Intravascular catheters-an ultrasound imaging based observational study of position and function.

Peripheral intravenous and intra-arterial catheters often block with movement of the limb in which they are inserted. Although the cause of this blockage is commonly attributed to a valve or other structure within the vein, evidence for this is lacking. We used ultrasound to assess the cause of blockage on movement, and degree of tip movement, of 62 venous and 21 radial arterial catheters. In both venous and arterial catheters, blockage was predominantly caused by impingement of the catheter on the vessel wall, with catheter kinking and spasm of the vessel also seen. Mean potential tip movement was 12.3 mm and 5.7 mm in hand and forearm venous catheters respectively and 9.5 mm in radial artery catheters. There was a significantly lower rate of blockage for forearm (20%) compared to dorsal hand venous catheters (83%, P <0.001) and 52% of radial artery catheters showed damping and blockage on wrist flexion. This study emphasises the advantages of placement of venous catheters in the straight veins of the forearm.

Cricothyroidotomy catheters: an investigation of mechanisms of failure and the effect of a novel intracatheter stylet.

Emergency catheter cricothyroidotomy often fails. Case reports have concentrated on kinking and displacement of the catheter as the major causes. We investigated catheter tip penetration of the trachea. Using insertion angles of 90°, 75°, 60°, 45° and 30° we advanced 14 G intravenous catheters into fresh isolated sheep tracheas during high pressure oxygen insufflation. At all angles, the catheter tip became blocked by pushing into the mucosa with submucosal gas injection on one or more attempts. Full thickness rupture with extratracheal gas also occurred on insertions at 90° and 60°. We then tested a Luer-mounted prototype wire stylet which remains in situ during insufflation. Using the same methodology, the stylet was able to be placed and prevented blockage at all angles of insertion. Mucosal trauma and submucosal gas injection occurred on insertions at 90° and 75°. Our results should guide further stylet design.

Comparison of extent of sensory block following posterior and subcostal approaches to ultrasound-guided transversus abdominis plane block.

Transversus abdominis plane block provides postoperative analgesia following abdominal surgery by targeting thoracolumbar nerves between the internal oblique and transversus abdominis muscles. Posterior and subcostal approaches using ultrasound guidance have been described. However there have been inconsistent results in relation to the extent of the sensory block. This observational study evaluated the distributions of sensory block following either a posterior or subcostal approach and the quality of analgesia achieved. Following ethics committee approval, 50 patients undergoing minimally invasive and major abdominal surgery were recruited. A total of 81 transversus abdominis plane blocks were performed preoperatively under real-time ultrasound guidance. Postoperatively, patients received multimodal analgesia including morphine via patient-controlled pumps. Ninety-eight percent of patients had some degree of demonstrable sensory block and the dermatomal spread differed between posterior and subcostal approaches (P < 0.001). The posterior approach produced a median sensory block of three dermatomal segments (interquartile range 2 to 4), the most cephalad being T10 (interquartile range T9 to T10), while the subcostal approach blocked a median of four segments (interquartile range 3 to 5), the most cephalad being T8 (interquartile range T7 to T9, P < 0.001). Maximum dermatomal block distribution was observed at 30 minutes and usually regressed by 24 hours. Median cumulative morphine consumption was 40.8 mg (interquartile range 17 to 50 mg) at 24 hours. Median pain scores at rest and with coughing were 20 (interquartile range 10 to 35) and 50 (interquartile range 29 to 67) respectively at 24 hours. The posterior approach appears to be more appropriate for lower abdominal surgery and the subcostal approach better suited to upper abdominal surgery. Whichever approach is used, transversus abdominis plane block is only one component of a multimodal analgesic technique.

Venous embolism of diathermy evolved gases complicating endometrial ablation using glycine irrigant.

A case is reported of venous gas embolism in a 44-year-old woman undergoing hysteroscopic endometrial ablation using glycine irrigation without gas insufflation. The postulated source of gases are the vapour and combustion products produced by the diathermy.