Dear Editor:
A recent advance in premedicating infants requiring intubation has
gained wide acceptance for humanitarian and physiological reasons.[1] The
use of muscle relaxation to facilitate intubation is quite separate from
sedation providing analgesia, amnesia and lack of awareness.
Practice is variable with little evidence-based guidance to suitable
drugs. Clinical Governance dictates continuing audit of any such practice
supported with written guidelines. We advocate a minimum monitoring policy
(Saturation, Pulse, Non-Invasive Blood Pressure and Respiratory rate) and
the presence of at least two skilled operators, one of which should be an
experienced specialist registrar or consultant, when using neuromuscular blockade. This
exercise is reserved for elective intubations and tube changes but not for
use in resuscitation on the labour suite.
Recent reports to the CSM (Committee for the Safety of Medicines) via the UK Yellow Card Scheme of mortality
associated with premedication using atracurium (dose 500 mcg/kg) and
diamorphine (dose 50 mcg/kg) in three premature infants (24, 26 and 26 weeks' gestation) have attributed the problem mainly to using atracurium,
which we consider debatable (Nicholas Rutter, Nottingham; Personal Communication). In addition, neuromuscular blockade should
be unnecessary in pre-term infants.
Diamorphine is a prodrug that is metabolised to active 6-0-acetylmorphine and then to morphine. It has faster CNS penetration than
morphine due to increased lipid solubility but its side effects are
similar. Bradycardia of vagal origin (in combination with laryngoscopy)
and decreased sympathetic response can cause a fall in cardiac output.
Both morphine and atracurium cause histamine release that can precipitate
bronchospasm and a fall in systemic vascular resistance (SVR).
Atracurium is a non-depolarising muscle relaxant that is slow onset
and long acting. It provides intubating conditions within 90 seconds (dose
300-600 mcg/kg) and has a recovery index of 16 minutes (adult data).
Premature infants have a small functional residual capacity (FRC)
particularly when paralysed. A rapid fall in alveolar oxygen in an already
under-ventilated infant may lead to pulmonary hypertension and increase
V/Q mismatch. Consequently, mask ventilation or tube placement becomes
necessary before the 90 seconds, which may not be long enough to reach
therapeutic levels. Patients receiving a long acting muscle relaxant that
cannot be ventilated for whatever reason will not start any independent
respiratory effort for at least 16 minutes!
Our guidelines propose using fentanyl (dose 2 mcg/kg), which does not
cause histamine release, so there is no bronchospasm. Cardiac output,
systemic vascular resistance, pulmonary vascular resistance, and pulmonary
artery occlusion pressure are preserved. High doses (10-15 mcg/kg) can lead
to vagal bradycardias or chest wall rigidity. Where a muscle relaxant is
indicated, we suggest suxamethonium (dose 1 mg/kg) which is to be preceded
with atropine.
References
(1) Whyte S, Birrell G, Wyllie J. Premedication before intubation in UK neonatal units. Arch Dis Child Fetal Neonatal Ed 2000;82:F38-F41.
Dear Editor:
A recent advance in premedicating infants requiring intubation has gained wide acceptance for humanitarian and physiological reasons.[1] The use of muscle relaxation to facilitate intubation is quite separate from sedation providing analgesia, amnesia and lack of awareness.
Practice is variable with little evidence-based guidance to suitable drugs. Clinical Governance dictates continuing audit of any such practice supported with written guidelines. We advocate a minimum monitoring policy (Saturation, Pulse, Non-Invasive Blood Pressure and Respiratory rate) and the presence of at least two skilled operators, one of which should be an experienced specialist registrar or consultant, when using neuromuscular blockade. This exercise is reserved for elective intubations and tube changes but not for use in resuscitation on the labour suite.
Recent reports to the CSM (Committee for the Safety of Medicines) via the UK Yellow Card Scheme of mortality associated with premedication using atracurium (dose 500 mcg/kg) and diamorphine (dose 50 mcg/kg) in three premature infants (24, 26 and 26 weeks' gestation) have attributed the problem mainly to using atracurium, which we consider debatable (Nicholas Rutter, Nottingham; Personal Communication). In addition, neuromuscular blockade should be unnecessary in pre-term infants.
Diamorphine is a prodrug that is metabolised to active 6-0-acetylmorphine and then to morphine. It has faster CNS penetration than morphine due to increased lipid solubility but its side effects are similar. Bradycardia of vagal origin (in combination with laryngoscopy) and decreased sympathetic response can cause a fall in cardiac output. Both morphine and atracurium cause histamine release that can precipitate bronchospasm and a fall in systemic vascular resistance (SVR).
Atracurium is a non-depolarising muscle relaxant that is slow onset and long acting. It provides intubating conditions within 90 seconds (dose 300-600 mcg/kg) and has a recovery index of 16 minutes (adult data). Premature infants have a small functional residual capacity (FRC) particularly when paralysed. A rapid fall in alveolar oxygen in an already under-ventilated infant may lead to pulmonary hypertension and increase V/Q mismatch. Consequently, mask ventilation or tube placement becomes necessary before the 90 seconds, which may not be long enough to reach therapeutic levels. Patients receiving a long acting muscle relaxant that cannot be ventilated for whatever reason will not start any independent respiratory effort for at least 16 minutes!
Our guidelines propose using fentanyl (dose 2 mcg/kg), which does not cause histamine release, so there is no bronchospasm. Cardiac output, systemic vascular resistance, pulmonary vascular resistance, and pulmonary artery occlusion pressure are preserved. High doses (10-15 mcg/kg) can lead to vagal bradycardias or chest wall rigidity. Where a muscle relaxant is indicated, we suggest suxamethonium (dose 1 mg/kg) which is to be preceded with atropine.
References
(1) Whyte S, Birrell G, Wyllie J. Premedication before intubation in UK neonatal units. Arch Dis Child Fetal Neonatal Ed 2000;82:F38-F41.