Apparatus and method for monitoring a patient in a hospital bed

• US 20060028350A1
• Filed: 12/10/2004
• Published: 02/09/2006
• Est. Priority Date: 08/09/2004
• Status: Active Grant

• Current Assignee: Hill-Rom Services Incorporated (Baxter International Inc.)
• Original Assignee: Hill-Rom Services Incorporated (Baxter International Inc.)
• Inventors: Bhai, Aziz A.
• Granted Patent: US 7,253,366 B2
• Time in Patent Office: Days
• US Class Current: 340/666
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/1115 Monitoring leaving of a patient support, e.g. a bed or a wheelchair
• CPC Class Codes: A61G 2203/34 for pressure
• CPC Class Codes: A61G 2203/36 for motion
• CPC Class Codes: G01G 19/445 in a horizontal position
• CPC Class Codes: G16H 40/63 for local operation

Abstract

A system for monitoring a patient on a hospital bed includes load cells and a controller for detecting patient movement on, exit from, and impending exit from the hospital bed, including movement across or outside a virtual boundary or region located on the bed. The controller is configured to detect changes in the distribution of patient weight among the load cells. The controller is also configured to accommodate the installation or removal of medical equipment or other tare weights on the bed, head incline adjustment, and bed frame deformation or other changes in the system causing redistribution of weight among the load cells, while minimizing false alarms. A caregiver may select between various patient monitoring modes and remotely monitor patient movement relative to a reference load cell distribution, impending patient exit from the bed and patient exit from the bed.

Claims

1. A method of monitoring a patient in a hospital bed having at least three load cells positioned about a periphery of the bed, each load cell producing a signal corresponding to a distribution of patient weight on that load cell, the method comprising the steps of:

establishing a plurality of sets of exit conditions about a periphery of the bed, each of the plurality of sets of exit conditions defining threshold values for each of the load cells,

determining a current distribution of patient weight on each of the load cells, and

determining that the patient is about to exit the bed if the current distribution of weight on at least some of the load cells exceeds corresponding ones of the threshold values of one of the sets of exit conditions.

2. The method of claim 1 further including the step of activating an alarm local to the bed if the patient is about to exit the bed.

3. The method of claim 1 further including the step of activating an alarm remote from the bed if the patient is about to exit the bed.

4. The method of claim 1 wherein the step of establishing a plurality of sets of exit conditions includes:

placing an object having a predefined calibration weight near one edge of the bed,

measuring a current distribution of the calibration weight on each of the load cells,

defining as one of the plurality of sets of exit conditions a set of normalized threshold values corresponding to the current distribution of the calibration weight on each of the load cells, and

moving the calibration weight about the periphery of the bed and executing the measuring and defining steps at each discrete placement of the calibration weight.

5. The method of claim 4 wherein the step of establishing a plurality of sets of exit conditions further includes forming a data table populated by the plurality of sets of exit conditions with each of the plurality of sets of exit conditions defined by a corresponding set of the normalized threshold values for each of the load cells.

6. The method of claim 4 wherein the step of determining that the patient is about to exit the bed includes:

determining from the current distribution of patient weight on each of the load cells a total patient weight on the bed,

multiplying selected ones of the normalized threshold values of one of the plurality of sets of exit conditions by a ratio of the total patient weight and the calibration weight to define computed threshold values,

comparing the current distribution of patient weight on the load cells that correspond to the selected ones of the normalized threshold values with corresponding ones of the computed threshold values, and

deciding that the patient is about to exit the bed if the current distribution of weight on the load cells that correspond to the selected ones of the normalized threshold values exceed the corresponding ones of the computed threshold values.

7. The method of claim 6 wherein the step of determining that the patient is about to exit the bed further includes:

selecting a subset of the plurality of sets of exit conditions; and

executing the multiplying, comparing and deciding steps for each set of exit conditions in the subset of the plurality of sets of exit conditions.

