Patent Application
20070062532
The present invention relates to an apparatus and method for determining and displaying functional residual capacity data and other pulmonary parameters, such as positive end expiratory pressure (PEEP) data, for patients breathing with the aid of a mechanical ventilator, such as a critical care ventilator. The invention also determines and displays relationships between these and other parameters.
Functional residual capacity (FRC) is the gas volume remaining in the lungs after unforced expiration or exhalation. Several methods are currently used to measure functional residual capacity. In the body plethysmography technique, the patient is placed in a gas tight body box. The patient's airway is sealingly connected to a breathing conduit connected to the exterior of the body box. By measuring lung pressures and pressures in the box, at various respiratory states and breathing gas valve flow control conditions, the functional residual capacity of the patient can be determined.
Another technique for measuring functional residual capacity is the helium dilution technique. This is a closed circuit method in which the patient inhales from a source of helium of known concentration and volume. When the concentration of helium in the source and in the lungs has reached equilibrium, the resulting helium concentration can be used to determine the functional residual capacity of the patient's lungs.
A further technique for determining functional residual capacity is the inert gas wash-out technique. This technique is based on a determination of the amount of gas exhaled from the patient's lungs and corresponding changes in gas concentrations in the exhaled gas. The gas used for the measurement is inert in the sense that it is not consumed by metabolic activity during respiration. While a number of gases may be used for such a measurement of functional residual capacity, it is convenient to use nitrogen for this purpose.
In a straightforward example in which the patient is initially breathing air, the lung volume forming the functional residual capacity of the lung will contain nitrogen in the same percentage as air, i.e. approximately 80%, the remaining 20% of air being oxygen. In a wash-out measurement, the subject commences breathing gases in which oxygen is at a different concentration than 20%. For example, the patient commences breathing pure oxygen. With each breath, nitrogen in the lungs is replaced by oxygen, or, stated conversely, the nitrogen is “washed out” of the lungs by the oxygen. While the breathing of pure oxygen could continue until all nitrogen is washed out of the lungs, in most cases, the breathing of oxygen continues until the nitrogen concentration in the exhaled breathing gases falls below a given concentration. By determining the volume of inert gas washed out of the lungs, and knowing the initial concentration of the inert gas in the lungs, the functional residual capacity of the lungs may be determined from these quantities.
Methods for determining functional residual capacity in this manner are well known and are described in such literature as The Biomedical Engineering Handbook, CRC Press, 1995, ISBN 0-8493-8346-3, pp. 1236-1239, Critical Care Medicine, Vol. 18, No. 1, 1990, pp. 8491, and the Yearbook of Intensive Care and Emergency Medicine, Springler, 1998, ISBN 3-540-63798-2, pp. 353-360. By analogy to the above described wash out measurement technique, it is also possible to use a wash in of inert gas for measurement of functional residual capacity. Such a method and apparatus is described in European Patent Publication EP 791,327.
The foregoing methods are used with spontaneously breathing patients and are typically carried out in a respiratory mechanics laboratory. But in many cases, patients that could benefit from a determination of functional residual capacity are so seriously ill as to not be breathing spontaneously but by means of a mechanical ventilator, such as a critical care ventilator. This circumstance has heretofore proven to be a significant impediment in obtaining functional residual capacity information from such patients. Additionally, the patient's illness may also make it impossible or inadvisable to move the patient to a laboratory or into and out of a body box for the determination of functional residual capacity.
It would therefore be highly advantageous to have an apparatus and method by which the functional residual capacity of mechanically ventilated patients could be determined. It would be further advantageous to associate the apparatus for carrying out the determination of functional residual capacity with the ventilator to reduce the amount of equipment surrounding the patient and to facilitate set up and operation of the equipment by an attending clinician. Such apparatus would also enable the determination of functional residual capacity to be carried out at the bedside of the patient, thus avoiding the need to move the patient.
A single determination of functional residual capacity provides important information regarding the pulmonary state of the patient. However, it is often highly desirable from a diagnostic or therapeutic standpoint to have available trends or changes in the functional residual capacity of a patient over time.
