to reduce risk of transmission of organisms and secretions

    .

    LHSC Hand Hygine Policy

    LHSC Routine Practices Policy

    LHSC Donning and Doffing Policy

    9.

    Ensure that lab requisition includes FiO2, PEEP, AC/SIMV, PS, Vt, minute volume and temperature if sending sample to the lab.

    For point of care testing machine (GEM), FiO2, PEEP, minute volume and temperature are required to be inputed into the GEM. See GEM policy: http://www.lhsc.on.ca/Health_Professionals/CCTC/home/gemPolicy.pdf

    NB: Note the cardiac output.

    		 9.
    • Blood gases are corrected to body temperature.
    • A decrease in mixed venous oxygen saturation indicates that the oxygen delivery (CO X SaO2 X Hb) is not high enough to meet the tissue needs.
    • A fall in mixed venous oxygen saturation can occur if the cardiac output, oxygen saturation or Hb is too low, or the metabolic rate is > the ability to respond. 
    10. Document results in the graphic record and communicate any significant findings to the physician and respiratory therapist. 10. To ensure appropriate interventions are made.


    November, 1988
    Last Update: Mach 23, 2010.
    Brenda Morgan, Clinical Educator, CCTC

    LHSCHealth Professionals

    Last Updated January 4, 2011 | © 2007, LHSC, London Ontario Canada