Part of our education day on Jan 4th 2023 focussed on the rare but confronting need to move to one lung ventilation (OLV) in the pre-hospital or retrieval environment. We heard from Dr John Floridis, a rural generalist and emergency physician who, while working remotely in the Northern Territory, found himself in that exact position. He presented a case of a severely injured trauma patient who required emergency thoracotomy and OLV, far from the bells and whistles of a trauma centre or cardiac surgeon. His tale had us on the edge of our seats, and his patient had a fantastic outcome thanks to the amazing care provided by John and the team at his health facility. I’ll take a deeper dive into OLV shortly, but what struck me by John’s talk was that although none of the team were thoracic specialists, what helped them to tackle the case so successfully was great teamwork, excellent communication, calling colleagues for advice to share the problem, and meticulous attention to detail to ensure that the simple stuff was done well.

We followed on briefly from John’s talk with a presentation from a previous HEMS registrar Dr Laura Connell, who has run a project to consider the cases from the last 10 years where OLV has been used, or a patient has been moved with a double lumen tube (DLT) in situ. Her work in this area has shown that these patients do come our way, and it is worth being aware of what a DLT is, how to check its position, and how to approach OLV in the retrieval patient. She ran a fantastic workshop in the afternoon to help us familiarise ourselves with this technique, and get hands on with a few different types of DLT.

OLV in a nutshell

Indications for OLV

There are absolute and relative indications for OLV. Relative indications essentially include surgical procedures where lung deflation is desirable to allow access to the structures of interest – for example oesophagectomy, thoracoscopy, lung volume reduction surgery, and so on. Absolute indications are of more interest to the critical care and retrieval practitioner, and tend to include problems where avoiding contamination of the unaffected lung is paramount, for example massive empyema, or pulmonary haemorrhage. In the case of bronchopleural fistula, selective ventilation of a single lung is necessary to avoid the delivered positive pressure tidal volumes disappearing via the fistula into the pleural/mediastinal spaces and subcutaneous tissues, instead of actually participating in ventilation.

Lung physiology, an extremely brief reminder

Clearly OLV is not a physiologically normal state, where we generate negative pressure within the thoracic cavity to inflate two lungs. In health our pulmonary circulation, a low pressure, low resistance circuit, tends to favour perfusion of alveoli where gravity is greatest, ie at the base of the chest in an upright, spontaneously ventilating human. Helpfully, this is also where ventilation is greatest, at the alveoli at the bases. This matching of Ventilation (V) and Perfusion (Q) sits in a balance where in normal physiology we achieve optimal gas exchange. This is fine tuned further by the process of hypoxic pulmonary vasoconstriction (HPV), which helps to divert blood away from oxygen-poor areas of the lung.

OLV pathophysiology

There are several problems, therefore, with taking a lung down. The first problem is that the patient is not starting from a place of health – the ‘good’ lung may not be that good, especially if there are co-morbidities like COPD, or concurrent problems like consolidation or atelectasis affecting that lung. The pulmonary circulation and right side of the heart may not be that good either – patients with chronic problems like OSA may have unrecognised right heart impairment, there may be innate problems with the heart itself such as mitral valve disease, which can cause pulmonary hypertension. The next problem with switching to positive pressure ventilation is that the fine balance of ventilation and perfusion is lost. No matter how fancy your ventilator, it will not distribute ventilation across the lung in the same way as in spontaneous ventilation. The patient is often supine, meaning that the perfusion of blood is spread preferentially across the posterior aspects of the lungs, rather than matched to the areas of best ventilation. The addition of PEEP, particularly higher PEEP required in problems like ARDS, can impair venous return and the distribution of pulmonary blood. Finally, the state of being ‘big sick’ can create havoc with HPV – acidosis, hypoxia, hypercarbia, the use of ketamine, and the effects of vasopressors/inotropes can all elevate pulmonary pressures.

