0At 37 C water has a specific gravity of 0.9937 , and a density of 993.37 Kg/ m3
% concentration in medicine is usually weight by volume
0.9% Saline means 9mg of NaCl in 1ml of saline or 9g in 1L of saline or 9000g or 9kg in 1m3
So 1009 kg/m3 if it is made at 4 C.
Assuming it is made at 37 C 993.37+9 Kg Density is 1002.37 Kg/m3 Specific gravity is 1.00237
1mg/ml = 1kg/m3
Specific Gravity (SG) of CSF varies from 1.0063 to 1.0075 at 37 C 1 (~1.007)
This means the ~1007kg is present in 1 m3
Another real world example is of Sea Water.
As temperature increases, density decreases. As salinity of the water increasaes, density also increases. Although the density of seawater varies at different points in the ocean, a good estimate of its density at the ocean’s surface is 1025 kilogram per cubic meter. Its specific gravity is therefore 1.025 or 1.025g/ml
Bupivicaine hydrochloride C18H29ClN2O Molecular Weight is 324.893 g/mol Which is totally not needed as we are talking about mg in % and not exactly moles while calculating the weight in the solution which is needed to calculate the density and the specific gravity respectively.
So 0.5% Bupivicaine means 0.5 kg in 1m3 and 8.25% dextrose means 8.25kg of dextrose in 1 m3 Total mass is hence 8.75Kg in 1m3 . Supposing this was made at 37 C 993.37 Kg/m3 + 8.75 Kg/m3
So the density of the above is 1002.12 Kg/m3 and the specific gravity is 1.0021 .
Now the specific gravity of CSF is 1.007 which makes the solution isobaric and totally wrong.
The Density on the other hand is 1.00065g/ml or 1000.65kg/m3 which is less than hyperbaric bupivacaine at 1002.12Kg/m3.
In 1964 the definition of litre was changed to 1/1000 of 1m3 f water
Density is mass by volume
At 37 C At the density of CSF is ~1.00065 g/ml or 1000.65kg/m3
At 37 C In pregnancy it is usually 1.00033 g/ml or 1000.33kg/m3
At 37 C waters density is 0.99337g/ml or 993.7 kg/m3
The solution is hyperbaric if its density exceeds 1.00099, (1001kg/m3)
hypobaric when its density is lower than 1.00019, (1000.2 Kg/m3)
and isobaric when its density is greater than 1.00019 and lower than 1.00099. 2
Specific gravity and density and a logarithmical paradox
Density = Mass / Volume. Specific gravity is the density of a substance divided by the density of water. Since (at standard temperature and pressure) water has a density of 1 gram/cm3, and since all of the units cancel, specific gravity is usually very close to the same value as density (but without any units).
Need the following articles
1. Density, specific gravity, and baricity of spinal anesthetic solutions at body temperature. Anesthesia and Analgesia. 76(5):1015-8, MAY 1993 T T Horlocker; D J Wedel
1. Anesth Analg. 1981 Nov;60(11):814-7. Density of normal human cerebrospinal fluid and tetracaine solutions. Levin E, Muravchick S, Gold MI.
2. Assessment of the Densities of Local Anesthetics and Their Combination with Adjuvants. An Experimental Study Luiz Eduardo Imbelloni, TSA1, Adriano Dias Moreira2, Flávia Cunha Gaspar3 , Marildo A. Gouveia, TSA4, José Antônio Cordeiro5. Rev Bras Anestesiol 2009; 59: 2: 154-165
3. Density of lumbar cerebrospinal fluid in pregnant and nonpregnant humans. Richardson MG1, Wissler RN. Anesthesiology. 1996 Aug;85(2):326-30.