The Theoretical Basis for Using Apnoeic Oxygenation via the Non-ventilated Lung during One-lung Ventilation to Delay the Onset of Arterial Hypoxaemia

Apnoeic oxygenation during neonatal intubation

'Apnoeic oxygenation' describes the diffusion of oxygen across the alveolar-capillary interface in the absence of tidal respiration. Apnoeic oxygenation requires a patent airway, the diffusion of oxygen to the alveoli, and cardiopulmonary circulation. Apnoeic oxygenation has varied applications in adult medicine including facilitating tubeless anaesthesia or improving oxygenation when a difficult airway is known or anticipated. In the paediatric population, apnoeic oxygenation prolongs the time to oxygen desaturation, facilitating intubation. This application has gained attention in neonatal intensive care where intubation remains a challenging procedure. Difficulties are related to the infant's size and decreased respiratory reserve. In addition, policy changes have led to limited opportunities for operators to gain proficiency. Until recently, evidence of benefit of apnoeic oxygenation in the neonatal population came from a small number of infants recruited to paediatric studies. Evidence specific to neonates is emerging and suggests apnoeic oxygenation may increase intubation success and limit physiological instability during the procedure. The best way to deliver oxygen to facilitate apnoeic oxygenation remains an important question.

One-lung ventilation duration-dependent stress response in thoracotomies and the effect of a low-volume, high-frequency differentiated ventilation strategy on this response

Background

This study aims to investigate the effect of ventilation of the non-ventilated lung in patients undergoing one-lung ventilation by a separate low-tidal-volume (1 mL/kg) ventilator at high frequency (30/min) on preventing the effect of one-lung ventilation-associated oxidative damage.

Methods

The study included 45 patients (24 males, 21 females; mean age 54.6±7.7 years; range, 18 to 65 years) with an American Society of Anesthesiologists risk group of 1 to 2 and scheduled for elective thoracotomy. Patients were randomly divided into three groups as those due for thoracotomy without one-lung ventilation (group 1, n=15), those due for thoracotomy with one-lung ventilation (group 2, n=15), and those due for thoracotomy in whom both lungs were ventilated (group 3, n=15). Blood specimens were collected for ischemia-modified albumin, malondialdehyde, and lactate measurements one minute before one-lung ventilation (t0), 30 minutes after one-lung ventilation (t1), 60 minutes after one-lung ventilation (t2), and at postoperative 24th hour (t3). For group 1, t0 was defined as the time at which the thorax was opened.

Results

A statistically significant increase in ischemia-modified albumin, malondialdehyde, and lactate levels occurred in group 2 as the duration of one-lung ventilation increased (p<0.01). Plasma ischemia-modified albumin and malondialdehyde levels in group 3 were statistically significantly lower at t1, t2, and t3 compared with group 2 (p<0.01). Plasma lactate levels were significantly lower in group 3 at t1 (p<0.05) and t3 compared with group 2 (p<0.01).

Conclusion

Separate ventilation of the non-ventilated lung with low tidal volume and high frequency reduces the response to one-lung ventilation-associated oxidative stress in thoracic surgery.

Arterial Oxygen Desaturation during only one of two Similar Thoracoscopic Procedures on the Same Patient

The present report describes two similar thoracoscopic procedures performed on the same 81-year-old male patient. Because acute hypoxia had developed during one-lung ventilation on the first occasion, serial blood gases were taken during the second. Also, whereas on the first occasion the non-ventilated lung had been left open to air when one-lung ventilation was initiated, on the second it was connected to an ambient pressure oxygen source with the object of theoretically enabling apnoeic oxygenation during lung collapse. It is argued that this fundamental difference in anaesthetic practice may have contributed to the improved oxygenation that was recorded during the second thoracoscopy.

The role of an ambient pressure oxygen source during one-lung ventilation for thoracoscopic surgery

Video-assisted thoracoscopic surgery is facilitated by prompt collapse of the non-ventilated (‘operated’) lung, and interrupted and impeded if there is a need for oxygen (O2) delivery by continuous positive airways pressure in order to manage hypoxaemia. It has been proposed that connecting an ambient pressure O2 source to the airway of the non-ventilated lung at the time one-lung ventilation is initiated and before the chest is opened will, by avoiding entrainment of ambient nitrogen, serve to facilitate lung collapse. It has also been proposed that leaving the O2 source connected will enable, not only ongoing apnoeic oxygenation before the chest is opened, but also the thoracoscopic procedure to commence with the operated lung fully pre-oxygenated (with an inspired oxygen fraction of 1), and apnoeic oxygenation to continue throughout the operative procedure in those patients who exhibit a degree of small airways patency at ambient pressure. In reality, several factors can influence the speed of collapse of the operated lung, and very many factors can influence the incidence of hypoxaemia during one-lung ventilation. It therefore appears unlikely that the necessary evidence to support these proposals will be forthcoming from randomised clinical studies on large numbers of patients. Rather, the necessary evidence may only be provided by specifically designed within-patient clinical measurement studies. Nevertheless, it is argued that, in the meantime, there is already sufficient rationale for an ambient pressure O2 source to be connected to the airway of the non-ventilated lung, and for it to remain connected for the duration of one-lung ventilation.

Anesthesia for Tracheobronchial Surgery

The airway is a crucial dynamic structure that spans different anatomical zones, including the intrathoracic, extrathoracic, tracheal, bronchial, and alveolar zones. Because of its vital role as the sole oxygen-conducting pathway to the alveoli, and hence to the human body, surgery involving any portion requires careful and specific planning by both the surgeon and the anesthesiologist. The review covers essential management points for proximal and distal tracheal procedures, including a discussion of tracheal stenting and tracheoplasty.

Theoretical and practical aspects of anaesthesia for thoracic surgery

Thoracic surgical procedures account for only a small fraction of all surgery undertaken in the NHS. Thoracic surgery is performed in specialist centres as patients often suffer serious co-morbidities and require vigilant care and observation by staff involved in their treatment. Anaesthesia for thoracic surgery challenges the theoretical and practical experience of all involved. This review briefly summarises the anaesthetic skills and knowledge required to deliver a safe and professional service to patients with thoracic pathology.