A feasibility study on bedside upper airway ultrasonography compared to waveform capnography for verifying endotracheal tube location after intubation

Background

In emergency settings, verification of endotracheal tube (ETT) location is important for critically ill patients. Ignorance of oesophageal intubation can be disastrous. Many methods are used for verification of the endotracheal tube location; none are ideal. Quantitative waveform capnography is considered the standard of care for this purpose but is not always available and is expensive. Therefore, this feasibility study is conducted to compare a cheaper alternative, bedside upper airway ultrasonography to waveform capnography, for verification of endotracheal tube location after intubation.

Methods

This was a prospective, single-centre, observational study, conducted at the HRPB, Ipoh. It included patients who were intubated in the emergency department from 28 March 2012 to 17 August 2012. A waiver of consent had been obtained from the Medical Research Ethics Committee. Bedside upper airway ultrasonography was performed after intubation and compared to waveform capnography. Specificity, sensitivity, positive and negative predictive value and likelihood ratio are calculated.

Results

A sample of 107 patients were analysed, and 6 (5.6%) had oesophageal intubations. The overall accuracy of bedside upper airway ultrasonography was 98.1% (95% confidence interval (CI) 93.0% to 100.0%). The kappa value (Κ) was 0.85, indicating a very good agreement between the bedside upper airway ultrasonography and waveform capnography. Thus, bedside upper airway ultrasonography is in concordance with waveform capnography. The sensitivity, specificity, positive predictive value and negative predictive value of bedside upper airway ultrasonography were 98.0% (95% CI 93.0% to 99.8%), 100% (95% CI 54.1% to 100.0%), 100% (95% CI 96.3% to 100.0%) and 75.0% (95% CI 34.9% to 96.8%). The likelihood ratio of a positive test is infinite and the likelihood ratio of a negative test is 0.0198 (95% CI 0.005 to 0.0781). The mean confirmation time by ultrasound is 16.4 s. No adverse effects were recorded.

Conclusions

Our study shows that ultrasonography can replace waveform capnography in confirming ETT placement in centres without capnography. This can reduce incidence of unrecognised oesophageal intubation and prevent morbidity and mortality.

Trial registration

National Medical Research Register NMRR11100810230.     

Detection of tracheal malpositioning of nasogastric tubes using endotracheal cuff pressure measurement

BACKGROUND: Insertion of a gastric tube (GT) in anaesthetized, paralyzed and intubated patients may be difficult. Tracheobronchial malposition of a GT may result in deleterious consequences. The purpose of this study was to determine the reliability of tracheal cuff pressure measurement to detect endobronchial malposition of GTs. We compared this new method with the measurement of exhaled CO(2) through the GT. METHODS: Thirty patients under general anesthesia and orotracheal intubation were analysed. First, the cuff pressure of the low-volume endotracheal tube (ET; ID 7.0-8.5 mm) was increased to 40 cmH(2)O. Then, in a randomized fashion, the GT (18 Charrière) was inserted consecutively into the trachea and oesophagus or vice versa. Cuff pressure was monitored continuously while advancing the GT. Furthermore, a capnograph was connected to the gastric tube and the aspirated PCO(2) was monitored. RESULTS: Advancement of the gastric tube into the oesophagus increased ET cuff pressure by 1 +/- 1 cmH(2)O, while endotracheal placement of the GT increased cuff pressure by 28 +/- 8 cmH(2)O (P < 0.001). Using an increase of >10 cmH(2)O in cuff pressure detected endotracheal malpositioning of the GT with 100% sensitivity and specificity. In 28 out of 30 cases, PCO(2) increased by more than 2.6 kPa. Thus, the PCO(2) approach failed to detect tracheal malpositioning in two cases resulting in a sensitivity of 93.3%. CONCLUSIONS: In intubated patients, cuff pressure measurement during insertion of a gastric tube is a new, simple and reliable bedside method to detect endotracheal malpositioning of a GT.     

Effects of Double Filtration Plasmapheresis on Nocturnal Respiratory Function in Myasthenic Patients

Assessment of respiratory function using combined oximetry‐cutaneous capnography has never been evaluated in patients with myasthenia gravis (MG). We investigated the effects of double filtration plasmapheresis (DFPP) on respiratory status in 18 MG patients. Results of combined oximetry and transcutaneous capnography, MG scores, and acetylcholine receptor antibody titers before and after DFPP treatment were compared. The respiratory monitoring was performed at three time periods (morning, afternoon, and sleep). Mean MG score was markedly lower after DFPP treatment (5.7) than before treatment (7.9). Before DFPP, the minimum pulse oximetric saturation (SpO₂) level obtained during the night session was significantly lower (P = 0.0513 and P = 0.0199) than the levels obtained during the two daytime sessions. A similar phenomenon was noted for maximum transcutaneous carbon dioxide tension (PtcCO₂). After DFPP treatment, the maximum and mean PtcCO₂ levels were significantly higher (P = 0.0056) in the morning than in the afternoon. Of all the respiratory function parameters measured, only minimum SpO₂ levels obtained during morning sessions before DFP treatment differed significantly from those obtained after DFPP treatment (P = 0.0322). Overall, however, minimum SpO₂ levels as well as mean and maximum PtcCO₂ levels improved significantly during sleep after DFPP. In conclusion, we found that respiratory function abnormalities were common in myasthenic patients without clinical respiratory symptoms. DFPP treatment resulted in minimal improvement of respiratory parameters.     

