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48 M. Hunasikatti et al.
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Chapter 4
Perioperative Assessment and Management
of Patients with Sleep Disorders
Vinh Nguyen, Brian Freeman, a nd Kumudhini Hendrix
Abstract In the United States, about 60,000 patients receive general anesthesia for
surgery per day. The most important postoperative cardiac, neurologic, and psychi-
atric complications occur frequently around the middle of the first postoperative
week—between postoperative day 2 and 5 (Lazic et al., Physiol Behav 168:41–54,
2017). In addition to acute myocardial infarction, myocardial ischemia, strokes, and
delirium, postoperative sleep disorders also have significant adverse impact on
postoperative outcomes. Animal models show that sleep deprivation leads to deple-
tion of glycogen stores and increases of oxidative stress and free radical formation
with product ion of pro-inflammatory cytokines all leading to poor postoperative
recovery. Impo rtantly, sleep-disordered breathing (SDB) is exacerbated, peaking on
postoperative day 3 and returning to baseline only on postoperative night 7 (Chung
et al., Anesthesiology 120:299–311, 2014).
Though sleep and general anesthesia share physiological common ground, they
are both different states of unconsciousness. Sleep is a state of decreased arousal
generated by nuclei in the hypothalamus, brain stem, and basal forebrain. Normal
human sleep cycles between two states: rapid eye movement (REM) sleep and
non-REM sleep at approximately 90 min intervals. REM sleep is characterized by
active high-frequency, low-amplitude rhythms with concomitant rapid eye move-
ments, dreaming, irregularities of respiration and heart rate, penile and clitoral
erection, and airway and skeletal muscle hypotonia. Non-REM sleep has three
distinct EEG stages—with higher-amplitude, lower frequency rhythms and is
accompanied by waxing and waning muscle tone, decreased body temperature and
decreased heart rate.
V. Nguyen
Anesthesiology Department, University of Minnesota, Minneapolis, MN, USA
B. Freeman
Georgetown University School of Medicine, Washington, DC, USA
K. Hendrix (
✉)
Anesthesia Devices, CDRH, Food and Drug Administration, Silver Spring, MD, USA
e-mail: Kumudhini.hendrix@fda.hhs.gov
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023
A. S. BaHammam, M. Hunasikatti (eds.), Sleep Apnea Frontiers, Progress in Sleep
Research,
https://doi.org/10.1007/978-981-99-7901-1_4
49
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50 V. Nguyen et al.
General anesthesia is a drug-induced reversible state that is characterized by
unconsciousness, amnesia, analgesia, and akinesia. If a procedure does not require
full general anesthesia, then lower doses of sedatives or hypnotics are used to
produce diminished cortical function or activity while maintaining intact respiratory
and cardiovascular function. In vitro and in vivo studies have identified GABA
λ
and
N-methyl-D-aspartate (NMDA) receptors in the cortex, thalamus, brain stem, and
striatum as two important targets of hypnotic drugs (Brown et al., NEJM 363:27,
2010). A bolus of hypnotic drugs rapidly reaching the brain stem arousal centers will
contribute to unconsciousness. Clinical signs are consistent with the actions of the
brain stem. Impaired brain stem function due to actions of hypnotic agents on
oculomotor, trochlear, abducens, trigeminal and facial nuclei in the midbrain and
the pons produce loss of oculocephalic and corneal reflexes. Apnea ensues due to
actions of hypnotic agents on GABA
λ
interneurons in the respiratory control
network in the ventral medulla and pons (Brown et al., NEJM 363:27, 2010).
Rapid atonia that ensues induction is most likely due to the actions of hypnotic
agents in the spinal cord, pontine, and medullary reticular nuclei that control
antigravity muscles.
Not surprisingly, sleep disorders have many implications, especially respiratory,
for the surgical patient during the perioperative period. Unfortunately, many sleep
disorders are often not diagnosed or remain misdiagnosed prior to surgery—espe-
cially in the pediatric populations. Type of surgery, anesthesia, type of sleep
disorders, type and severity of sleep disorder, comorbidities, and use of opioids
have significant effects on patient outcomes.
Keywords Perioperative sleep disorders · Sleep-disordered breathing (SDB) ·
Postoperative complications · General anesthesia and sleep · Preoperative
assessment and management
4.1 Preoperative Concerns
Obstructive sleep apnea (OSA) is characterized by recurrent episodes of upper
airway obstruction and desaturation leading to fragmentation of sleep and daytime
fatigue and sleepiness (Raveendran et al. 2017
). The severity of OSA is determined
by apnea hypopnea index (AHI). Apnea is a cessation of airflow for 10 s or more,
while hypopnea is reduced airflow with a concomitant desaturation of at least 4%.
