| Course | NU656 AGACNP Critical Care Management |
|---|---|
| Unit | Unit 7 |
| Paper type | Blood gas interpretation |
| Length | About 1,130 words, 7 pages double-spaced |
| Format | APA 7 student paper |
| School | Purdue University Global |
| Program | MSN |
| Updated | September 2026 |
Free sample paper for NU656 Unit 7
A Gap of 32 and an Osmolar Gap of 36: A Blood Gas Interpretation of Ethylene Glycol Poisoning Hidden Behind Two Days of Vomiting in a 47-Year-Old Man
[Student Name]
Purdue University Global
NU656: AGACNP Critical Care Management
Unit 7 Blood Gas Interpretation
[Instructor Name]
[Date]
The patient is composite; every value and time is bracketed.
The Values
Mr. [T.] is a [47]-year-old man brought in by his brother at [21:40] after two days of vomiting, followed this evening by slurred speech and confusion. He smells of nothing in particular. His blood ethanol is [zero]. On room air:
1. Arterial blood gas: pH [7.32], PaCO2 [32] mmHg, PaO2 [95] mmHg, bicarbonate [16] mEq/L.
2. Chemistry: sodium [140], chloride [92], potassium [3.4] mEq/L; glucose [108] mg/dL; blood urea nitrogen [28] mg/dL; creatinine [2.4] mg/dL; albumin [4.0] g/dL.
3. Measured serum osmolality: [332] mOsm/kg.
4. Urinalysis: many envelope-shaped crystals.
Six steps follow. Each shows its formula and its arithmetic, and each depends on the one before it.
Step One: Are the Numbers Consistent?
The Henderson-Hasselbalch equation predicts the pH from the bicarbonate and the carbon dioxide: pH = 6.1 + log (bicarbonate / (0.03 x PaCO2)).
6.1 + log (16 / (0.03 x 32)) = 6.1 + log (16 / 0.96) = 6.1 + log 16.7 = 6.1 + 1.22 = [7.32].
The calculated pH matches the measured pH, so the gas is internally consistent and can be interpreted. A mismatch here would mean a sampling or transcription error, and the gas would be repeated before anything else.
Step Two: What Is the Primary Process?
The pH of [7.32] is below 7.35, so the patient is acidemic. The bicarbonate of [16] is low and the PaCO2 of [32] is also low. A low bicarbonate with a low pH points to a metabolic acidosis as the primary process; the low carbon dioxide moves in the direction of compensation, not against it.
Step Three: Is the Respiratory Response Appropriate?
Winter's formula gives the PaCO2 expected when the lungs compensate fully for a metabolic acidosis: expected PaCO2 = (1.5 x bicarbonate) + 8, plus or minus 2 (Albert et al., 1967).
(1.5 x 16) + 8 = 24 + 8 = 32, so the expected range is [30 to 34] mmHg.
The measured PaCO2 of [32] sits in the middle of that range. His breathing has compensated as expected, so no independent disorder of ventilation is present. This matters because it narrows the search: whatever else is present must be metabolic.
Step Four: The Anion Gap
Anion gap = sodium minus (chloride plus bicarbonate) = 140 minus (92 + 16) = [32] mEq/L.
With an albumin of [4.0] g/dL there is no correction to make; albumin is the main unmeasured anion, and a low value would hide part of the gap (Kraut & Madias, 2007). A gap of [32] is well above a normal of about 12 and establishes a high anion gap metabolic acidosis. Lactate is [1.9] mmol/L, beta-hydroxybutyrate is not raised, and the creatinine of [2.4] mg/dL is not high enough to explain a gap of this size. The usual sources are therefore excluded, and an unmeasured toxic acid comes to the front of the list.
Step Five: The Delta Ratio
The delta ratio compares the rise in the anion gap with the fall in bicarbonate. In a pure high anion gap acidosis, each extra unit of acid consumes roughly one unit of bicarbonate, so the ratio lies between about 1 and 2.
Change in gap = 32 minus 12 = [20]. Change in bicarbonate = 24 minus 16 = [8]. Delta ratio = 20 / 8 = [2.5].
