Effectiveness of preoxygenation strategies: a systematic review and network meta-analysis.

BACKGROUND: Preoxygenation is universally recommended before induction of general anaesthesia to prolong safe apnoea time. The optimal technique for preoxygenation is unclear. We conducted a systematic review to determine the preoxygenation technique associated with the greatest effectiveness in adult patients having general anaesthesia. METHODS: We searched six databases for randomised controlled trials of patients aged ≥16 yr, receiving general anaesthesia in any setting and comparing different preoxygenation techniques and methods. Our primary effectiveness outcome was safe apnoea time, and secondary outcomes included incidence of arterial oxygen desaturation; lowest SpO2 during airway management; time to end-tidal oxygen concentration of 90%; and [Formula: see text] and [Formula: see text] at the end of preoxygenation. We assessed the quality of evidence according to Grading of Recommendations, Assessment, Development and Evaluation (GRADE) recommendations. RESULTS: We included 52 studies of 3914 patients. High-flow nasal oxygen with patients in a head-up position was most likely to be associated with a prolonged safe apnoea time when compared with other strategies, with a mean difference (95% credible interval) of 291 (138-456) s and 203 (79-343) s compared with preoxygenation with a facemask in the supine and head-up positions, respectively. Subgroup analysis of studies without apnoeic oxygenation also showed high-flow nasal oxygen in the head-up position as the highest ranked technique, with a statistically significantly delayed mean difference (95% credible interval) safe apnoea time compared with facemask in supine and head-up positions of 222 (63-378) s and 139 (15-262) s, respectively. High-flow nasal oxygen was also the highest ranked technique for increased [Formula: see text] at the end of preoxygenation. However, the incidence of arterial desaturation was less likely to occur when a facemask with pressure support was used compared with other techniques, and [Formula: see text] was most likely to be lowest when preoxygenation took place with patients deep breathing in a supine position. CONCLUSIONS: Preoxygenation of adults before induction of general anaesthesia was most effective in terms of safe apnoea time when performed with high-flow nasal oxygen with patients in the head-up position in comparison with facemask alone. Also, high-flow nasal oxygen in the head-up position is likely to be the most effective technique to prolong safe apnoea time among those evaluated. Clinicians should consider this technique and patient position in routine practice. SYSTEMATIC REVIEW PROTOCOL: PROSPERO CRD42022326046.

Pre-oxygenation using high-flow nasal oxygen versus tight facemask in trauma patients undergoing emergency anaesthesia.

BACKGROUND: Patients suffering from major traumatic injuries frequently require emergency anaesthesia. Due to often compromised physiology and the time-sensitive management, trauma patients may be more prone to desaturate during induction of anaesthesia. We hypothesised that pre-oxygenation using high-flow nasal oxygen would decrease the risk of desaturation during induction of anaesthesia in trauma patients and the study therefore aimed to compare the frequency of desaturation when pre-oxygenation was performed with high-flow nasal oxygen or a traditional facemask. METHODS: This exploratory, prospective, before-and-after study was conducted at the Karolinska University Hospital, Sweden. Adult (≥18 years of age) patients suffering major traumatic injuries needing emergency anaesthesia were included around the clock. Patients were pre-oxygenated using a tight-fitting facemask during the first nine months of enrollment. High-flow nasal oxygen was then introduced as a method for pre-oxygenation of trauma patients. The primary outcome was the proportion of patients desaturating <93% during induction of anaesthesia, assessed from the start of pre-oxygenation until one minute after intubation. Secondary outcomes included perceived difficulty of pre-oxygenation among anaesthetists (assessed on a scale between 1 and 10) and safety outcomes, such as incidence of regurgitations and intracranial gas (assessed radiologically). RESULTS: Data from 96 patients were analysed. Facemask pre-oxygenation was performed in 66 patients, while 30 patients were pre-oxygenated with high-flow nasal oxygen. The most frequent trauma mechanisms were stabbing injuries (n = 34 (35%)) and fall injuries (n = 21 (22%)). There were no differences in patient characteristics between the groups. Eight (12%) versus three (10%) patients desaturated <93% in the facemask and high-flow nasal oxygen group respectively, OR 0.81 (95% CI 0.20-3.28), p = .76. Anaesthetists assessed pre-oxygenation using high-flow nasal oxygen as easier compared to facemask pre-oxygenation. No patient in any group showed signs of regurgitation. Among patients with facial or skull fractures requiring anaesthesia before radiology was performed, intracranial gas was seen in four (40%) patients pre-oxygenated with a facemask and in no patient pre-oxygenated with HFNO (p = .23). CONCLUSION: In this prospective study investigating trauma patients undergoing emergency anaesthesia, we could not see any difference in the number of patients desaturating when pre-oxygenation was performed with high-flow nasal oxygen compared to a tight-fitting facemask. Pre-oxygenation using high-flow nasal oxygen was assessed as easier compared to facemask pre-oxygenation.