Prevalence of OSA is 13% in men and 6% in women when OSA is defined as AHI
more than 15 events/h. In morbidly obese patients scheduled for bariatric surgery,
prevalence of OSA is about 78%. Unfortunately, a significant portion of patients are
undiagnosed when scheduled for surgery. Furthermore, OSA is associated with
many serious comorbidities such as heart failure, myocardial ischemia , hyperten-
sion, arrhythmias, insulin resistance, gastroesophageal reflux, and obesity. Analgesic
and anesthetic drugs can impact these patients’ consciousness and sleep, upper
airway anatomy and physiology, arousal responses, muscle activation and ventila-
tory drive and thereby potentially increasing perioperative risks in patients with
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OSA. OSA patients remain at high risk for respiratory depression even for cases for
mere procedural sedation. Though these patients remain at risk for opioid-induced
respiratory depression, fragmentation and sleep deprivation heighten sensitivity to
pain. Importantly, there is a positive association between OSA and difficult mask
ventilation and intubation (Cozowicz et al.
2018).
4 Perioperative Assessment and Management of Patients with Sleep Disorders 51
Though the importan
ce of obstructive sleep apnea in surgical patients is widely
acknowledged and codified within professional guidelines (Society of Anesthesia
and Sleep Medicine Guideline on Intraoperative Management of Adult Patients with
OSA
2018), the importance of other disorders is less clear. Restless leg syndrome
(RLS), a sensorimotor sleep disorder, resulting in nocturnal leg discomfort and sleep
disruption was found to have an incidence of 9% in patients undergoing spinal
anesthesia (Hogl et al. 2002). Though this could not be reproduced, the perioperative
period of prolonged immobility, blood loss, iatrogenic sleep deprivation, temporary
hold on symptomatic treatment, and use of medications such as metoclopramide can
worsen RLS.
Similarly, very little is known about the anesthetic implications for patients with
central disorders of hypersomnolence (CDH). This group of disorders include
narcolepsy type 1 (with cataplexy), narcolepsy 2 (without cataplexy), and idiopathic
hypersomnia. CDH result in persistent and pathologic daytime sleepiness despite
adequate amount and quality of nocturnal sleep. Kleine–Levin syndrome, a CHD, is
characterized by bouts of recurrent hypersomnia punctuated by periods of relative
normalcy. Though only supported by case reports and small case series, CHD raises
following concerns for surgical patients in the perioperative period: (1) perioperative
cataplexy or sleepiness, (2) chronic use of psychotropic and/or vasoactive medica-
tions such as amphetamines, and importantly (3) delayed emergence form
anesthesia.
Additionally, most anesthesiologists are not aware of obesity hypoventilation
syndrome (OHS) and overlap syndrome (combination of OSA and chronic obstruc-
tive pulmonary disease). Both these syndromes are associated with significant
comorbid conditions and perioperative morbidity than OSA alone (Raveendran et
al.
2017). Daytime hypercapnia, defined as PaCO
2
of more than 45 mmHg during
wakefulness, differentiates OHS from OSA. OHS is defined as a combination of
BMI > 30 kg/m
2
, daytime hypercapnia, and absence of an alternative explanation
for hypoventilation such as neuromuscular, mechanical, or metabolic in origin.
Malignant obesity hypoventilation syndrome (MOHS) is severe OHS characterized
by multi-organ dysfunction in morbidly obese patients. Although 90% of patients
with OHS have OSA, 10% of OHS patients do not. OHS prevalence is approxi-
mately 0.6% of general population and increasing to 50% for cohort with
BMI > 50 kg/m
2
. Unfortunately, OHS is often not diagnosed and morbidity is
higher than patients with OSA. Most patients with OHS are diagnosed in their fifth
decade of life after hypercapnic respiratory failure or in sleep clinic evaluations.
OHS patients have a higher likelihood to develop heart failure, angina pectoris
and/or cor pulmonale. MOHS is defined as a patient with BMI > 40 kg/m
2
, awake
hypercapnia, metabolic syndrome (central obesity, hypertension, hyperlipidemia,
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and insulin resistance), and multi-organ function related to obesity (Raveendran
et al. 2017).
