Preoxygenation with tidal volume and deep breathing techniques: the impact of duration of breathing and fresh gas flow

Apneic Oxygenation: A Summarized Review and Stepwise Approach

Apneic oxygenation is a technique used during airway management procedures to maintain oxygenation and prevent desaturation during a lack of ventilation. Despite its importance, there is a lack of comprehensive information on how to achieve effective apneic oxygenation, leading to misunderstandings and suboptimal utilization of this technique. Apneic oxygenation involves several key steps. Firstly, patient selection is crucial, considering factors such as anticipated difficulty with airway management, reduced functional residual capacity, increased oxygen consumption, and medical conditions associated with impaired oxygenation. Secondly, adequate preoxygenation is essential to optimize oxygen reserves before the onset of apnea, utilizing methods like non-rebreather oxygen masks or specific breathing techniques. Thirdly, maintaining airway patency through techniques such as jaw thrust or nasopharyngeal airway placement allows for unobstructed airflow during the apneic period. Lastly, the selection of the appropriate oxygen delivery method, such as high-flow nasal oxygen or nasal cannula, depends on the patient's existing respiratory support. Despite the growing body of literature on apneic oxygenation, current review articles often lack a stepwise approach for its proper execution. This knowledge gap contributes to the misunderstanding and underutilization of this important tool during intubation and airway management. In conclusion, apneic oxygenation is a valuable technique for maintaining oxygenation during periods of apnea. However, the lack of comprehensive information and stepwise guidance in the current literature hinders its optimal utilization. Clear guidelines and educational resources should be developed to address this knowledge gap and ensure the safe and effective implementation of apneic oxygenation. By following a stepwise approach that includes patient selection, adequate preoxygenation, airway patency, and appropriate oxygen delivery, healthcare providers can enhance patient outcomes and minimize the risk of desaturation during airway management procedures.

A quasi-experimental study of fresh oxygen flow on patients' oxygen reserve during mask-assisted ventilation under general anesthesia induction

Background

To compare the effect of different amounts of fresh oxygen flow on oxygen reserve in patients undergoing general anesthesia.

Methods

Seventy-two patients were enrolled in this quasi-experimental study. Patients were randomly divided into experimental groups with a fresh oxygen flow of 1 L/min, 2 L/min, 4 L/min, and 8 L/min (denoted as G1, G2, G3, and G4, respectively) for 2 min of mask-assisted ventilation. Safe apnea time (SAT) was the primary endpoint; SAT was defined as the time from the cessation of ventilation to the time the patient's pulse oxygen saturation (SpO2) decreased to 90%. Ventilation indicators such as end-tidal oxygen concentration (EtO2), end-tidal carbon dioxide partial pressure (EtCO2), SpO2, and carbon dioxide (CO2) elimination amount, during mask-assisted ventilation, were the secondary endpoints.

Results

The SAT of G1, G2, G3, and G4 were 305.1 ± 97.0 s, 315 ± 112.5 s, 381.3 ± 118.6 s, and 359 ± 104.4 s, respectively (p > 0.05). The EtO2 after 2 min of mask-assisted ventilation in groups G1, G2, G3, and G4 were 69.7 ± 8.8%, 75.2 ± 5.0%, 82.5 ± 3.3%, and 86.8 ± 1.5%, respectively (p < 0.05). Also, there was a moderate positive correlation between the fresh oxygen flow and EtO2 (correlation coefficient r = 0.52, 95% CI 0.31-0.67, p < 0.0001). The CO2 elimination in the G1 and G2 groups was greater than that in the G4 group (p < 0.05). There was no significant difference in other indicators among the groups (all p > 0.05).

Conclusion

The amount of fresh oxygen flow during mask-assisted ventilation was positively correlated with EtO2. Also, even though there was no significant difference, the patients' oxygen reserves increased with the increase in fresh oxygen flow.

Effectiveness of Face mask only oxygenation and apnoeic oxygenation in addition to face mask in sustaining PaO2 during rapid sequence induction - A randomized control trial

Background and Aims

Apnoeic oxygenation, although useful during elective intubations, has not shown consistent beneficial results during emergency intubations in critically ill patients. We aimed to study the effectiveness of adding apnoeic oxygenation to our routine practice of using facemask alone, in emergency laparotomy patients needing rapid sequence induction (RSI), for sustaining partial pressure of oxygen (PaO2).

Material and Methods

Seventy-two patients undergoing RSI for emergency laparotomy were randomly allocated to either receive pre-oxygenation with 5 L/min of oxygen (O2) with a facemask (Group-FM) or apnoeic oxygenation with 10 L/min of O2 through a nasal catheter in addition to pre-oxygenation (Group-NC). Apnoea (90 s) was allowed from the removal of the facemask before the resumption of ventilation. Arterial blood gas analysis was done at the baseline, following pre-oxygenation and after 90 s of apnoea to study the PaO2 and partial pressure of carbon dioxide (PaCO2). The circuit O2 concentrations (fraction of inspired [FiO2] and end-tidal [EtO2]) were also noted to ensure a steady state of O2 uptake was reached.

Results

The circuit O2 concentrations were 90 ± 4% in group FM and 93 ± 5% in Group-NC. The FiO2-EtO2 difference was 4% in both groups. During the 90 s apnoea following pre-oxygenation, there was a fall in the PaO2 by 38% in Group-FM and 12% in Group-NC (P = 0.000). Increase in PaCO2 was similar in both groups (Group-FM: 44 [range: 32-55] mmHg; Group-NC: 42 [range: 33-54] mmHg, P = 0.809).

Conclusion

Apnoeic insufflation of O2 using a nasopharyngeal catheter along with facemask oxygenation is more effective in sustaining PaO2 for 90 s during RSI than facemask-only oxygenation in patients undergoing emergency laparotomy.

Deep breathing alleviates propofol-induced pain: a prospective, randomized, single-blind study

PURPOSE

Propofol is commonly used to induce general anesthesia; however, the pain caused during propofol injection is a disadvantage. This study aimed to assess whether deep breathing attenuates propofol injection pain.

