- Written by Jonathan Colledge Jonathan Colledge
- Last Updated: 08 January 2013 08 January 2013
An oesophageal Doppler probe should sit in the mid oesophagus. It uses ultrasound and the principle of Doppler shift to calculate the velocity in the descending aorta and from this the cardiac output can be derived.
An NG tube should sit with its tip well below the diaphragm. If the tip is sitting at the cardia, reflux is possible and the tube should be advanced. Chest radiography is frequently used to assess the position of the NG tube and is one of only two methods recommended by the NPSA.(1)
An ETT should be positioned at least two centimetres above the carina when the neck is flexed. Between the claviculosternal joints is appropriate, although variations in radiographic positioning may necessitate careful inspection.
Chest drains should lie within the pleural space. A combination of radiography and examination should be used. If a chest drain is swinging (the fluid in the tube swings on inspiration and expiration), the tube is likely to be within the pleural space. On radiography the tube may be positioned with the tip angled upwards, downwards or medially and may lie behind the diaphragmatic shadow on the AP or PA radiograph. Attention should be paid to ensure the side holes of the tube are all within the pleural cavity otherwise surgical emphysema may result.
The Swan-Ganz catheter is associated with misplacement (although this is not the mechanism through which the increased mortality occurs). The tip should lie within the main pulmonary artery when not in use, which includes when a radiograph is being taken. More distal placement may cause lung infarction.
Central venous lines may be of two broad types – those for long term use and those for short term use. Generally, if a line is intended for short term use and administration of non irritant substances, there are many acceptable placements. This, however, is infrequently the case. Placement within side branches of the SVC and directly against the wall of the SVC when placed on the left are suboptimal and may be associated with venous perforation. If used for central venous pressure monitoring, placement should be within the SVC or left brachiocepahlic vein (if placed on the left). Lines for long term use should be positioned at the sinoatrial junction. If venous perforation is suspected in a vein you cannot compress, DO NOT remove the line – interventional radiology advice should be taken. Premature removal may result in catastrophic haemorrhage due to the lack of muscular constriction in veins. Arterial placement is less concerning, though advice should be taken depending on the type of line. Remember to look for a pneumothorax on both sides as central venous catheter placement may have been attempted on the contralateral side before successful placement.
An intra-aortic balloon pump (IABP) inflates during diastole, enhancing coronary perfusion and deflates during systole, reducing afterload. They can be used to help treat cardiogenic shock. The correct placement is so that the balloon mechanism does not interfere with the perfusion of branches of the aorta. This can be assessed by ensuring the tip is at the level of the aortic knuckle on the chest radiograph (assuming the correct length balloon was chosen for the patient’s height).
Also, see Pacemaker leads
1. Reducing harm caused by the misplacement of nasogastric feeding tubes. Available at: http://www.nrls.npsa.nhs.uk/resources/?entryid45=59794&q=0%c2%acng+tube%c2%ac [Accessed September 28, 2010].