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* From the Department of Anaesthesia,
and Department of General SurgerySt. Mary's Hospital, 220 Royal Ave., New Westminster, B.C., V3L 1H6 Canada.
Address correspondence to: Dr. R. Hoskin. Phone: 604-527-3251; Fax: 604-527-3223; E-mail: rhoskin{at}home.com
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Clinical Features: An 83-yr-old female patient underwent sentinel node biopsy of the axilla followed by partial mastectomy for carcinoma of the left breast. Isosulfan blue was injected in the area of the tumour in the left breast. The SpO2 began to decrease 15 min after dye injection, reaching a nadir of 89-90% 30 min after injection. Arterial blood gas analysis showed normal arterial partial pressure of oxygen. Pulse oximeter readings did not return to normal until more than six hours after dye injection.
Conclusion: Review of the literature reveals a small number of case reports of similar occurrences of low pulse oximeter readings following injection of isosulfan blue or patent blue dye for lymphatic mapping. Data from these reports and the case described here suggest that the latency, magnitude and duration of effect on pulse oximeter readings following injection of these dyes is highly variable. It is important to rule out other causes of low pulse oximeter readings when this effect occurs; normal oxygenation can be verified with arterial blood gas analysis. Co-oximetry can be done to rule out methemoglobinemia as a cause of decreased SpO2.
PULSE oximetry relies on the differing absorption of red light by oxyhemoglobin and deoxyhemoglobin, allowing calculation of the percentage of hemoglobin that is saturated with oxygen (SpO2 ). Any substance which absorbs light in the red wavelengths may interfere with the ability of a pulse oximeter to measure oxygen saturation accurately. Dyes such as methylene blue and patent blue five have been reported to cause artificially low SpO2 readings.1–5
Recently, isosulfan blue (Lymphazurin 1%) has begun to be used to facilitate sentinel lymph node biopsy for carcinoma of the breast. In this technique, dye is injected into the area surrounding the tumour. Dye is absorbed into the lymphatics and causes visible discolouration of the lymphatic channels and nodes draining the area of the tumour. Selective biopsy and histopathological analysis of lymph nodes stained by the dye ("sentinel nodes") may provide diagnostic information of equal value to that provided by more extensive axillary node biopsy. One report has been published of intraoperative decrease in SpO2 following injection of isosulfan blue into the uterine cervix.6 Reports of this dye's ability to affect pulse oximetry during breast surgery have not appeared in the literature to date. Therefore, report of a case in which isosulfan blue was used intraoperatively for sentinel node biopsy for carcinoma of the breast is presented below.
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At the completion of surgery 90 min after the dye injection, SpO2 was measured as 93%. The patient was stable in the recovery room and was transferred to the surgical ward on oxygen via nasal cannula at 2 l•min-1. Pulse oximetry measurement on the ward showed that the patient's SpO2 returned to 99% by seven hours following dye injection. The greyish discolouration of her skin was beginning to fade by this time.
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Most previous reports of changes in SpO2 resulting from dyes have described transient decreases in SpO2 which resolved in minutes,1,4 although Morell et al. reported a decrease in SpO2 of several hours' duration following intradermal injection of patent blue dye.5 The only other report of changes in SpO2 after injection of isosulfan blue described a decrease in SpO2 from 98% to 89-90% beginning five minutes after injection of the dye into the uterine cervix and lasting for 10 min.6 In the patient described in the present report, SpO2 did not return to normal until more than six hours after the dye had been injected. The reason for the longer duration of the dye's effect on SpO2 in the present case is uncertain. Coleman et al.6 suggested that, as isosulfan blue is eliminated primarily by biliary excretion, patients with impaired hepatobiliary function may demonstrate prolonged duration of action of effects of the dye when absorbed intravascularly. While liver function tests were not done on the patient described in the present report, she had no history of hepatic or biliary disease and no clinical findings to suggest that this may have been the case. It is possible that in previous reports the absorption of dye may have occurred over a brief period of time, producing in effect an intravenous bolus of dye, whereas in the present case absorption may have continued over a more prolonged period of time.