8. The method of claim 6 wherein the step of determining a total patient weight on the bed includes:

determining a zero weight distribution on each of the load cells when the bed is empty,

determining a current distribution of weight on each of the load cells when the patient is supported by the bed,

determining the current distribution of patient weight on each of the load cells by subtracting the current distribution of weight on each of the load cells when the patient is supported by the bed from the zero weight distribution on each of the load cells when the bed is empty, and

computing the total patient weight as a function of the current distribution of patient weight on each of the load cells.

9. The method of claim 1 wherein the bed includes four load cells each positioned near a different corner of the bed, and wherein the plurality of sets of exit conditions includes a first plurality of sets of exit conditions defined along a first side of the bed, a second plurality of sets of exit conditions defined along a second side of the bed opposite to the first side, a third plurality of sets of exit conditions defined along a head end of the bed and a fourth plurality of sets of exit conditions defined along a foot end of the bed, and wherein the method further includes the steps of:

processing the current distribution of patient weight on some the load cells to determine only one of the first and second plurality of sets of exit conditions to monitor; and

monitoring the one of the first and second plurality of sets of exit conditions to determine whether the patient is about to exit the bed.

10. The method of claim 9 wherein the processing step includes:

determining from the current distribution of patient weight on the some of the load cells the one of the first and second sides of the bed that patient exit is most likely to occur, and

selecting the one of the first and second plurality of sets of exit conditions associated with the one of the first and second sides of the bed that patient exit is more likely to occur.

11. The method of claim 9 wherein the step of determining that the patient is about to exit the bed includes:

comparing the current distribution of patient weight on the load cells at the head and foot ends of the one of the first and second sides that patient exit is most likely to occur with corresponding ones of the threshold values of each of the selected one of the first and second plurality of sets of exit conditions, and

deciding that the patient is about to exit the bed if the current distribution of weight on the load cells at the head and foot ends of the one of the first and second sides that patient exit is most likely to occur exceed corresponding head end and foot end threshold values of one of the selected one of the first and second plurality of sets of exit conditions.

12. The method of claim 9 wherein the step of establishing a plurality of sets of exit conditions includes:

placing an object having a predefined calibration weight near one edge of the bed,

measuring a current distribution of the calibration weight on each of the load cells,

defining as one of the plurality of sets of exit conditions a set of normalized threshold values corresponding to the current distribution of the calibration weight on each of the load cells, and

discretely moving the calibration weight about the periphery of the bed and executing the measuring and defining steps at each discrete placement of the calibration weight.

13. The method of claim 12 wherein the step of determining that the patient is about to exit the bed includes:

determining from the current distribution of patient weight on each of the load cells a total patient weight on the bed,

for one of the selected one of the first and second plurality of sets of exit conditions, multiplying the normalized threshold values that correspond the head and foot end load cells of the one of the first and second sides of the bed that patient exit is most likely to occur by a ratio of the total patient weight and the calibration weight to define computed head and foot end threshold values,

comparing the current distribution of patient weight on the load cells at the head and foot ends of the one of the first and second sides that patient exit is most likely to occur with corresponding ones of the computed head and foot end threshold values,

deciding that the patient is about to exit the bed if the current distribution of patient weight on the load cells at the head and foot ends of the one of the first and second sides that patient exit is most likely to occur exceed the corresponding ones of the computed head and foot end threshold values, and

executing the multiplying, comparing and deciding steps for remaining ones of the selected one of the first and second plurality of sets of exit conditions.

14. The method of claim 9 wherein the step of determining that the patient is about to exit the bed includes:

comparing the current distribution of patient weight on the load cells at the head and foot ends of the one of the first and second sides of the bed that patient exit is most likely to occur with corresponding head and foot end threshold values of each of the selected one of the first and second plurality of sets of exit conditions,

of the selected one of the first and second plurality of sets of exit conditions, determining a first set of exit conditions where the current distribution of patient weight on the load cell at the head end of the one of the first and second sides of the bed that patient exit is most likely to occur exceeds a corresponding head end threshold value,

of the selected one of the first and second plurality of sets of exit conditions, determining a second set of exit conditions where the current distribution of patient weight on the load cell at the foot end of the one of the first and second sides of the bed that patient exit is most likely to occur exceeds a corresponding foot end threshold value,

identifying a third set of exit conditions, among the selected one of the first and second plurality of sets of exit conditions, that is defined between the first and second sets of exit conditions, and

deciding that the patient is about to exit the bed as a function of the current distribution of weight on each of the load cells and of each of the third set of exit conditions.

