Oxygen Reserve Index

High-flow oxygen for children's airway surgery: randomised controlled trial protocol (HAMSTER)

INTRODUCTION

Hypoxaemia during anaesthesia for tubeless upper airway surgery in children with abnormal airways is common due to the complexity of balancing adequate depth of anaesthesia with maintenance of spontaneous breathing and providing an uninterrupted field of view of the upper airway for the surgeon. High-flow nasal oxygenation (HIGH-FLOW) can prolong safe apnoea time and be used in children with abnormal airways but to date has not been compared with the alternative technique of low-flow nasal oxygenation (LOW-FLOW). The aim is to investigate if use of HIGH-FLOW can reduce the number of hypoxaemic events requiring rescue oxygenation compared with LOW-FLOW. METHODS AND ANALYSIS: High-flow oxygen for children's airway surgery: randomised controlled trial (HAMSTER) is a multicentre, unmasked, randomised controlled, parallel group, superiority trial comparing two oxygenation techniques during anaesthesia. Children (n=530) aged >37 weeks to 16 years presenting for elective tubeless upper airway surgery who fulfil inclusion but not exclusion criteria will be randomised prior to surgery to HIGH-FLOW or LOW-FLOW post induction of anaesthesia. Maintenance of anaesthesia with HIGH-FLOW requires Total IntraVenous Anaesthesia (TIVA) and with LOW-FLOW, either inhalational or TIVA at discretion of anaesthetist. The primary outcome is the incidence of hypoxaemic events requiring interruption of procedure for rescue oxygenation by positive pressure ventilation and the secondary outcome includes total hypoxaemia time, adverse cardiorespiratory events and unexpected paediatric intensive care admission admission. Hypoxaemia is defined as Sp0₂ <90%. Analysis will be conducted on an intention-to-treat basis.

ETHICS AND DISSEMINATION

Ethical approval has been obtained by Children's Health Queensland Human Research Ethics Committee (HREC/18/QRCH/130). The trial commenced recruitment in 2018. The primary manuscript will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

The HAMSTER is registered with the Australia and New Zealand Clinical TrialsRegistry: ACTRN12618000949280.

High-flow Nasal Cannulae Versus Non-invasive Ventilation for Preoxygenation of Obese Patients: The PREOPTIPOP Randomized Trial

BACKGROUND

In obese patients, preoxygenation with non-invasive ventilation (NIV) was reported to improve outcomes compared with facemask. In this setting, high-flow nasal cannulae (HFNC) used before and during intubation has never been studied against NIV.

METHODS

The PREOPTIPOP study is a randomised, single-centre, open-labelled, controlled trial including obese patients requiring intubation before scheduled surgery. Patients were randomised to receive preoxygenation by HFNC or NIV. HFNC was maintained throughout intubation whereas NIV was removed when apnea occurred to perform laryngoscopy. The study was designed to assess the superiority of HNFC. The primary outcome was the lowest level of end-tidal oxygen concentration (EtO2) within 2 min after intubation. Secondary outcomes included drop in pulse oximetry and complications related to intubation.

MAIN FINDINGS

A total of 100 patients were randomised. The intent-to-treat analysis found median [IQR] lowest EtO2 of 76% [66-82] for HFNC and 88% [82-90] for NIV (mean difference - 12·1 [- 15·1 to - 8·5], p < 0·0001). Mild desaturation below 95% was more frequent with HFNC (30%) than with NIV (12%) (relative risk 2·5, IC 95% [1·1 to 5·9], p = 0·03) and median lowest SpO2 during intubation was 98% [93-99] in HFNC vs. 99% [97-100] in NIV (p = 0·03). Severe and moderate complications were not different but patients reported more discomfort with NIV (28%) vs. HFNC (4%), p = 0·001.

INTERPRETATION

Compared with NIV, preoxygenation with HFNC in obese patients provided lower EtO2 after intubation and a higher rate of desaturation < 95%.

FUNDING

Institutional funding, additional grant from Fisher & Paykel.

TRIAL REGISTRATION

Clinical trial Submission: April 10, 2017. Registry name: Preoxygenation Optimization in Obese Patients: High-flow Nasal Cannulae Oxygen Versus Non-invasive Ventilation: A Single-centre Randomised Controlled Study. The PREOPTIPOP Study. Clinicaltrials.gov identifier: NCT03106441 N°ID RCB: 2017-A00305-48. Institutional review Board: CPP Nord-Ouest I, registration number 019/2017. URL registry:https://clinicaltrials.gov/ct2/show/NCT03106441.

Effects of indigo carmine intravenous injection on oxygen reserve index (ORi™) measurement

To retrospectively investigate the effects of indigo carmine intravenous injection on oxygen reserve index (ORi™) in 20 patients who underwent elective gynecologic surgery under general anesthesia. The study subjects were patients who underwent elective gynecologic surgery under general anesthesia between April 2016 and January 2017, and were administered a 5-ml intravenous injection of 0.4% indigo carmine for clinical purposes during surgery with ORi monitoring. Changes in ORi within 20 min after indigo carmine injection were observed. A relevant decrease in ORi was defined as ≥ 10% reduction in ORi from pre-injection level. ORi rapidly decreased after indigo carmine intravenous injection in all patients. In 10 of 19 patients, ORi decreased to 0 after indigo carmine injection. The median lowest value of ORi was 0 (range 0-0.16) and the median time to reach the lowest value of ORi was 2 min (range 1-4 min) after injection. ORi values returned to pre-injection levels within 20 min in 13 of 19 patients, and the median time to return to pre-injection levels was 10 min (range 6-16 min) after injection. During ORi monitoring it is necessary to consider the rapid reduction in ORi after intravenous injection of indigo carmine.

