Hypoxic and hypercapnic ventilatory responses during isoflurane sedation and anaesthesia in women

This study primarily examined the effect of three endtidal isoflurane concentrations (0.2, 1.0 and 1.4%) on the isocapnic hypoxic ventilatory response (HVR), as well as the hypercapnic ventilatory response (HCVR), in 18 women (ASA I) who were all in the follicular phase of their menstrual cycle. Capnography was used, together with pulseoximetry to indicate desired levels of hypoxia (SpO₂ 75–80%). This hypoxic challenge resulted, after 3–4 min, in a stable ventilation, and ventilation measurements were then taken during a 90 s period. The HCVR provocation (inhalation of 4.5% CO₂ in air) and measurements were conducted using a similar time frame as for HVR. Isoflurane 0.2% did not affect any ventilatory parameter. Isoflurane 1.0 and 1.4% dose-dependently increased endtidal CO₂ and respiratory rate, while tidal volumes decreased. Minute ventilation was not reduced. HVR, as well as HCVR, were both uninfluenced by isoflurane 0.2%. HVR was reduced by 60–70% at isoflurane 1.4% ( P <0.0l), and was parallelled by a similar depression of HCVR ( P <0.01). The HVR during anaesthesia was accomplished by a respiratory rate response, while the increase in tidal volume, seen in the awake state, was abolished. The HCVR during anaesthesia was, on the other hand, the result of a dose-dependently depressed tidal volume response, without any increase in respiratory rate. In conclusion, isoflurane 0.2% did not affect the ventilatory response to mild isocapnic hypoxia, nor to mild hypercapnic challenge. During anaesthesia with isoflurane (1.0 and 1.4%), there was a parallel reduction of HVR and HCVR.     

二氧化碳浓度测量法在诊断睡眠呼吸暂停综合征中的应用研究

目的　同时采用热敏传感器和二氧化碳浓度测量仪监测睡眠呼吸暂停综合征 (SAS)患者 ,探讨二氧化碳浓度测量法在诊断SAS中的临床价值。方法　对 2 5例患者进行多导睡眠图和呼出气二氧化碳浓度描记图及呼气末二氧化碳分压 (PetCO2 )监测 ,并对PetCO2 值与呼吸紊乱指数 (AHI)的关系进行分析 ,统计方法采用t检验和相关分析。结果　以热敏传感器所得结果为标准 ,呼吸暂停、低通气和呼吸紊乱阳性诊断率分别为 84.5 %± 9.6 % ,72 .7%± 8.0 % ,81.2 %± 8.4% ;未发现假阳性。夜间平均PetCO2 和最高PetCO2 与窒息指数 (AI)、低通气指数(HI)、AHI均无显著相关性。结论　二氧化碳浓度测量法监测SAS具有较高的诊断率。     

慢性阻塞性肺疾病中容积二氧化碳图死腔参数的变化及其临床价值

目的：探讨容积二氧化碳图(VCap)死腔参数在慢性阻塞性肺疾病(COPD)诊断中的应用价值。方法选取2013-2014年在我院门诊和住院治疗的74例COPD患者(COPD组)和38例健康志愿者(健康组)作为研究对象。测定受试者的肺通气、容量、弥散指标及Threshhold死腔(VDT)、Langley死腔(VDL)、Fowler死腔(VDF)、Wolff死腔(VDW)、Bohr死腔(VDB)参数。首先,在健康组中建立以死腔为应变量,性别、年龄、身高、体重、潮气量及呼吸频率为自变量的预计值计算公式,并运用公式计算各受试者的正常死腔预计值。采用配对t检验比较COPD组死腔预计值与实测值的差异。运用判别分析统计死腔对COPD患者和健康人的判别效率。采用偏相关分析统计死腔参数与常规肺功能参数的相关性。结果在COPD组中,VDT实测值[(79.51±39.29) mL]较预计值[（97.42±30.53）mL]减小(P<0.01),而VDF[(190.20±57.41) mL]、VDW[(214.04±73.35) mL]及VDB [(294.89±93.12) mL]实测值较预计值[(177.18±38.99) mL、183.86±46.63）mL、(237.44±62.27) mL]增大(P<0.05)。在运用死腔参数对COPD组和健康组的判别分析中只有VDT和VDB占预计值%进入判别函数,总归类正确率为87.9%(116/132)。在COPD组中,VDT及VDF与FEV1、FEV1/FVC、DLCO均呈负相关(P<0.05),VDW与FEV1、FEV1/FVC、DLCO均呈负相关(P<0.05),与RV、TLC呈正相关(P<0.05),VDB与FEV1、FEV1/FVC、DLCO均呈负相关(P<0.05),与RV、TLC、RV/TLC均呈正相关(P<0.05)。结论 VCap死腔对COPD的诊断及严重程度评估具有一定的临床参考价值。     

