Patient Safety Tip of the Week
June 17, 2014
SO2S Confirms Routine Oxygen of
No Benefit in Stroke
In several of our prior columns on use of oxygen (see our
Patient Safety Tips of the Week April 8, 2008 “Oxygen
as a Medication” and January 27, 2009 “Oxygen
Therapy: Everything You Wanted to Know and More!”) we have commented that
in the past we often routinely gave oxygen to patients with myocardial
infarction or stroke. But such use was more reflexive in nature and not
evidence-based.
In our What’s New in
the Patient Safety World columns for July 2010 “Cochrane
Review: Oxygen in MI” and February
2012 “More
Evidence of Harm from Oxygen” we discussed the lack of evidence to
support the routine use of oxygen in the acute MI patient and the possible
deleterious effects in these and some other cardiac patients.
Then in our March
2014 What’s New in the Patient Safety World column “Another
Strike Against Hyperoxia” we noted a study
(Rincon
2014) showing that hyperoxia was independently
associated with in-hospital death as compared with either normoxia
or hypoxia in ventilated stroke patients admitted to ICU’s.
Such studies have called for large randomized controlled
trials to answer the important questions about if and when to use oxygen in
patients with stroke or MI. Well, one such study has now been done in stroke
patients. The Stroke Oxygen Study (SO2S) in
the UK was established to determine whether routine use of oxygen acutely in
stroke patients is of value. The Stroke Oxygen Study website has a video of the
recent presentation of preliminary findings at the European Stroke Conference.
The video notes that many stroke patients have nocturnal
hypoxia. Over half (52%) have nocturnal hypoxia for 5 minutes or more, 23% for
30 minutes or more, and 15% for an hour or more. The study included over 8000
patients at 136 centers. Patients were randomized to one of three arms: (1)
routine continuous oxygen for 72 hours (2) nocturnal oxygen for 72 hours and
(3) no routine oxygen (O2 only as needed). The primary outcome was functional
status (disability as measured by a modified Rankin Score) at 90 days.
Secondary outcome was survival. The study showed no difference in the primary
outcome between the combined oxygen groups and the control group and no
difference between the continuous vs. nocturnal oxygen groups. Similarly, there
was no difference in the secondary outcome of survival. Subgroup analysis has
yet to be done but the message is clear: routine supplemental oxygen does not
benefit stroke patients.
As we’ve recommended before, hospitals need to look at their
existing protocols (and actual practices) for managing a variety of medical
conditions where oxygen use may be considered. How many of you have
standardized order sets that directly (or indirectly by poor use of checkboxes)
encourage inappropriate use of oxygen in MI or stroke patients? Going back to
our Patient Safety Tips of the Week April 8, 2008 “Oxygen
as a Medication” and January 27, 2009 “Oxygen
Therapy: Everything You Wanted to Know and More!” we strongly support
facilities doing audits of their oxygen practices. You’ll probably be surprised
at the opportunities you uncover to improve practices (and save money at the
same time!).
And don’t forget that in many cases high doses of oxygen are
administered by the pre-hospital emergency response teams. Making them aware of
the potential dangers is also important.
The other important consideration, in view of the high
incidence of nocturnal hypoxia in stroke patients, is sleep-disordered
breathing and obstructive sleep apnea (OSA) in particular. While we screen all
stroke patients for swallowing dysfunction prior to feeding them by mouth, there
are likely many stroke patients who have subclinical weakness of pharyngeal
muscles and may be prone to OSA. In fact, in a meta-analysis of the frequency
of sleep apnea in stroke and TIA patients, Johnson and Johnson found 72% of
stroke patients had sleep disordered breathing and almost all were due to
obstructive sleep apnea rather than central sleep apnea or Cheyne-Stokes
respirations (Johnson
2010). This was independent of the type of stroke or timing of the stroke
and there was little correlation with traditional symptoms of OSA such as
snoring. So clearly a high index of suspicion for OSA is needed in patients
with acute stroke.
If the cause of the nocturnal hypoxia in stroke patients is
OSA, it is not surprising that supplemental oxygen does not lead to
improvement. We’ve noted in many of our columns on OSA that oxygen
supplementation in OSA patients may provide a false sense of security and
actually mask the occurrence of apneic spells, particularly if the only
monitoring is oximetry. So it is imperative that you monitor such patients not
just with pulse oximetry but also with capnography
and/or some other monitoring for apnea.
So the purported lesson from the SO2S study is “don’t
routinely use oxygen in stroke patients”. But we are taking away a second,
perhaps more important, lesson: you need to consider stroke patients as being
at risk for obstructive sleep apnea and its potential acute and long-term
consequences.
Kudos to the UK researchers who did the SO2S study.
Recruiting patients for the study must have been difficult given that so many
physicians have followed the time-honored tradition of using oxygen in stroke
patients. This study has done a valuable service for all.
Some of our prior
columns on potential harmful effects of oxygen:
April 8, 2008 “Oxygen
as a Medication”
January 27, 2009 “Oxygen
Therapy: Everything You Wanted to Know and More!”
July 2010 “Cochrane
Review: Oxygen in MI”
February 2012 “More
Evidence of Harm from Oxygen”
March 2014 “Another
Strike Against Hyperoxia”
References:
Rincon F, Kang J, Maltenfort M, et
al. Association Between Hyperoxia
and Mortality After Stroke: A Multicenter Cohort Study. Critical Care Med 2014;
42(2): 387-396
Stroke Oxygen Study website
Johnson KG, Johnson DC. Frequency of sleep apnea in stroke
and TIA patients: a meta-analysis. J Clin Sleep Med 2010; 6: 131-137
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2854698/
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