Physiology Flashcards
(43 cards)
Which of the following would MOST likely be found in a patient with cyanide toxicity?
The most common and reliable sign of cyanide toxicity is an anion gap metabolic acidosis.
TrueLearn Insight : Anion gap is calculated by subtracting serum chloride and bicarbonate (anions) from serum sodium and potassium (cations). Anion gap = ([Na+] +[K+]) – ([Cl−] + [HCO3−]). In clinical practice, potassium is usually excluded.
Which of the following may be associated with INCREASED mixed venous oxygen saturation?
Mixed venous oxygen saturation (SvO2) is an indicator of global oxygen supply and demand balance. A low SvO2 indicates increased tissue oxygen extraction due to decreased oxygen supply relative to the demand. Septic shock and cyanide toxicity are conditions associated with normal or increased mixed venous oxygen saturation secondary to impaired tissue oxygen utilization.
TrueLearn Insight : Central venous oxygen saturation (ScvO2) measured by sampling blood through a central venous catheter located in the superior or inferior vena cava is often higher than SvO2. This is because of the venous blood with significantly low oxygen saturation entering from the coronary sinus and mixing in the right atrium.
Which of the following patients would be LEAST likely to have pronounced upregulation of nicotinic acetylcholine receptors?
Upregulation of NAChR’s is seen in spinal cord injuries, burn patients, prolonged immobilization, stroke patients, patients with neuromuscular disorders, and after prolonged exposure to certain pharmacologic agents.
A 50-year-old man weighing 70 kg is in the critical care unit after a motor vehicle accident in which he experienced multiple rib fractures, thoracic spine fractures, and pulmonary contusion bilaterally. He is currently intubated with the following ventilator settings: Mode: Volume control Tidal volume: 700 mL Rate: 10 breaths per minute PEEP: 8 cm H2O FiO2: 70% Peak inspiratory pressure: 30 cm H2O Plateau pressure: 30 cm H2O The patient has no intra-abdominal injuries, MAP is >70 mm Hg on no vasopressor or inotropic support, and he has no past medical history. Hemoglobin is 12 g/dL, creatinine is 1.6 mg/dL, and urine output is declining. Which of the following is MOST likely true?
Positive pressure ventilation exerts deleterious effects on renal function via alterations in hemodynamics, neurohormonal secretion, and biochemical mediator release.
Decreasing the tidal volume to 6 mL/kg (lung-protective strategy) could decrease the risk of renal injury related to positive pressure in the patient in this question by decreasing cytokine release.
Which of the following hormones is LEAST likely to be metabolized by the lungs or within the pulmonary circulation?
Dopamine, epinephrine (B), and histamine are not metabolized or removed from the pulmonary circulation since the pulmonary endothelium lacks an active transport mechanism for these hormones.
Sympathetic cardiac innervation includes which of the following adrenergic receptors?
The sympathetic cardiac innervation originates from T1-T4 and is associated with α1, β1, and β2 adrenergic receptors.
TrueLearn Insight : A left stellate ganglion block can be performed to reduce the risk of arrhythmias associated with long QT syndrome.
A 22-year-old man eats sausage from an expired and bloated can. A day later he develops trouble swallowing, muscle weakness, blurred vision, constipation, and dry mouth. On examination he is found to have decreased deep tendon reflexes. Which of the following is the toxin’s correct mechanism of action?
Botulinum toxin can cause symptoms of muscle paralysis by preventing the release of acetylcholine-containing vesicles from the axon terminal into the synaptic cleft.
TrueLearn Insight : Botulinum toxin acts inside the axon terminal at the neuromuscular junction. Tetanus toxin travels via retrograde axonal transport to the CNS where it acts.
Which of the following will cause a decrease in the P50 of oxygen?
A leftward shift, moving the curve to the left, results in a decrease in P50; oxygen affinity increases leading to less offloading of oxygen in the tissues at all PO2 values. This will occur under several circumstances - alkalosis, decreased temperature, decreased intracellular concentration of organic phosphates (the most important is 2,3-diphosphoglycerate in the red blood cells), carbon monoxide binding, and the presence of methemoglobin. A rightward shift is the exact opposite and will result in more oxygen offloading in the tissues at all arterial oxygen tensions (PO2). Rightward shift is seen with acidosis, increased temperature, and increased organic phosphate concentrations. The Bohr effect states that oxygen is more readily released from hemoglobin in the face of acidosis or hypercarbia.