It would also be helpful to be able to relate functional residual capacity to other pulmonary conditions existing in the lungs or established by the ventilator and to changes in these conditions. For example, it is known that the pressure established by the ventilator in the lungs at the end of expiration, the positive end expiratory pressure or PEEP, affects the functional residual capacity of the lungs.
Typically, an increase in PEEP increases functional residual capacity. There are two components to the increased functional residual capacity as PEEP is increased. One component is due to stretching of the lung by the increased pressure. A second component, particularly in diseased lungs, occurs from the effect of PEEP during breathing by the patient. As a patient expires, the pressure in the lungs drops until it approaches airway pressure. As the pressure within the lungs drops, the alveoli or air sacs in the lungs deflate. If alveolar sacs collapse completely, more pressure is required upon inspiration to overcome the alveolar resistance and re-inflate the alveolar sacs. If this resistance cannot be overcome, the volume of such sacs are not included in the functional residual capacity of the patient's lungs.
By applying PEEP, in the patient's airway, the additional pressure in the patient's lungs keeps more of these alveolar sacs from completely collapsing upon expiration and, as such, allows them to participate in ventilation. This increases the functional residual capacity of the patient's lungs and the increase is often described as “recruited volume.” Volume reductions are termed “de-recruitments.”
However, setting the PEEP too high can cause excessive lung distension. There may also be compression of the pulmonary bed of the lung, loading the right side of the heart and reducing the blood volume available for gas exchange. Either of these circumstances present the possibility of adverse consequences to the patient.
It would, therefore, be desirable to provide an apparatus and method by which a clinician could quickly, easily, and definitely determine an optimal PEEP for a given patient at a given point in the therapeutic regimen for the patient. An optimal PEEP is one that keeps the lung open but avoids overpressurization of the lung. It is often termed the “open lung PEEP.”
Still further, action such as performing a suction routine, administering a nebulized medication, or changing the ventilation parameters of the ventilator can also influence functional residual capacity and it would be helpful to be able to easily determine the effect of such actions on functional residual capacity.
An apparatus and method that would possess the foregoing characteristics and that would easily and cogently make such information available would be highly beneficial in conveniently obtaining a full understanding of the pulmonary condition of the patient and how the patient is reacting to the mechanical ventilation and to any associated therapeutic measures. The clinician could then carry out appropriate action beneficial to the patient in a timely and informed manner.
An embodiment of the present invention comprises an apparatus and method that achieves the highly advantageous features noted above. Thus, with the present invention the functional residual capacity of a mechanically ventilated patient may be determined at the bedside of the patient without the need to move the patient to a laboratory. By associating the apparatus with the ventilator, only a single device need be employed to both ventilate the patient and determine functional residual capacity.
The determined functional residual capacity may be advantageously displayed in conjunction with earlier determinations and in conjunction with other pulmonary conditions, such as PEEP. Changes, or trends, in functional residual capacity over time may thus be discerned, along with changes in the other pulmonary conditions.
The foregoing provides an attending clinician with significant information for assessing the state of, and trends in, the functional residual capacity of the patient, as well as the relationship between the patient's residual capacity and the other factors, so that the clinician can fully discern the functional residual capacity condition of the patient.
With respect to assisting the clinician in adequately determining an optimal PEEP for the patient, as noted above, the apparatus and method of the present invention determines and displays related PEEP and functional residual capacity values. This enables the clinician to note, for example, the point at which increases in PEEP produce little, if any, further increases in functional residual capacity.
The apparatus and method of the present invention also determines and displays a showing of the amount of lung volume recruited or de-recruited as the PEEP is changed. This allows the clinician to distinguish between changes in functional residual capacity due to lung stretching or contracting and those arising from recruitment or de-recruitment.
Further features of the apparatus and method of the present invention will be apparent from the following detailed description, taken in conjunction with the associated drawing.
a and 12b show a display showing relationships among functional residual capacity, PEEP, and recruited lung volume.
