Module 2 Acid-base balance/hemodynamics W.Pawliuk MPH MSNEd RN CEN

pH  Inverse logarithm of the H + concentration  If the H + are high in number, the pH is low (acidic). If the H + are low in number, the pH is high (alkaline).

pH  The pH scale ranges from 0 to 14: 0 is very acidic, 14 is very alkaline. Each number represents a factor of 10. If a solution moves from a pH of 6 to a pH of 5, the H + have increased 10 times.

pH  Acids are formed as end products of protein, carbohydrate, and fat metabolism  To maintain the body’s normal pH ( ) the H + must be neutralized or excreted  The bones, lungs, and kidneys are the major organs involved in the regulation of acid and base balance

pH  Body acids exist in two forms  Volatile  H 2 CO 3 (can be eliminated as CO 2 gas)  Nonvolatile  Sulfuric, phosphoric, and other organic acids  Eliminated by the renal tubules with the regulation of HCO 3 –

Normal Blood pH  Balance of acids and bases in body fluids  Normal for:  Arterial blood = 7.35 to 7.45  Venous blood = 7.31 to 7.41

Normal Blood pH (cont’d)  Changes can affect:  Shape of hormones and enzymes  Distribution of other electrolytes (fluid and electrolyte imbalance)  Excitable membranes  Effectiveness of hormones and drugs

Acid-Base Balance  Fluid contains equal number of positive charges, ions with negative charges  Balance occurs by matching rate of hydrogen ion production with loss

Introduction to Acid-Base Chemistry  Acids – release hydrogen ions when dissolved in water  Bases – bind with hydrogen ions in solutions  Buffers – critical in maintaining normal body fluid pH  Body fluid chemistry:  Bicarbonate ions (HCO 3 )  Relationship between CO 2 and hydrogen ions  Calculation of free hydrogen ion level

Sources of Acids  Incomplete breakdown of glucose  Destruction of cells  Bicarbonate

Sources of Acids & Bicarbonate  When acid is present, free hydrogen ions dissociate and must be controlled for pH balance  Body continuously generates acids and hydrogen ions as metabolism waste products

Bicarbonate  Weak base  Major buffer of ECF  From intestinal absorption of ingested bicarbonate into ECF, kidney absorption and breakdown of carbonic acid

Buffering Systems  A buffer is a chemical that can bind excessive H + or OH – without a significant change in pH  A buffering pair consists of a weak acid and its conjugate base  The most important plasma buffering systems are the carbonic acid–bicarbonate system and hemoglobin

Buffer System  Maintain body’s pH  Substances that change the pH when either acids or bases are added Copyright © 2013, 2009, 2005, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 14

Bicarbonate Buffer System  Most common  Activated as H + ions increase  Increased H + ions combined with HCO 3 to form carbonic acid (H 2 CO 3 )  Carbonic acid breaks down into H 2 O and CO 2 Copyright © 2013, 2009, 2005, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 15

Respiratory Buffer System  Excretes excess CO 2 from system when metabolic disorder occurs  Immediate action Copyright © 2013, 2009, 2005, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 16

Buffer Systems Copyright © 2013, 2009, 2005, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 17 Figure 9-9. The kidneys and lungs work together to compensate for acid-base imbalances in the respiratory or metabolic systems. HCO 3 –, Bicarbonate; H 2 CO 3, carbonic acid. (Modified from Harvey MA. Study Guide to the Core Curriculum for Critical Care Nursing. 3 rd ed. Philadelphia: Saunders; 2000.)

Carbonic Acid–Bicarbonate Pair  Operates in the lung and the kidney  The greater the partial pressure of carbon dioxide, the more carbonic acid is formed  At a pH of 7.4, the ratio of bicarbonate to carbonic acid is 20:1  Bicarbonate and carbonic acid can increase or decrease, but the ratio must be maintained

Carbonic Acid–Bicarbonate Pair  If the amount of bicarbonate decreases, the pH decreases, causing a state of acidosis  The pH can be returned to normal if the amount of carbonic acid also decreases  This type of pH adjustment is referred to as compensation

Carbonic Acid–Bicarbonate Pair  The respiratory system compensates by increasing or decreasing ventilation  The renal system compensates by producing acidic or alkaline urine

