A normal case of SpO2 in patients with severe hypoxemia

The patient, female, 38 years old, weight 55 kg, because of the "physical examination found the right lung accounted for 6d" hospital, diagnosed as the right lung lower leaf occupaic lesions, intended in the whole hemp lower chest mirror right lung lower endoscopic excisionPatients have a history of hypertension for 6 years, usually oral ammonia chloroline, Inapri, neutrino seyls treatment, blood pressure control is goodPreoperative ECG, lung function, blood routine, biochemical examination did not show significant abnormalitiespreoperative PaO2 91.3mmHg, SaO2 96.4%, SpO2 99%Regular electrocardiogram monitoring after admission, BP135/80mmHg, HR80 times/min, SpO2 99%Mask pre-charge, FiO2 100%, oxygen flow 6L/min, 5min after line full hemp induction, intravenous hydrochloric acid ethyl ether 0.5mg, propofol 100mg, shun adecex ammonium 10mg, Shufentani 15 mg, the induction process is smooth, SpO2 has always been maintained at 100%Mask ventilation 3min after visual laryngoscope inserted the left side 35 double-cavity bronchial tube, the process is smooth, depth of 29 cm, hearing-ath-mouthed double lung breathing sound clear, good position, fiber bronchoscopy positioning to determine the depthConnect ingess with mechanical ventilation, breathing parameters: FiO2 100%, oxygen flow 2L/min, VT450ml, RR13/minintravenous continuous pump with propofol 3.5mg kg-1 h-1, Riffentani 8?g-kg-1-h-1, 1.5% heptafluoroetheration compound maintenance anesthesiaThen the left side of the line of the artery puncturetube pressure measurement, the process is smooth, parallel left single lung ventilationAfter the patient changed the left sleeper, the air duct pressure increased to 40 cmH2O, the hearing left lung breathing sound decreased, changed the double lung ventilation, airway pressure decreased, the line fiber bronchoscopy examination saw the left bronchial tube position is too deep, and see more sputum, in the mirror will be double cavity tube back to 28 cm, sputum, lung, hearing double respiratory sound clearthe entire process SpO2 is always 100%, continue to the left lung ventilation, surgery beganConsideration of the patient's young and denial of the history of chronic respiratory disease is not taken seriouslyThe operation was performed at about 40min, the left side of the artery blood pumping blood gas test, the blood is dark redResults showed: PaO2 38.8mmHg, SaO2 80.6%, K.2.76mmol/L, Lac 1.0mmol/L, Carbon Oxygen Hemoglobin (COHb) 1.1%At this time the patient's vital signs are stable, SpO2 is 99%, replace the monitor, and change the finger oxygen saturation monitoring probe site, SpO2 is still 99% The right-hand artery punctures the tube and conducts two different blood gas analyzers at the same time, the results are the same Because at this time can not find the cause of the decline of PaO2 and SaO2, suspended surgery and restore double lung ventilation, the method of swelling of the lungs intravenous drip methyl strong pine dragon 80mg to prevent hypoxic brain damage, static drop potassium chloride to correct low potassium After 3min arterial blood and peripheral venous blood re-examination blood gas, PaO2 85.8mmHg, SaO2 98.8%, K-2.78mmol/L, Lac 1.0mmol/L, COHb 0.8%; intravenous Blood: PaO2 39.7mmHg, SvO2 80.7%, K-2.69mmol/L, Lac 1.4mmol/L, COHb 1%, SpO2 is about 98% throughout the process, not falling Double lung ventilation after 10min change left lung ventilation, continue surgery The entire operation lasted about 3h, the patient woke up, consciousness restored, sent to PACU observation When out of PACU patients are normal, SpO2 suction air state is 96%, review arterial blood gas, results show: PaO2 67.3mmHg, SaO2 95.9%, K.3.19mmol/L, Lac1.2mmol/L, COHb 0.8% the first and fourth days after surgery on the patient and another patient who performed the same surgery on the same day but during the operation PaO2 normal patient line simple mental status test scale (MMSE) test, the test score is 28 points, 7d after the patient recovered discharge discussion the monitoring and treatment of hypoxemia during single pulmonary ventilation is an important part of thoracic surgery anesthesia In this case, PaO2 38.8mmHg occurred during single pulmonary ventilation and developed severe hypoxemia The possible causes of hypoxemia are: (1) a serious imbalance in the blood flow ratio of the ventilation during single lung ventilation Blood flowing through the unventilated side lung during single pulmonary ventilation is returned to the left atrium without oxygenation, causing intravenous blood doping and causing PaO2 to drop And normally the blood flow of the right lung is about 10% more than the left lung, so the incidence of hypoxemia increases when the right lung is withering compared with the left lung In this case, the patient had blood flow due to the left side lysage, the right lung was not ventilated, resulting in a false diversion of the blood in the venous vein, and the blood flow ratio of the right pulmonary ventilation decreased, which eventually led to the decline of PaO2 (2) Left lung is not open In this case, the left broncus in the patient's left side is in the sputum, which is easy to clog the bronchial tube And when the abdominal cavity contents push and squeeze the shin muscle up shift, FRC drops, causing the left lung inflated, resulting in a decrease in the function of left lung ventilation, further aggravating the imbalance of the blood