The Difficult Airway
| Status: | Recruiting |
|---|---|
| Healthy: | No |
| Age Range: | 18 - 80 |
| Updated: | 9/19/2018 |
| Start Date: | June 2016 |
| End Date: | June 2019 |
| Contact: | Taylor Pak, BS |
| Phone: | 469-419-5790 |
The Difficult Airway: Incidence and Predictors in Lean vs. Obese Patients in a Large Public Teaching Hospital
Patients who are obese, as defined by a BMI ≥ 30 kg/m2 may be more difficult to intubate than
non-obese patients. Traditional methods of airway assessment such as Mallampati score, mouth
opening, and thyromental distance may not be the best predictors of difficult intubation.
Patients who are scheduled to have non-stat surgery at Parkland Memorial Hospital will be
asked to participate in this study and sign a written consent form. Physiologic measurements
including but not limited to thyromental distance, sternomental distance, Mallampati score,
mouth opening, interincisor distance, and mandibular protrusion will be measured and
recorded. All measurements are non invasive. The remaining aspects of perioperative care,
including the general anesthetic technique, will be standardized for all patients and will
not differ from the standard of care. There will be no incentive or payment to the patients.
This prospective study is intended to enroll 3000 consecutive surgical patients. Lean
patients (BMI < 30 kg/m2) who are intubated by the same anesthesia providers during the same
time period will be included as the control group and to report the incidence of difficult
mask ventilation and difficult intubation in our general surgical population, which has not
previously been defined.
non-obese patients. Traditional methods of airway assessment such as Mallampati score, mouth
opening, and thyromental distance may not be the best predictors of difficult intubation.
Patients who are scheduled to have non-stat surgery at Parkland Memorial Hospital will be
asked to participate in this study and sign a written consent form. Physiologic measurements
including but not limited to thyromental distance, sternomental distance, Mallampati score,
mouth opening, interincisor distance, and mandibular protrusion will be measured and
recorded. All measurements are non invasive. The remaining aspects of perioperative care,
including the general anesthetic technique, will be standardized for all patients and will
not differ from the standard of care. There will be no incentive or payment to the patients.
This prospective study is intended to enroll 3000 consecutive surgical patients. Lean
patients (BMI < 30 kg/m2) who are intubated by the same anesthesia providers during the same
time period will be included as the control group and to report the incidence of difficult
mask ventilation and difficult intubation in our general surgical population, which has not
previously been defined.
The study will enroll 3000 ASA physical status 1-4 patients who are scheduled to undergo
surgery under general endotracheal anesthesia (GETA) at Parkland Hospital. A research
assistant will identify eligible patients using the electronic medical record. After it is
deemed that the patient satisfies all inclusion and exclusion criteria, the anesthesia
provider or research assistant will approach the patient in the preoperative surgery holding
area to ask for their permission to enroll in the study. Only study team personnel will ask
potential patients for participation in the study; anesthesia providers who are not study
team personnel will not be allowed to consent patients for the study. All relevant
information to the study will be provided and the patient will be asked to sign an informed
consent. After consent is obtained, measurements of the patient's anatomical features
including thyromental distance, sternomental distance, neck circumference, interincisor
distance, mandibular protrusion, and Mallampati score will be taken and recorded by the
research assistant or anesthesia provider.
In the operating room, patients will have standard ASA monitors (NIBP, SpO2, EKG, ETCO2,
temperature) placed. Lean patients will be placed in the standard "sniffing" position while
obese patients will be placed in the "ramped" position as previously described. All patients
will undergo pre-oxygenation for at least 3 minutes prior to induction of anesthesia.
Patients will undergo induction of general anesthesia according to a standardized protocol
that does not differ from the usual standard of care. The initial blade used for laryngoscopy
will be selected by the anesthesia provider according to the characteristics of the patient
as has been recommended by previous authors. After induction of general anesthesia, a
research assistant will ask the anesthesia provider the degree of difficulty of mask
ventilation and laryngoscopy using a standardized questionnaire modified from the intubation
difficulty score. For mask ventilation, any adjunct use of equipment such as an oral airway
or nasopharyngeal airway will be recorded. If two-handed ventilation is used, it will be
recorded as well. The type of laryngoscope blade and Cormack-Lehane grade during laryngoscopy
will be recorded. The level of training of the laryngoscopist (resident vs CRNAs vs faculty)
and how many years they have been in that role will be recorded. The time from induction to
intubation will also be recorded, based on the time those events are marked in the electronic
medical record, as well as the lowest SpO2 that occurred between induction to intubation.
The intubation difficulty scale (IDS), which has previously been validated, will be used to
score the intubation. This scale has been used in comparing difficult tracheal intubation in
lean vs. obese patients.
