General anaesthesia, though indispensable for modern surgical practice, poses a significant risk to adequate oxygenation due to the reduction in functional residual capacity (FRC) and the creation of ventilation-perfusion mismatches. Anaesthetic agents and muscle relaxants diminish lung compliance and muscle tone, contributing to airway collapse and regional atelectasis, thereby impairing gas exchange even before airway instrumentation begins¹. A critical window of vulnerability exists during laryngoscopy and intubation, where patients are not ventilated—a period defined as apnoea. During this apnoeic interval, the absence of spontaneous or mechanical ventilation leads to rapid deoxygenation unless preventive measures are employed².

Apnoeic oxygenation—oxygen delivery during apnoea—has re-emerged as a promising technique to prolong safe apnoea time by leveraging the physiological concept of mass flow ventilation³. Through this mechanism, oxygen insufflated into the nasopharynx continues to diffuse into the alveoli and bloodstream despite the absence of respiratory movements, provided the airway remains patent⁴. This technique, although conceptualized over a century ago, is being adapted to modern airway management with the goal of extending non-hypoxaemic apnoea duration during intubation procedures, particularly in anticipated difficult airway scenarios⁵.

In clinical practice, preoxygenation using a tight-fitting facemask and 100% FiO₂ is routinely employed to displace nitrogen in the lungs and maximize oxygen reserves. This can extend the safe apnoea period up to 8 minutes in healthy patients⁶. However, in patients with limited neck mobility—such as those with cervical spine trauma, ankylosing spondylitis, or during simulated immobilization using manual in-line stabilization (MILS)—the risk of a difficult airway is compounded. In such situations, prolonged laryngoscopy may cause rapid desaturation, necessitating supplemental oxygenation strategies during apnoea⁷.

Among several methods for delivering oxygen during apnoea—such as high-flow nasal cannula, nasopharyngeal catheter, buccal RAE tubes—standard nasal prongs present a minimally invasive, simple, and cost-effective alternative⁸. These prongs can deliver continuous low-flow oxygen, typically at 5–10 L/min, and can remain in situ during laryngoscopy without obstructing the operator’s view, thus facilitating oxygenation throughout airway manipulation. Their utility is further emphasized by the NO DESAT (Nasal Oxygen during Efforts Securing a Tube) approach, which highlights the role of nasal cannulae in extending apnoeic oxygenation during difficult intubations⁹.

Despite these theoretical benefits, evidence remains limited and heterogeneous. Most prior studies evaluating nasal oxygenation during apnoea have limitations such as small sample sizes, absence of arterial blood gas (ABG) monitoring, and inconsistent documentation of haemodynamic parameters¹⁰. Furthermore, there is a lack of consensus on the efficacy of nasal prongs in the context of simulated cervical spine immobilization, a setting that mimics real-world clinical constraints in trauma and neurosurgical emergencies.

This study was designed to evaluate whether oxygen insufflation through nasal prongs during apnoea, in addition to standard preoxygenation, provides a significant advantage in maintaining oxygen saturation and preserving arterial oxygen tension in patients undergoing simulated cervical spine immobilization.

Study Design and Setting

This was a prospective, interventional, randomized, double-blind comparative study conducted in the Department of Anaesthesiology and Critical Care, Hindu Rao Hospital and North Delhi Municipal Corporation Medical College, Delhi, from August 2018 to May 2020. The institutional ethics committee approved the study, and written informed consent was obtained from all participants prior to inclusion.

Study Population

A total of 60 patients aged 18 to 60 years, of either gender, undergoing elective general surgical procedures under general anaesthesia were enrolled. All patients were classified as American Society of Anesthesiologists (ASA) physical status I or II, with body weight between 50–80 kg and height between 150–180 cm.

Inclusion Criteria

• Patients aged 18–60 years
• ASA Grade I–II
• BMI between 18–30 kg/m²
• Elective surgeries under general anaesthesia

Exclusion Criteria

• Patients refusing participation
• Nasal obstruction or history of epistaxis
• Known difficult airway or modified Mallampati Grade III/IV
• Grade 3a/3b or 4 Cormack-Lehane view
• Chronic respiratory illness, spinal deformities
• Significant cardiac, hepatic, renal, or neurological comorbidities

Randomization and Group Allocation

Patients were randomized using a block randomization technique with sealed opaque envelopes. They were assigned to one of two groups:

• Group P: Preoxygenation alone
• Group PN: Preoxygenation with apnoeic oxygenation using nasal prongs

The double-blind protocol ensured that neither the patient nor the observer recording outcome variables knew the group assignment.

Anaesthetic Protocol

Upon arrival in the operating room, standard monitors including ECG, non-invasive blood pressure (NIBP), and pulse oximetry were applied. Intravenous access was secured with an 18G cannula and Ringer’s lactate was initiated.

