Method and system for adjusting a level of ventilatory assist to a patient
The present disclosure relates to a method and a mechanical ventilation system for adjusting a level of ventilatory assist to a patient. A neuro-mechanical efficiency of the patient is determined. A control value is received at the mechanical ventilation system. The level of ventilatory assist to the patient is determined on the basis of the neuro-mechanical efficiency and of the control value. The mechanical ventilation system may be adjusted automatically based on the determined level of ventilatory assist to the patient. Alternatively, the determined level of ventilatory assist to the patient may be displayed for the benefit of an operator and a manual command may be received for adjusting the mechanical ventilation system.
1. A method implemented in a mechanical ventilation system for adjusting a level of ventilatory assist (ASSIST) to a patient, comprising:
receiving at the mechanical ventilation system a control value selected from:
a desired unloading level (UL) for the patient, and
an operator setting for a target tidal volume for the patient (Vt tgt ), wherein a relation between the desired unloading level and the target tidal volume, for a nominal tidal volume (Vt PBW ) determined based on a predicted body weight of the patient, is defined as:
UL
=
(
Vt
PBW
-
Vt
tgt
)
Vt
PBW
;
measuring an electrical activity (EAmsi, EAmsi occ ) of a patient's respiratory muscle synchronized with an inspiratory effort of the patient;
determining a neuro-mechanical efficiency (NME) of the patient, wherein the neuro-mechanical efficiency (NME) is calculated at least in part based on a ratio of a respiratory volume or pressure induced by the patient's respiratory muscle over the measured electrical activity (EAmsi) of the patient's respiratory muscle; and
determining the level of ventilatory assist (ASSIST) to the patient on the basis of the neuro-mechanical efficiency (NME) of the patient and of the desired unloading level (UL).
2. The method of claim 1 , comprising displaying the determined level of ventilatory assist (ASSIST).
3. The method of claim 2 , comprising receiving a command for adjusting the mechanical ventilation system.
4. The method of claim 1 , comprising automatically adjusting the mechanical ventilation system to provide the level of ventilatory assist (ASSIST) to the patient.
5. The method of claim 1 , wherein determining the neuro-mechanical efficiency (NME) of the patient comprises:
measuring a variation of a patient's airway pressure (ΔPaw occ ) during an unassisted inspiration attempt while causing a patient's inspiratory occlusion;
measuring the electrical activity (EAmsi occ ) of the patient's respiratory muscle synchronized with the inspiratory effort of the patient during the unassisted inspiration attempt while causing the patient's inspiratory occlusion; and
determining the neuro-mechanical efficiency (NME) as:
N
M
E
=
Δ
Paw
occ
EAmsi
occ
.
6. The method of claim 5 , wherein the control value is selected from (i) an operator setting representing a target electrical activity of the patient's respiratory muscle synchronized with an inspiratory effort for a normally breathing patient (EAmsi tgt ) and (ii) an operator setting for a variation of the patient's airway pressure (ΔPaw EAmsi tgt ) for the target electrical activity wherein (EAmsi tgt ) is calculated as:
EAmsi
tgt
=
Δ
Paw
EAmsi
tgt
N
M
E
.
7. The method of claim 6 , comprising calculating a total ventilatory requirement (Req total ) of the patient on the basis of the inspiratory effort for the normally breathing patient (EAmsi tgt ).
8. The method of claim 7 , wherein the level of ventilatory assist (ASSIST) to the patient is determined using the relation:
ASSIST=Req total −NME.
9. The method of claim 7 , comprising:
measuring an inspiratory volume (Vt) of the patient during an unassisted inspiration;
measuring the electrical activity (EAmsi) of the patient's respiratory muscle synchronized with the inspiratory effort of the patient during the unassisted inspiration;
determining a neuro-ventilatory efficiency of the patient as:
N
V
E
=
Vt
EAmsi
.
10. The method of claim 9 , wherein determining the total ventilatory requirement (Req total ) of the patient comprises:
determining a nominal tidal volume (Vt PBW ) on the basis of a predicted body weight of the patient;
estimating an expected electrical activity (EAmsi Vt PBW ) for the nominal tidal volume (Vt PBW ) as:
EAmsi
Vt
PBW
=
Vt
PBW
NVE
=
Vt
PBW
·
EAmsi
Vt
;
and
estimating the total ventilatory requirement (Req total ) of the patient as:
Req
total
=
EAmsi
VtPBW
EAmsi
tgt
·
NME
.
11. The method of claim 10 , wherein determining the nominal tidal volume (Vt PBW ) comprises:
specifying a gender of the patient;
specifying a height of the patient;
determining the predicted body weight (PBW) of the patient on the basis of the gender and height of the patient; and
determining the nominal tidal volume (Vt PBW ) by multiplying the predicted body weight (PBW) by a constant.
