Test 4 Cardio Flashcards
Describe how a weak acids behave in a solution such as blood?
Weak acids in solutions will act as an acid and donate a H+
Describe how a weak base behaves in solution such as blood?
Weak baes, like bicarbonate will reversibly bind H+ and accept H+
Compare the 3 mechanisms responsible for H+ regulation?
- Buffer systems (rapid, but incomplete)
- Ventilatory responses (less rapid)
- Renal responses (slow, but produces almonst near complete correct of pH)
ID 4 buffering systems the body uses in regulating acid-base balance
- Hemoglobin buffering system
- Protein buffering system
- Phosphate buffering system
- Bicarbonate buffering system
Describe the effect of O2 saturation on Hgb’s buffering capacity.
- Buffering capacity will vary wtih oxygenation (reduced hemoglobin is a weak acid)
- In the reduced form (carries less oxygen), more base is available to combine with H+ produced with the dissociation of carbonic acid in the tissues.
ID the most effective intracellular buffering system
- Protein buffering system about 75% of all IC buffering occurs form IC proteins
Describe the role of bicarb as a buffering system in the blood
- Bicarb accounts for over 50% of the total buffering capacity of the blood (EC)
- It easiliy diffuses into the RBC’s so that 1/3 of all bicarb buffering occurs here
- pKa is 6.1, so it’s a weak buffer.
Discuss rationale for why the bicarb system is the most important buffering system in the body
It can be regulated by both the kidneys and the lungs
Describe the role of ventilation in regulating H+ concentration
- Via ventilation, the CO2 produced by the reaction of H+ and bicarb is easily removed from the body
- Ability to maintain pH of 7.4 depends on:
- Free movement of CO2 out of the body (requires ventilation and renal function)
- Ventilatory responses occur within 1-5 minutes of a change in hydrogen ion concentration
- Doubling alveolar ventilation eliminate sufficient CO2 to increase pH to 7.6
- Decreasing alveolar ventilation to 1/4 of normal will decrease pH to 7.0
Describe renal regulation of H+ concentration
- Renal responses that regulate ph = making urine more acid or alkaline
- Via incomplete titration of H+ or bicarb, either enters the urine or gets excreted
- In acidosis: H+ is excreted
- In alkalosis: Bicarb is excreted
Describe how pH may be calculated by the HH equation using bicarb and CO2 concentrations in the blood
- The H equation cites that pH is related to the ration of conjugate base to the undissociated acid
- Equation is pH=6.1 + log of (Bicarb/(0.03xPaCO2))
- Essentially, as long as Bicarb: CO2 remains 20:1, the pH will remain 7.4
Compare and contrast ventilator and renal response to acidosis in regard to efficacy and speed in ventilatory response
Ventilatory Response
- Lungs excrete over 10K mEq of H2CO3 per day (kidneys are 50-500 mEq/day)
- By altering alveolar ventilation and elimination of CO2, body compensates for pH change in a matter of minutes
- Can buffer up to twice the amount of acid or base as all other buffers combined
Renal response:
- Regulation occurs by allowing H+ or Bicarb to be removed from ECF (slow, but completely neutralizes)
- Ordinarily, the kidneys can excrete up to 500 mEq of acid or alkaline each day (urine pH is 6.4)
- High concentration of CO2 = excretion of.. while hyperventilation = retention of H+
List 5 anesthetic considerations with acidosis
- Potentiation of depressant effects of sedatives and anesthetic agents on CNS (increased non-ionized fraction and increased penetration into brain)
- Decreased sympathetic tone
- Increased arrhythmogenic of volatiles
- Increased K+ with succinylcholine
- Augmentation of NMBD
Categorize a provided arterial blood gas as either compensated/uncompensated and ither primary metabolic or respiratory
- Look at the pH, and decipher from there.