The oxygen reserve index (ORI): a new tool to monitor oxygen therapy

Supplemental oxygen is administered in the vast majority of patients in the perioperative setting and in the intensive care unit to prevent the potentially deleterious effects of hypoxia. On the other hand, the administration of high concentrations of oxygen may induce hyperoxia that may also be associated with significant complications. Oxygen therapy should therefore be precisely titrated and accurately monitored. Although pulse oximetry has become an indispensable monitoring technology to detect hypoxemia, its value in assessing the oxygenation status beyond the range of maximal arterial oxygen saturation (SpO₂ ≥97%) is very limited. In this hyperoxic range, we need to rely on blood gas analysis, which is intermittent, invasive and sometimes delayed. The oxygen reserve index (ORI) is a new continuous non-invasive variable that is provided by the new generation of pulse oximeters that use multi-wavelength pulse co-oximetry. The ORI is a dimensionless index that reflects oxygenation in the moderate hyperoxic range (PaO₂ 100-200 mmHg). The ORI may provide an early alarm when oxygenation deteriorates well before any changes in SpO₂ occur, may reflect the response to oxygen administration (e.g., pre-oxygenation), and may facilitate oxygen titration and prevent unintended hyperoxia. In this review we describe this new variable, summarize available data and preliminary experience, and discuss its potential clinical utilities in the perioperative and intensive care settings.

Analysis of Physiological Respiratory Variable Alarm Alerts Among Laboring Women Receiving Remifentanil

BACKGROUND

Remifentanil may be used by laboring women for analgesia, despite controversy because of potential apneas. We evaluated candidate variables as early warning alerts for apnea, based on prevalence, positive predictive rate, sensitivity for apnea event detection, and early warning alert time intervals (lead time) for apnea.

METHODS

We performed a secondary analysis of respiratory physiological data that had been collected during a prospective IRB-approved study of laboring women receiving IV patient-controlled boluses of remifentanil 20 to 60 μg every 1 to 2 minutes. Analyzed data included the respiratory rate (RR), end-tidal CO2 (EtCO2), pulse oximetry (SpO2), heart rate (HR), and the Integrated Pulmonary Index (IPI; Capnostream 20; Medtronic, Boulder, CO) that had been recorded continuously throughout labor. We defined immediate early warning alerts as any drop in a variable value below a prespecified threshold for 15 seconds: RR < 8 breaths per minute (bpm), EtCO2 < 15 mm Hg, and SpO2 < 92%. We defined alerts as "sustained" when the value remained below the threshold for ≥ 10 further seconds. The IPI value (1 to 10; 10 = healthy patient, ≤4 = immediate attention required, 1 = dire condition) was generated from a proprietary algorithm using RR, EtCO2, SpO2, and HR parameters. Apnea was defined as maximal CO2 < 5 mm Hg for at least 30 consecutive seconds.

RESULTS

We counted 62 apneas, among 10 of 19 (52.6%) women who received remifentanil (total dose 1725 ± 1392 μg, administered over 160 ± 132 minutes). We counted 331 immediate early warning alerts for the variables; 271 (82%) alerts were sustained for ≥10 seconds. The positive predictive value of alerts for apnea was 35.8% (99% confidence interval [CI]: 27.1-45.6), 28.9% (99% CI: 20.8-38.7), 4.3% (99% CI: 1.9-9.6), and 24.6% (99% CI: 18.3-32.2) for RR, EtCO2, SpO2, and IPI, respectively. The sensitivity for apnea event detection was 100% (99% CI: 90.3-100) for RR (<8 bpm) and IPI (≤4); 75.8% (99% CI: 59.8-86.9) for EtCO2 <15 mm Hg; and 14.5% (99% CI: 6.5-29.4) for SpO2 <92%. We found a statistically significant difference in the timing of RR, EtCO2, SpO2, and IPI alerts for apnea; Friedman's Q = 33.53; P < .0001. The EtCO2 had a median (interquartile range) lead time of -0.2 (-12.2 to 0.7) seconds, and SpO2 had a median (interquartile range) lead time of 40.0 (40.0 to 40.0) seconds.

CONCLUSIONS

The majority of women receiving IV remifentanil for labor analgesia experienced apneas. Alerts for EtCO2 (<15 mm Hg), RR (<8 bpm), and IPI (≤4) detected most apneas, whereas SpO2 alerts missed the majority of apneas. All variables had a low positive predictive rate, demonstrating the limitations of the respiratory monitors utilized as early warning surveillance for apneas in this setting.

Airway Management During Upper GI Endoscopic Procedures: State of the Art Review

With the growing popularity of propofol mediated deep sedation for upper gastrointestinal (GI) endoscopic procedures, challenges are being felt and appreciated. Research suggests that management of the airway is anything but routine in this setting. Although many studies and meta-analyses have demonstrated the safety of propofol sedation administered by registered nurses under the supervision of gastroenterologists (likely related to the lighter degrees of sedation than those provided by anesthesia providers and is under medicolegal controversy in the United States), there is no agreement on the optimum airway management for procedures such as endoscopic retrograde cholangiopancreatography. Failure to rescue an airway at an appropriate time has led to disastrous consequences. Inability to evaluate and appreciate the risk factors for aspiration can ruin the day for both the patient and the health care providers. This review apprises the reader of various aspects of airway management relevant to the practice of sedation during upper GI endoscopy. New devices and modification of existing devices are discussed in detail. Recognizing the fact that appropriate monitoring is important for timely recognition and management of potential airway disasters, these issues are explored thoroughly.