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.     

Efficacy of preoxygenation with tidal volume breathing. Comparison of breathing systems

BACKGROUND: Preoxygenation before tracheal intubation is intended to increase oxygen reserves and delay the onset of hypoxemia during apnea. Various systems are used for preoxygenation. Designed specifically for preoxygenation, the NasOral system uses a small nasal mask for inspiration and a mouthpiece for exhalation. One-way valves in the nasal mask and the mouthpiece ensure unidirectional flow. This investigation compares the efficacy of preoxygenation using the standard circle system with the NasOral system and five different resuscitation bags. METHODS: Twenty consenting, healthy volunteers were studied in the supine position for 5-min periods of tidal volume breathing using the circle absorber system, the NasOral system, and five resuscitation bags in a randomized order. Data were collected during room air breathing and at 30-s intervals during 5 min of oxygen administration. Inspired oxygen, end-tidal oxygen, and end-tidal nitrogen were measured by mass spectrometry. RESULTS: At 2. 5 min of oxygenation, end-tidal oxygen plateaued at 88.1 +/- 4.8 and 89.3 +/- 6.4% (mean +/- SD) for the circle absorber and NasOral systems, respectively. This was associated with inverse decreases in end-tidal nitrogen. At no time did these end-tidal oxygen or nitrogen values differ from each other. Three of the resuscitation bags (one disk type and two duck-bill type with one-way exhalation valves) delivered inspired oxygen more than 90%, and the end-tidal oxygen plateaued between 77 and 89% at 2 min of tidal volume breathing. The other two resuscitation bags (both duck-bill bags without exhalation valves) delivered inspired oxygen less than 40%, and the end-tidal oxygen values ranged between 21.8 +/- 5.0 and 31.9 +/- 8.7%. CONCLUSIONS: The circle absorber and NasOral systems were equally effective in achieving maximal preoxygenation during tidal volume breathing. Resuscitation bags differed markedly in effectiveness during preoxygenation; those with duck-bill valves without one-way exhalation valves were the least effective. Thus, the use of these bags should be avoided for preoxygenation.     

Comparison of eight deep breaths and tidal volume breathing preoxygenation techniques in morbid obese patients

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.     

Total oxygen uptake with two maximal breathing techniques and the tidal volume breathing technique: a physiologic study of preoxygenation

BACKGROUND: Three common methods for preoxygenation are 3 min of tidal breathing, four deep breaths taken within 30 s (4DB), and eight deep breaths taken within 60 s (8DB). This report compares these three techniques in healthy volunteers. METHODS: Five healthy subjects breathed through a mouthpiece and wore a nose clip; oxygen was delivered at 180 l/min via a low-resistance T-piece. Each subject repeated each of the three oxygenation techniques four times. The end-tidal fraction of oxygen was measured, and the oxygen uptake at the mouth was measured breath by breath. The additional difference between oxygen uptake at the mouth during the period of breathing oxygen (as compared with that during air breathing) was taken to represent the total oxygen sequestrated into body stores. RESULTS: The mean +/- SD maximum end-tidal fraction of oxygen after the 4DB method was 0.83 +/- 0.09, which was significantly less than either after the 3-min method (0.92 +/- 0.01; P < 0.04) or after the 8DB method (0.91 +/- 0.04; P < 0.03). The mean additional oxygen taken up during oxygenation with the 4DB method was 1.67 +/- 0.45 l, which was significantly lower than with the 3-min method (2.23 +/- 0.85 l; P < 0.04) or with the 8DB method (2.53 +/- 0.74 l; P < 0.01). There were no significant differences for these variables between the 3-min and 8DB methods. CONCLUSIONS: For the physiologic measurements that were made, both the 3-min and the 8DB method are superior to the 4DB method. The 3-min and 8DB methods seem to be equally effective.     

Preoxygenation: comparison of maximal breathing and tidal volume breathing techniques.

