Evaluation of an alternative method of blood sampling from arterial cannulae

Abstract

SummaryA new system for sampling from arterial cannulae has been designed which avoids the need to aspirate flushing solution before taking a sample and limits blood loss. The new system was compared with a standard sampling system and direct arterial sampling using in vitro models. A series of haemoglobin concentrations wert> prepared and sampled using the three sampling methods. There were no clinically significant differences in the values obtained with the different sampling techniques. [5]. Some of these may be related to the practice of withdrawing and reinjecting a few ml of blood at the sampling port during the sampling procedure. This technique has evolved in order to avoid dilution of the sample by the flushing solution, but reinjection of the blood, although desirable to minimise blood loss in infants and small children, increases the risk of infection and embolisation, as does flushing of saline past a sampling port contaminated with old blood. Key words EquipmentMany paediatric units use an alternative sampling arrangement, in which a very small volume of blood is used to reduce dilution of the sample by the flushing solution. This study assesses the previously untested assumption that results do not differ from the standard method to a clinically significant extent. MethodThe haemoglobin content of blood samples taken using standard and alternative flush/sampling arrangements was estimated. An in-vitro model was used using bags of recently expired stored blood which were diluted to five different haemoglobin concentrations within the range seen in paediatric intensive care patients.The rubber injection hub of a standard blood administration set was used as the 'artery', (Fig. 1). This was cannulated with a 24 G Jelco cannula. The flushing/ sampling side of the circuit consisted of a pressure transducer connected by a three-way tap to a T-piece extension with rubber injection port (Abbott Venisystems No. F898). The tubing near the cannula was mounted on a board to allow tilting between sampling in order to prevent measurement errors due to gravitational separation of blood cells and plasma.The new sampling technique took place as follows: the three-way tap was opened, and the saline/blood interface was allowed to run back until it reached the tap, but stopped before any blood escaped. A 25 G needle on a 2 ml syringe was used to aspirate a 0.5 ml sample of blood from the rubber injection port of the T-piece connector. Following sampling in vivo, the blood/saline interface was flushed hick into the cannula. The standard method sample was collected after this, by opening the three-way tap, aspirating and discarding 2 ml of blood and then collecting .a 0.5 ml sample. Lastly a third 'direct' sample of the same volume was collected by inserting a 22 G needle directly in to the 'artery'.The sampling circuit was then flushed with saline, and the blood system run through, with a period of agitation before and afterwards. Five sets of three samples were taken from each of five bags of blood prediluted to dif...

Complications of dislodged tracheostomy

“…Recent discussion about arterial lines in the literature has concentrated on prevention of embolisation, infection and blood wastage [2][3][4]. Reduction of the real risk of injury to the patient from the inadvertent injection of inappropriate material has not been addressed in practice except for 'colour coding' of injection ports and three-way taps.…”