METHODS

This prospective, single-blind, randomized controlled study included 200 patients who were scheduled to undergo elective surgery under general anesthesia and randomly and equally divided them into group D and group C. The observers were not blinded to the pain-relieving modality, but each patient was blinded. Group D patients were requested to repeatedly take deep breaths throughout general anesthesia induction with propofol. Group C patients were requested to breathe in the usual manner. The intensity of propofol injection pain was evaluated using the visual analog scale (VAS). Furthermore, we recorded the patients' pain expressions, including grimace or hand-withdrawal, and the recalled pain measured using a VAS in the post-anesthetic care units (PACU).

RESULTS

Compared with patients in group C, those in group D showed significantly reduced VAS scores for propofol injection pain (20 [interquartile range (IQR): 0-48] vs. 37 [IQR 9-65], P = 0.017) and recalled pain in the PACU (16 [IQR 0-32] vs. 26 [IQR 0.5-51], P = 0.031). Further, the grimace incidence was significantly lower in group D (18%) than in group C (45%) (P < 0.001). There was no significant difference in the incidence of pain at induction, recalled pain, or hand-withdrawal.

CONCLUSIONS

Deep breathing could be an easy, safe, and inexpensive method for reducing pain during propofol injection.

Effect of high fresh gas flow and pattern of breathing on rapid preoxygenation

Background and Aims:

Preoxygenation is supplementation of 100% oxygen prior to induction of general anaesthesia to increase the body’s oxygen stores. Efficacy of preoxygenation can be increased by optimising fresh gas flow (FGF) rate and pattern of breathing.

Methods:

Based on pattern of breathing—Tidal Volume Breathing (TVB) or Deep Breathing (DB) and FGF-10 L/min or 15 L/min—100 subjects of the American Society of Anesthesiologists physical status I/II posted for elective surgery were recruited and randomised into four groups: T10 - TVB with 10 L/min; D10 - DB with 10 L/min; T15 - TVB with 15 L/min; and D15 - DB with 15 L/min. A tight-fitting anaesthesia mask along with continuous positive airway pressure of 5 cm of H₂O with 20° head-up was used for preoxygenation. The total time taken and the total number of breaths required to achieve end tidal oxygen concentration (EtO₂) of 90% were noted. Exhaled tidal volume (Vte), end tidal carbon dioxide, fraction of inspired oxygen, and EtO₂ were recorded at each breath. Analysis of variance (ANOVA) was used for inferential statistics and Tukey’s honestly significant difference (HSD) test was used to calculate mean difference in total time and number of breaths amongst the groups.

Results:

Total time taken was significantly low (P < 0.001) in DB compared to TVB (D10: 70.2 ± 19.91, D15: 68.4 ± 20.27 vs T10: 112.28 ± 47.96, T15: 113.6 ± 48.57 seconds). Number of breaths was significantly high (P < 0.001) in TVB with 22.84 ± 8.73, 23.76 ± 11.64, 10.56 ± 3.69, and 8.32 ± 1.8 in T10, T15, D10 and D15, respectively. Vte was significantly low in TVB (P < 0.001).

Conclusion:

Rapid preoxygenation can be achieved by DB at high FGF of a minimum of 10 L/min.

How early warning with the Oxygen Reserve Index (ORi™) can improve the detection of desaturation during induction of general anesthesia?

The Oxygen Reserve Index (ORi™) is a dimensionless parameter with a value between 0 and 1. It is related to the real-time oxygenation status in the moderate hyperoxic range. The purpose of this study is to investigate the added warning time provided by different ORi alarm triggers and the continuous trends of ORi, SpO₂, and PaO₂. We enrolled 25 patients who were scheduled for elective surgery under general anesthesia with planned arterial catheterization before induction. The participants received standardized preoxygenation, induction, and intubation. The patients remained apneic and ventilation was resumed when the SpO₂ fell below 90%. The ORi and SpO₂ were recorded every ten seconds and arterial blood was sampled every minute, from preoxygenation to resumed ventilation. Alarm triggers set to the ORi peak and the ORi 0.55 values provided 300 and 145 s of significant added warning time compared to SpO₂ (p < 0.0001). The coefficient of determination was 0.56 between the ORi and the PaO₂ ≤ 240 mmHg and showed a positive correlation. The ORi enables the clinicians to monitor the patients' oxygen status during induction of general anesthesia and can improve the detection of impending desaturation. However, further studies are needed to assess its clinical potential in the high hyperoxic range.The protocol was retrospectively registered at ClinicalTrials.gov on July 21, 2021 (NCT04976504).

Effect of anesthesia induction on cerebral tissue oxygen saturation in hypertensive patients: an observational study

OBJECTIVE

In hypertensive patients, the autoregulation curve shifts rightward, making these patients more sensitive than normotensive individuals to hypotension. Hypotension following the induction of anesthesia has been studied in normotensive patients to determine its effects on brain tissue oxygenation, but not enough studies have examined the effect of hypotension on brain oxygenation in hypertensive patients. The current study aimed to use near-infrared spectroscopy to evaluate brain tissue oxygen saturation after the induction of anesthesia in hypertensive patients, who may have impaired brain tissue oxygen saturation.

METHODS

The study included a total of 200 patients aged > 18 years old with ASA I-III. Measurements were taken while the patient was breathing room air, after the induction of anesthesia, when the lash reflex had disappeared following the induction of anesthesia, after intubation, and in the 5th, 10th, and 15th minutes of surgery. The patients were divided into nonhypertensive and hypertensive groups.

RESULTS

There was a significant difference in age between the groups (p = 0.000). No correlation was found between cerebral tissue oxygen saturation and age (r = 0.015, p = 0.596). Anesthesia induction was observed to decrease mean arterial blood pressure in both groups (p = 0.000). Given these changes, there was no significant difference in brain tissue oxygen saturation between the nonhypertensive and hypertensive groups (p > 0.05).

CONCLUSION

There was no difference between hypertensive and normotensive groups in terms of the change rates in cSO₂ values. However, there was a difference between the groups in terms of cSO₂ values.