BACKGROUND: Preoxygenation with tidal volume breathing for 3-5 min is recommended by Hamilton and Eastwood. This report compares tidal volume preoxygenation technique with deep breathing techniques for 30-60 s. METHODS: The study was conducted in two parts on patients undergoing elective coronary bypass grafting. In the first group (n = 32), each patient underwent all of the following preoxygenation techniques: the traditional technique consisting of 3 min of tidal volume breathing at an oxygen flow of 5 l/min; four deep breaths within 30 s at oxygen flows of 5 l/min, 10 l/min, and 20 l/min; and eight deep breaths within 60 s at an oxygen flow of 10 l/min. The mean arterial oxygen tensions after each technique were measured and compared. In the second group (n = 24), patients underwent one of the following techniques of preoxygenation: the traditional technique (n = 8), four deep breaths (n = 8), and eight deep breaths (n = 8). Apnea was then induced, and the mean times of hemoglobin desaturation from 100 to 99, 98, 97, 96, and 95% were determined. RESULTS: In the first group of patients, the mean arterial oxygen tension following the tidal breathing technique was 392+/-72 mm Hg. This was significantly higher (P<0.05) than the values obtained following the four deep breath technique at oxygen flows of 5 l/min (256+/-73 mm Hg), 10 l/min (286+/-69 mm Hg), and 20 l/min (316+/-67 mm Hg). In contrast, the technique of eight deep breaths resulted in a mean arterial oxygen tension of 369+/-69 mm Hg, which was not significantly different from the value achieved by the traditional technique. In the second group of patients, apnea following different techniques of preoxygenation was associated with a slower hemoglobin desaturation in the eight-deep-breaths technique as compared with both the traditional and the four-deep-breaths techniques. CONCLUSION: Rapid preoxygenation with the eight deep breaths within 60 s can be used as an alternative to the traditional 3-min technique.     

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

Various techniques of "preoxygenation" before anesthetic induction have been advocated, including tidal volume breathing (TVB) for 3-5 min, four deep breaths (DB) in 0.5 min, and eight DB in 1 min. However, no study has compared the effectiveness of these techniques, assessed extending deep breathing beyond 1 min, or investigated the influence of fresh gas flow (FGF) in the same subjects using a circle absorber system. In 24 healthy adult volunteers breathing oxygen from a circle absorber system by tight-fitting mask, we compared TVB/5 min and deep breathing at a rate of 4 DB/0.5 min for 2 min at 5, 7, and 10 L/min FGF. Inspired and end-tidal respiratory gases were measured at 0.5-min intervals. During TVB, end-tidal oxygen (ETO2) increased rapidly and plateaued by 2.5 min at 86%, 88%, and 88% with 5, 7 and 10 L/min FGF, respectively. ETO2 values of > or =90% were attained between 3 and 4 min. Four DB/0.5 min increased ETO2 to 75%, 77%, and 80% at 5, 7, and 10 L/min FGF. Eight DB/min resulted in ETO2 values of 82% and 87% at 7 and 10 L/min, respectively. Extending deep breathing to 1.5 and 2 min with 10 L/min FGF increased ETO2 by > or =90%, although a decrease in ETCo(2) was noted. We concluded that TVB/3-5 min was effective in achieving maximal "preoxygenation" whereas 4 DB/0.5 min resulted in submaximal "preoxygenation," and thus should be used only when time is limited. Increasing FGF from 5 to 10 L/min does not enhance "preoxygenation" with either TVB or 4 DB/0.5 min. Deep breathing yields maximal "preoxygenation" when extended to 1.5 or 2 min, and only when high (10 L/min) FGF is used. IMPLICATIONS: Using a circle absorber system, normal breathing of oxygen for 3-5 min achieves optimal oxygenation of the lungs; whereas 4 deep breaths in 30 s does not. However, extending deep breathing to 1.5-2 min and using a high flow of oxygen improves oxygenation of the lungs to the same degree as normal breathing for 3-5 min. This may have important implications for patient safety.     

