ICU/CTICU worked laboratory examples

Educational work by a pre-medical student — not medical advice. Not a clinical protocol, prescription, or patient handout, and not for patient care. See DISCLAIMER.

Evidence labels: Guideline/consensus recommendation (strength and population stated), general clinical knowledge, context-dependent clinical practice, and synthetic example. A case or original diagram is not a standardized treatment protocol.

28 October 2026. These 11 worked examples extend the 18 procedure pairs and 42 integrated ICU topics. Paired-case context lines name the matching procedure-casebook example; where an example is not one of the 18 pairs, it is labeled as an additional synthetic example. People, numerical results and trends are wholly synthetic; no clinical outcome is claimed. These are explanations of source-supported clinical reasoning, not quizzes or an order set.

Choose an investigation to answer a clinical question that may change care. Review prior results, specimen/site, timing, current support, exposures and local assay ranges. A result supports or challenges a diagnosis; it does not independently diagnose every cause or prescribe treatment. Urgent assessment and treatment can proceed in parallel with investigation. Frequency depends on instability and the decision at hand.

Postoperative bleeding and anemia

Paired case context — synthetic example: The coronary-bypass male example has a new fall in pressure, which raises a postoperative bleeding question among other causes; the endovascular aortic-repair female example develops new pain and a falling pressure.

Investigation and purpose — context-dependent clinical practice: CBC (hemoglobin/hematocrit and platelets); fibrinogen and appropriate coagulation studies if bleeding is clinically suspected. Compatibility testing is considered when transfusion may be needed.

Illustrative finding — synthetic data / clinical interpretation: A fictional hemoglobin decrease from 10 to 8 g/dL, interpreted with timing, dilution, drain losses and perfusion, raises an anemia/blood-loss question. It is not a transfusion threshold.

Effect on care — context-dependent clinical practice: The team evaluates a surgical source and clinically relevant coagulopathy; selected viscoelastic testing can help guide a local hemostatic pathway. A laboratory result cannot exclude tamponade or replace surgical review.

Classification note: General clinical knowledge and context-dependent bleeding assessment; the fictional hemoglobin change is not a standardized transfusion trigger. Evidence details.

Public clinical sources: PBM.

Carbon dioxide retention and acidemia

Paired case context — synthetic example: The ARDS female example develops hypercapnia and ventilator dyssynchrony; the coronary-bypass male example has shallow breathing with incisional pain, so analgesic exposure is also reviewed.

Investigation and purpose — context-dependent clinical practice: Arterial blood gas with documented oxygen/support conditions, interpreted alongside examination and delivered ventilation.

Illustrative finding — synthetic data / clinical interpretation: Fictional pH 7.28, PaCO2 60 mmHg and bicarbonate 27 mmol/L demonstrate acidemia with a respiratory component; baseline and other data are needed for acute/chronic or mixed classification.

Effect on care — context-dependent clinical practice: The team reviews airway patency, minute ventilation, mechanics and medication effects. Raising FiO2 alone does not correct inadequate ventilation. Sampling error or a venous sample changes interpretation.

Classification note: General clinical knowledge plus synthetic numerical interpretation; this is not a guideline-defined intubation or ventilator-adjustment threshold. Evidence details.

Public clinical sources: GAS, VENTASSESS.

Oxygenation under defined support

Paired case context — synthetic example: The male severe-pneumonia/ARDS example has worsening oxygenation; the female single-lung-transplant example develops hypoxemia with altered airway pressures.

Investigation and purpose — context-dependent clinical practice: An arterial gas when it can resolve the oxygenation question, with FiO2, PEEP/support and sample time recorded.

Illustrative finding — synthetic data / clinical interpretation: PaO2 80 mmHg on FiO2 0.50 gives a P:F ratio of 160 mmHg. This calculation alone does not diagnose ARDS or graft dysfunction.

Effect on care — context-dependent clinical practice: The team combines the finding with imaging, timing and competing cardiac/fluid/airway causes, then reassesses support and the underlying cause. A different support condition makes a serial ratio less comparable.

Classification note: General clinical knowledge/arithmetic; the P:F calculation is not a complete diagnostic criterion or treatment instruction. Evidence details.

Public clinical sources: GAS, ARDS.

