Acid-Base Regulation and Ventilation-Perfusion

Comprehensive vocabulary flashcards covering acid-base regulation, normal blood gas values, chemical buffer systems, primary and combined acid-base disturbances, anion gap calculations, ventilation-perfusion ratios, and shunting.

Acid

A substance that releases $H^+$ ions into solution; acts as a proton donor.

Base

A substance that accepts $H^+$ ions; acts as a proton acceptor. Major examples in the body include bicarbonate and ammonia.

Acidemia

an excess of $H^+$ in the blood

Alkemia

excess of $HCO_3^-$ in the blood.

Chemical Buffer System

The body's first line of defense in acid-base regulation with a response time of a fraction of a second; made up of the carbonic acid-bicarbonate buffer, phosphate buffer, and protein buffer systems.

Respiratory Acid-Base Compensation

Alteration of $CO_2$ excretion by the lungs to compensate for acidosis or alkalosis, responding within $1\text{--}3\text{ minutes}$.

Renal Acid-Base Compensation

Kidney regulation of acid-base balance taking a day or two; in acidosis, kidneys retain $HCO_3^-$ or excrete $H^+$, and in alkalosis, they excrete $HCO_3^-$ or retain $H^+$.

Henderson hassel bach equation

Calculation of the ph in the blood buffer bicarbonate system

Acute Respiratory Disturbance

no renal compensation ($HCO_3^-$ remains normal)

Chronic respiratory disturbance

Respiratory compensation (CO2 goes up or down)

Acute metabolic disturbance

No compensation, normal CO2

Chronic metabolic disturbance

Respiratory compensation, CO2 goes up or down

Partial compensation

All values are abnormal

Normal PCO2

35-45

Normal PO2

80-100

Respiratory Acidosis

increased $CO_2$ retention, caused by hypoventilation, pulmonary disorders, and brain/drug problems

Respiratory Alkalosis

decreased CO2 Retention, caused by pain, anxiety, hypoxia, brain problems and drugs

Metabolic Acidosis

decreased $HCO_3^-$, caused by lactic acidosis, ketoacidosis, loss of glucose

Anion Gap

used to determine the cause of metabolic acidosis. Number of anions must equal the number of cations. Gap is cations-anions=anions gap

Normal anion gap

9-14mEq/L

Causes of anion gap issues

Toxins, Azotemic (BUN and creatinine problems), Lactic, and Keto

Mixed metabolic and respiratory acidosis

CO2 retention and HCO3 reduction. Caused by acute ventilatory failure, latic acid (hypoxia) and apnea/poor ventilation

Metabolic Alkalosis

elevated $HCO_3^-$, caused by hypokalemia, hypochloremia, vomiting or gastric suction (loss of hydrochloric acid), excessive administration of steriods or NaHCO3

Partial CO2 compensation

Ph is abnormal and CO2 is high

Complete CO2 compensation

Normal ph and high CO2

How to treat metabolic alkalosis

Correct underlying electrolyte problem, administer ammonium chloride (NH4CI) or diluted solutions of hydrochloric acid

Base Excess / Deficit (B.E.)

used to calculate the dosage of $HCO_3^-$ needed during metabolic acidosis treatment.

Mixed metabolic and respiratory alkalosis

Excessive HCO3, less CO2. From hyperventilation, diuretic therapy, corticosteroids, hypokalemia

Ventilation-Perfusion Ratio ($\dot{V}/\dot{Q}$)

The relationship between the PACO2 and PAO2. As O2 decreases CO2 increases. Normal is 0.8

Low $\dot{V}/\dot{Q}$ Ratio

Low ventilation, increased perfusion, hypoxemia. Response is vasoconstriction of blood directed to ventilated alveoli, chance of causing mixing of pulmonary capillaries blood gases. Low ratio caused by hypoventilation, obstructive and restrictive lung disorders

High $\dot{V}/\dot{Q}$ Ratio

increased ventilation, low perfsuion, resulting increased physiological deadspace. Caused by Arterial obstruction, extrinsic pressure on or destruction of pulmonary vessels, decreased CO

Positive Airway Pressure (PAP) Therapy

Used to treat shunts by using positive pressure to open/recruit more alveoli so diffusion can increase

How does FiO2 therapy work on a shunt

It only works if the shunt is not absolute