The air and oxygen are mixed in conduit 28 of ventilator 10 and provided to inspiratory limb 30 of breathing circuit 32. Inspiratory limb 30 is connected to one arm of Y-connector 34. Another arm of Y-connector 34 is connected to patient limb 36. During inspiration, patient limb 36 provides breathing gases to lungs 38 of patient 12. Patient limb 36 receives breathing gases from the lungs of the patient during expiration. Patient limb 36 may include components such as a humidifier for the breathing gases, a heater for the breathing gases, a nebulizer, or a water trap (not shown). The breathing gases expired by patient 12 are provided through patient limb 36 and Y-connector 34 to expiratory limb 46 of breathing circuit 32. The expired breathing gases in expiratory limb 46 are provided through valve 54 and flow sensor 56 for discharge from ventilator 10. Valve 54 may be used to establish the PEEP for patient 12.
Patient limb 36 includes gas flow and pressure sensor 57 which may be of the type shown in U.S. Pat. No. 5,088,332. A pair of pressure ports and lines 58, 60 are placed on either side of a flow restriction in the sensor and the pressure difference developed across the flow restriction is used by flow measurement unit 62 in gas module 64 to measure gas flow in patient limb 36. One of the pressure lines is connected to pressure measurement unit 66 to measure the pressure in patient limb 36. Sensor 57 also provides for a gas sampling line 68 which is connected to gas analyzer 70. Gas analyzer 70 may measure the amount of oxygen and carbon dioxide in the breathing gases. Knowing the amounts of oxygen and carbon dioxide in the breathing gases enables the amount of nitrogen to be determined as the total amount less the amounts of carbon dioxide and oxygen. Respiratory and metabolic gas module 64 may comprise that made and sold by GE Healthcare as a Datex-Ohmeda MCOVX gas module. The output of gas module 64 is provided in data bus 72 to central processing unit 74 in ventilator display unit 76. Central processing unit 26 in ventilator 10 is also connected to central processing unit 74 via data bus 78.
To obtain an accurate indication of the pressure in lungs 38 of the patient 12, endotracheal tube 90 shown in
Endotracheal tube 90 includes pressure sensor catheter 94 that extends from end 96 to provide a pressure sampling point that is close to lungs 38 of patient 12 when the endotracheal tube is inserted in the patient and can thus obtain a highly accurate indication of the pressure in the lungs. An intermediate portion of catheter 94 may lie within endotracheal tube 90. The proximal portion exits the endotracheal tube and is connected via A-A to a pressure transducer and to an auxiliary input to ventilator display unit 76. The pressure obtained from catheter 94 is termed Paux. While
An endotracheal tube of the type shown in
Display unit 76 of ventilator 10 receives information from the ventilator and gas module 64 and is used by the clinician to control the pneumatic control components of ventilator 10 that deliver breathing gases to patient 12 via data bus 78. Additionally, central processing unit 74 in display unit 76 carries out the determination of functional residual capacity, recruited/de-recruited volumes, and other quantities employed in the present invention. It will be appreciated that other CPU configurations, such as a single CPU for the ventilator and its display unit may be used, if desired.
Ventilator display unit 76 includes user interface 100 and display 102. Display 102 is shown in greater detail in
Display portion 102a provides for the display of operating information of ventilator 10. The portion shows the type of ventilation being performed by ventilator 10, in the exemplary case of
Display portion 102b of display 102 shows airway pressure data as measured from sensor 57. Portion 102c shows textual information relating to the flow of breathing gases to the patient obtained from sensor 57, and portion 102d shows pressure data from catheter 94 in the endotracheal tube 90 during ventilation of patient 12.
Portion 102e of display 102 shows the information in regions 102b, 102c, and 102d in graphic form and includes an indication of certain other operating information, such as the mode of ventilation SIMV-VC, and whether certain features of the present invention are operational or not.
Display portion 102f of display 62 shows additional data as selected by the clinician. In the example of
Display portion 102a-f remain generally unchanged as the present invention is practiced although, as noted above, the clinician may select the information to be shown in certain portions, such as portion 102f.
