THG32-001
Q32.1
a. Name the test shown in the images A and B given above and its utility.
b. Mention the recommended sites for the procedure.
c. List of materials required.
d. What are the precautions to be taken?
e. What are the reasons for the precautions?
Answer
| a. | Modified Allen test and it is used to assess the integrity of the ulnar artery before radial artery puncture or cannulation at that site, to verify ulnar artery collateral circulation, and to ensure blood flow to the hand if occlusion of radial artery occurs due to thrombus or embolization. |
| b. | Radial artery is the common site chosen, other sites include femoral artery, brachial artery rarely dorsalis pedis artery. |
| c. | The following are required preheparinized ABG syringes if available or a normal syringe flushed with 0.05 mL of 1:1,000 heparin solution and emptied, gloves, and alcohol swabs. |
| d. | Procedure is performed after taking aseptic precautions, needle directed at an angle of 30–45° from the surface, and after 2 mL is collected, needle is removed, firm occlusive local pressure applied for over 5 minutes, check for hemostasis and apply adhesive plaster. If ABG syringe is used, needle protective sleeve applied, untwisted and removed with needle and placed in sharp container. Excess air removed by holding upright, gently tapped to bring air bubble if any to the top so that air can be expelled and after capping placed in ice bag and sent for analysis immediately after noting the details of the patient’s name, FiO2, temperature, date, and time. |
| e. | Reasons for the precautions: Aseptic precautions to prevent sepsis, needle is directed at an angle 30–45° in the direction of the artery to avoid trauma, to allow smooth fibers to occlude the site of the puncture after the procedure. Firm occlusion to avoid bleeds and hematoma. |
| Air bubbles expelled as it will increase PaO2 and cause error in interpretation. Sent in ice as change in pH is 0.001, PCO2 is 0.1 mm Hg and PaO2 is 0.01% in ice and without ice change in pH is 0.01, PCO2 is 1 mm Hg and PaO2 is 0.1%. The patient’s details for avoiding errors and correct interpretation based on the parameters like FiO2 etc. |
THG32-002
Q32.2
a. What is this curve seen in the image given above?
b. What is p50?
c. State two conditions which will cause shift of the curve to the left.
d. State two conditions which cause shift of the curve to the right.
e. What are the determinants of partial pressure of arterial oxygen (PaO2).
Answer
| a. | Oxygen—hemoglobin dissociation curve correlates the oxygen saturation of hemoglobin across a range of partial pressures of oxygen. |
| b. | The p50 is the pressure at which hemoglobin is 50% saturated (27 mm Hg on the X-axis). |
| c. | Left shift (dashed blue line) increases the oxygen affinity; hemoglobin holds more tightly onto oxygen and delivers less oxygen to the tissues at a given arterial oxygen pressure, e.g., fetal hemoglobin (Hb F), carboxy, Hb, methemoglobinemia (MetHb), low 2.3-diphosphoglycerate (2.3-DPG) higher pH, decrease in body temperature. |
| d. | Right shift (dashed red line) decreases oxygen affinity; hemoglobin holds less tightly onto oxygen and delivers more oxygen to the tissues at a given arterial oxygen pressure, e.g., increase in body temperature, higher 2.3-DPG, and lower pH. |
| e. | Age, as age increases PaO2 decreases (PaO2 is crudely calculated as 104.2- (0.27 × of age in years), as FiO2 increases PaO2 increases (roughly five times the FiO2), oxygen content and hemoglobin oxygen affinity. |
THG32-003
Calculate the alveolar-arterial oxygen difference (AaDO2) for the arterial blood gas (ABG) given below:
| ■ | pH 7.6 |
| ■ | Partial pressure of arterial carbon dioxide (PaCO2) 65 mm Hg |
| ■ | PaO2 160 mm Hg |
| ■ | HCO3 24 mmol/L |
| ■ | Fraction of inspired oxygen (FiO2) 50% |
Answer
The AaDO2 is calculated as follows:
PAO2 − PaO2
PAO2 = [FiO2 × (760 − 47) − 1.25 × PaCO2] and PaO2 is 160 mm Hg
(FiO2 × 713 − 1.25 × PaCO2) − PaO2
(0.5 × 713 − 1.25 × 65) – 160 = 115.25 which is increased alveolar-arterial gradient.
