Fluids

Chapter 5 Fluids



ACUTE CHANGES IN Paco2


Paco2 refers to partial pressure (P) of arterial (a) carbon dioxide (CO2). (An A used in this term would denote alveolar carbon dioxide.)


CO2 is produced by cellular metabolism and is not normally present in anesthetic gases.


In room air CO2 is negligible, constituting approximately 0.03%.



In Body Fluids


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▪ Units of measurement:
□ CO2 is measured as gaseous partial pressure, mm Hg (Paco2)

□ H+ is measured as units, the negative log of ionic concentration in moles/L (pH)

□ HCO3− is measured as ionic concentration, mEq/L (HCO3−)

▪ Average values in arterial blood in a normal, healthy, conscious animal at rest:
□ Paco2 = 40 mm Hg

□ pH = 7.4

□ HCO3− = 24 mEq/L

▪ Increased CO2 causes increased production of H+ (lowers the pH value) and HCO3−


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▪ During anesthesia, increased CO2 is caused by:
□ Inadequate ventilation
• Deep anesthesia

• Inappropriate ventilator settings

• Effects of some drugs

• Pulmonary disease

□ CO2 administration to the patient
• Absorbent is exhausted and is not removing CO2 from expired gas

• One-way valve is malfunctioning; expired gas is reaching patient

□ Increased cellular production
• Malignant hyperthermia (rare)

• High fever

▪ Decreased CO2 reduces the concentrations of H+ (increases the pH value) and HCO3−


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▪ During anesthesia, decreased Paco2 is caused by:
□ Excessive ventilation
• Inappropriate ventilator settings

• Excessive manual ventilation while practitioner checks several times for seal on endotracheal tube cuff

Table 5-1 lists guidelines for values expected with acute changes in Paco2. Actual changes in pH with changes in CO2 are not quite as large as shown in the table, but this is easy to remember, and the changes shown are relatively close to the true changes.


Table 5-1 Values Expected with Acute Changes in Paco2



































CO2 pH HCO3−
100 7.1 30
80 7.2 28
60 7.3 26
40 7.4 24
30 7.5 22
20 7.6 20
10 7.7 18

Shaded area indicates normal value. Note that increased Paco2 causes acidosis but also causes an increase in HCO3−.




Do not treat pure respiratory acidosis with bicarbonate.


Treat the primary disorder by improving ventilation.



ADDING DEXTROSE TO FLUIDS



▪ Based on using 50% dextrose but applicable to other concentrations

Related posts:

  1. Blood and Blood Substitutes
  2. Case Management
  3. Local Nerve Blocks
  4. Drug Combinations

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Oct 14, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Fluids

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