Display screen 102g is the part 6f display 102 employed in the present invention. As shown in
In general, each screen 102g will include a menu or control portion 108, a graphic portion 110 and tabular portion 112. For this purpose, graphic portion 110 contains a pair of orthogonal axes by which data can be graphically presented. The clinician may navigate and control the screen using control knob 106. Control knob 106 is rotated to scroll through the menu options displayed in menu portion 108, depressed to select a menu option, rotated again to establish a numerical value for the selected option when appropriate, and depressed again to enter the value into ventilator display unit 76 or to confirm selection of the menu option.
Menu portion 108 allows the clinician to select a number of options with respect to the display and use of the information shown in graphic and tabular portions 110 and 112. Menu portion 108 also allows the clinician to select a further screen at 116 for adjusting the scaling for the abscissa and ordinate of graph 110 and the setup for spirometry measurements at 118.
From menu portion 108, the clinician may also select screens that allow the functional residual capacity (FRC) features of the present invention and the spirometry features of the present invention to be carried out by selecting items 120 and 122, respectively. The spirometry features of the present invention are identified by applicant as SpiroDynamics or the abbreviation SpiroD.
By means of menu items 120 and 122, the clinician can select either a screen relating to functional residual capacity, namely screen 102g2 shown
The FRC INview showing of 102g2 includes screen shown in
A further selection on the FRC INview screen allows the clinician to select the FRC log screen shown in
Selections on either of the FRC INview screen 102g2 or the SpiroDynamic screen 102g3 allows selection of a PEEP INview screen shown in
Finally, an on/off selection option in PEEP INview screen 102g5 allows the clinician to display lung INview screen 102g6 shown in
The flow chart of
As noted above, in order to determine the functional residual capacity of patient 12 by a gas wash-out/wash-in technique, it is necessary to alter the composition of the breathing gases supplied to patient 12. To this end, the clinician sets a different level for the oxygen content of the breathing gases. This is performed by selecting the FRC 02 field 206 in menu portion 68 of screen 102g1 and appropriately establishing the FRC 02 value. The amount of change may be an increase or decrease from the previously set level established at step 200; however it must be an amount sufficient to perform the functional residual capacity analysis. A change of at least 10% is preferable in order to obtain an accurate indication of the functional residual capacity. To ensure that appropriate oxygen concentrations are supplied to patient 12 it is usually desired to increase the oxygen level and, unless the current oxygen level is very high (greater than 90%), a default setting of a 10% increase over the current setting may be provided. The level of oxygen set by the clinician “tracks” changes made in the oxygen content of the breathing gases at the ventilator, as for example by actuating button 104a. Thus, for example, if the ventilator oxygen is originally 50% as shown in
Next, the clinician must select the frequency, or interval, at which the functional residual capacity measurements will be carried out. This is performed at step 210. A single functional residual capacity determination by the present method may be selected by the appropriate field 212 in menu 68. Alternatively, a series of FRC determinations or cycles may be selected, with a series interval, set in field 214, between each determination. The interval may be between one and twelve hours in increments of one hour. The time when the next functional residual capacity determination begins is shown in field 115.
Alternatively, functional residual capacity measurements can be set to occur automatically in conjunction with certain procedures controlled by ventilator 10, such as immediately prior and/or after a period of nebulized drug therapy, recruitment maneuvers, a suction procedure, or a change in ventilator setting. Functional residual capacity measurement may be initiated, terminated, delayed, interrupted, or prevented in accordance with the occurrence of events, such as those noted above, that may affect the accuracy of the functional residual capacity measurement. For example, a functional residual capacity measurement may be terminated for a high oxygen procedure for patient 12 and then resumed or started after a “lock out” period.
The initial or base line amount of nitrogen in the expired breathing gases is determined at step 216. As noted above this may be determined by subtracting the amounts of oxygen and carbon dioxide, as determined by gas analyzer 70, from the total amount of the breathing gases, as determined using flow sensor 62.
While the present invention is described using nitrogen as the inert gas, it will be appreciated that other inert gas may also be used. For example, the breathing gases for patient 12 may include the inert gas helium and amounts of helium expired by the patient could be used in a functional residual capacity measure in the manner described herein.
