Australasian Anaesthesia 2011 - Australian and New Zealand ...

Jet Ventilation and Anaesthesia 79Jet Ventilation and AnaesthesiaA practical guide to understanding jet ventilation and its currentapplications in clinical anaesthetic practiceSASANKA S DHARA, FANZCA, VISITING MEDICAL OFFICER, DEPARTMENT OF ANAESTHESIA, ROYALHOBART HOSPITAL.Dr Dhara is a part time VMO Anaesthetist at the Royal Hobart Hospital. His career includes a long period as Directorof the Anaesthetic Department at Singapore General Hospital. Over his career he has pursued numerous interestsbut especially in the field of difficult airway management and particularly in anaesthesia for head and neck surgery.He has numerous publications in these areas, including the application of high frequency jet ventilation.INTRODUCTIONJet ventilation refers to the form of mechanical ventilation in which the inspiratory gas is delivered into the tracheaat high pressure (101– 405kPa) through a conduit of small diameter. In low frequency (< 1 Hz) mode it is mostlyused for emergency oxygenation (such as in “can’t intubate can’t ventilate” scenarios) but with higher frequency(1–10 Hz) it has numerous applications in anaesthesia and intensive care. This review summarises the physiology,mechanics and practicalities of using jet ventilation, both low and high frequency and then looks at its applicationin a range of clinical anaesthetic settings. This review does not cover the use of High Frequency Jet Ventilation(HFJV) in intensive care.HISTORYThe history of insufflating gases through tracheal cannulae to sustain life goes back several centuries. 1 However,most of our current understanding of the mechanical and physiological aspects of jet ventilation and its applicationsin anaesthesia and intensive care practice has developed through the 1970s and 80s. The most important pioneeringarticles [2-10] are summarised in table 1.Table 1. Landmark publications on transtracheal oxygenation and jet ventilation 2-10Jacoby 1951Jacoby 1956Sanders 1967Spoerel 1971Oultol 1971Jacobs 1972Smith 1973 & 1975Klain & Smith 1977Percutaneous, transtracheal, apnoeic oxygenation with 4-5L/min of oxygen.Use of the above technique for oxygenation in patients with airway obstruction.Jet ventilation at 344 kpa (50 psi) through a rigid bronchoscope providing unhinderedEarliest description of elective, percutaneous, trans tracheal jet ventilation (PTTJV) duringanaesthesia.Description of a dedicated jet channel in a Jako laryngoscope for ventilation duringlaryngoscopic procedures.Intermittent insufflation with a pressure of 413kpa (60psi) for resuscitation.Report of a series of patients undergoing PTTJV during elective surgery as wellDevelopment of a fluid logic based jet ventilator capable of 60-100 breaths per minute.MECHANISM OF ACTION OF HFJVHFJV is unusual in that it can produce adequate respiratory gas exchange even when the apparent tidal volume isa fraction of the anatomical dead space. It is thought that there are several mechanisms involved in driving gasexchange during high frequency jet ventilation, each at different levels of the respiratory anatomy having differentflow profiles and resistance characteristics. 11-12Within the trachea and large airwaysThere is direct ventilation of alveoli close to main bronchi in the normal manner by convection or “bulk flow”. Thehigh velocity stream of inspiratory flow occurring with a jet creates additional flow from entrainment in the presenceof a patent proximal airway. In low frequency jet ventilation, this entrainment will form a significant part of the tidalvolume. Together, the high velocity stream and entrainment cause turbulence and this leads to enhanced gas mixing.