Anion gap

 Anion gap =( Na+) + (K+)  -  (Hco3 -) + (Cl-)

Normal range-8 to 12 mmol/L

Ref-MD Vasudevan textbook of biochemistry 6th edition 

Vesicular breath sounds - Physiology

Normal breath sounds originate from the larynx. When the sound leaves the larynx it travels down the trachea and then divides when the airway divides. Some sound must be transmitted through the lung parenchyma but most travels down the airway. Eventually the sound travels along airways of different lengths and therefore becomes out of phase. Next it arrives in the respiratory bronchioles and alveoli and then gets transmitted through the chest wall to your stethoscope. The fat layer filters out much of the high frequency sound (above 4 kHz). The resulting sounds are much softer (because the sound has effectively been diluted throughout the whole of the lungs). There is no gap between inspiration and expiration (because all of the sound has become out of phase and therefore ‘filled in’ the gap). Finally, the first third of expiration is now the only part that is audible because the latter two-thirds are much quieter.

REFERENCE: Chamberlain’s, 13th edition, page no: 97

Cough Reflex

Chemical (e.g., capsaicin) and mechanical (e.g., particulates in air pollution) stimuli leads to  Stimulation of sensory nerve endings (rapidly adapting receptors and C fibers) .

 Sensory signals  travel via the vagus and superior laryngeal nerves to brainstem in the nucleus tractus solitarius (cough center) and inputs from cortex 

 The vocal cords adduct, leading to transient upper-airway occlusion. Expiratory muscles contract,
generating positive intrathoracic pressures as high as 300 mmHg leading to cough.

Reference: Harrisons 

Causes of Orthopnea

 CAUSES OF ORTHOPNEA :

1. Left ventricular failure.

2. Asthma

3. COPD

4. Bilateral diaphragmatic paralysis in the absence of heart disease.

Ref : Fraser 4th edition page no. 388

Antitussives and doses

NONOPIOIDS

Dextromethorphan- 10-20mg/day

Chlophedianol-20-40 mg/ days

Noscapine- 15-30 mg/ day

OPIODS

Codiene -10-30mg/day

Pholcodiene-10-15mg/day

ANTIHISTAMINE

Chlorphenirmanine-2-5 mg/ day

Diphenhydramine-15-25mg / days

Promethazine-15-25 mg / days

Prenoxdiazine -100-200 mg tds

Ref:Tripathy

RADS-Definition and Criteria

 DEFINITION:

RADS (Reactive airway dysfunction syndrome) is characterized by the onset of asthma symptoms within 24 hours after a single, most often accidental, high level exposure to a wide variety of irritant substances in subjects without pre-existing asthma.

DIAGNOSTIC CRITERIA:

1. Absence of pre-existing asthma symptoms or a history of asthma in remission

2. Onset of asthma symptoms after a single specific inhalational exposure or accident

3. Exposure to an irritant vapor, gas, fume or smoke in a very high concentration

4. Onset of asthma symptoms within minutes to hours and less than 24 hours after the exposure

5. Presence of airflow limitation with a significant bronchodilator response or non specific bronchial hyperresponsiveness to histamine or methacholine

6. Exclusion of other pulmonary disorders that can explain the symptoms or simulate asthma.

REFERENCE: Murray and Nadel's Textbook of respiratory medicine, Seventh Edition, Page number 1404

Differential Diagnosis of Orthopnoea

 Orthopnoea is dypnoea on lying flat due     to Heart failure 

Differential include:

Acute Asthma

Diaphragmatic nerve palsy / diaphragmatic weakness

Gross ascites

Morbid Obesity

Ref: Macleods page 77 ,14th ed 

Platypnoea

 Platypnoea causes

a. Left atrial thrombus

b. Left atrial tumours—myxomas

c. Pulmonary arteriovenous fistula

Pre xdr tb

 TB caused by Mycobacterium tuberculosis strains that fulfil the definition of multidrug resistant and rifampicin-resistant TB (MDR/RR-TB) and which are also resistant to any fluoroquinolone.

Hematocrit in Hemothorax

 

HEMOTHORAX

The pleural fluid hematocrit is >50% of the simultaneous peripheral blood hematocrit.

If the pleural fluid  hematocrit value is not available , one can estimate the pleural fluid hematocrit by dividing the pleural fluid RBC count by 100,000.

If the pleural fluid appears bloody and the hematocrit is <50%, it is considered a hemorrhagic effusion but not a true hemothorax

Ref: Fishman 6th ed