Passivating layer on alloy is dissolved completely by:

 # Passivating layer on alloy is dissolved completely by:

A. Basic acid

B. Borax

C. Potassium fluoride

D. Graphite

The correct answer is C. Potassium fluoride. 

# Aluminum, chromium, and titanium have high affinity for oxygen and they form protective oxide film, which prevents further oxidation and corrosion. This is called passivation. For soldering these alloys, the passivating film should be dissolved. Potassium fluoride used as a flux dissolves passivating film so that the solder can wet the parts. 

# Flux is a compound applied to metal surfaces that dissolves or prevents the formation of oxides and other undesirable substances that may reduce the quality or strength of a soldered or brazed area. 

# There are three types of fluxes according to their primary purpose: - 

Type I: Surface protection- covers the metal surface and prevents access to oxygen so that no oxides can form. 

Type II: Reducing agent- reduces any oxides present and exposes clean metal. 

Type III: Solvent- dissolves any oxides present and carries them away. 

Fluxes for use with noble metal alloys are generally based on boric acid, boric anhydride, and borax. Chromium oxides that form on base metal alloys are more stable and fluoride containing fluxes are used as solvents to dissolve chromium, nickel, and cobalt oxides. 

In long surgical procedure intubation method is:

 # In long surgical procedure intubation method is: 

A. Nasotracheal tube with cuff 

B. LMA 

C. Nasotracheal tube without cuff 

D. Endotracheal tube 

The correct answer is A. Nasotracheal tube with cuff.

LMA (laryngeal mask airway) is used mostly in situations of emergency and by non-anaesthesiologists. Endotracheal tube is commonly used method during general anaesthesia. For prolonged surgeries especially facio-maxillary surgeries nasaltracheal or Orotracheal intubation especially with cuff is used.

Best way to monitor perfusion of free flap:

 # Best way to monitor perfusion of free flap: 

A. Pulse oximeter 

B. Laser Doppler velocimetry 

C. Prick test 

D. Flourescin & dermoflourometer 

The correct answer is: C. Prick Test.

 During the postoperative phase, the flap is closely monitored for signs of compromised perfusion. Flaps are best assessed by inspection. Clinical monitoring is the current gold standard for assessing free flaps. Dermal bleeding or prick test is used to assess the colour of the blood within the flap circulation. Also scalpel mark on the flap can also be used to assess the colour of the blood.

Many high-end techniques are described in literature to monitor free flaps such as: 

• Serial fluorometry

• Plethysmography

• Laser doppler flow-metry

Reference: [Steel and Marran's head and neck surgery 4th ed 137]

Pulsating varicose vein is due to:

 # Pulsating varicose vein is due to 

A. Arterio venous fistula 

B. Sapheno femoral incompetence 

C. Deep vein thrombosis 

D. Abdominal tumour 

The correct answer is A. Arteriovenous fistula.

Communication between an artery and adjacent vein leads to arteriovenous aneurysm or arteriovenous fistula. When an arteriovenous fistula is created surgically, this is called iatrogenic arteriovenous fistula. For Renal dialysis,iatrogenic fistula is mostly used in the wrist or in the ankle and such temporary arteriovenous fistula is known as Cimino fistula. Presence of a pulsating thrill over the site of the lesion is quite characteristic, particularly if the lesion is located near the surface. If a finger is pressed on the artery proximal to the fistula,there will be slowing of pulse rate and rise in the diastolic pressure. This is known as Branham's sign.

Ref: S. Das Manual of Surgery, 3rd ed 194