Emergency medicine updates: Endotracheal intubation.

INTRODUCTION: Airway management including endotracheal intubation (ETI) is a key skill for emergency clinicians. Therefore, it is important for emergency clinicians to be aware of the current evidence regarding the identification and management of patients requiring ETI. OBJECTIVE: This paper evaluates key evidence-based updates concerning ETI for the emergency clinician. DISCUSSION: ETI is commonly performed in the emergency department (ED) setting but has many nuanced components. There are several tools that have been used to predict a difficult airway which incorporate anatomic and physiologic features. While helpful, these tools should not be used in isolation. Preoxygenation and apneic oxygenation are recommended to reduce the risk of desaturation and patient decompensation, particularly with noninvasive ventilation in critically ill patients. Induction and neuromuscular blocking medications should be tailored to the clinical scenario. Video laryngoscopy is superior to direct laryngoscopy among novice users, while both techniques are reasonable among more experienced clinicians. Recent literature suggests using a bougie during the first attempt. Point-of-care ultrasound is helpful for confirming correct placement and depth of the endotracheal tube. CONCLUSIONS: An understanding of literature updates can improve the ED care of patients requiring emergent intubation.

Selective Use of Positive-Pressure Ventilation for Preoxygenation During Air Medical Rapid Sequence Intubation.

BACKGROUND: Preoxygenation is critical to safe performance of rapid sequence intubation (RSI). The use of positive-pressure ventilation (PPV) has been advocated during preoxygenation but may increase the risk of aspiration. OBJECTIVE: To explore the risk-benefit analysis of using PPV during air medical RSI. METHODS: We performed a retrospective analysis of the Air Methods Airway Registry using patient data from over 175 bases across the U.S. over a 5-year period. Patients were separated into normoxemic (SpO2 ≥93%) and hypoxemic (SpO2 <93%) and compared in regard to demographics, clinical data, and use of PPV. Primary outcomes were first-attempt intubation success (FAS) and FAS without desaturation (FASWD). Chi-square, t-test, and logistical regression were used to analyze the data. RESULTS: There were 9778 patients who underwent intubations during the study period. FAS was 92% (8966 patients). FASWD was 90% (8775 patients). Mean SpO2 was 94.9%. There were 42% (4118 patients) of patients who received PPV prior to intubation and 1% (94) aspirated during RSI. Multivariate logistical regression showed an association between use of PPV and reduced intubation success for normoxemic patients but improved intubation success for hypoxemic patients. The use of PPV was associated with higher risk of aspiration events (p = 0.007). CONCLUSION: The use of PPV during preoxygenation prior to RSI appears beneficial for hypoxemic but not normoxemic patients due to lower intubation success and increased aspiration risk with PPV. This data supports selective use of PPV prior to the initial intubation attempt in patients undergoing RSI.

Pressure-controlled versus manual facemask ventilation for anaesthetic induction in adults: A randomised controlled non-inferiority trial.

BACKGROUND: Pressure-controlled face mask ventilation (PC-FMV) with positive end-expiratory pressure (PEEP) after apnoea following induction of general anaesthesia prolongs safe apnoea time and reduces atelectasis formation. However, depending on the set inspiratory pressure, a delayed confirmation of a patent airway might occur. We hypothesised that by lowering the peak inspiratory pressure (PIP) when using PC-FMV with PEEP, confirmation of a patent airway would not be delayed as studied by the first return of CO2 , compared with manual face mask ventilation (Manual FMV). METHODS: This was a single-centre, randomised controlled non-inferiority trial. Seventy adult patients scheduled for elective day-case surgery under general anaesthesia with body mass index between 18.5 and 29.9 kg m-2 , American Society of Anesthesiologists (ASA) classes I-III, and without anticipated difficult FMV, were included. Before the start of pre-oxygenation and induction of general anaesthesia, participants were randomly allocated to receive ventilation with either PC-FMV with PEEP, at a PIP of 11 and a PEEP of 6 cmH2 O or Manual FMV, with the adjustable pressure-limiting valve set at 11 cmH2 O. The primary outcome variable was the number of ventilatory attempts needed until confirmation of a patent airway, defined as the return of at least 1.3 kPa CO2 . RESULTS: The return of ≥1.3 kPa CO2 on the capnography curve was observed after mean ± SD, 3.6 ± 4.2 and 2.5 ± 1.9 ventilatory attempts/breaths with PC-FMV with PEEP and Manual FMV, respectively. The difference in means (1.1 ventilatory attempts/breaths) had a 99% CI of -1.0 to 3.1, within the accepted upper margin of four breaths for non-inferiority. CONCLUSION: Following induction of general anaesthesia, PC-FMV with PEEP was used without delaying a patent airway as confirmed with capnography, if moderate pressures were used.