52 V. Nguyen et al.
Patients with OHS have restrictive
respiratory physiology impairing lung com-
pliance by 60% compared to eucapnic obese counterparts who have 20% impaired
lung compliance. This has implications for increased work of breathing leading to
quicker fatigue of respiratory muscles. Typically, obese patients have higher carbon
dioxide production that leads to a concomitant drive to increase minute ventilation.
However, patients with OHS have blunting of ventilatory drive to carbon dioxide.
This blunted response is worsened by increased hypercapnia and serum bicarbonate.
Mortality for patients with OHS undergoing bariatric surgery is between 2% and 8%.
Also, patients with OHS and overlap syndrome are more likely to experience
postoperative respiratory failure, postoperative heart failure, prolonged intubation,
postoperative ICU transfer, and longer stay in the hospital.
A multipronged approach, including lifestyle modification and positive airway
pressure (PAP) and management of comorbid state is necessary for patients with
OHS. Use of BPAP (bi-level PAP) less than 4 h/night is the strongest independent
predictor of mortality among patients with OHS. Treatment of patients with OHS on
PAP may have protective benefits during perioperative period.
Though there may not be a clear pathophysiological link, overlap syndrome is the
combination of COPD and OSA. Overlap syndrome has a prevalence of 1% while
COPD alone is 10% while OSA 5–10% of adult populations. However, in those
patients with moderate to severe COPD, OSA has a prevalence rate of almost 66%.
Nocturnal hypoxemia is an important sing of overlap syndrome. Smoking and
obesity are two major predictors of overlap syndrome. Daytime hypercapnia, respi-
ratory failure, and pulmonary hypertension are higher in cohort with overlap syn-
drome than in isolated OSA or COPD. Within COPD, those with chronic bronchitis
than emphysema are more likely to have overlap syndrome.
In overlap syndrome, increased accessory muscles are used for breathing due to
flattening of the diaphragm and increased dead space ventilation. In contrast to OHS
patients, overlap patients have normal to enhanced respiratory drive to carbon
dioxide. Five-year survival in these patients is higher with CPAP and oxygen
compared to oxygen alone.
Children with SDB and OSA have been found to have increased perioperative
respiratory related adverse events (Scalzitti and Sarb
2018
). That is, they have a
higher rate of significant oxygen desaturations, airway obstructions, laryngospasms,
over-sedation, and need for escalation of care compared to their counterparts.
Unfortunately, most children with SDB undergo general anesthesia without PSG
or a diagnosis. One important clinical tool, the snoring, trouble breathing,
un-refreshed sleep questionnaire (STBUR)—a five question tool, has been shown
to be predictive of such adverse events. A score of three or more increased the risk of
opioid related adverse events and perioperative respiratory events. Children with
OSA who underwent adenotonsillectomy showed that hypoxemia reduced the
anesthesia requirement while opioids doubled the level of respiratory suppression.
Also, there is increasing evidence of codeine in children with SDB. Polymorphism
of CYP 2D6, a metabolic enzyme, leads to slower or no metabolism in 10% of this
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cohort while increasing metabolism in 2% of these children converting codeine to
morphine with production of higher blood levels of morphine than expected. This
has led to restriction on use of codeine and tramadol for children by the FDA.
4 Perioperative Assessment and Management of Patients with Sleep Disorders 53
4.1.1 Preoperative Screening and Risk Assessment
Careful preoperative screening is the first and most important step in management of
any morbidly obese patient with SDB. Most of these patients are often not diagnosed
or have been misdiagnosed. A sensitive screening tool to identify daytime hyper-
capnia such as an arterial blood gas analysis is considered invasive. However, serum
bicarbonate is a sensitive surrogate biomarker along with lower oxygen saturation. A
serum HCO
3
of 27 mEq/L in absence of other causes such as diuretics demonstrates
a 92% sensitivity in predicting hypercapnia in arterial blood gas. One unit increase in
serum HCO
3
increases possibility of having OHS by 14%. End tidal CO
2
can also
substitute for arterial blood gas to detect hypercarbia. A two-step screening process,
first with serum HCO
3
to exclude patients without OHS and then AHI improves
specificity. Additionally, hypoxemia defined as SpO
2
< 90% or PaO
2
< 60 mmHg
during wakefulness should lead clinicians to suspect OHS in patients with OSA.
Since polysomnography is expensive and time consuming, the STOP-Bang
Questionnaire can alternatively be used as a screening tool. STOP-Bang Question-
naire has the highest methodological validity and accuracy in predicting diagnosis of
OSA while a STOP-Bang score of 5–8 identifies those with high probability of
moderate to severe OSA. Therefore, in addition to HCO
3
of at least 28 mEq/L and a
STOP-Bang score of 3 or more improves the specificity for preoperative OSA
recognition. Patients with preoperative mean overnight SpO
2
of less than 93% or
oxygen desaturation index of 29 events/h have been shown to have higher risk for
postoperative adverse events.
Modified STOP-Bang score adds 1 additional point for BMI 35– 40 kg/m
2
,
2 points for BMI 40–45 kg/m
2
, 3 points for greater than 45 kg/m
2
, 1 point for
HCO
3
26–28 mEq/L, and 2 points for greater than 28 mEq/L. Modified score of 6 or
more has increased sensitivity with a decreased specificity (89.2% and 47.6%)
compared to original score of 6 or more (71.6% and 59.1%). Additionally, preoper-
ative clinicians should evaluate for clinical signs of pulmonary hypertension
(pretibial edema, jugular venous distension, etc.). When patients have poor e xercise
tolerance, a preoperative echocardiogram may be needed.
Recently published guidelines from Society of Anesthesia and Sleep Medicine
recommends OSA screening a part of routine preoperative evaluation. Preoperative
cardiopulmonary evaluation will be necessary in those with hypoventilation syn-
drome, pulmonary hypertension, and hypoxemia of unknown origin. They may need
preoperative sleep studies as well. ASA’s perioperative management of patients with
OSA is based on severity of OSA, invasiveness of surgery, type of anesthesia, and
need for perioperative opioids. The Society of Ambulatory Anesthesia Consensus
Statement recommends the STOP-Bang Questionnaire as a screening tool for all
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surgical patients. Ambulatory surgery may not be an option for patients with OHS or
overlap syndrome due to significant posto perative complications and comorbidi ties.
54 V. Nguyen et al.
4.2 Intraoperative Concerns
4.2.1 OSA
Adequate perioperative screening and reliable risk predictors help to devise an
anesthetic plan and mitigate risks. Although PSG is the gold standard for suspected
OSA patients, the time and resources to obtain this test may not suit all patients.
Therefore, using specific OSA screening questionnaires preoperatively can help
identify those at high risk for airway compromise (Chung et al.
2016). Intraoperative
challenges with OSA patients include difficult airway after induction, appropriate
dosage of hypnotic and sedative drugs, and neuromuscular blocking agents
(NMBA). OSA is an independent risk factor for difficulty masking or intubation
(Brodsky et al. 2002). Using AHI as a metric, those with AHI >40 had a signifi-
cantly higher prevalence of a difficult airway. One study categorized three groups as
AHI < 40, 40–70, AHI > 70. The incidence for a difficult airway was 3.3%, 19.3%,
and 27.6%, respectively (Kim and Lee 2006). These patient populations are at higher
risk for airway complications, including laryngeal injury, airway trauma, rapid
desaturation, aspiration, unexpected ICU admission, and possible death. As a result,
the American Society of Anesthesiology (ASA) has devised a practice guideline for
possible difficulty airway management, including mask ventilation and intubation.
This information allows anesthesia providers to be prepared for a potentially difficult
airway. During the anesthesia induction, mask ventilation can be challenging and
can lead to a higher incidence of inadequate oxygenation. It is imperative to have
other airway adjuncts available and possibly two trained providers for mask venti-
lation. A recent analysis demonstrated that during intubation of OSA patients, poor
visualization of the glottis was expected. The need for multiple intubations attempts
increased by more than threefold compared to non-OSA patients (Nagappa et al.
2018). Thereby, it is imperative to have other intubation methods such as
videolaryngoscopy, intubating laryngeal mask airway, or awake intubation.
The use of sedative or hypnotic can easily lead to airway collapsibility and
depression of central respiratory drive. The upper airway collapse is dose-dependent
with anesthetic agents. Anesthetic agents depress central respiratory output, which in
turn relaxes the upper airway dilator muscles and suppresses upper airway reflexes in
a dose-dependent manner. Occlusion is mainly at the soft palate level, but a higher
level of obesity can be at multiple sites, causing total airway occlusion (Hartfield
et al.
2023; Eastwood et al.
2005). Consequently, hypnotic agents should be titrated
to the anesthetic depth level by using bispectral indexing (BIS) monitor or A-line
autoregression. This, in turn, will eliminate the cumulative anesthetic dosages and
help potential postoperative airway complications.
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4 Perioperative Assessment and Management of Patients with Sleep Disorders 55
Opioid therapy is used to treat moderate to severe pain but can suppress ventila-
tory drive to breath. In general, the obese patient may have OSA or a component of
airway collapsibility. These patients are associated with a 50% increase in opioid-
induced respiratory depression. As well, chronically disturbed sleep continuity and
intermittent hypoxia are associated with heightened pain sensitivity. The working
theory is a hypoxia-triggered upregulation of opioid receptors, promoting sensitivity
to narcotics. As a result, there is a growing concern for intraoperative opioid usage
and appropriately safe opioid delivery in clinical practice. Studies point to a dose-
dependent pattern with increased odds for respiratory complications at increasing
opioid dose among OSA versus non-OSA patients (Subramani et al.
2017). These
observational studies demonstrated a higher use of naloxone and positive airway
pressure ventilation in the postoperative period (Weingarten et al.
2016; Lee et al.
2015). Opioid use in OSA patients presents a risk factor for critical postoperative
respiratory events. To help combat the potential respiratory events, intraoperative
opioids should be cautiously administered at a lower dose. They require far less than
the non-OSA type patient. Furthermore, a multimodal analgesic approach is neces-
sary to avoid post-extubation respiratory compromise, including non-opioids phar-
macology thera py. If applicable, a regional or neuraxial anesthetic may be an
appropriate anesthetic and potentially eliminate the use of narcotics.
The purpose of NMBA is used to improve intubation conditions and allow
optimal surgical relaxation. The incidence of residual NMBA has been reported by
up to 64% of patients in the PACU (Mur phy and Brull
2010). The current evidence
supports a relationship between OSA patients and higher postoperative events
secondary to residual NMBA (Pereira et al.
2013). Therefore, a good clinical
practice would include min imizing the NMBA dose given to OSA patients. During
a surgical case, monitoring the depth of the NMBA is critical to prevent a deep
neuromuscular block and prevent early NMB reversal with residual weakness. After
completing the case, a complete reversal on NMBA before extubation is vital in the
setting of any OSA patient. Two different pharmacological NMBA reversals are
commonly used, neostigmine, a cholinesterase inhibitor, or a more recent drug—
sugammadex, a cyclodextrin, used specifically for rocuronium. The evidence is
limited, but two studies suggest sugammadex has fewer postoperative respiratory
complications and fewer postoperative chest radiographic changes (Unal et al.
2015;
Llaurado et al.
2014).
Besides the potential airway management issue on induction, premature
extubation among OSA patients can lead to detrimental airway collapse. One
group reported an incidence of 5% after OSA corrective surgery causing airway
obstruction. Ultimately, this can lead to negative pressure pulmonary edema (Baluch
et al. 2009
). Ideally, all extubations would be performed when patients are fully
awake and following commands. In turn, complete NMBA reversal is needed, and
motor twitch verification is essential. Optimal body position is essential for adequate
chest and diaphragm movement. Therefore, a 30-degree reverse Trendelenburg
position will prevent abdominal compression against the diaphragm. The soft palate
is highly collapsible and worsens with rostral fluid shift due to pooling and edema in
the supine position. Airway adjuncts, either orally or nasally, should be applied
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before extubation to prevent airway collapse. Naturally, the neutral supine head
position causes the head to be more flexed, worsening OSA. Lateral head rotation
after extubation help alleviate the severity of OSA and maintain adequate ventilation
(Zhu et al.
2017).
56 V. Nguyen et al.
4.2.2 Restless Leg Syndrome
The perioperative environment can be linked to exacerbation of restless leg syn-
drome during surgery and ultimately affect postoperative outcomes. RLS can be
associated with iron deficiency, neuropa thy related to diabetes, pregnancy, chronic
renal failure, and spinal stenosis (Klingelhoefer et al. 2016). Furthermore, sleep
deprivation, immobility, and drug interference of the central nervous system’s
dopamine pathway can precipitate RLS (Goldstein
2015; Michaud et al. 2002;
Hening et al. 1999). Certain medications, including dopaminergic agonist and
alpha-2 delta calcium channel ligands, are known to improve RLS. Before
intraoperative management, assessment of the patient’s RLS symptoms and the
treatment options are essential. Narcotic therapy effectively controls RLS to allow
adequate pain control and sedation to allow less sleep disruption. Sequential com-
pression devices (SCD) are important to prevent deep vein thrombosis but are
equally important to control RLS exacerbations after surgery. SCD allows blood
to circulate freely and avoid muscle immobility. Since RLS is linked to iron
deficiency, clinicians should limit phlebotomy and aggressively treat blood loss
intraoperatively. In suspected anemic patients, a dose of IV iron can help with
RLS. Those patients with RLS under sedation anesthesia can benefit from a dose
of physostigmine to eliminate periodic limb movement. Continuous
dexmedetomidine infusion throughout the operation with a target dose rate of
0.4 μg/kg/h can benefit suspected RLS patients (Ohshita et al. 2020). The mecha-
nism may target the spinal cord by counteracting increased spinal excitability.