The IDS will be comprised of 7 questions with numerical values for each question, resulting
in a cumulative score. Those with an IDS score <5 will be considered "not difficult" and
those with an IDS score ≥5 will be considered "difficult." A "failed intubation" will be
defined as that in which the airway cannot be secured in a non-invasive fashion (e.g.,
cricothyrotomy) or the patient has to be awakened. The 7 questioned used to determine the IDS
score will be the same as those used by Adnet et al:
1. Number of additional intubation attempts
2. Number of additional operators
3. Number of alternative intubation techniques used
4. Laryngoscopic view (Grade 1 = 0, Grade 2 = 1, Grade 3 = 2, Grade 4 = 3)
Cormack Lehane grades [13]:
- Grade 1- vocal cords completely visible
- Grade 2- arytenoids visible but cords not completely visible
- Grade 3- only epiglottis visible
- Grade 4- epiglottis not visible
5. Lifting force applied during laryngoscopy (0 if inconsiderable and 1 if considerable
force used)
6. External laryngeal pressure applied for optimized glottic exposure (0 if no, 1 if yes)
7. Position of vocal cords at intubation (0 if abducted or not visible, 1 if adducted)
Protected patient information including name, medical record number, and date of birth will
be recorded. Demographic data such as height, weight, BMI, race, and gender will also be
recorded. All patients will receive a standardized general anesthetic that is usual and
customary for patients undergoing their scheduled operation.
Additional information gathered will include ASA status, presence of comorbidities (e.g, OSA,
HTN, DM), thyromental distance, sternomental distance, ability to protrude mandibular teeth
over maxillary teeth, interincisor distance, ability to have full range of motion of the
neck, Mallampati score, and neck circumference.
- Neck circumference will be measured at the level of the cricoid cartilage with the
patient's neck in neutral position.
- Thyromental distance is thought to be an indicator of mandibular space. It will be
measured as the distance from the prominentia laryngea of the thyroid cartilage to the
symphysis of the mandible with the patient in maximum neck extension with the mouth
closed.
- Sternomental distance will be measured as the distance from the sternal notch to the
symphysis of the mandible with the patient in maximum neck extension with the mouth
closed.
- Mallampati status will be obtained with the patient in an upright sitting position with
the head in neutral position. Patients will be asked to open their mouth as wide as
possible with tongue protrusion without phonation. Pharyngeal structures will be assess
and classification will be performed according to the structures seen (Class 1 = soft
palate, fauces, uvula, tonsillar pillars; Class 2 = soft palate, fauces, uvula; Class 3
= soft palate, base of uvula only; Class 4 = soft palate not visible).
- The ability of the patient to protrude their lower teeth over their upper lip (upper lip
bite test) will be assessed. Class 1 = lower incisors can bite the upper lip above the
vermilion line; Class 2 = lower incisors can bite the upper lip below the vermilion
line; Class 3 = lower incisors cannot bite the upper lip [9].
- Neck range of motion will be graded on a binary scale. Those will full range of motion
in flexion and extension will be graded as full and those without full range of motion
will be graded as limited.
- Interincisor distance will be measured as the maximum distance between the central
incisors (teeth 9 and 24 or teeth 8 and 25). Patients who are edentulous will have their
gum-to-gum distance recorded as the interincisor distance.
surgery under general endotracheal anesthesia (GETA) at Parkland Hospital. A research
assistant will identify eligible patients using the electronic medical record. After it is
deemed that the patient satisfies all inclusion and exclusion criteria, the anesthesia
provider or research assistant will approach the patient in the preoperative surgery holding
area to ask for their permission to enroll in the study. Only study team personnel will ask
potential patients for participation in the study; anesthesia providers who are not study
team personnel will not be allowed to consent patients for the study. All relevant
information to the study will be provided and the patient will be asked to sign an informed
consent. After consent is obtained, measurements of the patient's anatomical features
including thyromental distance, sternomental distance, neck circumference, interincisor
distance, mandibular protrusion, and Mallampati score will be taken and recorded by the
research assistant or anesthesia provider.
In the operating room, patients will have standard ASA monitors (NIBP, SpO2, EKG, ETCO2,
temperature) placed. Lean patients will be placed in the standard "sniffing" position while
obese patients will be placed in the "ramped" position as previously described. All patients
will undergo pre-oxygenation for at least 3 minutes prior to induction of anesthesia.
