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50196756413500Lung isolation and COVID-19M Steven, D Reid, B Shelley.Contact: mark.steven@gjnh.scot.nhs.ukIntroductionThe majority of thoracic surgical procedures require lung isolation. This is a skilled and technical task that puts the anaesthetist at risk as many of the steps involved in achieving and troubleshooting lung isolation are Aerosol Generating Procedures (AGP).The aim of this paper is to consider advantages and disadvantages of the available methods and to suggest options that minimise this risk while continuing to provide effective operating conditions. It is not intended to address PPE. It will be essential to keep up to date with national guidance on what level of PPE is appropriate for each patient risk group. These measures are all relatively simple and readily introduced into everyday practice. They can therefore be used in every patient requiring lung isolation. This will confer protection to the anaesthetist at this time when the risk from asymptomatic carriers is as relevant as proven Covid-19 positive patients. Normal practice and risksPre-oxygenation and inductionBag and mask ventilation:Typically utilised to allow sufficient time for muscle relaxation and optimal intubating conditions. High risk of AGP and environmental pollution through use of positive pressure ventilation and variable mask/ face seal.Intubation:High risk of AGP through manipulation of airway requiring close proximity of anaesthetist.Bronchoscopy:Utilised at various stages through the operation. This will include confirming correct tube placement and identifying anatomy+/- surgical pathology. It will also be used to troubleshoot hypoxia or ventilation problems, observe surgical suture lines and suction clearance of secretions. High risk of AGP as bronchoscopy requires open access to airway through disconnected or opened angle piece, agitation of airway and handling of a contaminated bronchoscope. (Especially with repeated use in the same patient.)Lung isolation:The angle piece arm to the surgical lung has to be clamped to prevent ventilation and the lumen to the surgical lung has to be opened to air. High risk of AGP as surgical lung collapses passively expelling alveolar air into the environment.CPAP:Used to surgical lung for correction of shunt driven hypoxia. Given either using a specific CPAP circuit or Oxygen via a suction catheter to the surgical lung. High risk of AGP as continuous venting of expelled air from surgical lung into the environment.Lung recruitment/reinflation:This can be used to manage hypoxia or to help surgeon assess surgical repair/ lung injury. High risk of AGP as high pressure ventilation may expose leaks from within the circuit, the ETT/DLT or injured parenchyma leading to environmental pollution of alveolar air.Extubation:High risk of AGP.Methods to achieve lung isolationSingle Lumen Tube (SLT)Uncut ETT can be advanced into the dependent/ non-surgical lung. Pro:SimplicityQuicker, more efficient intubationLess traumatic than larger DLT Could be checked clinically without using bronchoscope No requirement for ETT exchange for continued ventilation in ICUOption of using Bronchial blockerCon:Surgical lung when isolated will expel air passively, bypassing the ETT and polluting environment (AGP)No access to surgical lung during isolation for bronchoscopy, suction or CPAPUnpredictable collapse of surgical lungOcclusion with failure to ventilate the RUL when sited in Right Main Bronchus(RMB)Bronchoscopy likely to still be required to railroad and site ETT in bronchus especially when targeting the Left Main Bronchus(LMB) (AGP)Bronchial blocker (BB)Arndt, Vivasight and Cohen blockers are most commonly usedPro:Sited through a SLT and therefore most of the same advantages with the exception of No.4 above.Can be used in existing ETT when taking a patient from ICU to theatre. This would avoid messy tube exchange. NB minimum ETT size for 9.0Fr bronchial blocker will be 8.0mm. Con:Absolute requirement for bronchoscopy to confirm correct placement (AGP)High volume, low pressure cuff provides less reliable seal than DLT (Leak =AGP)Higher incidence of intra-operative displacement and need for repositioning, requiring bronchoscopy (Leak= AGP)Blocker remains open to air during lung collapse with continuous environmental pollution (AGP)No access to surgical lung during lung isolationLimited ability to suction or CPAP surgical lung during lung isolationDouble Lumen Tube (DLT)The vast majority of experience in the UK is achieving lung isolation with a DLTPro:Most efficient method in