In an operating theatre environment, we position a patient lateral, with the ‘bad’ lung uppermost, before taking that (non-dependent) lung down. This allows surgical access to the problem side of the chest, while the ventilated ‘dependent’ good lung is provided with better perfusion of blood thanks to gravity and the effect of HPV diverting blood away from the unventilated side. In the retrieval environment, it is problematic to position a patient laterally for transfer while a lung is down. The risk of tube/line dislodgement in that position is higher as monitoring is harder, and pressure area risks higher than when transported supine. That means that perfusion and ventilation might be extremely poorly matched in this patient, and inadequate gas exchange can produce hypoxia and hypercarbia, which in turn can produce a greater afterload for the right heart and poor forward flow into the left heart, with resultant haemodynamic mischief. This brings me to my main take home point:

OLV in PHARM – try not to unless you really can’t avoid it.

Can’t avoid it? Read on.

How to deliver OLV

While there are seemingly myriad devices and options, we can break them down like this:

• Single lumen tube
  • Deliberate endobronchial intubation (obviously easier to select the right lung here, although also easier to accidentally block off the right upper bronchus which branches straight off the right main)
  • Using a bronchial blocker (less common, and probably not relevant to a transport scenario)
• Double lumen tube (of which many flavours exist)

Using a single lumen tube

This is how John did it, and it’s a great option in an emergency. A single lumen ETT is something all crit care clinicians are familiar with, and it’s much easier and faster to position. A bougie can be used to help direct your tube into the right or left main bronchus.

Using a DLT

It’s pretty unlikely that a PHARM team will be required to position a DLT! However, as Laura’s project showed us, every so often we need to move a patient with one in situ, so let’s look at one in a bit more detail.

DLTs, the basics

What most people notice first about the DLT is that it’s big. The sizing is, annoyingly, conventionally described in French – a rule of thumb is 37Fr for women, 39Fr for men. 35Fr and 41Fr are also sometimes used. There are ways of formally assessing this sizing but we won’t focus on that here. It’s also much longer than a conventional ETT, comprising a tracheal lumen and a bronchial lumen. You’ll notice two cuffs – a clear, larger one for the trachea, and a smaller, blue one for the bronchus. Make sure to only use a 5mL syringe to inflate the bronchial cuff and always check cuff pressures. DLTs can be designed for either left main bronchus or right main bronchus insertion. By and large, the vast majority of DLTs used are left. This is because right sided DLTs are more tricky to position to avoid occlusion of that right upper bronchus. With a left sided DLT in situ, both lungs can be ventilated, the right (via the tracheal lumen) or the left (via the bronchial lumen).

Assessing a DLT: Position, position, position

The most common problem with the DLT is dislodgement. Even if the tube is well secured at the teeth (thoroughly recommended, as ever!), that does not exclude the possibility of micromovement at the distal end and dislodgement. The bronchial cuff can herniate into the trachea, or the whole tube can migrate into the left main bronchus. Your steps, in assessing a DLT, are therefore:

• Find out what has been placed
  • size
  • side
  • depth
  • ease of insertion
  • confirm both cuffs up
  • check cuff pressures for both cuffs
• Check that you can ventilate
  • Both lungs
  • Left lung (bronchial lumen in Left DLT)
  • Right lung (tracheal lumen in Left DLT)
• Fibreoptic check of position (using the tracheal lumen)

Using the fibreocope to check position of the DLT is crucial, as you may well need to repeat this throughout the journey. The view from the tracheal lumen should be of the carina, with trachealis lying posteriorly and the right main bronchus disappearing off to the right. The left main bronchus will be obscured by the bronchial lumen, with a visible crescent of the bronchial cuff in view. No visible cuff means the tube is too deep. If the cuff obscures the view of the carina or RMB then the tube is too shallow.

TIP: Do your first check at the referring hospital with the anaesthetist who placed the tube beside you to confirm you are both happy the tube is in a good spot. Take a photo of the ambu screen showing the tube in the correct position. You can use this for comparison if you need to re-review en route.