During a mitral valve repair and separation from cardiopulmonary bypass, the cardiac anesthesiologist determines the systemic vascular resistance to be 600 dynes per sec/cm5 with a central venous pressure of 22.5 mm Hg. As a result, norepinephrine is started.
Consequently, starting the norepinephrine infusion resulted in the following changes: the mean arterial pressure by arterial line increases from 45 mm Hg to 75 mm Hg, and cardiac output via thermodilution increases from 3 L/min to 3.5 L/min. Assuming the central venous pressure stays the same, how does the systemic vascular resistance change?
Systemic vascular resistance (SVR) is calculated as SVR = 80 × (MAP – CVP) / CO (CO, cardiac output; CVP, central venous pressure; MAP, mean arterial pressure).
Which of the following numbers corresponds to the most significant efflux of potassium from the myocyte during an action potential?
The influx of sodium in phase 0 causes membrane depolarization.
The net influx of calcium in phase 2 causes a plateau.
The efflux of potassium in phase 3 causes membrane repolarization.
Which of the following best describes the Haldane effect?
The Haldane effect explains the increased ability for hemoglobin to carry carbon dioxide (CO2) from the tissues to the lungs for exhalation
Which of the following is NOT true regarding the stress response and lipolysis?
Lipolysis is the hydrolysis of triglycerides into glyceride and free fatty acids which are then used as an energy source. In general, lipolysis is increased by beta-2 and beta-3 adrenergic stimulation but is inhibited by alpha-2 stimulation. Women are more sensitive to the lipolytic actions of catecholamines when compared to men. Increased catecholamines, cortisol, and glucagon secretion all promote lipolysis. Alpha-2 stimulation will inhibit lipolysis.
Which of the following is the MOST likely cause for the rapid reduction in core temperature during the first hour of general anesthesia?
Redistribution of heat from the core to the periphery is the largest contributor to the initial reduction in core temperature during general anesthesia. Prevention or reduction of this can be accomplished by pre-warming the patient’s extremities prior to the induction of general anesthesia. Radiation is the main mechanism for patient heat loss in the operating room following this initial redistribution of heat.
Which of the following will result in a leftward shift and increased slope of the carbon dioxide ventilatory response curve (i.e. a change from the black to the red curve)?
Surgical stimulus and heightened states of arousal (e.g. fear or anxiety) cause hyperventilation. This typically causes a leftward shift and increased slope of the carbon dioxide ventilatory response curve (VRC).
Factors that cause a leftward shift and an increased slope of a carbon dioxide ventilatory response curve include arterial hypoxemia, metabolic acidemia, surgical stimuli, and certain CNS pathologies. Factors that cause a rightward shift and a reduced slope of the curve include opioids, barbiturates, and sedative-hypnotic drugs. Volatile anesthetics ≤1 MAC cause a rightward, parallel shift of the VRC.
Which of the following is the dominant factor in causing bronchoconstriction?
The parasympathetic nervous system contributes a great deal to bronchoconstriction. The etiology behind bronchoconstriction is only partially known and research is ongoing.
Which of the following is TRUE regarding type 2 diabetes mellitus?
Insulin deficiency occurs secondary to a loss of beta-cell mass in the pancreas. A lack of insulin results in hyperglycemia and the symptoms associated with diabetes mellitus. Insulin deficiency can recover, at least partially, in patients with improved glycemic control.
Which of the following will MOST likely enhance hypoxic pulmonary vasoconstriction?
Since hypercarbia itself causes pulmonary vasoconstriction, the presence of hypercarbia in the setting of hypoxia enhances the effects of hypoxia pulmonary vasoconstriction (HPV).
Hypoxic pulmonary vasoconstriction occurs as a result of exposure of the pulmonary arteries to hypoxic lung segments and low alveolar oxygen tension. Direct inhibitors of the HPV mechanism include: hypocarbia, vasodilating drugs, infection, metabolic alkalemia, and volatile anesthetics >1 MAC. Indirect inhibitors of HPV include: hypervolemia, vasoconstricting drugs, hypothermia, thromboembolism, and a large hypoxic lung segment.
Which of the following is TRUE about the accumulation of hydromorphone metabolites in patients with end stage renal disease?
