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[Life in the Fast Lane]: 氧饱和度分离(4/4)
2020年09月28日 临床话题, 模拟诊室 暂无评论

Dissociated Oxygen Saturations

by Dr Paul Young, last update March 16, 2019

aka Hematology Hoodwinker 004

One of the emergency residents has just taken an ABG on the 44 year-old woman in cubicle 3. Prior to her current presentation she had no known medical problems. The patient’s pulse oximetry reading is SpO2 98% on air.

急诊科的一名住院医师刚刚为一名44岁的女性患者做了动脉血气检查。此次发病前,患者没有既往病史。患者吸空气时脉搏氧饱和度(SpO2)为98%。

This is the arterial blood gas:

患者动脉血气结果如下:

Questions 问题

Q1. What are the possible explanations for the discrepancy between the pulse oximetry reading and the oxygen saturation on the arterial blood gas?脉搏氧饱和度与动脉血气氧饱和度结果不一致的可能原因有哪些?

A1. Answer and interpretation回答与解释

Possible explanations for ‘pseudo-hypoxaemia’ include

假性低氧血症的可能原因包括

  • Equipment failure
    — faulty pulse oximeter
    — faulty blood gas analyser
  • Blood sample used was actually venous
  • Blood sample taken from a site affected by localised hypoxemia, e.g. ischaemic limb
  • Excessive oxygen consumption following blood sample collection (e.g. massive leukocytosis or thrombocytosis)
  • 设备故障
    — 脉搏氧饱和度仪错误
    — 血气分析仪错误
  • 使用的血液标本为静脉血
  • 采取血液标本的部位受到局部低氧血症的影响,如肢体缺血
  • 血液标本采集后过度氧耗(如严重的白细胞增多症或血小板增多症)

Dyshemoglobinemia can also cause a discrepancy between SpO2 and SaO2, but will not cause the decrease in measured PaO2 as seen in this case.

异常血红蛋白血症也可以导致SpO2 与 SaO2 不一致,但不会引起本例看到的PaO2降低。

  • In carbon monoxide poisoning SpO2 will read in the 90s despite high levels of COHb — but the PaO2 should still be high.
  • In methemoglobinemia, the SpO2 plateaus at about 86% with increasing levels of MetHb, but again the PaO2 will not be decreased.
  • 一氧化碳中毒时,SpO2可能仅为90%,尽管COHb水平很高 — 但PaO2 仍然应当很高
  • 高铁血红蛋白时,随着MetHb水平不断升高,SpO2在86%达到平台,但PaO2同样不会降低

Q2. What other blood test would be particularly helpful?其他哪些血液检查结果会有帮助?

A2. Answer and interpretation回答与解释

The full blood count

全血细胞计数

This is what the patient’s blood test showed:

以下是患者血液检查结果:

Q3. Describe the blood test result shown in Q2?

Q3. 请描述Q2中血液检查结果

A3. Answer and Interpretation

A3. 答案与解释

The key findings are

主要发现为:

  • massive leukocytosis, due to a large number of blasts
  • normocytic anemia (Hb 98 with normal MCHC), mild macrocytosis (MCV 98) and increased RDW (17.9)
  • thrombocytopenia
  • 因为大量母细胞造成的重度白细胞增多症
  • 正常细胞性贫血(Hb 98且MCHC正常),红细胞轻度增大(MCV 98),RDW升高 (17.9)
  • 血小板缺乏

Spurious hypoxaemia in this setting is also known as ‘leukocyte larceny’.

本例中假性低氧血症也被称为“白细胞盗窃”。

Q4. Interpret the blood test result shown in Q2? What is the likely underlying diagnosis?

Q4. 解释Q2中血液检查结果?最可能的诊断是什么?

A4. Answer and Interpretation

A4. 答案与解释

Acute myeloid leukemia

急性髓系白血病

Hyperleukocytosis (>100 x 10E9/L) is almost always due to a hematological malignancy.

白细胞增多 (>100 x 10E9/L) 几乎总是由于血液系统恶性肿瘤造成。

Blast cells in the blood suggest acute leukemia or a blast cell crisis. The presence of Auer rods in the blast cells would confirm the diagnosis of acute myeloid leukemia. Blast cell crisis occurs when chronic myeloid leukemia (CML) undergoes transformation into a more aggressive condition.

