The use of sedation in gastrointestinal endoscopic procedures reduces patient discomfort and anxiety while improving the technical quality of the procedure, and as a result, majority of the clinicians have adopted the practice with its potential complications.[4] The most important negative impact of sedation and analgesia is the compromise of respiratory functions in the form of hypoxemia, hypoxia and alveolar hypoventilation. The analysis of procedural sedation has revealed an overall incidence of respiratory depression of 4,1%, with 1,1% of patients requiring assisted ventilation or reversal agents for respiratory depression.[5]
Respiratory monitoring, which is a fundamental component of procedural sedation to ensure patient safety, even more substantial in comparison to general anesthesia practice due to working environment and sedation provider characteristics.[6] Consequently, pulse oximetry (SpO2) and oxygen supplementation have been used for decades. Despite its widespread use, SpO2 monitoring has been reported to have limited utility and nowadays it is well known that SpO2 is an essential and unsatisfactory monitoring.[7]
In view of the above, the 2010 House of Delegates of the American Society of Anaesthesiologists (ASA) amended its Standards for Basic Anaesthetic Monitoring to include mandatory exhaled end-tidal carbon dioxide (ETCO2) monitoring during both moderate and deep sedation to its existing requirement for endotracheal and laryngeal mask airway general anesthesia.[8] Monitoring ETCO2 is far superior to the pulse oximeter for immediate detection of an obstructed airway, opioid induced apnea, or other airway problems that only much later may be detected by the pulse oximeter. As hypoventilation is directly reflected by an increase in arterial carbon dioxide tension (PaCO2), capnography suggests itself as an additional monitoring parameter, which furthermore demonstrates respiration activity breath by breath. [9, 10] Actually in intubated patients or under stable conditions without oral leakage the measurement of ETCO2 tension in the exhaled air shows an adequate correlation with PaCO2.[11] Unfortunately, in the state of moderate or deep sedation during diagnostic or therapeutic procedures, regular breathing is often disturbed by moving, and squeezing and secretions can disrupt measurement. In our study supplemental oxygen resulted to inaccurately low ETCO2 levels concordant with earlier studies.
Slagelse et al. explored if the addition of capnography to standard monitoring during endoscopy could reduce number, duration and level of hypoxia in 540 patients. They found that the number and total duration of hypoxia was reduced by 39,3 and 21,1% in the intervention group compared to the control group (p > 0.05). [12] There is currently ongoing debate related to efficacy of capnography in clinical outcomes of endoscopic sedation. A meta-analysis has reported that addition of capnography to standard monitoring reduces hypoxemic events whereas a meta-analysis has reported no benefit for low risk population and short-term procedures. [2, 13] Beside admitting capnography, exploration of alternative monitoring technique for sedation is proceeding to ascertain the gold standard.
Recently, a new PaO2 monitoring has been discovered by the Masimo Corporation; Oxygen Reserve Index (ORi), which is a noninvasive, optical sensor. The ORi uses wavelengths of light to collect optical absorbance information in mild-to-moderate hyperoxic range (PaO2 of approximately 100–200 mm Hg) and resolves extremely small differences in absorbance into a unit-less index between 0.00 and 1.00. (Rainbow SET; Masimo Corp, Irvine, CA). The ORi can be trended and has optional alarms to notify clinicians of changes in a patient’s oxygen status. When utilized in conjunction with SpO2 monitoring the ORi may extend the visibility of a patient’s oxygen status into ranges previously unmonitored in this fashion with good concordance to PaO2.[14]
The administration of high levels of inspired O2 before tracheal intubation (pre-oxygenation) is considered to be a routine practice to increase body oxygen stores as oxygen reserves are not always sufficient to prevent hypoxia during the duration of intubation.[15, 16] The ORi may make this process visible, ensuring that the PaO2 is indeed rising in the presence of a constant maximal SpO2 level.[15, 17] It may also be extremely important during pre-oxygenation before suctioning hypoxemic patients [18], during emergency rapid sequence induction, in obese patients, during intubation in the ICU, and especially in hypoxic patients who may require non-invasive ventilation before intubation.[15]
However, there are few studies on the efficacy of pre-oxygenation in the procedural sedation with confusing results.[20] Rigg et al. [21] and Reed et al. [22] both recommended 4 L.min-1 nasal oxygen to be given at 5 min and 2 min respectively without monitoring. Wang et al. compared different time of pre-oxygenation from 0 to 5 minutes and reported that pre-oxygenation duration has no impact on the incidence of desaturation and hypoxia. No other study has attempted to monitor pre-oxygenation in sedation, as conducted in the present study by ORi guidance. For effective pre-oxygenation it is necessary to breathe 100% oxygen via tightly fitting face mask for 3 min. [23, 24] However, these recommendation studies did not figure on the effect of position and had applied oxygen in supine position. It has been demonstrated that twenty-degree head-up position for standard 3 min pre-oxygenation via circle breathing system is superior to supine.[25] Therefore, we applied preoxygenation in the sitting position to maximize the effect and shorten the duration. Though, pre-oxygenation has not been taken place in any national or international guideline for procedural sedation, present authors propose pre-oxygenation as preventive from hypoxemic events and the necessity of being introduce as a standard procedure.
There may be concern about adverse effect of hyperoxemia which applied in the present study. Foremost, applied hyperoxemia level was mild and period was very limited. Papers regarding toxic effect of hyperoxemia are generally on critically ills or with extremely high hyperoxemic state in healthy volunteers. [26, 27] In addition, there is a recently published study in general anesthesia with no negative effect.[28]
The limitation of our study is lack of anesthesia depth monitoring due to technical insufficiency. Instead of that we used care provider’s experience to arrange sedation level.
In conclusion, our study results showed that ORi has ability to diminish hypoxemic events and putting patients in a mild hyperoxemic state and endeavor to keep this state can be alternative and reliable method for endoscopic sedation to avoid cardio-respiratory complications. As a clinician we can signify that multi-monitoring can confuse care providers and make management more troublesome. Ideal monitoring should be user friendly, provide comprehensive data in an index.