OBJECTIVE: To investigate the effect of different fraction of inspired oxygen (FiO₂) baseline levels before endotracheal intubation on the time of expiratory oxygen concentration (EtO₂) reaching the standard in emergency patients with the EtO₂ as the monitoring index. METHODS: A retrospective observational study was conducted. The clinical data of patients receiving endotracheal intubation in the emergency department of Peking Union Medical College Hospital from January 1 to November 1 in 2021 were enrolled. In order to avoid interference with the final result due to inadequate ventilation caused by non-standard operation or air leakage, the process of the continuous mechanical ventilation after FiO₂ was adjusted to pure oxygen in patients who had been intubated was selected to simulate the process of mask ventilation under pure oxygen before intubation. Combined with the electronic medical record and the ventilator record, the changes of the time required to reach 0.90 of EtO₂ (that was, the time required to reach the standard of EtO₂) and the respiratory cycle required to reach the standard after adjusting FiO₂ to pure oxygen under different baseline levels of FiO₂ were analyzed. RESULTS: 113 EtO₂ assay records were collected from 42 patients. Among them, 2 patients had only one EtO₂ record due to the FiO₂ baseline level of 0.80, while the rest had two or more records of EtO₂ reaching time and respiratory cycle corresponding to different FiO₂ baseline level. Among the 42 patients, most of them were male (59.5%), elderly [median age was 62 (40, 70) years old] patients with respiratory diseases (40.5%). There were significant differences in lung function among different patients, but the majority of patients with normal function [oxygenation index (PaO₂/FiO₂) > 300 mmHg (1 mmHg ≈ 0.133 kPa), 38.0%]. In the setting of ventilator parameters, combined with the slightly lower arterial partial pressure of carbon dioxide of patients [33 (28, 37) mmHg], mild hyperventilation phenomenon was considered to be widespread. With the increased in FiO₂ baseline level, the time of EtO₂ reaching standard and the number of respiratory cycles showed a gradually decreasing trend. When the FiO₂ baseline level was 0.35, the time of EtO₂ reaching the standard was the longest [79 (52, 87) s], and the corresponding median respiratory cycle was 22 (16, 26) cycles. When the FiO₂ baseline level was increased from 0.35 to 0.80, the median time of EtO₂ reaching the standard was shortened from 79 (52, 78) s to 30 (21, 44) s, and the median respiratory cycle was also reduced from 22 (16, 26) cycles to 10 (8, 13) cycles, with statistically significant differences (both P < 0.05). CONCLUSIONS The higher the FiO₂ baseline level of the mask ventilation in front of the endotracheal intubation in emergency patients, the shorter the time for EtO₂ reaching the standard, and the shorter the mask ventilation time.
Aged ; Humans ; Male ; Middle Aged ; Female ; Intubation, Intratracheal ; Respiration ; Ventilators, Mechanical ; Arteries ; Blood Gas Analysis

OBJECTIVETo study the accuracy of pulse contour cardiac output (PCCO) during blood volume change.

METHODSHemorrhagic shock model was made in twenty dogs followed by volume resuscitation. Two PiCCO catheters were placed into each model to monitor the cardiac output (CO). One of catheters was used to calibrate CO by transpulmonary thermodilution technique (COTP) (calibration group), and the other one was used to calibrate PCCO (none-calibration group). In the hemorrhage phase, calibration was carried out each time when the blood volume dropped by 5 percents in the calibration group until the hemorrhage volume reached to 40 percent of the basic blood volume. Continuous monitor was done in the none-calibration group.Volume resuscitation phase started after re-calibration in the two groups. Calibration was carried out each time when the blood equivalent rose by 5 percents in calibration group until the percentage of blood equivalent volume returned back to 100. Continuous monitor was done in none-calibration group. COTP, PCCO, mean arterial pressure (MAP), systemic circulation resistance (SVR), global enddiastolic volume (GEDV) were recorded respectively in each time point.

RESULTS(1) At the baseline, COTP in calibration group showed no statistic difference compared with PCCO in none-calibration group (P >0.05). (2) In the hemorrhage phase, COTP and GEDV in calibration group decreased gradually, and reached to the minimum value (1.06 ± 0.57) L/min, (238 ± 93) ml respectively at TH8. SVR in calibration group increased gradually, and reached to the maximum value (5 074 ± 2 342) dyn · s · cm⁻⁵ at TH6. However, PCCO and SVR in none-calibration group decreased in a fluctuating manner, and reached to the minimum value (2.42 ± 1.37) L/min, (2 285 ± 1 033) dyn · s · cm⁻⁵ respectively at TH8. COTP in the calibration group showed a significant statistic difference compared with PCCO in the none-calibration group at each time point (At TH1-8, t values were respectively -5.218, -5.495, -4.639, -6.588, -6.029, -5.510, -5.763 and -5.755, all P < 0.01). From TH1 to TH8, the difference in percentage increased gradually. There were statistic differences in SVR at each time point between the two groups (At TH1 and TH4, t values were respectively 2.866 and 2.429, both P < 0.05, at TH2 - TH3 and TH5 - TH8, t values were respectively 3.073, 3.590, 6.847, 8.425, 6.910 and 8.799, all P < 0.01). There was no statistic difference in MAP between the two groups (P > 0.05). (3) In the volume resuscitation phase, COTP and GEDV in the calibration group increased gradually. GEDV reached to the maximum value ((394±133) ml) at TR7, and COTP reached to the maximum value (3.15 ± 1.42) L/min at TR8. SVR in the calibration group decreased gradually, and reached to the minimum value (3 284 ± 1 271) dyn · s · cm⁻⁵ at TR8. However, PCCO and SVR in the none-calibration group increased in a fluctuating manner. SVR reached to the maximum value (8 589 ± 4 771) dyn · s · cm⁻⁵ at TR7, and PCCO reached to the maximum value (1.35 ± 0.70) L/min at TR8. COTP in the calibration group showed a significant statistic difference compared with PCCO in the none-calibration group at each time point (At TR1-8, t values were respectively 8.195, 8.703, 7.903, 8.266, 9.600, 8.340, 8.938, 8.332, all P < 0.01). From TR1 to TR8, the difference in percentage increased gradually. There were statistic differences in SVR at each time point between the two groups (At TR1, t value was -2.810, P < 0.05, at TR2-8, t values were respectively -6.026, -6.026, -5.375, -6.008, -5.406, -5.613 and -5.609, all P < 0.05). There was no statistic difference in MAP between the two groups (P > 0.05).

CONCLUSIONPCCO could not reflect the real CO in case of rapid blood volume change, which resulting in the misjudgment of patient's condition. In clinical practice, more frequent calibrations should be done to maintain the accuracy of PCCO in rapid blood volume change cases.

Animals ; Blood Volume ; Calibration ; Cardiac Output ; Disease Models, Animal ; Dogs ; Humans ; Monitoring, Physiologic ; Shock, Hemorrhagic ; diagnosis ; Thermodilution