Oxygenation before Endoscopic Sedation Reduces the Hypoxic Event during Endoscopy in Elderly Patients: A Randomized Controlled Trial

Background: Sedation endoscopy increases patient and examiner satisfaction but involves complications. The most serious complication is hypoxia, the risk factors for which are old age, obesity, and American Society of Anesthesiologists physical status of 3 or greater. However, clear evidence of oxygenation during sedation endoscopy for elderly people is lacking in US, European, and Korean guidelines. Method: This study was conducted for 1 year starting in August 2018 to evaluate whether pre-oxygenation use 1 min before sedation endoscopy could reduce the incidence of hypoxia in patients older than 65 years of age. A total of 70 patients were divided into the non-oxygenated group (n = 35; control group) and oxygen-treated group (n = 35; experimental group) during endoscopy. Result: The incidence of hypoxia was 28 (80%) in the control group versus 0 (0%) in the pre-oxygenated group. Factors related to hypoxia in the non-oxygenated group were a relatively high dose of midazolam and concomitant injection with narcotic analgesics such as pethidine. Conclusion: The incidence of hypoxia during sedation endoscopy is high in patients over 65 years, but oxygenation during endoscopic sedation in elderly people can significantly reduce the incidence of intraprocedural hypoxic events.

Comparison of preoxygenation efficiency with Intersurgical Economy and Intersurgical QuadraLite anaesthetic face masks

BACKGROUND

Sufficient preoxygenation prevents arterial oxygen desaturation prior to intubation. An optimally sealed facemask is necessary for fast preoxygenation. The study was aimed at comparing the efficiency of preoxygenation using two different face masks.

MATERIALS AND METHODS

In 2018, a prospective study was conducted. Patients were classified into two groups: group A - Intersurgical Economy face masks, group B - Intersurgical QuadraLite masks. The circuit was flushed with 100% O2 for 30s, preoxygenation started with flow of 8l/min, FiO2100. The patients were asked to breathe deeply. Fentanyl (1-2 mcg/kg) was administered to increase mask toleration. End-tidal oxygen concentration (EtO2) ≥90% was the goal. EtO2 was monitored after 30, 60, 90, 120, 180, 210, 240, 270 and 300 seconds. Data was analyzed using the Independent-Samples T-test and the Mann-Whitney-U test.

RESULTS

Twelve patients were enrolled in group A and 19 in group B. Differences in sex, age, BMI and Mallampati class in the groups were statistically insignificant (p = 0.13, 0.39, 0.65, 0.43 respectively). Patients assigned to ASA I - 25.8% (n = 8->2/6), ASA II - 71.0 % (n = 22->10/12), ASA III - 3.2% (n = 1->0/1), p = 0.64. The success rate of preoxygenation to EtO290 within 5 min was statistically significantly different in the groups, with 33.3% in group A and 94.7% in group B (p < 0.01). Mean time to EtO290 was 228.3 ± 104.0/164.4 ± 84.3. Mean EtO2 after: 30s - 56.0 ± 13.5/69.3 ± 11.2 (p < 0.01); 60s - 63.8 ± 15.3/76.1 ± 11.7 (p = 0.02), 90s - 67.8 ± 17.7/80.7 ± 10.1 (p = 0.03); 120s-69.6 ± 18.2/83.4 ± 10.0 (p = 0.03), 150s-71.1 ± 19.0/87.1 ± 6.5 (p = 0.01); 180s - 72.9 ± 16.8/88.5 ± 5.3 (p = 0.01), 210s - 72.6 ± 18.0/89.2 ± 5.1 (p < 0.01); 240s - 74.17 ± 15.4/90.0 ± 4.3 (p < 0.01), 270s-76.3 ± 16.3/90.2 ± 3.6; 300s - 77.8 ± 14.6/90.2 ± 1.5 (p < 0.01).

CONCLUSIONS

Preoxygenation was significantly more efficient and faster with Intersurgical QuadraLite face masks.

Efficacy of preoxygenation using tidal volume breathing: a comparison of Mapleson A, Bain's and Circle system

Background

Methods

Results

Conclusions

[Efficacy of preoxygenation using tidal volume breathing: a comparison of Mapleson A, Bain's and Circle system]

BACKGROUND

Efficacy of preoxygenation depends upon inspired oxygen concentration, its flow rate, breathing system configuration and patient characteristics. We hypothesized that in actual clinical scenario, where breathing circuit is not primed with 100% oxygen, patients may need more time to achieve EtO₂≥90%, and this duration may be different among various breathing systems. We thus studied the efficacy of preoxygenation using unprimed Mapleson A, Bain's and Circle system with tidal volume breathing at oxygen flow rates of 5L.min^-1 and 10L.min^-1.

METHODS

Patients were randomly allocated into one of the six groups, wherein they were preoxygenated using either Mapleson A, Bain's or Circle system at O₂ flow rate of either 5L.min^-1 or 10L.min^-1. The primary outcome measure of our study was the time taken to achieve EtO₂≥90% at 5 and 10L.min^-1 flow rates.

RESULTS

At oxygen flow rate of 5L.min^-1, time to reach EtO₂≥90% was significantly longer with Bain's system (3.7±0.67min) than Mapleson A and Circle system (2.9±0.6, 3.3±0.97min, respectively). However at oxygen flow rate of 10L.min^-1 this time was significantly shorter and comparable among all the three breathing systems (2.33±0.38min with Mapleson, 2.59±0.50min with Bain's and 2.60±0.47min with Circle system).

CONCLUSIONS

With spontaneous normal tidal volume breathing at oxygen flow rate of 5L.min^-1, Mapleson A can optimally preoxygenate patients within 3min while Bain's and Circle system require more time. However at O₂ flow rate of 10L.min^-1 all the three breathing systems are capable of optimally preoxygenating the patients in less than 3min.

Low-positive pressure ventilation improves non-hypoxaemic apnoea tolerance during ear, nose and throat pan-endoscopy: A randomised controlled trial

BACKGROUND

It has been suggested that oxygenation using pressure support ventilation (PSV) before general anaesthesia can reduce the duration of non-hypoxaemic apnoea.

OBJECTIVE

The objective was to determine whether or not pre-oxygenation with PSV increases the duration of non-hypoxaemic apnoea in non-obese patients during pan-endoscopy.

