Using Poiseuille’s law and standardized gauge sizes, an 18-gauge (g) intravenous catheter (IV) should be 2.5 times faster than a 20-g IV, but this is not borne out by observation, in vitro testing, and manufacturer’s data. A nice simple study on normal volunteers compared simultaneous flow rates between a single 18G iv in one arm with two 20G ivs in the other arm. The two smaller ones provided significantly faster flow than the single larger one, although flow rates were slower than manufacturer’s estimates. This is in keeping with this other study on cannula flow rates. Are 2 smaller intravenous catheters as good as 1 larger intravenous catheter? Am J Emerg Med. 2010 Jul;28(6):724-7
An ultrasound study on infants and children under general anaesthesia evaluated the femoral vein with the patients’ legs at 30° and 60° of abduction and their hips externally rotated. Measurements were taken at the level of the inguinal crease and 1 cm below the crease.
Hip rotation with 60° leg abduction significantly decreased the overlap between femoral vein and femoral artery at the level of the inguinal crease in both infants and children.
The authors recommend the optimal place for femoral vein cannulation in paediatric patients seems to be at the level of the inguinal crease with 60° leg abduction and external hip rotation. Ultrasonographic evaluation of the femoral vein in anaesthetised infants and young children Anaesthesia. 2010;65(9):895–898
A study comparing sterile saline as a conduction agent with ultrasound gel showed adequate visualization of anatomic structures for ultrasound-guided vascular access. The authors state that given sterile saline’s theoretical advantages over gel in terms of availability, cost, safety and ease of use in the procedural field, it should be considered as a viable alternative to gel as a conduction agent.
While clearing up after teaching with my bald colleague Dr Phil Hyde yesterday I noticed his bulging scalp veins and this reminded me that we don’t talk about this route much in our Paediatric Emergency Medicine Course.
This prompted me to look up the complications of scalp vein access in neonates and infants, which include:
intracranial venous sinus air embolism
scalp necrotising fasciitis
Suggested ways to decrease the risk of complications include:
A vein should not be used for more than 24 h at a time
The needle entry point should not be covered
The butterfly needle should be immobilized to avoid movements of the needle into the tissue with consequent extravasation of fluid
The infusion site should be monitored by regular examination
If a swelling or leakage of fluid is noted, the infusion should be discontinued immediately from that site
The hair should be properly shaved
If the line is required for more than 24 h, a peripheral venous cutdown or central venous line should be considered, after initial resuscitation
An alternative route for rehydration (e.g. intraosseous infusion) should be considered initially, rather than risk multiple, unsuccessful attempts at scalp vein cannulation.
In a study of anaesthetised infants and children, the right internal jugular vein as assessed by ultrasonography was measured with the head in the neutral position, and then at 40 degrees and 80 degrees of rotation to the contralateral side. The 40 degree position resulted in an increase in IJV diameter but with less overlap with the carotid artery than the 80 degree position. The authors conclude that rotating the head 40 degrees to the left results in the best balance of increased IJV diameter versus overlap with the carotid. Effects of head rotation on the right internal jugular vein in infants and young children Anaesthesia Volume 65, Issue 3, Pages 272-276
Emergency medicine residents and paramedics cannulated patients who were anaesthetised. The external jugular vein (EJV) took longer to cannulate and had a higher failure rate than an antecubital vein. More than a quarter of the paramedics and a third of the doctors failed to cannulate the EJV. Is external jugular vein cannulation feasible in emergency care? A randomised study in open heart surgery patients Resuscitation. 2009 Dec;80(12):1361-4
An observational, prospective study comparing tibial and humeral intraosseous access using the EZ-IO
Emergency physicians at Singapore General Hospital found flow rates to be similar when comparing the tibia with the humerus as sites for adult IO access. The EZ-IO had a very high insertion success rate. It took about 12 minutes to infuse a litre of saline, which drops to about 6 minutes if a pressure bag is used.
Am J Emerg Med. 2009 Jan;27(1):8-15 http://www.ncbi.nlm.nih.gov/pubmed/19041528
Published flow rates for cannulae are derived from a test in which fluid runs through a perfectly straight cannula into an open receptacle. Laminar flow is expected in such a model in which the Hagen-Poisseuille formula tells us that flow is proportional to the fourth power of the radius. In this study manufacturers’ published flow rates were compared with an artifical vein model. Hartmann’s flowed faster than Gelofusine. For all cannulas flow was less than the manufacturers’ published rates. Although the radius was the biggest determinant of flow rate, the fourth power could not be used, suggesting a mixture of laminar and turbulent flow. The addition of pressurised infusions increased the flow rate with increasing pressure. Although the vein model used has limitations, and many other factors may influence flow rate in the clinical setting, the authors’ conclusions are helpful: While the effect of radius is less than commonly believed, it is still important. However, clinicians should be aware of the limitations of increasing radius and use other strategies to increase flow when needed. These could include use of pressure, choice of fluid to be infused, and using multiple cannulae in parallel. Fluid flow through intravenous cannulae in a clinical model Anesth Analg. 2009 Apr;108(4):1198-202