12. The method of claim 9 , wherein the patient's respiratory muscle is a diaphragm of the patient.
13. The method of claim 1 , wherein the level of ventilatory assist (ASSIST) to the patient is determined using the relation:
ASSIST
=
UL
(
1
-
UL
)
·
NME
.
14. The method of claim 1 , comprising:
obtaining, from the patient, a measurement corresponding to the control value;
calculating a deviation between the control value and the measurement; and
recalculating the level of ventilatory assist (ASSIST) to the patient on the basis of the neuro-mechanical efficiency (NME) of the patient, of the control value and of the deviation.
15. The method of claim 1 , wherein measuring the electrical activity (EAmsi, EAmsi occ ) of the patient's respiratory muscle synchronized with the inspiratory effort of the patient comprises removing cardiac signal components from a measured electrical activity representative signal.
16. A mechanical ventilation system for adjusting a level of ventilatory assist (ASSIST) to a patient, comprising:
an operator interface adapted to receive a control value selected from:
a desired unloading level (UL) for the patient, and
an operator setting for a target tidal volume for the patient (Vt tgt ), wherein a relation between the desired unloading level and the target tidal volume, for a nominal tidal volume (Vt PBW ) determined based on a predicted body weight of the patient, is defined as:
UL
=
(
Vt
PBW
-
Vt
tgt
)
Vt
PBW
;
an electrical activity sensor adapted to measure an electrical activity (EAmsi EAmsi occ ) of a patient's respiratory muscle synchronized with an inspiratory effort of the patient;
a detector of a neuro-mechanical efficiency (NME) of the patient, wherein the detector calculates the neuro-mechanical efficiency (NME) at least in part based on a ratio of a respiratory volume or pressure induced by the patient's respiratory muscle over the measured electrical activity (EAmsi) of the patient's respiratory muscle; and
a controller of the level of ventilatory assist (ASSIST) to the patient responsive to the control value from the operator interface and to the neuro-mechanical efficiency (NME) from the detector to determine the level of ventilatory assist (ASSIST) to the patient on the basis of the neuro-mechanical efficiency (NME) and of the desired unloading level (UL).
17. The mechanical ventilation system of claim 16 , comprising a display for displaying the determined level of ventilatory assist (ASSIST).
18. The mechanical ventilation system of claim 17 , wherein the operator interface is adapted to receive a command for adjusting the mechanical ventilation system.
19. The mechanical ventilation system of claim 16 , wherein the controller is adapted to automatically adjust the mechanical ventilation system to provide the level of ventilatory assist (ASSIST) to the patient.
20. The mechanical ventilation system of claim 16 , comprising an inspiratory valve operatively connected to the controller and adapted to cause a patient's inspiratory occlusion, wherein the detector of the neuro-mechanical efficiency (NME) comprises:
a pressure sensor adapted to measure a variation of a patient's airway pressure (ΔPaw occ ) during an unassisted inspiration attempt while the inspiratory valve causes a patient's inspiratory occlusion;
wherein the electrical activity sensor is further adapted to measure the electrical activity (EAmsi occ ) of the patient's respiratory muscle synchronized with the inspiratory effort of the patient during the unassisted inspiration attempt while the inspiratory valve causes the patient's inspiratory occlusion; and
wherein the controller is adapted to determine the neuro-mechanical efficiency (NME) using the relation:
NME
=
Δ
Paw
occ
EAmsi
occ
.
21. The mechanical ventilation system of claim 16 , wherein operator interface is adapted to receive the control value in a form selected from (i) an operator setting representing a target electrical activity of the patient's respiratory muscle synchronized with an inspiratory effort for a normally breathing patient (EAmsi tgt ) and (ii) an operator setting for a variation of the patient's airway pressure (ΔPaw EAmsi tgt ) for the target electrical activity wherein the controller is adapted to calculate the inspiratory effort for the normally breathing patient (EAmsi tgt ) as:
EAmsi
tgt
=
Δ
Paw
EAmsi
tgt
NME
.
22. The mechanical ventilation system of claim 16 , wherein the controller is adapted to calculate a total ventilatory requirement (Req total ) of the patient on the basis of the inspiratory effort for the normally breathing patient (EAmsi tgt ).
23. The mechanical ventilation system of claim 22 , wherein controller is adapted to determine the level of ventilatory assist (ASSIST) to the patient using the relation:
ASSIST=Req total −NME.
