Severe metabolic acidosis during haemodialysis: a rare but life threatening complication

Costas Fourtounas1,2,, Ioannis Kopelias1,2, George Dimitriadis1, Aris Paraskevopoulos1 and Basil Agroyannis2

1 Lefkos Stavros Renal Unit and 2 Department of Nephrology, Aretaieon University Hospital, Athens, Greece

Keywords: metabolic acidosis; haemodialysis



   Introduction
 Top
 Introduction
 Case 1
 Case 2
 Comment
 References
 
Dialysis fluids are real ‘drugs’ and as a consequence they need pharmacological preparation in order to meet the criteria of quality and standarization. Modern dialysis machines permit accurate proportioning of treated water and salts and also guarantee a continuous monitoring of the accuracy of the final composition and maintenance of the desired proportions. However, errors with dialysate concentrations are numerous and may go underdetected as causes of morbidity and mortality in patients undergoing haemodialysis (HD) [1].

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.



   Case 1
 Top
 Introduction
 Case 1
 Case 2
 Comment
 References
 
A 54-year-old male patient, on acetate HD for 5 years due to chronic glomerulonephritis, complained that ‘something strange was going on’, and asked the nursing staff to disconnect him from the machine. He was in the first hour of his HD session, during the first shift of the day, and was being dialysed with a Cobe Centry® 2000 HD machine. A relevant comorbidity, which he had, was chronic obstructive pulmonary disease. When examined after his complaint, his blood pressure was 155/85 mmHg, pulse 90/min and he was tachypneic (30 breaths/min). Blood gas analysis revealed severe metabolic acidosis: pH 7.03, HCO3 6 mmol/l, PCO2 27.4 mmHg and PO2 85 mmHg.

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.



   Case 2
 Top
 Introduction
 Case 1
 Case 2
 Comment
 References
 
A 68-year-old female patient, who had needed bicarbonate HD for the past 9 years due to nephropathy of unknown origin, started complaining that ‘something was going wrong’. She was in the second hour of her HD session, during the second shift of the day. She was being dialysed with a Fresenius 4008B HD machine. Upon examination after her complaint, her blood pressure was 130/80 mmHg and pulse 98/min; however, she was breathing at 30 breaths/min. An ECG was nomal. Blood gas analysis from the arterial port of the extracorporeal circuit revealed severe metabolic acidosis: pH 7.17, HCO3 5.2, TCO2 5.6, PCO2 14.7 mmHg, PO2 138.7 mmHg (without oxygen supplementation) and SBE 22.6 mmol/l. A sample from the dialysate was abnormal in composition: pH 5.97, HCO3 0.1 mmol/l, TCO2 0.3 mmol/l, sodium 123 mmol/l, and potassium 2.1 mmol/l.

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.



   Comment
 Top
 Introduction
 Case 1
 Case 2
 Comment
 References
 
Metabolic acidosis during HD can develop due to defective delivery of buffer base in the form of sodium acetate or sodium bicarbonate to the dialysate.

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 machines—such 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 patients—despite 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.



   Notes
 
Correspondence and offprint requests to: C. Fourtounas, MD, Astydamandos 28, Athens 11634, Greece. Email: cfourt{at}usa.net Back



   References
 Top
 Introduction
 Case 1
 Case 2
 Comment
 References
 

  1. Brueggemeyer CD, Ramirez G. Dialysate concentrate: a potential source for lethal complications. Nephron1987; 46: 397–398[ISI][Medline]
  2. Gainza FJ, Zarraga S, Minguela I, Lampreable I. Accidental substitution of acidic concentrate for acetate in dialysis fluid concentrate: a cause of severe metabolic acidosis. Nephron1995; 69: 480–482[ISI][Medline]
  3. Hartmann A, Reisaeter A, Holdaas H, Rolfsen B, Fauchard P. Accidental metabolic acidosis during hemodialysis. Artif Organs1994; 18: 214–217[ISI][Medline]
  4. Navarro JF, Mora-Fernandez C, Garcia J. Errors in the selection of dialysate concentrates cause severe metabolic acidosis during bicarbonate hemodialysis. Artif Organs1997; 21: 966–968[ISI][Medline]
Received for publication: 13. 3.01
Revision received 3. 7.01.



This Article
Extract
FREE Full Text (PDF)
Alert me when this article is cited
Alert me if a correction is posted
Services
Email this article to a friend
Similar articles in this journal
Similar articles in ISI Web of Science
Similar articles in PubMed
Alert me to new issues of the journal
Add to My Personal Archive
Download to citation manager
Disclaimer
Request Permissions
Google Scholar
Articles by Fourtounas, C.
Articles by Agroyannis, B.
PubMed
PubMed Citation
Articles by Fourtounas, C.
Articles by Agroyannis, B.