Page 470 - Clinical Application of Mechanical Ventilation

436 Chapter 13

paralyzing agent to maintain neuromuscular blockade. These alterations are likely
Acidemia intensifies the result of potassium shift (extracellularly) associated with acidemia. H moves
1
the effects of neuromuscular 1
blockade. into cells to be buffered, and K moves out to maintain ionic neutrality. One might
find these effects to be significant when intracranial pressure is being reduced via
hyperventilation (respiratory alkalosis).
Although the preceding factors can alter the action of neuromuscular blocking
Alkalemia diminishes agents, the net effects following the initial dosage can be titrated based on the results
the effects of neuromuscular
blockade. of patient monitoring. Since there is no standard level of paralysis to be achieved, the
desired depth of blockade will depend on the clinical objectives of the physician.

Adverse Effects

Apnea is the most immediate and life-threatening adverse effect associated with
both depolarizing and nondepolarizing agents. For this reason, practitioners expe-
rienced in airway management must be present when these drugs are administered.
For a patient who is already intubated and committed to a mechanical ventilator,
the following alarms should be active.
• Apnea alarm

• Low pressure/disconnect
• Low exhaled tidal/minute volume
• High/low heart rate

• Low SpO 2
Deaths due to apnea have been reported in cases where alarms were inappropri-
ately set or inactivated. It is possible that the incidence of fatal outcome is under-
reported (Halloran, 1991).
Other undesirable effects of neuromuscular blocking agents include loss of cough
mechanism, blunted neurologic assessment, emotional trauma due to inadequate
sedation, disuse muscle atrophy, pressure sores, and increased iatrogenic morbidity
and mortality associated with extended ICU exposure.
Histamine release is a property shared by most nondepolarizing agents. The presence
of histamine may be manifested clinically as vasodilation, flushing, and bronchospasm.
The degree of histamine release differs among the drugs. Succinylcholine, tubocurarine,
Succinylcholine and metocurine, and atracurium have been known to provoke bronchospasm and hypoten-
atracurium may provoke bron-
chospasm and hypotension sion related to moderate histamine release, whereas pancuronium elicits only minimal
due to histamine release. release. Histamine release is not likely with the use of vecuronium (Ebadi, 1993).
Cardiovascular effects range from minimal to moderate, including bradycardia, tachy-
cardia, arrhythmias, and circulatory collapse. Sudden changes in drug levels associated
with intermittent administration (versus continuous infusion) seem to be responsible
for these adverse effects (Watling et al., 1994). Table 13-10 summarizes the bronchopul-
monary and cardiovascular adverse effects of neuromuscular blocking agents.
A rare but very serious hazard of succinylcholine and inhaled anesthetics is a con-
dition known as malignant hyperthermia (MH). In individuals with the genetic pre-
disposition, MH causes skeletal muscle metabolism to suddenly surge out of control,

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