The incidence and types of acid-base imbalance for critically ill patients in emergency

Transcription

1 Hong Kong Journal of Emergency Medicine The incidence and types of acid-base imbalance for critically ill patients in emergency ZF Song, WH Gu, HJ Li, XL Ge Objective: To explore the incidence and types of acid-base imbalance or disorder (ABD) for critically ill patients in emergency room. Methods: Clinical data of all critically ill patients managed in the resuscitation room were collected prospectively during the period from 1st December 2008 to 31st March Arterial and venous blood samples were taken simultaneously for blood gas analyses and serum electrolytes. Acidbase homeostasis or imbalance was judged according to the criteria. Results: A total of 766 cases were collected and the incidence of ABD was 97.3% (N=745). Simple acid-base disorder (SABD) was present in 149 cases (20.0%). Dual acid-base disorder (DABD) was present in 525 patients (70.5%) while triple acid-base disorder (TABD) was found in 71 patients (9.5%). After calculating the anion gap (AG), the incidence of metabolic acidosis increased from 72.2% (N=538) to 91.0% (N=678) and the rate of missed diagnosis for metabolic acidosis was 20.6% (140 out of 678 cases). Meanwhile, the incidence of TABD increased from 1.6% (N=12) to 9.5% (N=71) and the rate of missed diagnosis for TABD was 83.1% (59 out of 71 cases). Similar phenomenon was observed when potential bicarbonate was calculated. The incidence of TABD increased from 1.1% (N=8) to 9.5% (N=71) and the rate of missed diagnosis of TABD was 88.7% (63 out of 71 cases). Patients with TABD (77.9±10.7 years old) were older (P<0.01) than the groups of SABD and DABD. APACHE II scores and the incidence of multiple organ dysfunction syndrome (MODS) were significantly higher among TABD patients. Mortality of patients with TABD on the first, second, third and seventh days were 14.1%, 23.9%, 26.8% and 38.0% respectively and were significantly higher than SABD and DABD. Conclusion: The incidence of ABD in our group of critically ill patients was 97.3%. The commonest type of ABD was DABD. Calculating AG and potential bicarbonate could help us to uncover metabolic acidosis and TABD in time. Patients with TABD had a poorer prognosis. Age and APACHE II scores were key factors closely related to TABD. (Hong Kong j.emerg.med. 2012;19:13-17) % 149 (20.0%) 525 (70.5%) 71 (9.5%) % % 20.6% % % 83.1% % % 88.7% 63 ( ) APACHE Correspondence to: Song Zhifang, MD Xinhua Hospital affiliated Medical University of Jiaotong University in Shanghai, Emergency and ICU Department of Chongming Branch, Shanghai, , China songzfk@hotmail.com Xinhua Hospital affiliated Medical University of Jiaotong University in Shanghai, Emergency Centre, Shanghai, , China Gu Wenhua, MD Li Haojun, MD Ge Xiaoli, MD

2 14 Hong Kong j. emerg. med. Vol. 19(1) Jan (14.1% 23.9% 26.8% 38.0%) (97.3%) APACHE Keywords: Acidosis, APACHE II, bicarbonates Introduction Acid-base homeostasis is crucial to the normal function of body. If acid-base disorder (ABD) is not detected timely, it may lead to serious or potentially fatal conditions. 1 It is natural to expect a high incidence of ABD in critical illness. However, the actual prevalence of ABD in emergency situation is not commonly reported. We performed a prospective study on critically ill patients managed in the resuscitation room of the Emergency Department of Xinhua Hospital (affiliated to Shanghai Jiaotong University) during the period from 1st December 2008 to 31st March The incidence, the types of ABD, and their outcomes were analysed. The aim was to explore whether an early diagnosis of ABD in critical illness would improve prognosis. Material and methods Study design and patients Clinical data was collected from all critically ill patients managed in the resuscitation room of the Emergency Department of Xinhua Hospital (affiliated to Shanghai Jiaotong University) during the period from 1st December 2008 to 31st March Exclusion criteria were: (1) those patients who died on or before arrival; (2) those who were transferred out of critical care area within two hours of arrival; (3) patients with "Do Not Resuscitate" orders; and (4) conscious stroke patients. Data collection The age, gender, primary disease, underlying problems, complications, duration of stay in resuscitation room and outcome were collected from clinical records. APACHE II scores were taken within two hours of arrival and were analysed by special computer system. 