DESIGN

A randomised, controlled trial.

SETTING

Amiens University Hospital, France.

PATIENTS

Fifty patients scheduled for ENT pan-endoscopy with a BMI lower than 35  kg  m(-2).

INTERVENTION

Patients scheduled for pan-endoscopy were enrolled to receive either 100% oxygen at neutral pressure (the control group) or 100% oxygen with positive-pressure ventilation (a positive inspiratory pressure of 4  cmH2O and a positive end-expiratory pressure of 4  cmH2O; the PSV group) during spontaneous ventilation with a face mask. The goal of pre-oxygenation was to obtain an end-tidal oxygen concentration of more than 90% prior to induction of anaesthesia.

MAIN OUTCOME MEASURES

The primary efficacy criterion was the duration of non-hypoxaemic apnoea (i.e. before the peripheral capillary oxygen saturation fell to 90%). Secondary outcomes were duration of pre-oxygenation, pre-oxygenation failure and tolerance.

RESULTS

The mean (interquartile range) duration of non-hypoxaemic apnoea was longer in the PSV group [598 (447 to 717) s] than in the control group [310 (217 to 451) s] (P < 0.001). Oxygenation time was shorter in the PSV group [190 (159 to 225) s] than in the control group [245 (151 to 435) s] (P = 0.037). Pre-oxygenation was unsuccessful (i.e. end-tidal oxygen concentration was < 90%) in 20% of the patients in the control group but none in the PSV group. The intergroup difference in the duration of pan-endoscopy was not significant. Tolerance was good or very good in all patients.

CONCLUSION

Our results show that pre-oxygenation with PSV is associated with a longer duration of non-hypoxaemic apnoea and a lower frequency of manual reventilation during ENT pan-endoscopy. CLINICALTRIALS.

GOV REGISTRATION NUMBER

NCT02167334.

Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults

These guidelines provide a strategy to manage unanticipated difficulty with tracheal intubation. They are founded on published evidence. Where evidence is lacking, they have been directed by feedback from members of the Difficult Airway Society and based on expert opinion. These guidelines have been informed by advances in the understanding of crisis management; they emphasize the recognition and declaration of difficulty during airway management. A simplified, single algorithm now covers unanticipated difficulties in both routine intubation and rapid sequence induction. Planning for failed intubation should form part of the pre-induction briefing, particularly for urgent surgery. Emphasis is placed on assessment, preparation, positioning, preoxygenation, maintenance of oxygenation, and minimizing trauma from airway interventions. It is recommended that the number of airway interventions are limited, and blind techniques using a bougie or through supraglottic airway devices have been superseded by video- or fibre-optically guided intubation. If tracheal intubation fails, supraglottic airway devices are recommended to provide a route for oxygenation while reviewing how to proceed. Second-generation devices have advantages and are recommended. When both tracheal intubation and supraglottic airway device insertion have failed, waking the patient is the default option. If at this stage, face-mask oxygenation is impossible in the presence of muscle relaxation, cricothyroidotomy should follow immediately. Scalpel cricothyroidotomy is recommended as the preferred rescue technique and should be practised by all anaesthetists. The plans outlined are designed to be simple and easy to follow. They should be regularly rehearsed and made familiar to the whole theatre team.

Age correlates with hypotension during propofol-based anesthesia for endoscopic retrograde cholangiopancreatography

OBJECTIVE

Endoscopic retrograde cholangiopancreatography (ERCP) is a procedure used for diagnostic and therapeutic purposes. Most of the patients may feel pain, anxiety, and discomfort during this procedure, so conscious sedation is usually used during ERCP. General anesthesia would be considered if conscious sedation fails to achieve the requirement of the endoscopists. Several studies showed that propofol-based sedation could provide a better recovery profile. However, propofol has a narrow therapeutic window and complications may occur beyond this window. The present study aimed to find out the complications and the associated risk factors during ERCP procedure under propofol-based deep sedation.

METHODS

We retrospectively reviewed data from anesthetic and procedure records of the patients who underwent ERCP under propofol-based deep sedation from January 2006 to July 2010 at Far Eastern Memorial Hospital, Taipei, Taiwan. All propofol-based deep sedations were conducted by anesthesiologists. The incidence of complications was determined and the independent risk factors identified by the multivariable logistic regression model.

RESULT

Propofol-based deep sedation was provided for 552 patients who received ERCP procedure. The majority of the patients were male, the mean age was 60 ± 16 years and American Society of Anesthesiologists physical status II-III. Almost 30% of patients experienced hypotension during the procedure, although no mortality or morbidity was associated with this complication. Sex, age, anesthetic time, American Society of Anesthesiologists status, hypertension, and arrhythmia were significantly different (p < 0.05) between patients with hypotension and without hypotension during the procedure. Multivariable logistic regression identified sex and age to be the independent predictors of hypotension.

CONCLUSION

Hypotension was the most frequent anesthetic complication during procedure under propofol-based deep sedation, but this method was safe and effective under appropriate monitoring. Age is the strongest predictor of hypotension and therefore propofol-based deep sedation should be conducted with caution in the elderly.

Comparison of margin of safety following two different techniques of preoxygenation

BACKGROUND AND AIMS

Shortening the duration of efficacious preoxygenation would provide benefit in emergency situations like fetal distress etc. This study aims to compare the margin of safety following preoxygenation using 8 vital capacity breaths (VCB) in 1 min and tidal volume breathing (TVB) for 3 min, by assessing changes in PaO2 and apnea induced desaturation time.

MATERIAL AND METHODS

Patients were randomly divided into Group A and B. In Group A, 3 min of TVB using O2 flow of 5 l/min and in Group B, 8 VCB in 60 s using O2 flow of 10 l/min were used. Anesthesia was induced in all patients with propofol followed by succinylcholine 2 mg/kg intravenously. Mask ventilation was not done and following intubation endotracheal tube was kept open to atmosphere. The time taken for the patients to desaturate to 90% was noted and immediately ventilation was resumed. Arterial blood gas samples were taken while patients were breathing room air, immediately after preoxygenation and at 90% desaturation.

