From the Guidelines
For a patient with a blood pressure of 110/70 mmHg, the best bore cannula would be the smallest practical size, which is typically 18 gauge or smaller, depending on the specific clinical situation and patient factors, as recommended by the Association of Anaesthetists of Great Britain and Ireland: Safe Vascular Access 2016 1. When considering the best bore cannula for a patient with normal blood pressure, several factors come into play, including the purpose of the cannulation, the patient's venous anatomy, and the potential risks associated with different cannula sizes.
- The Association of Anaesthetists of Great Britain and Ireland recommends using the smallest practical size of cannula to minimize trauma and risk of complications 1.
- While option B (18 gauge) might be considered a standard choice for many adult patients, the specific needs of the patient, such as the type of infusion or the presence of difficult venous access, might necessitate a different size.
- Options A (16 gauge), C (12 gauge), and D (14 gauge) are larger and typically reserved for situations requiring rapid volume resuscitation or the administration of blood products, which may not be necessary for a patient with a blood pressure of 110/70 mmHg.
- The use of needle guards to reduce needle stick injury is recommended for all procedures, regardless of the cannula size chosen 1.
- Ultimately, the selection of the best bore cannula should be guided by the principle of using the smallest size that is practical for the specific clinical situation, taking into account factors such as the patient's blood pressure, the purpose of the cannulation, and the potential risks and benefits associated with different cannula sizes, as outlined in the guidelines 1.
From the Research
BP and Cannula Size
The given blood pressure is 110/70. To determine the best bore cannula, we need to consider the flow rates and pressure properties of different cannula sizes.
Flow Rates and Pressure Properties
- A study on flow rates through intravenous access devices found that increasing the size of cannulas improved flow 2.
- The study compared flow rates through 14G cannulas and found that they had significantly higher mean flow rates compared to 14G central venous lines.
- Another study on pressure and flow properties of cannulae for extracorporeal membrane oxygenation found that flow is proportional to the fourth power of cannula inner diameter and inversely proportional to its length 3.
- However, the study also found that measured blood flows were in most cases 3-21% lower than those provided by manufacturers, especially in narrow cannulae.
Comparison of Cannula Sizes
- A study comparing alternative devices for tension hemopneumothorax and pulseless electrical activity found that 10G AC and 3-mm laparoscopic trocar performed superiorly compared to 14G AC 4.
- The study suggests that larger bore cannulas may be more effective in certain situations.
- However, another study on the safety and efficacy of peripheral versus centrally administered vasopressor infusion found that administration of vasopressor infusions for short duration via a peripheral venous cannula may be feasible, with low rates of complications 5.
Best Bore Cannula
Based on the studies, a larger bore cannula may be more effective in terms of flow rates and pressure properties. Considering the options provided: