Patient Safety Tip of the Week
May 22, 2012
Update on Preoperative Screening for Sleep Apnea
We have been advocates
for screening for obstructive sleep apnea (OSA) preoperatively (see links to
prior columns listed below). This month there are 2 new papers on this topic from
Frances Chung and her group in Toronto. One is further validation of the
utility of the STOP-Bang questionnaire in predicting OSA. The other is one that
looked at simple nocturnal oximetry and found that an oxygen desaturation index
(ODI) >10 would predict most cases of moderate and severe OSA (though not
good at picking up central apnea). Since delaying surgery to get formal
polysomnographic studies might not be feasible in many cases, having
alternative means of identifying high-risk patients is very desirable.
The first paper (Chung
2012a) extended their previous work on using the STOP-Bang questionnaire to
predict OSA. 746 patients scheduled for inpatient surgery underwent both the
STOP-Bang questionnaire and polysomnography (lab-based or home-based). Overall,
OSA was present in 68.4% of patients (note that it is highly likely that
patients having symptoms of OSA may have been more likely to consent to this
study). They then looked at the sensitivities and specificities and positive
and negative predictive values of various STOP-Bang scores to predict moderate
or severe OSA and concluded that a STOP-Bang score of 5-8 identified a
population with a high probability of moderate/severe OSA.
In the second study
(Chung 2012b)
475 patients scheduled for inpatient surgery underwent home-base
polysomnography and nocturnal oximetry with a wristwatch-based oximeter.
Compared to those patients having an oxygen desaturation index (ODI) less than
5, those with an ODI greater than 5 had a significant increase in frequency of
sleep disordered breathing. Using a cutoff ODI >10 had a sensitivity of 93%
to detect moderate or severe OSA. The nocturnal ODI was not as sensitive in
identifying central apnea.
Taking the two
studies together leads to a potential strategy for identifying patients with
OSA preoperatively without having to do a formal polysomnogram, that is using
the STOP-Bang questionnaire followed by nocturnal oximetry in appropriate
cases.
Though we don’t
know whether CPAP is effective perioperatively in this population (the only
study showed no benefit), knowing that someone has OSA has perioperative
implications in airway management, opiate and other drug selection, post-op
monitoring, pulmonary complications, overall complications and LOS. A
previous study (Kaw 2012)
found that patients with OSA undergoing cardiac surgery were almost 7 times
more likely to have overall complications, 8 times more likely to have
postoperative hypoxemia, and over 4 times more likely to require transfer to an
ICU. They also had longer lengths of stay. Another study (Memtsoudis
2011) had also shown about a 5-fold increase in respiratory failure in
patients with OSA undergoing noncardiac surgery. The latter study showed
patients with OSA developed pulmonary complications more frequently than their
matched controls after both orthopedic and general surgical procedures.
However, what we
need to do now is demonstrate that outcomes can be improved by doing such
preoperative screening and then implementing care management programs for this
high-risk population.
A recent review of sleep disorders in hospitalized patients (Venkateshiah 2012) describes the physiology of sleep disturbances in this population and the factors contributing to disturbed sleep in the hospital. It also summarizes the ASA recommendations for perioperative management of OSA. Pain is the most common cause of disturbed sleep. One of the key occurrences in the immediate post-surgical period is a suppression of REM (rapid eye movement) sleep. This may be related to factors such as catecholamine levels and treatment with opioids. Then, on the second and third post-op days there is a REM rebound. During this period there is a significant increase in episodic oxygen desaturations due to disordered breathing.
Venkateshiah and Collop go on to summarize the American Society of Anesthesiologists (ASA) practice guidelines for the perioperative management of patients with OSA (ASA 2006). Like other reviews of the perioperative management of patients with OSA (Chung 2008, Adesanya 2010) they readily admit there is a paucity of evidence-based recommendations for care of surgical patients with suspected or known OSA.
There are obviously many reasons to identify patients
preoperatively who are at high risk for OSA. Such patients are at greater risk
for difficult intubation and are at risk for multiple post-operative
complications. Anesthesiologists would like to use local anesthesia or
peripheral nerve blocks where appropriate or otherwise use short-acting
anesthetic agents in such patients and completely reverse the effects of
neuromuscular blocking agents. Avoidance
of the supine position as much as possible is recommended since some OSA is
position-dependent.
Monitoring of the patient with OSA is obviously a key
consideration. But Venkateshiah and Collop
are quick to point out that there is a lack of an evidence base that monitoring
with either pulse oximetry or capnography improves outcomes in this population.
Our February 22, 2011 Patient Safety Tip of the Week “Rethinking Alarms” highlighted an excellent study by Lynn and Curry (Lynn 2011) who describe 3 patterns of unexpected in-hospital deaths and demonstrate the problems with threshold-based alarms (almost all currently used alarm systems use threshold-based principles) in detecting early deterioration. Indeed, they posit that threshold-based alarms themselves often cause us to miss signs of early deterioration. Even systems using continuous pulse oximetry and end-tidal CO2 monitoring may fail to adequately identify these patients. Nevertheless, we recommend monitoring with oximetry, capnography, and a rate/apnea monitor post-operatively. And while the first 12-hours post-operatively is a vulnerable period, the REM rebound and REM-associated hypoxemic events may increase 3-fold on the second and third postoperative nights, with associated risk of complications. Thus, monitoring should not be stopped before this period
Similarly, most of
the recommendations for management of OSA in the post-op patient are consensus
recommendations, as there has been a paucity of evidence. So most
recommendations remain based on consensus opinion.
In patients with known
OSA who are on CPAP at home, it is usually recommended that you have the
patient bring in their CPAP machine from home. But in patients with suspected
OSA or just recently diagnosed OSA who have not yet been on CPAP the
effectiveness of CPAP in the hospital has not been demonstrated. In our November 22, 2011 Patient Safety Tip
of the Week “Perioperative
Management of Sleep Apnea Disappointing” we noted one of the few
randomized controlled studies of surgical patients deemed at high risk of OSA
had disappointing results (O’Gorman
2011). That study showed that autotitrating positive airway pressure (APAP)
failed to prevent obstructive apnea in surgical patients deemed high risk for
the disorder. They did find that patients deemed to be at high risk for OSA had
longer lengths of stay and more complications than those deemed to be at low
risk. They randomized 85 patients deemed at high risk for OSA to standard
postoperative care or standard care plus APAP but found no significant difference
in LOS or complications between the two groups. Admittedly, the number of
patients studied was small and further research is needed. But it leaves one
more gap of evidence-based recommendations.
Many of the
recommendations are to minimize the use of opioids. These would include using
regional analgesic techniques or use of NSAID’s where possible. Most also
recommend avoiding continuous background opioid infusions in patients on PCA
pumps.
The guidelines
recommend continuous oxygen supplementation until the patient has been shown to
maintain adequate baseline oxygen saturation on room air. When to stop oxygem
supplementation is less clear. We’ve cautioned on numerous occasions the
possibility that oxygen supplementation in patients receiving systemic opioids
may actually mask impending respiratory failure.
So, once again, we
recommend you consider setting up a screening program for likely OSA prior to
scheduled surgery. The STOP-Bang questionnaire is easy to administer in a few
minutes and could be done at the time of surgical booking or other time the
surgical team contacts the patient. Having a clinical guideline for dealing
with those who score high on the STOP-Bang would be wise, keeping in mind that
most of those recommendations will be consensus-based rather than evidence-based.
Our prior columns on obstructive sleep apnea in the perioperative period:
Patient Safety Tips of the Week:
June 10, 2008 “Monitoring the Postoperative COPD Patient”
August 18, 2009 “Obstructive Sleep Apnea in the Perioperative Period”
August 17, 2010 “Preoperative Consultation – Time to Change”
July 13, 2010 “Postoperative
Opioid-Induced Respiratory Depression”
February 22, 2011 “Rethinking
Alarms”
November 22, 2011 “Perioperative
Management of Sleep Apnea Disappointing”
What’s New in the Patient Safety World columns:
July 2010 “Obstructive Sleep Apnea in the General Inpatient Population”
November 2010 “More on Preoperative Screening for Obstructive Sleep Apnea”
March 2012 “Postoperative Complications with Obstructive Sleep Apnea”
References:
Chung F,
Subramanyam R, Liao P, Sasaki E,
Shapiro C, Sun Y. High STOP-Bang score indicates a high probability of
obstructive sleep apnoea. British Journal of Anaesthesia 2012; 108 (5): 768–75
(2012)
http://bja.oxfordjournals.org/content/108/5/768.full.pdf+html
Chung F, Liao P, Elsaid
H, et al. Oxygen Desaturation Index from Nocturnal Oximetry: A Sensitive and
Specific Tool to Detect Sleep-Disordered Breathing in Surgical Patients.
Anesthesia & Analgesia 2012; 114(5): 993-1000 Published online before print February 24,
2012
http://www.anesthesia-analgesia.org/content/114/5/993
Venkateshiah SB, Collop NA. Sleep and Sleep Disorders in the Hospital. CHEST 2012; 141(5): 1337-1345
http://chestjournal.chestpubs.org/content/141/5/1337.abstract
American Society of Anesthesiologists. Practice Guidelines for the Perioperative Management of Patients with Obstructive Sleep Apnea. A Report by the American Society of Anesthesiologists Task Force on Perioperative Management of Patients with Obstructive Sleep Apnea. Anesthesiology 2006; 104: 1081–93
Chung SA, Yuan H, Chung F. A Systemic Review of Obstructive Sleep Apnea and Its Implications for Anesthesiologists. Anesthesia & Analgesia 2008; 107(5): 1543-1563
http://www.anesthesia-analgesia.org/content/107/5/1543.short
Adesanya AO, Lee W, Greilich NB, Joshi GP. Perioperative Management of Obstructive Sleep Apnea. Chest December 2010; 138(6): 1489-1498
http://chestjournal.chestpubs.org/content/138/6/1489.abstract
Lynn LA, Curry JP. Patterns of unexpected in-hospital deaths: a root cause analysis. Patient Safety in Surgery 2011, 5:3 (11 February 2011)
http://www.pssjournal.com/content/pdf/1754-9493-5-3.pdf
O'Gorman S, Horlocker T, Huddleston J, et al. Does Self-Titrating CPAP Therapy Improve Postoperative Outcome in Patients at Risk for Obstructive Sleep Apnea Syndrome? A Randomized Controlled Clinical Trial. Chest 2011; 140: 4 Meeting Abstracts 1071A; doi:10.1378/chest.1119434
also reported in: Harrison L. Postop APAP Fails in High-Risk Sleep Apnea Patients. Medscape Medical News. November 3, 2011
http://www.medscape.com/viewarticle/752859
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