ID the role of the medulla in regulating respiration
Medulla respiratory centers will
- Regulate the initiation of inspiration (dorsal)
- Regulate forced expiration (ventral)
ID the role of the pons in regulating respiration
Pons respiratory centers:
- Apneustic center will prolong inspiration
- Pneumotaxic center will regulate the respiratory rate
Describe the effect on respiration of PCO2, O2, and pH on respiration
PaCO2
- Increased PaCO2 will affect the alveolar ventilation within 1 minute
- After several hours, the effect wanes due to the active transport of bicarb
- Bicarb combines with H+ ions to return CSF to normal pH
PO2
- Decreases PO2 increases sensitivity to PaCO2
- Lowering the PO2 form 110 mmHg to 47 mmHg produces a higher ventilator response to PCO2
- Lowering the PO2 to 37 mmHg increases both response and slope of response curve
pH
- reduction in arterial pH stimulates ventilation
- In pts with compensated metabolic acidosis, increased ventilation occurs in repsonse to low pH
- Effect usually mediated by peripheral chemoreceptors with contribution from central receptors.
Is the location of the central chemoreceptors and primary regulatory element
- Is the region on the anterolateral surface of the medulla that is sensitive to chem changes (CO2)
- CO2 readily crosses the BBB and forms carbonic acid, which dissociates into H+ ions; the CSF is poorly buffered, so pH changes rapidly
- 75-80% of the ventilatory response to CO2 is due to central chemoreceptor activity
Discuss the process which occurs in the medulla (central chemoreceptor) that occurs in the presence of chronic high PCO2
Process is called hypoxic drive, Raising the PaCO2 will increase the PaO2 response
ID the two peripheral chemoreceptors and the primary regulatory elements
- Carotid bodies
- Aortic bodies
Discuss the effects of PO2 on the carotid body chemoreceptor
- They respond to changes in the PaO2, PaCO2, blood pressure, and pH
- Respond mainly to low PaO2, but not high PaO2
- Activation doesn’t occur until PaO2 is less than 50 mmHg
- Not stimulated by O2 saturation abnormalities like CO poisoning
ID the location and innervation of the pulmonary stretch receptors and how they are stimulated
- Location: walls of bronchi and bronchioles
- Activated when stretched, and tend to inhibit inspiration and causes shortening of exhalation when the lung is deflated
- Herring-breur reflex is active when tidal volume is greater than 1.5L
- Inhibitory signals are carried centrally by the vagus nerve and protects against over inflation
ID the location and innervation of the irritant receptors and how they are stimulated
- Located between the airway epithelial cells
- Stimulated by: noxious gases (smoke, dust, cold air)
- Travel up vagus – relfex effects include bronchoconstriction and hyperpnea
- May play a role in bronchoconstriction during asthma attacks as a result of their response to released histamine
ID the location and inervation of the J receptors and how they are stimulated
- Location: Alvelolar walls close to the capillaries
- Impulses pass up the vagus nerve and result in rapid shallow breathing
- Engorgement of pulmonary capillaries and increased interstitial fluid volume of the alveolar wall activates these receptors
- Might play a role in:
- Rapid shallow breathing and dyspnea sensation assocaited wtih CHF and interstitial Dx
Describe the effect of pH on respiration
pH will stimulate the respiration
Describe the integrative effect of PCO2, PO2, and pH on respiration
- A low pH will shift the reponse curves to the left
- Exercise enhances the reponses to hypoxia (even if the PaCO2 is not raised) possibly due to lactic acidosis, afferents from the muscle, or catecholamine selection
Describe the effects of different anesthetic agents on the PCO2 response curve
- Decreases alveolar ventilation and increases PaCO2
Describe the effects of different anesthetic agents on the PO2 response curve
All anesthetics will depress the ventilatory response to PaCO2 and PaO2
Describe the effects of inhaled anesthetics on the control of ventilation
- All volatiles will depress minute ventilation, which is comprised to a degree by increased RR
- Inhalation anesthetics inhibit pulmonary irritatnt receptors and increase laryngeal receptors
Compare the effects of inhalation anesthetics on the genioglossus, intercostals, and diaphragm
Anesthetics created a reduced control of genioglossus, intercostals, and diaphragm, creating an environment that is more difficult for a patient to naturally breate
- Genioglossus doesnt hold tongue up as well
- Intercostal muscles dont allow for better expansion
- Diaphragm doesnt pull down as far and rest in a higher location
