Background: Elastomeric pumps (elastic balls into which analgesics or antibiotics can be inserted) push medicines through a catheter to a nerve or blood vessel. Since elastomeric pumps are small and need no power sour...Background: Elastomeric pumps (elastic balls into which analgesics or antibiotics can be inserted) push medicines through a catheter to a nerve or blood vessel. Since elastomeric pumps are small and need no power source, they fit easily into a pocket during infusion, allowing patient mobility. Elastomeric pumps are widely used and widely studied experimentally, but they have well-known problems, such as maintaining reliable flow rates and avoiding toxicity or other peak-and-trough effects. Objectives: Our research objective is to develop a realistic theoretical model of an elastomeric pump, analyze its flow rates, determine its toxicity conditions, and otherwise improve its operation. We believe this is the first such theoretical model of an elastomeric pump consisting of an elastic, medicine-filled ball attached to a horizontal catheter. Method: Our method is to model the system as a quasi-Poiseuille flow driven by the pressure drop generated by the elastic sphere. We construct an engineering model of the pressure exerted by an elastic sphere and match it to a solution of the one-dimensional radial Navier-Stokes equation that describes flow through a horizontal, cylindrical tube. Results: Our results are that the model accurately reproduces flow rates obtained in clinical studies. We also discover that the flow rate has an unavoidable maximum, which we call the “toxicity bump”, when the radius of the sphere approaches its terminal, unstretched value—an effect that has been observed experimentally. Conclusions: We conclude that by choosing the properties of an elastomeric pump, the toxicity bump can be restricted to less than 10% of the earlier, relatively constant flow rate. Our model also produces a relation between the length of time that the analgesic fluid infuses and the physical properties of the fluid, of the elastomeric sphere and the tube, and of the blood vessel into which the analgesic infuses. From these, we conclude that elastomeric pumps can be designed, using our simple model, to control infusion times while avoiding toxicity effects.展开更多
BACKGROUND Critically ill neonates and pediatric patients commonly require multiple low flow infusions.Volume limitations are imposed by small body habitus and comorbidities like cardiopulmonary disease,renal failure,...BACKGROUND Critically ill neonates and pediatric patients commonly require multiple low flow infusions.Volume limitations are imposed by small body habitus and comorbidities like cardiopulmonary disease,renal failure,or fluid overload.Vascular access is limited by diminutive veins.Maintenance fluids or parenteral nutrition in conjunction with actively titrated infusions such as insulin,fentanyl,prostaglandins,inotropes and vasopressors may necessitate simultaneous infusions using a single lumen to maintain vascular catheter patency.This requirement for multiple titratable infusions requires concentrated medications at low flows,rather than more dilute drugs at higher flows that in combination may volume overload small infants.AIM To determine whether carrier fluid reduces variability that variability of low flow drug infusions is proportional to syringe size in pediatric critical care.METHODS We assessed concentrations of orange“drug”in a 0.2 mL/h low flow clinical model with blue dyed carrier fluid at 5 mL/h,using 3-,10-,or 60-mL syringes.A graduated volumetric pipette was used to measure total flow.Mean time to target concentration was 30,21,and 46 min in 3-,10-,and 60-mL syringes,respectively(P=0.42).After achieving target concentration,more dilute drug was delivered by 60-mL(P<0.001)and 10-mL syringes(P=0.04)compared to 3-mL syringes.Drug overdoses were observed during the initial 45 min of infusion in 10-and 60-mL syringes.Total volumes infused after target concentration were less in the 60-mL condition compared to 3-mL(P<0.01)and 10-mL(P<0.001)syringes.RESULTS Linear mixed effects models demonstrated lesser delivered drug concentrations in the initial 30 min by 3-mL compared to 10-and 60-mL syringes(P=0.005 and P<0.001,respectively)but greater drug concentrations and total infused drug in the subsequent 30-60 and 60-90 min intervals with the 3-and 10-mL compared to 60-mL syringes.CONCLUSION With carrier fluid,larger syringes were associated with significantly less drug delivery,less total volume delivered,and other flow problems in our low flow drug model.Carrier fluid should not be used to compensate for inappropriately large syringes in critical low flow drug infusions.展开更多
