Adaptive alarm system

Abstract

An adaptive alarm system is responsive to a physiological parameter so as to generate an alarm threshold that adapts to baseline drift in the parameter and reduce false alarms without a corresponding increase in missed true alarms. The adaptive alarm system has a parameter derived from a physiological measurement system using a sensor in communication with a living being. A baseline processor calculates a parameter baseline from a parameter trend. Parameter limits specify an allowable range of the parameter. An adaptive threshold processor calculates an adaptive threshold from the parameter baseline and the parameter limits. An alarm generator is responsive to the parameter and the adaptive threshold so as to trigger an alarm indicative of the parameter crossing the adaptive threshold. The adaptive threshold is responsive to the parameter baseline so as to increase in value as the parameter baseline drifts to a higher parameter value and to decrease in value as the parameter baseline drifts to a lower parameter value.

Claims

1. An improved method of obtaining pulse oximetry measurements and reducing false alarms therefrom, the method comprising: continuously measuring, with a pulse oximeter in communication with an optical sensor, a physiological parameter over a first time window; establishing, with the pulse oximeter, a baseline for the physiological parameter, the parameter baseline being determined from values of the physiological parameter taken during a second window of time within the first time window, the baseline is reestablished using a new window of data on a continuing basis over the first time window; automatically determining, with the pulse oximeter, an upper alarm threshold and a lower alarm threshold at a delta difference from a most recent value of the baseline, the delta difference for the upper alarm threshold increases when the baseline drifts away from a maximum parameter limit and decreases when the baseline drifts toward the maximum parameter limit, the delta difference for the lower alarm threshold increases when the baseline drifts away from a minimum parameter limit and decreases when the baseline drifts toward the minimum parameter limit; dynamically adjusting, with the pulse oximeter, at predetermined regular intervals the delta difference between the alarm thresholds and the baseline during the first time window, the delta difference is adjusted based on a current value of the baseline, and the alarm thresholds are re-determined at the predetermined regular intervals over the first time window using the current delta difference; and triggering an alarm in response to the parameter measurement crossing either of the alarm thresholds.

2. The method according to claim 1 wherein establishing a baseline comprises: biasing a segment of the parameter measurement; determining a biased trend from the biased segment; and restricting a transient response of the biased trend.

3. The method according to claim 1 wherein adjusting the delta difference comprises: setting a parameter limit; and determining the delta difference between the alarm thresholds and the baseline as a linear function of the baseline according to the parameter limit.

4. The method according to claim 1, further comprising setting a parameter limit which includes: selecting a first parameter limit in relation to a delayed alarm; and selecting a second parameter limit in relation to an un-delayed alarm.

5. The method according to claim 2 wherein biasing a segment of the parameter comprises: windowing the parameter measurements; removing a lower value portion of the windowed parameter measurements; and averaging a remaining portion of the windowed parameter measurements.

6. An improved pulse oximeter with reduced false alarms comprising: an input configured to receive one or more signals from an optical sensor, the optical sensor measuring a change in light absorption of a patient's tissue; and at least one hardware processor, the hardware processor configured to determines a plurality of physiological parameter values over a span of time and determines a baseline according to a trend of the parameter values, the baseline is re-determined at predetermined regular intervals, the predetermined regular intervals occur when a new plurality of physiological parameter values are determined; the at least one hardware processor further configured to establishing an upper and lower alarm threshold at a delta difference from the baseline at each predetermined regular interval, the delta difference of the upper alarm threshold increasing when the baseline drifts away from a maximum parameter limit and decreasing when the baseline drifts toward the maximum parameter limit, the delta difference of the lower alarm threshold increasing when the baseline drifts away from a minimum parameter limit and decreasing when the baseline drifts toward the minimum parameter limit; and an alarm generator, the alarm generator is configured to trigger an alarm when a parameter transient from the baseline crosses the upper or lower alarm thresholds.

7. The improved pulse oximeter according to claim 6 wherein the at least one hardware processor is further configured to outputs a biased trend; and the baseline responsive to the biased trend to reduce the size of a transient that triggers the alarm.

8. The improved pulse oximeter according to claim 7 wherein the at least one hardware processor is further configured to reduces baseline movement due to parameter transients.

9. The improved pulse oximeter according to claim 6 wherein the alarm generator is responsive to both positive and negative transients from the baseline.

10. The improved pulse oximeter according to claim 9 wherein the at least one hardware processor is further configured to establishes a lower baseline biased above the parameter trend and an upper baseline biased below the parameter trend.

