Read the pH: below 7.35 is acidosis, above 7.45 alkalosis.
Find the value that explains it: PaCO₂ moving opposite to the pH is respiratory, HCO₃⁻ moving with the pH is metabolic.
Look at the other value: normal means uncompensated, abnormal in the compensating direction means partial compensation, and a normal pH with both abnormal means full compensation.
In a metabolic acidosis, compare PaCO₂ with Winter’s formula, 1.5·HCO₃⁻ + 8 ± 2, and calculate the anion gap Na⁺ − (Cl⁻ + HCO₃⁻).
Check a high anion gap with the delta ratio and, when albumin is low, with the corrected gap.
Clinical pharmacokinetics
Rate constant and half-life
k = ln 2/t½ = 0.693/t½
First-order decay
C = C₀·e−kt = C₀·(1/2)t/t½
Two levels
k = ln(C₁/C₂)/Δt
Volume and clearance
Vd = dose/C₀, CL = k·Vd
Loading dose
LD = Vd·C/(S·F)
Maintenance rate
R = CL·Css/(S·F)
Average steady state
Css,avg = S·F·D/(CL·τ)
Steady state
1 − (1/2)ⁿ after n half-lives; ≈ 97% after 5
Infusion
C = (R/CL)(1 − e−kt)
Interval and dose from peak and trough
τ = ln(Cpeak/Ctrough)/k, D = Vd·(Cpeak − Ctrough)
Cockcroft–Gault
CrCl = (140 − age) × kg/(72 × SCr mg/dL), × 0.85 for women
Pick the relation: C = C₀·e−kt, LD = Vd·C/(S·F), maintenance rate = CL·Css/(S·F), τ = ln(Cpeak/Ctrough)/k.
For kidney function, estimate CrCl with Cockcroft–Gault first, then scale the dose or the interval.
Check the result: levels fall by half every half-life, and steady state takes about five half-lives.
2Practice problems
1.Lab values & electrolytesMedium
A patient’s fasting glucose today is 98 mg/dL (5.4 mmol/L), but the HbA1c is 8.9% (74 mmol/mol). What is the best interpretation?
AThe HbA1c reflects only the past 24 hours
BGlucose control has been poor over the past 2–3 months
CToday’s good result shows that diabetes is well controlled
DThe patient does not have diabetes
2.Lab values & electrolytesHard
A patient with no kidney problems and a normal ECG has a potassium of 6.2 mEq/L. The laboratory comments that the sample was hemolyzed. What is the best interpretation?
ATreat immediately with insulin and glucose without further checks
BThe potassium is certainly normal and needs no follow-up
CThe result may be falsely high; assess the patient and arrange a repeat sample
DThe patient has kidney failure
3.Arterial blood gas interpretationMedium
A practice arterial blood gas shows pH 7.12, PaCO₂ 19 mmHg (2.5 kPa) and HCO₃⁻ 6 mmol/L. The primary disorder is metabolic acidosis. How far is it compensated? Click your answer.
pH 7.12PaCO₂ 19 mmHg (2.5 kPa)HCO₃⁻ 6 mmol/L
1uncompensated
2partially compensated
3fully compensated
4.Arterial blood gas interpretationHard
A practice gas shows a respiratory acidosis: pH 7.29, PaCO₂ 81 mmHg (10.8 kPa), HCO₃⁻ 38 mmol/L. Use the rules ‘HCO₃⁻ rises 1 mmol/L per 10 mmHg (acute) or 3.5 mmol/L per 10 mmHg (chronic)’ to classify it. Click your answer.
pH 7.29PaCO₂ 81 mmHg (10.8 kPa)HCO₃⁻ 38 mmol/L
1acute
2chronic
3acute on chronic
5.Clinical pharmacokineticsMedium
Practice exercise (made-up values, not clinical guidance). A patient has a lidocaine clearance of 600 mL/min. What infusion rate R in mg/min keeps the steady-state level at 4 mg/L?
CL = 600 mL/minCss = 4 mg/L
R = mg/min
6.Clinical pharmacokineticsHard
Practice exercise (made-up values, not clinical guidance). A 58 kg patient on regular tobramycin doses is at steady state. The target is a peak of 7 mg/L and a trough of 0.5 mg/L, and the volume of distribution is 0.25 L/kg. Assuming rapid IV doses, what dose D raises the level from the trough to the peak?
Modern wound care generally aims to keep a healing wound bed:
ATightly packed with dry gauze
BMoist but not wet
CCompletely dry and open to the air
DSoaked in antiseptic solution every day
8.Clinical nursingHard
A patient after major surgery has a falling blood pressure, rising heart rate and a swollen, tense abdomen, though the wound dressing is dry. What should you suspect?