24. The mechanical ventilation system of claim 22 , comprising:
a flow meter operatively connected to the controller and adapted to measure, in cooperation with the controller, an inspiratory volume (Vt) of the patient during an unassisted inspiration;
wherein the electrical activity sensor is further adapted to measure the electrical activity (EAmsi) of the patient's respiratory muscle synchronized with the inspiratory effort of the patient during the unassisted inspiration; and
wherein the controller is adapted to determine a neuro-ventilatory efficiency of the patient using the relation:
NVE
=
Vt
EAmsi
.
25. The mechanical ventilation system of claim 24 , wherein, to determine the total ventilatory requirement (Req total ) of the patient, the controller is adapted to:
determine a nominal tidal volume (Vt PBW ) on the basis of a predicted body weight of the patient;
estimate an expected electrical activity (EAmsi Vt PBW ) for the nominal tidal volume (Vt PBW ) using the relation:
EAmsi
Vt
PBW
=
Vt
PBW
NVE
=
Vt
PBW
·
EAmsi
Vt
;
and
estimate the total ventilatory requirement (Req total ) of the patient using the following relation:
Req
total
=
EAmsi
VtPBW
EAmsi
tgt
·
NME
.
26. The mechanical ventilation system of claim 25 , wherein the operator interface is adapted to receive specifications of a gender and of a height of the patient, and wherein the controller is adapted to:
determine the predicted body weight (PBW) of the patient on the basis of the gender and height of the patient; and
determine the nominal tidal volume (Vt PBW ) by multiplying the predicted body weight (PBW) by a constant.
27. The mechanical ventilation system of claim 24 , wherein the patient's respiratory muscle is a diaphragm of the patient.
28. The mechanical ventilation system of claim 16 , wherein the controller is adapted to determine the level of ventilatory assist (ASSIST) to the patient using the relation:
ASSIST
=
UL
(
1
-
UL
)
·
NME
.
29. The mechanical ventilation system of claim 16 , comprising:
a sensor adapted to obtain, from the patient, a measurement corresponding to the control value;
wherein the control is further adapted to calculate a deviation between the control value and the measurement, and to recalculate the level of ventilatory assist (ASSIST) to the patient on the basis of the neuro-mechanical efficiency (NME) of the patient, of the control value and of the deviation.
30. The mechanical ventilation system of claim 16 , comprising a cardiac signal extractor adapted to remove cardiac signal components from an electrical activity representative signal measured by the electrical activity sensor to provide the measured electrical activity (EAmsi, EAmsi occ ) of the patient's respiratory muscle synchronized with the inspiratory effort of the patient.
31. A method implemented in a mechanical ventilation system for determining whether a patient is ready to be weaned from the mechanical ventilation system, comprising:
receiving at the mechanical ventilation system a control value representing a target electrical activity of a respiratory muscle of a normally breathing patient (EAmsi tgt ), the respiratory muscle being synchronized with an inspiratory effort for the normally breathing patient;
measuring an inspiratory volume (Vt) of the patient during an unassisted inspiration;
measuring the electrical activity (EAmsi) of the patient's respiratory muscle synchronized with the inspiratory effort of the patient during the unassisted inspiration;
determining a nominal tidal volume (Vt PBW ) on the basis of a predicted body weight of the patient;
estimating an expected tidal volume for the normally breathing patient using the relation:
Vt
EAmsi
tgt
=
EAmsi
tgt
·
Vt
EAmsi
;
calculating a wean index (WEAN index ) using the following relation:
WEAN
index
=
Vt
EAmsi
tgt
Vt
PBW
;
and
determining whether the patient is ready to be weaned from the mechanical ventilation system as a function of a value of the (WEAN index ).
32. A mechanical ventilation system, comprising:
an operator interface adapted to receive a control value representing a target electrical activity of a respiratory muscle of a normally breathing patient (EAmsi tgt ), the respiratory muscle being synchronized with an inspiratory effort for the normally breathing patient;
a flow meter adapted to measure an inspiratory volume (Vt) of a patient during an unassisted inspiration;
an electrical activity sensor adapted to measure an electrical activity (EAmsi) of the patient's respiratory muscle synchronized with an inspiratory effort of the patient during the unassisted inspiration;
a controller operatively connected to the operator interface, the flow meter and the electrical activity sensor, the controller being configured to:
determine a nominal tidal volume (Vt PBW ) on the basis of a predicted body weight of the patient;
estimate an expected tidal volume for the normally breathing patient using the relation:
Vt
EAmsi
tgt
=
EAmsi
tgt
·
Vt
EAmsi
;
calculate a wean index (WEAN index ) using the following relation:
WEAN
index
=
Vt
EAmsi
tgt
Vt
PBW
;
and
determine whether the patient is ready to be weaned from the mechanical ventilation system as a function of a value of the wean index (WEAN index ).