11. The improved pulse oximeter according to claim 10 wherein the lower alarm threshold is increasingly responsive to negative transients and the upper alarm threshold is decreasingly responsive to positive transients as the baseline trends toward lower parameter values.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1-3 are exemplar graphs illustrating problems and issues associated with physiological parameter measurement systems having fixed threshold alarm schemas;

(2) FIGS. 4A-B are general block diagrams of an adaptive alarm system having lower parameter limits;

(3) FIGS. 5A-B are a graph of a physiological parameter versus delta space and a graph of delta versus baseline, respectively, illustrating the relationship between a baseline, a lower-limit adaptive threshold and a variable difference delta between the baseline and the adaptive threshold;

(4) FIG. 6 is an exemplar graph of a physiological parameter versus time illustrating an adaptive alarm system having a lower-limit adaptive threshold;

(5) FIG. 7 is a graph of oxygen saturation versus time illustrating a baseline for determining an adaptive threshold;

(6) FIG. 8 is a graph of oxygen saturation versus time comparing adaptive-threshold alarm performance with fixed-threshold alarm performance;

(7) FIGS. 9A-B are general block diagrams of an adaptive alarm system having upper parameter limits;

(8) FIGS. 10A-B are a graph of a physiological parameter versus delta space and a graph of delta versus baseline, respectively, illustrating the relationship between a baseline, an upper-limit adaptive threshold and a variable delta difference between the baseline and the adaptive threshold;

(9) FIG. 11 is an exemplar graph of a physiological parameter versus time illustrating an adaptive alarm system having an upper-limit adaptive threshold;

(10) FIGS. 12A-B are general block diagrams of an adaptive alarm system having both lower alarm limits and upper alarm limits;

(11) FIGS. 13A-E are physiological parameter versus delta space graphs illustrating a lower-limit adaptive threshold, an upper-limit adaptive threshold, and a combined lower- and upper-limit adaptive threshold in various delta spaces; and

(12) FIG. 14 is an exemplar graph of a physiological parameter versus time illustrating an adaptive alarm system having both lower and upper alarm limits.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(13) FIGS. 4A-B illustrate an adaptive alarm system 400 embodiment having lower parameter limits L.sub.1 and L.sub.2. As shown in FIG. 4A, the adaptive alarm system 400 has parameter 401, first limit (L.sub.1) 403, second limit (L.sub.2) 405 and maximum parameter value (Max) 406 inputs and generates a corresponding alarm 412 output. The parameter 401 input is generated by a physiological parameter processor, such as a pulse oximeter or an advanced blood parameter processor described above, as examples. The adaptive alarm system 400 has an alarm generator 410, a baseline processor 420, and an adaptive threshold processor 440. The alarm generator 410 has parameter 401 and adaptive threshold (AT) 442 inputs and generates the alarm 412 output accordingly. A baseline processor 420 has the parameter 401 input and generates a parameter baseline (B) 422 output. The baseline processor 420, is described in detail with respect to FIG. 4B, below. An adaptive threshold processor 440 has parameter baseline (B) 422, L.sub.1 403, L.sub.2 405 and Max 406 inputs and generates the adaptive threshold (AT) 442. The adaptive threshold processor 440 is described in detail with respect to FIGS. 5A-B, below.

(14) As shown in FIG. 4A, in an embodiment L.sub.1 403 and L.sub.2 405 may correspond to conventional fixed alarm thresholds with and without an alarm time delay, respectively. For an adaptive threshold schema, however, L.sub.1 403 and L.sub.2 405 do not determine an alarm threshold per se, but are reference levels for determining an adaptive threshold (AT) 442. In an embodiment, L.sub.1 403 is an upper limit of the adaptive alarm threshold AT when the baseline is near the maximum parameter value (Max), and L.sub.2 405 is a lower limit of the adaptive alarm threshold, as described in detail with respect to FIGS. 5A-B, below. In an exemplar embodiment when the parameter is oxygen saturation, L.sub.1 403 is set at or around 90% and L.sub.2 405 is set at 5 to 10% below L.sub.1, i.e. at 85% to 80% oxygen saturation. Many other L.sub.1 and L.sub.2 values may be used for an adaptive threshold schema as described herein.

(15) Also shown in FIG. 4A, in an embodiment the alarm 412 output is triggered when the parameter 401 input falls below AT 442 and ends when the parameter 401 input rises above AT 442 or is otherwise cancelled. In an embodiment, the alarm 412 output is triggered after a time delay (TD), which may be fixed or variable. In an embodiment, the time delay (TD) is a function of the adaptive threshold (AT) 442. In an embodiment, the time delay (TD) is zero when the adaptive threshold (AT) is at the second lower limit (L.sub.2) 405.

