Use of Nasal Pressure to Assess Inspiratory Effort Under Different Oxygen Treatments

Patients in the intensive care unit (ICU) often require different modalities of oxygen therapy to maintain adequate oxygenation.Common oxygen therapy modalities include nasal cannula oxygen, face mask oxygen and high flow nasal cannula oxygen (HFNC).These modalities of oxygen therapy not only affect the patient's oxygenation status, but may also influence nasal and esophageal pressures by altering the upper airway pressure gradient, which in turn affects respiratory mechanics and patient comfort.

Esophageal pressure fluctuations (ΔPes), as a reflection of mean transpulmonary pressure during unassisted voluntary breathing, provide an important basis for assessing inspiratory effort.However, esophageal manometry still faces many challenges for its bedside implementation in clinical practice, especially in unstable patients with respiratory distress and severely impaired gas exchange.Notably, the COVID-19 pandemic has led to a significant increase in the number of patients with acute respiratory failure, who often require condition-specific oxygen therapy of varying severity and are mostly treated outside the ICU.Given that such patients are at high risk of deterioration, it is particularly important to continuously monitor their inspiratory effort.

nasal pressure is an important physiological indicator for assessing upper airway resistance and airflow dynamics characteristics, whereas esophageal pressure is a key parameter that directly reflects intrathoracic pressure and respiratory effort.Previous studies have shown that there may be a physiological correlation between intranasal pressure and oesophageal pressure, and that this correlation may be influenced by a variety of factors, including airflow velocity, oxygen concentration, and the dynamics of upper airway resistance.Earlier physiological studies by comparing oesophageal pressure fluctuations (ΔPes) with nasal pressure fluctuations (ΔPnose) fluctuations found that when inspiratory effort was increased, there was no significant phase difference between these pressure waveforms.In addition, it was observed that there was a significant correlation between ΔPes and airway pressure fluctuations (ΔPaw) obtained by airway occlusion manoeuvres during inspiratory effort testing.However, although these findings provide important clues for understanding respiratory mechanics, studies on the correlation between nasal pressure and esophageal pressure under different oxygen therapy conditions are still relatively limited, especially lacking data support from prospective physiological studies.Therefore, further systematic studies are needed in the future to investigate in depth the effects of different oxygen therapy parameters (e.g., flow rate, humidity, and temperature, etc.) on the relationship between nasal pressure and esophageal pressure, so as to provide more precise guidance for clinical practice.

Inclusion criteria

• No mechanical ventilation required,Able to tolerate oxygen therapy via nasal cannula, standard face mask, or nasal high-flow oxygen therapy;
• Respiratory stability:Capable of spontaneous breathing with effective cough for secretion clearance.Oxygen saturation (SpO₂) > 90% or PaO₂/FiO₂ ≥ 150 mmHg when receiving nasal cannula oxygen at 3 L/min;
• Hemodynamic stability:Heart rate (HR) ≤ 120 bpm;Systolic blood pressure (SBP) 90-150 mmHg;No vasoactive medications OR norepinephrine dosage < 0.1-0.2 μg/kg·min (or equivalent doses of other vasoactive agents);
• Metabolic stability;
• Compliance with medical instructions.Able to follow prescribed tasks.Esophageal pressure monitoring catheter already in place;
• Patient or legal guardian agrees to participate and has signed the informed consent form.

Exclusion criteria

• Age < 18 years;
• Pregnancy;
• Hemodynamic instability:Mean arterial pressure (MAP) < 60 mmHg.Heart rate (HR) > 120 bpm or < 60 bpm;
• Respiratory instability:Respiratory rate (RR) > 35 bpm.Oxygen saturation (SpO₂) < 90%;
• Neuromuscular diseases or phrenic nerve injury;
• Recent trauma or surgery involving the trachea, esophagus, neck, or chest.Contraindications to esophageal catheter placement or inability to monitor esophageal pressure;
• Nasal obstruction or anatomical abnormalities:Complete nasal obstruction.Severe anatomical abnormalities (e.g., severe septal deviation, nasal polyps, or tumors) preventing catheter placement or compromising ventilation;
• High-risk craniofacial conditions:Severe facial trauma or skull base fracture with risk of catheter misplacement into the intracranial space.Active epistaxis or incomplete healing after nasal surgery;
• Bleeding risk:Severe coagulopathy.Esophageal/gastric varices or other conditions predisposing to hemorrhage.