Effectiveness of preoxygenation using the head-up position and noninvasive ventilation to reduce hypoxaemia during intubation

Objective

The purpose of this article was to present an update of the preoxygenation management in morbidly obese adults, parturient women and hypoxemic critically-ill patients.

Data sources

All references obtained from the medical database Medline^® related to the area and more specifically during the last five years were reviewed.

Data synthesis

Preoxygenation decreases the risk of hypoxia and should be optimized when the standard technique appears to be less effective as in morbidly obese adults, parturient women and critically-ill patients. The head-up position and noninvasive ventilation may be useful during preoxygenation probably because of the increase of ventilation and alveolar recruitment. The effectiveness of preoxygenation (when defined as the duration of the desaturation safety period) is enhanced in the head-up position as compared to supine position in the obese patient but not in parturient women. Noninvasive ventilation improves preoxygenation in the hypoxemic critically-ill patient but not in the obese patient. Neither the head-up position nor the noninvasive ventilation improve preoxygenation in parturient women.

Conclusion

Further studies are required to investigate other methods attempting to improve preoxygenation and prevent hypoxemia during intubation.     

Diffusion hyperoxia following preoxygenation

Several minutes of 100 percent O2 breathing prior to inhalation induction with 79 percent N23 results in consistently higher PaO2 values during the first 10 minutes compared with prior air breathing. The theoretic maximum concentrating action of N2O uptake upon O2 is approximately the same (60 torr) regardless of gas breathed before induction.     

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.     

Servo-plethysmo-manometry for continuous noninvasive blood pressure monitoring

Servoplethysmomanometry (Penáz method) is based on the principle of "vascular unloading" or "arterial volume clamp". It permits continuous recording of the arterial pressure pulse in a finger. We evaluated such a device (Finapres) intraoperatively in cardiac surgical patients and compared the results with those obtained using simultaneous intra-arterial pressure recording. METHODS. Intravenous anesthesia was employed in a total of 31 patients. Invasive pressure monitoring was carried out in the radial artery. The cuff of the Finapres was wrapped around the 3rd finger, either on the same side as the radial cannula (group I, n = 15) or on the contralateral side (group II, n = 16). Quantitative comparison was accomplished for the paired values obtained by the two methods by calculating linear regression equations and correlation coefficients (r), as well as for the differences between the paired values (means, SD, frequency distributions). RESULTS. In group I (ipsilateral recording), r was 0.74 for systolic (SAP), 0.52 for diastolic (DAP), and 0.77 for mean (MAP) pressure. The means +/- SD of the differences (mm Hg) were -1.6 +/- 16.6 (SAP), 4.6 +/- 11.5 (DAP), and 0.2 +/- 11.3 (MAP). In group II (contralateral recording), r was found to be 0.86 (SAP), 0.72 (DAP), and 0.82 (MAP). The mean differences were -2.7 +/- 13.1 (SAP), 4.7 +/- 9.8 (DAP), and -2.6 +/- 10.9 mm Hg (MAP). Prior to cardiopulmonary bypass (CPB) the results of the two methods corresponded to a higher degree than after CPB; during CPB the MAP values correlated poorly in the two groups (r = 0.62). DISCUSSION. The results obtained may be interpreted to mean that the Finapres will enable us to monitor arterial blood pressure continuously with satisfactory reliability when the cuff design has been improved.     

Continuous noninvasive blood pressure monitoring during thoracic surgery.

To evaluate the usefulness of noninvasive blood pressure monitoring during thoracic surgery, blood pressure measurements obtained with the Finapres 2300 (Ohmeda, Boulder, CO) were compared with an intraarterial catheter system in 10 patients undergoing thoracotomy for lobectomy or pneumonectomy. The Finapres measurements were compared with pressure data obtained ipsilaterally from a radial artery catheter-transducer system. The waveforms were recorded using a strip chart recorder; the systolic (SBP) and diastolic blood pressures (DBP) were measured every 20 seconds on the paper trace. Precision and bias were calculated for SBP and DBP for each patient and for the pooled data, with the invasive blood pressure being considered the gold standard. A total of 1,861 measurement pairs were recorded, 938 pairs during one-lung ventilation. The Finapres underestimated SBP during two-lung ventilation, and overestimated SBP during one-lung ventilation. The precision was good and the biases were small, but there were wide individual variations. It is concluded that the Finapres can be useful in estimating the variability and following the trends of radial arterial blood pressure during thoracic surgery, and is an acceptable alternative to invasive blood pressure monitoring.     

