Central Nervous System
Pregnant women demonstrate increased sensitivity to both regional
and general anesthetics. From early pregnancy, when neuraxial anesthesia is administered,
women require less local anesthetic than nonpregnant women do to reach a given dermatomal
sensory level. The minimum alveolar concentrations of halothane and isoflurane are
reduced by 25% and 40%, respectively, during pregnancy.[28]
The underlying mechanism of the decreased anesthetic requirements remains unclear.
Although early studies suggested that this finding could be explained by
TABLE 58-4 -- Values for renal function
|
Parameter |
Pregnant |
Nonpregnant |
|
Creatinine clearance |
140–160 mL/min |
90–110 mL/min |
|
Urea |
2.0–4.5 mmol/L |
6–7 mmol/L |
|
Creatinine |
25–75 µmol/L |
100 µmol/L |
|
Uric acid |
0.2 mmol/L |
0.35 mmol/L |
|
pH |
7.44 |
7.40 |
|
Bicarbonate |
18–22 mmol/L |
23–26 mmol/L |
|
From Birnbach DJ, Gatt SP, Datta S (eds): Textbook
of Obstetric Anesthesia. New York, Churchill Livingstone, 2000, p 37. |
mechanical effects, more recent data have suggested that the reduced local anesthetic
requirements predate the mechanical effects of the gravid uterus.[29]
In animal studies, chronically administered progesterone has been found to reduce
anesthetic requirements.[30]
In addition, it has
been suggested that the increased concentrations of endorphins and dynorphins found
in pregnant rats may be related to altered pain thresholds.[31]
[32]
This evidence suggests a multifactorial explanation
for the decreased anesthetic requirements.