(16) As shown in FIG. 4B, a baseline processor 420 embodiment has a sliding window 450, a bias calculator 460, a trend calculator 470 and a response limiter 480. The sliding window 450 inputs the parameter 401 and outputs a time segment 452 of the parameter 401. In an embodiment, each window incorporates a five minute span of parameter values. The bias calculator 460 advantageously provides an upward shift in the baseline (B) 422 for an additional margin of error over missed true alarms. That is, a baseline 422 is generated that tracks a higher-than-average range of parameter values, effectively raising the adaptive threshold AT slightly above a threshold calculated based upon a true parameter average, as shown and described in detail with respect to FIGS. 7-8, below. In an embodiment, the bias calculator 460 rejects a lower range of parameter values from each time segment 452 from the sliding window so as to generate a biased time segment 462.

(17) Also shown in FIG. 4B, the trend calculator 470 outputs a biased trend 472 of the remaining higher range of parameter values in each biased segment 462. In an embodiment, the biased trend 462 is an average of the values in the biased time segment 462. In other embodiments, the biased trend 462 is a median or mode of the values in the biased time segment 462. The response limiter 480 advantageously limits the extent to which the baseline 422 output tracks the biased trend 472. Accordingly, the baseline 422 tracks only relatively longer-lived transitions of the parameter, but does not track (and hence mask) physiologically significant parameter events, such as oxygen desaturations for a SpO.sub.2 parameter to name but one example. In an embodiment, the response limiter 480 has a low pass transfer function. In an embodiment, the response limiter 480 is a slew rate limiter.

(18) FIGS. 5A-B further illustrate an adaptive threshold processor 440 (FIG. 4A) having a baseline (B) 422 input and generating an adaptive threshold (AT) 442 output and a delta (Δ) 444 ancillary output according to parameter limits L.sub.1 403, L.sub.2 405 and Max 406, as described above. As shown in FIG. 5A, as the baseline (B) 422 decreases (increases) the adaptive threshold (AT) 444 monotonically decreases (increases) between L.sub.1 403 and L.sub.2 405. Further, as the baseline (B) 422 decreases (increases) the delta (Δ) 444 difference between the baseline (B) 422 and the adaptive threshold (AT) 442 monotonically decreases (increases) between Max−L.sub.1 and zero.

(19) As shown in FIG. 5B, the relationship between the delta (Δ) 444 and the baseline (B) 444 may be linear 550 (solid line), non-linear 560 (small-dash lines) or piecewise-linear (large-dash lines), to name a few. In an embodiment, the adaptive threshold processor 440 (FIG. 4A) calculates an adaptive threshold (AT) 442 output in response to the baseline (B) 422 input according to a linear relationship. In a linear embodiment, the adaptive threshold processor 440 (FIG. 4A) calculates the adaptive threshold (AT) 442 according to EQS. 1-2:

(20) $\begin{array}{cc}\Delta =-\left(\frac{\mathrm{Max}-L_1}{\mathrm{Max}-L_2}\right)\left(\mathrm{Max}-B\right)+\left(\mathrm{Max}-L_1\right)& \left(1\right)\\ \mathrm{AT}=B-\Delta & \left(2\right)\end{array}$
where Δ=Max−L.sub.1 @ B=Max; Δ=0 @ B=L.sub.2
and where AT=L.sub.1 @ B=Max; AT=L.sub.2 @ B=L.sub.2, accordingly.

(21) FIG. 6 illustrates the operational characteristics an adaptive alarm system 400 (FIG. 4A) having parameter limits Max 612, L.sub.1 614 and L.sub.2 616 and an alarm responsive to a baseline (B) 622, 632, 642; an adaptive threshold (AT) 628, 638, 648; and a corresponding Δ 626, 636, 646 according to EQS. 1-2, above. In particular, a physiological parameter 610 is graphed versus time 690 for various time segments t.sub.1, t.sub.2, t.sub.3 692-696. The parameter range (PR) 650 is:
PR=Max−L.sub.2  (3)
and the adaptive threshold range (ATR) 660 is:
ATR=L.sub.1−L.sub.2  (4)

(22) As shown in FIG. 6, during a first time period t.sub.1 692, a parameter segment 620 has a baseline (B) 622 at about Max 612. As such, Δ 626=Max−L.sub.1 and the adaptive threshold (AT) 628 is at about L.sub.1 614. Accordingly, a transient 624 having a size less than Δ 626 does not trigger the alarm 412 (FIG. 4A).

(23) Also shown in FIG. 6, during a second time period t.sub.2 694, a parameter segment 630 has a baseline (B) 632 at about L.sub.1 614. As such, Δ 636 is less than Max−L.sub.1 and the adaptive threshold (AT) 638 is between L.sub.1 and L.sub.2. Accordingly, a smaller transient 634 will trigger the alarm as compared to a transient 624 in the first time segment.