The value of sentinel node biopsy in predicting axillary disease in patients with carcinoma of the breast is uncertain. A multicentre NSABP (National Surgical Adjuvant Breast and Bowel Project) study is underway to evaluate this. If the sensitivity and specificity of sentinel node biopsy prove to be high, it is not unreasonable to expect that most axillary node dissections will be replaced by sentinel node biopsies. Therefore, the type of incident described in this report will probably become increasingly common. However, the frequency with which decreased SpO2 occurs following injection of isosulfan blue into the breast has not been reported.
Finally, although dye absorption may be suspected as the cause of an intraoperative decrease in SpO2, it is important to rule out causes of real arterial hypoxemia. In the case reported here, checking the FIO2 displayed on the Ohmeda 5250 gas analyzer and the O2 analyzer on the anaesthesia machine did not indicate delivery of a hypoxic gas mixture. Increasing the FIO2 to 1.0 to rule out delivery of a hypoxic gas mixture could also be considered, although this was not done in the case reported here. Integrity of the anesthetic breathing circuit should be checked. Inadvertent endobronchial intubation should be ruled out by checking for bilateral breath sounds and verifying that the endotracheal tube is appropriately positioned. A suction catheter can be passed down the tube to rule out kinking or obstruction. Pneumothorax should be ruled out by checking for equal air entry bilaterally, absence of tracheal deviation, and absence of hyperresonance on percussion of the chest. Chest X-ray can be performed if necessary. If pneumothorax is suspected, administration of nitrous oxide should be discontinued and, if tension pneumothorax is suspected, needle decompression of the affected hemithorax should be performed immediately. Breath sounds should be auscultated for expiratory wheeze or prolongation of the expiratory phase, and peak inspiratory pressure and shape of the expired CO2 waveform should be checked to rule out bronchospasm. Causes of ventilation-perfusion mismatch such as atelectasis or pulmonary edema must be ruled out. The pulse oximeter probe may be replaced or moved to another site on the patient to rule out probe malfunction or poor sensing due to local hypoperfusion or vasoconstriction.
In summary, a case is presented in which intraoperative decrease in SpO2 occurred following injection of isosulfan blue dye into the breast for sentinel lymph node mapping. The most likely explanation for this change is absorption of dye into the circulation from the injection site. Arterial blood gases showed PaO2 and SaO2 consistent with the oxygen delivery, confirming the suspicion that the pulse oximeter was delivering falsely low readings. However, when intraoperative desaturation occurs, it is important to rule out possible causes of desaturation such as pneumothorax, bronchospasm or endotracheal tube malpositioning. The duration of the effect on SpO2 in this patient was greater than six hours, much longer than the five minutes duration reported by Coleman et al.6 following isosulfan blue injection into the cervix. Data from the present case and others reported in the literature3,5,6 indicate that, following dye injection for lymphatic mapping, the magnitude and duration of effect on SpO2 are highly variable.
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Accepted for publication October 9, 2000.
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References |
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2 Kessler MR, Eide T, Humayun B, Poppers PJ. Spurious pulse oximeter desaturation with methylene blue injection. Anesthesiology 1986; 65: 435–6.[Medline]
3 McEwan, D, Lam K. Oximetry and patent blue five dye (Letter). Anaesth Intensive Care 1997; 25: 587–8.[Medline]
4 Saito S, Fukura H, Shimada H, Fujita T. Prolonged interference of blue dye "patent blue" with pulse oximetry readings. Acta Anaesthesiol Scand 1995; 39: 268–9.[Medline]
5 Morell RC, Heyneker T, Kashtan HI, Ruppe C. False desaturation due to intradermal patent blue five dye. Anesthesiology 1993; 78: 363–4.[Medline]
6 Coleman RL, Whitten CW, O'Boyle J, Sidhu B. Unexplained decrease in measured oxygen saturation by pulse oximetry following injection of Lymphazurin 1% (isosulfan blue) during a lymphatic mapping procedure. J Surg Oncol 1999; 70: 126–9.[Medline]
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