Hypoxia Clinical Trial
Official title:
Influence of High-flow Nasal Oxygenation on Spontaneous Ventilation in Patients of Different Anesthesia Risk Class During Analgo-sedation for Vitrectomy, Randomized Controlled Trial
Pars plana vitrectomy is minimally invasive endoscopic procedure which is usually performed
in moderate analgo-sedation given by anesthesiologist combined with topical anesthesia and
retrobulbar or Subtenon block performed by surgeon. Intravenously applied anesthetics can
often lead to slower breathing rate or cessation of breathing which introduces risk of low
blood oxygen level despite careful adjustment of anesthetics' dose and application of
standard low-flow nasal oxygenation (LFNO). Respiratory instability is often accompanied by
circulatory instability manifested by disturbances of heart rate and blood pressure. LFNO
provides maximally 40% inspired fraction of oxygen and can cause discomfort of a patient due
to coldness and dryness of inspired gas.
On the other hand, high-flow nasal oxygenation (HFNO) can bring up to 100% of inspired oxygen
fraction to patient, providing noninvasive pressure support of 3-7 cmH2O in patients' upper
airway which ensures better oxygenation especially in higher anesthesia risk patients.
Because of carrying warmed and humidified air/oxygen mixture via soft nasal cannula, HFNO is
better tolerated by patients.
In this trial investigators will compare effect of HFNO to LFNO during intravenously applied
standardized analgo-sedation given for vitrectomy in normal weight patients of low and high
anesthesia risk.
Investigators hypothesize that normal weight patients of low and high anesthesia risk, whose
breathing pattern is preserved, receiving HFNO vs. LFNO during standardized analgo-sedation
for vitrectomy will be more respiratory and circulatory stable, preserving normal blood O2
and CO2 level, breathing pattern, heart rate and blood pressure.
Pars plana vitrectomy (PPV) is minimally invasive micro-endoscopic surgery of posterior eye
chamber. Most often patients receive combination of loco-regional anesthesia (topical
anesthetic plus retrobulbar or Subtenon block), performed by a surgeon, and moderate
analgo-sedation, performed by an anesthesiologist. Although applied intravenous anesthetics
are short-acting, carefully titrated and continuously infused, anesthesia can lead to
cessation of adequate spontaneous patients' breathing detected as bradypnoea, hypoxia and
hypercapnia reflecting respiratory instability of patient. Respiratory instability is
accompanied by circulatory one, reflected in heart rate and blood pressure deflections from
baseline values. Usually, before, during and after analgo-sedation until patient is awaken,
low-flow nasal oxygenation (LFNO) of 2-6 L/min O2 is applied through nasal catheter providing
maximum inspiratory fraction of oxygen (FiO2) of 40%. Beside coldness and dryness of LFNO
(therefore causing discomfort to patient), LFNO is often inadequate to prevent respiratory
instability manifested as hypoxia and hypercapnia and subsequent circulatory disturbances.
Anesthesia risk is classified by American Society of Anesthesiologists Physical Status
Classification System (ASA classification system) where patients of ASA class I anesthesia
risk are generally healthy without systemic disease, patients deployed to ASA class II group
have mild disease, having no functional impairment, higher risk ASA III patients have one or
more significant organ function impairment.
High-flow nasal oxygenation (HFNO) delivers to patient high flow heated and humidified
oxygen/air mixture (up to 70 L/min, up to 100% FiO2) using soft nasal cannula. HFNO produces
3-7 cmH2O of positive end-expiratory pressure therefore supporting patients breathing effort
and providing apnoeic oxygenation, decreasing pharyngeal airway dead space and resistance.
The patients find HFNO more comfortable as delivered gas is heated and humidified. HFNO is
usually used for oxygenation of patients with predicted difficult oroendotrachial intubation
prior to anesthesia, in process of awakening from anesthesia in postanesthesia care units and
during process of weaning from mechanical respiratory support in intensive care units.
Goal of this trial is to compare effect of HFNO and LFNO on oxygenation maintenance during
standardized procedure of intravenous analgo-sedation in normal weight ASA I, II and III risk
class patients for elective PPV.
Investigators hypothesize that application of HFNO compared to LFNO in patients with
preserved spontaneous breathing during procedural analgo-sedation for PPV contributes to
maintaining adequate oxygenation, consequently adding to greater patients periprocedural
respiratory and circulatory stability. Investigators expect that HFNO will provide reduced
bradypnoea intervals (bradypnoea <12 breaths/min, FoB 1/min), longer maintenance of adequate
oxygenation, shorter intervals of desaturation (peripheral blood oxygen saturation -
SpO2≤92%), reducing hypercapnia (expiratory carbon-dioxide - expCO2≥45 mmHg) and less airway
opening maneuvers performed by attending anesthesiologist (AOM). These will prevent partial
respiratory insufficiency detected by low SpO2 accompanied by low or normal expiratory
carbon-dioxide level (expCO2), and global respiratory insufficiency detected by decreased
SpO2≤92% and increased expCO2≥45 mmHg.