To commence the determination of functional residual capacity, breathing gases having the increased amount of oxygen shown in data field 105 are provided to patient 12 in step 218. The increased percentage of oxygen in the breathing gases will wash a portion of the nitrogen or other inert gas out of lungs 38 of patient 12 with each breath of the patient. The amount of breathing gases inspired and expired by patient 12 with each breath, i.e. the tidal volume, is a lung volume that is in addition to the residual volume of the lungs found after expiration. The tidal volume is also smaller than the residual volume. For a healthy adult a typical tidal volume is 400-700 ml whereas the residual volume or functional residual capacity is about 2000 ml. Therefore, only a portion of the nitrogen in the lungs 38 of patient 12 is replaced by the increased amount of oxygen with each breath.
The amount of nitrogen washed out of the lungs in each breath is determined by subtracting the amount of oxygen and carbon dioxide from the amount of breathing gases expired by patient 12 during each breath obtained using flow sensor 68. See step 220. Knowing the amount of expired breathing gases, the initial amount of expired nitrogen and the amount expired in each expiration by patient 12, a functional residual capacity quantity can be determined for each successive breath in steps 222a, 222b . . . 222n. Any inert gas wash out/wash in functional residual capacity measurement technique may be used, a suitable technique for determining functional residual capacity for use in the present invention being described in U.S. Pat. No. 6,139,506.
The functional residual capacity quantity as determined after each successive breath, will tend to increase as nitrogen continues to be washed out of the lungs of the patient by the increased oxygen in the breathing gases. This results from the fact that the breathing gases that are inspired by patient 12, i.e., the tidal volume, are not fully equilibrated inside the entire functional residual capacity volume before being exhaled by the patient. In particular, functional residual capacity volume that lies behind intrinsic lung resistance does not mix as quickly with inspired gases compared to functional residual capacity volume that is pneumatically connected to the trachea through a lower resistance path. As such, the magnitude of breath-to-breath increases in functional residual capacity that are noted are an indication of the amount of intrinsic resistance within the lung gas transfer pathways. Thought of another way, additional functional residual capacity volume that is registered many breaths into the functional residual capacity measurement procedure is lung volume that is not participating well in the gas transfer process.
As the determination of functional residual capacity proceeds, the determined values for functional residual capacity for the breaths are displayed in graphic portion 110 of screen 102g2 as a capacity or volume curve 224 in steps 226a, 226b . . . 226c at the end of the determination for each breath. This confirms to the clinician that the determination of functional residual capacity is working properly. Also, as curve 224 forms from left to right, the shape of the curve is an indication to the clinician of the intrinsic resistance and quality of ventilation of lung functional residual capacity, as discussed above. In the example shown, the clinician can appreciate that patient 12 has a homogeneously ventilated lung volume, as indicated by the qualitative flatness of the functional residual capacity curve, with a lung capacity of about 2500 ml.
The scaling of graph 110 of
It will be appreciated that, if desired, the data relating breath number to the corresponding functional residual capacity value can also be displayed in tabular form in portion 112 of display portion 102g. This could comprise a column containing the breath numbers and a column containing the corresponding functional residual capacity values.
Mechanical ventilator 10 continues to supply breathing gases having increased oxygen concentration for x number of breaths, for example, 20 breaths. A final value for functional residual capacity is determined at the end of the x breaths at step 228 and volume or capacity curve 224 extends to this breath to show the final determination of functional residual capacity at the end of 20 breaths. The functional residual capacity measurement may conclude earlier if sufficient stability of breath-to-breath functional residual capacity is found in curve 224.
Thereafter, at step 230 the concentration of oxygen in the breathing gases is altered to the original level of, for example 50%, set at step 208 and ventilator 10 is operated at step 232 to repeat steps 216-228 to make a second determination of functional residual capacity with this alteration of the oxygen concentration in the breathing gases. It will be appreciated that this determination uses a wash-in of nitrogen, rather than a wash-out. This second determination is graphed and displayed in graphic portion 110 as graph 234, in the same manner as graph 224, described above. The values for the two final functional residual capacity determinations are shown in data field 236 of tabular portion 112 of screen 102g2 in step 236. In the example shown, these values are 2500 and 2550 ml.