Volumetric capnography and chronic obstructive pulmonary disease staging

Spirometry is difficult for some COPD patient to perform. Volumetric capnography could be a second choice test to evaluate the severity of functional disturbances. The aim of this work is to test this hypothesis. A total number of 98 subjects were classified either as normal ex-smokers (N = 14) or COPD patients. The latter were staged following GOLD recommendations. Spirometry and volumetric capnography recordings were obtained from each patient. Spirometry parameters, Bohr Dead Space (V_D ^Bohr), Airways Dead Space from the pre-interface expirate corrected curve (V_D ^aw), Phase III slope (Sl_III) and Volume of alveolar ejection (V_AE) were measured. Index of Ventilatory Efficiency (IVE), and Index of Airways Heterogeneity (IAH) were calculated as: IVE = V_AE/(V_T – V_D ^aw) and IAH = 1 – [(V_T – V_D ^Bohr)/(V_T – V_D ^aw)]. In ANOCOVA analysis IAH showed the greatest association with stage (F > 40), with no significant covariant dependence on V_T. A receiver operating characteristics curve analysis showed values of the area under the curve greater than 0.9 for IAH and IVE at all stage levels, with a sensitivity = specificity value greater than 80%. We conclude that IAH and IVE can be used when spirometry cannot be reliably performed, as an alternative test to evaluate the degree of functional involvement in COPD patients.     

容积二氧化碳图在气道反应性测定中的应用

目的 探讨容积二氧化碳图（volumetric capnography,Vcap）参数在组胺激发试验中的反应性变化并与肺通气测定法做比较.方法 对60例门诊慢性咳嗽,疑诊咳嗽变异性哮喘患者进行组胺支气管激发实验,于基础状态、每次吸入组胺后,及吸入支气管扩张药后,先进行Vcap测定,再进行肺通气功能测定.使用Vcap来评价气道反应性.结果 60例患者气道高反应性的阳性率为50%.激发试验阳性组第1秒用力呼气容积（FEV1）、最大用力呼气峰流量（PEF）及Vcap参数Threshold死腔（VDT）、Fowler死腔（VDF）、Wolff死腔（VDW）、Ⅲ期斜率（dC3/DV）在基础值和激发后值之间差异均有统计学意义（P＜0.01）,激发后和舒张后值之间差异也有统计学意义（P＜0.05）.阴性组FEV1、PEF在基础值和激发后值之间、激发后和舒张后值之间差异无统计学意义（P＞0.05）,VDT、VDF、VDW激发后和舒张后值之间差异有统计学意义（P＜0.05）.所有患者的基础值、激发后、舒张后数据,FEV1均与PEF、Vcap各参数（除dC2/DV、dC3/DV、SR23外）呈显著直线相关（P＜0.05）.激发试验过程中各死腔参数的下降提前于FEV1和PEF的下降.激发试验终止时,ROC曲线提示VDT、VDF为最敏感指标,VDT较基础值增加28%、VDF较基础值增加20%,可作为Vcap气道高反应性阳性判断标准.结论 Vcap是一种定量评估支气管阻塞严重性的有效方法,可应用于气道反应性测定.     

