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Low saturation readings by pulse oximetry in a child with Haemoglobin Köln disease
- Benoit Beauve, Oliver R Dearlove (24 September 2008)
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Benoit Beauve, Consultant Anaesthetist Royal Manchester Children's Hospital, Oliver R Dearlove
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Dear Sir We were very interested to read the case report on the abnormal saturation that Holdcroft and Quinn reported in the BJA1 and would like to report another case with further observations. A five year old girl was admitted to hospital with a four day history of abdominal pain accompanied by episodes of vomiting and diarrhoea. The only relevant condition in the past medical history of the child was a rare haemoglobinopathy; Hb Köln2. The child’s haemoglobin level was normally around 10 g dl-1. On admission, her heart rate was 150 bpm, respiratory rate 40 per minute, arterial pressure 106/75 mm Hg, oxygenation saturation 90% in air, oscillating between 90% and 95% in 3L per minute face mask oxygen. Temperature was 38.9°C. The child’s mother, also affected by the same haemoglobin condition, reported that low saturation readings with pulse oximeter had been common in her case. After appropriate fluid resuscitation, the surgeon decided to proceed to an urgent laparotomy. In the induction room, standard monitoring was established including pulse oximetery (Finger sensor Oxy-F-DB, GE Medical®) with a finger probe showing a reading of 90% with 3 L per min oxygen delivered via a loose fitting face mask. Three minutes preoxygenation, with a tight fitting face mask did not have any effect on the level of saturation which remained at 90-91%. A standard rapid sequence induction was performed, air entry was symmetric following an uneventful intubation. Recruitment manoeuvres with the Jackson-Rees circuit at 100% FiO2 did not change the SpO2 which stuck at 90 % . Et CO2 remained stable between 5.1 and 5.5 kPa. There were no other abnormal signs. Anaesthesia was maintained with sevoflurane(1.3 MAC), and an eventful appendicectomy was performed. Intraoperative and postoperative analgesia was provided with fentanyl, chirocaine 0.25% wound infiltration and diclofenac rectally and paracetamol. Extubation after reversal with neostigmine 50 μg kg-1 and glycopyrrolate 10μg kg-1 was uneventful. The child made an otherwise uneventful recovery from anaesthesia and surgery. Respiratory and haemodynamic parameters remained within normal ranges but the saturation readings were again 90% in air and 92-94% with supplemental oxygen 3L per min through a facial mask(Finger sensor OXY-F4-N, Datex- Ohmeda®). Because of the suspected inaccuracy in saturation measurement as a result of the haemoglobinopathy, an arterial blood sample was taken during the operation. The results were as follows (Radiometer ABL 700 series Blood Gas Analyser) : pH 7.32, PaCO2 4.9 kPa, PaO2 43.8 kPa, actual bicarbonate 19 mmol L-1, base excess -6 mmol L-1, Oxygen saturation (CO- Oximetry) 96.3%, Lactate 1.0 mmol L-1 Carboxyhaemoglobin 0.5% and methaemoglobin 1.2%. Discussion: Hb Köln is one of the commonest unstable haemoglobins, a group of autosomal dominant inherited haemoglobinopathies characterised by the presence of an abnormal haemoglobin which precipitates within the red cells to form Heinz bodies2. Hb Köln leads to an usually well tolerated non-spherocytic haemolytic anaemia which can be exacerbated by oxidant- type agents (e.g. sulfonamides), fever or infections. Other features in Hb Köln disease are jaundice, dark urine and splenomegaly due to hypersplenism. Treatment of Hb Köln is non specific and includes folic acid supplements and avoidance of oxidant drugs. Blood transfusion might be necessary as well as splenectomy in some cases. Hb Köln has an increased tendency to produce methaemoglobin3. Pulse oximetry estimates the arterial saturation of haemoglobin by measuring the absorption by the capillary bed of 2 wavelengths of light, one in the red light spectrum(660 nm) and the other nearer to infrared light(940 nm) 4-8. Because of the use of 2 wavelengths, pulse oximeters are only capable of identifying two haemoglobins at most, and these are, oxyhaemoglobin and deoxyhaemoglobin. The