WEANING AND DECISION SUPPORT SYSTEM FOR MECHANICAL VENTILATION

• US 20080236582A1
• Filed: 08/20/2007
• Published: 10/02/2008
• Est. Priority Date: 03/31/2007
• Status: Active Grant

• Current Assignee: Fleur T Tehrani
• Original Assignee: Fleur T Tehrani
• Inventors: Tehrani, Fleur T.
• Granted Patent: US 8,695,593 B2
• Time in Patent Office: Days
• US Class Current: 128/204.22
• CPC Class Codes: A61H 2230/207 partial O2-value
• CPC Class Codes: A61H 2230/40 Respiratory characteristics
• CPC Class Codes: A61H 31/02 "Iron-lungs" , i.e. involving chest expansion by applying underpressure thereon, whether or not combined with gas breathing means
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 2016/0042 in the expiratory circuit
• CPC Class Codes: A61M 2205/3561 local, e.g. within room or hospital
• CPC Class Codes: A61M 2205/502 User interfaces, e.g. screens or keyboards
• CPC Class Codes: A61M 2205/52 with memories providing a history of measured variating parameters of apparatus or patient
• CPC Class Codes: A61M 2230/205 partial oxygen pressure (P-O2)
• CPC Class Codes: A61M 2230/42 Rate
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs
• CPC Class Codes: A61M 2230/50 Temperature

Abstract

A system for mechanical ventilation treatment is described. In one embodiment the system provides advice on treatment and/or weaning of patients from mechanical ventilation based on the patient'"'"'s conditions. In another embodiment the system includes apparatus to monitor and analyze the patient'"'"'s data and data from the mechanical ventilator and controls the ventilator automatically.

Claims

1. A method for optimizing mechanical ventilation of a patient, comprising steps of:

(a) receiving patient input data representing respiratory airway resistance (RES), respiratory compliance (COMP), and data indicative of patient'"'"'s ideal body weight (WEIGHT);

(b) receiving data representing patient oxygen level (PO2);

(c) receiving input data representing measured spontaneous breathing rate (FSP), tidal volume (VTMS), inspired oxygen fraction (FIO), and positive end-expiratory pressure (PEEP);

(d) determining optimal ventilation level and optimal respiratory rate for the patient based on data received in step (a);

(e) determining a level of controlled ventilation for the patient based on the FSP, the VTMS, the optimal ventilation level, and the optimal respiratory rate;

(f) determining required levels of FIO and PEEP based on the patient oxygen level data received in step (b) and the patient FIO and PEEP data received in step (c); and

(g) generating outputs representing the required levels of FIO, PEEP, and the controlled ventilation for a next breath of the patient.

2. The method of claim 1 wherein step (e) further comprises determining whether to start or continue weaning the patient based on the FSP, the VTMS, the optimal ventilation level, and the optimal respiratory rate, and if so, determining the level of controlled ventilation for optimal weaning.

3. The method of claim 1 wherein the optimal respiratory rate is computed to minimize respiratory work rate.

4. The method of claim 3 wherein data received in step (a) includes data representing patient body temperature (TEMP).

5. The method of claim 4 wherein data representing inspiratory to expiratory time ratio (TI/TE) is provided in step (c).

6. The method of claim 4 wherein the optimal ventilation level, MV, in liters/minute is calculated as:

MV=V′

+α

×

V′

×

(TEMP−

37) for TEMP ≧

37,

MV=V′

for TEMP<

37,

where V′

=β

×

WEIGHT, WEIGHT is in Kg, TEMP is in degrees C, and α and

β

are constants.

7. The method of claim 6 wherein the optimal respiratory rate is calculated as:

$F<br><br><br><br>1=60\times <br><br>\left[\frac{\begin{array}{c}-K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{VD}+\\ \sqrt{{\left(K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{VD}\right)}^2+4\times <br><br>K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{RES}\times <br><br>{\mathrm{\Pi <br><br>}}^2\times <br><br>\left(\frac{\mathrm{VALV}}{60}\right)\times <br><br>\mathrm{VD}}\end{array}}{2\times <br><br>\mathrm{RES}\times <br><br>{\mathrm{\Pi <br><br>}}^2\times <br><br>\mathrm{VD}}\right]$

where F1 is the optimal respiratory rate in breaths/minute, K′

is respiratory elastance (reciprocal of COMP) in cmH₂O/liter, RES is in cmH₂O/liter/second, VD is respiratory dead space in liters, and VALV=MV−

F1 ×

VD.

8. The method of claim 7 wherein VD is received as patient input data.

9. The method of claim 7 wherein VD is calculated as:

VD=0.0026 ×

WEIGHT.