Pre-oxygenation using high-flow nasal oxygen in parturients undergoing caesarean section in general anaesthesia: A prospective, multi-centre, pilot study.

BACKGROUND: Parturients undergoing caesarean section in general anaesthesia have an increased risk of desaturating during anaesthesia induction. Pre- and peri-oxygenation with high-flow nasal oxygen prolong the safe apnoea time but data on parturients undergoing caesarean section under general anaesthesia are limited. This pilot study aimed to investigate the clinical effects and frequency of desaturation in parturients undergoing caesarean section in general anaesthesia pre- and peri-oxygenated with high-flow nasal oxygen and compare this to traditional pre-oxygenation using a facemask. METHODS: In this prospective, non-randomised, multi-centre study we included pregnant women with a gestational age ≥30 weeks undergoing caesarean section under general anaesthesia. All parturients were asked to participate in the intervention group consisting of pre-oxygenation using high-flow nasal oxygen. Parturients declining participation were pre-oxygenated with a traditional facemask. Primary outcome was the proportion of parturients desaturating below 93% from start of pre-oxygenation until 1 min after tracheal intubation. Secondary outcomes investigated end-tidal oxygen concentrations after tracheal intubation and the proportion of parturients with signs of regurgitation. RESULTS: A total of 34 parturients were included, 25 pre- and peri-oxygenated with high-flow nasal oxygen and 9 pre-oxygenated with facemask. No difference in patient or airway characteristics could be seen except for a higher BMI in the high-flow nasal oxygen group (31.4 kg m-2 [4.7] vs. 27.7 kg m-2 [3.1]; p = .034). No woman in any of the two groups desaturated below 93%. The lowest peripheral oxygen saturation observed, in any parturient, was 97%. There was no difference detected in end-tidal oxygen concentration after tracheal intubation, 87% (6) in the high-flow nasal oxygen group vs 80% (15) in the facemask group (p = .308). No signs of regurgitation, in any parturient, were seen. CONCLUSION: Pre- and peri-oxygenation with high-flow nasal oxygen maintain adequate oxygen saturation levels during induction of anaesthesia also in parturients. Regurgitation of gastric content did not occur in any parturient and no other safety concerns were observed in this pilot study.

Effect of reverse Trendelenburg position and positive pressure ventilation on safe non-hypoxic apnea period in obese, a randomized-control trial.

PURPOSE: There is an elevated incidence of hypoxemia during the airway management of the morbidly obese. We aimed to assess whether optimizing body position and ventilation during pre-oxygenation allow a longer safe non-hypoxic apnea period (SNHAP). METHODS: Fifty morbidly obese patients were recruited and randomized for this study. Patients were positioned and preoxygenated for three minutes in the ramp position associated with spontaneous breathing without additional CPAP or PEEP (RP/ZEEP group) or in the reverse Trendelenburg position associated with pressure support ventilation mode with pressure support of 8 cmH2O and an additional 10 cmH2O of PEEP while breathing spontaneously (RT/PPV group) according to randomization. RESULTS: The SNHAP was significantly longer in the RT/PPV group (258.2 (55.1) vs. 216.7 (42.3) seconds, p = 0.005). The RT/PPV group was also associated to a shorter time to obtain a fractional end-tidal oxygen concentration (FEtO2) of 0.90 (85.1(47.8) vs 145.3(40.8) seconds, p < 0.0001), a higher proportion of patients that reached the satisfactory FEtO2 of 0.90 (21/24, 88% vs. 13/24, 54%, p = 0.024), a higher FEtO2 during preoxygenation (0.91(0.05) vs. 0.89(0.01), p = 0.003) and a faster return to 97% oxygen saturation after ventilation resumption (69.8 (24.2) vs. 91.4 (39.2) seconds, p = 0.038). CONCLUSION: In the morbidly obese population, RT/PPV, compared to RP/ZEEP, lengthens the SNHAP, decreases the time to obtain optimal preoxygenation conditions, and allows a faster resuming of secure oxygen saturation. The former combination allows a more significant margin of time for endotracheal intubation and minimizes the risk of hypoxemia in this highly vulnerable population. TRIAL REGISTRATION: NCT02590406, 29/10/2015.