Lessons learned with noninvasive cardiac monitoring for acute rejection

INTRODUCTION: Computerized Heart Allograft Rejection Monitoring (CHARM), used for noninvasive rejection monitoring in heart transplant recipients, is based on the analysis of ventricular evoked response (VER) signals. This study evaluated the prognostic validity of the TslewC, a parameter extrapolated from the VER. METHODS: During orthotopic heart transplantation (OHT) 2 unipolar, fractally coated, screw-in leads implanted epimyocardially were connected to a telemetric pacemaker. Recordings of IEGMs were performed routinely at hospital and at outpatient visits. Data processing yielded trend curves. TslewC was calculated from the tangent of VER. One hundred five patients divided into survivors and nonsurvivors, were compared using a two-tailed Student's t test. RESULTS: In the final follow-up a significant lower TslewC was observed among patients in the nonsurvivor compared with the other group (P<.001). Tests to find an optimal prognostic threshold of the TslewC yielded the value of 26 mV. CONCLUSION: TslewC functioned as a prognostic factor after OHT. Further studies must provide a prognostic threshold to avoid patient visits all 4 weeks. Patients would only have to be admitted to the hospital if the TslewC was under this prognostic threshold.     

Validation of esophageal Doppler for noninvasive hemodynamic monitoring under pneumoperitoneum

Background Commonly used perioperative measurements of hemodynamics, such as Swan-Ganz catheter assessment, are invasive and may not be reliable under pneumoperitoneum. The purpose of this study was to validate the use of esophageal Doppler for noninvasive hemodynamic monitoring under pneumoperitoneum in an experimental pig model. Methods Eight female pigs were submitted to two 30-min study periods, one each for the baseline (no interventions) and pneumoperitoneum (12-mmHg carbon dioxide pneumoperitoneum) conditions. One pig was excluded because of tachycardia (>140 at baseline). A Swan-Ganz pulmonary artery catheter was used to measure cardiac output (CO-SG) and pulmonary capillary wedge pressure (PCWP). An esophageal Doppler probe was inserted to record cardiac output (CO-ED) and corrected flow time (FTc), an index of preload. Transthoracic echocardiography was used to measure left ventricular end-diastolic diameter (LVEDD) and cardiac output (CO-TTE). Pearson correlation was used to assess individual associations between the measured hemodynamic parameters. Results There was good correlation between CO-ED and CO-SG (r = 0.577; p < 0.001) and excellent correlation between CO-ED and CO-TTE (r = 0.815; p < 0.001). There was no correlation between FTc and LVEDD or PCWP. These relationships were consistent when analyzed separately at baseline and during pneumoperitoneum. Conclusion Esophageal Doppler monitoring is a valid noninvasive method of estimating cardiac output at baseline and during pneumoperitoneum in a porcine model. Corrected flow time did not correlate with other estimates of preload at baseline or during pneumoperitoneum. Presented at the annual meeting of the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES), Dallas, TX, USA, April 2006     

Inspiratory support improves preoxygenation in healthy subjects

Canadian Journal of Anesthesia/Journal canadien d'anesthésie -     

Evaluation of noninvasive hemoglobin measurements in trauma patients

Background

Reliable, accurate, noninvasive, and continuous determination of hemoglobin would be an important advance in the care of trauma patients. The aim of this study was to evaluate the utility of the Masimo Radical 7 device in severely injured trauma patients.

Methods

Highest level trauma activation patients were enrolled over a 1-year period. Laboratory hemoglobin values were compared with Masimo hemoglobin values using Bland-Altman analysis.

Results

A total of 525 patients were enrolled in the study. Comparison of 861 paired values from 418 patients showed a variance of 3.89 to −3.84 g/dL, showing a nonsignificant correlation between Masimo hemoglobin and laboratory hemoglobin values.

Conclusions

The Masimo Radical 7 system evaluated in this study holds promise, but it is not ready to be used as an initial noninvasive evaluation tool in the acute treatment of severely injured trauma patients. There was a poor correlation between Masimo hemoglobin and laboratory hemoglobin and large numbers of missing data. On the basis of the poor correlation, the Masimo Radical 7 device cannot currently be used to guide transfusion therapy.     

Single vital capacity breath for preoxygenation

PURPOSE: The report investigates, in awake patients before induction of anesthesia, the effect of preoxygenation by the single vital capacity breath technique following forced exhalation on the mean arterial PO2 (PaO2). METHODS: In 10 adult patients undergoing elective surgery, the mean PaO2 values achieved 30 sec after preoxygenation by the single vital capacity breath technique was compared with the mean PaO2 values achieved by preoxygenation by the traditional tidal volume breathing for three minutes. Each patient served as her/his own control. RESULTS: The mean PaO2 following the single vital capacity breath technique was higher (295 +/- 67 mmHg) than that achieved by the traditional tidal volume breathing technique at 30 sec and 60 sec, and was not significantly different from that achieved by the traditional technique after three minutes (307 +/- 70 mmHg). CONCLUSION: The single vital capacity breath technique following forced exhalation can rapidly provide adequate preoxygenation within 30 sec.     

Acute dermal capillary rupture associated with noninvasive blood pressure monitoring

We report a case of Rumpel-Leede phenomenon, or acute dermis capillary rupture, secondary to noninvasive blood pressure monitoring in a patient with type 2 diabetes mellitus. The most likely cause was increased venous pressure during cycling of the blood pressure cuff during a hypertensive state. Anesthesiologists need to be aware that acute dermal capillary rupture, although rare, can occur in patients with thrombocytopenia and/or long-standing diabetes.