Obesity Clinical Trial
Official title:
The Effect of High-flow Nasal Oxygenation vs. Low-flow Nasal Oxygenation on Oxygen Saturation During Analgo-sedation in Obese Adult Patients, Randomized Controlled Trial
Obesity is omnipresent problem in everyday anesthesiology practice associated with low level
of blood oxygen (hypoxemia) during analgo-sedation. Overweight outpatients are often
scheduled for colonoscopy usually undergo analgo-sedation. In obese patients, intravenous
analgo-sedation often diminish respiratory drive causing hypoxemia. To avoid hypoxemia,
low-flow nasal oxygenation (LFNO) of 2-6 L/min is applied via standard nasal catheter to
provide maximum 40 % of inspired fraction of oxygen (FiO2). LFNO comprises applying cold and
dry oxygen which causes discomfort to nasal mucosa of patient. LFNO is often insufficient to
provide satisfying oxygenation. Insufficient oxygenation adds to circulatory instability -
heart rate (HR) and blood pressure (BP) disorder.
On the other side, high-flow nasal oxygenation (HFNO) brings 20 to 70 L/min of heated and
humidified of O2/air mixture up to 100% FiO2 via specially designed nasal cannula. Heated and
humidified O2/air mixture is much more agreeable to patient. HFNO brings noninvasive support
to patients' spontaneous breathing by producing continuous positive pressure of 3-7 cmH2O in
upper airways consequently enhancing oxygenation.
Investigators intend to analyze effect of HFNO vs. LFNO on oxygen saturation during
procedural analgo-sedation for colonoscopy in obese adult patients.
Investigators expect that obese patients with preserved spontaneous breathing, oxygenized by
HFNO vs. LFNO, will be less prone to hypoxemia thus more respiratory and circulatory stable
during procedural analgo-sedation for colonoscopy.
Obese patients with applied HFNO should longer preserve: normal oxygen saturation, normal
level of CO2 and O2, reflecting better respiratory stability. Investigators expect obese
participnts to have more stable HR and BP, reflecting improved circulatory stability. There
will be less interruption of breathing pattern of obese patients and less necessity for
attending anesthesiologist to intervene.
Obese patients are often scheduled for colonoscopy under analgo-sedation. Analgo-sedation is
characterized by deep conscious sedation and preserved spontaneous breathing. Continuous
intravenous application of sedatives favors patients' circulatory stability and application
of oxygenation contributes to maintaining adequate patients' oxygenation. Typically, low-flow
nasal oxygenation (LFNO) of 2-6 L/min is applied via standard nasal catheter to provide
maximum 40% of inspired fraction of oxygen (FiO2) before (preoxygenation), during (procedural
oxygenation) and after (postprocedural oxygenation) until patient regains consciousness.
During analgo-sedation obese patients are prone to intervals of bradypnea and
hypoventilation. Transitory apnea in obese patients could lead to hypoxemia, hypoxia,
hypercapnia and hemodynamic insufficiency despite LFNO application. Fatal outcome may occur,
especially at higher risk overweight patients (ASA III class). Respiratory and hemodynamic
stability of morbidly obese outpatients during analgo-sedation for endoscopic procedures
represent challenge to anesthesiologists. There is no generally accepted protocol of
preoxygenation and intraoperative ventilatory management for obese patients. Obese (30<BMI<40
kg/m2, BMI= body mass index) and morbidly obese patients (BMI ≥40 kg/m2) are classified to
higher anesthesia risk groups, even if obese patients may not have other comorbidities
(30<BMI<40 kg/m2 = ASA II, BMI ≥40 kg/m2 = ASA III).
Partial relaxation of pharyngeal muscles characteristic for analgo-sedation in overweight
patients causes prolapse of fatty tissue that partially obstructs pharynx and can cause
obstructive sleep apnoea (OSA). Although OSA is not related to obesity, OSA can accompany
obesity. Besides perioperatively, hypoxia and bradypnoea episodes occur postoperatively in
obese patients, which makes additional observation of obese patients necessary. More frequent
hypoxia and bradypnoea during awakening require additional respiratory effort. Ventilation
strategies in obese patients are necessary to optimize gas exchange and pulmonary mechanics
in order to reduce pulmonary complications.