A ratio of 2.5 means the bicarbonate is higher than the acid load alone would leave it, so a second process has been adding bicarbonate: a metabolic alkalosis. Two days of vomiting explain it; loss of gastric acid raises the serum bicarbonate and lowers the chloride, and a chloride of [92] fits. This is why the pH is only [7.32]. Without the vomiting, the same acid load would have left the bicarbonate near [4] and the pH far lower. The two disorders pull in opposite directions and make a severe poisoning look moderate.
Step Six: The Osmolar Gap and the Oxygen Gradient
Calculated osmolality = (2 x sodium) + (glucose / 18) + (blood urea nitrogen / 2.8) = 280 + 6 + 10 = [296] mOsm/kg. Measured osmolality is [332], so the osmolar gap is 332 minus 296 = [36] mOsm/kg, far above a usual upper limit of about 10. With ethanol at zero, a raised osmolar gap alongside a high anion gap acidosis points strongly to a toxic alcohol (Kraut & Mullins, 2018). Envelope-shaped crystals in the urine are calcium oxalate, a product of ethylene glycol metabolism, and the rising creatinine fits oxalate injury to the kidneys.
The alveolar-arterial gradient checks whether the lungs are involved. Alveolar PO2 = 0.21 x (760 minus 47) minus (32 / 0.8) = 149.7 minus 40 = [109.7] mmHg. Gradient = 109.7 minus 95 = [14.7] mmHg, within the normal range for his age. The fast breathing is compensation, not lung disease.
The Pattern and What Happens in the Next Hour
Put together, the gas shows two metabolic disorders and a fitting ventilatory response: an acid load that widened the anion gap, and an alkalosis from vomiting that partly hid it, with an osmolar gap and oxalate crystals that point to ethylene glycol poisoning. His brother later found an empty antifreeze container in the garage.
Three actions follow within the hour.
1. Fomepizole [15] mg/kg intravenously, [1,200] mg for his [80] kg, without waiting for a confirmed level. Fomepizole blocks alcohol dehydrogenase and stops the conversion of ethylene glycol into its toxic acids; in a prospective study it prevented further kidney injury in patients treated before their creatinine rose and was well tolerated (Brent et al., 1999).
2. A call to nephrology for hemodialysis. The EXTRIP workgroup recommends extracorporeal treatment in ethylene glycol poisoning with an anion gap above 27 mmol/L, and suggests it with a gap of 23 to 27 (Ghannoum et al., 2023). His gap of [32] meets the stronger recommendation, and dialysis removes both the parent compound and its acids.
3. A serum ethylene glycol level, repeat gas and chemistry every [two] hours, and potassium replacement, since his potassium of [3.4] will fall as the acidosis is corrected. Poison control is informed, and a psychiatric assessment is arranged once he is medically stable, because the ingestion may have been intentional.
The vomiting that hid the acidosis also needs care: chloride-containing fluid will correct the alkalosis, but it is given with attention to his volume status and kidney function, which are both now at risk.
References
Albert, M. S., Dell, R. B., & Winters, R. W. (1967). Quantitative displacement of acid-base equilibrium in metabolic acidosis. Annals of Internal Medicine, 66(2), 312-322. https://doi.org/10.7326/0003-4819-66-2-312
Brent, J., McMartin, K., Phillips, S., Burkhart, K. K., Donovan, J. W., Wells, M., & Kulig, K. (1999). Fomepizole for the treatment of ethylene glycol poisoning. New England Journal of Medicine, 340(11), 832-838. https://doi.org/10.1056/NEJM199903183401102
Ghannoum, M., Gosselin, S., Hoffman, R. S., Lavergne, V., Mégarbane, B., Hassanian-Moghaddam, H., Rif, M., Kallab, S., Bird, S., Wood, D. M., Roberts, D. M., & EXTRIP Workgroup. (2023). Extracorporeal treatment for ethylene glycol poisoning: Systematic review and recommendations from the EXTRIP workgroup. Critical Care, 27(1), Article 56. https://doi.org/10.1186/s13054-022-04227-2
Kraut, J. A., & Madias, N. E. (2007). Serum anion gap: Its uses and limitations in clinical medicine. Clinical Journal of the American Society of Nephrology, 2(1), 162-174. https://doi.org/10.2215/CJN.03020906
Kraut, J. A., & Mullins, M. E. (2018). Toxic alcohols. New England Journal of Medicine, 378(3), 270-280. https://doi.org/10.1056/NEJMra1615295
NU656 Unit 7 instructions, in plain terms
For Unit 7 you are given an arterial blood gas with a chemistry panel and asked to interpret it step by step, then say what the result means for the patient's care. Prompts usually expect a check of internal consistency, the primary disorder, the expected compensation, the anion gap, the delta ratio where the gap is high, and any further calculations the case invites, such as the osmolar gap or the alveolar-arterial gradient. Two to four pages is typical. Each step should show the formula and the numbers, because the arithmetic is graded. The interpretation should end in clinical actions tied to the findings, not only a label. Name the pattern only after the steps have earned it, and cite sources for each formula used.
