Although some of the preceding studies were from older case
studies, the problem still exists today. In 2012, Mendels23
performed a literature review to determine the occurrence and type of vocal
cord injury and hoarseness in adults using an ETT in short-term anesthesia
(<5 hours). Thirteen studies met the inclusion criteria. After analysis of
the studies, the authors concluded hoarseness and vocal cord injuries were
common after short-term anesthesia and lasted up to 6 months. The authors found the following risk factors of laryngeal
injury caused by an ET: direct intubation trauma or tracheal extubation, ET
size, cuff design, cuff pressure, type of tube, use of an introducer, use of a
gastric tube, muscle relaxation, use of propofol, duration of the operation,
intubation conditions, and movement of the tube, as well as demographic factors
such as sex, weight, history of smoking and gastroesophageal reflux. The
limitation of the study is that the authors reviewed were heterogeneous and,
therefore, hard to compare.
Verhagen27 describes an 80-year-old man who
sustained left RLN palsy after total hip arthroplasty. The two theories for cause were either
an injury from the intubation or a stretch injury from positioning. Whichever
the cause, it demonstrates we need to be concerned with the tracheal nerves
just as we are with the extremities.
Discussion:
. The
studies that were discussed in this paper make clear that clinicians have poor
ability to properly inflate cuffs to safe pressures without a cuff manometer.28
As stated before, an ETTc pressure
lower than 20 cm H2O pressure places the patient at risk of
micro-aspiration and pneumonia19 and a pressure higher than 30 cm H2O
places the patient at risk of tracheal ischemia, necrosis and stenosis.12,28,29
Wujtewizc7 found cuff
pressures frequently exceed safe limits. It is imperative to maintain the cuff
pressure of 20-30 cm H2O. Wujtewicz,7 Chen,19 Hoffman,2 Stridermma,30 Watson31 and Braz29 all suggest routine measurement and
control of ETT cuff pressure with a cuff manometer to maintain cuff pressure
between 20-30 cm H2O.
It is unclear where the standardized sizes of 7.0 ETT for
females and 8.0 ETT for men originated. Exhaustive literature searches have not
revealed the reasoning behind these sizes. Stoelting and Miller, in their book Basics
of Anesthesia (3rd edition),
state, “Most adult tracheas (after 14 years of age) readily accept a cuffed 8-
to 9- mm ID (smaller size often selected for females) tracheal tubes.”32
No supporting evidence or references were provided for their sizing choices.
One hypothesis of adult ETT sizing is that when endotracheal tubes were first
introduced, they did not have pilot balloons, requiring large sizes to prevent
air and gas leaks and to provide adequate ventilation. Larger sizes were then
handed down as routine practices. As stated before, this is just a hypothesis
and cannot be proven. Similarly, the reasoning for the historical standard
sizes of 7.0 for women and 8.0 for men remains hidden.
Work
of breathing (WOB) is frequently cited as the rationale for choosing larger
size tubes. Fiastro33
disputed this in 1988 with the conclusion that pressure support can be used to
compensate for the added inspiratory work due to artificial airway resistance. In
1998 Koh34 discussed WOB, and found positive pressure ventilation
could be achieved with the use of small sizes of tracheal tubes and that there
is evidence that glottis damage is less likely when smaller sizes of tube are
used.
To
improve patient safety and prevent life altering complications like subglottic
tracheal stenosis, it is imperative to downsize routine adult endotracheal tubes
and to check the cuff pressure with a manometer with each and every intubation.
Copyright 2013. <References>
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