experienced handsRepositioning rarely required (Left more so than Right)Access to the surgical lung throughout for bronchoscopy, suction or CPAP (AGP)Can be placed without bronchoscopyCon:Bronchoscopy is the norm and can be utilised throughout the case (AGP)The lumen to the surgical lung is opened to facilitate collapse. There is direct environmental pollution of alveolar air (AGP)Placement can be traumatic (AGP)Larger size of DLT causes problems in difficult airway potentially requiring airway manipulation and multiple attempts (AGP)Too bulky for continued/ long-term ventilation requiring exchange to SLT at end of surgery (AGP)More difficult in RSI leading to prolonged intubation +/- multiple attempts (AGP)It would be sensible for an individual anaesthetist to use the technique for lung isolation that is most familiar to them. This will minimise the risks of AGP while managing lung isolation.The remainder of the paper therefore concentrates on the DLT. All of the techniques can be adapted for use with either an uncut SLT or SLT/BB. Special consideration will need to be given to intubated patients transferred to theatre for surgery where a SLT has been used to secure the airway and similarly patients who will require ICU care post-operatively. These patients may have high FiO2 and ventilator requirements. Tube exchange in these patients will carry a significant risk of Aerosol Generation(AG) and clinical decompensation which will make a SLT +/- a bronchial blocker a more attractive and safer option.How to minimise AGP during lung isolationThere is existing guidance to minimise COVID exposure during intubation. This can be adapted according to local practice for lung isolation in Thoracic anaesthesia.Key principles:Minimise personnel in theatre for intubation. This should include anaesthetist, assistant (Nurse/ODP) and theatre assistant.Most experienced anaesthetist plans and performs intubationBrief to cover induction and intubation planNecessary airway equipment prepared and available. This will include selected laryngoscope/s, 12 or 14 gauge 800mm bougie and airway adjuncts. Sized SLT or DLT with different sizes available immediately from clean area. Clamp x 2, an additional HEPA viral filter(HEPAvf) and a stethoscope.Adequate pre-oxygenation for 3 minutes or ETCO2 >90%. The aim is to achieve sufficient apnoeic time to allow safe intubation.Modified RSI using high dose rocuronium or equivalent.Avoid bag/mask ventilation if possible. (Any bag/mask ventilation provided should use a 2 operator technique to optimise face seal and minimise airway pollution.)Intubation with immediate inflation of tracheal and bronchial cuffs.Connect circuit and confirm bilateral ventilation. Confirm DLT placementClinical check (If aim to avoid bronchoscopy)Placement of DLT can be checked without disconnection of the circuit. The following applies to a left-sided DLT;No clamp applied and bilateral air entry is a good start.No clamp and isolated L sided air entry suggests the DLT has advanced too far into LMB. Do not deflate bronchial cuff and slowly withdraw DLT until bilateral air entry returns.No clamp applied and isolated R sided air entry suggests a RMB intubation. This will be corrected most efficiently using a bronchoscope. (Refer first to bronchoscopy technique) This will minimise AGP. There will be guidance for this salvage procedure at the end of the paper.Apply clamp to tracheal lumen, do not open angle piece or disconnect. Confirm only ventilating Left side. If continue to ventilate bilaterally then distal end of DLT or the bronchial cuff are above the carina. Deflate only the bronchial cuff and advance the DLT until held up. Re-inflate the bronchial cuff and repeat steps above. If there is resistance to advancing the DLT or still unable to confirm correct placement clinically then will require bronchoscopy to troubleshoot placement.If confident DLT is correctly placed, then continue with surgery. This process will need to be repeated after turning the patient to ensure the DLT position has not changed.These steps may avoid the need for bronchoscopy and therefore significantly reduce the risk of AGP. However, if the necessary preparations are made and steps followed bronchoscopy can be performed with minimal risk and will provide the most reliable means of confirming and troubleshooting tube placement.BronchoscopyThe risk of AGP will be extremely high if attempts are made to perform bronchoscopy while actively ventilating the patient or if the patient is inadequately paralysed and able to generate a cough. Consider increasing FiO2 to 100%Ensure bronchoscope