容积二氧化碳图对支气管哮喘患者急性加重分级的意义

目的 探讨容积二氧化碳图(Vcap)参数对支气管哮喘(简称哮喘)诊断的临床价值.方法 2006年7月至2007年5月对64例哮喘急性发作期患者(哮喘组)及20名健康者(健康对照组)进行肺通气功能以及Vcap测定,并依据FEV,占预计值%将哮喘患者分为A组(＞80%,18例)、B组(40%～80%,26例)、c组(＜40%,20例),所有受试者先行Vcap测定,随后完成FEV1占预计值%、FEV1/FVC、FVC占预计值%、最大呼气中段流量(MMEF)占预计值%测定.统计学处理采用SPSS 13.0软件.计量资料采用-x±s表示,计数资料采用卡方检验,计量资料两组间比较采用t检验.肺通气参数与Vcap参数间的相关性采用一元线性回归检验;哮喘组与对照组间的差异采用独立样本t检验;健康对照组及哮喘各亚组间的比较采用单因素方差分析.结果 哮喘组患者FEV1占预计值%、FEV1/FVC、PEF占预计值%、MMEF占预计值%分别为(52±20)%、(50±10)%、(49±16)%、(28±16)%,与健康对照组[(98±9)%、(80±6)%、(91±15)%、(73±7)%]比较差异有统计学意义(t值分别为6.93～13.29,P均＜0.01);哮喘组患者Ⅱ期斜率(dC2/DV)、Ⅲ期斜率(dC3/DV)、Ⅲ期与Ⅱ期斜率之比(SR23)分别为(19±6)%/L、(2.9±1.2)%/L、(16.8±10.6)%,与健康对照组[(31±8)%/L、(1.0±0.4)%/L,(3.3±1.5)%]比较差异有统计学意义(t值分别为5.09、-6.14、-6.54,P均＜0.01);哮喘B、C组dC2/DV分别为(17±5)%/L、(13±4)%/L,与健康对照组[(31±8)%/L]比较差异有统计学意义(t=-11.82、-16.75,P均＜0.01);哮喘B、C组患者dC3/DV、SR23分别为(3.2±0.8)%/L、(17.2±3.5)%,(4.1±1.2)%/L、(28.3±6.9)%,与健康对照组[(1.0±0.4)%/L、(3.3±1.5)%]比较差异有统计学意义(t值分别为2.16～26.08,P均＜0.01);哮喘A、B、C组间dC3/DV、SR23比较差异有统计学意义(t值分别为0.91～22.18,P均＜0.05);相关分析结果表明dC2/DV与FEV1占预计值%、FEV1/FVC、PEF占预计值%、MMEF占预计值%呈正相关(r值分别为0.69、0.54、0.59、0.54,P均＜0.01);dC3/DV与FEV1占预计值%、FEV1/FVC、PEF占预计值%、MMEF占预计值%呈显著负相关(r值分别为-0.62、-0.45、-0.69、-0.58,P均＜0.01);SR23与FEV1占预计值%、FEV1/FVC、PEF占预计值%、MMEF占预计值%呈显著负相关(r值分别为-0.75、-0.52、-0.74、-0.62,P均＜0.01).结论 Vcap是一种简便易行、可定量评估哮喘患者支气管阻塞严重程度的有效方法.     

Combined oximetry-cutaneous capnography in patients assessed for long-term oxygen therapy

STUDY AIM: To evaluate the feasibility of combined oximetry (pulse oximetric saturation [Spo(2)]) and cutaneous capnography (transcutaneous carbon dioxide tension [Ptcco(2)]) for oxygen titration in patients requiring long-term oxygen therapy. METHODS: Twenty patients with obstructive or restrictive lung disease underwent oxygen titration using a combined cutaneous oximetry-capnography sensor. The goal of titration was to achieve an oxygen saturation of > 90% without a significant rise in carbon dioxide. Spo(2) and Ptcco(2) measurements at the end of titration were compared with blood gas levels using Bland-Altman analysis and linear regression analysis. RESULTS: The mean (+/- SE of the estimate) Pao(2) while breathing room air was 53.2 +/- 8.1 mm Hg and increased to 75.9 +/- 13.3 mm Hg with oxygen supplementation (p < 0.0001). The mean Paco(2) was 45.9 +/- 8.7 mm Hg at baseline and 47.8 +/- 9.0 mm Hg after oxygen titration (p = 0.003). Bland-Altman analysis for comparison of Ptcco(2) and Paco(2) showed a bias of 0.86 mm Hg with a precision of 3.48 mm Hg. Bland-Altman analysis for the comparison of Spo(2) and arterial oxygen saturation showed a bias of 0.14% with a precision of 1.13%. CONCLUSION: Combined oximetry and cutaneous capnography is feasible during oxygen titration in patients needing long-term oxygen therapy. This noninvasive approach has the potential to reduce the number of arterial blood gas samplings performed.     

