Effect of Interscalene Block on Obstructive Sleep Apnea in Shoulder Surgery Patients

History & Significance:

Obstructive sleep apnea (OSA) is a syndrome of sleep related airway obstruction (snoring)
and reduction in blood oxygen levels affecting between 2% and 24% of the general
population1. In other words, a person stops breathing repeatedly during sleep when they have
OSA. Breathing stops because the airway collapses and prevents air from getting into the
lungs. The impact of OSA on systemic heart and lung disease is slow and progressive over a
course of years. Exposure to anesthesia increases the tendency for postoperative airway
obstruction and reduction in oxygen levels2, both of which could have significant impact on
patient well-being.

Recent advances in general anesthetics, opioid analgesic drugs and surgical techniques have
made outpatient surgery common for a significant proportion of patients. It is estimated
that approximately 50% of procedures currently performed in the University of Michigan
Health System are day-case procedures, the vast majority of which require deep sedation or
general anesthesia. The reduction in postoperative hospital based care has placed
considerable emphasis on the efficient delivery of pain relief and has resulted in an
increased usage of peripheral nerve blocks to reduce the need for intravenous sedative
opioid analgesics and deep levels of anesthesia.

Shoulder surgery is a particularly good example where a nerve block in the neck region
(typically an inter-scalene brachial plexus block) placed before anesthesia provides good
pain relief with early recovery and less side effects directly related to opioid analgesics.
Nevertheless, one of the side effects of the interscalene nerve block is temporary (12-18
hours) weakness of the diaphragm muscle on the same side as the block, due to phrenic nerve
blockade. As a result, there is a change in the patient's breathing pattern which is
typically compensated by increased work by other muscles in the respiratory system3.
However, it is important to note that shoulder joint disease is more common in middle-aged
patients who are typically at greater risk of OSA. The baseline abnormalities in respiration
in OSA patients put them at increased risk of breathing abnormalities after the
inter-scalene nerve block. As a result, this surgery presents unique challenges to the
anesthesiologist looking to balance the benefit and risks of inter-scalene nerve blocks.
Unfortunately, there are no studies that look at the effect of anesthesia and inter-scalene
blocks on breathing patterns and oxygen saturation levels after discharge from outpatient
surgery, as measured by spirometry, sleep studies and pulse oximetry. We therefore propose
to study the changes in lung function tests and blood oxygen levels after an inter-scalene
block and general anesthesia for outpatient shoulder surgery.

It is possible that future screening for out-patient shoulder surgery includes preoperative
overnight oxygen saturation measurement to identify patients at high-risk of changes in
oxygen levels. These patients may benefit from hospital admission after surgery for close
observation. Thus, this study could have significant implications for patient safety and
resource utilization.

Sample Size Estimation:

We hypothesize that all patients undergoing inter-scalene block and general anesthesia for
shoulder surgery will develop a doubling of significant oximetric changes based on standard
measures used in sleep studies. At least 8 patients are required for a study with 5% type-I
and 20% type-II error to prove this hypothesis. We plan to recruit 10 patients for the
study, with each patient doubling as their own control, to allow for a 20% (2 subjects)
withdrawal rate. We anticipate having 50 screen failures.

Outcome Measures:

The primary outcome measure for this study is the incidence of postoperative sleep
disordered breathing (apnea-hypopnea index) defined as ≥5 episodes per hour of >50%
reduction of expiratory air flow associated with a ≥4% reduction in oxygen saturation
(referred to as ODI4 or oxygen desaturation index > or = to 4 points drop in SpO2) that
lasts for at least 10 seconds each as measured by the pulse oximeter. Secondary outcome
measures include changes in lung function tests and lowest and mean oxygen saturation levels
during sleep.

Study Design:

This is an observational longitudinal study, wherein each patient acts as their own control.
10 patients with high risk prediction factors of OSA, as screened by the Perioperative-
Sleep Apnea Prediction Score(P-SAP) of ≥6, presenting for outpatient shoulder surgery, will
be approached for participation in this study.The P-SAP score consists of three demographic
variables (age> 43 years, male gender and obesity), three medical history variables (history
of snoring, type 2 diabetes mellitus and hypertension) and three airway measures (thick
neck, modified Mallampati class of 3 or 4 and reduced thyromental distance) and the number
of significant variables present in a given patient is the P-SAP score. The respiratory
effects of the anesthetic and block will be assessed by using pulse oximetry, spirometry,
and overnight sleep studies. Preoperative and postoperative values will be compared for
significant differences.

Standard monitoring will be employed during anesthesia including continuous
electrocardiography, non-invasive blood pressure measurement every 3 minutes, continuous
pulse oximetry, continuous capnography, continuous respiratory gas measurements,
neuromuscular function monitoring and continuous body temperature. Anesthesia technique will
include the preoperative interscalene block, followed by induction of anesthesia with
midazolam, fentanyl, propofol and muscle relaxation with succinylcholine and/or vecuronium
as indicated. This will be followed by tracheal intubation to protect the airway and ensure
conduit for adequate intraoperative controlled ventilation. Anesthesia will be maintained
with total intravenous anesthesia (TIVA), oxygen and air, titrated to ensure adequate depth
of anesthesia. Additional analgesia will be provided with bolus or continuous infusion
remifentanil as needed. Institutional protocols for prevention of nausea and vomiting will
be employed. At the end of the surgical procedure, full recovery of neuromuscular function
will be facilitated by use of neostigmine and glycopyrrolate, before removal of the
endotracheal tube. On arrival to the post anesthesia care unit, the patient will be
monitored and managed to ensure safe and comfortable recovery from the surgical procedure.
Additional fentanyl will be used for pain relief if needed and standard postoperative
protocols for management of care will be followed. Discharge from the PACU will be done on
full recovery to satisfy institutional PACU discharge criteria. Prior to discharge from PACU
a second set of pulmonary function tests will be performed by the research assistant.
Patients will be discharged home on standard postoperative analgesia including acetaminophen
and hydrocodone or at surgical resident's discretion.

