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2005 Acid-Base Disorders Commonly Seen at a Tertiary Health Care Center Larina Chu

Carrington Horton

Sophea Johansen

Irish Faye Pugao

Tricia Sol

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Recommended Citation Chu, Larina; Horton, Carrington; Johansen, Sophea; Pugao, Irish Faye; and Sol, Tricia, "Acid-Base Disorders Commonly Seen at a Tertiary Health Care Center" (2005). Loma Linda University Research Reports. 10. https://scholarsrepository.llu.edu/rr/10

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Larina Chu, CLS, BS; Carrington Horton, PTA, BS; Sophea Johansen, RCP, BS; Irish Faye Pugao, MT (ASCP), BS; Tricia Sol, COTA, BSPH; Robert L. Wilkins, RRT, PhD; Kenrick C. Bourne DrPH, PA-C; Noha Daher, DrPH

Purpose: The purpose of this study was to identify the frequency of acid-base disorders at a tertiary health care center. Methods: Arterial blood gas (ABG) samples (n=l 80) were randomly selected from the medical and surgical intensive care units (MICU/SICU) at Loma Linda University Medical Center over a given four month period. Each sample was interpreted and descriptive statistics were generated. Results: Approximately 31 % of ABG samples were normal. The most common acid-base disorder among both ICUs was simple , occurring 39.2% out of all abnormal ABG results. Twenty-two percent of abnormal ABGs were found to be mixed acid-base disorders. There was no difference between the MICU and SICU when comparing normal, simple, or mixed acid-base disorders. Conclusion: Despite the results of our study, we do not recommend any changes in current curriculum or practice, nevertheless, educators and clinicians should be conscious that respiratory alkalosis was the most common acid­ base disorder. Furthermore, mixed disorders occur with enough frequency that they must be a part of ABG education.

INTRODUCTION purpose of this study was to professionals should be familiar identify the frequency of simple with the various presentations of Arterial blood gas (ABG) results and mixed acid-base disorders in these acid-base disorders and the are used to identify respiratory and two specific ICUs in a tertiary different approaches to their metabolic acid-base disorders, and medical center. The findings may management for the following play an important role in the have meaningful implications in reasons: 1) Decisions about assessment and treatment of that they may allow clinicians to treatment are often based on the critically ill patients. It is common emphasize the most common acid­ patient's acid-base status. 2) The practice for intensive care unit base disorders in determining the results of the test may imply the (ICU) patients to have one or more differential diagnosis. Secondly, presence of undiagnosed problems AB Gs each day, and more information ascertained from this (R. L. Wilkins, PhD, oral . frequently, if the patient is study may also influence the communication, March 2004). mechanically ventilated. The educational content of healthcare Treatment for the acid-base programs. disorder is essential in preventing Larina Chu, Carrington Horton, acute and long-term consequences Sophea Johansen, Irish Faye Pugao, LITERATURE REVIEW of acid-base derangements. 1 and Tricia Sol are students in the History and physical examination Assistant Program, School of Acid-base disorders are common are useful in the initial assessment Allied Health Professions, Loma Linda clinical problems resulting from a of a patient's condition, however, University. wide variety of pathophysiological acid-base disorders are primarily Robert L. Wilkins is a Professor in the conditions, such as pneumonia, diagnosed on the basis of 1 3 4 Department of Cardiopulmonary renal failure, and diabetes. They laboratory studies. ' Some acid­ Science; Noha Daher is an Associate are classified as simple or mixed. base imbalances require rapid Professor ofResearch and Statistics; Simple acid-base disorders include diagnosis and intervention to avoid and Kenrick C. Bourne is an Assistant metabolic , metabolic disastrous outcomes. 3 Raffin3 Professor and Chairman ofthe alkalosis, , and suggests if the clinician suspects Department ofPhysician Assistant respiratory alkalosis. 2 Mixed acid­ that the patient has a significant Sciences, School ofAllied Health base disorders result from a aberration in oxygen or carbon Professions, Loma Linda University. combination of two or more simple dioxide gas exchange or acid-base acid-base disorders. Healthcare balance, arterial blood gas analysis

