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 mmHg. 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 mmHg), 10 l/min (286 +/- 69 mmHg), and 20 l/min (316 +/- 67 mmHg). In contrast, the technique of eight deep breaths resulted in a mean arterial oxygen tension of 369 +/- 69 mmHg, 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.     

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.     

潮气呼吸肺功能检测在儿童支气管肺炎中的临床应用

目的 分析潮气呼吸肺功能检测应用于儿童支气管肺炎临床诊治中的作用。方法 选取2021年 8月-2022年8月我院收治的43例支气管肺炎患儿为研究对象,将其作为观察组,同时纳入同时间段于我院 门诊进行潮气呼吸检测的35名健康婴幼儿作为对照组,分别进行潮气呼吸功能检测,比较两组肺功能参 数。结果 两组潮气量比较,差异无统计学意义（P＞0.05）;观察组呼吸比、达峰容积比、达峰时间比、 呼吸流速25%、呼吸流速50%、呼吸流速75%均低于对照组,呼吸频率高于对照组,差异有统计学意义 （P＜0.05）。结论 潮气呼吸监测对儿童支气管肺炎的诊断具有良好的辅助作用,可以更好地了解患儿的 肺部情况,无需进行其他辅助配合,患儿及家属的接受度较高,值得临床应用。     

Preoxygenation techniques: the value of nitrous oxide

Changes in arterial oxygen saturation during induction of anaesthesia and intubation were studied using the pulse oximeter. Seventy-five young ASA I patients undergoing elective uncomplicated surgery were divided equally into three groups. The patients were preoxygenated with 100% oxygen, 50% oxygen: 50% nitrous oxide or 30% oxygen: 70% nitrous oxide for 1 min. All were then induced with thiopentone, paralysed with suxamethonium and orally intubated. Arterial oxygen saturations were continuously recorded by a separate investigator. All groups showed similar arterial desaturation during suxamethonium-induced apnoea and intubation, but the degree of desaturation was not clinically significant and no patient showed clinical signs of hypoxaemia. Preoxygenation with mixtures of oxygen and nitrous oxide can hasten the build-up of alveol nitrous oxide concentration and help to smooth induction without compromising oxygenation of patients.     

Preoxygenation: a comparison of three different breathing systems

An end-tidal expiratory oxygen concentration (FE'_O2) greaterthan 0.90 is considered to be adequate for preoxygenation. Thisis generally achieved using a face mask, but this can be unsatisfactoryin some patients. We compared preoxygenation in 30 healthy volunteersusing a face mask, the NasOral system, which is a novel preoxygenationdevice, and a mouthpiece with a nose-clip. We measured the maximalFE'_O2, the FE'_O2 after 2 min and the time to reach maximalFE'_O2 and recorded the subjective judgement of the volunteers.The maximal FE'_O2 with face mask and mouthpiece was significantlygreater than with the modified NasOral system (P<0.05 andP<0.01). With the former devices, a FE'_O2 of 0.90 was achievedin 73% of the volunteers vs 46% with the modified NasOral system.Using the mouthpiece, the FE'_O2 after 2 min was significantlyhigher than using the face mask (P<0.01) or the modifiedNasOral system (P<0.01). The time to maximal FE'_O2 was significantlyshorter using the modified NasOral system than with the facemask or mouthpiece (P<0.001 and P=0.0001). The volunteersgave more positive ratings to the face mask and mouthpiece thanto the modified NasOral system (P<0.001 and P<0.01). Weconclude that the use of a mouthpiece can improve preoxygenationin some patients. The results obtained with the modified NasOralsystem do not justify its introduction into clinical practice. Br J Anaesth 2001; 87: 928–31     

全麻中IPPV时潮气量与呼气末CO2分压的关系

在30例无心肺异常的全麻病人中,观察了1PPV时PetCO_2和肺通气量以及气道压之间的关系。在VT_(10～4)ml/kg范围,气道压降低1 mbar,PetCO_2约增加0.2667kPa(2mmHg)。调节VE可较准确地间接控制PetCO_2。VT>8ml/kg或VE>100ml/kg/min会引起中度至严重低CO_2血症,对机体不利。     

Amsorb: A New Carbon Dioxide Absorbent for Use in Anesthetic Breathing Systems

Background: This article describes a carbon dioxide absorbent for use in anesthesia. The absorbent consists of calcium hydroxide with a compatible humectant, namely, calcium chloride. The absorbent mixture does not contain sodium or potassium hydroxide but includes two setting agents (calcium sulphate and polyvinylpyrrolidine) to improve hardness and porosity.

Methods: The resultant mixture was formulated and subjected to standardized tests for hardness, porosity, and carbon dioxide absorption. Additionally, the new absorbent was exposed in vitro to sevoflurane, desflurane, isoflurane, and enflurane to determine whether these anesthetics were degraded to either compound A or carbon monoxide. The performance data and inertness of the absorbent were compared with two currently available brands of soda lime: Intersorb (Intersurgical Ltd., Berkshire, United Kingdom) and Dragersorb (Drager, Lubeck, Germany).

Results: The new carbon dioxide absorbent conformed to United States Pharmacopeia specifications in terms of carbon dioxide absorption, granule hardness, and porosity. When the new material was exposed to sevoflurane (2%) in oxygen at a flow rate of 1 l/min, concentrations of compound A did not increase above those found in the parent drug (1.3-3.3 ppm). In the same experiment, mean +/-SD concentrations of compound A (32.5 +/- 4.5 ppm) were observed when both traditional brands of soda lime were used. After dehydration of the traditional soda limes, immediate exposure to desflurane (6%), enflurane (2%), and isoflurane (2%) produced concentrations of carbon monoxide of 600.0 +/- 10.0 ppm, 580.0 +/- 9.8 ppm, and 620.0 +/- 10.1 ppm, respectively. In contrast, concentrations of carbon monoxide were negligible (1-3 ppm) when the anhydrous new absorbent was exposed to the same anesthetics.     

The Measurement of Tidal Volumes in Spontaneously Breathing Children during General Anaesthesia using a Haloscale Infant Wright Respirometer

The accuracy of tidal volume measurements made with a Wright Haloscale infant respirometer in children breathing spontaneously during general anaesthesia was assessed by a bench test. The tidal volumes and peak flow rates of 20 spontaneously breathing, anaesthetised children were measured with a pneumotachograph before and during surgery, and similar volumes, at the same flow rates, were delivered by a calibrated syringe simultaneously to the respirometer and a pneumotachograph. The results reveal that the mean (+/- s.d.) peak gas flow rates of children aged 6 years and less, 7.5 (+/- 1.6) and 9.3 (+/- 0.1) l/min before surgery and during surgery respectively, are significantly less than the peak flow rates, 11.3 (+/- 1.0) and 11.9 (+/- 1.5) before and during surgery, respectively, of children aged more than 6 years; and that the respirometer underestimates tidal volume by 10% when the peak flow rate is 11 l/min, and the percentage error in tidal volume estimation by the respirometer increases as the peak gas flow declines below 10 l/min.     

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.