Atelectasis after pre-oxygenation with high-flow nasal cannula oxygen confirmed by electrical impedance tomography.

Sir,

It is well-known that high-concentration oxygen can cause atelectasis, but pre-oxygenation with 100% oxygen before endotracheal intubation is recommended by the Difficult Airway Society (DAS) guidelines.[1] Does pre-oxygenation with 100% oxygen cause atelectasis? We introduce a case of atelectasis after pre-oxygenation using high-flow nasal cannula (HFNC) oxygen therapy confirmed by electrical impedance tomography (EIT).

A 54-year-old male with a body mass index of 36 kg/m2 underwent partial hepatectomy. Pre-anaesthesia airway evaluation acquired the following results: the mouth opening was 4 cm and the neck size was 48 cm, with unlimited neck extension and a Mallampati score of 2. Images of end-tidal volume map (ETVM) and tidal volume wave by EIT were continuously monitored [Figure 1]. After 3 minutes of pre-oxygenation with 60 L per minute of HFNC humidified oxygen (37°C, with a fraction of inspired oxygen [FiO2] of 100%), the patient's end-tidal fraction of oxygen (ETO2) ramped up to 82%, and the partial pressure of arterial oxygen (PaO2) to FiO2 ratio (PaO2/FiO2) decreased from 409.3 to 319.1 mmHg. The ETVM derived from EIT gradually decreased. After 1 minute rapid sequence induction with propofol and rocuronium, successful intubation using video laryngoscope (UEScope, Zhejiang UE Medical Corp, Zhejiang, China) was completed in 73 seconds. HFNC was continued until the intubation was completed. After induction and conventional mechanical ventilation, the PaO2/FiO2 ratio fell to 183.2 mmHg, and the ETVM continuously decreased. After inflating the lung with a recruitment manoeuvre and increasing the positive end-expiratory pressure (PEEP), the ETVM significantly enlarged, and the PaO2/FiO2 ratio rose to 418.3 mmHg. The operation was successfully completed in 3 hours, and the patient was discharged from the hospital after 8 days of recovery. No atelectasis and the other pulmonary complications occurred postoperatively.

Figure 1

EIT images of regional ventilation distribution before and after pre-oxygenation with HFNC. EIT, electrical impedance tomography; HFNC, high-flow nasal cannula; CT, computed tomography; ROI, region of interest; TV, tidal volume; ETVM, end-tidal volume map; PEEP, Positive end-expiratory pressure

The literature supports HFNC use for preoxygenation before endotracheal intubation.[2] Intubation may be difficult in obese patients, and they may require pre-oxygenation.[3] Similar to computed tomography, EIT can be used to assess regional ventilation distribution and lung volume change.[4] ETVM from EIT images dwindled significantly after pre-oxygenation, suggesting the presence of atelectasis. Anaesthetics could further reduce functional residual capacity and promote airway closure. In that scenario, oxygen was rapidly adsorbed behind closed airways, causing lung collapse (atelectasis). Furthermore, prolonged untreated atelectasis may provide a potential locus for infection, thereby causing pneumonia. Therefore, we recommend that atelectasis caused by hyperoxic pre-oxygenation should be detected and treated in time. Usually, inflating the lung and executing mechanical ventilation with proper PEEP are suggested, especially in obese patients.

Herein, we only report a case of atelectasis after hyperoxic pre-oxygenation, and no severe pulmonary complications were reported postoperatively. Certainly, future randomised controlled trials are warranted to determine the long-term outcomes after pre-oxygenation with HFNC oxygen therapy in obese patients. Additionally, strategies to improve EIT spatial resolution should also be considered.

Declaration of patient consent

In the form, the patient has consent for his images and other clinical information to be reported in the journal.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.