Decompression strain in parachute jumpmasters during simulated high-altitude missions: a special reference to preoxygenation strategies.

PURPOSE: Military parachute operations are often executed at high altitude, from an unpressurized aircraft compartment. Parachute jumpmasters (JM) are thus regularly exposed to 29,500 ft for 60 min. The aim was to investigate the decompression strain during a simulated JM mission at high altitude and to compare two strategies of preoxygenation, conducted either at sea-level or below 10,000 ft, during ascent to mission altitude. METHODS: Ten JM completed, on separate occasions, a 45-min preoxygenation either at sea-level (normobaric: N) or 8200ft (hypobaric: H), followed by exposure to 28,000 ft for 60 min, whilst laying supine and breathing 100% oxygen. At min 45 of the exposure to 28,000 ft, the JM performed 10 weighted squats. Decompression strain was determined from ultrasound assessment of venous gas emboli (VGE) during supine rest (5-min intervals), after three unloaded knee-bends (15-min intervals) and immediately following the weighted squats. The VGE were scored using a six-graded scale (0-5). RESULTS: In condition H, two JM experienced decompression sickness (DCS), whereas no DCS incidents were reported in condition N. The prevalence of VGE was higher in the H than the N condition, at rest [median(range), 3(0-4) vs 0(0-3); p = 0.017], after unloaded knee-bends [3(0-4) vs 0(0-3); p = 0.014] and after the 10 weighted squats [3(0-4) vs 0(0-3); p = 0.014]. VGE were detected earlier in the H (28 ± 20 min, p = 0.018) than the N condition (50 ± 19 min). CONCLUSIONS: A preoxygenation/altitude procedure commonly used by JM, with a 60-min exposure to 28,000 ft after pre-oxygenation for 45 min at 8200 ft is associated with high risk of DCS. The decompression strain can be reduced by preoxygenating at sea level.

Comparison of preoxygenation efficiency measured by the oxygen reserve index between high-flow nasal oxygenation and facemask ventilation: a randomised controlled trial.

BACKGROUND: High-flow nasal oxygenation and the oxygen reserve index (ORI), which is a non-invasive and innovative modality that reflects the arterial oxygen content, are used in general anaesthesia. This study compares the preoxygenation efficiency (measured by the ORI) of high-flow nasal oxygenation and facemask ventilation during the induction process. METHODS: This single-centre, two-group, randomised controlled trial included 197 patients aged ≥ 20 years who underwent orotracheal intubation for general anaesthesia for elective surgery. The patients were randomly allocated to receive preoxygenation via facemask ventilation or high-flow nasal oxygenation. The ORI was measured and compared between both groups. RESULTS: The ORI increased during preoxygenation in all patients. At 1 min of preoxygenation, the ORI was significantly higher in the high-flow nasal oxygenation group (0.34 ± 0.33) than in the facemask ventilation group (0.21 ± 0.28; P = 0.003). The highest ORI was not significantly different between the two groups (0.68 ± 0.25 in the high-flow nasal oxygenation group vs. 0.70 ± 0.28 in the facemask ventilation group; P = 0.505). CONCLUSIONS: High-flow nasal oxygenation results in an oxygenation status similar to that provided by facemask ventilation during the induction process of general anaesthesia; therefore, high-flow nasal oxygenation is a feasible preoxygenation method. TRIAL REGISTRATION: Clinicaltrials.gov (NCT04291339).

Peri-intubation oxygenation for Caesarean delivery: is there an optimal technique?

