Pre-oxygenation: the Hudson mask as an alternative technique

A Practical Solution for Preoxygenation in the Prehospital Setting: A Nonrebreather Mask with Flush Rate Oxygen

OBJECTIVE

Prehospital clinicians need a practical means of providing adequate preoxygenation prior to intubation. A bag-valve-mask (BVM) can be used for preoxygenation in perfect conditions but is likely to fail in emergency settings. For this reason, many airway experts have moved away from using BVM for preoxygenation and instead suggest using a nonrebreather (NRB) mask with flush rate oxygen.Literature on preoxygenation has suggested that a NRB mask delivering flush rate oxygen (on a 15 L/min O2 regulator, maximum flow, ∼50 L/min) is noninferior to BVM at 15 L/min held with a tight seal. However, in the prehospital setting, where emergency airway management success varies, preoxygenation techniques have not been deeply explored. Our study seeks to determine whether preoxygenation can be optimally performed with NRB at flush rate oxygen.

METHODS

We performed a crossover trial using healthy volunteers. Subjects underwent 3-min trials of preoxygenation with NRB mask at 25 L/min oxygen delivered from a portable tank, NRB at flush rate oxygen from a portable tank, NRB with flush rate oxygen from an onboard ambulance tank, and BVM with flush rate oxygen from an onboard ambulance tank. The primary outcome was the fraction of expired oxygen (FeO2). We compared the FeO2 of the BVM-flush to other study groups, using a noninferiority margin of 10%.

RESULTS

We enrolled 30 subjects. Mean FeO2 values for NRB-25, NRB-flush ambulance, NRB-flush portable, and BVM-flush were 63% (95% confidence interval [CI] 58-68%), 74% (95%, CI 70-78%), 78% (95%, CI 74-83%), and 80% (95%, CI 75-84%), respectively. FeO2 values for NRB-flush on both portable tank and ambulance oxygen were noninferior to BVM-flush on the ambulance oxygen system (FeO2 differences of 1%, 95% CI -3% to 6%; and 6%, 95% CI 1-10%). FeO2 for the NRB-25 group was inferior to BVM-flush (FeO2 difference 16%, 95% CI 12-21%).

CONCLUSIONS

Among healthy volunteers, flush rate preoxygenation using NRB masks is noninferior to BVM using either a portable oxygen tank or ambulance oxygen. This is significant because preoxygenation using NRB masks with flush rate oxygen presents a simpler alternative to the use of BVMs. Preoxygenation using NRB masks at 25 L/min from a portable tank is inferior to BVM at flush rate.

A modified Montpellier protocol for intubating intensive care unit patients is associated with an increase in first-pass intubation success and fewer complications

BACKGROUND

The Montpellier protocol for intubating patients in the intensive care unit (ICU) is associated with a decrease in intubation-related complications. We sought to determine if implementation of a simplified version of the Montpellier protocol that removed selected components and allowed for a variety of pre-oxygenation modalities increased first-pass intubation success and reduced intubation-related complications.

METHODS

A prospective pre/post-comparison of a modified Montpellier protocol in two medical and one medical/surgical/cardiac ICU within a hospital system. The modified eight-point protocol included: fluid administration, ordering sedation, two intubation trained providers, pre-oxygenation with non-invasive positive pressure ventilation, nasal high flow cannula or non-rebreather mask, rapid sequence intubation, capnography, sedation administration, and vasopressors for shock.

RESULTS

Patient characteristics and indications for intubation were similar for the 275 intubations in the control (137) and intervention (138) periods. In the intervention vs. control periods, the modified Montpellier protocol was associated with a significant 16.2% [95% CI: 5.1-30.0%] increase in first-pass intubation success and a 12.6% [95% CI: 1.2-23.6%] reduction in all intubation-related complications.

CONCLUSION

A simplified version of the Montpellier intubation protocol for intubating ICU patients was associated with an improvement in first-pass intubation success rates and a reduction in the rate of intubation-related complications.

Evaluation of the self-inflating bag-valve-mask and non-rebreather mask as preoxygenation devices in volunteers

OBJECTIVE

To evaluate and compare the effectiveness and tolerability of preoxygenation with the self-inflating bag-valve-mask (BVM) and non-rebreather mask (NRM) as are used before emergency anaesthesia.

DESIGN

Device performance evaluation.

SETTING

Experimental study.

PARTICIPANTS

12 male and 12 female healthy volunteers (age range 24-47) with no history of clinically significant respiratory disease.

INTERVENTIONS

End-expiration oxygen measurements (F(E)O(2)) after 3 min of preoxygenation with BVM (without mechanical assistance) and NRM devices. Mask pressures were measured and subjective difficulty of breathing was also assessed with a visual analogue score (VAS).

PRIMARY AND SECONDARY OUTCOME MEASURES

The final F(E)O(2) achieved was 58.0% (SD 7.3%) for the NRM compared to 53.1% (SD 13.4%) for the BVM (p=0.072). Preoxygenation was associated with small increases in F(E)CO(2) that were greater for the BVM (0.50%; 95% CI 0.48 to 0.52) than the NRM (0.29%; 95% CI 0.31 to 0.28); this difference was statistically significant (p=0.028). Both devices were well tolerated on VAS assessment of difficulty of breathing although this was higher for the BVM than the NRM (median VAS 1.85/10 compared to 1.1/10; p=0.041). Inspiratory and expiratory mask pressures were higher for the BVM.

CONCLUSIONS

In healthy volunteers, the NRM performs comparably to the BVM in terms of the degree of denitrogenation achieved although neither performed well. Although it was well tolerated, the BVM was subjectively more difficult to breathe through and was associated with greater mask pressures and a small increase in F(E)CO(2) consistent with hypoventilation or rebreathing. Our results suggest that preoxygenation with the NRM may be a preferable approach in spontaneously breathing patients.

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.

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%.

Routine pre-oxygenation using a Hudson mask. A comparison with a conventional pre-oxygenation technique

Two techniques of pre-oxygenation were studied by continuous analysis of respired gases using a mass spectrometer in 10 healthy volunteers. The first was a conventional technique as commonly used in anaesthesia with a Bain system and tightly-fitting anaesthetic face-mask and an oxygen flow of 8 l.min-1. The second technique also used a Bain system with an oxygen flow of 8 l.min-1, but with a Hudson mask attached. The mean fractional end-tidal oxygen concentrations after 3 min were 0.812 and 0.46 respectively for each of the pre-oxygenation techniques against 0.16 for subjects breathing air. This represents a considerable increase in pulmonary oxygen reserve for both techniques. The second technique is not an alternative to conventional pre-oxygenation for emergency anaesthesia, but is a useful and simple method that is acceptable to both patient and anaesthetist in routine cases.

End-tidal oxygen measurement compared with patient factor assessment for determining preoxygenation time

Time to adequate preoxygenation was assessed in 200 elective surgical patients, using measurement of end-tidal oxygen concentration. A variety of patient factors were assessed as to their ability to predict the time required to preoxygenate a patient. Of the 200 patients, 23 (11.5%) were unable to be adequately preoxygenated; most of these cases were due to a poor mask fit. The average time for preoxygenation was 154 seconds (range 43-364 seconds). Of those patients who could be preoxygenated, 46 (23%) required more than three minutes. Although a regression equation could be constructed to calculate time required for preoxygenation, the wide standard errors of the coefficients preclude a clinically useful predictive equation. We thus found that we could not accurately predict time required for preoxygenation and that a routine three minutes preoxygenation may not be sufficient for many patients. However, the measurement of end-tidal oxygen concentration is a very useful method of determining the end-point for preoxygenation.