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 PPV under
analgo-sedation. Eligible participants will be interviewed and examined ambulatory by
anesthesiologist, their ASA status, difficulty of airway management and body mass index (BMI)
evaluated. After initial examination inclusive and exclusive criteria will be distinguished.
Eligible participants who give voluntarily their written consent of participation will be
included in this study. After that, participants will be assigned to equal ASA I, II and III
risk class group. Each group will be randomized to intervention (HFNO) and control (LFNO)
subgroup by computer random numbers generator. Randomization will be used until adequate
number of participants in every subgroup 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 PPV maintaining spontaneous breathing. In
control subgroups, LFNO will be applied via nasal catheter (Bauerfeind d.o.o. Zagreb,
Croatia) using standard low-flow oxygen (5 L/min, FiO2 40%). 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 circulatory function (heart rate - EKG, intermittent mean arterial pressure -
sphygmomanometer) will be set (Compact 7; Medical Econet GmbH, Germany). Respiratory vital
functions: oxygenation (pulse oximeter), heart rate and expCO2 by using capnometer
(Capnostream™35 Portable Respiratory Monitor, Medtronic, Belgium).
Every participant will have established intravenous infusion of 250 ml NaCl 0.9% via
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).
Oxygenation (HFNO or LFNO) will be continuously administered before institution of
analgo-sedation until patients' awakening. It will be started 3 minutes before
analgo-sedation (preoxygenation), continued during analgo-sedation and procedure of PPV
(perioperative oxygenation) and up to 5 minutes after PPV and until patient is awake
(postprocedural oxygenation).
Induction of analgo-sedation will be instituted by droperidol 1.25 -2.5 mg bolus accompanied
by continuous infusion of target remifentanyl concentration up to 0.05 mcg/kg/min. Intensity
of sedation will be measured by Ramsay's sedation scale (RSS). Moderate sedation (RSS 4) is
characterized by: purposeful response to verbal or tactile stimulation, no intervention
required for airway patency maintenance, adequate spontaneous ventilation and sufficient
cardiovascular function. Surgeon will apply topical local anesthetic on conjunctiva which is
followed by regional anesthesia (Subtenon or retrobulbar block). Intravenous analgo-sedation
will be administered via perfusor (B.Braun, Melsungen, Germany). Analgo-sedation will be
discontinued immediately after end of PPV.
Control of nasopharyngeal airway is achieved by using oropharyngeal airway, if necessary.
Oropharyngeal airway (Airway; Vigon-Medicpro d.o.o.) will be inserted after achieving
moderate analgo-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).
Measuring:
SpO2, expCO2, heart rate (fC) and respiratory rate (fD) will be measured continuously, and
simultaneously continuously noted in 5 minutes intervals - T0=before oxygenation, T1=15
minutes after instituting LFNO or HFNO after beginning of analgo-sedation, T2=when patient is
awake after oxygenation ends.
Noninvasive measurement SpO2 will be performed by indirect method using a pulse oximeter on
the index finger of the left hand (Compact 7, Medical ECONET GmbH, Germany).
Blood pressure measuring and mean arterial pressure calculation will be repeated
intermittently in 5 minutes intervals prior to-, during analgo-sedation and after patient is
awaken. All measured parameters will be noted in identical intervals.
The data will be collected uniformly by three researchers: an anesthesiologist who interviews
and examines patients ambulatory, an anesthesiologist designated for procedural
analgo-sedation and an anesthesiologist who will collect the data after the completion of the
analgo-sedation procedure.
The investigator in charge of the data collection will collect it from the pre-operative
ambulatory list and the anesthesiologist list. The anesthesiology sheet will include all data
from the trend table of the monitored vital parameters and from the simultaneously noted
respiratory rate (fD) per minute and the expCO2.
The data will be collected through non-invasive measurements: peripheral blood oxygen
saturation (SpO2), heart rate (fC), respiratory rate (fD), blood pressure (mean arterial
pressure - MAP), carbon dioxide exhaled values before, in the stabilization and at the end of
the analgo-sedation, i.e. 5 minutes after awakening of the patient.
A fourth researcher will be in charge of entering the collected data into the database. The
statistician will analyze the data.
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: ≤88 and ≥99%. 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).
Possible biases and confounding variables could be caused by hypothermia of the participant
and by sphygmomanometer pressure on the same arm where peripheral oxygenation level is
measured. These difficulties can be bypassed by: adjustment of room temperature where
analgo-sedation for PPV is performed and blood pressure measuring cuff placed on right arm
(pulse oximeter placed on left index-finger).
Any possible event that may occur during analgo-sedation that causes deviation from the study
protocol will be the reason for exclusion of the subjects from the study and the PPV will be
continued under anesthesia according to the rules of good clinical practice.
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