1 Lefkos Stavros Renal Unit and 2 Department of Nephrology, Aretaieon University Hospital, Athens, Greece
Keywords: metabolic acidosis; haemodialysis
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Introduction |
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Two cases of severe metabolic acidosis as complications of HD have been recorded in two dialysis units, which have been dialysing more than 50 patients daily during the last 5 years. Early recognition and proper treatment resulted in favourable outcome.
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Case 1 |
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This was due to the accidental substitution of acidic concentrate for acetate. The patient received intravenous bicarbonate, and was switched to another HD machine and bicarbonate buffer. After 4 h of HD, he recovered fully and his blood gas analysis revealed a pH of 7.46, HCO3 25 mmol/l, PCO2 44 mmHg and PO2 70 mmHg.
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Case 2 |
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Dialysis was stopped; the patient received intravenous bicarbonate and was transferred to another machine. After 2 h, her blood gases changed: pH 7.43, HCO3 18 mmol/l, TCO2 18.7 mmol/l, PCO2 27.5 mmHg and PO2 78.3 mmHg. The patient had an uncomplicated recovery, and remains well. The metabolic acidosis was due to an incorrect bicarbonate concentration in the dialysate along with the failure of the conductivity and pH alarms to sound.
The nursing staff reported that they had observed a problem regarding conductivity during the priming mode of HD, but everything seemed fine when the patient was connected (conductivity 142 ms/cm).
The local Fresenius technical staff were surprised to find that the HD machine was totally out of calibration. However, no one in the unit was aware of it. They started to calibrate the machine and discovered that it displayed higher conductivity values than the external conductivity meter (for example 16.5 instead of 13.5). The hydraulic parts were not malfunctioning. The problem was in the computer of the HD machine. After adjustment, the machine worked well for 2 days and then lost calibration again during a priming mode.
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Comment |
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During acetate HD the acetate concentrate can accidentally be replaced by the acid concentrate component of a two-component, bicarbonate-based dialysate generating system. As this concentrate has no buffer base, its use removes bicarbonate from the blood by osmosis and results in metabolic acidosis. Metabolic acidosis has been reported during bicarbonate dialysis resulting from damaged tubes responsible for the siphoning-off of bicarbonate concentrate in machines not equipped with pH sensors [3]. The first patient we describe was undergoing acetate dialysis, and had a course similar to those described in other reports [14], a consequence of an error made in the selection of the dialysate concentrate. The acidic concentrate is capable of replacing the acetate without sounding alarms and matching conductivity. The largest difference and potential problem is the low pH. Metabolic acidosis has been reported after accidental substitution of acidic concentrate for acetate in many HD machinessuch as Gambro® AK-10 [1] or Hospal Monitral® N [2]. These machines lack a pH meter. It has been proposed that all HD machines should be fitted with pH meter and alarms, especially in centres where both acetate and bicarbonate dialysis are used [2]. (Our patient's severe acidosis (pH 7.03) also had a respiratory component due to his chronic obstructive pulmonary disease.) Many manufacturers safeguard against some of the potential errors by colour-coding the concentrate containers, but this is not foolproof when multiple equipments from a list of manufacturers are utilized in a dialysis unit.
The second patient, however, was being dialysed with a newer generation machine with sensors for both pH and conductivity. Nevertheless, that did not prevent a potentially lethal complication because the computer software of the machine malfunctioned. Otherwise, the machine would be able to recognize early the incorrect dialysate concentration, an alarm would sound and the bypass mode would be activated, protecting the patient.
So far, we do not know what led to the failure of the computer software, but the local technical staff suggested possible interference by cellular phones used by many dialysis patientsdespite our recommendations against their use.
Metabolic acidosis during HD is rare but dangerous. Being aware that it can occur is the best safeguard against human or machine errors. Intravenous administration of bicarbonate and dialysis with bicarbonate dialysate of a correct composition are the appropriate therapeutic measures when metabolic acidosis occurs.
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Notes |
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References |
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