Premium
Nasopharyngeal tubes in pediatric anesthesia: Is the flow‐dependent pressure drop across the tube suitable for calculating oropharyngeal pressure?
Author(s) -
Papoff Paola,
Rosini Talitha,
Oliva Salvatore,
Luciani Stefano,
Midulla Fabio,
Montecchia Francesco
Publication year - 2021
Publication title -
pediatric anesthesia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.704
H-Index - 82
eISSN - 1460-9592
pISSN - 1155-5645
DOI - 10.1111/pan.14194
Subject(s) - medicine , anesthesia , airway , peak inspiratory pressure , leak , pressure drop , tube (container) , tracheal tube , respiratory system , materials science , tidal volume , mechanics , thermodynamics , physics , composite material
Background Nasopharyngeal tubes are useful in pediatric anesthesia for insufflating oxygen and anesthetics. During nasopharyngeal tube‐anesthesia, gas insufflation provides some positive oropharyngeal pressure that differs from the proximal airway pressure owing to the flow‐dependent pressure drop across the nasopharyngeal tube (ΔP NPT ). Aims This study aimed to investigate whether ΔP NPT could be used for calculating oropharyngeal pressure during nasopharyngeal tube‐assisted anesthesia. Methods In a physical model of nasopharyngeal tube‐anesthesia, using Rohrer's equation, we calculated ΔP NPT for three nasopharyngeal tubes (3.5, 4.0, and 5.0 mm inner diameter) under oxygen and several sevoflurane in oxygen combinations in two ventilatory scenarios (continuous positive airway pressure and intermittent positive pressure ventilation). We then calculated oropharyngeal pressure as proximal airway pressure minus ΔP NPT . Calculated and measured oropharyngeal pressure couples of values were compared with the root mean square deviation to assess accuracy. We also investigated whether oropharyngeal pressure accuracy depends on the nasopharyngeal tube diameter, flow rate, gas composition, and leak size. Using ΔP NPT charts, we tested whether ΔP NPT calculation was feasible in clinical practice. Results When we tested small‐diameter nasopharyngeal tubes at high‐flow or high‐peak inspiratory pressure, proximal airway pressure measurements markedly overestimated oropharyngeal pressure. Comparing measured and calculated maximum and minimum oropharyngeal pressure couples yielded root mean square deviations less than 0.5 cmH 2 O regardless of ventilatory modality, nasopharyngeal tube diameter, flow rate, gas composition, and leak size. Conclusion During nasopharyngeal tube‐assisted anesthesia, proximal airway pressure readings on the anesthetic monitoring machine overestimate oropharyngeal pressure especially for smaller‐diameter nasopharyngeal tubes and higher flow, and to a lesser extent for large leaks. Given the importance of calculating oropharyngeal pressure in guiding nasopharyngeal tube ventilation in clinical practice, we propose an accurate calculation using Rohrer's equation method, or approximating oropharyngeal pressure from flow and pressure readings on the anesthetic machine using the ΔP NPT charts.