AInternal bleeding
BConstipation
CNormal postoperative swelling with no concern
DUrinary tract infection
3Solutions
1.Lab values & electrolytes
Answer: B · Glucose control has been poor over the past 2–3 months
Why this is the answer
HbA1c shows the average glucose over about 2–3 months. One normal fasting value does not show long-term control. An HbA1c of 8.9% is well above common targets such as below 7%.Checked against:Hemoglobin A1C (HbA1c) Test · MedlinePlus (NIH) (2025)
Answer
B · Glucose control has been poor over the past 2–3 months
2.Lab values & electrolytes
Answer: C · The result may be falsely high; assess the patient and arrange a repeat sample
Why this is the answer
Red cells are rich in potassium. When they break in the tube (from a tight tourniquet, fist clenching or a small needle), potassium leaks out and the result is falsely high. The nurse still assesses the patient and repeats the test, because true hyperkalemia must not be missed.Checked against:Potassium Blood Test · MedlinePlus (NIH) (2024)
Answer
C · The result may be falsely high; assess the patient and arrange a repeat sample
3.Arterial blood gas interpretation
Answer: partially compensated
Reading a blood gas (ROME): first the pH: below 7.35 is acidaemia, above 7.45 alkalaemia. Then find the value that explains it. PaCO₂ (normal 35–45 mmHg, 4.7–6.0 kPa) is the respiratory part and moves Opposite to the pH in a respiratory disorder; HCO₃⁻ (normal 22–26 mmol/L) is the metabolic part and moves in the same direction as the pH (Respiratory Opposite, Metabolic Equal). The other value shows the compensation: normal means uncompensated; abnormal in the direction that pulls the pH back while the pH is still abnormal means partially compensated; a normal pH with both values abnormal means fully compensated. Ranges differ slightly between laboratories; these are practice values.
ROME, value by value
pH 7.12: acidaemia (below 7.35)
PaCO₂ 19 mmHg: low (35–45)
HCO₃⁻ 6 mmol/L: low (22–26)
Compensation
partially compensated
Answer
partially compensated
4.Arterial blood gas interpretation
Answer: chronic
Expected compensation: in metabolic acidosis Winter’s formula predicts PaCO₂ = 1.5·HCO₃⁻ + 8 ± 2 mmHg; a measured value above that range points to an additional respiratory acidosis, below it to an additional respiratory alkalosis. The anion gap AG = Na⁺ − (Cl⁻ + HCO₃⁻), normally about 8–12 mmol/L, separates high-gap from normal-gap metabolic acidosis; low albumin hides a high gap (add 2.5 per g/dL that albumin is below 4.0). The delta ratio (AG − 12)/(24 − HCO₃⁻) between about 0.8 and 2 fits a pure high-gap acidosis (some texts use 1 instead of 0.8), below that an added normal-gap acidosis, and above 2 an added metabolic alkalosis.
Expected HCO₃⁻
acute: 24 + 1·4.1 = 28.1 mmol/L
chronic: 24 + 3.5·4.1 = 38.35 mmol/L
Compare
measured: 38 mmol/L → chronic
Answer
chronic
5.Clinical pharmacokinetics
Answer: R = 2.4 mg/min
Clearance and volume: at steady state the dosing rate equals the elimination rate, so the maintenance rate = CL × Css. A loading dose is LD = Vd × C/(S × F), with S the salt factor (fraction of active drug in the salt) and F the bioavailability (1 for IV). From two levels, k = ln(C₁/C₂)/Δt; for an IV bolus Vd = dose/C₀ and CL = k × Vd. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Clearance in L/min
600 mL/min = 0.6 L/min
Infusion rate
R = 0.6·4 = 2.4 mg/min
Answer
R = 2.4 mg/min
6.Clinical pharmacokinetics
Answer: D = 94.25 mg
Designing a regimen: with rapid IV doses the level falls from peak to trough during the interval, so τ = ln(Cpeak/Ctrough)/k and the dose that restores the peak is Vd × (Cpeak − Ctrough). The average steady-state level is Css,avg = S·F·dose/(CL·τ). An infusion rises as C = (R/CL)(1 − e−kt). For a drug cleared by the kidneys, the dose is scaled with the creatinine clearance. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Volume of distribution
Vd = 0.25·58 = 14.5 L
Dose
D = 14.5·(7 − 0.5) = 94.25 mg
Answer
D = 94.25 mg
In practice the dose is rounded to a convenient amount.
7.Clinical nursing
Answer: B · Moist but not wet
Why this is the answer
A moist wound environment speeds epithelial cell migration and healing. Too much moisture causes maceration, so dressings are chosen to manage exudate.
Answer
B · Moist but not wet
8.Clinical nursing
Answer: A · Internal bleeding
Why this is the answer
Haemodynamic signs of shock with abdominal distension suggest intra-abdominal haemorrhage, even without visible blood loss. Urgent surgical review is required.