A colleague (Dr Bisanth Batuwitage) recently attended the Difficult Airway Society Annual Scientific Meeting, in Ascot, November 2013.
In order to allow those who were unable to attend the meeting to gain a flavour of the topics covered by the speakers he has kindly created a summary of the key points of each talk.
The RCOA Matrix Codes for each talk are shown along with the details of the speaker.
How we cause and treat airway stenosis (2A01, 3A02): Mr Guri Sandhu, Imperial College/UCL
- More than 50% of cases of adult laryngotracheal stenosis are due to a period of ventilation on ICU.
- Incidence is unknown, risk factors: size of tube, cuff pressures, immunity, infection and natures of patients healing biology.
- The remainder of cases is due to disorders such as Wegener’s granulomatosis, idiopathic subglottic stenosis and sarcoidosis.
- Nearly two thirds of tracheal reconstructions can be managed endoscopically, the surgeon and anaesthetist need to work closely and utilize shared airway techniques.
- They usually perform IV induction, give muscle relaxant and ventilate with positive pressure down an LMA.
- They use a technique of suspension laryngoscopy and supraglottic jet ventilation at high frequency (100 breaths per minute) delivered by an automated device (Mistral/Monsoon, Acutronic systems). This device alarms if the delivered jet or return of gas is obstructed.
- They prefer this technique as it employs an open breathing system, so there is no need for an airtight connection between the airway and the breathing system. Thus, the trachea can be open with good surgical access and ventilation still maintained
Gas induction for critical airways in adults is pointless (2A01, 2A06): Dr Anil Patel, Royal National Ear, Nose and Throat Hospital
- When an inhalational induction is commenced in a patient with a severely obstructed airway, despite the application of CPAP and PEEP, induction is slow there are apnoeic periods and the patient often becomes hypoxic and hypercarbic, there are long periods of instability, arrhythmias and episodes of total airway obstruction.
- Following airway obstruction the patient often does not awaken and relieve the obstruction, apnoea continues and the hypoxia worsens.
- If this continues in clinical practice the use of positive pressure is required to relieve the hypoxia. Positive pressure ventilation following IV induction and muscle paralysis is physiologically superior to spontaneous respiration in adult stridulous patients with airway compromise due to laryngotracheal stenosis.
Physiological problems with inhalational induction and maintenance of spontaneous ventilation:
- Reduction in airflow
- Reduction in respiratory drive as anaesthetic depth is increased
- Increased collapsibility of the airway
- Increased work of breathing
- Critical instability at points of narrowing leading to further airway collapse
- Reduction in FRC
- The only mechanisms to counteract these changes in a gas induction are to provide CPAP and PEEP.
- For non-obstructed adult airways and children this is often enough but for critically obstructed adults airways the application of CPAP and PEEP is not enough to counteract the physiological principles that impair inspiratory airflow and ultimately obstruct the airway.
- Positive pressure ventilation however produces positive pressure during both phases of ventilation by positive pressure of the bag during inspiration and elastic recoil of the lungs on expiration.
Ultrasound in Airway management (1A03, 2A12): Dr Michael Seltz Kristensen, Righospitalet University Hospital, Copenhagen, Denmark.
Ultrasound hardly penetrates air: as soon as the beam reaches air a strong echo appears, this is seen as a bright white line, this line delineates the border between tissue and air; everything beyond it is artifact. The airway can be visualised with US from the tip of the chin until the mid-trachea and pleura.
Clinical applications of airway ultrasonography:
- Screening of difficult airway management
- Diagnosing pathology that can affect airway management
- Identification of the cricothyroid membrane
- Measuring gastric content prior to airway management
- Airway related nerve blocks
- Prediction of appropriate diameter of ET tube or tracheostomy tube
- Differentiating between tracheal and oesophageal intubation
- Differentiating between tracheal and endobronchial intubation
- Confirmation of gastric tube placement
- Diagnosis of pneumothorax
- Differentiating between different causes of dyspnoea/hypoxia and pulmonary oedema
- Prediction of successful weaning from ventilator
- Localisation of trachea and tracheal ring interspaces for tracheostomy and percutaneous dilatational tracheostomy
Dr Kristensen admits that a lot of these techniques are research based although the two that he thought had real potential to have an impact on clinical practice are localising the trachea/cricothyroid membrane when it cannot be identified easily and the detection of a pneumothorax.
His group’s website is http://www.airwaymanagement.dk/ultrasonography-in-airway-management
Every Obstetric GA does not have to be a Rapid Sequence Induction (2B05, 3B00): Dr Wendy Teoh, KK Women and Children’s Hospital, Singapore
- Mallampati score has been shown to increase in pregnancy and labour.
- In obstetric patients Mallampati class 3 and 4 strongly associate with difficult laryngoscopy, with increased relative risks of 7.6 and 11.3 respectively.
- The use of “Macintosh-like” videolaryngoscopes (eg C-MAC, McGrath) are being used as a first line device for securing the maternal airway on a routine basis in some units.
- Increasing reports of supraglottic airways not only used as a rescue device but also for elective cesarean sections (may want to avoid intubating e.g Pre-eclampsia).
Declining use of general anaesthesia in obstetrics: implications for training and strategies for improvement (2B02, 3B00): Dr Ashutosh Wali, College of Medicine, Texas, USA
- The use of general anaesthesia for cesarean section has decreased from 45% in 1981 to 0.7% in 2005 in the United States. A similar decline over the same period has been seen in the UK, 79% to less than 10%.
- Lack of exposure of GA for caesarean section resulted in a severe lack of exposure amongst US trainees and many residents graduated without having performed a GA in an obstetric patient.
- Solutions to the decline include use of a structured advanced airway management rotation, formal repetitive training of difficult airway algorithms on manikins and in the operating room on non-obstetric healthy patients and use of simulation based training.
DAS/OAA Obstetric difficult airway guidelines (1H02, 2B05): Dr Mary Mushambi, Leicester Royal Infirmary
- Update on the DAS/OAA national obstetric difficult airway guidelines. The project is expected to take around 2 years to complete.
- Needs to be different to standard DAS guideline due to physiological/anatomical changes of pregnancy, presence of foetus and remoteness of delivery suite theatres in many hospitals.
- There is currently no national airway guideline in the UK and wide variation in practice.
- The guidelines working party of the OAA published six example guidelines on their website having invited hospitals to submit their local guidelines.