2 Sampling, index, assessment Arterial and venous blood samples were taken simultaneously from all patients for blood gas analyses (using ABL 725, Radiometer, Baye, USA) and measurement of sodium (Na + ), potassium (K + ), chloride (Cl ), glucose (Glu), blood urea nitrogen (BUN), creatinine (Cr), alanine aminotransferase (ALT), glutamic oxaloacetic transminase (GOT), total bilirubin (TBIL) and direct bilirubin (DBIL) by fully automated analyser (Johnson, USA). Serum lactic acid and ammonia were tested in selected patients according to their condition and diseases. Acid-base homeostasis or imbalance was judged according to the samples taken upon arrival. Subsequent blood gas and serum electrolytes were monitored simultaneously at 6 hours, 12 hours, 24 hours, 48 hours and 72 hours after therapy. Acid-base status was assessed and judged by Expected Compensation Formulae (Table 1), anion gap (AG) and potential bicarbonate (HCO 3 ). 3-5 AG was calculated by Na + - (HCO 3 + Cl ); and the potential bicarbonate was calculated by HCO 3 + AG. 6 A ph <7.35 combining with increase of partial pressure of arterial carbon dioxide (PaCO 2 ) or decrease of bicarbonate is defined as respiratory or metabolic acidosis respectively. A ph >7.45 combining with decrease of PaCO 2 or increase of bicarbonate is defined as respiratory or metabolic alkalosis respectively. Diagnosis of multiple organ dysfunction syndrome (MODS) was made according to the diagnostic criteria of MODS by Wang & Wang. 7 All patients received general supportive and specific therapy in the resuscitation room according to their underlying condition. Mortality on the first, second, third and seventh days were measured. The incidence of MODS was calculated only according to the data obtained in resuscitation room. Use of glucocorticoid and potassium-wasting diuretic within 3 days of arrival and during resuscitation were collected.

3 Song et al./acid-base imbalance in critically ill patients 15 All data were analysed by SPSS statistics software (SPSS11.0). The mean (x) and standard deviation (SD) were shown as x±s. The measurement materials use the t test and counts the materials use the chi square (χ 2 ) test as R C table. P values of <0.05 was taken as statistically significant. Continuous data of several groups were compared by ANOVA. Results Clinical characteristics and primary diseases A total of 766 critically ill patients (415 males and 351 females) were admitted to our resuscitation room during the study period. The mean age was 70.5±17.4 (52-94) years old. The categories of primary diseases were classified into cardiovascular diseases (N=243, 31.7%); respiratory diseases (N=161, 21.0%); neurologic diseases (N=156, 20.4%); gastrointestinal diseases (N=51, 6.7%); poisoning or intoxication (N=38, 5.0%); malignant tumour (N=32, 4.2%); septic shock (N=22, 2.9%); metabolic and endocrine diseases (N=20, 2.6%), acute abdomen (N=15, 2.0%) and others (N=28, 3.7%). Among the cardiovascular diseases, there were 100 acute cardiac failure (41.2%), 78 acute coronary syndrome (32.1%), 47 lifethreatening arrhythmias (19.3%) and 18 others (7.4%). Among the respiratory diseases, there were 85 acute exacerbation of chronic obstructive pulmonary disease (52.8%), 56 severe pneumonia (34.8%) and 20 others (12.4%). Among the neurologic diseases, there were 132 stroke (84.6%) and 24 others (15.4%). Among the gastrointestinal diseases, there were 40 haemorrhage (78.4%) and 11 others (21.6%). Among the metabolic and endocrine diseases, there were 11 diabetic coma (55.0%) and 9 others (45.0%). ABD and types Among the 766 cases managed in the resuscitation room, ABD occurred in 745 cases (97.3%). Simple acid-base disorder (SABD) was found in 149 cases (20.0%). Among them were 96 metabolic acidosis (64.4%), 31 respiratory alkalosis (20.8%), 21 respiratory acidosis (14.1%) and 1 metabolic alkalosis (0.7%). Dual acid-base disorder (DABD) was present in 525 patients (70.5%). Metabolic acidosis combining with respiratory alkalosis was present in 371 patients (70.7%). Respiratory acidosis combining with metabolic acidosis was present in 136 patients (25.9%). Respiratory alkalosis combining with metabolic alkalosis was present in 11 patients (2.1%). Respiratory acidosis combining with metabolic alkalosis was present in 3 patients (0.6%). Mixed metabolic acidosis was present in 2 patients (0.4%) and metabolic acidosis combining metabolic alkalosis was present in 2 patients (0.4%). Triple acid-base disorder (TABD) was present in 71 patients (9.5%) with respiratory alkalosis in 63 (88.7%) and respiratory acidosis in 8 (11.3%). Thirty six (50.7%) of them already suffered from TABD upon arrival to the emergency room and 35 (49.3%) of them developed TABD subsequently. AG and potential bicarbonate in ABD Prior to the calculation of AG, there were 538 cases with metabolic acidosis. After calculating AG, the number of metabolic acidosis increased from 538 to 678 cases. It means that the incidence of metabolic acidosis increased from 72.2% to 91.0%. If we never calculated AG, these 140 cases of metabolic acidosis would have been missed and the rate of missed diagnosis was 20.6% (140 out of 678 cases). Meanwhile, before we calculated AG, there were only 12 cases with TABD. After calculation of AG, there were 71 cases with TABD. It means that the number of TABD