High-flow nasal oxygenation (HFNO) brings 20 to 70 L/min heated and humidified O2/air mixture
up to 100% FiO2 via specially designed, soft nasal cannula. HFNO brings non-invasive support
to patients' inspiratory effort by developing 3-7 cmH2O of continuous pressure in upper
airway, decreasing it's resistance and dead space. Also, heated and humidified oxygen/air
mixture with possibility to bring higher FiO2 adds to better patients' oxygenation
preservation and improved patients' comfort during procedure.
AIM of this study is to compare effect of HFNO vs. LFNO during standardized procedure of
intravenous analgo-sedation on periprocedural oxygenation maintenance in patients of
different weight groups: 18<BMI<30 kg/m2, 30<BMI<40 kg/m2 and BMI ≥40 kg/m2.
Investigators hypothesized that application of HFNO compared to LFNO, in obese patients with
preserved spontaneous breathing during procedural analgo-sedation, contributes to maintaining
adequate oxygenation, consequently adding to greater peri-procedural circulatory and
respiratory stability of obese patients. Investigators expect that HFNO will ensure reduced
bradypnoea intervals (frequency of breathing, FoB 1/min), longer maintenance of adequate
oxygenation, shorter intervals of desaturation (SpO2 ≤ 92%), reducing hypercapnia (PaCO2 ≥ 6
kPa) and less airway - opening maneuvers performed by attending anesthesiologist (Aom). These
will prevent partial respiratory insufficiency detected by low SpO2 or low PaO2 ≤ 11 kPa
accompanied by normal or low PaCO2 ≤ 6 kPa, and global respiratory insufficiency detected by
decreased SpO2 ≤ 92% and PaO2 ≤ 11 kPa with increased PaCO2 ≥ 6 kPa.
Investigators plan to conduct prospective, parallel group, randomized controlled clinical
trial. Trial will be managed according to principles of Declaration of Helsinki for
scientific clinical research and will be planned and guided according to CONSORT guidelines
(Consolidated Standards of Reporting Trials). The trial has been approved by hospital's Ethic
Committee.
The source of information are going to be 126 adult patients scheduled for colonoscopy under
analgo-sedation in the setting of daily outpatient gastroenterology ambulance. Eligible
participants will be interviewed and examined ambulatory by anesthesiologist together with
evaluation of ASA status, difficulty of airway management and BMI. After initial examination
inclusive and exclusive criteria will be distinguished. Eligible participants who give
written consent of participation will be included in this trial. After that, participants
will be assigned to equal normal weight (18<BMI<30 kg/m2), obese (30<BMI<40 kg/m2) or
morbidly obese (BMI ≥40 kg/m2) group. Each group will be randomized to intervention (HFNO)
and control (LFNO) subgroup by random numbers generator. Randomization will be used until
adequate number of participants in every group is reached.
Interventions: intervention subgroups participants will be oxygenated via nasal cannula using
high flow (40 L/min) of humidified and heated oxygen in air mixture (FiO2 40%). HFNO will be
applied by oxygenator (AirVO™2, Fisher and Paykell, New Zealand, Technomedika Croatia d.o.o.)
during procedural analgo-sedation for colonoscopy with maintained spontaneous breathing. In
control subgroups, oxygenation will be applied via nasal catheter (Bauerfeind d.o.o, Zagreb,
Croatia) using standard low flow oxygen (5 L/min, FiO2 40%) LFNO. In both groups
concentration of oxygen delivered depends on oxygen flow which is regulated by standard
flow-regulator (flowmeter). Oxygen is delivered through pipelines from central hospital gas
supply or from portable cylinder gas supply.
Anesthesia procedure will be uniformed for all participants. Integrated noninvasive
monitoring of vital functions will be set: EKG - (heart rate/min), SpO2 (%), blood pressure
(mmHg), indirect respiration (number of breaths/min) (Compact 7; Medical Econet GmbH,
Germany).