血液中的母细胞提示为急性白血病或母细胞危象。母细胞内发现Auer小体可以确诊急性髓系白血病。慢性髓系白血病(CML)发生急变时即可出现母细胞危象。

Blast cells are immature precursors of either lymphocytes (lymphoblasts), or granulocytes (myeloblasts). They do not normally appear in peripheral blood. They can be recognized microscopically by their large size and primitive nuclei (ie the nuclei contain nucleoli).

The anemia and thrombocytopenia is consistent with bone marrow failure.

贫血与血小板缺乏与骨髓功能衰竭相符合。

Q5. What other complications is this patient at risk of?. 此例患者还可能出现什么其他并发症?

A5. Answer and Interpretation 答案与解释

Potential complications include

可能的并发症包括

  • hyperviscosity syndrome due to massive leukocytosis (e.g. altered mental state, stroke, pulmonary leukostasis, renal insufficiency, and priapism)
  • bleeding and disseminated intravascular coagulation (DIC)
  • infections due to immune suppression
  • syncope and ischemia due to anemia (decreased oxygen delivery)
  • acute respiratory distress syndrome (ARDS) due to haematopoietic mediators, leukostasis and leukaemic cell lysis pneumopathy
  • complications of treatment (e.g. chemotherapy side effects,  tumour lysis syndrome, transfusion reactions, bone marrow transplant)
  • 因严重白细胞增多造成的高粘滞度综合征(如,意识改变,卒中,肺白细胞滞留,肾功能衰竭和阴茎异常勃起)
  • 出血和DIC
  • 免疫功能抑制导致感染
  • 贫血导致昏迷和缺血(氧输送降低)
  • 造血介质、白细胞滞留及白血病细胞溶解肺病引起的ARDS
  • 治疗并发症(如化疗副作用,溶瘤综合征,输血反应,骨髓抑制)

Note the possible respiratory complications of conditions that cause hyperleukocytosis — measured hypoxaemia may be real or spurious!

注意引起白细胞增多的病因可能合并的呼吸系统并发症 - 测定的低氧血症可能是真的,也可能是假的!

Q6. What are the treatment options?治疗选择有哪些?

A6. Answer and Interpretation 答案与解释

Management of hyperleukocytosis (>100 x 10E9/L in the context of AML) includes

白细胞增多 (AML患者>100 x 10E9/L)的治疗包括

  • Treat the underlying condition (e.g. chemotherapy for AML) and subsequent complications such as tumour lysis syndrome
  • Hydration
  • Leukophoresis
  • Avoid unnecessary blood transfusions
  • Supportive care
  • 治疗基础疾病(如AML的化疗)及后续并发症如溶瘤综合征
  • 水化
  • 白细胞置换
  • 避免不必要的输血
  • 支持治疗

Q7. How could the abnormal blood gas result be avoided?如何避免得到异常血气结果?

A7. Answer and Interpretation 答案与解释

Abnormalities in PaO2, PaCO2 and pH may be mitigated in the presence of massive leukocytosis by

严重白细胞增多时,PaO2, PaCO2和pH值异常可能通过以下方法减轻

  • processing the sample rapidly
  • transporting the sample on ice
  • 迅速处理标本
  • 转运标本时采用冰浴

Note that massive leukocytosis can also result in pseudohypoglycemia due to ongoing glucose metabolism after a blood sample is collected.

注意,严重白细胞增多时,由于采集血液标本后糖代谢仍在持续,因此还可能导致假性低血糖

References

参考文献

  • Cammalleri L, Malaguarnera M. Rasburicase represents a new tool for hyperuricemia in tumor lysis syndrome and in gout. Int J Med Sci. 2007 Mar 2;4(2):83-93. Review. PubMed PMID: 17396159; PubMed Central PMCID: PMC1838823.
  • Chillar RK, Belman MJ, Farbstein M. Explanation for apparent hypoxemia associated with extreme leukocytosis: leukocytic oxygen consumption. Blood. 1980 Jun;55(6):922-4. PubMed PMID: 7378581. [fulltext]
  • Lele AV, Mirski MA, Stevens RD. Spurious hypoxemia. Crit Care Med. 2005 Aug;33(8):1854-6. Review. PubMed PMID: 16096465.
  • Mehta A, Lichtin AE, Vigg A, Parambil JG. Platelet larceny: spurious hypoxaemia due to extreme thrombocytosis. Eur Respir J. 2008 Feb;31(2):469-72. PubMed PMID: 18238952. [fulltext]
  • Sacchetti A, Grynn J, Pope A, Vasso S. Leukocyte larceny: spurious hypoxemia confirmed with pulse oximetry. J Emerg Med. 1990 Sep-Oct;8(5):567-9. PubMed PMID: 2254603.

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