(24) Further shown in FIG. 6, during a third time period t.sub.3 696, a parameter segment 640 has a baseline (B) 642 at about L.sub.2 616. As such, Δ 646 is about zero and the adaptive threshold (AT) 648 is at about L.sub.2. Accordingly, even a small negative transient will trigger the alarm. As such, the behavior of the alarm threshold AT 628, 638, 648 advantageously adapts to higher or lower baseline values so as to increase or decrease the size of negative transients that trigger or do not trigger the alarm 412 (FIG. 4A).

(25) FIG. 7 is a parameter versus time graph 700 illustrating the characteristics of an adaptive alarm system 400 (FIGS. 4A-B), as described with respect to FIGS. 4-6, above, where the parameter is oxygen saturation (SpO.sub.2). The graph 700 has a SpO.sub.2 trace 710 and a superimposed baseline trace 720. The graph 700 also delineates tracking periods 730, where the baseline 720 follows the upper portions of SpO.sub.2 values, and lagging periods 740, where the baseline 720 does not follow transient SpO.sub.2 events. The tracking time periods 730 illustrate that the baseline 720 advantageously tracks at the higher range of SpO.sub.2 values 710 during relatively stable (flat) periods, as described above. Lagging time periods 740 illustrate that the baseline 720 is advantageously limited in response to transient desaturation events so that significant desaturations fall below an adaptive threshold (not shown) and trigger an alarm accordingly.

(26) FIG. 8 is a parameter versus time graph 800 illustrating characteristics of an adaptive alarm system 400 (FIGS. 4A-B), as described with respect to FIGS. 4-6, above, where the parameter is oxygen saturation (SpO.sub.2). Vertical axis (SpO.sub.2) resolution is 1%. The time interval 801 between vertical hash marks is five minutes. The graph 800 has a SpO.sub.2 trace 810 and a baseline trace 820. The graph 800 also has a fixed threshold trace 830, a first adaptive threshold (AT) trace 840 and a second AT trace 850. The graph 800 further has a fixed threshold alarm trace 860, a first adaptive threshold alarm trace 870 and a second adaptive threshold alarm trace 880. In this example, L.sub.1 is 90% and L.sub.2 is 85% for the first AT trace 840 and first AT alarm trace 870. L.sub.2 is 80% for a second AT trace 850 and a second AT alarm trace 880. The fixed threshold 830 results in many nuisance alarms 860. By comparison, the adaptive threshold alarm with L.sub.2=85% has just one time interval of alarms 872 during a roughly 6% desaturation period (from 92% to 86%). The adaptive threshold alarm with L.sub.2=80%, has no alarms during the 1 hour 25 minute monitoring period.

(27) FIGS. 9A-B illustrate an adaptive alarm system 900 embodiment having upper parameter limits U.sub.1 and U.sub.2. As shown in FIG. 9A, the adaptive alarm system 900 has parameter 901, first limit (U.sub.1) 903, second limit (U.sub.2) 905 and minimum parameter value (Min) 906 inputs and generates a corresponding alarm 912 output. The parameter 901 input is generated by a physiological parameter processor, such as a pulse oximeter or an advanced blood parameter processor described above, as examples. The adaptive alarm system 900 has an alarm generator 910, a baseline processor 920, and an adaptive threshold processor 940. The alarm generator 910 has parameter 901 and adaptive threshold (AT) 942 inputs and generates the alarm 912 output accordingly. A baseline processor 920 has the parameter 901 input and generates a parameter baseline (B) 922 output. The baseline processor 920, is described in detail with respect to FIG. 9B, below. An adaptive threshold processor 940 has parameter baseline (B) 922, U.sub.1 903, U.sub.2 905 and Min 906 inputs and generates the adaptive threshold (AT) 942. The adaptive threshold processor 940 is described in detail with respect to FIGS. 10A-B, below.

(28) As shown in FIG. 9A, in an embodiment U.sub.1 903 and U.sub.2 905 may correspond to conventional fixed alarm thresholds with and without an alarm time delay, respectively. For an adaptive threshold schema, however, U.sub.1 903 and U.sub.2 905 do not determine an alarm threshold per se, but are reference levels for determining an adaptive threshold (AT) 942. In an embodiment, U.sub.1 903 is a lower limit of the adaptive alarm threshold AT when the baseline is near the minimum parameter value (Min), and U.sub.2 905 is an upper limit of the adaptive alarm threshold, as described in detail with respect to FIGS. 10A-B, below. In an exemplar embodiment when the parameter is oxygen saturation, U.sub.1 903 is set at or around 85% and U.sub.2 905 is set at or around 90% oxygen saturation. Many other U.sub.1 and U.sub.2 values may be used for an adaptive threshold schema as described herein.

