Flashcards in OSA: evaluating and managing perioperative risk Deck (37)
what should be considered with all overweight patients?
possibility of OSA
-80% of patients with OSA are undiagnosed
describe OSA diagnosis
-gold standard is polysomnography
-monitors: EEG, airflow, oxygen saturation
-observes for restlessness and leg movements
-results use apnea hypopnea index (AHI)
what is a split study of OSA?
diagnosis then CPAP titration
describe apnea hypopnea index (AHI)
number of abnormal respiratory events per hour of sleep
define mild OSA
AHI between 5 and 15 (6-20)
define moderate OSA
AHI between 15 and 30 (21-40)
define severe OSA
AHI > 30 (>40)
how can degree of OSA be determined during patient assessment?
ask for CPAP settings if patient unable to tell you severity of OSA
what are symptoms of OSA?
-sleep arousal (wakes up a lot during the night)
-decreased cognition and intellectual function
-concentration and memory problems
what are risk factors for OSA?
-middle age > age 40 (weight gain and loss of muscle tone)
-central abdominal fat distribution
describe the link between OSA and weight
-every 10 kg of weight, risk increases two times
-60-70% of OSA patients are obese (BMI > 30)
-weight loss greatly reduces severity of OSA
-as BMI increases by 6, OSA risk increases by 4
what is the best predictor of OSA risk?
-for every 15 cm in WC the risks of OSA increases 4 times
what else is used to predict OSA risk although less effective than WC?
neck circumference > 16.5 inches
how does OSA affect CRNAs?
-perioperative pharyngeal obstruction
-higher postop re-intubation rate
-difficult mask ventilation and laryngoscopy (difficult intubation 8x more likely)
-more sensitive to anesthesia drugs
what are some perioperative complications associated with OSA?
-increased length of stay; unplanned ICU admissions
-most common complication is oxygen desaturation
-increased pulmonary complications after orthopedic and general surgery d/t increased need of pain meds
what are most common co morbidities found with OSA?
-cardiovascular disease (CHF, CAD)
-HTN (systemic and pulmonary)
-obesity (probably the cause of co-morbidities)
what results from chronic hypoxemia in OSA?
-pulmonary vasoconstriction leads to pulmonary HTN which leads to right and left ventricular hypertrophy
what does polycythemia in OSA lead to ?
-increased risk of ischemic heart disease (IHD) and cerebrovascular disease
-increased SNS tone, cardiac arrhythmias
-increased RVH and LVH
what is the relationship between obesity and airway area?
-increased airway resistance/obstruction d/t increased fat which decreases airway patency
-adipose tissue in all pharyngeal structures/walls is increased
-pharyngeal muscles relax and airway collapse occurs
describe changes in airway physiology in OSA
-even during wakefulness, pharyngeal airway narrower
-anatomically narrower and more collapsible airways
-GA and sleep causes depressed neural control mechanisms leading to pharyngeal narrowing and closure (awake have increased neuronal activity and increased pharyngeal muscle tone)
-higher closure pressures in OSA patients
-trachea moves caudally up to 1 cm during inspiration
-longitudinal tension of the airway created
-reduced total lung capacity adds to instability of upper airway
what cycle of events is caused by depression of neural control with sleep onset in OSA patients?
1) anatomical imbalance; pharyngeal closure
2) apnea or hypoventilation (decrease O2; increase CO2)
3) increase of chemical stimuli
4) activation of neural control
5) arousal (wakes up gasping for air)
6) pharyngeal opening
7) hyperventilation (blows off CO2; increase O2)
8) reduction in chemical stimuli
9) depression of neural control
10) asleep and cycle restarts
what effects do benzodiazepines have on OSA?
-midazolam shown to cause airway obstruction
-midazolam increases the frequency and duration of apneic events
-midazolam causes same critical closing pressure that sleep does on the airway
*can profoundly impair respiration in post op period
*concurrent use of opioids and benzos increases risk of respiratory depression and airway obstruction
what effects do opioids have on OSA?
-increased sensitivity to exogenous opioids d/t recurrent hypoxia
-opioids exacerbate OSA and prevent arousal
-concurrent use also with benzos increase the risk of respiratory depression and airway obstruction
what inhalation agent is best with OSA?
-earlier return of protective reflexes
-reduced extubation time
what induction agents are effective analgesics in OSA patients?
-dexmedetomidine: sedative analgesic; reduces salivary secretions; can be used to reduce opioid requirements
-ketamine: effective analgesia; less depressant effect on dilating pharyngeal muscle
what are the most common treatments of OSA?
-continuous positive airway pressure (CPAP): titrate pressure case by case; noncompliance as high as 50%
-dental appliances: mandible movement; tongue retention; compliance rate about 60%
-surgical treatment: range from tonsils, nasal, UP3, maxillary mandibular advancement, etc.
what are the various screening tools for OSA?
-Epworth sleepiness scale
-Sleep apnea clinical score
describe the STOP BANG tool
-eight yes/no questions
-easily administered during pre-anesthesia evaluation
-stratifies patients into high and low risk OSA (high risk 3 or more yes answers; low risk less than 3 yes answers)
-patients identified as high risk found to have a higher occurrence of postop complications
*more valid test
what are the 8 questions in the STOP BANG tool?
S: snoring- do you snore loudly
T: tired- do you often feel tired or sleepy during the day
O: observed- anyone observed you stop breathing sleep
P: blood pressure- do you have or being treated for HTN
B: BMI- BMI more than 35 kg/m2
A: age- age > 50 y/o
N: neck- neck circumference > 40 cm
G: gender- male