A 63-year-old man with peptic ulcer disease comes to the emergency department after several bouts of melena followed by large hematemesis. He reports nausea and feels faint. Temperature is 34.5 C (94.1 F), blood pressure is 90/46 mm Hg, pulse is 126/min, and respirations are 28/min. Physical examination reveals a lethargic man with cold extremities and sluggish capillary refill. Type O, Rh-D negative red blood cells are given as rapidly as possible via intravenous access. However, the blood transfusion rate is unacceptably slow, and the patient remains hypotensive. Which of the following will lead to the greatest improvement in flow rate?

Question

A 63-year-old man with peptic ulcer disease comes to the emergency department after several bouts of melena followed by large hematemesis.  He reports nausea and feels faint.  Temperature is 34.5 C (94.1 F), blood pressure is 90/46 mm Hg, pulse is 126/min, and respirations are 28/min.  Physical examination reveals a lethargic man with cold extremities and sluggish capillary refill.  Type O, Rh-D negative red blood cells are given as rapidly as possible via intravenous access.  However, the blood transfusion rate is unacceptably slow, and the patient remains hypotensive.  Which of the following will lead to the greatest improvement in flow rate?

Quizplus · Accepted Answer

11ec160b_3cc8_dabf_9249_efa120b2157a_MD0001_00 This patient has brisk upper gastrointestinal bleeding and is developing hypovolemic hemorrhagic shock (ie, hypotension, cold extremities, delayed capillary refill). He requires rapid transfusion of red blood cells. His condition is unstable, so there is no time for cross-matching. Therefore, he is receiving type O, Rh-D negative blood. With blood available at the bedside, the time-limiting factor is the transfusion flow rate. The flow rate is determined by the geometry of the intravenous access. The flow of viscous fluids (eg, blood) through hollow tubes (eg, intravenous catheters) is described by Poiseuille law. Flow is proportional to pressure (P) divided by resistance. The resistance is inversely proportional to the radius (equivalent: diameter) raised to the fourth power (r⁴) but only directly proportional to the length (L) and viscosity of the fluid. Therefore, small changes in the radius result in large changes in flow rate: A 19% increase in radius doubles the flow rate (1.19⁴ = 2); similarly, doubling the radius multiplies the flow rate by 16-fold (2⁴= 16). (Choice B) Doubling the length doubles the resistance, resulting in half the flow. To achieve the equivalent flow of doubling the diameter, the length would need to be shortened to 1/16 of the original. For this reason, shorter catheters are preferred for rapid transfusion (eg, a large-bore peripheral [L = 2 cm] is preferred over a central venous catheter [L = 20 cm]). (Choice C) Doubling the pressure results in double the flow. To achieve the equivalent flow of doubling the radius, the infusion pressure would need to be increased by a factor of 16. Although it is possible to transfuse blood at high pressure, doing so risks hemolyzing the blood or blowing out the intravenous site. (Choice D) If the radius, length, and pressure are kept constant, placing a second identical catheter would result in double the flow. To achieve the equivalent flow of doubling the radius, an additional 15 catheters would need to be inserted. For this reason, a few low-resistance intravenous access sites (eg, 2 large-bore peripheral intravenous catheters) are preferable to many high-resistance sites. Educational objective: The most important determinant of intravenous infusion rate is the radius (diameter) of the intravenous catheter. For patients requiring a rapid blood transfusion, the shortest possible catheter with the widest possible diameter (eg, a large-bore peripheral intravenous catheter) should be selected.

A 63-Year-Old Man with Peptic Ulcer Disease Comes to the Emergency