(29) Also shown in FIG. 9A, in an embodiment the alarm 912 output is triggered when the parameter 901 input rises above AT 942 and ends when the parameter 901 input falls below AT 942 or is otherwise cancelled. In an embodiment, the alarm 912 output is triggered after a time delay (TD), which may be fixed or variable. In an embodiment, the time delay (TD) is a function of the adaptive threshold (AT) 942. In an embodiment, the time delay (TD) is zero when the adaptive threshold (AT) is at the second upper limit (U.sub.2) 905.

(30) As shown in FIG. 9B, a baseline processor 920 embodiment has a sliding window 950, a bias calculator 960, a trend calculator 970 and a response limiter 980. The sliding window 950 inputs the parameter 901 and outputs a time segment 952 of the parameter 901. In an embodiment, each window incorporates a five minute span of parameter values. The bias calculator 960 advantageously provides a downward shift in the baseline (B) 922 for an additional margin of error over missed true alarms. That is, a baseline 922 is generated that tracks a lower-than-average range of parameter values, effectively lowering the adaptive threshold AT slightly below a threshold calculated based upon a true parameter average. In an embodiment, the bias calculator 960 rejects an upper range of parameter values from each time segment 952 from the sliding window so as to generate a biased time segment 962.

(31) Also shown in FIG. 9B, the trend calculator 970 outputs a biased trend 972 of the remaining lower range of parameter values in each biased segment 962. In an embodiment, the biased trend 962 is an average of the values in the biased time segment 962. In other embodiments, the biased trend 962 is a median or mode of the values in the biased time segment 962. The response limiter 980 advantageously limits the extent to which the baseline 922 output tracks the biased trend 972. Accordingly, the baseline 922 tracks only relatively longer-lived transitions of the parameter, but does not track (and hence mask) physiologically significant parameter events, such as oxygen desaturations for a SpO.sub.2 parameter to name but one example. In an embodiment, the response limiter 980 has a low pass transfer function. In an embodiment, the response limiter 980 is a slew rate limiter.

(32) FIGS. 10A-B further illustrate an adaptive threshold processor 940 (FIG. 9A) having a baseline (B) 922 input and generating an adaptive threshold (AT) 942 output and a delta (Δ) 944 ancillary output according to parameter limits U.sub.1 903, U.sub.2 905 and Min 906, as described above. As shown in FIG. 10A, as the baseline (B) 922 decreases (increases) the adaptive threshold (AT) 944 monotonically decreases (increases) between U.sub.1 903 and U.sub.2 905. Further, as the baseline (B) 922 decreases (increases) the delta (Δ) 944 difference between the baseline (B) 922 and the adaptive threshold (AT) 942 monotonically decreases (increases) between Min−U.sub.1 and zero.

(33) As shown in FIG. 10B, the relationship between the delta (Δ) 944 and the baseline (B) 944 may be linear 550 (solid line), non-linear 560 (small-dash lines) or piecewise-linear (large-dash lines), to name a few. In an embodiment, the adaptive threshold processor 940 (FIG. 9A) calculates an adaptive threshold (AT) 942 output in response to the baseline (B) 922 input according to a linear relationship. In a linear embodiment, the adaptive threshold processor 940 (FIG. 9A) calculates the adaptive threshold (AT) 942 according to EQS. 5-6:

(34) $\begin{array}{cc}\Delta =-\left(\frac{U_1-\mathrm{Min}}{U_2-\mathrm{Min}}\right)\left(B-\mathrm{Min}\right)+\left(U_1-\mathrm{Min}\right)& \left(5\right)\\ \mathrm{AT}=B+\Delta & \left(6\right)\end{array}$
where Δ=U.sub.1−Min @ B=Min; Δ=0 @ B=U.sub.2
and where AT=U.sub.1 @ B=Min; AT=U.sub.2 @ B=U.sub.2, accordingly.

(35) FIG. 11 illustrates the operational characteristics an adaptive alarm system 900 (FIG. 9A) having parameter limits Min 1112, U.sub.1 1114 and U.sub.2 1116 and an alarm responsive to a baseline (B) 1122, 1132, 1142; an adaptive threshold (AT) 1128, 1138, 1148; and a corresponding Δ 1126, 1136, 1146 according to EQS. 5-6, above. In particular, a physiological parameter 1110 is graphed versus time 1190 for various time segments t.sub.1, t.sub.2, t.sub.3 1192-1196. The parameter range (PR) 1150 is:
PR=U.sub.2−Min  (7)
and the adaptive threshold range (ATR) 1160 is:
ATR=U.sub.2−U.sub.1  (8)

(36) As shown in FIG. 11, during a first time period t.sub.1 1192, a parameter segment 1120 has a baseline (B) 1122 at about Min 1112. As such, Δ 1126=U.sub.1−Min and the adaptive threshold (AT) 1128 is at about U.sub.1 1114. Accordingly, a transient 1124 having a size less than Δ 1126 does not trigger the alarm 912 (FIG. 9A).