RESULTS

Baseline PaO2 of both the groups were comparable. After preoxygenation Group B had a significantly high PaO2 value than Group A (439.05 ± 62.20 vs. 345.16 ± 20.80). At 90% desaturation there was no significant difference between groups. Group B showed a significantly high apnea induced desaturation time when compared to Group A (6.87 ± 1.78 vs. 3.47 ± 0.38 min).

CONCLUSIONS

Preoxygenation by 8 VCB in 1 min provides a greater margin of safety, as it results in a significantly high PaO2 with an almost doubled apnea induced desaturation time, in comparison with TVB for 3 min.

Techniques of preoxygenation in patients with ineffective face mask seal

Background:

Ineffective face mask seal is the most common cause for suboptimal pre-oxygenation. Room air entrainment can be more with vital capacity (VC) breaths when the mask is not a tight fit.

Aims:

This study was designed to compare 5 min tidal volume (TV) breathing and eight VC breaths in patients with ineffective face mask seal.

Methods:

Twenty eight ASA I adults with ineffective face mask seal were randomized to breathe 100% oxygen at normal TV for 5 min (Group TV) and eight VC breaths (Group VC) in a cross over manner through circle system at 10 L/min. End tidal oxygen concentration (EtO₂) and arterial blood gas analysis was performed to evaluate oxygenation with each technique.

Statistical and Analysis:

Data were analysed using SPSS statistical software, version 16. Friedman's two-way analysis of variance by ranks was used for non-parametric data.

Results:

Significant increase in EtO₂ (median 90) and PaO₂ (228.85) was seen in group TV when compared to group VC (EtO₂ median 85, PaO₂ 147.65), P<0.05. Mean total ventilation volume in 1 min in group VC was 9.4±3.3 L/min and more than fresh gas flow (10 L/min) in seven patients. In group TV, the fresh gas flow (50 L/5 min) was sufficient at normal TV (mean total ventilation in 5 min 36.7±6.3 L/min).

Conclusions:

TV breathing for 5 min provides better pre-oxygenation in patients with ineffective mask seal with fresh gas flow of 10 L/min delivered through a circle system.

What is the accuracy of the high-fidelity METI Human Patient Simulator physiological models during oxygen administration and apnea maneuvers?

BACKGROUND

A widely used physiological simulator is generally accepted to give valid predictions of oxygenation status during disturbances in breathing associated with anesthesia. We compared predicted measures with physiological measurements available in the literature, or derived from other models.

METHODS

Five studies were selected from the literature which explored arterial oxygenation, with or without preoxygenation, in clinical situations or through mathematical modeling as well as the evolution of the fraction of expired oxygen (Feo2) during preoxygenation maneuvers. Scenarios from these studies were simulated on the METI-Human Patient Simulator™ simulator, and the data were compared with the results in the literature.

RESULTS

Crash-induction anesthesia without preoxygenation induces an O2 pulse saturation (Spo2) decrease that is not observed on the METI simulator. In humans, after 8 minutes of apnea, Spo2 decreased below 90% while the worst value was 95% during the simulation. The apnea time to reach 85% was less with obese patients than with healthy simulated patients and was shortened in the absence of preoxygenation. However, the data in the literature include METI simulator confidence interval 95% values only for healthy humans receiving preoxygenation. The decrease in Pao2 during 35-second apnea started at end-expiration was slower on the METI simulator than the values reported in the literature. Feo2 evolution during preoxygenation maneuvers on the METI simulator with various inspired oxygen fractions (100%, 92%, 84%, and 68%) was very close to those reported in humans when perfect mask seal is provided. In practice, this seal is impossible to obtain on the METI simulator.

CONCLUSIONS

Spo2 decreased much later during apnea on the METI simulator than in a clinical situation, whether preoxygenation was performed or not. The debriefing after simulation of critical situations or the use of the METI simulator to test a new equipment must consider these results.

Anesthesia in prehospital emergencies and in the emergency department

PURPOSE OF REVIEW

Recently, notable progress has been made in the field of anesthesia drugs and airway management.

RECENT FINDINGS

Anesthesia in prehospital emergencies and in the emergency department is reviewed and guidelines are discussed.

SUMMARY

Preoxygenation should be performed with high-flow oxygen delivered through a tight-fitting face mask with a reservoir. Ketamine may be the induction agent of choice in hemodynamically unstable patients. The rocuronium antagonist sugammadex may have the potential to make rocuronium a first-line neuromuscular blocking agent in emergency induction. Experienced healthcare providers may consider prehospital anesthesia induction. Moderately experienced healthcare providers should optimize oxygenation, hasten hospital transfer and only try to intubate a patient whose life is threatened. When intubation fails twice, ventilation should be performed with an alternative supraglottic airway or a bag-valve-mask device. Lesser experienced healthcare providers should completely refrain from intubation, optimize oxygenation, hasten hospital transfer and ventilate patients only in life-threatening circumstances with a supraglottic airway or a bag-valve-mask device. Senior help should be sought early. In a 'cannot ventilate-cannot intubate' situation, a supraglottic airway should be employed and, if ventilation is still unsuccessful, a surgical airway should be performed. Capnography should be used in every ventilated patient. Clinical practice is essential to retain anesthesia and airway management skills.

[Inspiratory support versus spontaneous breathing during preoxygenation in healthy subjects. A randomized, double blind, cross-over trial]

OBJECTIVE

Applying an inspiratory support (AI) and a positive end expiratory pressure (PEP) could increase the effectiveness of the preoxygenation.

STUDY DESIGN

This randomized double blinded controlled study compares the impact on the expiratory oxygen fraction (FEO(2)) of two levels of AI with PEP to a traditional preoxygenation.

PATIENTS AND METHODS

Twenty healthy volunteers were studied. The criteria of exclusion were a body mass index >30, the presence of beard or moustache and the claustrophobia. Each subject went through three modes of preoxygenation during 3 minutes each in a random order: 1-spontaneous ventilation (VS), 2-preoxygenation with AI with 4 cmH(2)O/PEP 4 cmH(2)O (AI-4/PEP-4), 3-preoxygenation with AI with 6 cmH(2)O/PEP 4 cmH(2)O (AI-6/PEP-4). Subject's tolerance and leaks were also noted.