15. The method of claim 14 wherein the deciding step includes:

computing a first difference between the distribution of patient weight on the load cell at the head end of the one of the first and second sides of the bed that patient exit is most likely to occur and the distribution of patient weight on the load cell at the head end of the other of the first and second sides of the bed,

computing a second difference between the head end threshold value of the third set of exit conditions that corresponds to the load cell at the head end of the one of the first and second sides of the bed that patient exit is most likely to occur and the head end threshold value of the third set of exit conditions that corresponds to the load cell at the head end of the other of the first and second sides of the bed,

computing a third difference between the distribution of patient weight on the load cell at the foot end of the one of the first and second sides of the bed that patient exit is most likely to occur and the distribution of patient weight on the load cell at the foot end of the other of the first and second sides of the bed,

computing a fourth difference between the foot end threshold value of the third set of exit conditions that corresponds to the load cell at the foot end of the one of the first and second sides of the bed that patient exit is most likely to occur and the foot end threshold value of the third set of exit conditions that corresponds to the load cell at the foot end of the other of the first and second sides of the bed, and

determining that the patient is about to exit the bed if a sum of a difference between the first and second differences and a difference between the third and fourth differences is greater than zero.

16. The method of claim 15 further including:

determining a fifth difference between the head end threshold value of the third set of exit conditions that corresponds to the load cell at the head end of the one of the first and second sides of the bed that patient exit is most likely to occur and the distribution of patient weight on the load cell at the head end of the one of the first and second sides of the bed that patient exit is most likely to occur,

determining a sixth difference between the distribution of patient weight on the load cell at the foot end of the other of the first and second sides of the bed that patient exit is most likely to occur and the foot end threshold value of the third set of exit conditions that corresponds to the load cell at the foot end of the other of the first and second sides of the bed,

computing an exit adjust value as a ratio of the fifth and sixth differences,

computing an exit adjust clamp value as a function of the exit adjust value and one or more of a total patient weight on the bed, a total weight on the bed and a location of the third set of exit conditions relative to the one of the first and second plurality of sets of exit conditions, and

multiplying the second and fourth differences by the exit adjust clamp value prior to the step of determining that the patient is about to exit the bed.

17. The method of claim 9 further includes the steps of:

processing the current distribution of patient weight on each of the load cells to determine only one of the third and fourth plurality of sets of exit conditions to monitor; and

monitoring the one of the third and fourth plurality of sets of exit conditions to determine whether the patient is about to exit the bed.

18. The method of claim 17 wherein the processing step includes:

determining from the current distribution of patient weight on each of the load cells the one of the head and foot ends of the bed that patient exit is most likely to occur, and

selecting the one of the third and fourth plurality of sets of exit conditions associated with the one of the head and foot ends that patient exit is more likely to occur.

19. The method of claim 17 wherein the step of determining that the patient is about to exit the bed includes:

comparing the current distribution of patient weight on the load cells at the one of the head and foot ends of the bed that patient exit is most likely to occur with corresponding ones of the threshold values of each of the selected one of the third and fourth plurality of sets of exit conditions, and

deciding that the patient is about to exit the bed if the current distribution of weight on the load cells at the one of the head and foot ends of the bed that patient exit is most likely to occur exceed corresponding threshold values of one of the selected one of the third and fourth plurality of sets of exit conditions.

20. The method of claim 17 wherein the step of establishing a plurality of sets of exit conditions includes:

placing an object having a predefined calibration weight near one edge of the bed,

measuring a current distribution of the calibration weight on each of the load cells,

defining as one of the plurality of sets of exit conditions a set of normalized threshold values corresponding to the current distribution of the calibration weight on each of the load cells, and

moving the calibration weight about the periphery of the bed and executing the measuring and defining steps at each discrete placement of the calibration weight.

