Methods and Systems For Assessing Muscle Electrical Activity in Response to Stimulation of a Motor Nerve

1 . A method for assessing neuromuscular blockade in a subject having been administered a muscle relaxant agent, comprising:

stimulating a motor nerve to cause an evoked muscle response;

recording the evoked muscle response, the evoked muscle response comprising a floating differential signal;

quantifying the recorded muscle response; and

comparing the quantified muscle response to a control muscle response, wherein the comparison indicates a level of neuromuscular blockade in the subject.

2 . The method of claim 1 , wherein the floating differential signal is a non-ground-referenced differential signal.

3 . The method of claim 1 , wherein recording the evoked muscle response further comprises:

recording for muscle electrical activity in a muscle innervated by the motor nerve using two recording electrodes; and

determining a difference between the muscle electrical activity recorded by the each of the two recording electrodes.

4 . The method of claim 3 , wherein determining a difference between the muscle electrical activity recorded by each of the two recording electrodes is accomplished without recording for muscle electrical activity using a common reference electrode.

5 . The method of claim 3 , wherein recording for muscle electrical activity in a muscle innervated by the motor nerve comprises using no more than two recording electrodes.

6 . The method of claim 1 , wherein stimulating the motor nerve comprises stimulating the motor nerve with a repeated train of temporally-spaced stimuli.

7 . The method of claim 6 , wherein the control muscle response is a quantified muscle response caused by a prior or subsequent stimulus in the repeated train of temporally-spaced stimuli.

8 . The method of claim 6 , wherein the motor nerve is stimulated according to a train-of-four protocol or a tetanic protocol.

9 . A system for assessing neuromuscular blockade in a subject having been administered a muscle relaxant agent, comprising:

a stimulator configured to generate one or more stimuli for stimulating a motor nerve to cause an evoked muscle response;

a patient-stimulus interface configured to supply each stimulus generated by the stimulator to the patient;

a patient-recording interface configured to record the evoked muscle response in a muscle innervated by the motor nerve, the evoked muscle response comprising a floating differential signal; and

at least one processing device configured to:

quantify the recorded muscle response; and

compare the quantified muscle response to a control muscle response, wherein the comparison indicates a level of neuromuscular blockade in the subject.

10 . The system of claim 9 , wherein the floating differential signal is a non-ground-referenced differential signal.

11 . The system of claim 9 , wherein the patient-recording interface comprises at least two recording electrodes for recording muscle electrical activity in the muscle innervated by the motor nerve, the non-ground-referenced differential signal being a difference between the muscle electrical activity recorded by the each of the at least two recording electrodes.

12 . The system of claim 9 , wherein the stimulator is configured to stimulate the motor nerve with a repeated train of temporally-spaced stimuli.

13 . The system of claim 12 , wherein the control muscle response is a quantified muscle response caused by a prior or subsequent stimulus in the repeated train of temporally-spaced stimuli.

14 . The system of claim 12 , wherein the motor nerve is stimulated according to a train-of-four protocol or a tetanic protocol.

15 . A system for assessing neuromuscular blockade in a subject having been administered a muscle relaxant agent, comprising:

a stimulator configured to generate one or more stimuli for stimulating a motor nerve to cause an evoked muscle response;

a patient-stimulus interface configured to supply each stimulus generated by the stimulator to the patient;

a patient-recording interface comprising at least two recording electrodes and configured to record muscle electrical activity of a muscle innervated by the motor nerve, wherein the patient-recording interface does not include a common reference electrode; and

at least one processing device configured to:

quantify the recorded muscle electrical activity; and

compare the quantified muscle electrical activity to a control muscle electrical activity, wherein the comparison indicates a level of neuromuscular blockade in the subject.

16 . The system of claim 15 , wherein the recorded muscle electrical activity is a floating differential signal.

17 . The system of claim 15 , wherein the recorded muscle electrical activity is a non-ground-referenced differential signal.

18 . The system of claim 16 , wherein the recorded muscle electrical activity comprises a difference between the muscle electrical activity recorded at each of the at least two recording electrodes.

19 . The system of claim 15 , wherein the stimulator is configured to stimulate the motor nerve with a repeated train of temporally-spaced stimuli.

20 . The system of claim 19 , wherein the motor nerve is stimulated according to a train-of-four protocol or a tetanic protocol.

21 . An electrode system for use with a system for assessing neuromuscular blockade in a subject, comprising:

one or more stimulation electrodes configured to deliver a stimulus to a motor nerve of the subject; and

at least two recording electrodes configured to record muscle electrical activity of a muscle innervated by the motor nerve, wherein the electrode system does not include a common reference electrode.

22 . The electrode system of claim 21 , wherein the recorded muscle electrical activity is a difference between muscle electrical activity recorded at each of the at least two recording electrodes.

23 . The system of claim 21 , wherein the recorded muscle electrical activity is a floating differential signal.

24 . The system of claim 21 , wherein the recorded muscle electrical activity is a non-ground-referenced differential signal.

25 . A system for assessing muscle electrical activity in a subject, comprising:

a motor nerve stimulator configured to stimulate a targeted motor nerve of the subject;

a recording apparatus for recording electrical activity of a muscle innervated by the motor nerve; and

a recording apparatus for recording electrical activity of the targeted motor nerve.

26 . The system of claim 25 , further comprising at least one processor configured to identify whether an electrical response to the stimulus was recorded in the muscle.

27 . The system of claim 25 , further comprising at least one processor configured to identify whether an electrical response to the stimulus was recorded in the motor nerve.

28 . The system of claim 25 , further comprising a processing system configured to identify whether an electrical response to the stimulus was recorded in the muscle and whether an electrical response to the stimulus was recorded in the motor nerve.