RESULTS

The FEO(2) at the end of the 3 minutes of preoxygenation was higher (p<0,001) with AI-4/PEP-4 (94+/-3%) and AI-6/PEP-4 (94+/-4%) than with technique VS (89+/-6%). One hundred percent and 90% of the participants reached one FEO(2)=90% with AI-4/PEP-4 and AI-6/PEP-4 respectively vs 65% with VS (p=0.0013). The participants tolerated better the VS and the AI-4/PEP-4 than the AI-6/PEP-4. More leaks were noted with the AI-6/PEP-4 than with the VS and the AI-4/PEP-4.

CONCLUSION

This study shows applying AI plus PEP during preoxygenation improves its effectiveness in the healthy subjects. It also suggests that, in a population of healthy volunteers, combination AI-4/PEP-4 is preferable to AI-6/PEP-4 because so effective, but better tolerated.

Factors influencing oxygen store during denitrogenation in the healthy patient

STUDY OBJECTIVE

To define the various factors that influence the rate of effective preoxygenation.

DESIGN

Prospective, randomized study.

SETTING

Procedure room in a teaching hospital.

SUBJECTS

14 ASA physical status I volunteers who performed 4 sessions of breathing in random order. Of these volunteers, 7 performed two extra sessions using vital capacity breathing, which were also completed in random order.

INTERVENTIONS

Using the circle system, volunteers breathed with a mouthpiece and nose-clip until expired nitrogen reached 5%, using either a fresh gas flow of 5 L/min or 10 L/min or a system flushed with O(2).

MEASUREMENTS

End-expired levels of O(2), nitrogen, and CO(2) were recorded.

MAIN RESULTS

Minute ventilation, functional residual capacity, and age were significant factors for rate of denitrogenation. However, height and weight were not significant factors in predicting time to denitrogenation. At low flow rates, flushing with O(2) significantly decreased the time of denitrogenation. There appeared to be little clinical benefit of flushing with O(2) when a 10 L/min O(2) flow was used.

CONCLUSIONS

A high gas flow rate appears critical to achieving rapid preoxygenation.

Optimizing preoxygenation in adults

PURPOSE

Preoxygenation increases oxygen reserves and duration of apnea without desaturation (DAWD), thus it provides valuable additional time to secure the airway. The purpose of this Continuing Professional Development (CPD) module is to examine the various preoxygenation techniques that have been proposed and to assess their effectiveness in healthy adults and in obese, pregnant, and elderly patients.

PRINCIPAL FINDINGS

The effectiveness of preoxygenation techniques can be evaluated by measuring DAWD, i.e., the time for oxygen saturation to decrease to <90%. Clinically, preoxygenation is considered adequate when end-tidal oxygen fraction is >90%. This is usually achieved with a 3-min tidal volume breathing (TVB) technique. As a rule, asking the patient to take four deep breaths in 30 sec (4 DB 30 sec) yields poorer results. Eight deep breaths in 60 sec (8 DB 60 sec) is equivalent to TVB 3 min. The DAWD is decreased in obese patients, pregnant women, and patients with increased metabolism. Obese patients may benefit from the head-up position and positive pressure breathing. A TVB technique is preferable in the elderly. Failure to preoxygenate is often due to leaks, which commonly occur in edentulous or bearded patients. In cases of difficult preoxygenation, directly applying the circuit to the mouth might be a useful alternative. Supplying extra oxygen in the nasopharynx during apnea might increase DAWD.

CONCLUSION

Since ventilation and tracheal intubation difficulties are unpredictable, this CPD module recommends that all patients be preoxygenated. The TVB 3 min and the 8 DB 60 sec techniques are suitable for most patients; however, the 4 DB 30 sec is inadequate.

Extending the preoxygenation period from 4 to 8 mins in critically ill patients undergoing emergency intubation

OBJECTIVE

To determine the effectiveness of increasing the preoxygenation period with 100% oxygen in the critically ill patient from 4 to 8 mins in preparation for emergency tracheal intubation.

DESIGN

Nonrandomized, controlled trial.

SETTING

Large, level one trauma center, tertiary care intensive care unit.

PATIENTS

Critically ill patients failing noninvasive respiratory support techniques who required tracheal intubation followed by mechanical ventilation.

INTERVENTIONS

A baseline arterial blood gas was obtained on noninvasive passive therapy and at 4, 6, and 8 mins of active preoxygenation efforts with 100% oxygen therapy with a noncollapsing resuscitator bag and mask. Best effort to achieve a tight fitting mask seal was pursued coupled with other mask ventilation maneuvers to optimize noninvasive oxygenation and ventilation.

MEASUREMENTS AND MAIN RESULTS

Thirty-four patients consecutively intubated by the author during the 7-month study period were studied. The baseline PaO2 (mean +/- SD) with concurrent noninvasive support was 61.9 +/- 14.6 mm Hg (range: 44-109 mm Hg) and increased a mean of 22 mm Hg to 83.8 +/- 51.5 mm Hg after 4 mins of preoxygenation (p < 0.01). Continued preoxygenation efforts (6 mins) increased the PaO2 to 88.2 mm Hg +/- 48.5 and after 8 mins to 92.7 mm Hg +/- 55.2. At the 8-min mark, 5 of 34 patients achieved > 10% increase in their PaO2 and only two patients increased their 4-min PaO2 by > or = 50 mm Hg after the additional 4 mins of preoxygenation. One quarter of the patients experienced a reduction in their PaO2 from the 4 to the 8-min time period. Nearly, 50% of the patients met the criteria for desaturation during the intubation procedure.

CONCLUSIONS

Extending the preoxygenation period from the customary 4 mins to either 6 or 8 min seems to be marginally effective in the majority of patient suffering from cardiopulmonary deterioration and such an extension may jeopardize oxygenation efforts in some patients.

The effectiveness of noninvasive positive pressure ventilation to enhance preoxygenation in morbidly obese patients: a randomized controlled study

BACKGROUND

Noninvasive positive-pressure ventilation (NPPV) with pressure support-ventilation and positive end-expiratory pressure are effective in providing oxygenation during intubation in hypoxemic patients. We hypothesized administration of oxygen (O2) using NPPV would more rapidly increase the end-tidal O2 concentration (ETO2) than preoxygenation using spontaneous ventilation (SV) in morbidly obese patients.