THG32-004
A 5-year-old child admitted in pediatric intensive care unit (PICU) with the following results:
a. Calculate the anion gap.
b. What is the metabolic abnormality?
c. What is the exact compensation?
d. What are the delta anion gap, delta HCO3, and delta-delta ratio?
e. Name two conditions with decreased anion gap?
Answer
| a. | Anion gap: Na – (Cl + HCO3), i.e., 136 – (100 + 12) = 24. |
| b. | HAGMA with normal oxygenation. |
| c. | Compensation using Winter’s formula |
| Expected PCO2 is (HCO3 × 1.5) + 8 ± 2 = 12 × 1.5 + 8 ± 2 = 26 ± 2 = 24–28 mm Hg but actual is 32 mm Hg, so added respiratory acidosis. | |
| d. | Delta anion gap is 24 − 12 = 12, delta HCO3 is 12, so delta-delta ratio is 1, so pure HAGMA and respiratory acidosis. |
| e. | Conditions with decreased anion gap: Hypoalbuminemia, paraproteinemia (multiple myeloma), bromide intoxication, and hypermagnesemia. |
THG32-005
A 7-year-old child admitted with repeated vomiting was evaluated and as her serum electrolytes were Na 132 mEq/L, K 3.1 mEq/L, Cl 84 mEq/L, and HCO3 34 mEq/L, ABG was done which showed pH 7.48, PaCO2 47 mm Hg, HCO3 34 mEq/L, PaO2 96 mm Hg, and arterial oxygen saturation (SaO2) 100%, Hb 8 gm/dL.
a. What is the disorder?
b. What is the compensation?
c. Is there another disorder?
d. What is the cause for low Na and K?
e. Comment on the oxygenation and oxygen content.
Answer
| a. | The disorder is metabolic alkalosis as the HCO3 is high (34 mEq/L). |
| b. | Compensation is: |
| Expected PaCO2 raise 0.5–1 mm Hg for each 1 mEq raise in HCO3 | |
| 34 − 24 = 10 × (0.5 − 1) = (5 − 10), i.e., expected PaCO2 is 45–50 mm Hg. Compensation is appropriate as the actual PaCO2 is 47 mm Hg. | |
| c. | Is there another disorder—No. |
| d. | Cause for low Na and K: Loss of HCl, contraction alkalosis increased aldosterone loss of K, Hypovolemic hyponatremia, replacement with dilute ORS |
| e. | Normal oxygenation, oxygen content (CaO2) = Hb × 1.34 × SaO2% + (PaO2 × 0.003) |
| 8 × 1.34 × 1 + 96 × 0.003 = 10.72 + 0.28 = 11.00 mL. |
THG32-006
ABG of a 5-year-old child is as follows:
a. What is the metabolic abnormality?
b. How is the compensation estimated?
c. What is the inference?
d. Comment on the anion gap.
Answer
| a. | Metabolic acidosis. |
| b. | Expected PCO2 using Winter’s formula (18 × 1.5) + 8 ± 2 = 35 ± 2 = 33 to 37 mm Hg |
| c. | Simple metabolic acidosis with appropriate compensation. |
| d. | Normal anion gap metabolic acidosis (NAGMA). |
THG32-007
The ABG of a 5-week-old infant with persistent vomiting is given below:
a. What is primary disturbance?
b. Is the compensation appropriate?
c. What is the oxygenation status?
d. Is it a simple or mixed disorder?
e. What is the clinical application?
Answer
| a. | Metabolic alkalosis. |
| b. | Expected PaCO2 raise 0.5–1 mm Hg for each 1 mEq raise in HCO3 |
| (36 − 24) = 12 × 0.5 − 1, i.e., 6–12 | |
| Expected PaCO2 − (40 + 6 or + 12) = 46–52. | |
| Actual PaCO2 49; appropriate compensation. | |
| c. | Normal oxygenation. |
| d. | Simple metabolic alkalosis. |
| e. | Clinical implication: One must look for visible gastric pulsations, do an ultrasonogram abdomen, obtain a surgical opinion to diagnose, and manage conditions like idiopathic hypertrophic pyloric stenosis. |
THG32-008
An 8-year-old girl presented with history of polyuria and polydipsia of 2 weeks duration. On examination, child is dehydrated, comatose with deep and rapid breathing.
a. What is the initial impression and oxygenation?
b. What is the comment on the clinical condition?
c. What is the compensation?
d. What is the anion gap?
e. Name two conditions with high anion gap metabolic acidosis (HAGMA).