Moving to one lung

If you need to take your patient from two to one lung ventilation, this is relatively simple once a correctly positioned DLT is in situ. Using either a clamp or a device built into the tube connectors, you can occlude the ventilation of either the tracheal or bronchial lumens. Always perform a clinical check and confirm your ventilator settings and pressures every time you do this. Where possible, an ABG on one lung will help you to understand the quality of gas exchange before you start moving.

Clearly avoiding injury to the one ventilated lung is crucial. As a rule of thumb, aim for a tidal volume of 6mL/kg IBW, with peak airway pressures <35 cmH2O. Aim for PEEP between 5-8cmH2O. Try to avoid using high fractions of O2 given the risk of pulmonary injury from hyperoxia.

Moving a patient who is on one lung

Dislodgement is a common problem. ALWAYS confirm the tube position after repositioning the patient (ie moving to the stretcher), and be suspicious any time you go over a speed bump that the tube may have moved. You will need to have the fibreoscope out and ready to use throughout the transfer to help you do your position check.

Moving back to two lungs

Should you need to ventilate both lungs, be mindful that the unventilated lung will have now collapsed. Much like the metaphor of the deflated balloon, it will require support to help reinflate again. Doing this with hand ventilation via a self-inflating bag is more effective than trying to use the ventilator.

Troubleshooting – hypoxia on one lung

Hypoxia on One Lung is a common anaesthetic exam question which calls for a structured approach. I am a fan of Laura’s ABC-style strategy, which she adapted for our retrieval setting.

Hypoxia on OLV	Stop transport if possible Increase FiO2 to 100% Check breathing circuit connections Have a low threshold for calling DRC for advice
Airway	Confirm DLT depth Examine DLT position using fibreoscope Consider suction
Breathing	Assess the chest – auscultate if you can, otherwise consider lung ultrasound to exclude a new PTX Check ventilator settings, has anything changed? Are you definitely delivering the volumes and FiO2 you have dialled up? Titrate PEEP to the ventilated lung Consider additional O2 to the bad lung – connect a tracheal suction catheter to oxygen tubing and feed down the lumen to the unventilated lung. Insufflate with no more than 2L/min O2 Consider CPAP to the unventilated lung – use a dedicated CPAP device (available in some operating theatres) or attach your laerdel bag + PEEP valve set to no greater than 5cmH2O
Circulation	Consider bedside echo Support cardiac output where necessary to ensure adequate lung perfusion. Consider blood if indicated Be aware that high doses of certain vasoactive/inotropic medications (particularly alpha 1 agonists) may impact on pulmonary vascular pressures
Disability	Ensure adequate sedation Ensure adequate paralysis
Exposure	Check temp and maintain normothermia where possible
Still failing?	Consider switching to intermittent two lung ventilation If you haven’t called for advice yet, you should do so!
Problem solved?	Downtitrate the FiO2 again as tolerated

Finally

Once you have arrived and safely handed over to the receiving team, make sure you reward yourself with an ice cream and a pat on the back! We would love to hear about your case at coffee and cases, or at a HEMS education day!

Some reading

Tarry, D & Powell, M (2017) Hypoxic pulmonary vasoconstriction, BJA Education, Volume 17, Issue 6, June 2017, Pages 208–213, https://doi.org/10.1093/bjaed/mkw076

Heseltine, N & Knowles, A. (2021) Bronchoscopic insertion of double lumen endotracheal tubes and bronchial blockers. Anaesthesia and Intensive Care Medicine, Volume 22, Issue 3, March 2021, Pages142-147 https://doi.org/10.1016/j.mpaic.2021.01.012

Ashok, V & Francis, J (2018) A practical approach to adult one lung ventilation. BJA Education, Volume 18, Issue 3, March 2018, Pages 69-74 https://doi.org/10.1016/j.bjae.2017.11.007

As ever, the supremely excellent Life In The Fast Lane has a great page on Selective Lung Ventilation