For future use, the final determination of functional residual capacity made in step 232 is compared to that determined in step 228. This is carried out at step 238. It is then determined, in step 240, whether the difference between the two determinations of functional residual capacity is less or greater than some amount, such as 25%. If the difference is less than 25%, the two values are averaged and will be subsequently displayed in text form in data field 245 in step 244 when determination becomes part of the chronological record following a later functional residual capacity determination.
If the difference between the two values for the functional residual capacity is greater than some amount, such as than 25%, both the final value determined at step 228 and the final value determined in step 232 will be displayed by step 246 in data field 245 of
The final value(s) for the functional residual capacity are preferably displayed along in tabular portion 112 of screen 102g2 along with additional associated data such as the time and date at which functional residual capacity was determined, or the values of PEEPe and PEEPi existing when the functional residual capacity determination was made. PEEPe is the end expiratory pressure established by ventilator 10. PEEPi, also known as auto PEEP, is the intrinsic end expiratory pressure and is a measurement in pressure of the volume of gas trapped in the lungs at the end of expiration to the PEEPe level.
While the determination of functional residual capacity has been described as being carried out for a given number of breaths, such as 20, it can be terminated sooner if it is apparent that the functional residual capacity measurement has become stable on a breath-to-breath basis. This can be conveniently determined by measuring the O2 content of the expired breathing gases at the end of the patient's expirations, that is, the end tidal oxygen level. When the amount of oxygen in the expired breathing gases attains and remains at the altered level, it is an indication that the wash out/wash in the inert gas is complete and that the functional residual capacity determination can be terminated.
Thereafter, if a series of functional residual capacity determinations has been selected at step 210, steps 218 through 246 are repeated after the time interval indicated in data field 214 with the start of the functional residual capacity determination occurring at the time displayed in data field 248. The predetermined time interval may be overridden or the functional residual capacity determination terminated by appropriate commands from the clinician entered into menu 68.
The volume curves, such as 224, 234, and functional residual capacity data, such as that in field 236, generated in the course of successive functional residual capacity determinations are saved by ventilator display unit 76 and, as such, can be compared to data from previous or subsequent functional residual capacity determinations. This comparison requires that a previous determination of functional residual capacity be selected as a reference curve using the time at which it was obtained as identified in data field 250. When a reference curve is selected, an indication is made in data field 250 and that functional residual capacity curve is displayed as the reference curve 252. Curve 252 shows a lung that is not well ventilated. Further indication of the reference curve and reference curve values may be made by a color indication for this data, different from that of the other functional residual capacity data in graph 110 and table 112. The result is a visual indicator that can easily be referred to by the clinician to quickly assess improvement or deterioration in the functional residual capacity condition of patient 12 over time. In the example shown in
Also, it is common practice to alter, usually increase, the PEEP to improve ventilation of lungs 38 of patient 12 by opening areas of the lung that are not being properly ventilated. Tabulating the actual measured values for PEEPe and PEEPi, along with the corresponding functional residual capacity determination, as shown in
Certain clinical or other events can affect the value for functional residual capacity determined from the method steps shown in
By selecting the FRC Log field 252 in menu 68 of screen 102g2 shown in
An aspect of the present invention allows the clinician to ascertain the relationship between the functional residual capacity of patient 12, and PEEP applied to the patient, thereby to assist the clinician in establishing a PEEP level deemed optimal for patient 12. An optimal PEEP level, in the present context, is one beyond which diminishing functional residual capacity increases in association with PEEP increases is noted. The PEEP INview screen 102g5 of
The series of measurements of functional residual capacity starting at the initial value of PEEP and incrementally moving to the end value of PEEP is then performed as in a manner of steps 216-228 or steps 216-246 shown in
Curve 408 and table 112 provide guidance to the clinician in selecting a PEEP level for ventilating patient 12. For example, from the graph and table of
Curve 408 can be saved in a memory in ventilator 10 or display unit 76. If ventilator settings are not changed or are not changed in any significant way, curves 408 obtained at different times in the course of the patient's treatment can be usefully presented in graphic portion 110 of screen 102g to enable the clinician to note changes in the PEEP curve over time by comparing the data of two or more curves 408 over time.