Patients will undergo induction of general anesthesia according to a standardized protocol
that does not differ from the usual standard of care. The initial blade used for laryngoscopy
will be selected by the anesthesia provider according to the characteristics of the patient
as has been recommended by previous authors. After induction of general anesthesia, a
research assistant will ask the anesthesia provider the degree of difficulty of mask
ventilation and laryngoscopy using a standardized questionnaire modified from the intubation
difficulty score. For mask ventilation, any adjunct use of equipment such as an oral airway
or nasopharyngeal airway will be recorded. If two-handed ventilation is used, it will be
recorded as well. The type of laryngoscope blade and Cormack-Lehane grade during laryngoscopy
will be recorded. The level of training of the laryngoscopist (resident vs CRNAs vs faculty)
and how many years they have been in that role will be recorded. The time from induction to
intubation will also be recorded, based on the time those events are marked in the electronic
medical record, as well as the lowest SpO2 that occurred between induction to intubation.
The intubation difficulty scale (IDS), which has previously been validated, will be used to
score the intubation. This scale has been used in comparing difficult tracheal intubation in
lean vs. obese patients.
The IDS will be comprised of 7 questions with numerical values for each question, resulting
in a cumulative score. Those with an IDS score <5 will be considered "not difficult" and
those with an IDS score ≥5 will be considered "difficult." A "failed intubation" will be
defined as that in which the airway cannot be secured in a non-invasive fashion (e.g.,
cricothyrotomy) or the patient has to be awakened. The 7 questioned used to determine the IDS
score will be the same as those used by Adnet et al:
1. Number of additional intubation attempts
2. Number of additional operators
3. Number of alternative intubation techniques used
4. Laryngoscopic view (Grade 1 = 0, Grade 2 = 1, Grade 3 = 2, Grade 4 = 3)
Cormack Lehane grades [13]:
- Grade 1- vocal cords completely visible
- Grade 2- arytenoids visible but cords not completely visible
- Grade 3- only epiglottis visible
- Grade 4- epiglottis not visible
5. Lifting force applied during laryngoscopy (0 if inconsiderable and 1 if considerable
force used)
6. External laryngeal pressure applied for optimized glottic exposure (0 if no, 1 if yes)
7. Position of vocal cords at intubation (0 if abducted or not visible, 1 if adducted)
Protected patient information including name, medical record number, and date of birth will
be recorded. Demographic data such as height, weight, BMI, race, and gender will also be
recorded. All patients will receive a standardized general anesthetic that is usual and
customary for patients undergoing their scheduled operation.
Additional information gathered will include ASA status, presence of comorbidities (e.g, OSA,
HTN, DM), thyromental distance, sternomental distance, ability to protrude mandibular teeth
over maxillary teeth, interincisor distance, ability to have full range of motion of the
neck, Mallampati score, and neck circumference.
- Neck circumference will be measured at the level of the cricoid cartilage with the
patient's neck in neutral position.
- Thyromental distance is thought to be an indicator of mandibular space. It will be
measured as the distance from the prominentia laryngea of the thyroid cartilage to the
symphysis of the mandible with the patient in maximum neck extension with the mouth
closed.
- Sternomental distance will be measured as the distance from the sternal notch to the
symphysis of the mandible with the patient in maximum neck extension with the mouth
closed.
- Mallampati status will be obtained with the patient in an upright sitting position with
the head in neutral position. Patients will be asked to open their mouth as wide as
possible with tongue protrusion without phonation. Pharyngeal structures will be assess
and classification will be performed according to the structures seen (Class 1 = soft
palate, fauces, uvula, tonsillar pillars; Class 2 = soft palate, fauces, uvula; Class 3
= soft palate, base of uvula only; Class 4 = soft palate not visible).
- The ability of the patient to protrude their lower teeth over their upper lip (upper lip
bite test) will be assessed. Class 1 = lower incisors can bite the upper lip above the
vermilion line; Class 2 = lower incisors can bite the upper lip below the vermilion
line; Class 3 = lower incisors cannot bite the upper lip [9].
- Neck range of motion will be graded on a binary scale. Those will full range of motion
in flexion and extension will be graded as full and those without full range of motion
will be graded as limited.
- Interincisor distance will be measured as the maximum distance between the central
incisors (teeth 9 and 24 or teeth 8 and 25). Patients who are edentulous will have their
gum-to-gum distance recorded as the interincisor distance.
Inclusion Criteria:
- 18-80 years old
- ASA physical status classification 1 to 4
- Scheduled for an operation that requires general endotracheal anesthesia
- Willing and able to consent in English or with use of appropriate language translator
- Anesthesia providers who are caring for patients who have enrolled in the study will
also be potential subjects who will be verbally consented and asked to fill out a
questionnaire.
Exclusion Criteria:
- Age less than 18 or older than 80
- Unable to give informed consent for participation in the study
- Stat cases
- Patients who will not be expected to have general anesthesia (e.g., monitored
anesthesia care or regional anesthesia)
- Patient refusal
- History of difficult intubation
- Planned awake fiberoptic intubation
- Previous neck surgery (on bone, joint, or soft tissues in neck) or radiation
- Obvious neck pathology/abnormality
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