Abbreviations and definitions

Abbreviations

ACh = acetylcholine
CABG = coronary artery bypass grafting
CL = clearance from plasma
HPLC = high-performance liquid chromatography
ICU = intensive care unit
LMA = laryngeal mask airway
MOF = multiple organ failure
MRT = mean residence time
NMBA = neuromuscular blocking agent
RSI = rapid sequence induction
ST = single twitch
STR = single twitch response
TOF = train-of-four (T₄/T₁ ratio)
t1/2 - beta = elimination half-life
UV/MV = umbilical venous / maternal venous ratio
Vd ss = volume of distribution at steady state

Definitions

ED 50 ; ED 90 ; ED 95
the dose of a muscle relaxant that produces a mean percentage of maximum block of 50, 90 or 95 percent. The ED values are derived from the dose response curve, constructed by linear regression analysis of dose response data (mg/kg)

Maintenance dose
a dose of a muscle relaxant administered at predefined intervals (i.e. at 25% recovery of the twitch height after the previous dose) for the maintenance of
muscle paralysis for as long as required (mg/kg)

Dur 0.7 / 0.8
the time between the end of administration of the last dose of muscle relaxant to recovery of the TOF ratio to 0.7 / 0.8 (hr. min. sec.)

Dur 25
clinical duration: the time from the end of injection of a single dose of a neuromuscular blocking agent to recovery of the STR or T₁ to 25% of the control value or to reappearance of T₃ (hr. min. sec.)

Maximum block
percentage depression of the STR or T₁ at the time of peak effect after any given dose (%)

Onset time
the time from the end of injection of the neuromuscular blocking agent to a maximum or 100% neuromuscular block (sec.)

Recovery time (25-75)
the time required for recovery of the STR or T₁ from 25% to 75% of its control value, after the last dose, either during spontaneous or induced recovery
(hr. min. sec.)

Recovery time (25-70)
the time between recovery of the STR or T₁ from 25% of its control value to a recovery of the T₄ / T₁ ratio to 0.7, after the last dose, either during
spontaneous or induced recovery (hr. min. sec.)

TOF
train-of-four: 4 consecutive square wave supramaximal stimuli of 0.2 ms. duration delivered at the frequency of 2 Hz (repeated for example every 15
seconds)

T₁
amplitude of the first response to TOF stimulation, expressed as percentage of control T₁

T₄
amplitude of the fourth response to TOF stimulation, expressed as percentage of control T₁

TOF ratio (T₄ /T₁)
the ratio of T₄ over T₁ (within one TOF stimulus) expressed in decimals. At complete recovery, the T₄ /T₁ ratio is 1.0.

Monitoring of neuromuscular function

Monitoring neuromuscular function during and after anesthesia is important, as it provides information about a patient’s response to NMBAs. In general, it is assessed by monitoring the ‘twitch’ response (acceleromyography, mechanomyography or electromyography) of thumb adduction after peripheral electrical stimulation of the ulnar nerve. There are various patterns of stimulation; those detailed for the studies of Esmeron discussed below are single twitch stimulation, train-of-four (TOF) or a combination of the two. The TOF stimulation delivers four successive monophasic pulses at a low frequency (2 Hz) every 15 seconds. The advantage of TOF ratio is that it requires no control response. The first twitch in the TOF ratio is termed T₁ and is considered to be the control value. Successive twitches in the TOF are termed T₂ , T₃ and T₄ , respectively. The twitch responses are recorded until the TOF ratio (T₄ /T₁ ) is > 0.7 to 0.9 or the T₁ is > 90% of the control value.

Important terms used in monitoring neuromuscular transmission:

• Onset time: interval between NMBA administration and maximum twitch suppression
• Clinical duration: interval from administration of NMBA to 25% recovery of T₁ (duration 25%)
• Recovery index: time between 25% and 75% recovery of T₁ (recovery time 25 - 75%)
• Recovery : time to a TOF ratio (T₄ /T₁ ) of 0.9.