What will be the ABG When HCO3 is increased with increased Ph
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Here is the complete ABG interpretation:
ABG: Increased HCO3- + Increased pH = Metabolic Alkalosis
Primary ABG Values
| Parameter | Value | Direction |
|---|---|---|
| pH | > 7.45 | ↑ (Alkalotic) |
| HCO3- | > 26 mEq/L | ↑ (Primary disturbance) |
| PCO2 | > 45 mmHg | ↑ (Compensatory) |
Why PCO2 is also HIGH
The raised HCO3- causes a rise in pH, which inhibits peripheral chemoreceptors. The body responds with hypoventilation (respiratory compensation), which retains CO2 and raises PCO2. This is the body's attempt to normalize the HCO3-/CO2 ratio and bring pH back toward normal.
Using the Henderson-Hasselbalch equation:
pH = pK + log ( HCO3- ↑ / PCO2 ↑ )
Both numerator and denominator rise, but the HCO3- rise dominates - so pH stays elevated.
Expected Compensation Formula
Expected PCO2 = 0.7 × [HCO3-] + 21 ± 2
- If measured PCO2 matches this: simple metabolic alkalosis
- If PCO2 is lower than expected: additional respiratory alkalosis
- If PCO2 is higher than expected: additional respiratory acidosis
Common Causes of Metabolic Alkalosis
| Cause | Mechanism |
|---|---|
| Vomiting / NG suction | Loss of gastric HCl → HCO3- retained in blood |
| Diuretics (loop/thiazide) | Cl- and volume loss → HCO3- rises |
| Hyperaldosteronism | Renal H+ loss → HCO3- rises |
| Antacid/NaHCO3 ingestion | Direct HCO3- load |
| Hypokalemia | K+ leaves cells, H+ enters → extracellular alkalosis |
Quick Memory Aid
"Met ALK = HCO3 UP, pH UP, PCO2 UP (hypoventilation compensates)"
Compare with other disorders:
| Disorder | pH | HCO3- | PCO2 |
|---|---|---|---|
| Metabolic Alkalosis | ↑ | ↑ (primary) | ↑ (compensation) |
| Metabolic Acidosis | ↓ | ↓ (primary) | ↓ (compensation) |
| Respiratory Acidosis | ↓ | ↑ (compensation) | ↑ (primary) |
| Respiratory Alkalosis | ↑ | ↓ (compensation) | ↓ (primary) |
Sources: Costanzo Physiology 7th Edition, pp. 1615-1638; Guyton and Hall Textbook of Medical Physiology, p. 2840
Dysdiadochokinesia refers to
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Dysdiadochokinesia
Dysdiadochokinesia refers to the inability to perform rapid alternating movements smoothly and rhythmically. The term comes from Greek:
- dys = difficult/abnormal
- diadochos = succeeding/alternating
- kinesis = movement
Definition (Precise)
"Abnormal alternating movements" - the patient cannot rapidly and smoothly alternate between opposing movements (e.g., pronation and supination of the forearm).
Pathological Basis
It is a cardinal sign of cerebellar dysfunction. The cerebellum normally coordinates the rapid succession of agonist and antagonist muscle contractions required for smooth alternating movements. When the cerebellum is damaged, this sequencing breaks down - movements become:
- Irregular in rhythm
- Variable in amplitude
- Slow and clumsy
How it is Tested Clinically
| Test | Method |
|---|---|
| Pronation-supination test | Patient rapidly alternates palm up/palm down on their thigh or the examiner's hand |
| Finger-tapping test | Rapidly tapping index finger on thumb |
| Hand-patting test | Wiping one palm alternately with the palm and dorsum of the other hand |
A positive test shows slow, irregular, poorly timed alternating movements.
Associated Cerebellar Signs (occurs together with)
- Dysmetria - past-pointing / overshoot on finger-nose-finger test
- Intention tremor - tremor that worsens as the limb approaches a target
- Ataxic gait - wide-based, unsteady walk
- Scanning speech - slow, slurred, monotonous speech
- Nystagmus
- Hypotonia
Localization
| Lesion Site | Features |
|---|---|
| Cerebellar hemisphere | Ipsilateral limb dysdiadochokinesia + appendicular ataxia |
| Cerebellar vermis | Truncal ataxia, gait ataxia (less prominent limb signs) |
Key Differentiator
Dysdiadochokinesia is not caused by weakness or sensory loss - it is specifically a coordination deficit from cerebellar pathology. This distinguishes it from similar-looking clumsiness in upper motor neuron or extrapyramidal disease.