How this NU656 Unit 7 example is built
The values sit in a numbered list at the top: gas, chemistry, measured osmolality and a urinalysis with envelope-shaped crystals. Step one runs the Henderson-Hasselbalch equation and gets 7.32, matching the measured pH. Step two names a primary metabolic acidosis. Step three applies Winter's formula, cited to Albert and colleagues, and finds the PaCO2 of 32 right in the expected range. Step four computes a gap of 32 and excludes lactate, ketones and kidney failure as its source. Step five finds a delta ratio of 2.5 and explains, in the highlighted sentence, that a second process has been adding bicarbonate. Step six computes the osmolar gap and a normal oxygen gradient. Three orders close the paper, each traced to a number.
Where the points sit in the NU656 Unit 7 rubric
Rubrics for a gas interpretation usually score the systematic approach, accuracy of calculations, identification of all disorders present, clinical application and use of sources. The systematic row expects every step in a logical order, with none skipped because the answer seemed obvious. Accuracy is checked line by line, so a transcription slip in the anion gap can cost more than a weak paragraph. Identification earns full points only when mixed disorders are found, which is why the delta ratio carries weight in this unit. Clinical application rewards orders that follow directly from the findings, with dosing and thresholds from current guidance. Source points go to the original formula papers and toxicology guidance rather than a general textbook.
NU656 Unit 7 help: mistakes that cost points
The trap students fall into most is stopping at a moderate pH and calling it a simple acidosis, which misses the hidden alkalosis. Another is forgetting the delta ratio, the only step here that exposes the second disorder. Some papers compute the anion gap without checking albumin, which can hide a raised gap. Others see a normal ethanol level and never calculate the osmolar gap. Waiting for a confirmed ethylene glycol level before giving fomepizole is a common and costly error. Students also treat the fast breathing as a lung problem instead of compensation, which the oxygen gradient disproves. And listing a diagnosis without actions leaves the clinical application row nearly empty.
Get an NU656 Unit 7 example written to your instructions
Whichever gas the NU656 Unit 7 prompt supplies, the reading is built on it, together with any chemistry panel and your rubric. The reading is back within 24-48h, the first one free, each formula written out, compensation computed rather than assumed and the pattern translated into what should happen in the next hour. The paper above is an original model document written by our desk, not a submitted student paper and not an official Purdue University Global document.
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NU656 Unit 7 questions, answered
Why compute compensation instead of using a rule of thumb?
Because a rule of thumb cannot tell compensation from a second disorder. Winter's formula gives an expected PaCO2 range for a given bicarbonate; a measured value outside it means a separate respiratory process is present. The sample writes out the formula and arithmetic so a grader can check them, and it applies the matching formula for whichever primary disorder a case presents.
Where can I find a free NU656 Unit 7 sample paper?
This page holds the full NU656 Unit 7 blood gas interpretation, with the values, six worked steps, the pattern and three orders for the next hour, plus five references. A new interpretation can be written for the gas your prompt supplies.
What does the delta ratio show in NU656 Unit 7?
The anion gap rose by 20 while bicarbonate fell by only 8, giving a ratio of 2.5. A ratio above 2 means bicarbonate is higher than the acid load alone would leave it, pointing to a coexisting metabolic alkalosis, here from two days of vomiting.
When is dialysis recommended in the NU656 Unit 7 case?
The EXTRIP workgroup recommends extracorporeal treatment in ethylene glycol poisoning when the anion gap is above 27 and suggests it at 23 to 27. The patient's gap of 32 meets the stronger recommendation, so nephrology is called within the hour.
Is the NU656 Unit 7 patient a real person?
He is not. The man, his brother and every value are composite and bracketed on the page. The case was designed to show how vomiting can make a severe toxic acidosis look moderate, and the six steps work the same way on any gas your course provides.