Lactate in sepsis or postoperative shock

Paired case context — synthetic example: The esophagectomy female example has fever and hypotension, raising a sepsis question; the VA-ECMO male example has cool extremities and a rising lactate despite displayed circuit flow.

Investigation and purpose — context-dependent clinical practice: Lactate when shock/sepsis evaluation calls for it, alongside pressure, examination, urine output and cardiac/source assessment.

Illustrative finding — synthetic data / clinical interpretation: A fictional lactate trend from 4 to 3 mmol/L is one improving measurement, not proof that shock has resolved. Production, clearance and treatments affect the value.

Effect on care — context-dependent clinical practice: The team reassesses perfusion and the cause. Persistent elevation does not automatically mandate more fluid, particularly when congestion or respiratory deterioration is present.

Classification note: Guideline recommendation G24 is conditional (low certainty) for measuring lactate in sepsis; interpretation and response in this case are context-dependent. Evidence details.

Public clinical sources: SEPSIS, HEMO, SHOCK25.

Kidney injury after major surgery

Paired case context — synthetic example: The open AAA-repair male example has abdominal distension and reduced urine output; the arch-repair female example has reduced urine output with a focal neurological change. The heart-transplant male example (low output with worsening kidney function) adds a medication-exposure question.

Investigation and purpose — context-dependent clinical practice: Creatinine/BUN, electrolytes and relevant acid-base measures, urine-output/balance trends; urinalysis or imaging when a specific cause is being evaluated.

Illustrative finding — synthetic data / clinical interpretation: A fictional creatinine rise from 1.0 to 1.6 mg/dL within 48 hours is compatible with an AKI creatinine criterion after measurement/context checks. It does not identify the cause.

Effect on care — context-dependent clinical practice: Assessment distinguishes perfusion, congestion, obstruction and renal injury/exposure. Dialysis is considered from clinical needs and trajectory, not this creatinine value alone.

Classification note: Guideline diagnostic definition G25 is not graded. The fictional creatinine change fits a definition component after context checks; the cause and management remain clinical assessments. Evidence details.

Public clinical sources: AKI, RRT. KDIGO 2012 remains the final published guideline; a 2026 KDIGO AKI/AKD update was in public-review draft at the time of writing and is not used here as final guidance.

Potassium and rhythm/perfusion changes

Paired case context — synthetic example: The mechanical aortic-valve male example develops bradycardia and reduced urine output; the limb-revascularization male example has increasing pain, tense swelling and sensory change after reperfusion, a setting in which potassium release and kidney injury are also considered.

Investigation and purpose — context-dependent clinical practice: Potassium and renal/acid-base chemistry; magnesium where the rhythm or exposure question makes it relevant, with ECG/clinical assessment.

Illustrative finding — synthetic data / clinical interpretation: A fictional potassium result of 6.2 mmol/L raises an urgent hyperkalemia concern. Sample hemolysis can mislead; confirmation is coordinated without delaying necessary treatment of a clinically dangerous presentation.

Effect on care — context-dependent clinical practice: The clinical team assesses electrical effects, medications, kidney function and the need for correction or renal support. This example is not a universal treatment threshold or replacement dose.

Classification note: General clinical knowledge and context-dependent urgent assessment. The fictional potassium value is not asserted to be one universal treatment threshold. Evidence details.

Public clinical sources: RRT, HEMO.

New fever and a suspected source

Paired case context — synthetic example: The esophagectomy female example has shock with altered drain findings; the male pneumonia example has compatible respiratory findings.

Investigation and purpose — context-dependent clinical practice: Blood cultures in suspected sepsis and source-directed microbiology; respiratory sampling or other studies only when clinically indicated.

Illustrative finding — synthetic data / clinical interpretation: A positive culture must be interpreted for pathogen, collection quality, contamination, source and prior therapy. A white count alone neither proves nor excludes infection.

Effect on care — context-dependent clinical practice: Results help refine antimicrobial/source management. Sampling should not harmfully delay time-critical treatment. The general new-fever guideline excludes severe immunocompromise; transplant investigation follows the transplant service plan.

Classification note: Guideline recommendation G23 is strong (low certainty) for blood cultures in the stated sepsis population. Other source-directed investigations remain context-dependent; general fever guidance excludes severe immunocompromise. Evidence details.

