Dermatomes and corresponding Nerve supply !!

Dermatomes and corresponding Nerve supply !!

Advertisements

Concept of Delta Gap in Acid-Base Balance

To understand if a patient has both increased anion gap acidosis and non-gap acidosis at the same time or metabolic acidosis + metabolic alkalosis at the same time, you will need to know the concept of “Delta Gap

The Delta Gap = Measured SAG – Normal SAG

Logically, if the serum bicarbonate (Hco3-) falls more than the change in the anion gap,then a patient has both non-gap+increased gap acidosis.

If the serum bicarbonate falls less than the change in the anion gap, then the patient has mixed disorder – metabolic acidosis + metabolic alkalosis.

For example, if the anion gap is 20 –> you can say the change in the anion gap is 8 ( because normal anion gap is 12. ) In this scenario let us say if the MCQ gave serum Hco3- as 10, drop in the serum bicarb here is 14 ( remember, for calculation normal serum bicarb is taken as 24. so, if it is 10 now, the drop in bicarb is obviously, 14). –> this means when your anion gap has increased by 8 your bicarb has fallen more than 8 i.e; by 14….that means some other factor apart from the factor responsible for increased gap acidosis is also contributing to acidosis here! – this suggests co-existing increased anion-gap+normal-gap acidosis .

A classic example is diarrhea with shock – where diarrhea causes non gap acidosis but shock can lead to lactic acidosis which increases the gap – so, things can co-exist!

To understand if your patient has a mixed disorder of metabolic acidosis + respiratory acidosis or metabolic acidosis + respiratory alkalosis, you will need to be familiar with Winter’s formula. 

Winter;s formula :
Expected pCo2 = {1.5(Hco3-) +8} +/-2

If your patient has metabolic acidosis, you expect him to breathe fast and wash out the Co2 so as to maintain the pH in normal limits …this is called “Compensation”. Compensation brings the serum pH towards the normal but never makes it completely normal – so, if you are seeing a normal pH in a metabolic acidosis , you can right away say that you are dealing with a Mixed disorder rather than a compensation alone.
The expected Pco2 in the above formula is the one that is expected as a comprnsation if your patient has low bicarbonate or metabolic acidosis. You need to compare this expected Pco2 with the real value of Pco2 obtained on the arterial blood gases ( measured Pco2).

Pearls for answering questions on Mixed Disorders:
A) If measured Pco2 is lower than the expected Pco2, that means your patient is washing out more C02 than expected —meaning, he has respiratory alkalosis co-existent with metabolic acidosis ( one example of such mixed disorder is Salicylate toxicity) .

B) If measured Pco2 is higher than expected Pco2, that means your patient is retaining Co2 which means he has a co-existent Respiratory acidosis along with metabolic acidosis ( eg: Cardiac arrest can cause such mixed acidosis because reduced respiratory drive causes CO2 retention leading to respiratory acidosis where as shock because of cardiac arrest causes lactic acidosis which is metabolic acidosis).

Eg: If Hc03 – is 16, the expected PCo2 as per Winter;s formula should range between 30 to 34 ( see the above formula). However, let us say your patients Pco2 on the arterial blood gas is 20 –> you can call this metabolic acidosis + respiratory alkalosis. eg : Salicylate Toxicity

If Hc03 – is 16, the expected PCo2 as per Winter;s formula should range between 30 to 34 ( see the above formula). However, let us say your patients Pco2 on the arterial blood gas is 44 –> you can call this metabolic acidosis + respiratory acidosis. eg : Cardiac arrest

CENTRAL VENOUS CATHETERIZATION: MCQ POINTS

central venous catheterisation:

INDICATION:
1) Monitoring central venous pressure for fluid management of hypovolemia and shock.
2)giving total parenteral nutrition.
3) infusion of caustic drugs that cause phlebitis when infused through peripheral vein as hypertonic saline,  calcium chloride.
4)aspiration of air emboli.
5)insertion of transcutaneous pacing leads.
6) gaining venous ascess in patients with poor periferal veins.

some NEET/DNB points:
1) non tunneled catheters are fixed at site of insertion eg Quinton catheter and catheter and attachment come out directly
2) tunneled catheter r passed under the skin to a separate exit site eg Hickman catheter & Groshong catheter. These catheter have decreased chance of infection and dislodgement.

PROCEDURE:
Q1) Which site of Central venous line is best for long term use…
a. basilic
b. external jugular
c. internal jugular
d. subclavian
e.  femoral

ans ; d ) subclavian
rating d>c>b>a>e ie femoral vein is least suitable for long term use.
REF Pg 100 lange clinical anesthesiology 3e.

Q2) technique related complications are most likely to occur with which site….
a)basilic
b) external jugular
c) internal jugular
d) subclavian
e) femoral

ans : d ) subclavian
rating. d>b>e>b>a ie technique related complications are most likely to occur with subclavian and least likely in basilic vein.
Ref : pg 100 lange clinical anesthesiology 3e.

Q3) according to ease of cannulation best site is. ..
a) basilic
b) external jugular
c) internal jugular
d) subclavian
e) femoral

ans: a)basilic vein
best to worst list a>c>b=e>d
Ref: pg100 lange clinical anesthesiology 3e.

NOTE: RIGHT INTERNAL JUGULAR VEIN PROVIDES A COMBINATION OF ACCESSIBILITY AND SAFETY FOR CENTRAL VENOUS CATHETERISATION.

* Seldinger technique is used ie insertion of catheter over guide wire.
* placing the patient in trendelenberg position while catheterising decreases the chance of air embolism & distends the vein.
*catheter tip should not be allowed to migrate in heart chambers which if happens can lead to arrythmias.
*central venous pressure= right atrial pressure = major determinant of right ventricular end diastolic volume.

COMPLICATIONS:
Infection, air embolism,  thrombosis,pneumo/hydro /chylo thorax,  arrythmias, cardiac perforation,  tamponade.