10. The method of claim 5 further comprising adjusting the TI/TB ratio so that expiration time TB=0.5/fmax, where fmax is a maximum allowed respiratory rate calculated as:

fmax=1/(5×

RES×

COMP).

11. The method of claim 1 wherein step (b) further comprises receiving data representing patient carbon dioxide level (PCO2) and wherein step (d) further comprises determining optimal ventilation level and optimal respiratory rate for the patient based on data received in step (a) and step (b).

12. The method of claim 11 wherein the optimal respiratory rate is computed to minimize respiratory work rate.

13. The method of claim 12 wherein optimal alveolar ventilation, VALV, is calculated as:

VALV=(VAO+VAC)×

VALV(rest)

where VAO=4.72×

10<sup>−

9</sup>×

(104−

PaO2<

104 mm Hg, and VAO =0 for PaO2≧

104 mm Hg, and VAC=C1×

PaCO2−

C2 for PaCO2 greater than a predefined value and VAC=0 otherwise, and VALV(rest)=K×

WEIGHT, where VALV and VALV(rest) are alveolar ventilation and alveolar ventilation at rest in liters/minute respectively, PaO2 and PaCO2 are partial pressures of oxygen and carbon dioxide in patient'"'"'s arterial blood in mmHg respectively, and C1, C2, and K are constants.

14. The method of claim 13 wherein PaCO2 is obtained from:

PaCO2=PCO2+K1, where PCO2 is patient'"'"'s end-tidal pressure of carbon dioxide and K1 is a constant.

15. A method in accordance with claim 13 wherein PaO2 is obtained as:

$P_{a<br><br><br><br>O<br><br><br><br>2}=\frac{-\ln <br><br>\left[1-{\left(\mathrm{SP}<br><br>O<br><br><br><br>2\right)}^{0.5}\right]}{0.046}+C<br><br><br><br>3$

where SPO2 is patient'"'"'s arterial oxygen saturation measured by pulse oximetry and C3 is a shifting constant that depends on patient blood pH level.

16. A method in accordance with claim 13 wherein the optimal respiratory rate is calculated as:

$F<br><br><br><br>1=60\times <br><br>\left[\frac{\begin{array}{c}-K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{VD}+\\ \sqrt{{\left(K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{VD}\right)}^2+4\times <br><br>K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{RES}\times <br><br>{\mathrm{\Pi <br><br>}}^2\times <br><br>\left(\frac{\mathrm{VALV}}{60}\right)\times <br><br>\mathrm{VD}}\end{array}}{2\times <br><br>\mathrm{RES}\times <br><br>{\mathrm{\Pi <br><br>}}^2\times <br><br>\mathrm{VD}}\right]$

where F1 is the optimal respiratory rate in breaths/minute, K′

is respiratory elastance (reciprocal of COMP) in cmH₂O/liter, RES is in cmH₂O/liter/second, VD is respiratory dead space in liters, and VALV=MV−

F1 ×

VD.

17. The method of claim 16 wherein VD is received as patient input data.

18. The method of claim 16 wherein VD is calculated as:

VD=0.1698×

(VALV/60)+0.1587.

19. The method of claim 1 wherein PO2 is set equal to measured arterial oxygen saturation of the patient (SPO2), and wherein FIG is computed by using a sequential procedure, with SPO2 compared to predefined threshold levels successively and FIO adjusted accordingly.

20. The method of claim 19 wherein the sequential procedure comprises the following steps:

comparing SPO2 with a high threshold value;

if SPO2 is higher than or equal to the high threshold value, reducing FIO down to a predefined low value FR1 but not lower than FR1 as;

new FIO=FR1+(FIO−

FR1)×

K″

where K″

is a factor less than 1;

if SPO2 is lower than the high threshold value, comparing SPO2 with a lower second threshold value, and if it is higher than or equal to the lower second threshold value, reducing FIO down to a predefined value FR2 but not lower than FR2 as;

new FIO=FR2+(FIO−

FR2)×

K″

;

if SPO2 is lower than the second threshold value, comparing it with a lower third threshold value, and if SPO2 is higher than or equal to the third threshold value, raising FIO to a predefined value FR3 if it is lower than FR3;

if SPO2 is lower than the third threshold value, comparing it with a lower fourth threshold value, and if it is higher than or equal to the fourth threshold value, raising FIO to a predefined value FR4 if it is lower than FR4; and

if SPO2 is lower than the fourth threshold value, comparing FIO with a predefined high value, and if it is lower than the predefined high value, raising FIO to the predefined high value.