21. The method of claim 20 wherein the step of determining that the patient is about to exit the bed includes:

determining from the current distribution of patient weight on each of the load cells a total patient weight on the bed,

for one of the selected one of the third and fourth plurality of sets of exit conditions, multiplying the normalized threshold values that correspond the load cells on either side of the one of the head and foot ends of the bed that patient exit is most likely to occur by a ratio of the total patient weight and the calibration weight to define computed first and second side threshold values,

comparing the current distribution of patient weight on the load cells at the first and second sides of the one of the head and foot ends of the bed that patient exit is most likely to occur with corresponding ones of the computed first and second side threshold values,

deciding that the patient is about to exit the bed if the current distribution of patient weight on the load cells at the first and second sides of the one of the head and foot ends of the bed that patient exit is most likely to occur exceed the corresponding ones of the computed first and second side threshold values, and

executing the multiplying, comparing and deciding steps for remaining ones of the selected one of the third and fourth plurality of sets of exit conditions.

22. The method of claim 1 wherein the step of determining that the patient is about to exit the bed if the current distribution of weight on at least some of the load cells exceeds corresponding ones of the threshold values of one of the sets of exit conditions includes determining that the patient is about to exit the bed only if the current distribution of weight on at least some of the load cells exceeds corresponding ones of the threshold values of one of the sets of exit conditions for a predefined time period.

23. The method of claim 1 wherein the threshold values of each of the plurality of sets of exit conditions are threshold weight values.

24. The method of claim 1 wherein the threshold values of each of the plurality of sets of exit conditions are threshold weight percentage values.

25. A system for monitoring a patient, comprising:

a patient support surface configured to support the patient,

at least three load cells each configured to produce a signal indicative of weight impressed on that load cell via the patient support surface, and

a controller responsive to the signals produced by each of the at least three load cells to determine a current distribution of patient weight on each of the load cells, the controller determining that the patient is about to exit the bed if the current distribution of weight on at least some of the at least three load cells exceeds corresponding threshold values comprising one of a plurality of sets of exit conditions.

26. The system of claim 25 further including a memory having stored therein the plurality of sets of exit conditions defined about a periphery of the patient support surface, each of the plurality of sets of exit conditions defining threshold values for each of the load cells.

27. The system of claim 25 wherein the patient support surface is a hospital bed.

28. The system of claim 25 further including an alarm local to the bed, the controller activating the alarm if the patient is about to exit the bed.

29. The system of claim 25 further including an alarm remote from the bed, the controller activating the alarm if the patient is about to exit the bed.

30. A method of monitoring a patient in a hospital bed having at least three load cells positioned about a periphery of the bed, each load cell producing a signal corresponding to a distribution of patient weight on that load cell, the method comprising the steps of:

establishing a first plurality of sets of excessive patient movement conditions, each of the first plurality of sets of excessive patient movement conditions defining first threshold values for each of the at least three load cells,

determining a total patient weight on the bed,

for each of the first plurality of sets of excessive patient movement conditions, computing weight change values for each of the at least three load cells according to a patient movement model as a function of the total patient weight on the bed, and

determining that patient movement is excessive if at least some of the weight change values exceed corresponding ones of the first threshold values for at least one of the first plurality of sets of excessive patient movement conditions.

31. The method of claim 30 wherein the step of computing weight change values further includes computing weight change values for each of the at least three load cells according to the patient movement model further as a function of a patient movement sensitivity value.

32. The method of claim 30 further including the step of activating an alarm remote from the bed if the patient movement is excessive.

33. The method of claim 30 wherein the first threshold values are percentage weight values and the weight change values are percentage weight change values.

34. The method of claim 30 wherein the bed includes four load cells each positioned near a different corner of the bed, and wherein the step of determining that patient movement is excessive includes determining that patient movement is excessive if at least three of the weight change values exceed corresponding ones of the first threshold values for at least one of the first plurality of sets of excessive patient movement conditions.

