Our study demonstrated that two innovations of oxygen delivery for sedation during endoscopy – NMs and trimmed NC – markedly reduced the incidence of nasal symptoms compared with oxygen delivery using conventional NC. In the comparison between the NC and TNC groups in which the same oxygen flow rate was used, trimming the nasal prongs to 2 mm in the TNC group significantly reduced the incidence of rhinorrhea and/or sneezing. Using NMs with a higher oxygen flow rate in the NM group also demonstrated a remarkable effect on lowering the incidence of rhinorrhea and/or sneezing.
The mechanism of nasal symptoms following oxygen supplementation for endoscopy sedation is unclear and has rarely been studied previously. Because history of allergy had no impact on the occurrence of rhinorrhea and/or sneezing in our study, these symptoms were likely nonallergic reactions. Nonallergic rhinitis encompasses a wide range of diagnoses and a heterogeneous group of subjects, and is believed to be related to mast cell activation and autonomic stimuli (9
). Some individuals have a known trigger such as cold air, certain drugs, food or hormones, while the etiology in others is unknown. Usually the diagnosis is made through a process of exclusion. Given the frequent complaints of chill in the examination rooms and the great resemblance between our patients’ symptoms and those of the cold-air rhinitis patients (9
), we investigated the temperature of the oxygen delivered. The ambient temperature of the examination rooms was 24°C to 25°C, with a relative humidity of 50% to 60%. In contrast to the sub-freezing temperature of oxygen used in cold air provocation testing, the temperature of the oxygen at the distal end of the tubing delivered from the wall-mounted flowmeter was 24.3°C, which is far warmer than the frigid air that induces cold air rhinitis. Although lacking a control arm of subjects using NC without supplemental oxygen in this cohort due to ethical reasons, we believe that the nature of the profuse rhinorrhea and/or excessive sneezing in our cohort is not likely to be cold-air rhinitis because different incidences of rhinitis were shown in patients using different apparatuses while receiving the same dry medical air from the wall flowmeter under the same room conditions.
We considered the possibility of rhinitis symptoms being provoked by mechanical irritation of the nasal prongs in the setting of moderate sedation during endoscopy. The incidence was as high as 7.1% when traditional NCs were used. However, the underlying mechanism is still unclear. It is believed that the response of the nose to mechanical or chemical stimuli are neuronal reflexes mediated by nociceptive C-fiber neurons (14
). Studies (17
) have shown the effects of mechanical or noxious stimuli on the nasal symptoms of subjects with nonallergic rhinitis with undefined etiology.
Nevertheless, the NC group showed results superior to the TNC and NM groups with respect to the incidence of hypoxia. The overall incidence of hypoxia among the three groups was 5.7%. All subjects experiencing hypoxia recovered within 30 s without clinical sequelae. In a study with a small sample size (n=30 in each arm) (19
), hypoxia was shown to be a common problem during endoscopy with or without sedation, and that sedation significantly increased the incidence of hypoxia. However, hypoxia was completely abolished by supplemental oxygenation at a flow rate of 4 L/min via NC in that study. In contrast to the study in which a single drug (midazolam) was used (19
), our combined use of midazolam and alfentanil for synergism, and adjunctive use of propofol may have resulted in a higher proportion (3.1%) of subjects experiencing hypoxia in the NC group.
The efficiency of oxygen supply appeared to be worse in the NM group than in the NC group. The NM group consumed more oxygen (6 L/min versus 4 L/min), and the mean SpO2 was significantly lower than in the NC group (P=0.004). This may have been due to the design of the apparatus in the NM group, with an adapter open to room air for the convenience of connection with a resuscitation bag in case of hypoxia. Although ideal sealing on the nose could be achieved by inflating an air-cushioned anesthesia mask (size 1) and securing it with a head strap, positive pressure could not be produced because oxygen could escape freely through the open end of the adapter. The severity of hypoxia, in terms of the range of the lowest SpO2, appeared to be worse in the NM group, although all of the subjects experiencing hypoxia returned to normoxia within 30 s after the head tilt manoeuvre and/or resuscitation bag application. To determine an adequate minimum flow rate, more studies investigating the efficiency of oxygen delivery and possible carbon dioxide rebreathing in this novel design is warranted.
There was a statistically significant difference in the mean value of each patient’s lowest SpO2 between subjects in the NC and TNC groups (P=0.018). The ranges of the lowest SpO2 were parallel in these two groups. The incidence of hypoxia was significantly higher in the TNC group (7.8%) than in the NC group (3.1%) (P=0.012). The problem frequently encountered in the TNC group was that the location of the trimmed NC prongs were easily shifted. The anesthetist must pay close attention to keep them in place during the procedure. This may have contributed to the high incidence of mild and transient hypoxia.
There were some limitations in the present study. We recognize that the pattern of breathing was not considered as a variable for practical reasons. Our subjects were sedated and kept their mouths open for a significant duration of the procedure. Strohl et al (20
) showed that the inhalation of air in through the nose and out through the mouth induces an increase in nasal airway resistance compared with inhalation and exhalation both through the nose. Without the 30% recovery of water during exhalation through the nose, the stimulus of cold, dry air could be amplified. The probable breathing pattern in our subjects with inhalation of air through the nose and out through the mouth could have contributed to the discomfort reported. The objective of the present study was to determine the causal relationship between the route of oxygen delivery and troublesome nasal symptoms. We did not use any scoring system to comprehensively evaluate the severity and all dimensions of nasal symptoms because most subjects were not sufficiently lucid to be assessed thoroughly during their recovery from sedation. This may have underestimated the occurrence of rhinitis if it was so mild that the subject could tolerate it and/or the anesthetist was not able to notice it. We recognized the possibility of additional ventilatory disturbances occurring even before the development of hypoxia during the procedure than we detected by monitoring hypoxia alone. First, we used oxygen saturation detected by oximetry to monitor ventilatory function. However, oxygen saturation is relatively insensitive to the earliest signs of hypoventilation because significant changes in the arterial partial pressure of oxygen may occur with little alteration in oxygen saturation (1
). Second, because the gastroenterologists and their assistants have access to subjects’ cephalic sites, monitoring of ventilatory function by patient observation was not feasible for the anesthetist. Third, we did not use capnography, even though it is recommended by the ASA for patients whose ventilation cannot be observed directly during moderate sedation for early detection of respiratory depression (2