Peri-intubation oxygen administration to the pregnant patient during induction of general anaesthesia is critical to avoiding hypoxaemia and harm to the mother and fetus. Recent modelling comparing low-flow with high-flow nasal oxygen in simulated term pregnant women of varying body habitus, taken together with previous work, suggests that face mask preoxygenation with the use of low-flow or high-flow nasal oxygen during the period of apnoea prolongs the safe apnoea period, with the benefit varying by body habitus. Low-flow compared with high-flow nasal oxygen may be easier to combine with face mask preoxygenation and is readily available in all operating theatres, although future improvements in high-flow nasal oxygen delivery systems may improve ease of use for this indication.

Optimizing Physiology During Prehospital Airway Management: An NAEMSP Position Statement and Resource Document.

Airway management is a critical component of resuscitation but also carries the potential to disrupt perfusion, oxygenation, and ventilation as a consequence of airway insertion efforts, the use of medications, and the conversion to positive-pressure ventilation. NAEMSP recommends:Airway management should be approached as an organized system of care, incorporating principles of teamwork and operational awareness.EMS clinicians should prevent or correct hypoxemia and hypotension prior to advanced airway insertion attempts.Continuous physiological monitoring must be used during airway management to guide the timing of, limit the duration of, and inform decision making during advanced airway insertion attempts.Initial and ongoing confirmation of advanced airway placement must be performed using waveform capnography. Airway devices must be secured using a reliable method.Perfusion, oxygenation, and ventilation should be optimized before, during, and after advanced airway insertion.To mitigate aspiration after advanced airway insertion, EMS clinicians should consider placing a patient in a semi-upright position.When appropriate, patients undergoing advanced airway placement should receive suitable pharmacologic anxiolysis, amnesia, and analgesia. In select cases, the use of neuromuscular blocking agents may be appropriate.

Pre-oxygenation with facemask oxygen vs high-flow nasal oxygen vs high-flow nasal oxygen plus mouthpiece: a randomised controlled trial.

High-flow nasal oxygen used before and during apnoea prolongs time to desaturation at induction of anaesthesia. It is unclear how much oxygenation before apnoea prolongs this time. We randomly allocated 84 participants to 3 minutes of pre-oxygenation by one of three methods: 15 l.min-1 by facemask; 50 l.min-1 by high-flow nasal cannulae only; or 50 l.min-1 by high-flow nasal cannulae plus 15 l.min-1 by mouthpiece. We then anaesthetised and intubated the trachea of 79 participants and waited for oxygen saturation to fall to 92%. Median (IQR [range]) times to desaturate to 92% after pre-oxygenation with facemask oxygen, high-flow nasal oxygen only and high-flow nasal oxygen with mouthpiece, were: 309 (208-417 [107-544]) s; 344 (250-393 [194-585]) s; and 386 (328-498 [182-852]) s, respectively, p = 0.014. Time to desaturation after facemask pre-oxygenation was shorter than after combined nasal and mouthpiece pre-oxygenation, p = 0.006. We could not statistically distinguish high-flow nasal oxygen without mouthpiece from the other two groups for this outcome. Median (IQR [range]) arterial oxygen partial pressure after 3 minutes of pre-oxygenation by facemask, nasal cannulae and nasal cannulae plus mouthpiece, was: 49 (36-61 [24-66]) kPa; 57 (48-62 [30-69]) kPa; and 61 (55-64 [36-72]) kPa, respectively, p = 0.003. Oxygen partial pressure after 3 minutes of pre-oxygenation with nasal and mouthpiece combination was greater than after facemask pre-oxygenation, p = 0.002, and after high-flow nasal oxygen alone, p = 0.016. We did not reject the null hypothesis for the pairwise comparison of facemask pre-oxygenation and high-flow nasal pre-oxygenation, p = 0.14.

Ease and comfort of pre-oxygenation with high-flow nasal oxygen cannulae vs. facemask: a randomised controlled trial.

