Our tiny babies have very tiny tracheas. So far you are probably all with me. Putting that tube in the right position is therefore tricky. In particular avoiding the right mainstem bronchus, which is the wrong position, is important.
So first of all; where should the tip be? That seems obvious, it should be in the trachea, high enough above the carina that the tube never slips into the carina, but low enough that it doesn’t slip out. On a plain AP radiograph, however, it isn’t always clear exactly where the tube tip should be. In general ,studies have suggested that on the radiograph the tip of the tube should be T1-T2. That is based on studies where the position was directly observed, such as in post-mortem studies, and compared with an X-ray.
A study from 7 years ago (Thayyil S, et al: Optimal endotracheal tube tip position in extremely premature infants. American journal of perinatology 2008, 25(1):13-16.) noted that babies who had a tube tip lower than T1-T2 were more likely to have right upper lobe collapse, localized PIE and pneumothorax. I think that confirms that T1-T2 is the appropriate location.
Now how do we ensure that the tube tip is in that, optimal, position? The NRP (which clearly is not focussed on very preterm babies) suggests to add 6 cm to the infants weight in kg, which leads to tube insertion depths which are too low for most babies under 1 kg (see for example : Peterson J, et al: Accuracy of the 7-8-9 Rule for endotracheal tube placement in the neonate. J Perinatol 2006, 26(6):333-336.) I think it is clear we should not use that rule for babies under 1 kg.
Various methods of calculation have been suggested, some are based on calculations using the babies weight, some on gestation, one on foot length (which actually seems to be a good idea, and relatively easy to get to during resuscitation, but I don’t know if anyone does that. Embleton ND, et al: Foot length, an accurate predictor of nasotracheal tube length in neonates. Archives of Disease in Childhood – Fetal and Neonatal Edition 2001, 85(1):F60-F64) maybe Nick Embleton will let me know if anyone uses it.
A newly published trial from Colm O’Donnel in Dublin (Flinn AM, et al: Estimating the Endotracheal Tube Insertion Depth in Newborns Using Weight or Gestation: A Randomised Trial. Neonatology 2015, 107(3):167-172.) randomly compared weight and gestational age based standards, unfortunately the weight based standard they used was depth= weight + 6, and they compared this to a table based on gestational age. The number of ET tubes in the right place was higher with the weight calculation, but it was not statistically significant, and there were very many that were malpositioned in both groups, 50% with the weight based calculation, and 60% with the GA table.
Another study, which also trashed the 7-8-9 rule promoted by NRP, (Kempley ST, et al: Endotracheal tube length for neonatal intubation. Resuscitation 2008, 77(3):369-373) was a report of a quality improvement initiative in London. It is interesting in part because they showed that intubating the baby and then doing a clinical exam to see if it was in the right place was associated with more than half of the ETTs being mal-positioned. While using a table of distances (either GA based or weight based) was much better, with less than 20% needing repositioning.
Colm O’Donnell has also published a letter with photos of endotracheal tubes (Gill I, O’Donnell CP: Vocal cord guides on neonatal endotracheal tubes. Archives of disease in childhood Fetal and neonatal edition 2014, 99(4):F344.) which clearly shows that you can’t rely on the ETT marks to decide where to put the tube. Non-one ever evaluated this previously, as far as I can tell in the literature, but using those marks will lead to many being in the wrong place. I think it should be obvious that all babies who are intubated with a 2.5 tube do not have the same length of trachea! So using the same ETT tube marking wll often be wrong.
So how best to do this?
I think that the first step should be to use a table of insertion depth against body weight. (we are a center which attracts a lot of extremely growth restricted babies, so I would be wary of using a GA standard). I think the table below looks to be the best (UPDATE** I failed to mention previously that the table is from the study which I refer to above by Stephen Kempley) , I have added a column for nasal intubation based on the demonstration (autopsy study,with body weights down to 500 g) that the distance from nostril to carina is almost exactly 1.2 cm on average longer than the distance from lip to carina (Rotschild A, Chitayat D: Optimal Positioning of Endotracheal Tubes for Ventilation of Preterm Infants. AJDC 1991, 145:1007.)
During the intubation procedure, prior to fixing the tube, palpation in the supra-sternal notch can confirm good tube position with very good accuracy, once you have been trained to do it. A randomized trial from Neil Finer’s group (Jain A, et al: A randomized trial of suprasternal palpation to determine endotracheal tube position in neonates. Resuscitation 2004, 60(3):297-302.) who showed me the technique when I was his fellow) found a much higher proportion of tubes in the right position after adequate training, and another RCT (Saboo AR, et al: Digital palpation of endotracheal tube tip as a method of confirming endotracheal tube position in neonates: an open-label, three-armed randomized controlled trial. Pediatric Anesthesia 2013, 23(10):934-939) had a high proportion of tubes in good position, 83%, following a process such as I have just described, a table of insertion depths, accompanied by palpation to validate position.
Here is that table:
|ETT length at the lips (cm)||ETT length at nostril (cm)||Current weight (kg)||Gestational Age (sem)|
|5.5||6.5||0.5–0.6 (to 0.69)||23–24|
((This is the initial length to which the tube should be inserted, followed by palpation of the tube to ensure good position, and then a chest radiograph to check its position. The tube length should then be adjusted to align its tip with the thoracic vertebrae T1–T2.))
Another important point, flexion of the neck advances the end of the ETT, but, in fact, the sze of the effect is fairly minor. A severe flexion of 55 degrees only advances the tube tip by about 3 mm (Rost JR, Frush DP, Auten RL: Effect of neck position on endotracheal tube location in low birth weight infants. Pediatric Pulmonology 1999, 27(3):199-202). So if the tube is on the carina when you do the x-ray and the head is flexed, you still need to reposition the tube, you can’t rely on good head position to move the tube tip up much.
Finally there are some data to support using ultrasound to confirm tube position, (Chowdhry R, Dangman B, Pinheiro JM: The concordance of ultrasound technique versus X-ray to confirm endotracheal tube position in neonates. J Perinatol 2015. Dennington D, Vali P, Finer NN, Kim JH: Ultrasound confirmation of endotracheal tube position in neonates. Neonatology 2012, 102(3):185-189.) It looks like this could be a reliable way of identifying malposition of the tube, and we should consider maybe training everyone to do this, including me!