Other Buffering Systems  Protein buffering  Proteins have negative charges, so they can serve as buffers for H +  Renal buffering  Secretion of H + in the urine and reabsorption of HCO 3 –  Cellular ion exchange  Exchange of K + for H + in acidosis and alkalosis

Acid-Base Control Actions & Mechanisms: Respiratory  When chemical buffers alone cannot prevent blood pH changes, respiratory system is second line of defense:  Hyperventilation: increased RR > decreased CO2 thus raises pH  Ex pH 7.50 V RR > Increase CO2 levels >brings pH back down to 7.45  Hypoventilation: decreased RR > increased CO2 thus lower the pH  Ex. pH 7.30 ^ RR > decreased CO2 >increase pH to 7.35

Acid-Base Control Actions & Mechanisms: Respiratory (cont’d)

Acid-Base Control Action& Mechanisms: Kidneys  Third line of defense against pH changes  Stronger for regulating acid-base balance; take longer than chemical and respiratory  Kidney movement of bicarbonate  Formation of acids  Formation of ammonium

Compensation  pH 7.8 usually fatal  Respiratory system more sensitive to acid-base changes; can begin compensating in seconds to minutes  Kidneys more powerful; result in rapid changes in ECF composition; fully triggered for imbalance of several hours to days

Acid-Base Imbalances  Normal arterial blood pH  7.35 to 7.45  Obtained by arterial blood gas (ABG) sampling  Acidosis  Systemic increase in H + concentration  Shift left or lower numbers  Alkalosis  Systemic decrease in H + concentration  Shift right or higher numbers

Respiratory Compensation  Lungs compensate for acid-base imbalances of metabolic origin

Kidney Compensation  Kidneys can correct/compensate for pH changes when respiratory system is overwhelmed or unhealthy

Acid-Base Imbalances  Metabolic acidosis  Respiratory acidosis  Combined metabolic and respiratory acidosis  Metabolic alkalosis  Respiratory alkalosis

Metabolic Acidosis  Hydrogen ions  Overproduction  Under-elimination  Bicarbonate ions  Under-production  Over-elimination

Interventions: Metabolic Acidosis  Hydration  Drug therapy  Insulin to treat DKA  Antidiarrheals  Bicarbonate (only with low serum level)

Metabolic Acidosis

Respiratory Acidosis  Respiratory function is impaired, causing problems with O 2 and CO 2  Retention of CO 2 :  Respiratory depression  Inadequate chest expansion  Airway obstruction  Reduced alveolar-capillary diffusion

Interventions: Respiratory Acidosis  Focus is on improving ventilation and oxygenation, maintaining patent airway  Drug therapy  Bronchodilators  Anti-inflammatories  Mucolytics  Oxygen therapy  Pulmonary hygiene  Ventilation support

Respiratory Acidosis

Metabolic Alkalosis  Base excess—excessive intake bicarbonates, carbonates, acetates, citrates  Acid deficit—prolonged vomiting, excess cortisol, hyperaldosteronism, thiazide diuretics, prolonged NG suction

Metabolic Alkalosis

Respiratory Alkalosis  Hyperventilation—anxiety, fear, improper vent settings, stimulation of central respiratory center due to fever, CNS lesion, salicylates

Respiratory Alkalosis

Combined Metabolic & Respiratory Acidosis  Uncorrected respiratory acidosis leads to poor oxygenation and lactic acidosis  More severe than metabolic or respiratory acidosis alone  Combined problem of DKA and COPD lead to this

Reading the ABG result Step 1: What is the pH? Normal Acidic (acidosis)<7.35 Alkalitic(alkalosis)> 7.45 Step 2: What is the PaCO2 ? Normal mm/Hg <35 alkalotic (alkalosis) > 45 acidic (acidosis)

Reading the ABG result Step 3: What is your base or HCO3 (bicarbonate) Normal: mEg/L < 22 acidic (acidosis) > 26 alkalitc (alkalosis) Step 4: look at the PaCO2 and HCO3, which are abnormal? PaCO2 or HCO3 ? Step 5: What is the PaO2 ? may need to supplement their oxygen

ABG examples pH 7.30 PaCO2 55mmHg HCO3 24 mEq/L PaO2 96 % What you have? pH 7.50 PaCO2 30 mmHg HCO3 23 mEq/L PaO2 89% What do you have?