29 . The system of claim 29 , wherein the processing system is further configured to indicate that the nerve was not stimulated if there is no electrical response to the stimulus recorded in the nerve.

30 . The system of claim 26 , wherein the subject has been administered a muscle relaxant agent.

31 . The system of claim 30 , wherein the processing system is further configured to indicate the presence of neuromuscular blockade in the subject when an electrical response to the stimulus is recorded in the nerve and there is an absent or diminished electrical response to the stimulus recorded in the muscle.

32 . A method for identifying whether a motor nerve in a subject has been stimulated, comprising:

applying a stimulus to the subject, wherein the stimulus is targeted to stimulate the motor nerve;

recording for an electrical response to the applied stimulus in the targeted motor nerve; and

recording for an electrical response to the applied stimulus in a muscle innervated by the targeted motor nerve, wherein the presence or absence of an electrical response to the applied stimulus in the muscle and the presence or absence of an electrical response to the applied stimulus in the targeted motor nerve is used to assess whether the motor nerve was simulated.

33 . The method of claim 32 , wherein an electrical response to the applied stimulus is recorded in the muscle and an electrical response to the applied stimulus is recorded in the targeted motor nerve indicating the motor nerve was stimulated.

34 . The method of claim 32 , wherein an electrical response to the applied stimulus is recorded in the muscle and an electrical response to the applied stimulus is not recorded in the targeted motor nerve indicating that the motor nerve was not stimulated.

35 . The method of claim 32 , wherein an electrical response to the applied stimulus is not recorded in the muscle and an electrical response to the applied stimulus is not recorded in the targeted motor nerve indicating that the motor nerve was not stimulated.

36 . The method of claim 32 , wherein the subject has been administered a muscle relaxant agent prior to application of the stimulus to the subject.

37 . The method of claim 36 , wherein an electrical response to the applied stimulus is not recorded in the muscle and an electrical response to the applied stimulus is recorded in the motor nerve indicating neuromuscular blockade in the subject.

38 . The method of claim 36 , wherein a diminished electrical response to the applied stimulus is recorded in the muscle and an electrical response to the applied stimulus is recorded in the motor nerve indicating neuromuscular blockade in the subject.

39 . A method for assessing neuromuscular blockade in a subject having been administered a muscle relaxant agent, comprising:

applying a stimulus to the subject, wherein the stimulus is targeted to stimulate a motor nerve;

recording for an electrical response to the applied stimulus in the targeted motor nerve; and

recording for an electrical response to the applied stimulus in a muscle innervated by the targeted motor nerve, wherein the recorded electrical response of the nerve and the recorded electrical response of the muscle are used to assess neuromuscular blockade in the subject.

40 . The method of claim 39 , wherein an electrical response to the applied stimulus is recorded in the muscle and an electrical response to the applied stimulus is recorded in the targeted motor nerve indicating that the target motor nerve was stimulated.

41 . The method of claim 39 , wherein an electrical response to the applied stimulus is recorded in the muscle and an electrical response to the applied stimulus is not recorded in the targeted motor nerve indicating that the targeted motor nerve was not stimulated.

42 . The method of claim 39 , wherein an electrical response to the stimulus is not recorded in the muscle and an electrical response to the stimulus is not recorded in the targeted motor nerve indicating that the target motor nerve was not stimulated.

43 . The method of claim 39 , wherein an electrical response to the stimulus is not recorded in the muscle and an electrical response to the stimulus is recorded in the motor nerve indicating neuromuscular blockade in the subject.

44 . The method of claim 39 , wherein a diminished electrical response to the stimulus is recorded in the muscle and an electrical response to the stimulus is recorded in the nerve indicating neuromuscular blockade in the subject.

45 . The method of claim 43 , further comprising determining an amplitude of the recorded electrical activity of the muscle, wherein the determined amplitude compared to a control amplitude indicates a level of neuromuscular blockade in the subject.

46 . The method of claim 45 , wherein the control amplitude is an amplitude of recorded electrical activity of a prior or subsequent stimulus.

47 . The method of claim 39 , wherein the stimulus is applied during application a train-of-four stimulus protocol.

48 . A method for assessing neuromuscular blockage in a subject having been administered a muscle relaxant agent, comprising:

applying a stimulus to the subject, wherein the stimulus is targeted to stimulate a motor nerve;

recording for an electrical response to the stimulus in a muscle innervated by the targeted motor nerve; and

recording for an electrical response to the stimulus in the targeted motor nerve, wherein an absent or diminished electrical response to the stimulus in the muscle and the presence of an electrical response to the stimulus in the motor nerve indicates neuromuscular blockade in the subject.

49 . The method of claim 48 , wherein the stimulus is applied during application a train-of-four stimulus protocol to the subject.

50 . A system for assessing muscle electrical activity in a subject, comprising:

a motor nerve stimulator configured to stimulate a targeted motor nerve of the subject, the motor nerve stimulator comprising:

a power source; and

at least one stimulating electrode; and

a recording apparatus for recording electrical activity of a muscle innervated by the motor nerve and for recording electrical activity of the targeted motor nerve, the recording apparatus including:

a power source; and

at least one recording electrode, wherein the motor nerve stimulator and the recording apparatus are in galvanic isolation.

51 . The system of claim 50 , wherein the power source of the motor nerve stimulator and the power source of the recording apparatus are dedicated power sources, each providing power to only the motor nerve stimulator or the recording apparatus, respectively.

52 . The system of claim 51 , wherein the motor nerve stimulator comprises no more than two stimulating electrodes, and the recording apparatus comprises no more than two recording electrodes.