21. The method of claim 20 wherein PEEP is increased incrementally if SPO2 is found to be lower than the fourth threshold value and if a predefined minimum time has elapsed since a most recent adjustment in PEEP.

22. The method of claim 21, further comprising

determining a ratio of PEEP to FIO (RATIO);

comparing RATIO to predefined minimum and maximum values for the ratio;

increasing PEEP if RATIO is lower than the minimum value and a predefined minimum time has elapsed since a most recent adjustment in PEEP; and

decreasing PEEP if RATIO exceeds the maximum value to bring RATIO lower than or equal to the maximum value.

23. The method of claim 2 further comprising comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

if FSP and VTMS are both within their respective acceptance ranges, determining that weaning should start or continue with a lowered level of controlled ventilation.

24. The method of claim 2 further comprising comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

if FSP exceeds a maximum of the FSP acceptance range, if VTMS is less than a maximum of the VTMS acceptance range, and if PO2 exceeds a predefined value, determining that weaning should continue with an increased level of controlled ventilation.

25. The method of claim 2 further comprising comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should continue if the FSP is higher than or equal to a minimum value of the FSP acceptance range, if PO2 exceeds a predefined value, and if VTMS exceeds a maximum of the VTMS acceptance range.

26. The method of claim 2 wherein step (b) further comprises receiving data representing patient carbon dioxide level (PCO2);

wherein step (d) further comprises determining optimal ventilation level and optimal respiratory rate for the patient based on data received in step (a) and step (b); and

further comprising comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should start, or should continue with lowered level of controlled ventilation if started already, if FSP and VTMS are both within their respective acceptance ranges.

27. The method of claim 2 wherein step (b) further comprises receiving data representing patient carbon dioxide level (PCO2);

wherein step (d) further comprises determining optimal ventilation level and optimal respiratory rate for the patient based on data received in step (a) and step (b); and

further comprising comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should continue if FSP is higher than or equal to a minimum value in the FSP acceptance range, if PO2 is above a predefined value, if PCO2 is below a predefined value, and if VTMS exceeds a maximum of the VTMS acceptance range.

28. The method of claim 2 wherein step (b) further comprises receiving data representing patient carbon dioxide level (PCO2);

wherein step (d) further comprises determining optimal ventilation level and optimal respiratory rate for the patient based on data received in step (a) and step (b); and

further comprising comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should continue with increased level of controlled ventilation if VTMS is below a maximum of the VTMS acceptance range, if PO2 exceeds a predefined value, if PCO2 is below a predefined value, and if the FSP exceeds a maximum of the FSP acceptance range.

29. The method of claim 2 wherein step (b) further comprises receiving data representing patient carbon dioxide level (PCO2);

wherein step (d) further comprises determining optimal ventilation level and optimal respiratory rate for the patient based on data received in step (a) and step (b); and

further comprising comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should start, or should continue with a lowered level of controlled ventilation if started already, if FSP and VTMS are both within their respective acceptance ranges, if PO2 exceeds a predefined value, and if PCO2 is below a predefined level.

30. The method of claim 29 further comprising determining that weaning should start, or should continue with a lowered level of controlled ventilation if already started, if required FIO is below a predefined value and if required PEEP is also below a predefined value.

31. The method of claim 1 implemented on a digital computer wherein the input data is provided manually through a user interface.

32. The method of claim 1 implemented on a digital processor wherein the input data is provided to the processor automatically.

65. The method of claim 31 comprising an advisory decision support system, wherein the generated outputs in step (g) cause instructions for a user.

66. The method of claim 1 wherein the outputs generated in step (g) are signals that are supplied to a mechanical ventilator to control it automatically.

67. The method of claim 2 wherein the outputs generated in step (g) are signals that are supplied to a mechanical ventilator to control it automatically.

33. An apparatus for optimizing mechanical ventilation of a patient, comprising:

a computing system;

digital readable memory coupled to the computing system; and

transducers providing patient input signals to the computing system representing respiratory airway resistance (RES), respiratory compliance (COMP), and ventilation data representing patient'"'"'s spontaneous breathing rate (FSP), and measured tidal volume (VTMS);

wherein the computing system executing a program stored in the memory determines output data representing optimal ventilation level and optimal respiratory rate of the patient based on data indicative of WEIGHT stored in memory and data representing RES and COMP, and provides output data representing optimal ventilation and optimal respiratory rate and a controlled level of mechanical ventilation based on the optimal ventilation data, the optimal respiratory rate data, FSP, and VTMS.

34. The apparatus of claim 33 further comprising a display unit coupled to the computing system for displaying the output data representing at least one of optimal ventilation level, optimal respiratory rate, and the controlled level of mechanical ventilation.