文摘Background: Elastomeric pumps (elastic balls into which analgesics or antibiotics can be inserted) push medicines through a catheter to a nerve or blood vessel. Since elastomeric pumps are small and need no power source, they fit easily into a pocket during infusion, allowing patient mobility. Elastomeric pumps are widely used and widely studied experimentally, but they have well-known problems, such as maintaining reliable flow rates and avoiding toxicity or other peak-and-trough effects. Objectives: Our research objective is to develop a realistic theoretical model of an elastomeric pump, analyze its flow rates, determine its toxicity conditions, and otherwise improve its operation. We believe this is the first such theoretical model of an elastomeric pump consisting of an elastic, medicine-filled ball attached to a horizontal catheter. Method: Our method is to model the system as a quasi-Poiseuille flow driven by the pressure drop generated by the elastic sphere. We construct an engineering model of the pressure exerted by an elastic sphere and match it to a solution of the one-dimensional radial Navier-Stokes equation that describes flow through a horizontal, cylindrical tube. Results: Our results are that the model accurately reproduces flow rates obtained in clinical studies. We also discover that the flow rate has an unavoidable maximum, which we call the “toxicity bump”, when the radius of the sphere approaches its terminal, unstretched value—an effect that has been observed experimentally. Conclusions: We conclude that by choosing the properties of an elastomeric pump, the toxicity bump can be restricted to less than 10% of the earlier, relatively constant flow rate. Our model also produces a relation between the length of time that the analgesic fluid infuses and the physical properties of the fluid, of the elastomeric sphere and the tube, and of the blood vessel into which the analgesic infuses. From these, we conclude that elastomeric pumps can be designed, using our simple model, to control infusion times while avoiding toxicity effects.
基金Supported by NIH National Center for Advancing Translational Sciences(NCATS)UCLA CTSI,No.UL1TR001881.
文摘BACKGROUND Critically ill neonates and pediatric patients commonly require multiple low flow infusions.Volume limitations are imposed by small body habitus and comorbidities like cardiopulmonary disease,renal failure,or fluid overload.Vascular access is limited by diminutive veins.Maintenance fluids or parenteral nutrition in conjunction with actively titrated infusions such as insulin,fentanyl,prostaglandins,inotropes and vasopressors may necessitate simultaneous infusions using a single lumen to maintain vascular catheter patency.This requirement for multiple titratable infusions requires concentrated medications at low flows,rather than more dilute drugs at higher flows that in combination may volume overload small infants.AIM To determine whether carrier fluid reduces variability that variability of low flow drug infusions is proportional to syringe size in pediatric critical care.METHODS We assessed concentrations of orange“drug”in a 0.2 mL/h low flow clinical model with blue dyed carrier fluid at 5 mL/h,using 3-,10-,or 60-mL syringes.A graduated volumetric pipette was used to measure total flow.Mean time to target concentration was 30,21,and 46 min in 3-,10-,and 60-mL syringes,respectively(P=0.42).After achieving target concentration,more dilute drug was delivered by 60-mL(P<0.001)and 10-mL syringes(P=0.04)compared to 3-mL syringes.Drug overdoses were observed during the initial 45 min of infusion in 10-and 60-mL syringes.Total volumes infused after target concentration were less in the 60-mL condition compared to 3-mL(P<0.01)and 10-mL(P<0.001)syringes.RESULTS Linear mixed effects models demonstrated lesser delivered drug concentrations in the initial 30 min by 3-mL compared to 10-and 60-mL syringes(P=0.005 and P<0.001,respectively)but greater drug concentrations and total infused drug in the subsequent 30-60 and 60-90 min intervals with the 3-and 10-mL compared to 60-mL syringes.CONCLUSION With carrier fluid,larger syringes were associated with significantly less drug delivery,less total volume delivered,and other flow problems in our low flow drug model.Carrier fluid should not be used to compensate for inappropriately large syringes in critical low flow drug infusions.