End-tidal PCO2 monitoring via nasal cannulae in pediatric patients: Accuracy and sources of error

Objective. To assess the correlation and accuracy of end-tidal PCO₂ (PetCO₂) sampled via nasal cannulae in pediatric patients by comparison to the criterion standard PaCO₂, and to identify sources of error during PetCO₂ monitoring via nasal cannulae.Methods. PetCO₂ was monitored continuously by sampling end-tidal gas through nasal cannulae that had been designed and manufactured for this purpose in spontaneously breathing children undergoing conscious or deep sedation during either cardiac catheterization (n = 43) or critical care (n = 54). When both the capnographic wave form and the PetCO₂ value had been stable for at least 10 minutes, the PetCO₂ value was recorded while blood was drawn from an indwelling arterial line for PaCO₂ measurement. The effects of age, weight, respiratory rate, oxygen delivery system, airway obstruction, mouth breathing, and cyanotic heart disease were evaluated by linear regression analysis and calculation of absolute bias (PaCO₂-PetCO₂).Results. Mouth breathing, airway obstruction, oxygen delivery through the ipsilateral nasal cannula, and cyanotic heart disease adversely affected accuracy. In patients without those factors, PetCO₂ correlated well with PaCO₂ (R² = 0.994), and absolute bias was 3.0 ± 1.8 mmHg.Conclusions. Several factors — some controllable and all recognizable — affect the accuracy of PetCO₂ monitored via nasal cannulae in pediatric patients. When these factors are not present, PetCO₂ correlates well with PaCO₂ and appears to be a useful monitor of ventilatory status during conscious or deep sedation.     

Colorimetric End–tidal CO2Detector for Verification of Endotracheal Tube Placement in Out–of–hospital Cardiac Arrest

Objective: To evaluate the ability of a disposable, colorimetric end–tidal CO₂ detector to verify proper endotracheal (ET) tube placement in out–of–hospital cardiac arrest, and to correlate semiquantitative CO₂ measurements with the rate of return of spontaneous circulation (ROSC).
Methods: Prospective, observational study using a convenience sample of intubated out–of–hospital cardiac arrest patients. A disposable, colorimetric end–tidal CO₂ detector was attached to the ET tube after intubation. In the absence of a colorimetric change, the paramedics reassessed the tube placement and could reintubate the patient. Tube placement was verified at the hospital. Paramedics were instructed to contact the base station and report the colorimetric change upon hospital arrival. ROSC was defined as restoration of a self–sustaining pulse until hospital arrival.
Results: Between December 1990 and May 1993, ET tubes were placed in 566 victims of out–of–hospital cardiac arrest. 541 of the 566 intubations (95.6%) were associated with a color change. In one case with a color change and out–of–hospital clinical evidence of proper tube placement, the tube was determined to be in the esophagus at the hospital. Correct placement of the remaining 565 of 566 (99.8%) tubes was verified. Of the 566 patients who had a colorimetric change, 91 (16%) had ROSC vs one of 25 (4%) patients who did not have a color change. In one subgroup (n = 179), the degree of color change was highly associated with ROSC (p = 0.004).
Conclusions: A disposable, colorimetric end–tidal CO₂ detector appears reliable in verifying proper ET tube placement in victims of out–of–hospital cardiac arrest. The degree of color change correlates with the probability of ROSC.     

