Effect of intravenous fluid and drug solution coadministration on final-infusate osmolality, specific gravity, and pH

The effects of i.v. fluid rates and i.v. drug delivery rates on osmolality, specific gravity, and pH of the resulting infusate were examined. Selected drug solutions of various osmolalities and 5% dextrose and 0.2% sodium chloride injection or Ringer's injection, lactated, were administered simultaneously using a drug delivery system capable of controlling the flow rates independently. The i.v. fluid and drug infusion rates were varied from 4 to 46 and from 2 to 31 ml/hr, respectively. Osmolality, pH, and specific gravity of the drug solutions and final infusate were measured. Using alligation, the osmolality, pH, and specific gravity of the final infusate were calculated; correlations between observed and calculated values were computed. Guidelines for achieving an osmolality of the final infusate less than 500 mOsm/kg water were calculated. The observed and calculated osmolality and specific gravity of the final infusate were significantly correlated (r = 0.91, p less than 0.001, and r = 0.99, p less than 0.01, respectively). The pH of the final infusate was dependent on the pH of the original drug solution and was not affected by i.v. fluid and drug delivery flow rates. Osmolality may be an important factor to consider when establishing ideal drug solution infusion rates or concentrations. The infusate osmolality can be controlled by adjusting the concentration of the drug solution, drug infusion rate, or the i.v. fluid flow rate.