is prepared and ready for useEnsure adequate muscle relaxation.Turn ventilator off and ensure APL valve is fully open (Zero cmH2O)Clamp tracheal lumen of DLT and clamp arm of angle piece connected to tracheal lumen (1a). This will ensure you can disconnect this arm without pollution (1b).Apply HEPAvf to tracheal lumen (1c) and remove clamp from tracheal lumen to allow pressure from lung to vent through HEPAvf(1d). This will take a few seconds only.Remove HEPAvf and perform bronchoscopy to confirm tube placement, orientation of bronchial cuff and R sided anatomy (1e).Reconnect angle piece and remove remaining clamp to ventilate both lumens.Repeat process on bronchial lumen to allow brochoscopic confirmation that distal end of bronchial lumen is above the LMB bifurcation.Repeat process after turning the patient to ensure no tube movement has occurred965327035115500This should ensure that DLT position can be confirmed with minimal Aerosol Generation(AG) and contamination.-5080762000-12701143000-50801143000Lung isolationThe main threat of environmental contamination once the airway is secured and surgery underway is from having the lumen to the surgical lung disconnected and open to air for deflation. The application of a HEPA viral filter to the tracheal lumen will protect against any peri-operative loss of lung isolation where a leak of any ventilated gas into the tracheal lumen would otherwise cause environmental pollution and contamination.Patient positioned and surgery underway. Lung isolation required.Apply clamp to surgical lumen of DLT.Apply clamp to arm of angle piece serving this lumen.Disconnect this arm of angle piece and apply HEPAvf to surgical lumen of DLTRemove clamp from surgical lumen of DLT to facilitate collapse of the surgical lung through the HEPAvf.Ensure the HEPAvf remains attached (2) throughout the duration of lung isolation, only remove for specific procedures and reconnect when finishedBronchoscopy performed following lung isolation at other times through the course of surgery should follow the same principles as in bronchoscopy above. This may be required to troubleshoot hypoxia, ventilation issues or following surgical request:Consider increasing FiO2 to 100%Ensure bronchoscope is prepared and ready for useEnsure adequate muscle relaxationTurn ventilator off and ensure APL valve is fully open (Zero cmH2O)Remove HEPAvf from tracheal lumenPerform bronchoscopy through tracheal lumenReattach HEPAvf to tracheal lumen after every interventionIf there is indication to bronchoscope the ventilated lung, then repeat the process above using the 2 clamps and the HEPA viral filter.CPAPExisting techniques for applying CPAP will lead to a high risk of Aerosol Generation. This excludes administration of oxygen via a suction catheter through the lumen to the surgical lung.It is possible to attach a CPAP circuit to the HEPAvf to the surgical lung (3a, 3b). It is unclear how the resistance of the filter will reduce the measured level of CPAP. The CPAP could still be titrated until there is clinical improvement. -5080762000If this option is not available, then it may be possible to safely generate CPAP to the surgical lung using the following:Increase oxygen to 100%Ensure adequate muscle relaxationRemove the HEPAvf (2) and reconnect angle piece to the surgical lumen (4a) (Clamp is still in place to prevent ventilation)Turn ventilator off and ensure APL valve is fully open (Zero cmH2O)Remove clamp from angle piece to surgical lumen and apply oppositely to the ventilated lung. Do not disconnect the angle piece (4b)Raise CPAP valve to desired level, when airway pressure within the surgical lung has reached this level then apply a second clamp to the surgical lumen of the DLT. This will trap 100% O2 at the desired pressure within the surgical lung.Remove clamp from the dependent/ non-surgical lung and resume ventilation at the previous FiO2 (4c). A recruitment manoeuvre can be performed as required.It may be necessary to repeat this process at regular intervals to maintain a reasonable level of CPAP within the surgical lung.