Every participant will have established intravenous infusion of 250 ml NaCl 0.9% through
intravenous cannula regulated by continuous flow (Extension set/CONTROL-A-FLO Regulator 19"
Male Luer Lock Adapter, Baxter/Agmar d.o.o. United States of America/Croatia).
Arterial cannula (REF30401, 20 G - 1,10 mm x 45 mm 49 ml, atraumatic needle tip, Medbar LTD,
Izmir, Turkey) will be placed in radial artery in a previously anesthetized area with local
anesthetic (EMLA).
Oxygenation (HFNO or LFNO) will be administrated in continuity until patients' awakening.
Oxygenation will be started 3 minutes before starting analgo-sedation (preoxygenation),
continued during analgo-sedation and procedure of colonoscopy (perioperative oxygenation) and
up to five minutes after colonoscopy and until patient is awaken (postprocedural
oxygenation).
Intravenous analgo-sedation will be started through continuous infusions of propofol and
fentanyl. Induction of sedation will be guided by TCI (Target control Infusion) (B. Braun
Melsungen, Germany) with initial target propofol concentration of 6 micrograms/minute.
Expected time of induction with this concentration is 60-120 seconds. This target
concentration allows hemodynamic and respiratory stability. Required analgesia will be
simultaneously applied through slow continuous infusion in dose of 0.05 mcg/kg/min in order
to preserve spontaneous breathing. Slow infusion will be applied through perfusor (B.Braun,
Melsungen, Germany). Analgo-sedation will be discontinued immediately after end of the
procedure.
Control of nasopharyngeal airway passage during procedure is achieved by using oropharyngeal
airway, if necessary. Oropharyngeal airway (Airway; Vigon-Medicpro d.o.o.) will be inserted
after achieving moderate sedation, and only if base of tongue is closing airway by dropping
on posterior pharyngeal wall. Every manipulation of patients' airway by anesthesiologist will
be documented (insertion of airway, jaw thrust maneuver).
Sampling: one milliliter of arterial blood will be collected as three consecutive samples
from arterial cannula before, during and after analgo-sedation. Sample of arterial blood will
be drawn from left radial or cubital artery.
Measurements: measurement of oxygenation will be done using two methods: indirect
(noninvasive) method using pulse oxymeter (Compact 7, Medical ECONET GmbH, Germany) and
direct (invasive) method from obtained arterial blood sample. Measurement of SpO2 and drawing
arterial blood sample will be done simultaneously. Direct measurements of SpO2 and PaO2 will
be taken in intervals of time. SpO2 will be measured on the left-hand index finger. Data will
be uniformly collected through indirect - noninvasive (SpO2, heart rate, blood pressure,
respiratory rate) and direct - invasive (arterial blood gas analysis - pH, PaO2, PaCO2, SaO2)
measurements.
Possible biases and confounding variables could be caused by hypothermia of participant, by
sphygmomanometer cuff pressure on the same arm where blood samples are drawn and by prolonged
time of arterial blood analysis. These difficulties can be bypassed by: adjustment of room
temperature where analgo-sedation is performed, blood pressure measuring on opposite arm from
where samples of blood are taken and by arterial blood gas analysis without delay.
Basic data analyses will be performed by statistician. Sample size is determined by statistic
computing web program: http://www.stat.ubc.ca/~rollin/stats/ssize used statistic test
Inference for Proportions: Comparing Two Independent Samples. Assessment of sample size is
computed for two independent samples with assumption of clinically significant difference in
patients' oxygenation: ≤11 and ≥14.4 kPa with delta 4.4. Statistical significance of
difference will be inferred with 5% α-error, 50% β-error and study power 0.80. Calculated
size of sample is: 21 participant pro subgroup (total of 126 participants).
Investigators expect no changes to methods after trial commencement. All potential unwanted
events which may happen during analgo-sedation and colonoscopy that could cause deviation
from this trial's protocol will be reason for exclusion of participant from this trial. If
circumstances change, anesthesiologist responsible for application of anesthesia will carry
out procedure in way which is in patients' best interest.
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