THRIVE, or apnoeic oxygenation, is not explicitly mentioned in the curriculum, though is included here as one must be able to describe "equipment and airways devices used for surgery on and below the vocal chords".
Induction of anaesthesia and neuromuscular blockade begins an apnoeic window, during which a failure to secure an airway will:
Cause hypoxia
Result in the need to re-oxygenate the patient before further attempts at securing the airway are made
Potentially lead to morbidity and mortality e.g. airway trauma, cardiorespiratory decompensation, CICO scenarios
Enter: THRIVE
Trans-nasal Humidified Rapid-Insufflation Ventilatory Exchange is a method for increasing safe apnoea time (by up to 65mins!) in patients with difficult airways
In addition to prolonging safe apnoea time, THRIVE can:
Optimise peri-procedural oxygenation
Increase the margin of safety for securing a definitive airway
Facilitate training in difficult airway management
Facilitate tubeless airway surgery
Oxygenation
The USP is apnoeic oxygenation a.k.a aventilatory mass flow
This is possible owing to the difference between:
The rate of alveolar oxygen removal: ~250mls/min
The rate of alveolar carbon dioxide excretion: 20mls/min
This generates a negative pressure gradient of up to 20cmH2O
The pressure gradient draws oxygen from the pharynx into the lungs
Therefore, if pharyngeal oxygen concentration is increased e.g. using HFNO, you can increase the oxygen drawn into the lungs
HFNO provide a degree of flow-dependent PEEP generation (up to 7cmH2O), although this is not the primary mechanism of oxygenation during apnoea
Ventilation
Pulsatile movement of blood within the pulmonary vasculature causes compression and expansion of the small airways
These cardiac oscillations interact with highly turbulent supraglottic flow vortices to enhance CO2 removal from the lower airways
Said CO2 removal aids alveolar oxygenation (see: alveolar gas equation)
There is also flow-dependent flushing of dead-space
Despite this, PaCO2 increases by 0.15kPa/min during apnoeic oxygenation and does not reach a steady state
One must have a patent upper airway for THRIVE to work
THRIVE is not suitable for airway rescue e.g. CICO or total airway obstruction
Contra-indicated if:
Known or suspected base of skull fracture e.g. post-pituitary surgery
Airway surgery utilising LASER or diathermy due to airway fire risk
Obesity
The greater tissue metabolic demands of obese patients, and a general habitus ill-suited to oxygenation, perhaps limit the effectiveness of THRIVE in obese patients
Evidence from several RCT's of obese patients (without other major cardiac or respiratory disease) undergoing elective bariatric surgery seems to demonstrate some benefit for HFNO during periods of apnoea compared to other methods of oxygenation:
In an RCT from 2019,
Wong and colleagues compared HFNO against facemask oxygenation in patients with a BMI >40kg/m2
They found safe apnoea time was significantly (>1min) longer in those where HFNO was used
The minimum peri-intubation saturations were non-significantly higher in the HFNO group
An RCT from 2021 of patients with a BMI >35kg/m2
compared HFNO to nasal cannulae for apnoeic oxygenation
They found a significantly increased duration of apnoea until desaturation to <95% using HFNO vs. nasal cannulae
Patients with HFNO had a non-significantly lower risk of reaching saturations <95%, and a lower rate of decrease of PaO2
There was no difference in the rate of increase of carbon dioxide
A further similar RCT in 2022 again
compared HFNO vs. facemask oxygeation in those with a BMI >40kg/m2 and found:
The risk of desaturation to <92% within 18mins of apnoea was significantly lower in the HFNO group
In those who did saturate, there was a non-significantly increased time to desaturation in the HFNO group (median 8mins) vs. the facemask group (median 4mins)
HFNO didn't appear to significantly increase PaO2
CO2 accumulation was still an issue to the tune of 0.23kPa/min, a higher rate than that quoted above
Laryngeal surgery
In a 2017 case series
of 28 patients undergoing laryngeal/tracheal surgery using THRIVE and apnoeic oxygenation, the median apnoea time was 19mins
The authors deemed THRIVE "satisfactory" for tubeless laryngeal surgery
In view of the greater frequency of desaturation, hypercarbia, and requirement for rescue intervention, the authors conclude HFNO should only be used with caution in this cohort
Naturally, the decision to use THRIVE vs. other methods of oxygenation will depend on various surgical & patient factors, so should be discussed with your friendly neighbourhood surgeon