35. The apparatus of claim 33 further comprising a transducer providing input signal representing patient'"'"'s measured oxygen level (PO2) to the computing system.

36. The apparatus of claim 35 wherein the transducers include a pulse oximeter providing the PO2 input signal and one or more sensors providing the RES and COMP signals.

37. The apparatus of claim 36 further comprising a transducer providing input signal representing measured carbon dioxide level (PCO2) of the patient and wherein the computing system executing the program further determines, based on PO2 and PCO2, required levels of ventilation and respiratory rate of the patient.

38. The apparatus of claim 37 wherein the transducers include an end-tidal carbon dioxide analyzer for providing the PCO2 patient input signal.

39. The apparatus of claim 38 further comprising one or more A/D converters connected between the transducers and the computing system for converting analog signals from the transducers into digital form.

40. The apparatus of claim 33 further comprising a mechanical ventilator, wherein the determined output data representing either optimal ventilation level and optimal respiratory rate of the patient or a controlled level of mechanical ventilation is supplied to the mechanical ventilator to control it automatically.

41. The apparatus of claim 40 further comprising one or more D/A converters for converting digital output signals from the computing system to analog signals and supplying the analog signals to the mechanical ventilator.

42. The apparatus of claim 35 wherein the transducers further provide to the computing system patient input signals representing positive end-expiratory pressure (PEEP) and inspired oxygen fraction (FIG) and wherein the computing system executing the program determines output data representing required PEEP and required FIO and supplies the required PEEP and the required FIO to the mechanical ventilator.

43. A method for automatically controlling a mechanical ventilator to wean a patient from mechanical ventilation, comprising the steps of:

(a) providing patient data representing respiratory airway resistance (RES) and respiratory compliance (COMP);

(b) providing patient data indicative of ideal body weight (WEIGHT);

(c) providing patient data representing measured oxygen level (PO2);

(d) providing patient data representing tidal volume (VTMS) and spontaneous breathing rate (FSP);

(e) providing patient data representing positive end-expiratory pressure (PEEP);

(f) determining based on data provided in steps (a) and (b), optimal ventilation and optimal respiratory rate of the patient;

(g) determining whether weaning should start or continue and a level of controlled mechanical ventilation based on the optimal ventilation, the optimal respiratory rate, and patient data provided in step (d); and

(h) providing a control signal representing a controlled ventilation level based on data from step (g) and supplying the control signal to the mechanical ventilator to control it automatically for a next breath of the patient.

44. The method of claim 43 wherein data received in step (b) includes data representing patient body temperature (TEMP).

45. The method of claim 43 wherein step (c) further comprises providing data representing patient carbon dioxide level (PCO2) and wherein data provided in steps (a), (b), and (c) are used in step (f) to determine the optimal ventilation and the optimal respiratory rate of the patient.

46. The method of claim 45 further comprising providing patient input data representing inspired fraction of oxygen (FIO), and wherein the FIO data, data in step (c), and data representing PEEP are also used in step (g) to determine whether weaning should begin.

47. The method of claim 44 wherein the optimal ventilation, MV, in liters/minute is calculated in step (f) as:

MV=V′

+α

×

V′

×

(TEMP−

37) for TEMP≧

37,

MV=V′

for TEMP<

37,

where V′

=β

×

WEIGHT, WEIGHT is in Kg, TEMP is in degrees C, and α and

β

are constants.

48. The method of claim 47 wherein the optimal respiratory rate is calculated as:

$F<br><br><br><br>1=60\times <br><br>\left[\frac{\begin{array}{c}-K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{VD}+\\ \sqrt{{\left(K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{VD}\right)}^2+4\times <br><br>K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{RES}\times <br><br>{\mathrm{\Pi <br><br>}}^2\times <br><br>\left(\frac{\mathrm{VALV}}{60}\right)\times <br><br>\mathrm{VD}}\end{array}}{2\times <br><br>\mathrm{RES}\times <br><br>{\mathrm{\Pi <br><br>}}^2\times <br><br>\mathrm{VD}}\right]$

where F1 is the optimal respiratory rate in breaths/minute, K′

is respiratory elastance (reciprocal of COMP) in cmH₂O/liter, RES is in cmH₂O/liter/second, VD is respiratory dead space in liters, and VALV=MV−

F1×

VD.

49. The method of claim 48 wherein VD is provided as patient data.

50. The method of claim 48 wherein VD is calculated as:

VD=0.0026 ×

WEIGHT.

