Description of the macro infusion sets
The size of a drop in an intravenous (IV) setup depends on the width of the IV tubing: thinner tubing produces smaller drops, and wider tubing produces larger ones.
There are two major categories of IV tubings:
(1) Macrodrip tubing is wider and produces larger drops. Medical staff commonly used the tubing for routine IV administration, such as infusion of IV fluids that do not contain sensitive medications. Macro drip tubing comes in three sizes: 10 gtt/mL, 15 gtt/mL, and 20 gtt/mL.
(2) Micro drip tubing is narrower and so produces smaller drops. Medical workers use it for children and infants or to infuse sensitive medications where precision in the flow rate is essential. Micro drip or mini drip tubing comes in only one size: 60 gtt/mL. This means 60 drips per milliliter.
Specific uses of the macro infusion sets
As mentioned in the preceding, medical staff use the micro infusion set to provide lower doses of IV medicine to patients. Medical staff uses it for more delicate drugs.
However, if medical workers need to infuse higher dosages of medications admixed in the IV fluid, they use the macro infusion set instead. Medical staff uses a macro infusion set when significant volumes of fluid, such as saline solution, are meant to be quickly infused. The macro infusion set can deliver between 10 to 20 gtt/mL. Thus, only ten up to twenty drops are required to infuse one milliliter.
Specifically, in anesthesiology, medical practitioners frequently use gravity-driven macro-drip infusion sets. This setup can deliver 15 drops/mL. They control the flow rate by adjusting the roller clamp and monitor the flow rate by counting the number of drop formations in the dripping chamber. This setup allows the anesthesiologists to deliver high flow rates (>100 ml/min); therefore, the system is suitable for volume replacement and rapid administration of medications.
Specifically, thus, anesthesiologists use macro infusion sets to achieve the following:
(1) To deliver intravenous fluids to patients who need fluid deficit replenishment brought about by fasting before surgery;
(2) To replace ongoing losses of fluids during surgery;
(3) To serve as a vehicle for infusing intravenous medications and anesthetics.
Advantages of using gravity-driven macro infusion sets
Establishing a reliable intravenous infusion is an essential component of anesthesia practice. Advances in technology have brought several powered infusion devices (infusion pumps). To this day, however, the gravity-driven intravenous infusion sets remain the most frequently used, including anesthesia practice, because of the following reasons:
(1) Use of gravity-driven infusion saves medical practitioners from spending so much funds to acquire the infusion pumps;
(2) The maintenance cost for gravity-driven infusion sets is very much less compared to the maintenance expenses for powered infusion sets;
(3) Using the gravity-driven infusion sets does not require continuing costs for specialized infusion cartridges of IV sets; and
Based on the preceding reasons, prospective and existing health workers, especially anesthesiologists, prefer to use gravity-driven macro infusion sets. Medical workers find them easy to control, and the said infusion set exacts lesser expenses.
Dangers of using the macro infusion sets
The most bothering and worrisome danger of using a macro infusion set is the over-administration of fluids and medications.
Over infusion happens when medical workers open the roller clamp so widely to compensate for increased flow impedance. Then suddenly, the flow of fluid normalizes after the obstruction has spontaneously disappeared. Medical practitioners use newer powered infusion pumps to avoid this danger for effective control and higher infusion rates. However, using powered infusion pumps proves to be more costly and labor-intensive.
Percentage utilization of macro infusion sets
To better understand anesthesiologists’ use and choice of intravenous infusion sets, researchers surveyed anesthesiologists during the annual convention of the American Society of Anesthesiologists (ASA) in Orlando, Florida, USA, in October 1998. One hundred and twenty anesthesiologists who attended the scientific exhibits were asked to complete a questionnaire regarding the use of IV infusion sets in their practice and their choice of an infusion set for a particular clinical case. Ensuing are the results of the survey:
(1) Overwhelming majority (90%) of the surveyed anesthesiologists reported that the practitioners in their departments routinely used gravity-driven IV sets rather than power infusion pumps;
(2) The selection between the micro drip IV and the macro drip IV set varied considerably depending on the clinical scenarios.
Elderly diabetic patient with congestive heart failure
| IV set selected | Percentages |
| Macro drip | 33% |
| Micro drip | 24% |
| Both | 39% |
| Undecided | 4% |
Young adult patient for craniotomy
The same population of anesthesiologists was asked which IV set to use for a 40-year-old man undergoing craniotomy (surgery in the brain) to remove a cerebral tumor (tumor in the brain). The following were the results:
| IV set selected | Percentages |
| Macro drip | 50% |
| Micro drip | 7% |
| Both | 42% |
| Undecided | 1% |
The rationale for the selection of macro infusion sets
An elderly patient with existing diseases
In a 70-year-old man with diabetes mellitus and a history of CHF undergoing a minor surgery under spinal anesthesia, over-administration of fluids can be hazardous and precipitate CHF. Thus, micro-drip would seem to be better suited in this case as it carries less risk of accidental fluid overload.
However, hypotension is also very common after spinal anesthesia. Thus, macro-drip needs to be used so that fast fluid delivery and fast infusion of fluid boluses can be accomplished if they are needed.
Young adult patient for brain surgery
Similarly, intracranial or lung surgery both require fluid restriction to prevent brain edema or “wet lungs” after the operations, thus selecting the micro infusion set as the first logical choice.
However, these surgeries may result in unexpected, sudden, and substantial blood loss, requiring larger boluses of fluids to maintain or increase blood pressure. For this reason, macro-drip infusion needs to be used so that a large amount of fluid can be infused in a shorter time.