Vital capacity and tidal volume preoxygenation with a mouthpiece

We have measured oxygen wash-in in 20 volunteers undergoing preoxygenation with a face mask, mouthpiece alone and a mouthpiece with a noseclip, in a crossover study. Tidal volume breathing and maximal deep breath techniques were studied with each type of equipment. When tidal volume breathing was used, the face mask and mouthpiece with noseclip were comparable, but the mouthpiece alone achieved a lower end- expiratory oxygen concentration than the two other methods after 3 min (P < 0.001 and P < 0.01), and after 5 min (P < 0.05 in each case). Conversely, during preoxygenation with vital capacity breaths, the mouthpiece and mouthpiece with noseclip were comparable, and both were more effective than the face mask (P < 0.001). In a second study, 20 patients who had undergone preoxygenation before induction of anaesthesia were asked later if they would have preferred the face mask or mouthpiece for this procedure. Significantly more patients (14 of 18 who expressed a preference) favoured the mouthpiece (P < 0.05; confidence limits 0.56-0.92).      

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%.     

Methacholine bronchial challenge using a dosimeter with controlled tidal breathing.

A new inhalation synchronised dosimeter triggered by low inspiratory flow rates has been assessed. The methacholine challenge test using dosimeter nebulisation with controlled tidal breathing was compared with continuous nebulisation using De Vilbiss No 40 nebulisers with deep inhalations in 11 asthmatic subjects. Within subject PD20 FEV1 values were lower with the dosimeter method than with the continuous nebulisation method (geometric means 158 and 588 micrograms). The repeatability of the dosimeter method with controlled tidal breathing was studied in 11 asthmatic subjects, and the 95% range for a single measurement was +/- 0.72 doubling doses of methacholine. The dosimeter method has greater efficacy because aerosol is delivered during the first part of an inhalation, minimising loss of aerosol outside the respiratory tract. The dosimeter technique combined with controlled tidal breathing appears to be a useful method for carrying out standardised non-specific bronchoprovocation tests.     

Effect of tidal volume and respiratory rate on the power of breathing calculation

BACKGROUND: The power of breathing (PoB) is used to estimate the mechanical workload of the respiratory system. Aim of this study was to investigate the effect of different tidal volume-respiratory rate combinations on the PoB when the elastic load is constant. In order to assure strict control of the experimental conditions, the PoB was calculated on an airway pressure-volume curve in mechanically ventilated patients. METHODS: Ten patients received three different tidal volume-respiratory rate combinations while minute ventilation was constant. Respiratory mechanics, PoB and its elastic and resistive components were calculated. Alternative methods to estimate the elastic workload were assessed: elastic work of breathing per litre per minute, elastic workload index (the square root of elastic work of breathing multiplied by respiratory rate) and elastic double product of the respiratory system (the elastic pressure multiplied by respiratory rate). RESULTS: Despite constant elastance and minute ventilation, the elastic PoB showed an increment greater than 200% from the lower to the greater tidal volume, accounting for approximately 80% of the whole PoB increment. On the contrary, elastic work of breathing per litre per minute, elastic workload index and elastic double product did not change. CONCLUSION: Changes in breathing pattern markedly affect the PoB despite constant mechanical load. Other indexes could assess the elastic workload without tidal volume dependence. Power of breathing use should be avoided to compare different mechanical loads or efficiencies of the respiratory muscles when tidal volume is variable.     

An audible indication of exhalation increases delivered tidal volume during bag valve mask ventilation of a patient simulator

Self-inflating manual resuscitators (SIMRs) can mislead caregivers because the bag, unlike a Mapleson-type device, reinflates even without patient exhalation. We added a whistle as an audible indicator to the exhalation port of a SIMR. In randomized order, each participant provided two sets of breaths via mask ventilation with a SIMR, one with and one without audible feedback, to a Human Patient Simulator modified to log lung volume changes. The last three breaths in each set were used to compare average tidal volume (Vt) under both conditions. Eighty-seven advanced cardiac life support trainees (54 males, 33 females) with clinical experience averaging 6.4 +/- 9.4 yr were recruited. Average Vt delivered with the standard SIMR was 486 +/- 166 mL and 624 +/- 96 mL with the modified SIMR. Average Vt delivered by a modified SIMR was significantly larger by 40% when it followed standard SIMR use and 19% when using the modified SIMR first. Use of a SIMR with an audible indicator of exhalation significantly (P < 0.001) increased mask ventilation of a patient simulator, suggesting that mask ventilation of a patient with a SIMR may also be increased by objective, real-time feedback of exhaled Vt.     