51. The method of claim 45 wherein optimal alveolar ventilation, VALV, is calculated as:

VALV=(VAO+VAC)×

VALV(rest)

where VAO=4.72 ×

10<sup>−

9</sup>×

(104−

PaO2)^4.9 for PaO2<

104mm Hg, and VAO=0 for PaO2≧

104 mm Hg, VAC=C1×

PaCO2−

C2 for PaCO2 greater than a predefined value and VAC=0 otherwise, and VALV(rest)=K ×

WEIGHT, where VALV and VALV(rest) are alveolar ventilation and alveolar ventilation at rest in liters/minute respectively, PaO2 and PaCO2 are partial pressures of oxygen and carbon dioxide in patient'"'"'s arterial blood in mm hg respectively, and C1, C2, and K are constants.

52. The method of claim 51 wherein PaCO2 is obtained from:

PaCO2 =PCO2+K1, where PCO2 is patient'"'"'s end-tidal pressure of carbon dioxide and K1 is a constant.

53. A method in accordance with claim 51 wherein PaO2 is obtained as:

$P_{a<br><br><br><br>O<br><br><br><br>2}=\frac{-\ln <br><br>\left[1-{\left(\mathrm{SP}<br><br>O<br><br><br><br>2\right)}^{0.5}\right]}{0.046}+C<br><br><br><br>3$

where SPO2 is patient'"'"'s arterial oxygen saturation measured by pulse oximetry and C3 is a shifting constant that depends on patient blood pH level.

54. A method in accordance with claim 51 wherein the optimal respiratory rate is calculated as:

$F<br><br><br><br>1=60\times <br><br>\left[\frac{\begin{array}{c}-K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{VD}+\\ \sqrt{{\left(K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{VD}\right)}^2+4\times <br><br>K^{\mathrm{\prime <br><br>}}\times <br><br>\mathrm{RES}\times <br><br>{\mathrm{\Pi <br><br>}}^2\times <br><br>\left(\frac{\mathrm{VALV}}{60}\right)\times <br><br>\mathrm{VD}}\end{array}}{2\times <br><br>\mathrm{RES}\times <br><br>{\mathrm{\Pi <br><br>}}^2\times <br><br>\mathrm{VD}}\right]$

where F1 is the optimal respiratory rate in breaths/minute, K'"'"' is respiratory elastance (reciprocal of COMP) in cmH₂O/liter, RES is in cmH₂O/liter/second, VD is respiratory dead space in liters, and VALV=MV−

F1 ×

VD.

55. The method of claim 54 wherein VD is provided as patient data.

56. The method of claim 54 wherein VD is calculated as:

VD=0.1698×

(VALV/60)+0.1587.

57. The method of claim 43 further comprising

comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should start or continue with a lowered level of controlled ventilation if FSP and VTMS are both within their respective acceptance ranges.

58. The method of claim 43 further comprising

comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should continue with an increased level of controlled ventilation if VTMS is below a maximum value of the VTMS acceptance range, if PO2 exceeds a predefined value, and if FSP exceeds a maximum value of the FSP acceptance range.

59. The method of claim 43 further comprising

comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should continue if FSP is higher than or equal to a minimum value of the FSP acceptance range, if PO2 exceeds a predefined value, and if VTMS exceeds a maximum value of the VTMS acceptance range.

60. The method of claim 45 further comprising

comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should start, or should continue with lowered level of controlled ventilation if started already, if FSP and VTMS are both within their respective acceptance ranges.

61. The method of claim 45 further comprising

comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should continue if the FSP is higher than or equal to a minimum value of the FSP acceptance range, if PO2 exceeds a predefined value, if PCO2 is below a predefined value, and if VTMS exceeds a maximum value of the VTMS acceptance range.

62. The method of claim 45 further comprising

comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should continue with increased level of controlled ventilation if VTMS is lower than a maximum value of the VTMS acceptance range, if PO2 exceeds a predefined value, if PCO2 is below a predefined value, and if FSP exceeds a maximum value of the FSP acceptance range.

63. The method of claim 45 further comprising

comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should start, or should continue with a lowered level of controlled ventilation if started already, if FSP and VTMS are both within their respective acceptance ranges, if PO2 exceeds a predefined value, and if PCO2 is below a predefined value.

64. The method of claim 46 further comprising

comparing FSP to an FSP acceptance range based on the determined optimal respiratory rate;

comparing VTMS to a VTMS acceptance range; and

determining that weaning should start, or should continue with a lowered level of controlled ventilation if started already, if FSP and VTMS are both within their respective acceptance ranges, if PO2 exceeds a predefined value, if PCO2 is below a predefined value, if FIO is lower than a predefined value, and if PEEP is lower than a predefined value.