Also, while the foregoing has described obtaining and presenting a graph and table of functional residual capacity and PEEP, other aspects of the ventilation of patient 12 by ventilator 10 may affect the functional residual capacity. For example, the respiration rate, or the related quantities of expiration time and inspiratory:expiratory (I:E) ratio, can affect functional residual capacity primarily through the mechanism of intrinsic PEEP. Determining and displaying the relationship of one or more of these quantities to functional residual capacity may be useful to a clinician. To this end, the functional residual capacity of the lungs 38 of patient 12 can be determined at differing respiration rates and the data displayed in graphic or tabular form to show the relationship between functional residual capacity and respiration rate. In graphic portion 110, the abscissa would show the respiration rate while the abscissa continues to show functional residual capacity. A tabular presentation comprises a column of respiration rates and a column of corresponding functional residual capacity determinations.
While screen 102g5 of
One way such information may be obtained using the PEEP INview screen 102g5 of
After the recruitment maneuver has been completed, the functional residual capacity is again determined for the same series of PEEPs used prior to performing the recruitment maneuver to produce another curve 408a. The two curves can be displayed in graphic portion 110 of screen 102g5 in the manner shown in
Another way such information can be obtained using the spirometry aspects of the present invention, as shown in the SpiroD screen 102g3 of
In general, spirometry is used to determine the mechanics of a patient's lungs by examining relationships between breathing gas flows, volumes, and pressures during a breath of a patient. A commonly used relationship is that between inspired/expired breathing gas flows and volumes that, when graphed, produces a loop spirogram. The size and shape of the loop is used to diagnose the condition of the lung.
A relationship also exists between inspired/expired gas volumes and pressure in the lungs. In the past, a problem with the use of this relationship has been that pressure has been measured at a point removed from the lungs so that the measured pressure may not be an accurate reflection of actual pressure in the lungs thus lessening the diagnostic value of the pressure-volume loop. Through the use of catheter 94 extending from endotracheal tube 90 shown in
In graph 110 of
With PEEP applied to patient 12 by ventilator 10, there will be a movement of the graph away from the origin of the axes along the abscissa. The graph will move right by the amount of the PEEP, i.e. the lung pressure at the end of expiration by patient 12.
The menu portion 108 of SpiroD screen 102g3 shown in
Various other selections on menu 108 of screen 102g3 of
The “SpiroD loops” and “SpiroD curves” menu items may be turned on or off. Selecting “on” for both the curve and loop will display both the loop and the curve at once in the manner shown in
For the graphical showing of graph 110 of the screen 102g3 in
Various compliance values for the patient's lungs are shown in the table 112 of screen 102g3 of
The table 112 of display 102g3 of
The present invention provides a unique way of viewing the relationship among functional residual capacity, PEEP, and recruited:de-recruited lung volume that is deemed helpful in enabling a clinician to determine a suitable value for PEEP. To carry this out, the PEEP INview screen 102g5 shown in
To proceed with the Lung INview display, in the PEEP INview screen 102g5 shown in
For an embodiment of the invention using a wash in/wash out determination of functional residual capacity, in field 430 of menu 108 of display 102g6 of
The graph 110 of screen 102g6 of
As shown in
In step 506, the functional residual capacity of patient 12 is determined by the wash in/wash out technique using the altered oxygen concentration level as described above in connection with
Next, the PEEP pressure is altered to the next decremental level, in the present instance from 25 cmH2O to 20 cmH2O, and the patient is ventilated at the new PEEP level in step 510. In step 512, the functional residual capacity is again determined and displayed with respect to PEEP in the same manner as in step 506 at point 514. Curve 516 is formed in graph 110 from points 508 and 514.
A dynostatic curve is also obtained for the ventilation of the patient's lungs at the PEEP of 20 cmH2O.