(37) Also shown in FIG. 11, during a second time period t.sub.2 1194, a parameter segment 1130 has a baseline (B) 1132 at about U.sub.1 1114. As such, Δ 1136 is less than U.sub.1−Min and the adaptive threshold (AT) 1138 is between U.sub.1 and U.sub.2. Accordingly, a smaller transient 1134 will trigger the alarm as compared to a transient 1124 in the first time segment.

(38) Further shown in FIG. 11, during a third time period t.sub.3 1196, a parameter segment 1140 has a baseline (B) 1142 at about U.sub.2 1116. As such, Δ 1146 is about zero and the adaptive threshold (AT) 1148 is at about U.sub.2. Accordingly, even a small positive transient will trigger the alarm. As such, the behavior of the alarm threshold AT 1128, 1138, 1148 advantageously adapts to higher or lower baseline values so as to increase or decrease the size of positive transients that trigger or do not trigger the alarm 912 (FIG. 9A).

(39) FIGS. 12A-B illustrate an adaptive alarm system 1200 embodiment having lower limits L.sub.1, L.sub.2 1203, such as described with respect to FIGS. 4A-B above, or upper limits U.sub.1, U.sub.2 1205 such as described with respect to FIGS. 9A-B above, or both. As shown in FIG. 12A, the adaptive alarm system 1200 has parameter 1201, lower limit 1203 and upper limit 1205 inputs and generates a corresponding alarm 1212 output. The parameter 1201 input is generated by a physiological parameter processor, such as a pulse oximeter or an advanced blood parameter processor described above, as examples. The adaptive alarm system 1200 has an alarm generator 1210, a baseline processor 1220 and an adaptive threshold processor 1240. The alarm generator 1210 has parameter 1201 and adaptive threshold (AT) 1242 inputs and generates the alarm 1212 output accordingly. A baseline processor 1220 has the parameter 1201 input and generates one or more parameter baseline 1222 outputs. The baseline processor 1220, is described in detail with respect to FIG. 12B, below. An adaptive threshold processor 1240 has parameter baseline 1222, lower limit L.sub.1, L.sub.2 1203 and upper limit U.sub.1, U.sub.2 1205 inputs and generates lower and upper adaptive threshold AT.sub.l, A.sub.u 1242 outputs. The adaptive threshold processor 1240 also generates ancillary upper and lower delta 1244 outputs. The adaptive threshold processor 1240 is described in detail with respect to FIGS. 13A-E, below.

(40) As shown in FIG. 12A, in an embodiment L.sub.1, L.sub.2 1203 and U.sub.1, U.sub.2 1205 may correspond to conventional fixed alarm thresholds with an alarm delay (L.sub.1, U.sub.1) and without an alarm delay (L.sub.2, U.sub.2). For an adaptive threshold schema, however, these limits 1203, 1205 do not determine an alarm threshold per se, but are reference levels for determining lower and upper adaptive thresholds AT.sub.l, AT.sub.u 1242.

(41) Also shown in FIG. 12A, in an embodiment the alarm 1212 output is triggered when the parameter 1201 input falls below AT.sub.l 1242 and ends when the parameter 1201 input rises above AT, 1242 or the alarm is otherwise cancelled. Further, the alarm 1212 output is triggered when the parameter 1201 input rises above AT.sub.u 1242 and ends when the parameter 1201 input falls below AT.sub.u 1242 or the alarm is otherwise cancelled. In an embodiment, the alarm 1212 output is triggered after a time delay (TD), which may be fixed or variable. In an embodiment, the time delay (TD) is a function of the adaptive thresholds (AT.sub.l, AT.sub.u) 1242. In an embodiment, the time delay (TD) is zero when the lower adaptive threshold (AT.sub.l) 1242 is at the second lower limit (L.sub.2) 1203 or when the upper adaptive alarm threshold AT 1242 is at the second upper limit (U.sub.2) 1205.

(42) As shown in FIG. 12B, a baseline processor 1220 embodiment has a sliding window 1250, an over-bias calculator 1260, an under-bias calculator 1265, trend calculators 1270 and response limiters 1280. The sliding window 1250 inputs the parameter 1201 and outputs a time segment 1252 of the parameter 1201. In an embodiment, each window incorporates a five minute span of parameter 1201 values.

