Evaluation of the clinical application of TcPCO2 measurements during rigid laryngoscopy or microlaryngeal surgery in children

ENT (ear, nose, throat) surgeons often perform procedures in the laryngeal
area, for example on the vocal cords. Due to the use of endoscopic optics to
reach and magnify these small structures that lie deep within the larynx, these
minimally invasive procedures are called *laryngoscopies*. Microlarynx surgery
is performed using an operating microscope with the patient in suspension
during laryngoscopy. During these procedures patients are under general
anaesthesia. The success rate of these kinds of procedures depends on the
exposure of the larynx during surgery. Therefore endotracheal intubation is
unwanted.
As a consequence, less invasive ventilation has to be performed via the rigid
bronchoscope or laryngoscope. In patients that have a poor pulmonary status the
use of high-frequency jet ventilation is also an option. Some procedures are
performed with the patients breathing spontaneously. In children ventilation
during these procedures is often particularly difficult because children have
less oxygen buffering capacity than adults and a relatively smaller alveolar
surface with which to exchange oxygen and carbon dioxide. Blood oxygen levels
can be measured with a pulse oximetry finger clip during the procedure. In
patients with an endotracheal tube, the washout of carbon dioxide from the
blood by the lungs is usually measured in the expired air. However, the methods
for ventilation during rigid laryngoscopy and microlarynx surgery are
accompanied by a large amount of air leakage, making these end-tidal carbon
dioxide (etCO2) measurements very unreliable at best, and most often simply
useless.
More complex laryngoscopic procedures can last over an hour, during which a
harmful build-up of blood carbon dioxide, hypercapnia, can occur. These high
levels of carbon dioxide cause respiratory acidosis, which in turn is harmful
to the entire body metabolism.
Also hypocapnia, low levels of blood carbon dioxide, can occur when the
patients is hyperventilated. Hypocapnia can cause vasoconstriction in the
brain, which is especially dangerous in young children. To prevent the patient
from becoming either hypercapnic or hypocapnic it is important that
anesthesiologists can measure the blood CO2 levels of the patient during the
procedure.
In neonatology an alternative form of carbon dioxide monitoring is now widely
used, called transcutaneous monitoring. By slightly heating the skin to above
core body temperatures the peripheral skin blood vessels dilate to such an
extent that so much blood flows through these capillary vessels that the
production of carbon dioxide by local skin cells does not have a noteworthy
influence on the amount of carbon dioxide in the blood at this spot. The heat
and vasodilation cause evaporation of carbon dioxide through the skin, which in
turn can be measured by a sensor. In this way, a reliable measurement of blood
carbon dioxide levels can be attained. While this transcutaneous monitoring
technique is widely validated and applied in neonatology and sleep studies in
children up to 18 years (and older), it has surprisingly not often found its
way into the operating room. In our hospital the decision has been made to use
transcutaneous monitoring of carbon dioxide during laryngoscopic procedures for
management of ventilation of patients under general anesthesia.

The objective of this study is to observe the effect of the planned
implementation of transcutaneous carbon dioxide monitoring as standard of care
during laryngoscopic and microlaryngeal procedures on the quality of care.

This controlled intermittent time series evaluates the clinical introduction of
transcutaneous carbon dioxide monitoring during laryngoscopic procedures in
children. The aim of this study is to quantify the quality of care effect of
the introduction of this monitoring modality.

At this moment all laryngoscopic and microlaryngeal procedures in children at
our hospital are performed without adequate carbon dioxide monitoring. To be
able to compare carbon dioxide management before and after the clinical
introduction of transcutaneous carbon dioxide monitoring, during the first
group of up to 70 patients of which a target of 60 successfully measured
procedures in which monitoring is applied the measured values will not be
visible to the anesthesiologist. No alternative method for measuring carbon
dioxide during these procedures is present for comparison to post-introduction
transcutaneous measurements. During the following 70 patients with a target of
60 successfully measured procedures the measured values will be visible to
anesthesiologists. Children of any age up to 18 years are eligible for
inclusion in this study. As standard of care, SpO2, electrocardiography, blood
pressure and other vital parameters are measured during these procedures.

After inclusion of each of the first group of up to 70 patients with a target
of 60 successfully measured patients, transcutaneous monitoring will be applied
with the measurements visible to the anesthesiologist. To measure a patient
baseline carbon dioxide level, the measurement will preferably be started 30
minutes before the start of the procedure. Return to baseline will be monitored
during 30 minutes after the procedure. All temperature settings, sensor site
skin inspections and sensor location changes will be performed in concordance
with standard of care protocols as used in our neonatal and pediatric intensive
care units. Logged data is saved anonymously before it can be extracted for
analysis.

During the thirty minutes prior to the planned rigid laryngoscopy or
microlaryngeal surgery, during the procedure and during the 30 minutes after
the procedure transcutaneous CO2 levels will be measured continuously using
either an OxiVenT or a V-Sign sensor (SenTec AG, Therwil, Switzerland). This
sensor will be placed at a measuring site that is either or both proven to
provide good measurements or easiest to manage during such a procedure.

Transcutaneous carbon dioxide (and oxygen) sensors locally heat the skin to
several degrees above the body temperature, potentially causing discoloration
of the skin and can eventually lead to burns when left in place for too long.
For standard of care, protocols have been implemented in our neonatal and
paediatric intensive care departments to eliminate this risk by regularly
changing the measuring site to prevent burns. In practice burns have not been
seen in recent years. These standard protocols are adhered to in the operating
theatre. Due to the observational nature of this study, there is no influence
on the application of transcutaneous monitoring and its clinical indication.