Dosage
General Dosage Guidelines
It is important to select the proper dose of a nondepolarizing
neuromuscular blocker to ensure that the desired effect is achieved without excessive
overdosage. In addition to a general knowledge of the guidelines, precise practice
requires the use of a peripheral nerve stimulator to adjust the relaxant dosage to
the individual patient. Overdosage must be avoided for two reasons: (1) to limit
the duration of drug effect to match the anticipated length of surgery and (2) to
avoid unwanted cardiovascular side effects.
Initial and Maintenance Dosage
The initial dosage is determined by the purpose of administration.
Traditionally, doses used to facilitate tracheal intubation are 2 ×
ED95
(this dose also approximates to 4 × ED50
)
( Table 13-7
). If the trachea
has already been intubated without a nondepolarizing blocker or with succinylcholine
and the purpose is simply to produce
surgical relaxation, a dose slightly less than the ED95
( Table
13-8
) should be given, with adjustment upward as indicated by responses
evoked by peripheral nerve stimulation. Downward adjustment of the initial dose
is necessary in the presence of any of the potent inhaled anesthetics (see the section
"Drug Interactions").
TABLE 13-8 -- Pharmacodynamic effects of succinylcholine and nondepolarizing neuromuscular
blockers
|
Anesthesia |
Intubating Dose (mg/kg) |
Approximate ED95
Multiples |
Maximum Block (%) |
Time to Maximum Block (min) |
Clinical Duration
*
(min) |
Reference |
|
Succinylcholine |
Narcotic or halothane |
0.5 |
1.7 |
100 |
— |
6.7 |
[70]
|
|
Succinylcholine |
Desflurane |
0.6 |
2 |
100 |
1.4 |
7.6 |
[151]
|
|
Succinylcholine |
Narcotic or halothane |
1.0 |
3 |
100 |
— |
11.3 |
[70]
|
|
Succinylcholine |
Desflurane |
1.0 |
3 |
100 |
1.2 |
9.3 |
[151]
|
|
Succinylcholine |
Narcotic |
1.0 |
3 |
— |
1.1 |
8 |
[248]
|
|
Succinylcholine |
Narcotic |
1.0 |
3 |
— |
1.1 |
9 |
[249]
|
|
Succinylcholine |
Isoflurane |
1.0 |
3 |
100 |
0.8 |
9 |
[250]
|
|
Steroidal Compounds |
|
Rocuronium |
Narcotic |
0.6 |
2 |
100 |
1.7 |
36 |
[251]
|
|
Rocuronium |
Isoflurane |
0.6 |
2 |
100 |
1.5 |
37 |
[250]
|
|
Rocuronium |
Isoflurane |
0.9 |
3 |
100 |
1.3 |
53 |
[250]
|
|
Rocuronium |
Isoflurane |
1.2 |
4 |
100 |
0.9 |
73 |
[250]
|
|
Vecuronium |
Isoflurane |
0.1 |
2 |
100 |
2.4 |
41 |
[250]
|
|
Vecuronium |
Narcotic |
0.1 |
2 |
100 |
2.4 |
44 |
[252]
|
|
Pancuronium |
Narcotic |
0.08 |
1.3 |
100 |
2.9 |
86 |
[253]
[254]
|
|
Pancuronium |
Narcotic |
0.1 |
1.7 |
99 |
4 |
100 |
[255]
|
|
Pipecuronium |
Narcotic |
0.05 |
1 |
93 |
6.3 |
29 |
[194]
|
|
Pipecuronium |
Narcotic |
0.06 |
1.2 |
96 |
5.4 |
45 |
[256]
|
|
Pipecuronium |
Narcotic |
0.08 |
1.6 |
99 |
3.9 |
74 |
[256]
|
|
Pipecuronium |
Narcotic |
0.1 |
2 |
100 |
3.6 |
94 |
[256]
|
|
Benzylisoquinolinium Compounds |
|
Mivacurium |
Narcotic |
0.15 |
2 |
100 |
3.3 |
16.8 |
[10]
|
|
Mivacurium |
Narcotic |
0.15 |
2 |
100 |
3 |
14.5 |
[251]
|
|
Mivacurium |
Halothane |
0.15 |
2 |
100 |
2.8 |
18.6 |
[217]
|
|
Mivacurium |
Narcotic |
0.2 |
2.6 |
100 |
2.5 |
19.7 |
[10]
|
|
Mivacurium |
Narcotic |
0.25 |
3.3 |
100 |
2.3 |
20.3 |
[10]
|
|
Mivacurium |
Narcotic |
0.25 |
3.3 |
— |
2.1 |
21 |
[249]
|
|
Atracurium |
Narcotic |
0.5 |
2 |
100 |
3.2 |
46 |
[209]
|
|
Cisatracurium |
Narcotic |
0.1 |
2 |
99 |
7.7 |
46 |
[257]
|
|
Cisatracurium |
Narcotic |
0.1 |
2 |
100 |
5.2 |
45 |
[209]
|
|
Cisatracurium |
Narcotic |
0.2 |
4 |
100 |
2.7 |
68 |
[209]
|
|
Cisatracurium |
Narcotic |
0.4 |
8 |
100 |
1.9 |
91 |
[209]
|
|
Doxacurium |
Narcotic |
0.04 |
1.6 |
100 |
7.6 |
77.4 |
[198]
|
|
Doxacurium |
Narcotic |
0.05 |
2 |
100 |
4.5 |
125 |
[198]
|
|
Doxacurium |
Narcotic |
0.06 |
2.4 |
100 |
4.4 |
123 |
[198]
|
|
d-Tubocurarine |
Narcotic |
0.6 |
1.2 |
97 |
5.7 |
81 |
[255]
|
|
Metocurine |
Narcotic |
0.4 |
1.3 |
99 |
4.1 |
107 |
[255]
|
|
Diallyl Derivative of Toxiferine |
|
Alcuronium |
Narcotic |
0.25 |
1.4 |
100 |
2.2 |
54 |
[258]
|
|
For atracurium and mivacurium, slower injection (30 seconds)
is recommended to minimize circulatory effects. |
*Time
from injection of the intubating dose to recovery of twitch to 25% of control.
To avoid prolonged residual paralysis or inadequate antagonism
of residual blockade, or both, the main goal should be to use the lowest possible
dose that will provide adequate relaxation for surgery. Management of individual
patients should always be guided by monitoring with a peripheral nerve stimulator.
In an adequately
anesthetized and monitored patient, there is little reason to completely abolish
twitch or TOF responses to peripheral nerve stimulation during maintenance of relaxation.
Supplemental (maintenance) doses of neuromuscular blockers should be about a fourth
(in the case of intermediate- and short-acting neuromuscular blockers) to a tenth
(in case of long-acting neuromuscular blockers) the initial dose and should not be
given until clear evidence of initiation of recovery from the previous dose is apparent.
Maintenance of relaxation by continuous infusion of intermediate-
and short-acting drugs can be performed and is useful to keep relaxation smooth and
to rapidly adjust the depth of relaxation to surgical needs. The depth of block
in each patient is kept moderate, if possible, to ensure prompt spontaneous recovery
or easy reversal at the end of the procedure. Table
13-7
lists approximate dose ranges that are usually required during infusion
to maintain 90% to 95% block of the twitch (one twitch visible on TOF stimulation)
under nitrous oxide-oxygen anesthesia supplemented with intravenous anesthetics.
The infusion dosage is usually decreased by about 30% to 50% in the presence of
potent inhaled anesthetics.
