THRIVE: a solution to the difficult intubation on labour ward?
It is well recognized that intubation of the parturient is difficult; for many years there has been little change from a recognized failure rate of 1 in 390 . Increased fatty tissue, increased pharyngeal and laryngeal tissue oedema, full dentition and large breasts combined with both a reduced oxygen reserve and increased oxygen consumption can rapidly lead to multiple attempts at laryngoscopy and subsequent desaturations. This highly pressurized scenario negatively impacts on an anesthetist’s ability to perform, resulting in human error and consequent failure [2, 3].
THRIVE (transnasal humidified rapid-insufflation ventilatory exchange) can increase oxygenated apnoea time to an average of 17 minutes and up to 65 minutes in some individuals . A trans-nasal oxygen delivery device, such as Optiflow, is applied to the patient prior to induction and flow rates of 70 litres per minute of humidified oxygen are delivered. This provides pre-oxygenation and maintains oxygenation without ventilation throughout induction and paralysis, until a definitive airway is achieved. In a recent randomised controlled trial comparing the use of facemask pre-oxygenation and THRIVE in a rapid sequence induction, the use of THRIVE resulted in an extended apnoea time during intubation and no difference in post intubation PaO2 . The maintenance of oxygenation is achieved through a combination of aventilatory mass flow, together with continuous positive airway pressure and gaseous exchange by flow dependent dead space flushing. Provided the airway remains patent, THRIVE has proven efficacy in both stridulous and obese individuals .
Figure 1: Optiflow applied to a patient. (Figure courtesy of Fisher Paykel Healthcare)
Use of THRIVE may transform managing the difficult obstetric airway from a pressurised, anxious situation to one where there is time to carefully make considered decisions. By dramatically increasing the time to desaturation, THRIVE may enable secondary and tertiary airway intubation plans to be enacted without recourse to bagging to maintain oxygenation. The method may buy time for more senior help to arrive to assist the struggling junior trainee.
A transnasal delivery device such as Optiflow could be prepared for immediate use within obstetric theatres, set up ready to be applied for a Category 1 Caesarean section call. The transnasal device is comfortable and acceptable to almost all patients. Despite high oxygen flow rates, the humidification means it is well tolerated. Many patients prefer it to the claustrophobia of pre-oxygenation with a full face mask. Some obstetric anaesthetists like to pre-oxygenate whilst attempting a 'rapid sequence spinal' and this also would be possible with the transnasal device in place.
After induction of anaesthesia, if it becomes apparent that laryngoscopy is likely to be difficult, and intubation of the trachea will not be immediate, anaesthesia will have to be maintained by other routes. This can easily be achieved with a propofol infusion, again, prepared in advance for the emergency situation. Until the trachea is intubated, cricoid pressure can be maintained.
There could be two criticisms with the use of THRIVE during the rapid sequence induction of a parturient. The first is that the aim of a rapid sequence induction in a parturient is to achieve intubation of the trachea, and a definitive airway, as quickly as possible. THRIVE will not achieve this. However, we maintain that by eliminating the anxiety associated with recurrent desaturation and intubation attempts, anesthetists may be better placed to perform under pressure. The risk of aspiration could actually be reduced using THIRVE in a difficult airway, as the need to bag the patient to maintain oxygenation and anaesthesia, is eliminated.
There may also be concerns about the wellbeing of the fetus. A Caesarean section under general anaesthesia is most frequently required when the fetus is severely compromised. A rise in carbon dioxide associated with prolonged apneoa may be further detrimental to the situation. However preliminary studies have shown that the rate of rise of CO2 with THRIVE in place is not as rapid as has been described during total apnoea. The rate of rise of end tidal CO2 is only 0.15 kPa.min-1, considerably less than the usual rate of rise of during apneoa (0.35-0.45kPa.min-1) . Provided that other physiological parameters are maintained, the maintenance of oxygenation during intubation attempts may mean THRIVE is actually beneficial to the fetus.
Our experience of THRIVE in the difficult airway suggests that it may have a very useful role of providing a safe extended apnoea window in the obstetric rapid sequenceinduction. It has the potential to transform difficult intubation of the parturient into a more relaxed and considered undertaking, consequently reducing the associated morbidity of multiple failed intubations attempts. We look forward to working with obstetric units in the future to introduce this method.
Consultant Anaesthetist, Royal National Throat, Nose and Ear Hospital, London UK
1. Kinsella SM, Winton AL, Mushambi MC, Ramaswamy MC, Swales H, Quinn AC, Popat M. Failed tracheal intubation during obseteric general anaesthesia: a literature review. Int J Obstet Anesth 2015; 24: 356-374.
2. Preston R. Management of the obstetric airway - time for a paradigm shift (or two)? Inj J Obstet Anesth 2015;24: 293-296.
3. Flin R, Fioratou E, Frerk C, Trotter C, Cook TM. Human factors in the development of complications of airway management: preliminary evaluation of an interview tool. Anaesthesia 2013; 68: 817–825
4. Patel A, Nouraei SAR. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE): a physiological method of increasing apnoea time in patients with difficult airways. Anaesthesia 2015; 70: 323–329
5. Mir F, Nouraei, R, Iqbal R, Cecconi M, Patel A. Use of Transnasal Humdified Rapid-Insufflation Ventilatory Exchange (THRIVE) for rapid sequence induction. WAMM 2015 Abstracts; 006