flow ratio of ventilation when a patient is found to have severe hypoxemia, we immediately resume double pulmonary ventilation and pneumoconiosis treatment, reducing the imbalance in the blood flow ratio of ventilation, hypoxemia also improved rapidly In clinical work, we often use SpO2 as an important indicator to monitor the oxygenation status of the body, and SpO2 as the threshold of hypoxemia, however, during the patient's single lung ventilation, SpO2 99% under pure oxygen ventilation conditions, while PaO2 38.8mmHg, SaO2 80.6%, which suggests that we SpO2 has a certain "negative" when it finds hypoxemia After troubleshooting the instrument and misentering the puncture needle into the vein, the patient found that the change in SaO2 was not in serious conformity with SpO2 The reason for the difference is analyzed: SaO2 is the percentage of oxygen content and oxygen capacity, and its value is related to PaO2 in a certain range blood gas analyzer is based on this principle, through the determination of the blood PaO2, and the actual SaO2 value is converted SpO2 is based on the principle that different wavelengths of light will occur after crossing the arterial blood, and are measured by photovolume tracing Pulse blood oxygen saturation monitoring the side of the probe simultaneously emits red light at the same time and 940 nm infrared light, oxidizing hemoglobin (HbO2) and reducing hemoglobin (Hb) absorption of the above two kinds of light is different, it is based on this difference, the photoelectric sensor located on the other side of the probe by measuring the intensity of infrared light and red light through the tissue, using the photometric conversion method to determine the absorption of infrared light and red Differences in SaO2 and SpO2 measurements resulted in the case being inconsistent in severe hypoxemia There are several conditions that can lead to an increase in SpO2 falseity: increase in COHb in the blood (1) COHb is close to HbO2, while pulse oxicosis can only distinguish between HbO2 and Hb, and CANnot exclude COHb, thus resulting in a high value of SpO2 (2) MetHb haemogloba MetHb's absorption coefficient of red and infrared light is larger, with a light absorption coefficient similar to Hb at the 660nm wavelength, and higher to Hb and HbO2 at 940nm wavelength Therefore, if the actual arterial oxygen saturation is low, the reading of SpO2 will be falsely high, whereas, the spO2 reading will be false low patients with severe anemia (3) Anemia patients due to the total oxygen carrying of hemoglobin decreased, and caused anemia hypoxia At low oxygen fractions, although the amount of oxygenated hemoglobin decreases, but the oxygen capacity of the blood also decreases, at this time the values of SaO2 and SpO2 will show normal, resulting in measurement errors (4) hereditary fetal hemoglobin (HbF) haemogloba Under normal circumstances, the blood of HbF with the growth of the fetus gradually decreased, the content of the body after 6 to 12 months of birth to less than 2%, at this time mainly adult hemoglobin (HbA), but some genetic factors will make HbF content increased Compared with HbA, HbF cannot bind 2,3 bisphosphoric acid (2,3-DPG) in the blood, so it is less than adult hemoglobin, and HbF's oxygen-dissoced curve moves to the left, which is not conducive to oxygen release However, because HbF and oxygen have a higher affinity, even in the case of low oxygen pressure, the oxygenated hemoglobin content in the body can still be maintained at a high level, according to the principle of SpO2 determination, at this time its value can be maintained at normal levels, and PaO2 and SaO2 show a reduced state In this case, the content of COHb was in the normal range (COHb 2%) during anesthesia, and Hb was always higher than 120g/L, and there was no symptoms of cyanosis deficiency in the skin mucosa, bed and other purple hypoxia before surgery the results of hemoglobin and monitoring during the combination, the analysis suggested that the cause of the serious difference between SpO2 and SaO2 during surgery in the patient may be hereditary fetal hemoglobinemia Because of the correlation between SpO2 and SaO2, and because of its portable and inexpensive characteristics, hemogas analysis is often used to monitor oxygenation in patients during anesthesia and ICU mechanical ventilation However, Ouyang Yu and other found single lung ventilation when PaO2 in 70 to 60mmHg below, SpO2 is 90% to 94% The patient's single lung ventilation period SpO2 and PaO2 and SaO2 showed a serious mismatch, if SpO2 is simply used as the only indicator to determine the oxygenation state of the body, there will be an unpredictable risk through timely treatment during surgery and evaluation of postoperative nerve function, the patient did not experience hypoxic-induced damage to the central nervous system function In summary, in clinical practice, we need to recognize that although SpO2 has been used as a routine monitoring during anesthesia, it is not a complete substitute for blood gas monitoring In this case, saO2 decreased while SaO2 was normal, considering that the patient is a genetic fetal hemoglobinemia is likely, but the patient refused further examination, can not be diagnosed Therefore, for patients with increased risk of hypoxemia in surgery, the joint arterial blood gas monitoring should be combined with the operation to judge the patient's oxygenation status and ensure the safety of anesthesia