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January 2016

Extreme acidosis and mortality – a retrospective clinical study

Summarized from Allyn J, Vandroux D, Jabot J et al. Prognosis of patients presenting extreme acidosis (pH <7.0) on admission to intensive care. J Crit Care 2016; 31: 243-48

Health demands that blood pH is maintained within narrow limits (7.35-7.45). Acidosis (i.e. pH <7.35) is a common feature of many acute/critical conditions that warrant admission to intensive care. pH <6.8 is commonly reported in medical texts as incompatible with life, but there are rare individual case reports of survival with no long-term ill effect, despite a blood pH below this level. 

A recently published study was designed to investigate mortality rates among intensive care patients who present with extreme acidosis, which the authors arbitrarily defined as pH <7.00. This retrospective study was conducted at a 23-bed adult medical/surgical intensive care unit of a French hospital, where during a 30-month long study period, 2156 patients were admitted. 

Of these 2156 patients, 77 (3.6 %) presented with pH <7.0 (median pH 6.94, range 6.86-6.97). The clinical details and outcome for these 77 patients were retrieved. These were very sick patients; admission assessment using Simplified Acute Physiology Score (SAPS) revealed a median score of 82 (range 69-93) which translates to a predicted mortality in the range of 75-90 %. 

A cause of the extreme acidosis was identified in practically all cases and in most (86 %), lactic acidosis (serum lactate >4.0 mmol/L) was a feature. Of the 77 patients, 30 (39 %) had suffered cardiac arrest prior to admission to intensive care. The mortality for this group was particularly high (90 %); only three patients survived (for these three patients cardiac arrest occurred in the presence of medical team). 

Overall, 52 of the 77 patients died (mortality rate 67.5 %) but in the absence of cardiac arrest, mortality rate (57 %) was much lower than predicted by SAPS score at admission. The study has demonstrated that extreme acidosis is a relatively rare occurrence with many possible causes although it is nearly always a metabolic (lactic) acidosis. Cardiac arrest is a common cause. 

Results of the study suggest that survival following extreme acidosis depends to a great extent on the cause of the acidosis. Despite a universally poor prognosis at admission, over half of all patients who had not suffered a cardiac arrest survived. The authors of this study conclude that in the absence of cardiac arrest, extreme acidosis, even if associated with poor prognostic signs, should not preclude aggressive intensive care therapy.


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Chris Higgins

has a master's degree in medical biochemistry and he has twenty years experience of work in clinical laboratories.

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