35. The method of claim 30 further including the steps of:

establishing a second plurality of sets of excessive patient movement conditions, each of the second plurality of sets of excessive patient movement conditions defining normalized threshold values for each of the at least three load cells,

determining a current distribution of patient weight on each of the at least three load cells,

for each of the second plurality of sets of excessive patient movement conditions, computing second threshold values for each of the at least three load cells each as a function of a corresponding one of the normalized threshold values and the total patient weight on the bed, and computing weight differential values for each of the at least three load cells as a function of the current distribution of patient weight on that load cell and a reference weight for that load cell, and

determining that patient movement is excessive if at least some of the weight differential values exceed corresponding ones of the second threshold values for at least one of the second plurality of sets of excessive patient movement conditions.

36. The method of claim 35 wherein the step of computing second threshold values further includes computing the second threshold values for each of the at least three load cells further as a function of a patient movement sensitivity value.

37. The method of claim 35 wherein the second threshold values are percentage weight values and the weight differential values are percentage weight differential values.

38. The method of claim 35 wherein the bed includes four load cells each positioned near a different corner of the bed, and wherein the step of determining that patient movement is excessive includes determining that patient movement is excessive if at least three of the weight differential values exceed corresponding ones of the second threshold values for at least one of the second plurality of sets of excessive patient movement conditions.

39. The method of claim 35 wherein the bed includes four load cells each positioned near a different corner of the bed, and wherein the step of determining that patient movement is excessive includes determining that patient movement is excessive if at least two of the weight differential values exceed corresponding ones of the second threshold values for at least one of the second plurality of sets of excessive patient movement conditions.

40. The method of claim 35 further including the step of determining that patient movement is excessive if at least one of the weight differential values is less than a corresponding one of the second threshold values while at least another of the weight differential values exceeds a corresponding one of the second threshold values for at least one of the second plurality of sets of excessive patient movement conditions.

41. A system for monitoring a patient, comprising:

a patient support surface configured to support the patient,

at least three load cells each configured to produce a signal indicative of weight impressed on that load cell via the patient support surface, and

a controller responsive to the signals produced by each of the at least three load cells to determine a total patient weight on the patient support surface, the controller computing weight change values for each of the at least three load cells according to a patient movement model as a function of the total patient weight on the bed for each of a plurality of sets of excessive patient movement conditions, the controller determining that patient movement is excessive if at least some of the weight change values exceed corresponding ones of the first threshold values for at least one of the plurality of sets of excessive patient movement conditions.

42. The system of claim 41 further including a memory having stored therein the plurality of sets of excessive patient movement conditions, each of the plurality of sets of excessive patient movement conditions defining threshold values for each of the load cells.

43. The system of claim 41 wherein the patient support surface is a hospital bed.

44. The system of claim 41 further including an alarm remote from the bed, the controller activating the alarm if the patient is about to exit the bed.

45. A method of monitoring a patient in a hospital bed, the method comprising the steps of:

determining whether the patient is within a safe arming zone of the hospital bed, and

enabling monitoring of the patient in the hospital bed only if the patient is within the safe arming zone.

46. The method of claim 45 wherein the hospital bed has at least three load cells positioned about a periphery of the bed, each load cell producing a signal corresponding to a distribution of patient weight on that load cell, and wherein the determining step includes:

determining a current distribution of patient weight on each of the load cells, and

determining that the patient is not within the safe arming zone of the hospital bed if the current distribution of patient weight on each the load cells exceed corresponding load cell threshold values of one of a plurality of sets of arming conditions defined about a periphery of the bed.

47. The method of claim 46 wherein the method of monitoring a patient includes a patient exit mode configured to determine whether the patient is about to exit the hospital bed, and wherein the enabling step includes enabling activation of the patient exit mode only if the patient is within the safe arming zone.