The origin for dynostatic curve 522 will be the PEEP value of 20 cmH2O and the associated functional residual capacity value so that the origin corresponds to point 514 of
Steps 510, 512 and 518 are then repeated for the next decremented PEEP of 15 cmH2O. This produces a new point 530 of functional residual capacity and PEEP in curve 516 in
Steps 524, 526 and 528 are used to determine the amount of recruited or de-recruited volume obtained in the lungs of patient 12. At PEEPs of 15 and 10 cmH2O, some de-recruitment of lung volume is noted and steps 524, 526 and 528 of
The amount of volume on the ordinate scale represented by the line segment 538a between points 530 and 540 is also determined. In the present instance, this amounts to approximately 180 ml. In step 528, this value is placed in table 112 of screen 102g6 in association with the previous PEEP of 15 cmH2O. In step 526, point 540 is placed in graph 110 of screen 102g5 as shown in
b shows the completed Lung INview process, including the final measurement of functional residual capacity at a PEEP of 5 cmH2O. This is carried out by repeating steps 510, 512, and 518, for a PEEP of 5 cmH2O to produce plot 542 of functional residual capacity and PEEP and dynostatic curve 544. Repeating steps 524, 526, and 528 produces point 546 and line segment 548a representing a volume of about 120 ml. The data is displayed in a manner corresponding to that described above in graph 110 and table 112 of screen 102g6. As the determination of the “difference” requires both functional residual capacity measurement taken at a previous PEEP and a dynostatic curve from subsequent PEEP and is referenced to the previous PEEP, no difference value will appear in the graph and table of screen 102g6 of
Reverting now to the situation with respect to the PEEPs of 25 and 20 cmH2Om, as noted above, at these higher PEEPs, there is little de-recruitment of lung volume as the alveolar sacs are continuously open during the respiratory cycle. This is expressed in
An analogous situation exists for dynostatic curve 532 generated for the PEEP of 15 cmH2O. That is, dynostatic curve 532 passes through point 514 formed using the functional residual capacity for 20 cmH2O. Again, there is a zero difference as tabulated in table 112 for 20 cmH2O. In graph 110 of
An analogous situation exists when the PEEP is lowered from 10 cmH2O to 5 cmH2O as shown by line segment 548a. The de-recruitment of lung volume in that case is about 120 ml.
It will be appreciated, that a clinician may readily discern an optimal PEEP for patient 12 from the graphic and tabular data provided in screen 102g6 of
As PEEP is further reduced to 15 cmH2O and then to 10 cmH2O, a difference in volume will occur and curve 548 will separate below curve 516 in graph 110. The clinician will be able to note that at a PEEP of 10 cmH2O, a portion of the lung volume that had been open at a PEEP of 15 cmH2O will remain closed as pressure is increased from the PEEP of 10 cmH2O to 15 cmH2O during the course of inspiration while moving up the dynostatic curve. This difference, 180 ml in the example shown in
Further lowering the PEEP to 5 cmH2O results in an additional de-recruited loss of lung volume of 120 ml as shown by line segment 548a. As can be seen from the graph, the lung begins to lose volume or “derecruits” at PEEP settings below 15 cmH2O and this suggests that 15 cmH2O is a PEEP that is best suited or optimal for patient 12. In selecting an optimal PEEP, the clinician may set the PEEP at 15 cmH2O so as to obtain some recruitment of lung volume over a PEEP of 10 cmH2O. This may be preceded by a recruitment maneuver, such as at step 500, if desired. Or, the clinician may leave the PEEP at 10 cmH2O since some recruitment is obtained at that level of PEEP.
As described above in connection with the determination of functional residual capacity, the determination of a suitable PEEP can be set to automatically occur in conjunction with certain procedures carried out by ventilator 10 or treatment procedures carried out on patient 12.
While the foregoing describes an example in which PEEP is decreased as the amount of recruitment or de-recruitment is determined, it will be appreciated that the technique may also be carried out using incremented, increasing values of PEEP.
Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.
The present application claims the priority of U.S. Provisional Application No. 60/719,329, filed Sep. 21, 2005.
| Number | Date | Country | |
|---|---|---|---|
| 60719329 | Sep 2005 | US |