Capnography and the bain circuit II: Validation of a computer model

Validation of a computer model is described. The behavior of this model is compared both with mechanical ventilation of a test lung in a laboratory setup that uses a washout method and with manual ventilation. A comparison is also made with results obtained from a volunteer breathing spontaneously through a Bain circuit and with results published in the literature. This computer model is a multisegment representation of the Bain circuit and connecting tubing. For each segment, gas pressure, gas volume flow, and partial pressure of carbon dioxide are calculated for any number of breaths wanted. As a result, the time course of these variables can be generated for any location or, conversely, the carbon dioxide distribution in the system can be calculated for any time instant. A test lung, the human lungs, the ventilator bellows, and the reservoir bag are each represented by a single segment. The shapes of pressure and flow curves and of the capnograms taken at different locations in the Bain tubing are in good agreement. The washout study permits measurement of the time delay between the first expiration and the arrival of carbon dioxide at a particular location. The carbon dioxide level in the test lung decreases during inspiration and is stable during expiration. Quantitative agreement between model and experimental transport delays and carbon dioxide levels is such that the differences can be explained by the inaccuracy of the measurement. This is concluded from a sensitivity analysis. The study of the effect of segment size shows an almost optimal agreement between model behavior and experimental results for a 36-segment model. Execution of a thorough validation is imperative before such models can be used for clinical management and decision making or for teaching.     

E ND - TIDAL C ARBON D IOXIDE M ONITORING IN THE P REHOSPITAL S ETTING

End-tidal carbon dioxide (ETCO₂) monitoring is an exciting technology and has the potential to become a very useful tool in the prehospital setting. It can be useful in verifying endotracheal tube position and during cardiopulmonary resuscitation in the field. Recent reports of misplaced endotracheal tubes in the prehospital setting make it important to ensure that paramedics learn correct techniques of endotracheal intubation, and that they verify tube placement with an ETCO₂ monitor. The new American Heart Association guidelines require secondary confirmation of proper tube placement in all patients by exhaled CO₂ immediately after intubation and during transport. This article covers the terminology, the basic physiology, the technology (both colorimetric detectors and infrared capnometers), and the clinical applications of ETCO₂ monitoring with special reference to the pediatric patient.     

Acute Alcohol Intoxication in Adolescents: Frequency of Respiratory Depression

Background

Adolescents and young adults are frequent users of alcohol. Younger patients may be more sensitive to the effects of alcohol than their adult counterparts, and toxicity has been known to occur at lower doses. Respiratory depression is a serious adverse effect of alcohol intoxication; however, current monitoring practices may not adequately detect respiratory depression.

Objective

Our objective was to determine the frequency of hypoventilation as measured by capnography among adolescents with acute alcohol intoxication. Our secondary objective was to determine if an association exists between alcohol levels and incidence of hypoventilation.

Methods

This was a prospective observational pilot study of patients 14–20 years of age with acute alcohol intoxication. Blood or breath alcohol measurements were obtained on arrival. Hourly measurements of vital signs including capnography were recorded.

Results

Sixty-five subjects were analyzed. Mean alcohol level was 185 mg/dL. Twenty-eight percent of subjects had episodes of hypoventilation. Episodes occurred in similar proportions on arrival and during the first 5 h of measurements. There was no difference in alcohol levels between subjects who did and did not hypoventilate (185 mg/dL vs. 186 mg/dL; 95% confidence interval −29 to 25). Oxygen desaturations occurred in 14 subjects and were associated with hypoventilation (p = 0.015).

Conclusions

Hypoventilation is common among adolescents who are acutely intoxicated with alcohol. It is independent of alcohol level and occurs at a steady rate during the first several hours of intoxication. Capnography should be considered as an additional monitoring device to detect these episodes and enhance patient safety.