Many opioids have metabolites that accumulate in patients with renal insufficiency/failure and caution must be taken. Morphine has two major metabolites that accumulate, morphine-3-glucuronide (neuroexcitatory) and morphine-6-glucuronide (potent analgesic and respiratory depressant), hydromorphone’s metabolite is hydromorphone-3-glucuronide (neuroexcitatory), and meperidine’s is normeperidine (neuroexcitatory). Fentanyl is generally considered the safest opioid for use in renal failure patients due to a lack of active or toxic metabolites.
A 45-year-old man in the intensive care unit is brought to the operating room for a tracheostomy. A modern anesthesia machine is being used with a circle system. Which of the following is MOST LIKELY to cause an INCREASE in dead space ventilation or dead space fraction?
Dead space is the volume of inspired air that does not participate in gas exchange. During anesthesia and mechanical ventilation, dead space ventilation or dead space fraction is increased with additions to the circuit on the patient side of the Y-piece connector (in other words, proximal, not distal, to the patient, between the Y-piece and unidirectional valves), when alveoli are hyperinflated, or when pulmonary perfusion decreases.
When tidal volume decreases, anatomic dead space remains the same; thus, the fraction of gas participating in gas exchange decreases and the fraction of dead space ventilation increases. When tidal volume equals the alveolar dead space, effective alveolar ventilation ceases.
A patient has a respiratory system compliance of 100 mL/cm H2O and a lung compliance of 200 mL/cm H2O. What is the patient’s chest wall compliance?
The following formula summarizes the relationship of respiratory system compliance and its two components: 1/CRS = 1/CL + 1/CCW.
TrueLearn Insight : Chest wall compliance is relatively high in neonates due to a pliable rib cage. However, this increases work of breathing since the rib cage provides less mechanical support, which in turn leads to significant retractions and earlier functional airway closure.
Rapid and excessive normal saline administration would MOST likely result in which of the following sets of lab values?
Excessive and rapid administration of normal saline can lead to a non-anion gap hyperchloremic metabolic acidosis with decreased plasma bicarbonate (HCO3-), increased plasma chloride (Cl-), and a decreased plasma strong ion difference (SID).
Therapy for saline-induced hyperchloremic acidosis consists of intravenous administration of a crystalloid solution with a high SID, such as sodium bicarbonate or tromethamine (“Tham” solution).
Which of the following statements about aerobic and anaerobic glycolysis is TRUE?
Aerobic metabolism produces approximately 16 times the ATP of anaerobic metabolism. The additional ATP is produced within the mitochondrion via the citric acid cycle and oxidative phosphorylation. Both anaerobic and aerobic metabolism start with glucose, but anaerobic metabolism generates lactate while aerobic metabolism produces carbon dioxide and water.
TrueLearn Insight : In anaerobic glycolysis, the free energy of oxidation (NADH to NAD+) is wasted as heat, whereas in aerobic glycolysis 2.5-3 ATP are produced per NADH.
A 67-year-old male with history of COPD is admitted to the pre-op area for an elective herniorrhaphy. The nurse notices his pulse oximeter to be 90% and places a nasal cannula at 4 L/min oxygen. You find that last week his blood gas pCO2 was 45 mmHg and you decide to confirm the number by drawing another sample. The resultant pCO2 comes back as 56 mmHg. Which of the following alterations is the cause for the observed hypercapnea in the setting of oxygen administration?
Hypercapnia following administration of oxygen to a patient with chronic obstructive pulmonary disease is primarily due to ventilation-perfusion mismatching, driven by inhibition of hypoxic pulmonary vasoconstriction.
In patients with COPD, hypoxic pulmonary vasoconstriction is the most efficient way to alter the V/Q ratios to improve gas exchange. This physiological mechanism is counteracted by oxygen therapy and accounts for the largest increase of oxygen-induced hypercapnia. A titrated oxygen therapy to achieve saturations of 88% to 92% is recommended in patients with an acute exacerbation of COPD to avoid hypoxemia and reduce the risk of oxygen-induced hypercapnia.
An action potential at the muscle postsynaptic membrane is triggered through a sequence of events. Which of the following molecules is most involved in the first step of generating an action potential in a postsynaptic neuromuscular junction?
The opening of sodium channels on the postsynaptic terminal triggers an action potential.