48. The method of claim 47 wherein the patient exit mode includes:

establishing a plurality of sets of exit conditions about a periphery of the bed, each of the plurality of sets of exit conditions defining threshold values for each of the load cells,

determining a current distribution of patient weight on each of the load cells, and

determining that the patient is about to exit the bed if the current distribution of weight on at least some of the load cells exceeds corresponding ones of the threshold values of one of the sets of exit conditions.

49. The method of claim 48 further including determining the one of a plurality of sets of arming conditions by scaling a corresponding one of the plurality of sets of exit conditions by a first predefined scaling factor.

50. The method of claim 48 wherein the method of monitoring a patient includes a patient movement mode configured to determine whether the patient movement relative to a reference distribution of weight on the load cells is excessive, and wherein the enabling step includes enabling activation of the patient movement mode only if the patient is within the safe arming zone.

51. The method of claim 50 wherein the patient movement mode includes:

establishing a first plurality of sets of excessive patient movement conditions, each of the first plurality of sets of excessive patient movement conditions defining first threshold values for each of the at least three load cells,

determining a total patient weight on the bed,

for each of the first plurality of sets of excessive patient movement conditions, computing weight change values for each of the at least three load cells according to a patient movement model as a function of the total patient weight on the bed, and

determining that patient movement is excessive if at least some of the weight change values exceed corresponding ones of the first threshold values for at least one of the first plurality of sets of excessive patient movement conditions.

52. The method of claim 51 further including determining the one of a plurality of sets of arming conditions by scaling a corresponding one of the plurality of sets of exit conditions by a second predefined scaling factor.

53. The method of claim 45 wherein the method of monitoring a patient includes a patient exit mode configured to determine whether the patient is about to exit the hospital bed, and wherein the enabling step includes enabling activation of the patient exit mode only if the patient is within the safe arming zone.

54. The method of claim 45 wherein the method of monitoring a patient includes a patient movement mode configured to determine whether the patient movement relative to a reference distribution of weight on the load cells is excessive, and wherein the enabling step includes enabling activation of the patient movement mode only if the patient is within the safe arming zone.

55. The method of claim 45 further including determining a total patient weight on the bed, and wherein the enabling step is further conditioned upon the total patient weight being less than a maximum total patient weight.

56. The method of claim 45 further including determining a total patient weight on the bed, and wherein the enabling step is further conditioned upon the total patient weight being greater than a minimum total patient weight.

57. The method of claim 56 wherein the enabling step is further conditioned upon the total patient weight being less than a maximum total patient weight.

58. A method of monitoring a patient in a hospital bed having a head section that may be controllably elevated, the method comprising the steps of:

determining a total patient weight on the bed, and

enabling monitoring of the patient in the hospital bed if the total patient weight is greater than about 50 pounds and the head section of the bed is elevated in excess of 45 degrees relative to bed flat.

59. The method of claim 58 wherein the head section of the hospital bed may be controllably elevated to a maximum head angle of at least about 65 degrees relative to bed flat, and wherein the enabling step includes enabling monitoring of the patient in the hospital bed if the total patient weight is greater than about 50 pounds and the head section is elevated anywhere between bed flat and the maximum head angle.

61. The method of claim 58 further including the step of determining whether the patient is within a safe arming zone of the hospital bed, and wherein the enabling step is further conditioned upon the patient being within the safe arming zone of the hospital bed.

62. A method of monitoring a patient in a hospital bed according to a patient movement mode configured to determine whether patient movement relative to a reference distribution of weight on the bed is excessive, the bed having a head section that may be controllably elevated to a maximum head angle of at least about 65 degrees relative to bed flat, the method comprising the steps of:

enabling monitoring of the patient according to the patient movement mode regardless of elevation of the head section of the bed relative to bed flat, and

continuing to monitor the patient according to the patient movement mode without activating an alarm if the head section is articulated to an elevation, between the maximum head angle and bed flat, that is different than the elevation of the head section when the patient movement mode was enabled.

63. The method of claim 62 further including determining a total patient weight on the bed, and wherein the enabling step is conditioned upon the total patient weight being greater than a minimum total patient weight.