The Difficult Airway Society recommends that all patients should be pre-oxygenated before the induction of general anaesthesia, but this may not always be easy or comfortable and anaesthesia may often be induced without full pre-oxygenation. We tested the hypothesis that high-flow nasal oxygen cannulae would be easier and more comfortable than facemasks for pre-oxygenation. We randomly allocated 199 patients undergoing elective surgery aged ≥ 10 years to pre-oxygenation using either high-flow nasal oxygen or facemask. Ease and comfort were assessed by anaesthetists and patients on 10-cm visual analogue scale and six-point smiley face scale, respectively. Secondary endpoints included end-tidal oxygen fraction after securing a definitive airway and time to secure an airway. A mean difference (95%CI) between groups in ratings of -0.76 (-1.25 to -0.27) cm for ease of use (p = 0.003) and -0.45 (-0.75 to -0.13) points for comfort (p = 0.006), both favoured high-flow nasal oxygen. A mean difference (95%CI) between groups in end-tidal oxygen fraction of 3.89% (2.41-5.37%) after securing a definitive airway also favoured high-flow nasal oxygen (p < 0.001). There was no significant difference between groups in the number of patients with hypoxaemia (Sp O2 < 90%) or severe hypoxaemia (Sp O2 < 85%) lasting ≥ 1 min or ≥ 2 min; in the proportion of patients with an end-tidal oxygen fraction < 87% in the first 5 min after tracheal intubation (52.2% vs. 58.9% in facemask and high-flow nasal oxygen groups, respectively; p = 0.31); or in time taken to secure an airway (11.6 vs. 12.2 min in facemask and high-flow nasal oxygen groups, respectively; p = 0.65). In conclusion, we found pre-oxygenation with high-flow nasal oxygen to be easier for anaesthetists and more comfortable for patients than pre-oxygenation with a facemask, with no clinically relevant differences in end-tidal oxygen fraction after securing a definitive airway or time to secure an airway. The differences in ease and comfort were modest.

Comparison of the effectiveness of high-flow nasal oxygen vs. standard facemask oxygenation for pre- and apneic oxygenation during anesthesia induction: a systematic review and meta-analysis.

BACKGROUND: In recent years, high flow nasal oxygen (HFNO) has been widely used in clinic, especially in perioperative period. Many studies have discussed the role of HFNO in pre- and apneic oxygenation, but their results are controversial. Our study aimed to examine the effectiveness of HFNO in pre- and apneic oxygenation by a meta-analysis of RCTs. METHODS: EMBASE, PUBMED, and COCHRANE LIBRARY databases were searched from inception to July 2021 for relevant randomized controlled trails (RCTs) on the effectiveness of HFNO versus standard facemask ventilation (FMV) in pre- and apenic oxygenation. Studies involving one of the following six indicators: (1) Arterial oxygen partial pressure (PaO2), (2) End expiratory oxygen concentration (EtO2), (3) Safe apnoea time, (4) Minimum pulse oxygen saturation (SpO2min), (5) Oxygenation (O2) desaturation, (6) End expiratory carbon dioxide (EtCO2) or Arterial carbon dioxide partial pressure(PaCO2) were included. Due to the source of clinical heterogeneity in the observed indicators in this study, we adopt random-effects model for analysis, and express it as the mean difference (MD) or risk ratio (RR) with a confidence interval of 95% (95%CI). We conducted a risk assessment of bias for eligible studies and assessed the overall quality of evidence for each outcome. RESULTS: Fourteen RCTs and 1012 participants were finally included. We found the PaO2 was higher in HFNO group than FMV group with a MD (95% CI) of 57.38 mmHg (25.65 to 89.10; p = 0.0004) after preoxygenation and the safe apnoea time was significantly longer with a MD (95% CI) of 86.93 s (44.35 to 129.51; p < 0.0001) during anesthesia induction. There were no significant statistical difference in the minimum SpO2, CO2 accumulation, EtO2 and O2 desaturation rate during anesthesia induction between the two groups. CONCLUSIONS: This systematic review and meta-analysis suggests that HFNO should be considered as an oxygenation tool for patients during anesthesia induction. Compared with FMV, continuous use of HFNO during anesthesia induction can significantly improve oxygenation and prolong safe apnoea time in surgical patients.

Non-invasive ventilation for preoxygenation before general anesthesia: a systematic review and meta-analysis of randomized controlled trials.

