OSA: evaluating and managing perioperative risk

Question 1

what should be considered with all overweight patients?

Answer 1

possibility of OSA

-80% of patients with OSA are undiagnosed

Question 2

describe OSA diagnosis

Answer 2

• gold standard is polysomnography
• monitors: EEG, airflow, oxygen saturation
• observes for restlessness and leg movements
• results use apnea hypopnea index (AHI)

Question 3

what is a split study of OSA?

Answer 3

diagnosis then CPAP titration

Question 4

describe apnea hypopnea index (AHI)

Answer 4

number of abnormal respiratory events per hour of sleep

Question 5

define mild OSA

Answer 5

AHI between 5 and 15 (6-20)

Question 6

define moderate OSA

Answer 6

AHI between 15 and 30 (21-40)

Question 7

define severe OSA

Answer 7

AHI > 30 (>40)

Question 8

how can degree of OSA be determined during patient assessment?

Answer 8

ask for CPAP settings if patient unable to tell you severity of OSA

Question 9

what are symptoms of OSA?

Answer 9

• sleep arousal (wakes up a lot during the night)
• loud snoring
• daytime somnolence
• fatigue
• decreased cognition and intellectual function
• concentration and memory problems
• headaches

Question 10

what are risk factors for OSA?

Answer 10

• male
• middle age > age 40 (weight gain and loss of muscle tone)
• obese
• central abdominal fat distribution
• short mandible

Question 11

describe the link between OSA and weight

Answer 11

• 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

Question 12

what is the best predictor of OSA risk?

Answer 12

• waist circumference

- for every 15 cm in WC the risks of OSA increases 4 times

Question 13

what else is used to predict OSA risk although less effective than WC?

Answer 13

neck circumference > 16.5 inches

Question 14

how does OSA affect CRNAs?

Answer 14

• perioperative pharyngeal obstruction
• higher postop re-intubation rate
• difficult mask ventilation and laryngoscopy (difficult intubation 8x more likely)
• more sensitive to anesthesia drugs

Question 15

what are some perioperative complications associated with OSA?

Answer 15

• 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

Question 16

what are most common co morbidities found with OSA?

Answer 16

• cardiovascular disease (CHF, CAD)
• acute MI
• DM
• arrhythmias
• HTN (systemic and pulmonary)
• cerebrovascular disease
• metabolic syndrome
• obesity (probably the cause of co-morbidities)
• GERD

Question 17

what results from chronic hypoxemia in OSA?

Answer 17

-pulmonary vasoconstriction leads to pulmonary HTN which leads to right and left ventricular hypertrophy

Question 18

what does polycythemia in OSA lead to ?

Answer 18

• increased risk of ischemic heart disease (IHD) and cerebrovascular disease
• increased SNS tone, cardiac arrhythmias
• increased RVH and LVH

Question 19

what is the relationship between obesity and airway area?

Answer 19

• 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

Question 20

describe changes in airway physiology in OSA

Answer 20

• 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

Question 21

what cycle of events is caused by depression of neural control with sleep onset in OSA patients?

Answer 21

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

Question 22

what effects do benzodiazepines have on OSA?

Answer 22

• 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

Question 23

what effects do opioids have on OSA?

Answer 23

• 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

Question 24

what inhalation agent is best with OSA?

Answer 24

desflurane

• earlier return of protective reflexes
• reduced extubation time

Question 25

what induction agents are effective analgesics in OSA patients?

Answer 25

- dexmedetomidine: sedative analgesic; reduces salivary secretions; can be used to reduce opioid requirements - ketamine: effective analgesia; less depressant effect on dilating pharyngeal muscle

Question 26

what are the most common treatments of OSA?

Answer 26

- 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.

Question 27

what are the various screening tools for OSA?

Answer 27

- STOP BANG - Epworth sleepiness scale - Snore scale - Sleep apnea clinical score - Berlin Questionnaire - P-SAP score - ASA checklist

Question 28

describe the STOP BANG tool

Answer 28

- 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

Question 29

what are the 8 questions in the STOP BANG tool?

Answer 29

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

Question 30

what are the advantages of the STOP BANG tool?

Answer 30

- 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

Question 31

describe preoperative management of OSA

Answer 31

- 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

Question 32

describe intraoperative management of OSA

Answer 32

- 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)

Question 33

what are some emergence considerations with OSA?

Answer 33

- 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)

Question 34

describe post op management of OSA

Answer 34

- 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

Question 35

describe the OSA scoring system

Answer 35

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

Question 36

describe post op discharge of OSA patients

Answer 36

- 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

Question 37

describe ambulatory surgeries with OSA

Answer 37

- 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