Critically ill patients and those undergoing general anesthesia usually require repeated collection of blood samples to assess their clinical status and response to treatment. Those blood samples can be obtained by direct venipuncture or through an indwelling IV catheter. Repeated venipuncture can cause trauma to blood vessels and pain and anxiety for the patient. To minimize patient stress and decrease vascular trauma, blood samples are often obtained from indwelling IV catheters.1 Although collection of blood samples from indwelling IV catheters is routinely performed in human medicine,2 information regarding the effect of blood collection by an indwelling catheter versus direct venipuncture on hematologic and biochemical variables in veterinary medicine is limited. Results of routine hematologic and biochemical profiles for horses3 and coagulation profiles for dogs4–6 obtained for blood samples collected via an indwelling IV catheter after complete removal of dead space volume were comparable to those obtained for blood samples collected by direct venipuncture. In cats, statistically significant but clinically irrelevant differences in potassium, TP, and albumin concentrations were detected between blood samples collected by direct venipuncture and those obtained from a venous access port.7
A concern when collecting a blood sample from an indwelling IV catheter is the volume of blood that is discarded (presample) prior to collection of the blood sample that is analyzed. Generally, the presample should represent 300% of the catheter dead space3; therefore, in small patients, repeated collection of blood samples from an indwelling IV catheter could result in substantial iatrogenic blood loss and anemia.8,9 One method for addressing that concern is the reinfusion of the presample to the patient after the blood sample for analysis is collected. Possible adverse events associated with reinfusion of the presample include the infusion of blood clots; hemolysis, hemodilution, or contamination of the presample; and accidental submission of the presample instead of the correct blood sample to the laboratory for analysis.8,10,11 To minimize the risk for adverse events associated with reinfusion of the presample, the push-pull, or mixing, technique was devised whereby the presample blood volume (ie, a volume equal to 300% of the catheter dead space) is aspirated into a syringe and then reinfused without disconnecting the syringe from the catheter 3 times, after which the syringe is disconnected from the catheter and a second syringe is used to obtain the blood sample required for analysis. This method limits iatrogenic blood loss and the potential for contamination of the presample.8 The push-pull technique has been validated in adult human patients11,12 and children8 but, to our knowledge, has not been evaluated in veterinary patients.
Aside from evaluation of critically ill patients, serial blood sample collection is frequently necessary for anesthetized patients. Unfortunately, some anesthetics can affect vascular tone, splenic size, and fluid distribution, all of which can alter blood cell counts.13,14 In dogs, administration of ketamine, thiopental, or propofol can decrease Hct,14 which indicates that hematologic results should be interpreted with caution following administration of certain anesthetic drugs. However, further research is needed to quantify the effect of various anesthetic drugs on blood electrolyte concentrations and other biochemical variables. In North America, alfaxalone is gaining popularity as a general anesthetic for both routine and emergency surgical procedures as well as for use in critically ill patients that require mechanical ventilation. To our knowledge, the effects of alfaxalone on hematologic and biochemical variables relative to those of propofol have not been assessed.
The primary objective of the study reported here was to determine the effect of blood collection by the push-pull technique from an indwelling IV catheter versus direct venipuncture on venous blood gas variables as well as PCV and electrolyte, glucose, lactate, and TP concentrations in healthy dogs. The secondary objective of the study was to assess differences in those variables before and after propofol or alfaxalone administration.
Supported by the Frankie's Friends Resident Clinical Study Grant.
Base excess in extracellular fluid
Clinical Laboratory Improvement Amendments
Alfaxan, Jurox Inc, Kansas City, Mo.
Diprivan, Fresenius Kabi USA LLC, Lake Zurich, Ill.
BD Insyte, Becton Dickinson Infusion Therapy Systems Inc, Sandy, Utah.
Extension set with T-Connector, Abbot Laboratories, North Chicago, Ill.
Nova Stat Profile Prime, NOVA Biomedical, Waltham, Mass.
Stata 14 for MAC, Stata Corp, College Station, Tex.
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