BACKGROUND AND OBJECTIVES: Preoxygenation is crucial for providing sufficient oxygen reservoir to a patient before intubation and enables the extension of the period between breathing termination and critical desaturation (safe apnoea time). Conventionally, face mask ventilation is used for preoxygenation. Non-invasive ventilation is a new preoxygenation method. The study objective was to compare the outcomes of non-invasive ventilation and face mask ventilation for preoxygenation. METHOD: PubMed, Embase, Cochrane Library, and the ClinicalTrials.gov registry were searched for eligible studies published from database inception to September 2021. Individual effect sizes were standardized, and a meta-analysis was conducted using random effects models to calculate the pooled effect size. Inclusion criteria were randomised controlled trials of comparing the outcomes of non-invasive ventilation or face mask ventilation for preoxygenation in patients scheduled for surgeries. The primary outcome was safe apnea time, and the secondary outcomes were post-operative complications, number of patients who achieved the expired O2 fraction (FeO2) after 3 min of preoxygenation, minimal SpO2 during tracheal intubation, partial pressure of oxygen in the arterial blood (PaO2) and partial pressure of carbon dioxide (PaCO2) after preoxygenation, and PaO2 and PaCO2 after tracheal intubation. RESULTS: 13 trials were eligible for inclusion in this study. Significant differences were observed in safe apnoea time, number of patients who achieved FeO2 90% after preoxygenation for 3 min, and PaO2 and PaCO2 after preoxygenation and tracheal intubation. Only in the non-obese subgroup, no significant difference was observed in safe apnoea time (mean difference: 125.38, 95% confidence interval: - 12.26 to 263.03). CONCLUSION: Non-invasive ventilation appeared to be more effective than conventional methods for preoxygenation. We recommend non-invasive ventilation based on our results.

Fraction of Expired Oxygen as a Measure of Preoxygenation Prior to Rapid Sequence Intubation in the Pediatric Emergency Department.

BACKGROUND: Pulse oximetry (SpO2) is a flawed measure of adequacy of preoxygenation prior to intubation. The fraction of expired oxygen (FeO2) is a promising but understudied alternative. OBJECTIVE: To investigate FeO2 as a measure of preoxygenation prior to intubation in a pediatric emergency department. METHODS: We conducted a prospective, observational study of patients 18 and younger. We collected data using video review, and FeO2 was measured via inline sampling. The main outcomes were FeO2 and SpO2 at the start of preoxygenation, end of preoxygenation/start of intubation attempt, and the end of intubation attempt. We compared FeO2 and SpO2 at the end of preoxygenation for patients with and without oxyhemoglobin desaturation. RESULTS: We enrolled 85 of 88 eligible patients during the 14-month study period. FeO2 data were available at the start of preoxygenation for 53 of 85 patients (62%), and for the end of preoxygenation for 59 of 85 patients (69%). Median FeO2 at the start and end of preoxygenation was 90% (interquartile range [IQR] 88, 92) and 90% (IQR 88, 92). Median SpO2 at the start and end of preoxygenation was 100% (IQR 100, 100). There were 11 episodes of desaturation, with median FeO2 at the start of intubation attempt of 89.5 (IQR 54.5, 91.5) and median SpO2 of 100 (IQR 99, 100). Patients who did not have a desaturation event had a median FeO2 of 90.0 (IQR 88.0, 92.0). CONCLUSIONS: Measuring FeO2 during rapid sequence intubation is challenging with feasibility limitations, but may be a more discriminatory metric of adequate preoxygenation.

Effectiveness of preoxygenation by conventional face mask versus non-invasive ventilation in morbidly obese patients: measurable by the oxygen-reserve index?

Preoxygenation is a crucial manoeuvre for patients' safety, particularly for morbidly obese patients due to their reduced pulmonary reserve and increased risk for difficult airway situations. The oxygen reserve index (ORI™) was recently introduced as a new parameter of multiple wavelength pulse oximetry and has been advocated to allow assessment of hyperoxia [quantified by the resulting arterial oxygen partial pressure (PaO2)]. This study investigates if ORI can be used to evaluate the impact of two different preoxygenation manoeuvres on the grade of hyperoxia. Two preoxygenation manoeuvres were sequentially evaluated in 41 morbidly obese patients: First, breathing 100% oxygen for 5 min via standard face mask. Second, after achieving a second baseline, 5 min of non-invasive ventilation (NIV) with 100% oxygen. The effect of preoxygenation on ORI compared to PaO2 was evaluated and whether differences in the two preoxygenation manoeuvres can be monitored by ORI. Overall correlation of PaO2 and ORI was significant (Spearman-Rho coefficient of correlation 0.818, p < 0.001). However, ORI could not differentiate between the two preoxygenation manoeuvres although the PaO2 values for NIV preoxygenation were significantly higher compared to standard preoxygenation (median 505 mmHg (M1) vs. 550 mmHg (M3); p < 0.0001). In contrast, ORI values did not differ significantly (median 0.39 (M1) vs. 0.38 (M3); p = 0.758). Absolute values of ORI cannot be used to assess effectiveness of a preoxygenation procedure in bariatric patients, mainly because its range of discrimination is considerably lower than the high ranges of PaO2 attained by adequate preoxygenation. Trial registration German Clinical Trials Register: DRKS00025023 (retrospectively registered on April 16th, 2021).