ABG examples pH 7.30 PaCO2 36 mmHg HCO3 20 mEq/L PaCO2 98% What do we have here? pH 7.50 PaCO2 40 mmHg HCO3 30 mEq/L PaCO2 96% What do we have here?

Laboratory Assessment: Respiratory Acidosis  pH < 7.35  PaO 2 low  PaCO 2 high  Serum bicarbonate variable  Serum potassium levels elevated (if acute acidosis)  Serum potassium levels normal or low (if renal compensation present)

Remember…  Hallmark of respiratory acidosis:  Decreased PaO 2 with rising PaCO 2

Laboratory Assessment: Metabolic Acidosis  pH < 7.35  Bicarbonate < 21 mEq/L  PaO 2 normal  PaCO 2 normal or slightly decreased  Serum potassium high

Remember…  Hallmark of metabolic acidosis:  ABG result with ↓ pH and ↓ bicarbonate level with normal O 2 and CO 2 levels  Hallmark of metabolic alkalosis:  ABG result with ↑pH and ↑ bicarbonate levels with normal O2 and CO2 levels

Remember…  Hallmark of respiratory alkalosis:  ABG result with ↑ pH coupled with ↓ CO 2 level  O 2 and bicarbonate usually normal

Acidosis: Patient-Centered Collaborative Care  History  CNS changes  Neuromuscular changes  ↓ muscle tone, deep tendon reflexes  Cardiovascular changes  Early: ↑ heart rate, cardiac output changes  Worsening: hyperkalemia; ↓ heart rate; T wave peaked and QRS widened; weak peripheral pulses; hypotension

Acidosis: Patient-Centered Collaborative Care (cont’d)  Respiratory changes  Kussmaul respiration  Skin changes (metabolic and respiratory acidosis)  Warm, dry, and pink (vasodilation)  Psychosocial assessment

Alkalosis: Patient-Centered Collaborative Care  Assessment (same for metabolic and respiratory alkalosis)  Hypocalcemia  Hypokalemia  CNS changes—positive Chvostek’s and Trousseau’s signs  Neuromuscular changes—tetany  Cardiovascular changes  Respiratory changes

Interventions: Alkalosis  Prevent further losses of hydrogen, potassium, calcium, chloride ions  Restore fluid balance  Monitor changes, provide safety  Modify or stop gastric suctioning, IV solutions with base, drugs that promote hydrogen ion excretion

Acidosis and Alkalosis  Four categories of acid-base imbalances  Respiratory acidosis—elevation of pCO 2 as a result of ventilation depression  Respiratory alkalosis—depression of pCO 2 as a result of alveolar hyperventilation

Acidosis and Alkalosis  Four categories of acid-base imbalances (cont’d)  Metabolic acidosis—depression of HCO 3 – or an increase in noncarbonic acids  Metabolic alkalosis—elevation of HCO 3 – usually caused by an excessive loss of metabolic acids

Ventilator’s and ABG’s

Endotracheal Tube

Verifying Tube Placement  End-tidal carbon dioxide levels  Chest x-ray  Assess for breath sounds bilaterally, symmetrical chest movement, air emerging from ET tube

Stabilizing the Tube

Endotracheal Tubes: Nursing Care  Assess tube placement, minimal cuff leak, breath sounds, chest wall movement  Prevent movement of tube by patient  Check pilot balloon  Soft wrist restraints  Mechanical sedation

Modes of Ventilation  Assist-control ventilation (AC)  Synchronized intermittent mandatory ventilation (SIMV)  Bi-level positive airway pressure (BiPAP)  Others

Ventilator Controls and Settings  Tidal volume (Vt)  Rate—breaths/min  Fraction of inspired oxygen (Fi O 2 )  PEEP

Nursing Management  Always assess patient first, ventilator second  Monitor patient response  Manage ventilator system  Prevent complications!

ABG and Ventilator support Respiratory acidosis is too much CO2. So how do we use the ventilator to correct the pH? Respiratory alkalosis is to little CO2. Same question?

Hemodynamics

Interesting YouTube clips (cut-n-paste)  Acid-base     ABG     Ventilator settings   Hemodynamic monitoring    