Public clinical sources: FEVER, SEPSIS.

Bleeding/thrombosis balance with anticoagulation

Paired case context — synthetic example: The mechanical aortic-valve male example and the female LVAD or Impella examples receive different anticoagulant therapies.

Investigation and purpose — context-dependent clinical practice: The assay appropriate to the actual agent and indication, such as INR for vitamin-K antagonist effect, or a protocol-defined aPTT/anti-Xa assessment for heparin. CBC and clinical bleeding/device findings add context.

Illustrative finding — synthetic data / clinical interpretation: An INR result cannot be treated as the effect of every anticoagulant. Results depend on medication, assay, timing and clinical context.

Effect on care — context-dependent clinical practice: The team evaluates bleeding and thrombotic risk before adjusting therapy under the actual valve/device plan. No common target can be assigned to both examples.

Classification note: General clinical knowledge and drug/device-specific practice; there is no universal assay or target across these therapies. Evidence details.

Public clinical sources: PBM, MCS.

Anemia or dark urine during mechanical support

Paired case context — synthetic example: The established-LVAD female example has alarms, dark urine and a falling hemoglobin; the Impella female example has dark urine and a falling hemoglobin. The Impella male example has access-site swelling, so blood loss must be distinguished from hemolysis.

Investigation and purpose — context-dependent clinical practice: CBC, renal chemistry and selected hemolysis measures, such as plasma-free hemoglobin, LDH, bilirubin or haptoglobin, interpreted with device/imaging findings.

Illustrative finding — synthetic data / clinical interpretation: A rising LDH alone does not establish pump thrombosis. Hemolysis, blood loss and other tissue injury must be distinguished.

Effect on care — context-dependent clinical practice: The support team evaluates position, loading, circuit/device problems and patient effects. No speed or anticoagulant change is selected from one result.

Classification note: General clinical knowledge and specialist practice; no isolated marker establishes pump thrombosis. Evidence details.

Public clinical sources: MCS, LVAD.

Fluid, electrolyte and acid-base needs during CRRT

Additional synthetic example (not one of the 18 procedure pairs): A male with multiorgan failure remains fluid overloaded; a female with AKI has evolving acid-base/electrolyte abnormalities.

Investigation and purpose — context-dependent clinical practice: Chemistry and appropriate blood gas assessment, fluid balance and urine output; monitoring is tailored to modality, anticoagulant and clinical course.

Illustrative finding — synthetic data / clinical interpretation: Improved potassium or bicarbonate after treatment reflects part of the response, not kidney recovery by itself. Delivered therapy and ongoing losses matter.

Effect on care — context-dependent clinical practice: The renal/ICU team adjusts the prescription to patient needs and tolerance; fluid removal is balanced against perfusion. No fixed effluent, fluid-removal or laboratory interval is implied.

Classification note: Guideline statements G26 are not graded; CRRT preference in unstable patients (G27) is conditional, 2B. Monitoring and adjustment remain individualized. Evidence details.

Public clinical sources: RRT.

A displayed number that conflicts with the patient

Additional synthetic example (not one of the 18 procedure pairs): A male with continuous-flow LVAD support has an unreliable pulse-oximetry signal; a female ventilated patient has an unexpected gas result.

Investigation and purpose — context-dependent clinical practice: Check measurement method, waveform/signal, specimen identity/site, timing and current support; use an appropriate independent assessment when necessary.

Illustrative finding — synthetic data / clinical interpretation: SpO2 estimates saturation; it does not measure PaCO2 or prove adequate ventilation. Low perfusion and other factors can impair accuracy.

Effect on care — context-dependent clinical practice: The team investigates the patient and the measurement together instead of escalating support solely from an unverified value. A blood gas addresses a specific unresolved question.

Classification note: General measurement knowledge and official device-safety information, applied to fictional observations. Evidence details.

Public clinical sources: SPO2, GAS, LVAD.

Source scope

The public source register identifies source type, DOI where applicable, support and review limits. The guideline recommendation is distinct from the fictional numbers and their authored application. Numerical findings are not society-approved cutoffs unless expressly identified as a diagnostic criterion. The earlier 20-category investigation catalogue provides additional test-purpose/limitation explanations.