Dexmedetomidine specifically enhances the descending inhibition and decreases
the descending facilitation to modulate pain and nociception (You et al. 2016).
Finally, avoiding intraoperative medication including dopamine antagonists, first-
generation antihistamine, metoclopramide, haloperidol, or selective serotonin reup-
take inhibition can ameliorate RLS.
4.2.3 Narcolepsy
Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness, cata-
plexy, hypnagogic or hypnopompic hallucinations, and sleep paralysis. This disor-
der has autonomic dysregulation, especially control of heart rate and body
temperature. Intraoperative management is essential in these patients to prevent
manifestations of narcoleptic symptoms. Narcolepsy is an incurable, lifelong disease
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that requires chronic pharmacologic treatment to prevent adverse events. As a result,
narcoleptic medications should be continued preoperatively. Worse narcolepsy
symptoms were seen in those who discontinued preoperatively or those who previ-
ously used medications for symptom control (Wang and Greenberg
2013). Medical
therapy includes stimulants (amphetamine, methylphenidate, and modafinil) or
sodium oxybate. Chronic use of stimulant downregulates sympathetic nervous
system while increasing anesthetic requirement. This leads to profound hypotension.
A few case reports reported serious adverse effects, including brief hypertension
during laryngoscopy and intraoperative hypotension (Fischer et al.
2006; Burrow
et al.
2005). Close hemodynamic monitoring is advised throughout the case, espe-
cially upon induction. Direct-acting vasoactive or vasodilator agents should be
readily available to counteract the either hypotension or hypertension, respectively.
Arterial line monitoring may be necessary if refractory hypotension persists despite a
large dose of vasoactive agents. Chronic stimulants usage, especially modafinil, may
carry the risk of intraoperative awareness. A common p
ractice is to utilize BIS
monitoring to guide the appropriate awareness depth and prevent delayed emergence
(Morimoto et al.
2011). To limit the sedative properties of hypnotic and opioids
drugs, short-acting narcotics such as remifentanil or fentanyl are ideal. The use of
TIVA, utilizing propofol, has been described to benefit narcoleptic patients (Pelaez
et al.
2004). Regional anesthesia, such as epidural, is effective and advantageous
because patients can be monitored for narcolepsy signs. Obstetric populations are at
a high risk for narcolepsy exacerbation; thus, epidural can provide the appropriate
anesthetic while monitoring such symptoms.
4 Perioperative Assessment and Management of Patients with Sleep Disorders 57
4.2.4 Obesity Ventilation Syndrome or Malignant Obesity
Ventilation Syndrome and Overlap Syndrome
OHS patients who present to the operating room are typically obese
(BMI > 30 kg/m
2
) with daytime hypercapnia (elevated carbon dioxide
level > 45 mmHg). About 90% of OHS patients develop OSA. On the other hand,
malignant obesity ventilation syndrome (MOHS) is a severe form of OHS involving
multi-organ dysfunction. Intraoperative management for OHS or MOHS patients
can be quite challenging. These patient populations are morbidly obese with high
likelihood of airway collapse during anesthesia induction. Difficulty of mask venti-
lation and intubation is proportionate to patient’s BMI. The airway management
principle is similar to OSA patients. Critical respiratory depression is a concern upon
anesthesia induction. One technique to limit the fall of oxygenation after induction is
to position the patient at a 25-degree head-up position and applying positive
end-expiratory pressure of 10 cm H
2
O during preoxygenation. Preoxygenation
should be greater than 3 min to prevent increase apnea tolerance time. After the
loss of consciousness and apnea, use of nasopharyngeal oxygen insufflation or
transnasal humidified rapid insufflation ventilatory exchange (THRIVE) technique
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