Answer
| a. | Initial impression: Metabolic acidosis, hyperglycemia with no hypoxia. |
| b. | Probably diabetic ketoacidosis. |
| c. | Compensation: Using Winter’s formula: (1.5 × 11) + 8 ± 2 = 25 ± 2 = 23–27 |
| Actual PCO2 is 16, so partially compensated metabolic acidosis/added respiratory alkalosis. | |
| d. | Anion gap = 136 – (99 + 11) = 26 (high anion gap). |
| e. | Conditions with high anion gap metabolic acidosis diabetic ketoacidosis, uremia, poisons or drug intoxication (e.g., methanol, ethylene glycol, paraldehyde, salicylates), lactic acidosis (e.g., sepsis, heart failure). |
THG32-009
A 5-month-old admitted with afebrile seizures, acute encephalopathy, shock, fast breathing, and normal chest X-ray (CXR). No history of poisoning. On ventilator, FiO2 90%. Investigations: Glucose, Ca, Mg, renal function test (RFT), CT, and cerebrospinal fluid (CSF) analysis were normal. Sodium 138 mEq/L, K 3.5 mEq/L, chloride 100 mEq/L, pH 6.648, PCO2 25.8 mm Hg, PO2 396.4 mm Hg, SaO2 100%, HCO3 2.7 mmol/L.
a. What is the anion gap?
b. What is the initial interpretation of the above ABG?
c. What is the expected PCO2?
d. What are the delta anion gap, delta HCO3, delta gap, and delta-delta ratio?
e. What is the final interpretation?
Answer
| a. | Anion gap is Na 138 – (Cl 100 + HCO3 2.7) = 35.3. |
| b. | Severe metabolic acidosis (HCO3 2.7 mmol/L) with hyperoxia (PaO2 396 mm Hg). |
| c. | Expected PCO2 is (1.5 × 2.7) + 8 ± 2 = 12 ± 2 = 10–14 mm Hg. Actual PCO2 is 25.8 mm Hg, so respiratory acidosis. |
| Mixed high anion gap metabolic acidosis and respiratory acidosis. | |
| d. | Delta anion gap = 35.3 – 12 = 23.3 |
| Delta HCO3 = 24 – 2.7 = 21.3 | |
| Delta gap = 2 | |
| Delta-delta ratio = 23.3/21.3 = 1.09 | |
| e. | Final interpretation, to know if there metabolic alkalosis or non-anion gap metabolic acidosis along with high anion gap metabolic acidosis (HAGMA) |
| As delta gap* here is 2 and delta-delta ratio** is 1.09 it is HAGMA with respiratory acidosis. | |
| [(*If delta gap is negative (<−6): Mixed HAGMA and a NAGMA | |
| If delta gap −6 to 6: Consider only a HAGMA | |
| If delta gap is positive (>6): Mixed HAGMA and metabolic alkalosis | |
| **If the ratio is <0.8 = HAGMA + NAGMA | |
| If the ratio is 0.8–2 = Pure HAGMA | |
| If the ratio is >2 = HAGMA + metabolic alkalosis)]. |
THG32-010
Child resuscitated following cardiac arrest:
a. What is the initial interpretation of the above ABG result?
b. Calculate delta anion gap and delta bicarbonate.
c. What is the final interpretation and oxygenation?
Answer
| a. | Respiratory acidosis and metabolic acidosis (anion gap is 24, so HAGMA) with hypoxia. |
| b. | Delta anion gap = 12, delta HCO3 = 11.3. |
| c. | Delta gap = 0.7 and delta-delta ratio = 12/11.3 = 1.06, so pure HAGMA with respiratory acidosis, severe hypoxia (as PaO2 is less than 40 mm Hg). |
THG32-011
A 15-year-old boy presented with repeated vomiting of 4 days duration with mental confusion, giddiness, and tiredness for 1 day. Examination revealed tachycardia, hypotension, and dehydration.
a. What is the interpretation of oxygen status?
b. How is hypoxia classified and what are the clinical features?
c. What is the initial impression?
d. What is the final interpretation?
