OSA: evaluating and managing perioperative risk Flashcards
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)
- loud snoring
- daytime somnolence
- fatigue
- decreased cognition and intellectual function
- concentration and memory problems
- headaches
what are risk factors for OSA?
- male
- middle age > age 40 (weight gain and loss of muscle tone)
- obese
- central abdominal fat distribution
- short mandible
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?
- waist circumference
- 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)
- acute MI
- DM
- arrhythmias
- HTN (systemic and pulmonary)
- cerebrovascular disease
- metabolic syndrome
- obesity (probably the cause of co-morbidities)
- GERD
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?
- inverse relationship
- 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?
desflurane
- 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?
- STOP BANG
- Epworth sleepiness scale
- Snore scale
- Sleep apnea clinical score
- Berlin Questionnaire
- P-SAP score
- ASA checklist
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
what are the advantages of the STOP BANG tool?
- high level of sensitivity and specificity in surgical patients (identifies who does and does not have OSA)
- if tool ranks as low risk, unlikely to have severe OSA
- score > or = 6 88% probability of having AHI > 30
- score of 6.7 or 8 = high probability of severe OSA
- highest degree of predictability of any tool esp. for moderate to severe OSA
describe preoperative management of OSA
- suspect and screen all obese pts. for OSA
- be aware of comorbid conditions present but undiagnosed (pulm. HTN as high as 20% in OSA)
- Mallampati class 3 or 4: suspect OSA
- caution when using pre op Versed
- be prepared for difficult intubation (cricoid pressure may increase difficulty in OSA)
- confirm CPAP therapy and brought to facility; consider preop use of OSA severe
describe intraoperative management of OSA
- consider regional or local for peripheral surgery
- regional/neuraxial improves OSA outcomes vs. GA
- caution in selecting respiratory depressant drugs
- use muscle relaxant sparingly
- mild hypercarbia improves tissue oxygenation and perfusion (body use to this state)
what are some emergence considerations with OSA?
- extubate fully awake, esp. if difficult intubation
- fully reverse pt. prior to extubation
- increase HOB to facilitate patent pharyngeal airway (supine promotes pharyngeal collapse)
- consider placing nasal airway prior to extubation (nasal airway more effective)
describe post op management of OSA
- ASA task force recommends determining post op disposition based on a risk factor scoring system
- write OSA specific orders if suspected or confirmed
- use supplemental oxygen; use CPAP if pt. uses at home
- avoid supine position; increase HOB (supine promotes pharyngeal closure; pharyngeal edema post op increases risk of obstruction)
- oximetry and/or telemetry if transferred to floor
describe the OSA scoring system
A) severity of sleep apnea based on sleep study or clinical indications (0-3 pts.)
-none 0; mild 1; moderate 2; severe 3 (subtract a point if use of CPAP; add a point if CO2 > 50)
B) invasiveness of surgery and anesthesia (0-3 pts.)
-superficial under local or block/no sedation- 0
-superficial with mod. sedation or GA- 1
-peripheral with spinal or epidural (mod. sedation)- 1
-peripheral with GA; airway surgery/mod. sed.- 2
-major surgery/airway surgery GA- 3
C)Requirement for post op opioids (0-3 pts.)
-none 0
-low dose oral- 1
-high dose oral/parenteral/neuraxial- 3
D) estimation of risk; total score = A + (higher of B & C) (0-6 pts.)
*overall score of 4 or >- increased risk for perioperative risk
*score of 5 or greater significant risk
describe post op discharge of OSA patients
- ASA task force: keep 3 hrs longer
- most complication occur within 2 hrs. of recovery
- up to 7 hrs. after last airway obstruction or hypoxemia event in an unstimulating environment
- educate on home opioid use: anxiety, pain, fragmented and deprived sleep can result in rebound REM sleep (increasing vulnerability to airway obstruction); respiratory depressant effects can last days
- not good candidates for outpatient surgery
- if suspected OSA, refer to primary care for evaluation
describe ambulatory surgeries with OSA
- use STOP BANG guideline; simple and easy; evidence indicates higher score = higher probability of severe OSA
- laparoscopic upper abdominal procedures suitable
- painful ambulatory surgery may not be suitable if unable to control pain with non-opioid analgesia