increased from 12 to 71 cases and the incidence of TABD increased from 1.6% to 9.5%. Fifty nine cases with TABD would have been missed and the rate of missed diagnosis was 83.1% (59 out of 71 cases). The same phenomenon occurred when potential bicarbonate was calculated. The number of TABD increased from 8 to 71 and the incidence of TABD increased from 1.1% to 9.5%. It means that 63 patients with TABD would have been missed and the rate of missed diagnosis was 88.7% (63 out of 71 cases). For age and APACHE II scores, there were no significant difference between the groups of SABD and DABD (p>0.05). However, patients from these 2 groups were younger than those suffering from TABD (p<0.01). APACHE II scores in TABD patients were significantly higher than those with SABD or DABD (p<0.01). Iatrogenic factors with ABD (Table 2). It is

4 16 Hong Kong j. emerg. med. Vol. 19(1) Jan 2012 more common to encounter patients taking glucocorticoid or potassium wasting diuretic in the group of TABD than in those with SABD or DABD (p<0.01). There was no significant difference in the incidence of MODS between the groups of SABD and DABD (p>0.05). However, MODS was more common in the group of TABD (p<0.01). As for mortality on the first, second, third and seventh days, there was no significant difference existed between the groups of SABD and DABD (p>0.05). However, mortality was higher in the group of TABD (p<0.05). There were a total of 7 cases missing follow up with 3 in the group of SABD and 4 from the DABD group. The major causes of losing follow up were either no way to follow up or wrong telephone number. No missing follow up happened in the group of TABD. Discussion It is well known that various ABD are very common in critical illness. Prompt correction of ABD and treatment of the underlying causes as soon as possible is the key to reduce morbidity and mortality. However, the prevalence of ABD among emergency cases is seldom reported. Our findings have shown that the incidence of ABD in emergency room is very high (97.3%) and was comparable to previously reported figures (94.2%-96.8%). 8,9 It suggests that we should pay more attention to the diagnosis and management of ABD for critical patients. We took arterial and venous blood samples simultaneously from all patients in order to measured blood gas analyses and serum electrolytes (Na +, K + and Cl ). The aim was to calculate AG and potential bicarbonate. In general, AG helps us diagnose metabolic acidosis while potential bicarbonate helps diagnose metabolic alkalosis. Both of them help us diagnose TABD. In our study, before calculating AG, the number of patients with metabolic acidosis was assumed to be 538 cases (72.2%). However, after calculating AG, it increased to 678 (91%). Before AG was calculated, only 12 patients (1.6%) with TABD were in metabolic acidosis. However, after calculation, the number increased to 71 (9.5%). It indicated that 59 cases (83.1%) of TABD would have been missed if AG was not calculated. Meanwhile AG also influences the potential bicarbonate. If the potential bicarbonate was not calculated, the metabolic acidosis with high AG combining with metabolic alkalosis would have been missed and so would the TABD. In our findings, before we calculated potential bicarbonate, there were only 8 patients with TABD and the missing rate was as high as 88.7% (63 out of 71 cases). This is even worse than that due to non-calculation of AG (83.1%). TABD is a serious metabolic derangement not to be missed in critical care. Although treatment of TABD should be directed to the underlying cause, timely diagnosis of TABD allows us to understand more about the factors contributing to the patients' conditions and minimise treatment failure. Among the 745 cases with ABD, DABD was the commonest (N=525, 70.5%) with 371 (70.7%) of them having metabolic acidosis combining with respiratory alkalosis and 136 (25.9%) of them having respiratory acidosis combining with metabolic acidosis. Among SABD patients, metabolic acidosis was the commonest (N=96, 64.4%). There were 71 patients (9.5%) having TABD and most of them were of type of respiratory alkalosis (N=63, 88.7%). These suggested that majority of patients who suffered from ABD could keep their plasma ph to nearly normal level (7.35~7.45) by body compensation mechanism in early phase. The reason that most SABD were metabolic acidosis could be explained by hypoxaemia and poor systemic perfusion which induced pathophysiological injury with more acid production and less acid removal. For TABD patients, the commonest type was respiratory alkalosis which indicated that respiratory compensatory mechanism would play a major role. 10 Some iatrogenic factors should be considered in addition to body compensatory mechanism. Among the 71 cases of TABD, nearly half of them (N=36, 50.7%) suffered from TABD in the initial stage and half of them (N=35, 49.3%) during resuscitation. In general, taking glucocorticoid or especially potassium wasting diuretic can induce various types of ABD or exacerbate a pre-existing ABD by inducing serum electrolyte imbalance. Some studies suggested that inappropriate intake of potassium wasting diuretic, inadequate potassium replacement, excessive bicarbonate intake, prolonged gastrointestinal suction, excessive gastric lavage and mechanical ventilation are common iatrogenic factors inducing

