NURS241 Lecture Notes - Lecture 7: Renal Compensation, Sphygmomanometer, Asthma
Acid-base balance and Imbalances
o Acid- a substance that donates a proton, specifically a hydrogen ion, has a low pH
o pH is the negative log of the hydrogen ion concentration. More acid equals a lower
pH
o Alkaline- readily accepts a proton/hydrogen ion, has a higher pH
o Very high or very low extremes are very damaging to body tissues
o Normal body pH- 7.40 (slightly basic, more alkaline)
o pH of less than 6.8 or higher than 7.8 is very damaging to the body
o essential for
▪ enzyme systems- only work in a very narrow range of pH
▪ hormonal activity
▪ conduction of nerve impulses
o regulation of body fluid pH
o depends on the relationship between
▪ bicarbonate (HCO3)- base (accepts a proton)
▪ carbonic acid (H2CO3)- acid (donates proton)
▪
o our bodies are about 2/3 water
o Carbon dioxide (CO2) of many metabolic processes and we are always making it.
▪ CO2 and Water readily combine to form carbonic acid
▪ Carbonic acid can break down into bicarbonate and free hydrogen ions
o Normal ratio of bicarbonate to carbonic acid
▪ 20 molecules HCO3 to 1 molecule H2Co3
o Arterial Blood gases
o Lab tests used to measure pH and dissolved gasses in arterial blood
o Reflects pH in the ECF, which reflects pH in the ICF
▪ Since we can’t put a needle into the ICF directly
o Blood comes from a deeper vein the arm
o Normal blood gases
▪ pH: 7.35- 7.45
▪ pO2: 80-100 mmHg
▪ pCO2: 35-45 mmHg
▪ HCO3: 22-29
▪ O2 saturation: 95-100%
o pCO2- controlled the lungs and respiration
▪ exhaled when we breath
▪ change occurs rapidly
▪ we can raise our CO2 levels in the body by holding our breath
▪ lower CO2 levels in the body by breathing rapidly
o HCO3- controlled by the kidneys
▪ An involuntary change that we can’t control
▪ Change occurs slowly
o Things that can go wrong with acid base balance
▪ Respiratory issues
• Too little carbonic acid/regular bicarbonate leves- causes an
increase in pH→respiratory alkalosis
• Too much carbonic acid/regular bicarbonate levels- decrease in
pH→ respiratory acidosis
▪ Metabolic issues
• Regular carbonic acid, too much bicarbonate- raises pH→ metabolic
alkalosis
• Regular carbonic acid, too little bicarbonate- lowers pH→ metabolic
acidosis
o Buffer Systems
o Bicarbonate buffer system- helps to keep pH from changing too rapidly
▪ Weak acid- carbonic acid
▪ Weak base- sodium bicarbonate
o Phosphate buffer system- keeps urine within the correct pH
▪ Protects body from MO infection
o Hemoglobin buffer system- proteins in the blood help to prevent rapid changes in
pH
o Respiratory Control of pH
o Lungs retain or eliminate CO2
▪ Retaining CO2 (holding your breath) decreases pH
• Water and Co2 combine to make carbonic acid
▪ Eliminating CO2 (hyperventilating) increases pH
o Renal control of pH
o Kidneys retain or eliminate HCO3
▪ HCO3 retention increases pH→ alkalosis
▪ HCO3 elimination decreases pH → acidosis
o Potassium- hydrogen Ion exchange
o Excess H+ in the ECF causes acidosis- inside of the cells has to keep a neutral
electrical charge so some potassium ions move out into the ECF and the blood
stream to help maintain a balance
▪ H+ moves into cells
▪ K+ moves out of cells and causes an elevated serum potassium level
o Steps in Arterial Blood gas analysis
o Determine the basic problem
o Look for compensation- how the body deals with or makes up for a change
▪ Compensation
• Renal compensation for respiratory imbalances- happens slowly
• Respiratory compensation for metabolic imbalances- happens
quickly
o Acid-Base imbalances
o Respiratory Acidosis
▪ pH <7.35