Comparison of actual tidal volume in neonatal lung model volume control ventilation using three ventilators

In neonates, small changes in tidal volumes (V(T)) may lead to complications. Previous studies have shown a significant difference between ventilator-measured tidal volume and tidal volume delivered (actual V(T)). We evaluated the accuracy of three different ventilators to deliver small V(T) during volume-controlled ventilation. We tested Servo 300, 840 ventilator and Evita 4 Neoflow ventilators with lung models simulating normal and injured neonatal lung compliance models. Gas volume delivered from the ventilator into the test circuit (V(TV)) and actual V(T) to the test lung were measured using Ventrak respiration monitors at set V(T) (30 ml). The gas volume increase of the breathing circuit was then calculated. Tidal volumes of the SV300 and PB840 in both lung models were similar to the set V(T) and the actual tidal volumes in the injured model (20.7 ml and 19.8 ml, respectively) were significantly less than that in the normal model (27.4 ml and 23.4 ml). PB840 with circuit compliance compensation could not improve the actual V(T). V(TV) of the EV4N in the normal and the injured models (37.8 ml and 46.6 ml) were markedly increased compared with set V(T), and actual V(T) were similar to set V(T) in the normal and injured model (30.2 ml and 31.9 ml, respectively). EV4N measuring V(T) close to the lung could match actual V(T) to almost the same value as the set V(T) however the gas volume of the breathing circuit was increased. If an accurate value for the patient's actual V(T) is needed, this V(T) must be measured by a sensor located between the Y-piece and the tracheal tube.     

Efficacy of preoxygenation with non-invasive low positive pressure ventilation in obese patients: Crossover physiological study

Objective

The impact of non-invasive positive pressure ventilation (NIPPV), which is a combination of inspiratory positive airway pressure (IPAP) and positive end expiratory pressure (PEEP), on the effectiveness of preoxygenation in obese patients was evaluated.

Design

Randomized, controlled, double blinded, crossover study comparing NIPPV vs. tidal volume breathing (TVB) with regard to the expiratory O₂ fraction (FeO₂).

Patients and methods

Thirty participants with body mass index (BMI) greater or equal to 30 kg/m² scheduled for elective surgery were included. Patients with facial hair, and airway anomalies were excluded. Each patient underwent 3 minutes 100% O₂ preoxygenation with the two following methods in a random order: 1: TVB; 2: NIPPV (4 cmH₂O IPAP + 4 cmH₂O PEEP). Primary outcome was FeO₂ after 3 minutes. Secondary outcomes were the number of patients reaching FeO₂ greater or equal to 90%, tidal volume, respiratory rate, and patient comfort on a 4-point scale.

Results

No differences between methods were found regarding the FeO₂ change with time or after 3 minutes (89 ± 6% with TBV vs. 91 ± 4% with NIPPV). FeO₂ greater or equal to 90% was reached more frequently with NIPPV (80%) than with TVB (60%) (P = 0.008). Tidal volume (m ± SD) was larger throughout preoxygenation with TBV (837 ± 440 mL) than with NIPPV (744 ± 368 mL), (P = 0.0005). Respiratory rate did not differ between regimens. Patient comfort was good and similar.

Conclusion

This study suggests that providing a positive pressure of 4 cmH₂O throughout inspiration and expiration during preoxygenation in obese patients provided benefits with regard to the FeO₂.     

Sevoflurane: a comparison between vital capacity and tidal breathing techniques for the induction of anaesthesia and laryngeal mask airway placement

Sixty unpremedicated adult day-case patients were randomly assigned to either vital capacity or tidal breathing inhalational induction techniques. End points assessed included loss of eyelash reflex, time to drop a weighted syringe, time to jaw relaxation and time to the end of laryngeal mask airway insertion. Complications occurring during the induction of anaesthesia were recorded. The data show that there is no statistical or clinical difference between the two induction techniques. Patient acceptance of both techniques was similarly high. When the time taken to prime the anaesthetic breathing system is taken into consideration, the vital capacity technique is more expensive for induction of anaesthesia. These results therefore question the need for the vital capacity induction technique with sevoflurane 8%.