5 Song et al./acid-base imbalance in critically ill patients 17 TABD. 11,12 We found that 36.6% (N=26) of TABD patients had taken glucocorticoid and 8.5% (N=6) had taken potassium wasting diuretic during the three days prior to emergency room admission. The situation was much less serious in SABD and DABD patients (p<0.01). Potassium and chloride replacement should be adequate in order to avoid hypokalaemic hypochloraemic alkalosis during therapy with glucocorticoid and/or diuretic so as to prevent iatrogenic TABD In TABD, respiratory alkalosis is more common than respiratory acidosis which reflects that respiratory compensatory mechanism is the major way leading to ABD. 14 Among the various forms of ABD, TABD is the most complicated and challenging, and may lead to serious morbidity or mortality. Most of our patients were elderly (70.5±17.4 years old). TABD patients were significantly older (p<0.01) than those having SABD or DABD. However, there was no significant difference existed between SABD and DABD patients (p>0.05). The same phenomenon is also observed in APACHE II scores, MODS and total mortality on the first, second, third and seventh days. The results reflected that TABD is more dangerous than other types of ABD and the prognosis is influenced by age and severity of diseases. 15 Proactive supplementation of electrolytes during glucocorticoid and diuretic therapy should decrease the development of TABD and improve prognosis. Although TABD may not be the direct cause of mortality, its prevention and prompt detection and correction should be contributory to improved prognosis. 16 Metabolic homeostasis in critical patients should always be closely monitored. There are limitations to our study. Firstly, an elevated AG does not always mean acidosis because AG and potential bicarbonate were calculated and not directly measured. Some unknown factors may influence the results of AG and potential bicarbonate. Secondly, there are many different factors contributing to the mortality of critically ill patients. TABD may just be one of them. Conclusion In critically ill emergencies, ABD was extremely common (97.3%). DABD was the commonest. Calculating AG and potential bicarbonate could help us detect metabolic acidosis or alkalosis, and therefore TABD promptly. Patients with TABD had a poor prognosis. Age, APACHE II score, primary pathology and events in our resuscitation room may be contributory. Iatrogenic factors, such as glucocorticoid or potassium wasting diuretic therapy without close monitoring, may be key factors leading to TABD. References 1. Adrogué HJ, Madias NE. Management of life-threatening acid-base disorders. Second of two parts. N Engl J Med 1998;338(2): APACHE II calculator. [cited 2011 Nov 07]. Available from: _4.shtml. 3. Qian GS. Modern clinical arterial blood gas analysis. Beijing: People's Military Medical Publisher; p Oh MS, Carroll HJ. The anion gap. N Engl J Med 1977, 297(15): Gabow PA. Disorders associated with an altered anion gap. Kidney Int 1985,27(2): Qian GS. Modern clinical arterial blood gas analysis. Beijing: People's Military Medical Publisher;2002. p Wang JD, Wang BE. Diagnosis for disease staging and guideline for severe degree of multiple organ dysfunction syndrome. Chin J Crit Care Med 1995;7(6): Ren CS, Qian GS, Zhao ZQ. Arterial blood gas analysis and acid-base disturbance in critically ill patients. Chin J Crit Care Med;1995,15(2): Zhao ZQ, Ren CS, Qian GS. Acid-base disturbance in patients with emergent critical diseases: analysis of 1239 patients. Chin J Crit Care Med 2002;14(4): Laffey JG, Kavanagh BP. Hypocapnia. N Engl J Med 2002; 347(1): Ren CS, Lu HH, Zhao HQ. Analysis and triple acid-base disturbances in critical ill patients. Chin J Crit Care Med 2003;23(5): Gu ZY, Deng WW, Huang SG. Chronic obstructive pulmonary disease and triple acid-base disorder. J Shanghai Jiaotong Univ (medical science) 1992;12(4); Funk G.C, Doberer D, Heinze G, Madl C, Holzinger U, Schneeweiss B. Changes of serum chloride and metabolic acid-base state in critical illness. Anaesthesia 2004;59(11): Malhotra A. Low tidal volume ventilation in the acute respiratory distress syndrome. N Engl J Med 2007;357(11): Hu SX. Diagnosis of triple acid-base disturbance in patients with acute exacerbation of chronic pulmonary heart disease. Anthology Med 2005;24(3): Xiao J, Li XL. Analyzing of the prognosis of the critically ill patients with trible acid-base disorder. Chin J Emerg Med 1998;7(4):