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 with sickle cell disease takes hydroxyurea. Which laboratory test is monitored regularly for an adverse effect?
ASerum lithium level
BSerum amylase level
CUrine ketone level
DComplete blood count
2.Lab values & electrolytesHard
A patient with chronic kidney disease has a phosphate of 7.2 mg/dL (2.3 mmol/L). Which dietary teaching is most appropriate?
ATake calcium supplements on an empty stomach instead of the binder
BLimit phosphate-rich foods, such as processed foods and colas
CDrink more cola-type soft drinks to stay hydrated
DIncrease milk and cheese to protect the bones from calcium loss
3.Arterial blood gas interpretationMedium
A practice arterial blood gas shows pH 7.53, PaCO₂ 47 mmHg (6.3 kPa) and HCO₃⁻ 38 mmol/L. The primary disorder is metabolic alkalosis. How far is it compensated? Click your answer.
pH 7.53PaCO₂ 47 mmHg (6.3 kPa)HCO₃⁻ 38 mmol/L
1uncompensated
2partially compensated
3fully compensated
4.Arterial blood gas interpretationHard
A practice gas shows pH 7.32, PaCO₂ 36 mmHg (4.8 kPa) and HCO₃⁻ 18 mmol/L, with Na⁺ 138 and Cl⁻ 92 mmol/L. Use the anion gap and the delta ratio to click the best interpretation.
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 97 kg patient takes oral theophylline (F = 1) every 12 h. The clearance is 0.03 L/kg/h. What dose D in mg gives an average steady-state level of 10 mg/L?
A patient with type 1 diabetes is vomiting and eating little. What is correct sick-day advice?
ACheck glucose once a day only
BHalve fluid intake to prevent vomiting
CDo not stop insulin; check glucose and ketones more often
DStop insulin until eating normally again to avoid hypoglycaemia
8.Clinical nursingHard
A patient with metastatic breast cancer is confused and constipated, with a corrected calcium of 3.3 mmol/L (about 13.2 mg/dL). What is usually the first treatment?
AStrict fluid restriction to protect the kidneys
BOral calcium supplements and vitamin D
CA high-calcium diet
DIV fluid rehydration, followed by a bisphosphonate
3Solutions
1.Lab values & electrolytes
Answer: D · Complete blood count
Why this is the answer
Hydroxyurea increases fetal hemoglobin and reduces sickling crises, but it can suppress the bone marrow. The CBC, including neutrophils and platelets, is monitored regularly, and doses are adjusted if counts fall.Checked against:Sickle cell disease · MedlinePlus (NIH) (2026)
Answer
D · Complete blood count
2.Lab values & electrolytes
Answer: B · Limit phosphate-rich foods, such as processed foods and colas
B · Limit phosphate-rich foods, such as processed foods and colas
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 7.53: alkalaemia (above 7.45)
PaCO₂ 47 mmHg: high (35–45)
HCO₃⁻ 38 mmol/L: high (22–26)
Compensation
partially compensated
Answer
partially compensated
4.Arterial blood gas interpretation
Answer: added metabolic alkalosis
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.
Anion gap
AG = 138 − (92 + 18) = 28
Delta ratio
(28 − 12)/(24 − 18) = 2.667
added metabolic alkalosis
Answer
added metabolic alkalosis
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 = 349.2 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.
Clearance
CL = 0.03·97 = 2.91 L/h
Dose
D = Css,avg·CL·τ/(S·F) = 10·2.91·12/(1·1) = 349.2 mg
Answer
D = 349.2 mg
7.Clinical nursing
Answer: C · Do not stop insulin; check glucose and ketones more often
Why this is the answer
Stopping insulin in type 1 diabetes can quickly cause DKA. Patients should continue insulin, monitor glucose and ketones, drink fluids and seek help if ketones rise.
Answer
C · Do not stop insulin; check glucose and ketones more often
8.Clinical nursing
Answer: D · IV fluid rehydration, followed by a bisphosphonate
Why this is the answer
Hypercalcaemia of malignancy causes dehydration, so IV fluids are given first, followed by a bisphosphonate to reduce bone resorption. Calcium, renal function and fluid balance are monitored.
Answer
D · IV fluid rehydration, followed by a bisphosphonate