presence of a dyshaemoglobin like methaemoglin, carboxyhaemoglobin or unstable haemoglobin such as Hb Köln can interfere with an accurate estimation of the SpO2 by this method. It is natural to ask if it is the methaemoglobin or the Hb Koln itself which is causing the low saturations readings. Two other cases illustrate this point. The first case involved a 9 year-old boy. An unexpected saturation level of 89% had been found in the operation room before induction of anaesthesia9. The discrepancy between PaO2 level and oxygen saturation measured by pulse oximetry had been explained by the probable direct implication of Hb Köln abnormal structure what was supported by the study of absorbance curves of haemoglobin fractions in the patient. In the second case10, the pulse oximeter displayed an oxygen saturation in air of 89% . Breathing 100% oxygen increased saturation to 92%. Methaemoglobin and carboxyhaemoglin levels, were higher than the normal range and may have accounted for some but probably not all of the spurious low saturations. This means the low saturation readings would have to be due, in part, to the abnormal structure of Hb Köln itself. In our case, no chronic condition or any acute clinical symptoms or signs other than the low SpO2 could be found. The discrepancy between oxygen saturation recorded by pulse oximetry(90%), the arterial oxygen saturation(Sa O2) measured by CO-Oxymetry(96.3%) and Pa O2 (43.8 kPa) confirmed the absence of hypoxaemia and the presence of an artifactually low pulse oximetry reading. In both previously reported cases, a raised level of carboxyhaemoglobin or methaemoglobin had been reported at some point concomitantly with the low SpO2 readings. In our case, the presence of an artifactually low pulse oximetry reading associated with normal range levels of carboxyhaemoglobin and methaemoglobin lead to the conclusion that Hb Köln itself was responsible for the inaccurate SpO2 readings by pulse oximetry in our patient Hohl et all. reporting a case of low saturation by pulse oximetry associated with haemoglobin Cheverly11 concluded that pulse oximetry might not be suitable to monitor patient with unstable haemoglobins. The case we report supports this finding. This differs from the studies about sickle cell disease which showed that pulse oximetry reliably assessed arterial capillary blood saturation11. In patients with unstable haemoglobin, if a long procedure is considered, we suggest the use of arterial gas samples to evaluate the oxygenation of the patient is mandatory. Benoit Beauve MD Oliver Dearlove MB FRCA Royal Manchester Children's Hospital Table of references 1. Holbrook SP, Quinn A. An unusual explanation for low oxygen saturation. Br J Anaesth 2008; 101: 350-353 2. Horst J, Oehme R, Kohne E. Hemoglobin Köln: direct analysis of the gene mutation by synthetic DNA probes. Blood 1986; 68(5): 1175-7 3. Hurford W E, Kratz A. Case records of the Massachusetts General Hospital : Case 23-2004. New Engl J Med 2004; 351(4): 380-387 4. Lang SA, Chang PC, Laxdal VA} Huisman THJ. Haemoglobin Hammersmith precludes monitoring with conventional pulse oximetry. Can J Anaesth 1994; 41: 965-8 5. H. Razafimahefa, P. Gatel. Oxygen therapy in newborn : equipments for non-invasive monitoring. J Gynecol Obstet Biol Reprod 2005; 34(1 suppl.) : S42-46 6. Yitzhak Mendelson. Pulse Oximetry: Theory and Applicationsfor Noninvasive Monitoring. Clin Chem 1992; 38(9) : 1601-1607 7. KK Tremper. Pulse oximetry. Chest 1989; 95: 713-715 8. Kevin K. Tremper, Steven J. Barker. Pulse Oximetry. Anesthesiology 1989; 70: 98-108 9. Katoh R, Miyake T, Arai T. Unexpectedly low pulse oximeter readings in a boy with unstable hemoglobin Köln. Anesthesiology 1994; 80(2): 472-4 10. Gottschalk A, Silverberg M. An unexpected finding with pulse oximetry in a patient with hemoglobin Köln. Anesthesiology 1994; 80(2): 474-6 11. Hohl RJ, Sherburne AR, Feeley JE, Huisman TH, Burns CP. Low pulse oximeter-measured hemoglobin oxygen saturations with hemoglobin Cheverly. Am J Hematol 1998; 59(3): 181-4 Conflict of Interest:Dr O Dearlove was previously ex officio member of the BJA Trust Mgt Board up to 2007, by reason of being Joint Treasurer of the Royal College of Anaesthetists |
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