Question

The client is admitted following a motor vehicle accident. Extensive internal bleeding is suspected. The serum pH is \(7.0\), the \(\mathrm{PaCO}_2\) is \(32 \mathrm{~mm} / \mathrm{Hg}\) and the \(\mathrm{HCO}_3\) is \(20 \mathrm{mEq} / \mathrm{dl}\). The nurse should assess the laboratory finding as which of the following? A. Metabolic acidosis B. Metabolic alkalosis C. Respiratory acidosis D. Respiratory alkalosis

Short answer

A. Metabolic acidosis B. Metabolic alkalosis C. Respiratory acidosis D. Respiratory alkalosis

Step-by-step solution

Determine normal values for serum pH, PaCO2, and HCO3-

Normal values for each laboratory finding are as follows: - Serum pH: 7.35 to 7.45 - PaCO2: 35 to 45 mm Hg - HCO3-: 22 to 26 mEq/dL

Identify deviations in the given data

Now, let's compare the given data to the normal values: - Serum pH: 7.0 (lower than normal, indicating acidosis) - PaCO2: 32 mm Hg (lower than normal, indicating alkalosis) - HCO3-: 20 mEq/dL (lower than normal, indicating acidosis)

Determine the type of acid-base imbalance

Based on the observed deviations, we can determine the type of acid-base imbalance: - Since the serum pH is lower than normal, it indicates acidosis. - Both the PaCO2 and the HCO3- levels are lower than normal, which might be confusing. However, we should focus on the primary cause of acidosis in this case, which is the low HCO3- level, indicating a metabolic problem. Therefore, the correct answer is: A. Metabolic acidosis

Key concepts

Metabolic Acidosis

Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base levels. Specifically, it occurs when there is an excess of acid in the body or when the kidneys are not removing enough acid from the body. In the clinical scenario provided, the patient's serum pH is noted to be 7.0, which is substantially lower than the normal range of 7.35 to 7.45. This low pH indicates a high level of hydrogen ions in the blood, a hallmark of acidosis.

In assessing acid-base imbalances, it's crucial to determine which system, metabolic or respiratory, is causing the issue. Since the primary issue is with the bicarbonate (HCO3-) levels — it is low at 20 mEq/dL compared to the normal range of 22 to 26 mEq/dL — we can confirm the problem is metabolic in nature. This points towards metabolic acidosis. Typically, causes of metabolic acidosis can include conditions like kidney failure, lactic acid buildup due to shock or severe dehydration, ketoacidosis from diabetes, or ingestion of toxins.

When we see metabolic acidosis in a patient with extensive internal bleeding, as in this scenario, the body may be producing excess acid due to inadequate oxygenation of tissues or loss of bicarbonate through blood. It is vital to recognize and promptly treat metabolic acidosis since it can be indicative of an underlying life-threatening condition requiring immediate attention.

PaCO2 and HCO3- Levels

Understanding PaCO2 (partial pressure of carbon dioxide) and HCO3- (bicarbonate) levels is essential in diagnosing and managing acid-base imbalances. These values provide insight into the respiratory and metabolic components of the body's pH balance.

PaCO2 is a measure of carbon dioxide in the blood and is regulated by the lungs. Normal PaCO2 levels are typically between 35 to 45 mm Hg. In our exercise, the PaCO2 was 32 mm Hg, signaling a lower level than normal, which could often suggest a respiratory alkalosis if considered in isolation. However, since we are dealing with acidosis, this slightly low PaCO2 is, in fact, a compensatory mechanism; the lungs are trying to exhale more CO2 in an attempt to balance the pH by reducing acidity.

The HCO3- level, on the other hand, reflects the metabolic component and is controlled by the kidneys. It helps to buffer the acids in the blood. The lower than normal bicarbonate level suggests that either the body is producing too much acid, losing too much bicarbonate, or not excreting enough acid. The patient's HCO3- level, measured at 20 mEq/dL, reinforces the diagnosis of metabolic acidosis.

Serum pH Analysis

Serum pH analysis is a crucial laboratory test that helps determine the acidity or alkalinity of a patient's blood. The pH scale ranges from 0 to 14, with 7 being neutral. Human blood is naturally slightly alkaline, with a normal range between 7.35 and 7.45. Values below 7.35 signify acidosis, and values above 7.45 indicate alkalosis.

In the context of the given exercise, the patient has a serum pH of 7.0. This significant deviation from the normal range indicates a severe acidotic state, and immediate clinical intervention is necessary to address the underlying cause and to prevent further complications. pH alone does not tell us the origin of the imbalance — whether it is metabolic or respiratory — so we must look at PaCO2 and HCO3- levels for a comprehensive analysis.

Clinicians use the pH in conjunction with PaCO2 and HCO3- to assess the body's response to the imbalance. In a compensatory response, the body will attempt to correct pH changes through respiratory or renal adjustments, affecting PaCO2 and HCO3- levels accordingly. In our patient's case, both compensation and the primary cause of acid-base disturbance suggest that metabolic processes are the drivers in lowering the blood pH.