Sources: Neuroanatomy through Clinical Cases 3rd Edition, p. 1982; Localization in Clinical Neurology 8e, p. 902; Bradley and Daroff's Neurology in Clinical Practice, p. 1854
Test for assess rotator cuff impingment
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Here is a complete breakdown of all clinical tests used to assess rotator cuff impingement:
Tests for Rotator Cuff Impingement
1. Neer Impingement Sign
- How: Examiner stabilizes the scapula with one hand to prevent scapular rotation, then raises the patient's straightened arm in full forward flexion (passively, to overhead) with the arm internally rotated
- Positive: Pain in the arc between 70 and 120 degrees of flexion
- Mechanism: Forces the greater tuberosity against the anteroinferior acromion, compressing the supraspinatus tendon
2. Hawkins-Kennedy Test
- How: Examiner positions the patient's shoulder at 90° of abduction + 90° of elbow flexion, then internally rotates the shoulder, pushing the arm across the front of the body
- Positive: Pain with internal rotation
- Mechanism: Drives the greater tuberosity under the coracoacromial ligament, compressing the supraspinatus
3. Painful Arc Sign
- How: Patient actively abducts the arm from 0° to 180°
- Positive: Pain specifically between 60° and 120° of abduction (the arc where the greater tuberosity passes under the acromion)
- Significance: Highly specific for subacromial impingement
4. Empty Can Test (Jobe Test) - Supraspinatus
- How: Arm abducted to 90°, forward-flexed 30°, with the thumb pointing downward ("empty can" position). Examiner applies downward resistance
- Positive: Pain or weakness against resistance
- Tests: Supraspinatus integrity specifically
5. Drop-Arm Test
- How: Patient abducts arm to 90°, then slowly lowers it to the side
- Positive: Arm drops suddenly or patient cannot lower it smoothly
- Tests: Significant rotator cuff tear (more than just impingement)
6. Neer Impingement Test (Lidocaine Test)
- How: Inject 10 mL of 1% lidocaine into the subacromial space; then re-test Neer and Hawkins
- Positive: Pain relief = confirms subacromial impingement as the source
- Note: Also positive in 46% of SLAP lesions and 69% of AC joint arthritis - so not perfectly specific
7. Specific Rotator Cuff Muscle Tests
| Muscle | Test | Position |
|---|---|---|
| Supraspinatus | Empty can / Jobe | Arm 90° abduction, 30° forward flex, thumb down |
| Infraspinatus & Teres minor | External rotation test | Arm at side, elbow 90°, resist external rotation |
| Subscapularis | Lift-off test | Hand behind back, push dorsum away from back |
Sensitivity & Specificity (Campbell's Operative Orthopaedics)
| Test | Sensitivity | Specificity | Best Use |
|---|---|---|---|
| Painful arc | 73.5% | 81.1% | Rule in impingement |
| Hawkins-Kennedy | 71.5% | 66.3% | Sensitive screen |
| Neer sign | 68% | 68.7% | Standard screen |
| Jobe (empty can) | 44.1% | 89.5% | Rule in supraspinatus tear |
| Drop-arm | 26.9% | 88.4% | Confirm full thickness tear |
The painful arc has the best overall accuracy (76.1%) for subacromial impingement. The Hawkins-Kennedy is the most sensitive (71.5%). For confirming diagnosis, the lidocaine injection test is used.
Memory Tip
"Neer = Forward flexion | Hawkins = Internal rotation at 90°" Both compress the supraspinatus - Neer against the acromion, Hawkins against the coracoacromial ligament.
Sources: Campbell's Operative Orthopaedics 15th Ed 2026, Table 51.2; Tintinalli's Emergency Medicine, p. 2249-2251; Gray's Anatomy for Students, p. 4267
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