-5080762000-1270762000-5080762000If hypoxia is problematic and all treatable causes have been excluded, then the only option left would be intermittent 2 lung ventilation. ExtubationSimilar to intubation there is existing guidance to minimise COVID exposure during extubation. This can be adapted according to local practice for extubation in Thoracic anaesthesia with a DLT.CaveatsA DLT is a bulkier tube, more prone to produce coughing and potentially biting. High risk of Aerosol Generation(AG) compared to SLT extubation.Respiratory patients generally have irritable airways and more copious secretions. High risk of AG.Deep extubation may appear attractive but significant risk of narcotised patient having poor tidal volumes, breath holding, developing atelectasis and needing airway support either with airway adjuncts or manual manoeuvres. Additional risk of coughing and laryngospasm as anaesthesia lightens.General principlesOnly essential staff in theatre for extubation.All staff wearing appropriate PPE for the patient risk group.Endobronchial suction, if necessary, should be performed before reversing muscle relaxation.Facemask, nasal cannulae and/or Hudson mask available.Oropharyngeal suction to clear all secretions.Do not suction via SLT/DLT at the point of extubation. This would precipitate coughingPatient breathing spontaneously in an upright position on bed/trolley. No Pressure Support and APL valve at zero at point of extubation to ensure to minimise positive pressure within the airway.Full reversal of muscle relaxation confirmed.Clinical waste bin placed beside patient for immediate disposal of removed tube.Disconnect circuit leaving the HEPAvf and angle piece attached to the tube.Extubate patient and place tube directly in the clinical waste.Apply Hudson mask directly. This will avoid changing the facemask over at a time when the patient is potentially coughing.Apply surgical facemask over Hudson mask if applicable. This will cover the entrainment vents on the mask and reduce the risk of contamination from coughing.Nasal cannulae can be used in place of the Hudson mask if FiO2 requirements are acceptable.Wait for 10 minutes post extubation before transferring patient from theatre (this time may vary according to the current advice).DLT with embedded camera These DLTs have been manufactured to provide continuous monitoring of DLT position relative to the carina. Once correctly sited they may reduce the incidence of bronchoscopy and subsequently risk of exposure during lung isolation. These DLTs utilise an integrated flushing system to clean the camera should the view become obscured. Care will need to be taken as the necessary lavage and suction will involve aerosol generation.There will be a learning curve associated with using these if unfamiliar and the camera will not replace the wider uses of bronchoscopy during lung isolation. The principles of minimising the risk from AG during lung isolation are exactly the same for these DLTs as for the standard DLT described above.It would be sensible for an individual anaesthetist to use the technique for lung isolation that is most familiar to them. This will minimise the risks of AGP while managing lung isolation.Management or RMB intubation with L DLTThe DLT will need to be repositioned in the LMB expediently to minimise AG and risk of contamination. The most experienced anaesthetist performs bronchoscopy and manipulation of the DLT.Ventilate with 100% oxygen.Do not deflate the tracheal cuff. The tracheal cuff should remain inflated throughout. This will ensure there is no leak generated while the DLT is moved. It will also serve as a break at the level of the vocal cords to minimise the risk of inadvertent extubation.The bronchial cuff should be deflated.Turn ventilator off and ensure APL valve is fully open (Zero cmH2O).Clamp bronchial lumen of DLT and clamp arm of angle piece connected to bronchial lumen. This will ensure you can disconnect this arm without pollution.Apply HEPAvf to bronchial lumen and remove clamp from bronchial lumen to allow pressure from lung to vent through HEPA. This will take a few seconds only.Remove HEPAvf and insert bronchoscope to distal end of DLT bronchial lumen. This should reveal the terminal bifurcation of bronchus intermedius into right middle and lower lobe bronchi.Withdraw DLT under direct vision until carina is visible.Guide bronchoscope down LMB.Railroad DLT over bronchoscope and confirm distal end of bronchial lumen is above upper and lower lobe bifurcation.Remove bronchoscope, reconnect angle piece, remove clamp and resume ventilation.Confirm bilateral ventilation.Follow previous steps for safe bronchoscopy to now visualise the RMB and confirm correct DLT placement. Inflate bronchial cuff under direct vision.Continue with surgery.SummaryLung isolation and thoracic surgery will have a significant risk of aerosol generation and potential contamination of the anaesthetist and theatre staff.The measures described are designed to minimise the risk but will not negate the risk entirely. ................
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