(43) Also shown in FIG. 12B, the over-bias calculator 1260 advantageously provides an upward shift in the lower baseline (B.sub.l) 1282 for an additional margin of error over missed lower true alarms. That is, a lower baseline (B.sub.l) 1282 is generated that tracks a higher-than-average range of parameter values, effectively raising the lower adaptive threshold AT, slightly above a threshold calculated based upon a true parameter average. In an embodiment, the over-bias calculator 1260 rejects a lower range of parameter values from each time segment 1252 of the sliding window 1250 so as to generate an over-biased time segment 1262.

(44) Further shown in FIG. 12B, the under-bias calculator 1265 advantageously provides a downward shift in the upper baseline (B.sub.u) 1287 for an additional margin of error over missed upper true alarms. That is, an upper baseline (B.sub.u) 1287 is generated that tracks a lower-than-average range of parameter values, effectively lowering the upper adaptive threshold AT.sub.u slightly below a threshold calculated based upon a true parameter average. In an embodiment, the under-bias calculator 1267 rejects an upper range of parameter values from each time segment 1252 of the sliding window 1250 so as to generate an under-biased time segment 1267.

(45) Additionally shown in FIG. 12B, the trend calculator 1270 outputs an over-biased trend 1272 of the remaining higher range of parameter values in each over-biased segment 1262. Further, the trend calculator 1270 outputs an under-biased trend 1277 of the remaining lower range of parameter values in each under-biased segment 1267. In an embodiment, the biased trends 1272, 1277 are each an average of the values in the corresponding biased time segments 1262, 1267. In other embodiments, the biased trends 1272, 1277 are each a median or mode of the values in the corresponding biased time segments 1262, 1267. The response limiter 1280 advantageously limits the extent to which the baseline 1222 outputs track the biased trends 1272, 1277. Accordingly, the baseline 1222 outputs track only relatively longer-lived transitions of the parameter 1201, but do not track (and hence mask) physiologically significant parameter events. In an embodiment, the response limiter 1280 has a low pass transfer function. In an embodiment, the response limiter 1280 is a slew rate limiter.

(46) FIGS. 13A-E illustrate parameter (P) operating ranges and ideal ranges in view of both lower and upper parameter limits. As shown in FIG. 13A, as the baseline (B.sub.l) 1317 decreases (increases) the adaptive threshold (AT.sub.l) 1318 monotonically decreases (increases) between L.sub.1 and L.sub.2. Further, as the baseline (B.sub.l) 1317 decreases (increases) the delta (Δ.sub.l) 1319 difference between the baseline (B.sub.l) 1317 and the adaptive threshold (AT.sub.l) 1318 monotonically decreases (increases) between Max−L.sub.1 and 0.

(47) As shown in FIG. 13B, as the baseline (B.sub.u) 1327 increases (decreases) the adaptive threshold (AT.sub.u) 1328 monotonically increases (decreases) between U.sub.1 and U.sub.2. Further, as the baseline (B.sub.u) 1327 increases (decreases) the delta (Δ.sub.u) 1329 difference between the adaptive threshold (AT.sub.u) 1328 and the baseline (B.sub.u) 1327 monotonically decreases (increases) between Min−U.sub.1 and 0.

(48) As shown in FIG. 13C, combining FIGS. 13A-B, the parameter (P) operating range is bounded by the overlapping regions of 13A and 13B 1330 having an upper bound of U.sub.2 and a lower bound of L.sub.2. In particular, L.sub.1, L.sub.2 are the upper and lower limits of the lower adaptive alarm threshold AT.sub.l; and U.sub.2, U.sub.1 are the upper and lower limits of the upper adaptive alarm threshold AT.sub.u.

(49) FIG. 13D illustrates parameter (P) versus the overlapping independent delta domains F.sub.u, F.sub.l for upper and lower baselines B.sub.u, B.sub.l; adaptive thresholds AT.sub.u, AT.sub.l and deltas Δ.sub.u, Δ.sub.l, based upon FIGS. 13A-C. FIG. 13E illustrates parameter (P) versus the overlapping independent delta domains F.sub.u, F.sub.l (reversed); for upper and lower baselines B.sub.u, B.sub.l; adaptive thresholds AT.sub.u, AT.sub.l and deltas Δ.sub.u, Δ.sub.l,

(50) As shown in FIG. 13E, the equations for bi-lateral adaptive thresholds are:

(51) $\begin{array}{cc}{\Delta }_u=-\left(\frac{U_1-L_2}{U_2-L_2}\right)\left(B-L_2\right)+\left(U_1-L_2\right)& \left(9\right)\\ {\mathrm{AT}}_u=B+{\Delta }_u& \left(10\right)\end{array}$
where Δ.sub.u=U.sub.1−L.sub.2 @ B=L.sub.2; and Δ=0 @ B=U.sub.2; and
where AT.sub.u=L.sub.1 @ B=L.sub.2; and AT.sub.u=U.sub.2@ B=U.sub.2.
Further:

(52) $\begin{array}{cc}{\Delta }_l=\left(\frac{U_2-L_1}{U_2-L_2}\right)\left(B-L_2\right)& \left(11\right)\\ {\mathrm{AT}}_l=B-{\Delta }_l& \left(12\right)\end{array}$
where Δ.sub.l=U.sub.2−L.sub.1 @ B=U.sub.2; and Δ.sub.l=0 @ B=L.sub.2; and
where AT.sub.l=L.sub.1 @ B=U.sub.2; AT.sub.l=L.sub.2 @ B=L.sub.2.

(53) Although shown as a linear relationship, in general:
Δ.sub.l=ƒ.sub.1(B);Δ.sub.u=ƒ.sub.2(B)
That is, Δ.sub.l and Δ.sub.u can each be a linear function of B, a non-linear function of B or a piecewise linear function of B, to name a few, in a manner similar to that described with respect to FIGS. 5B and 10B, above.

(54) FIGS. 14A-B illustrate the operational characteristics an adaptive alarm system 1200 (FIGS. 12A-B) having upper limits U.sub.1, U.sub.2 1412, 1414 and lower limits L.sub.1, L.sub.2 1422, 1424. An alarm 1212 (FIG. 12A) output is responsive to a baseline (B) 1432, 1442, 1452, 1462; an upper delta (Δ.sub.u) 1437, 1447, 1457, 1467; and a corresponding upper adaptive threshold (AT.sub.u) 1439, 1449, 1459, 1469, according to EQS. 9-10, above. Further, the alarm 1212 (FIG. 12A) output is responsive to a lower delta (Δ.sub.l) 1436, 1446, 1456, 1466 and a corresponding lower adaptive threshold (AT.sub.l) 1438, 1448, 1458, 1468, according to EQS. 11-12, above.

(55) As shown in FIGS. 14A-B, a physiological parameter 1410 is graphed versus time 1490 for various time segments t.sub.1, t.sub.2, t.sub.3, t.sub.4 1492-1498. The parameter range (PR) 1480 is:
PR=U.sub.2−L.sub.2  (13)
the lower adaptive threshold AT.sub.l range is:
ATR.sub.l=L.sub.1−L.sub.2  (14)
the upper adaptive threshold AT.sub.u range is:
ATR.sub.l=U.sub.2−U.sub.1  (15)

(56) As shown in FIG. 14A, during a first time period t.sub.1 1492, a parameter segment 1430 has a baseline (B) 1432 at about U.sub.2 1414. As such, Δ.sub.l 1436=U.sub.2−L.sub.1; Δ.sub.u 1437=0; AT.sub.l 1438=L.sub.1; AT.sub.u 1439=U.sub.2. Accordingly, a negative transient 1434 having a size less than U.sub.2−L.sub.1 does not trigger an alarm.

(57) Also shown in FIG. 14A, during a second time period t.sub.2 1494, a parameter segment 1440 has a baseline (B) 1442 less than U.sub.2. As such, Δ.sub.l 1446 is less than U.sub.1−L.sub.1 and the adaptive threshold (AT.sub.u) 1447 is between U.sub.1 and U.sub.2. Accordingly, a smaller negative transient 1444 will trigger the alarm as compared to the negative transient 1434 in the first time segment 1430.

(58) Further shown in FIG. 14A, during a third time period t.sub.3 1496, a parameter segment 1450 has a baseline (B) 1452 less than U.sub.1 1412. As such, a smaller negative transient 1454 will trigger the alarm as compared to the negative transient 1444 in the second time segment 1440. However, a larger positive transient 1455 is needed to trigger the alarm as compared to the positive transient 1445 in the second time segment 1440.

(59) Additionally shown in FIG. 14A, during a fourth time period t.sub.4 1460, a parameter segment 1460 has a baseline (B) 1462 at about L.sub.2 1424. As such, Δ.sub.l 1466=0; Δ.sub.u 1467=U.sub.1−L.sub.2; AT.sub.l 1468=L.sub.2; AT.sub.u 1469=U.sub.1. Accordingly, a positive transient 1465 having a size less than U.sub.1-L.sub.2 does not trigger an alarm.

(60) An adaptive alarm system has been disclosed in detail in connection with various embodiments. These embodiments are disclosed by way of examples only and are not to limit the scope of the claims that follow. One of ordinary skill in the art will appreciate many variations and modifications.