Premedication with IV midazolam 0.02 mg/kg was administered. Both groups underwent preoxygenation via tight-fitting face mask with 100% oxygen at 10 L/min until an end-tidal oxygen concentration (EtO₂) >90% was achieved. At this point, arterial blood gas (ABG1) was sampled.

Anaesthesia was induced with IV fentanyl 2 µg/kg and propofol 2.5 mg/kg. After confirming the ability to mask ventilate, rocuronium 1 mg/kg was administered. In Group PN, nasal prongs were connected to oxygen at 5 L/min during apnoea, while in Group P, nasal prongs were in place but without oxygen flow.

Apnoea Simulation and Airway Management

One minute after rocuronium administration, laryngoscopy was performed. If Cormack-Lehane grade was 1 or 2, the patient proceeded to apnoea phase. Manual in-line stabilization was applied to simulate cervical spine immobilization, and an oropharyngeal airway was inserted to maintain patency.

Apnoea was allowed to continue until SpO₂ dropped to 95% or a maximum of 6 minutes. At this point, a second ABG (ABG2) was taken, and the patient was intubated with an appropriate-sized endotracheal tube.

Outcome Measures

• Primary outcome: Duration (in seconds) until SpO₂ dropped to 95%
• Secondary outcomes:
• ABG parameters (PaO₂, PaCO₂, pH, SpO₂) before and after apnoea
• Haemodynamic changes (heart rate and MAP at 1-minute intervals)
• Resaturation time after ventilation initiation
• Patient awareness assessed postoperatively using the Modified Brice Interview

Statistical Analysis

Sample size calculation was based on a previous study by Ramachandran et al., considering a power of 90% and significance level of 5%. Continuous variables were presented as mean ± SD and analyzed using Student’s t-test. Categorical variables were expressed as percentages and analyzed using Chi-square or Fisher’s exact test. A p-value <0.05 was considered statistically significant.

The study included 60 patients evenly distributed between two groups: Group P (preoxygenation alone) and Group PN (preoxygenation plus nasal prong apnoeic oxygenation). The primary outcome—apnoea duration until SpO₂ fell to 95%—was significantly longer in Group PN (339.03 ± 35.24 seconds) compared to Group P (269.73 ± 72.82 seconds), with a highly significant p-value < 0.001 (Table 1, Graph 1). This indicates that oxygen insufflation through nasal prongs substantially prolonged the duration of safe apnoea.

Pre-apnoea arterial blood gas (ABG-1) values were statistically comparable between the two groups, confirming baseline equivalence. Mean PaO₂ was 304.20 ± 53.14 mmHg in Group P and 331.70 ± 71.56 mmHg in Group PN (p = 0.097), while PaCO₂, pH, and SpO₂ were also similar, showing no significant difference (Table 4). This ensured that the observed differences in outcomes were attributable to the intervention rather than initial physiological variation.

Post-apnoea arterial blood gas analysis (ABG-2) revealed significantly better oxygenation in Group PN. PaO₂ was considerably higher at 182.36 ± 74.99 mmHg versus 115.29 ± 46.45 mmHg in Group P (p < 0.001), while SpO₂ was also better preserved in Group PN (97.32 ± 2.69%) than in Group P (94.76 ± 3.42%) with a statistically significant difference (p = 0.002) (Table 2, Graph 2). PaCO₂ and pH, although elevated due to apnoea, did not differ significantly between groups, confirming the safety of the intervention in terms of CO₂ accumulation and acid–base balance.

Minute-wise analysis of SpO₂ saturation (Table 3) demonstrated that Group PN maintained significantly higher SpO₂ levels from the 4th minute onwards. At 5 minutes, SpO₂ in Group P had fallen to 98.80 ± 2.01%, while Group PN sustained 99.83 ± 0.59% (p = 0.011), and similar significance was observed at the 6th minute (p = 0.032) (Graph 3). These trends highlight the clinical relevance of nasal prong oxygenation in prolonging the window of non-hypoxaemic apnoea.

Heart rate monitoring over the study period showed no significant differences between the two groups. Baseline and per-minute heart rate values remained comparable, suggesting that nasal oxygen insufflation did not adversely impact haemodynamic stability (Graph 4). Both groups maintained stable mean arterial pressure throughout the apnoeic period.

Table 1: Comparison of Apnoea Durations between the Two Groups

In group P the mean apnoea time was 269.73± 72.82 seconds whereas it was 339.03±35.24 seconds in group PN with a p value of <0.001 which is highly significant.