Study Design Rationale The American Society of Anesthesiologists' practice guideline on
obstructive sleep apnea (Anesthesiology 2006) clearly supports the use of regional
anesthesia and analgesia as a way to reduce perioperative opioid usage. The technique
described in our proposal is essentially a "single intervention" as the anesthetic always
includes a general anesthesia. As this is the standard of care, we would not be able to
employ a randomized control design that denies this "better care" randomly to some patients.

A non-random selection of cases to study the effects of general anesthesia vs. block would
be difficult because in the absence of the block, the patients get higher doses of opioids
and general anesthetics. This makes it impossible to compare perioperative sleep
disturbances with patients who get the additional inter-scalene block (as both opioids and
general anesthetic agents directly impact the severity of sleep related breathing
disturbances) Also, since these patients have medical or personal reasons to avoid the
block, this would negatively impact our likelihood of recruiting comparable study
populations We will use a longitudinal study design and pre-block and postoperative
spirometry, as a way to account for inter-individual differences in the effects of scalene
block on lung volumes. At lower lung volumes, patients are more likely to develop airway
obstruction. As a first step, we would like to test the influence of this lung volume change
on the outcomes, rather than identify which part of the anesthetic is causing the lung
volume change. We therefore, will not include a control group.

Research Procedures:

1. Pre-Operative Clinic Visit Patients will be approached based on the inclusion criteria
stated above. Patients will be screened and consented for the study during their visit
to the Dominos Preoperative Clinic. The subject will receive a phone call two days
before their scheduled surgery to answer any questions they may still have, to remind
them to use the portable sleep study machine (Compumedics Somte System Ambulatory
Cardio-respiratory system) at night, and to remind them to bring the Somte sleep device
with them on the day of their scheduled surgery. Once patients are consented for the
study, study measurements will begin the day prior to surgery.

2. Pre-Operative At Home The study team will call the subject and arrange a convenient
time to come to the subject's house to teach them how to use a portable sleep study
machine that has an elastic band that fits around their chest and a pulse oximeter,
which records the level of oxygen in their blood. The subject will keep the portable
sleep study machine and pulse oximeter in their home and wear these two nights before
the scheduled shoulder surgery.

3. Pre-Operative Day Of Surgery On the morning of the scheduled surgery after the subject
arrives at the outpatient surgical center, the subject will be given a baseline lung
function test. After this procedure is completed, an interscalene nerve block will be
placed by the anesthesiologist before the subject goes to the operating room. An
interscalene nerve block is a procedure done to make the shoulder and arm numb for the
first hours after surgery to help with pain after an operation. It is an injection of a
numbing medication, similar to what a dentist would use, around or near the nerves in
the area that is being operated on to temporarily control pain.

Most shoulder surgeons, recommend having this nerve block placed by the
anesthesiologist as part of the normal standard of care before surgery. Before the
block is placed, the subject will have an IV put in and monitors hooked up, including
heart rate, blood pressure, breathing rate, and a pulse oximeter. These procedures are
all part of normal pre-operative care. Sedation or general anesthesia is used for the
nerve block, as decided by the anesthesiologist, but the subject is not completely
asleep for the procedure. An ultrasound machine and a nerve stimulating device are used
to find the correct nerves and help with accurate placement of the block at the base of
the neck. After the block is placed, the subject will go to the operating room and
general anesthesia for the shoulder surgery per normal standard of care will be
administered.

4. Post-Operative Day of Surgery After the surgery another spirometry lung function test
will be performed. The subject will use the Somte device the night of surgery as well.

5. After Going Home The subject will wear the portable sleep study elastic band and pulse
oximeter at home for the first night after surgery. We will arrange for a convenient
time to have someone pick up these two items from the subjects home. The patient's
involvement in the study ends the day after surgery.

Inclusion Criteria:

- Any adult 18 years of age or older

- Six or more of the following risk factors (P-SAP score): age > 43, male gender, body
mass index >30, diabetes, high blood pressure, snoring at night, neck circumference >
17 inches, reduced thyromental distance, and/or modified Mallampati class of 3 or 4

- Scheduled for an outpatient elective shoulder surgery for which an interscalene nerve
block is scheduled for postoperative pain control along with a general anesthetic per
the surgeon

Exclusion Criteria:

- Age <18 years old

- Patients on home oxygen therapy, existing OSA that is treated with Continuous
Positive Airway Pressure or Bilevel Positive Airway Pressure machine

- Unable or unwilling to provide consent

- Prisoners

- Non-English speaking

- Pregnant

- Hearing impaired

- Chronic pain present for 3 months or longer requiring >3 pills a day of opioid
pain/pain modifying medications

- Daily use of gabapentin, pregabalin, tricyclic antidepressant,
serotonin-norepinephrine reuptake inhibitor, tramadol, corticosteroids, or clonidine.

- Preexisting nerve damage/peripheral neuropathy

- Significant respiratory, kidney, liver or cardiovascular impairment

- Coagulation/bleeding disorders

- Uncontrolled diabetes

- Drug or alcohol abuse

- Uncontrolled anxiety, schizophrenia or bipolar disorder

- Hearing impairment

- American Society of Anesthesiologists class IV or V