64. The method of claim 62 further including determining a total patient weight on the bed, and wherein the enabling step is conditioned upon the total patient weight being less than a maximum total patient weight.

65. The method of claim 62 further including determining whether the patient is within a safe arming zone of the bed, and wherein the enabling step is conditioned upon the patient being within the safe arming zone of the bed.

66. The method of claim 62 further including:

determining a total patient weight on the bed, and

determining whether the patient is within a safe arming zone of the bed,

and wherein the enabling step is conditioned upon the total patient weight being greater than a minimum total patient weight, on the total patient weight being less than a maximum total patient weight and on the patient being within the safe arming zone of the bed.

67. The method of claim 62 wherein the continuing step is conditioned upon articulating the head section via a control panel mounted to the bed.

68. The method of claim 62 further including the step of activating an alarm if the head section is articulated to the elevation that is between the maximum head angle and bed flat via a patient control pendant.

69. A method of monitoring a patient in a hospital bed according to a patient movement mode configured to determine whether patient movement relative to a reference distribution of weight on the bed is excessive, the method comprising the steps of:

enabling monitoring of the patient according to the patient movement mode, and

continuing to monitor the patient according to the patient movement mode without activating an alarm after further weight, less than a maximum further weight, is added to the bed regardless of total patient weight on the bed prior to adding the further weight.

70. The method of claim 69 further including determining the total patient weight on the bed, and wherein the enabling step is conditioned upon the total patient weight being greater than a minimum total patient weight.

71. The method of claim 69 further including determining the total patient weight on the bed, and wherein the enabling step is conditioned upon the total patient weight being less than a maximum total patient weight.

72. The method of claim 69 further including determining whether the patient is within a safe arming zone of the bed, and wherein the enabling step is conditioned upon the patient being within the safe arming zone of the bed.

73. The method of claim 69 further including:

determining the total patient weight on the bed, and

determining whether the patient is within a safe arming zone of the bed,

and wherein the enabling step is conditioned upon the total patient weight being greater than a minimum total patient weight, on the total patient weight being less than a maximum total patient weight and on the patient being within the safe arming zone of the bed.

74. The method of claim 69 wherein the maximum further weight is about 30 pounds.

75. A method of monitoring a patient in a hospital bed according to a patient exit mode configured to determine whether the patient is about to exit the bed, the method comprising the steps of:

determining a bed zero weight without the patient supported by the bed,

determining a total patient weight on the bed as a function of the bed zero weight when the patient is supported by the bed,

enabling monitoring of the patient in the bed according to the patient exit mode, and

continuing to monitor the patient according to the patient exit mode without activating an alarm after further weight, less than a maximum further weight, is added to the bed after determining the bed zero weight.

76. The method of claim 75 wherein the maximum further weight is about 30 pounds.

77. The method of claim 75 wherein the bed includes a head end and a foot end, and wherein the further weight is added to one of the head and foot ends.

78. The method of claim 75 wherein the enabling step is conditioned upon the total patient weight being greater than a minimum total patient weight.

79. The method of claim 75 wherein the enabling step is conditioned upon the total patient weight being less than a maximum total patient weight.

80. The method of claim 75 further including determining whether the patient is within a safe arming zone of the bed, and wherein the enabling step is conditioned upon the patient being within the safe arming zone of the bed.

81. The method of claim 75 further including determining whether the patient is within a safe arming zone of the bed, and wherein the enabling step is conditioned upon the total patient weight being greater than a minimum total patient weight, on the total patient weight being less than a maximum total patient weight and on the patient being within the safe arming zone of the bed.

82. A system for controlling air pressure in a number of different zones of an air mattress supporting an occupant, comprising:

a plurality of load cells each configured to produce a signal indicative of weight impressed upon that load cell via the air mattress, and

a controller responsive to the signals produced by the plurality of load cells to determine a current distribution of occupant weight on each of the load cells, the controller controlling air pressure within any one or more of the number of different zones of the air mattress based on the current distribution of occupant weight on at least some of the plurality of load cells.