31 is recommended. Common reasons Medical (MICU) and Surgical abnormal (simple and mixed) acid­ for obtaining an ABG analysis (SICU) Intensive Care Units. The base disorders, we collected 90 include acute and chronic results were acquired from a samples from each ICU. Patient pulmonary disease, acute and computerized blood gas analysis confidentiality was assured by chronic renal disease, and other instrument (Bayer 855), which removing the patient's medical metabolic disorders.3 Moreover, analyzes oxygenation and record number and name and by serial arterial blood gas analyses ventilation of arterial blood. It assigning each ABG result a new are used with critically ill patients provides data on the following identification number. in intensive care units, as well as factors: After the ABG samples were postoperative patients, and patients • Hydrogen ion concentration acquired, a critical care physician with chronic respiratory failure, (pH) analyzed each sample for an 3 who are not critically ill. • Partial pressure of arterial official interpretation. A mixed

ABG results are used to (PaC02 ) acid-base problem is present when monitor a patient's progress; to • Partial pressure of arterial the predicted compensation is not adjust oxygen and other medication oxygen (Pa02) present. See Table 1 for expected regimens; and to make • Arterial blood compensation for acid-base management decisions concerning (HC03") disorders. Each sample was assisted ventilation, positive end­ • Base excess (BE) classified as either a simple or respiratory pressure, and weaning mixed acid-base disorder or as 3 We collected data from from ventilatory support. December 2003 to April 2004 and being normal. Therefore, ABG evaluation is an limited data to ABG results upon The data was analyzed using integral part of patient assessment admission to the MICU or upon the Statistical Package for the and determining the course of Social Sciences software (SPSS, post-operative admission to the 6 treatment, specifically for ICU SICU. version 12.0). Frequencies and patients. Wilkins (oral Random sampling was used to relative frequencies were calculated communication, March 2004) select our sample from a total of for simple and mixed acid-base reports there is no descriptive 396 results in the SICU and 247 disorders and those with normal research that identifies the results in the MICU. We utilized findings found in the MICU and frequency of possible acid-base Sample Power (version 2.0, SICU. The proportions of normal, disorders. obtained from SPSS, Inc.) to simple, and mixed acid-base calculate the sample size needed disorders were compared between METHODS from each ICU. We chose to have a MICU and SICU using the Chi­ 5% Type I error with 80% power. square test for homogeneity. We obtained arterial blood gas In order to compare frequency as a (ABG) results from Loma Linda proportion among the normal and University Medical Center's

Table 1. Summary of Expected Compensation for Acid-Base Disorders1 Primary Disorder Expected Compensation

Acute Respiratory Acidosis For a 15 mm Hg increase in PaC02, the HC03 increases 1 mEq/L

Chronic Respiratory Acidosis For every 10 mm Hg the PaC02increases, the HC03 increases 4 mEq/L

Acute Respiratory Alkalosis For every 5 mm Hg decrease in PaC02, HC03 decreases 1 mEq/L. Chronic Respiratory Alkalosis HC03 falls 5 mEq/L for every 10 mm Hg fall in PaC02•

Metabolic Acidosis PaC02= last two digits of pH; PaC02= (1.5 x HC03) + 8 ± 2 For each 1 mEq/L increase in HC03 PaC02 increases 0.6 mm Hg

32 RESULTS 16 in the MICU and 12 in the SICU (n=l6) occurred in the MICU and (see Figure 1). 53% (n=l8) occurred in the SICU Among the combined SICU and (Figure 2). Respiratory alkalosis MICU patients, 30.6% (n=55; 27 in Analysis showed that the was found significantly more often MICU and 28 in SICU) had normal proportions of simple and mixed than any other disorder occurring ABGs and 69.4% (n=l25) had disorders were similar in both ICUs as 39.2% of all abnormal results abnormal ABGs indicating a simple (x2=0.66; p=.42). Of all simple (x2=48.0; p=

11 Normal ABG

• Simple Respiratory Acid-Base Disorder 19%· D Simple Metabolic Acid­ Base Disorder D Mixed Acid-Base Disorder 34%

Figure 1. Normal vs abnormal acid -base disorders in the medical and surgical intensive care units (n=l80).

