Clinical relevance of osmotic effects

Osmotic effects are particularly important from a physiological viewpoint since bio- 

The osmotic pressures of many of the products of Table 3.1 are in excess of that of plasma (291 mosmol dm ). It is generally recommended that any fluid with an osmotic pressure above 550 mosmol dm should not be infused rapidly as this would increase the incidence of venous damage. The rapid infusion of marginally hypertonic solutions (in the range 300-500 mosmol dm ) would appear to be clinically practicable the higher the osmotic pressure of the solution within this range, the slower should be its rate of infusion to avoid damage. Patients with centrally inserted lines are not normally affected by limits on tonicity as infusion is normally slow and dilution is rapid. 

Certain oral medications commonly used in the intensive care of premature infants have very high osmolalities. The high tonicity of enteral feedings has been implicated as a cause of necrotising enterocolitis (NEC). A higher frequency of gastrointestinal illness including 

Drug (route) Concentration of drug Mean measured osmolality (mosmol kg ) Calculated available milliosmoles in 1 kg of drug preparation  

The aqueous solubilities of several volatile anaesthetics can be related to the osmolarity of the solution. The inverse relationship between solubility (expressed as the liquid/gas partition coefficient) of those anaesthetics and the osmolarity is shown in Table 3.4. 

---