Prehospital End-tidal Carbon Dioxide Predicts Mortality in Trauma Patients

Background: End-tidal carbon dioxide (EtCO₂) measurement has been shown to have prognostic value in acute trauma. Objective: Evaluate the association of prehospital EtCO₂ and in-hospital mortality in trauma patients and to assess its prognostic value when compared to traditional vital signs. Methods: Retrospective, cross-sectional study of patients transported by a single EMS agency to a level one trauma center. We evaluated initial out-of-hospital vital signs documented by EMS personnel including EtCO₂, respiratory rate (RR), systolic BP (SBP), diastolic BP (DBP), pulse (P), and oxygen saturation (O₂) and hospital data. The main outcome measure was mortality. Results: 135 trauma patients were included; 9 (7%) did not survive. The mean age of patients was 40 (SD17) [Range 16–89], 97 (72%) were male, 76 (56%) were admitted to the hospital and 15 (11%) went to the ICU. The mean EtCO2 level was 18 mmHg (95%CI 9–28) [Range 5–41] in non-survivors compared to 34 mmHg (95%CI 32–35) [Range 11–51] in survivors. The area under the ROC curve (AUC) for EtCO₂ in predicting mortality was 0.84 (0.67–1.00) (p = 0.001), RR was 0.82 (0.63–1.00), SBP was 0.72 (0.49–0.96), DBP was 0.72 (0.47–0.97), pulse was 0.51 (0.26–0.76), and O₂ was 0.64 (0.37–0.91). Cut-off values at 30 mmHg yielded sensitivity = 89% (51–99), specificity = 68% (59–76), PPV = 13% (6–24) and NPV = 99% (93–100) for predicting mortality. There was no correlation between RR and EtCO₂ (correlation 0.16; p = 0.06). Conclusion: We found an inverse association between prehospital EtCO₂ and mortality. This has implications for improving triage and assisting EMS in directing patients to an appropriate trauma center.     

Weaning with end-tidal CO2 and pulse oximetry

Study Objective: To determine whether continuous measurement of arterial oxyhemoglobin saturation (SpO₂) and end-tidal carbon dioxide (P_ETCO₂) can be used to wean patients safely and efficiently from postoperative mechanical ventilation after cardiac surgery.

Design: Prospective study comparing SpO₂ and P_ETCO₂ to calculated arterial oxygen saturation (SaO₂ and arterial carbon dioxide tension (PaCO₂) obtained from blood gas analysis.

Setting: Cardiac surgical intensive care unit at a university-affiliated hospital.

Patients: Ten patients requiring elective coronary artery bypass grafting (CABG) were studied in the postoperative period during weaning from mechanical ventilation.

Interventions: Continuous monitoring of SpO₂ and P_ETCO₂ was used to wean patients from mechanical ventilation.

Measurements and Main Results: The patients were weaned from mechanical ventilation in an average time of 6.5 ± 1.5 hours (mean ± SD). A plot of SaO₂ versus SpO₂ indicated a high correlation (r = 0.84) with sensitivity (100%) for hypoxemia (SaO₂ less than 90%). P_ETCO₂ was a good indicator of PaCO₂ (r = 0.76); its sensitivity to detect hypercarbia (PaCO₂ less than 45 mmHg) was 95%. The gradient between SpO₂ and SaO₂ was not significantly affected by the weaning process, but the PaCO₂---P_ETCO₂ gradient decreased significantly as the ventilator rate was decreased (p < 0.001). The weaning process was discontinued on four separate occasions because of metabolic acidosis. Ninety-five percent of arterial blood samples confirmed the weaning recommendations based on the continuous monitoring of SpO₂ and P_ETCO₂.

Conclusions: Continuous monitoring of SpO₂ and P_ETCO₂ can be used to wean patients safely and effectively after CABG when adjustment of minute ventilation compensates for an increased PaCO₂---P_ETCO₂ gradient during controlled ventilation.     

Monitored arterial and end-tidal carbon dioxide during in-flight mechanical ventilation

Introduction: Mechanical ventilation with monitored arterial carbon dioxide tension is necessary for optimum pulmonary support and hemodynamic stability. Ongoing monitoring is necessary to ensure adequate ventilation parameters. The prospective study purpose was to (1) compare mechanical ventilation to historic manual ventilation, (2) evaluate the effectiveness of institutional tidal volume parameters, (3) determine the effect of institutional tidal volume manipulation on end-tidal carbon dioxide tension, and (4) explore the relationship between in-flight end-tidal carbon dioxide tension and arterial carbon dioxide tension.

Methods: Randomized groups were mechanically ventilated (tidal VOLUME = 12 cc/kg, RATE = 14/min) with a target arterial carbon dioxide tension between 30 and 35 torr. Group I was monitored with in-line end-tidal carbon dioxide tension, and group II was monitored with arterial carbon dioxide tension by means of inflight arterial blood gas.

Results: Arterial carbon dioxide tension varied less with monitored mechanical than with manual ventilation (p = 0.001). The gradient between arterial and end-tidal carbon dioxide tension was 5.3 ± 4.4 (mean ± standard deviation [SD]). End-tidal and arterial carbon dioxide tension positively correlated (r = 0.76, P = 0.001), yet end-tidal carbon dioxide tension accounted for only 58% variation of arterial carbon dioxide tension (r² = 0.58).

Conclusion: Mechanical ventilation is more precise but inconsistent in achieving a target arterial carbon dioxide tension with current ventilation parameters. End-tidal carbon dioxide tension is a reasonable estimate of, but cannot exclusively replace, arterial carbon dioxide tension in critically ill patients.