Answer
| a. | Normal oxygenation—above 80 mm Hg is normal |
| b. | Mild hypoxemia—PaO2: 60–79 mm Hg (tachypnea) |
| Moderate hypoxemia—PaO2: 40–59 mm Hg (tachycardia, cool extremities) | |
| Severe hypoxemia—PaO2: <40 mm Hg (arrhythmias, brain injury, and death) | |
| c. | Initial impression is metabolic alkalosis. |
| d. | For 1 mEq rise in HCO3 the PCO2 will increase by 0.5–1 mm Hg |
| For 33 − 24 = 9 mEq HCO3, PCO2 will increase by 4.5–9 mm Hg, i.e., 44.5–49 mm Hg. Actual PCO2 is 49 mm Hg, so adequate compensation and final impression is metabolic alkalosis. |
THG32-012
A 11-month-old infant presented with effortless tachypnea with depressed consciousness. The ABG is as follows:
a. What is the initial impression?
b. What is the anion gap?
c. What is the expected PCO2 and its interpretation?
d. What are the delta anion gap, delta bicarbonate, and final impression?
e. Mention the possible clinical condition with this result?
Answer
| a. | Metabolic acidosis. |
| b. | Anion gap 141 − (105 + 8) = 28 high anion gap. |
| c. | Expected PCO2 = (1.5 × 8) + 8 ± 2 = 18–22 mm Hg, actual is 34, so there is additional respiratory acidosis. |
| d. | Delta anion gap is 28 – 12 = 16, delta bicarbonate is 24 – 8 = 16, delta-delta ratio is 16/16 = 1, delta-delta gap is 16 − 16 = 0, so pure HAGMA and respiratory acidosis. |
| e. | Inborn errors of metabolism (IEM) with respiratory depression, chronic kidney disease (CKD) with pneumonia, septic shock with pneumonia, and postcardiac arrest. |
THG32-013
ABG report:
a. Interpret the ABG.
b. What is the normal PaO2 if child breathes room air with normal lungs?
c. What is the normal PaCO2 and write the unit of measurement?
d. What is normal serum bicarbonate? Write the unit of measurement.
Answer
| a. | Acute respiratory acidosis with moderate hypoxia and the compensation is adequate. It is acute as pH has fallen by 0.16 for 20 mm increase in PCO2 and HCO3 has increased by 2 mEq/L for 20 mm increase in PCO2. |
| b. | Normal PaO2 if child breathes room air with normal lungs is 80–100 mm Hg. |
| c. | Normal PaCO2 with unit is 35–45 mm Hg (40 mm Hg). |
| d. | Normal serum bicarbonate with unit is 22–26 mmol/L (24 mmol/L). |
THG32-014
ABG values of a 3-year-old child who is hyperventilating are as follows:
a. What is the likely disorder?
b. Comment on final interpretation and oxygenation.
Answer
| a. | Respiratory alkalosis. |
| b. | Compensation for 10 mm fall in PCO2 the HCO3 will fall by 2 mEq/L, i.e., it must be 22 mEq/L but actual HCO3 is 28 mEq/L, so there is added metabolic alkalosis with mild hypoxemia. |
THG32-015
ABG shows the following:
a. What is the initial impression?
b. What is the anion gap and its inference?
c. What is the expected compensation and its inference?
d. What are the delta anion gap, delta bicarbonate, delta-delta ratio, delta gap, and its inference?
e. Mention a clinical situation where this is likely.
Answer
| a. | pH is normal but HCO3 and PCO2 are abnormal, so a mixed disorder, metabolic acidosis, respiratory alkalosis and normal oxygenation. |
| b. | Anion gap is 134 − (106 + 6) = 22, high anion gap. |
| c. | Expected compensation for a bicarbonate of 6 mEq/L is (1.5 × 6 + 8 ± 2, i.e., 17 ± 2: 15–19) but actual PCO2 is 12, so there is respiratory alkalosis too. |
| d. | Delta gap is 22 − 12 = 10 |
| Delta bicarbonate is 24 − 6 = 18 | |
| Delta-delta ratio is 10/18 = 0.55 | |
| Delta gap is 10 − 18 = −8, so the inference is HAGMA + NAGMA | |
| Inference: HAGMA + NAGMA + respiratory alkalosis. | |
| e. | IEM with diarrhea dehydration, CKD with fever, and diarrhea. |
Figure Sources
All the figures are from author’s personal collection.