Page 176 - Basic Monitoring in Canine and Feline Emergency Patients

Table 8.5. Continued.

VetBooks.ir concentration of sodium can be administered instead (lactated Ringer’s solution, Plasmalyte, 0.9% saline) to slow the rate of sodium
decline.
With ACUTE hypernatremia, sodium levels can be corrected quickly with high fluid rates (i.e. if you know the abnormality occurred
c within the last 8 hours, you can correct it within the next 8 hours).
When replacing sodium levels in CHRONIC hyponatremia (>24–48 hours), sodium levels should not increase at a rate faster than
0.5–1.0 mEq/L/h to avoid dehydrating the cells of the brain by increasing the osmolality of the blood too quickly (and drawing water
out of the brain cells into the bloodstream). As with hypernatremia, sodium levels are typically checked every 4-6 hours to monitor the
rate of the sodium increase and adjust the fluid rates accordingly.
With ACUTE hyponatremia, the sodium levels can be corrected as quickly as they occurred without concern.
8.5 Pitfalls of the Monitor present in the approximately 7% of the blood
occupied by proteins and lipids. However, flame
In general, electrolyte monitoring (whether done on photometric techniques report the amount of
a point-of-care instrument or a laboratory-based sodium per total volume of sample. Because the
machine) is widely performed and time tested. lipid and protein component is usually fairly
Many publications have compared a variety of small, for most samples this does not significantly
point-of-care instruments versus laboratory-based affect the measured value. However, if the protein
instrumentation in humans and various animal spe- or lipid content of the blood is significantly
cies. Electrolyte testing (Na, K, iCa) has high agree- greater than 7%, there will be a much smaller
ment between the two types of instrumentation in proportion of the sample which is aqueous from
dogs and cats. which to derive the sodium content. Therefore,
As with any laboratory machine, quality control when the sodium value is compared to the total
and calibration should be performed per the instruc- sample volume (which is higher because of the
tions included with that instrument. Many of the lipemia and/or hyperproteinemia), the sodium
point-of-care instruments do internal calibration concentration will be falsely lowered. This is
and quality control. For example, an i-STAT system termed pseudohyponatremia.
performs internal electronic simulation several Typically, if lipid is causing pseuohyponatremia,
times daily on its own to ensure viability of the ion- the lipid is visible to the naked eye in the blood
specific electrodes and notifies the operator with a sample. Generally, 1 mg/dL of serum triglyceride
warning message if the internal electronic simula- reduces the sodium by 0.002 mEq/L so large
tion fails. Most point-of-care instruments still rec- amounts of triglyceride are required to significantly
ommend periodic intermittent operator calibration. alter sodium concentrations. Similarly, patients
When point-of-care instruments use cartridges to with dramatic enough hyperproteinemia to affect
effect electrolyte measurement, calibration is done laboratory results usually have viscous plasma. For
automatically when the cartridges are inserted into hyperproteinemic cases, each 1 g/dL of protein above
the machine. In most cases, the manufacturer does the level of 8 g/dL reduces the sodium concentra-
not suggest that cartridges in a lot or box be tion by 0.25 mEq/L.
checked against controls as long as cartridges are When using ISE testing (whether it be a point-
stored within the temperature limits, used within of-care analyzer or a laboratory machine), hyper-
the expiration dates, and otherwise handled accord- lipidemia and hyperproteinemia generally do not
ing to the manufacturer’s recommendations. Some alter sodium measurements unless there are large
laboratories will independently test the cartridges changes in lipid levels (typically triglyceride levels
according to protocols dictated by individual greater than 650 mg/dL), since the concentration
institutions.
of sodium is measured directly rather than versus
the volume of the plasma. However, inappropriate
dilution of the sample with anticoagulant or intra-
Sodium
venous (IV) fluid contamination can alter results.
The biggest interference with flame photometric Anticoagulant dilution occurs when too little
testing of sodium occurs when there is excessive blood is added to a tube containing sodium hepa-
lipemia or hyperproteinemia. Sodium is present in rin anticoagulant. The ‘extra’ sodium heparin that
the aqueous portion of a blood sample (usually is unbound to blood will falsely elevate the
about 93% of the sample in health), but is not sodium. Similarly, if a patient is receiving sodium

168 E.J. Thomovsky