METHODS

Twenty-eight morbidly obese patients were enrolled in this prospective randomized study. Administration of O2 for 5 min was performed either with SV group or with NPPV (pressure support = 8 cm H2O, positive end-expiratory pressure = 6 cm H2O) (NPPV group). ETO2 was measured using the anesthesia breathing circuit, and is expressed as a fraction of atmospheric concentration. The primary end-point was the number of patients with an ETo(2) >95% at the end of O2 administration. Secondary end-points included the time to reach the maximal ETO2 and the ETO2 at the conclusion of O2 administration.

RESULTS

A larger proportion of patients achieved a 95% ETO2 at 5 min with NPPV than SV (13/14 vs 7/14, P = 0.01). The time to reach the maximal ETO2 was significantly less in the NPPV than in the SV group (185 +/- 46 vs 222 +/- 42 s, P = 0.02). The mean ETO2 at the conclusion of O2 administration was larger in the NPPV group than the SV group (96.9 +/- 1.3 vs 94.1 +/- 2.0%, P < 0.001). A modest, although significant, increase in gastric distension was observed in the NPPV group. No adverse effects were observed in either group.

CONCLUSION

Administration of O2 via a facemask with NPPV in the operating room is safe, feasible, and efficient in morbidly obese patients. In this population NPPV provides a more rapid O2 administration, achieving a higher ETO2.

[Airway management]

Managing the difficult airway poses an enormous challenge for anaesthesiologists, intensivists and A&E physicians, particularly because of the high probability of a potentially fatal outcome. Development and (pre-) clinical distribution of supraglottic airway devices (e.g. LMA, LT) and their enhancements, as well as the broad acceptance of awake fibre-optic intubation, led to a profound change in the strategy for managing the difficult airway. This is reflected in the revised ASA guidelines, implementing the use of the laryngeal mask airway and fibre-optic intubation. In view of the utmost importance of this topic the German Society of Anaesthesiology and Intensive Care Medicine (DGAI) framed an independent German guideline, considering German national terms and conditions. In analogy algorithms and guidelines of the ILCOR, ERC and ATLS were revised as well as those of many other national anaesthesiological boards. Nevertheless, massive national and international deficits exist in implementing these guidelines into practice and the implicated structural requirements with respect to education, reflection, team building and equipment concerning the individual institution.

Efficacy of preoxygenation using tidal volume and deep breathing techniques with and without prior maximal exhalation

PURPOSE

We evaluated the influence of prior maximal exhalation on preoxygenation in 15 adult volunteers using tidal volume breathing (TVB) for five minutes and deep breathing (DB) for two minutes with and without prior maximal exhalation.

METHODS

Inspired and end-tidal oxygen, nitrogen and carbon dioxide were monitored continuously and recorded during room air breathing and at 30-sec intervals during 100% oxygen TVB or DB (rate of 8 breaths.min(-1)).

RESULTS

Tidal volume breathing with prior maximal exhalation resulted in an end-tidal oxygen concentration (ETO(2)) slightly higher (P = 0.028) at 0.5 and 1.0 min as compared with TVB without prior maximal exhalation at the same time periods. Regardless of whether TVB was preceded by maximal exhalation or not, 2.5 min was required to reach a mean ETO(2) value of 90% or higher. With DB, there were no differences in ETO(2) values at any time period and 1.5 min was required to reach an ETO(2) of 90% or greater, with or without prior maximal exhalation.

CONCLUSIONS

Maximal exhalation prior to TVB slightly steepens the initial rise in ETO(2) during the first minute, but confers no real benefit if maximal preoxygenation is the goal. Maximal exhalation prior to DB has no added value in enhancing preoxygenation.

Clinical review: management of difficult airways

Difficulties or failure in airway management are still important factors in morbidity and mortality related to anesthesia and intensive care. A patent and secure airway is essential to manage anesthetized or critically ill patients. Oxygenation maintenance during tracheal intubation is the cornerstone of difficult airway management and is always emphasized in guidelines. The occurrence of respiratory adverse events has decreased in claims for injuries due to inadequate airway management mainly at induction of anesthesia. Nevertheless, claim reports emphasize that airway emergencies, tracheal extubation and/or recovery of anesthesia phases are still associated with death or brain damage, indicating that additional educational support and management strategies to improve patient safety are required. The present brief review analyses specific problems of airway management related to difficult tracheal intubation and to difficult mask ventilation prediction. The review will focus on basic airway management including preoxygenation, and on some oxygenation and tracheal intubation techniques that may be performed to solve a difficult airway.

When a leak is unavoidable, preoxygenation is equally ineffective with vital capacity or tidal volume breathing

PURPOSE

Ideally, preoxygenation is performed using a tight fitting mask either by breathing normally for three to five minutes or with four to eight vital capacity (VC) breaths in 0.5 to one minute, but in practice leaks are frequent and sometimes unavoidable. This study was designed to determine which breathing method provided the best oxygenation in the presence of leak.

METHODS

Twenty volunteers were instructed to breathe from a circle circuit supplied with 6 L x min(-1) of fresh oxygen. Each subject was tested under four situations selected in random order: 1) normal breathing for three minutes without leak; 2) normal breathing for three minutes with a leak; 3) four VCs in 30 sec without a leak; and 4) four VCs in 30 sec with a leak. The leak was created by a piece of size 18 French nasogastric tube, 5 cm long, taped under the face mask. Inspired and expired O(2) and CO(2) were sampled at the nostrils.

RESULTS

In the absence of a leak, the end-tidal oxygen fraction (F(EO(2)) was greater after three minutes of tidal breathing (89 +/- 3%; mean +/- SD) in comparison with the response to four VCs (76 +/- 7%; P < 0.001). Introduction of a leak decreased the F(EO(2)) significantly (P < 0.001). With a leak, the F(EO(2)) was similar with normal breathing (61 +/- 8%) and after four VCs (59 +/- 11%).