33 60

50

40 111 Frequency in MICL 30 • Frequency in SICU D Total 20 *Res= Respiratory 10 +Met= Metabolic 0 Res* Res Met+ Met Acidosis Alkalosis Acidosis Alkalosis

Figure 2. Simple acid-base disorders in the medical and surgical intensive care units.

Met Alkalosis/RT Acidosis

RT Alkalosis/Met Alkalosis

Met Acidosis/RT Alkalosis

RT Acidosis/Met Acidosis

Met Alkalosis

Met Acidosis

*RT Alkalosis

RT Acidosis

0 5 10 15 20 25 30

*p=<0.001 / 11 Freqency in SICU• Freqency in MICUJ

Figure 3. Frequency of simple and mixed acid-base disorders in the medical and surgical intensive care units.

34 DISCUSSION time period may reflect different REFERENCES results than this study. Secondly, Studies in the past have not our sample size did not allow for 1. Gluck SL. Acid-base. Lancet. identified the frequency of acid­ detailed analysis of the frequency 1998; 352:474-486. base disorders in intensive care of mixed acid-base disorders. units. Our study showed that there Therefore, we recommend a larger 2. Williamson JC. Acid-Base was no difference between the sample size in future studies if disorders: classification and medical and surgical intensive care specific simple or mixed acid-base management strategies. Am units when comparing acid-base disorders are to be analyzed. Fam Physician. l 995;52:584- disorders. Respiratory alkalosis Lastly, variables such as the length 590. was the most frequent overall acid­ of study time, seasons of the year, base disorder found. Among the and diseases prevalent during that 3. Raffin TA. Indications for mixed disorders, time period may have affected the arterial blood gas analysis. and respiratory alkalosis was most results. Consideration of these Ann Intern Med. common, occurring twice as variables in future studies may 1986; 105:390-398. frequently as other mixed acid-base result in more generalizable disorders. conclusions. 4. Dubose, TD Jr. Acid-base One explanation for the results The outcome of this study may emergencies. Patient Care. of the study is that patients who be used in conjunction with the l 992;26:214-230. undergo ABG puncture may tend to current know ledge and teachings of hyperventilate causing respiratory acid-base disorders. Since the most 5. Wilkins RL, Krider SJ, alkalosis. Mechanical ventilation common acid-base disorder among Sheldon RL. Clinical may explain why respiratory both units was respiratory alkalosis, Assessment in Respiratory alkalosis is common because the educators can emphasize diseases Care. 5th ed. St. Louis, Mo: patient may be hyperventilated by and conditions associated with this Mosby Inc; 2005. high tidal volumes or an increased disorder. Clinicians should also be frequency compared to taught to recognize mixed acid­ 6. SPSS User's Guide for spontaneous breathing. Being base disorders, since they occurred Windows Version 12.0. hospitalized in itself may contribute in 22.4% of the abnormal cases. Chicago, Ill: SPSS Inc; 2004. to due to anxiety and pain. The presence of acute CONCLUSION and chronic renal patients may explain why metabolic acidosis and We do not recommend any changes respiratory alkalosis was the most in curriculum, assessment, or common mixed acid-base disorder. treatment of a patient because our Further research should be done to study was to determine frequency identify the frequency and and is solely limited to educational correlation of certain acid-base purposes. Educators and clinicians disorders and diseases. should be conscious that respiratory Our literature review indicated alkalosis was the most common that our study is the first study to acid-base disorder. identify the frequency of simple and mixed acid-base disorders in a ACKNOWLEDGEMENTS tertiary medical center. An additional strength of our study was We would like to thank Michael H. random sampling. This method Terry, BS, RCP, RRT, Clinical was used to control bias and may Supervisor, Respiratory Care, have contributed to why there was Loma Linda University Medical no difference in the distribution of Center for his help in getting the acid-base disorders between the ABG samples. We would also like two ICUs. to thank Loma Linda University Limitations of our study Medical Center's Medical and included sample size and seasonal Surgical Intensive Care Units for variation. A study identifying allowing us to use their facilities. consecutive ABGs in a specified

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