Preoxygenation: from hardcore physiology to the operating room.

If we define the human body by the mass of the elements that compose it, we could say that we are oxygen and other elements. Oxygen, in addition to being fundamental in our composition, is an element that we constantly need to support cellular respiration and, therefore, life. Interestingly, despite its importance, humans have not developed mechanisms that allow us to store it and, therefore, we are unable to sustain life if we are deprived of ventilation, even for brief periods. Accordingly, the ability to induce the cessation of ventilation in a patient must be accompanied by different technical and non-technical skills that allow the patient's safety to be maintained in this highly vulnerable state. Through the use of basic mathematical tools and comparative physiology, we hereby propose to review the physiological foundations of preoxygenation to understand the reasons behind the clinical recommendations in this field.

High-flow nasal cannula versus face mask for preoxygenation in obese patients: A randomised controlled trial.

BACKGROUND: Preoxygenation efficacy with high-flow nasal cannula (HFNC) in obese patients is not clearly established. The primary aim of this study was to compare heated, humidified, high-flow nasal cannula with face mask for preoxygenation in this population. METHODS: We conducted a single-centre, randomised, controlled trial. Forty subjects with BMI ≥ 35 kg m-2 were randomly assigned to receive 5.0 min of preoxygenation with face mask and 7 cm H2 O of PEEP (PEEP group) or HFNC at 70 L min-1 (HF group). Following induction, bag-mask ventilation continued until laryngoscopy, whereas HFNC was maintained before and during intubation. The primary outcomes were end-tidal fraction of oxygen (EtO2 ) at 2.5 and 5.0 min duration of preoxygenation. Secondary outcomes included PaO2 and PaCO2 at 2.5 and 5.0 min of preoxygenation and at intubation. RESULTS: Mean (±SD) EtO2 was 0.89 (±0.04) versus 0.90 (±0.05) after 2.5 min (95% CI for mean difference -0.02, 0.04) and 0.93 (±0.02) versus 0.91 (±0.02) after 5.0 min of preoxygenation (95% CI for mean difference -0.03, -0.002) in the PEEP (n = 18) and HF group (n = 20), respectively. All subjects reached an EtO2  ≥ 0.85 at 5.0 min. There were no differences in mean PaO2 or PaCO2 during preoxygenation. Subjects in the HF group had a mean (±SD) apnoea time of 199 (±38) s, but no desaturation (SpO2  < 100%) occurred. CONCLUSIONS: Face mask with PEEP was superior to HFNC for preoxygenation in obese subjects. HFNC provided adequate preoxygenation quality in all subjects and may be considered as an alternative to face mask in selected patients. TRIAL REGISTRATION: #ISRCTN37375068 (www.isrctn.com).

Pre-oxygenation using high-flow nasal oxygen vs. tight facemask during rapid sequence induction.

Pre-oxygenation using high-flow nasal oxygen can decrease the risk of desaturation during rapid sequence induction in patients undergoing emergency surgery. Previous studies were single-centre and often in limited settings. This randomised, international, multicentre trial compared high-flow nasal oxygen with standard facemask pre-oxygenation for rapid sequence induction in emergency surgery at all hours of the day and night. A total of 350 adult patients from six centres in Sweden and one in Switzerland undergoing emergency surgery where rapid sequence induction was required were included and randomly allocated to pre-oxygenation with 100% oxygen using high-flow nasal oxygen or a standard tight-fitting facemask. The primary outcome was the number of patients developing oxygen saturations <93% from the start of pre-oxygenation until 1 min after tracheal intubation. Data from 349 of 350 patients who entered the study were analysed (174 in the high-flow nasal oxygen group and 175 in the facemask group). No difference was detected in the number of patients desaturating <93%, five (2.9%) vs. six (3.4%) patients in the high-flow nasal oxygen and facemask group, respectively (p = 0.77). The risk of desaturation was not increased during on-call hours. No difference was seen in end-tidal carbon dioxide levels in the first breath after tracheal intubation or in the number of patients with signs of regurgitation between groups. These results confirm that high-flow nasal oxygen maintains adequate oxygen levels during pre-oxygenation for rapid sequence induction.