Table 2: Comparison of PaO₂, PaCO₂, pH and SpO₂ between the Groups in Post Apnoea ABG Analysis (ABG-2)

Table 3: Intergroup and Intragroup Comparison between SpO₂ (%)

Table 4: PaO₂, PaCO₂, pH, SpO₂ Distribution in Pre-Apnoea ABG Analysis (ABG-1)

Apnoeic oxygenation is a physiologically sound technique that has regained relevance in the context of airway management, particularly in patients with anticipated difficult airways. This study evaluated the effectiveness of nasal prong oxygenation in maintaining oxygen saturation during apnoea in patients undergoing simulated cervical spine immobilization—a clinical situation where airway instrumentation may be prolonged due to restricted neck mobility.

Our findings demonstrated that patients in the nasal oxygenation group (Group PN) had significantly prolonged safe apnoea time compared to those who received preoxygenation alone (Group P). The mean apnoea duration before SpO₂ fell to 95% was 339.03 seconds in Group PN compared to 269.73 seconds in Group P (p < 0.001). These results align with the work of Ramachandran et al., who reported that nasal oxygenation extended apnoea time and prevented desaturation in obese patients during simulated difficult laryngoscopy using 5 L/min oxygen flow via nasal prongs¹¹. Similarly, Patel and Nouraei emphasized the potential of transnasal humidified oxygenation to significantly prolong apnoea duration during intubation procedures, especially in challenging airways¹².

Pre-apnoea arterial blood gas values (PaO₂, SpO₂, pH, and PaCO₂) were statistically comparable between the two groups, ruling out preexisting physiological differences. However, post-apnoea ABG results revealed significantly higher PaO₂ (182.36 ± 74.99 mmHg) and SpO₂ (97.32 ± 2.69%) in the oxygenation group, reinforcing the effectiveness of supplemental oxygen during apnoea. This is consistent with studies by Baraka et al. and Taha et al., who found that nasopharyngeal oxygen insufflation delayed desaturation in both morbidly obese and normal patients undergoing laryngoscopy¹³,¹⁴.

The principle of apnoeic oxygenation is rooted in the concept of mass flow ventilation, where the gradient between oxygen consumption (~250 mL/min) and minimal carbon dioxide excretion (~8–20 mL/min into alveoli) creates a subatmospheric pressure in the alveoli. This allows for passive diffusion of oxygen from the upper airway into the alveoli despite the absence of active ventilation¹⁵. This physiological basis was demonstrated in early studies by Frumin et al., who maintained normoxia for over 30 minutes using apnoeic oxygenation in anaesthetised patients¹⁶. In our study, this principle was effectively employed using low-flow nasal cannula oxygenation during the apnoea phase.

Another important observation was the maintenance of haemodynamic stability across both groups. No significant differences were observed in heart rate or mean arterial pressure between the two arms. This supports the safety profile of nasal prong oxygenation, particularly in high-risk settings. These findings correspond to the work by Semler et al., who noted that while apnoeic oxygenation may not always significantly impact lowest SpO₂ in critically ill patients, it does not lead to adverse haemodynamic events¹⁷.

The NO DESAT technique (Nasal Oxygen during Efforts Securing a Tube), popularized by Levitan and colleagues, highlighted the utility of keeping nasal prongs on during preoxygenation and laryngoscopy, thus allowing continuous oxygenation throughout the intubation process¹⁸. Our study adds to this body of evidence, especially in the setting of cervical spine immobilization—a situation often encountered in trauma, where traditional intubation strategies may be limited.

Despite these encouraging results, not all literature supports a universal benefit. Sahay et al. conducted a randomized controlled trial and concluded that while nasal oxygen supplementation did not significantly prolong desaturation time, it helped improve resaturation rates post-ventilation initiation¹⁹. Similarly, Caputo et al. found no significant difference in lowest SpO₂ during intubation in emergency settings using apnoeic oxygenation versus standard care²⁰. These discrepancies highlight the variability in outcomes based on patient selection, oxygen flow rate, airway patency techniques, and the definition of outcome measures.

Our study adds value by using a simulation of difficult airway with manual in-line stabilization and consistent use of oropharyngeal airways to maintain patency. It also included ABG analysis for objective measurement of gas exchange and oxygenation, which many previous studies lacked.

Nevertheless, limitations exist. The study was limited to ASA I–II patients undergoing elective surgery, excluding high-risk groups like obese or hypoxaemic patients. Additionally, while 5 L/min oxygen flow was adequate in this setting, higher flow systems such as HFNC (High Flow Nasal Cannula) delivering humidified oxygen at 60–70 L/min may provide additional benefit, especially in critical care environments.

The use of nasal prongs for apnoeic oxygenation significantly prolonged the duration of safe apnoea and maintained higher arterial oxygen saturation and partial pressure of oxygen during simulated cervical spine immobilization. This simple, low-cost intervention demonstrated physiological benefits without causing haemodynamic instability, making it a valuable adjunct in difficult airway scenarios. Its inclusion in standard preoxygenation protocols may improve patient safety during intubation, especially in high-risk or trauma cases.

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