CONCLUSION

Preoxygenation with tidal volume breathing for three minutes yields higher F(EO(2)) in comparison to four VCs. If a small leak (4 mm internal diameter) is introduced, the F(EO(2)) decreases significantly with both breathing methods to approximately 60%.

Preoxygenation in critically ill patients requiring emergency tracheal intubation

OBJECTIVE

To determine the effectiveness of preoxygenation with 100% oxygen in the critically ill patient in preparation for emergency tracheal intubation.

DESIGN

Nonrandomized, controlled trial.

SETTING

Large, level 1 trauma center, tertiary care intensive care unit.

PATIENTS

Critically ill patients failing noninvasive respiratory support techniques who require tracheal intubation followed by mechanical ventilation.

INTERVENTIONS

A baseline arterial blood gas was obtained on noninvasive therapy and 4 mins post-100% oxygen therapy with a bag-mask assembly. Best effort to achieve a tight-fitting mask seal was pursued coupled with other mask ventilation maneuvers to optimize noninvasive oxygenation and ventilation.

MEASUREMENTS AND MAIN RESULTS

A total of 42 patients consecutively intubated during the 15-month study period were studied. The baseline Pao2 (mean +/- sd) with concurrent noninvasive support was 67 +/- 19.6 mm Hg (range, 43-88 mm Hg) and increased a mean of 37 mm Hg to 103.8 +/- 63.2 mm Hg after 4 mins of preoxygenation with 100% oxygen. A total of 36% of patients had minimal changes (+/-5%) in their baseline Pao2, and only 19% increased their baseline Pao2 by at least 50 mm Hg after preoxygenation maneuvers.

CONCLUSIONS

The critically ill patient has little reserve to tolerate interruption of oxygen delivery and, thus, is at risk for hypoxemia during emergency airway management. Preoxygenation efforts as described in this clinical trial appear to be marginally effective in regard to providing a reasonable safeguard against hypoxemia during laryngoscopy and endotracheal intubation.

Comparaison de la technique de préoxygénation à huit capacités vitales et à volume courant chez les patientes ayant une obésité morbide

OBJECTIVE

To compare two techniques of preoxygenation, eight deep breaths (8DB) and tidal volume breathing in obese patients by measuring end-tidal fractional oxygen concentration (FETO2) and apnea time from 100% of hemoglobin saturation to 95% (T95%).

STUDY DESIGN

Prospective randomized study.

METHODS

Twenty obese patients (BMI >40 kg/m2) without cardiorespiratory disease nor difficult intubation criteria were randomized into two groups of ten. One group received preoxygenation with eight deep breaths in one minute (8DB) and the other with three minutes tidal volume preoxygenation (3TV) both under FIO2 100%. FETO2 every minute of preoxygenation and T95% were measured. Data were analyzed with Mann and Whitney test. A p <0.05 was considered significant.

RESULT

There was no significant difference between the groups regarding FETO2 values [84 +/- 4% (8DB) and 88 +/- 5% (3TV)] and T95% [176 +/- 23 s (8DB) and 181 +/- 35 s (3TV)]. The PETCO2 was significantly inferior in the 8DB group at the end of preoxygenation [PETCO2 =29 +/- 1 mmHg (8DB) and PETCO2 =36 +/- 5 mmHg (3TV)].

CONCLUSION

8DB and 3TV preoxygenation techniques in morbid obese patients induce similar FETO2 and T95%. However hyperventilation effects in the 8DB group are unknown.

Oxygenation using tidal volume breathing after maximal exhalation

We compared, in volunteers, the oxygenation achieved by tidal volume breathing (TVB) over a 3-min period after maximal exhalation with that achieved by TVB alone. Twenty-three healthy volunteers underwent the two breathing techniques in a randomized order. A circle absorber system with an oxygen flow of 10 L/min was used. The end-expiratory oxygen concentration (EEO(2)) was monitored at 15-s intervals up to 3 min. TVB after maximal exhalation produced EEO(2) values of 68% +/- 5%, 75% +/- 5%, and 79% +/- 4% at 30, 45, and 60 s, respectively, which were significantly larger (P < 0.05) than the corresponding values obtained with TVB alone (58% +/- 5%, 66% +/- 6%, and 71% +/- 5%, respectively). In both techniques, the EEO(2) increased exponentially, with time constants of 35 s during TVB after maximal exhalation versus 58 s during TVB without prior maximal exhalation. In conclusion, maximal exhalation before TVB can hasten preoxygenation by decreasing the nitrogen content of the functional residual capacity, with a consequent increase of EEO(2) to approximately 70% in 30 s and 80% in 60 s.

IMPLICATIONS

Oxygenation by using maximal exhalation before tidal volume breathing produced a significantly faster increase in end-expiratory oxygen concentration than oxygenation with tidal volume breathing alone.

[Preoxygenation and upper airway patency control]

During preoperative assessment, risk factors of upper airway obstruction should be evaluated: respiratory insufficiency, low O(2) reserve, preoxygenation failure or difficult face mask ventilation. In healthy subjects, spontaneous breathing O(2) for 3 min is the reference method. Apnoea duration is longer after preoxygenation than after denitrogenation, even if FEO(2) and SpO(2) do not change during the two last minutes of preoxygenation. The apnea time is longer after 3 min spontaneous breathing than after four deep breaths for 1 min in most of the literature. Maximal breathing during 2 min can produce values comparable to those obtained with tidal volume breathing for 3 min. FEO(2) monitoring is helpful in the assessment of preoxygenation quality: In case of oxygenation impairment during anaesthesia induction, algorithm use is helpful. Because desperate emergencies will occur in association with anaesthesia, every location should have the immediate availability of Fastrach and trans tracheal ventilation. Every anaesthesiologist should be familiar with and well practised in a variety of airway management techniques. Teaching programs are organised in order to develop anaesthesiologist sensitisation and skill.

Anesthesia for tracheal and endobronchial interventions

Tracheal and endobronchial interventions constitute a wide variety of procedures offering unique challenges in perioperative airway management and ventilatory support. Elective or emergent anesthetic management is individualized according to underlying airway pathology, coexisting disease, and patient age. This review explores recent literature and reports on relevant advances in anesthetic care.