Trachea pressure determination method and device
According to various embodiments, methods and systems for determining pressure in the lungs may employ intracuff pressure measurements. The intracuff pressure measurements may calibrated or adjusted based on a set of calibration coefficients or a set of calibration curves, which may reflect patient parameters and cuff/tube geometry factors. The resulting calibration may be used to determine a more accurate estimate of lung pressure, which in turn may be used to control a ventilator and provide breathing assistance to a patient. Also provided are tracheal tubes with couplers or other memory devices for storing calibration information. Such tubes may allow calibration at the level of an individual tracheal tube to account for changes in tube geometry and individual patient factors.
1. A method for determining trachea pressure comprising:
using a processor:
determining a monitored cuff pressure in an inflated cuff of a tracheal tube disposed in the trachea of a subject;
selecting a relationship from a plurality of relationships between the monitored cuff pressure and the trachea pressure; and
determining the trachea pressure based upon the selected relationship; and
determining a lung pressure from the tracheal pressure and an offset, wherein the offset is a reference cuff pressure.
2. The method of claim 1 , wherein the selected relationship is a function of the monitored cuff pressure, and wherein the method comprises monitoring a current cuff pressure during respiration of the subject, and determining the trachea pressure based upon the relationship and the current cuff pressure.
3. The method of claim 2 , wherein the trachea pressure is determined by multiplying a sensed cuff pressure by a ratio of the empirically determined lung pressure to the cuff pressure determined by the selected relationship.
4. The method of claim 3 , wherein the lung pressure is determined by subtracting a reference cuff pressure from the product of the sensed cuff pressure and the ratio.
5. The method of claim 1 , wherein the lung pressure is determined by an algorithm that implements an equation generally of the form:
P T =rP Cs −P Co ,
wherein P T is the trachea pressure, P Cs is a cuff pressure monitored during respiration of the subject, P Co is the reference cuff pressure, and r is a ratio of the lung pressure to a sensed cuff pressure.
6. The method of claim 5 , wherein the ratio is a non-constant value.
7. The method of claim 6 , wherein the ratio varies with the monitored cuff pressure, and wherein the method includes monitoring the current cuff pressure during respiration of the subject and determining the ratio based upon the monitored cuff pressure.
8. The method of claim 6 , wherein the ratio is a function of a relationship between the tracheal tube and the trachea of the subject.
9. The method of claim 1 , wherein the reference cuff pressure is the initial pressure of the cuff or the lowest trachea pressure seen in the breathing cycle after ventilation has begun.