Critical Care

What is the formula for mean arterial pressure (MAP)?

• MAP = DBP + 1/3 × (SBP − DBP)

What is the normal range for cardiac output (CO)?

• 4 to 8 L/min

What is the normal range for cardiac index (CI)?

• 2.5 to 4 L/min

What is the normal range for systemic vascular resistance (SVR)?

• 800 to 1400 dyn · s/(cm⁵)

What is the normal range for SVR index (SVRI)?

• 1500 to 2400 dyn · s/(cm⁵)

What is the normal range for pulmonary capillary wedge pressure (PCWP)?

• 7 to 15 mm Hg

What is the normal range for central venous pressure (CVP)?

• 2 to 6 mm Hg

What is the normal range for pulmonary artery (PA) pressure?

• 20 to 30/6 to 15 mm Hg

What is the normal range for mixed venous oxygen saturation (SvO₂)?

• 70% ± 5%

What is SvO₂?

• The oxygen saturation of blood in the right ventricle/pulmonary artery that serves as an indirect measure of peripheral oxygen supply and demand

What factors influence SvO₂?

• Oxygen delivery and oxygen extraction

Approximate percentage of CO that goes to the kidney:

• 25%

Approximate percentage of CO that goes to the brain:

• 15%

Approximate percentage of CO that goes to the heart:

• 5%

What complications can occur during central venous catheter placement?

• Arterial puncture, air or catheter embolism, dysrhythmias, hemorrhage or arteriovenous fistulization, pneumothorax, pseudoaneurysm formation

What should you immediately do if a patient receives an air embolus?

• Roll the patient to the left and place head down to keep air in right atrium/ventricle; attempt to aspirate air with central catheter/pulmonary artery catheter

Relative contraindications for pulmonary artery catheter placement:

• Left bundle branch block, previous pneumonectomy

Treatment for hemoptysis after pulmonary artery catheter placement:

• Immediately pull the pulmonary artery catheter slightly back and reinflate balloon, increase positive end expiratory pressure (PEEP) to help tamponade the bleeding, mainstem intubate the nonaffected side; attempt can be made to place a fogarty catheter down the affected side; if recalcitrant, may need thoracotomy and lobectomy

What West zone of the lung is the desired location for a pulmonary artery catheter?

• Zone III (Pa > Pv > PA); pressure in the arteries (Pa), pressure in the veins (Pv), pressure in the alveoli (PA)

Which portion of the lung has the highest V/Q ratio and which portion has the lowest V/Q ratio?

• V/Q ratio highest in upper lobes

• V/Q ratio lowest in lower lobes

At what point in the respiratory cycle is the PCWP most accurate in a ventilated patient?

• End expiration

At what point in the respiratory cycle is the PCWP most accurate in a nonventilated patient?

• Peak inspiration

What conditions may make the wedge pressure unreliable?

• Aortic regurgitation, high PEEP, mitral stenosis, mitral regurgitation, poor left ventricular compliance, pulmonary hypertension, pulmonary disease (acute respiratory distress syndrome [ARDS]), tamponade, pneumothorax

Pulmonary artery catheters allow the direct measurement of which physiologic parameters?

• CVP, right atrial pressure, pulmonary arterial pressure, right ventricular end-diastolic pressure, pulmonary artery wedge pressure, SVO₂

What complications are associated with pulmonary artery catheter placement?

• Arrhythmias and conduction defects, knotting or catheter entrapment, pulmonary infarction, pulmonary artery rupture, valvular damage.

What is an intra-aortic balloon pump?

• A mechanical device that consists of a cylindrical balloon that actively deflates in systole increasing forward blood flow by reducing afterload, and actively inflates in diastole increasing blood flow to the coronary arteries resulting in decreased myocardial oxygen demand and increased CO

When does the balloon from an intra-aortic balloon pump inflate on ECG?

• T wave (diastole)

When does the balloon from an intra-aortic balloon pump deflate on ECG?

• P wave or start of Q wave (systole)

Indications for intra-aortic balloon pump placement:

• Bridge to heart transplant for patients with left ventricular failure; cardiogenic shock, percutaneous coronary angioplasty, post cardiothoracic surgery, preoperative use for high-risk patients (unstable angina with stenosis >70% main coronary artery), reversible intracardial mechanical defects complicating infarction, unstable angina pectoris, ventricular dysfunction with ejection fraction <35%

Absolute contraindications to intra-aortic balloon pump placement:

• Aortic regurgitation, aortic dissection, severe aortoiliac occlusive disease

Relative contraindications to intra-aortic balloon pump placement:

• Prosthetic vascular grafts in the aorta, aortic aneurysm, aortofemoral grafts

Desired location for the tip of the intra-aortic balloon pump catheter?

• 1 to 2 cm below the top of the aortic arch just distal to the left subclavian

What is preload?

• End diastolic length of cardiac myocytes, which is linearly related to end-diastolic volume (EDV) and filling pressure

What is afterload?

• Resistance against ventricular contraction (SVR)

What is contractility?

• The force of myocardial contraction

What 3 things determine stroke volume?

• Left ventricular EDV (LVEDV) (preload), contractility, afterload

How is stroke volume calculated?

• LVEDV − left ventricular end-systolic volume

How is the ejection fraction calculated?

• Stroke volume/EDV

What is the normal O₂ delivery to consumption ratio?

• 5 to 1

What are the primary determinants of myocardial O₂ consumption?

• Heart rate (HR), increased ventricular wall tension

What is the normal range for the alveolar:arterial gradient?

• 10 to 15 mm Hg

What shifts the oxygen-hemoglobin dissociation curve to the left?

• Decrease temperature

• Decrease 2,3-diphosphoglycerate (DPG)

• Decrease pCO₂

• Increase pH

What shifts the oxygen-hemoglobin dissociation curve to the right?

• Increase temperature

• Increase 2,3-DPG

• Increase pCO₂

• Decrease pH

What is the definition of shock?

• Inadequate perfusion to meet the body's metabolic needs

What are the 5 broad categories of shock?

• Hypovolemic, obstructive, neurogenic, septic, cardiogenic

What is the formula for the O₂ content of blood (CaO₂)?

• CaO₂ = [Hb × SaO₂ × 1.34] + [0.003 × PaO₂]; Hb is hemoglobin in g/dL, SaO₂ is arterial O₂ saturation (%), PaO₂ is partial pressure of O₂ (mm Hg) in arterial blood

What is the formula for O₂ delivery (DO₂)?

• DO₂ = Cao₂ × CO; [(Hb × Sao₂ × 1.34) + (0.003 × PaO₂)] × (HR × SV); Hb is hemoglobin in g/dL, SaO₂ is arterial O₂ saturation (%), PaO₂ is partial pressure of O₂ (mm Hg) in arterial blood, HR is heart rate (beats/min [bpm]), SV stroke volume (mL)

What is the formula for O₂ consumption (VO₂)?

• VO₂ = CO × (CaO₂ − CVO₂) × 10

• (This can be rearranged to estimate the mixed venous saturation; the Fick equation)

How many milliliters of oxygen will a gram of hemoglobin bind when hemoglobin is fully saturated with oxygen?

• 1.34 mL of oxygen is bound to each gram of hemoglobin. (1.39 mL of oxygen is normally bound to hemoglobin, but you subtract the 3%–5% of circulating hemoglobin present as methemoglobin and carboxyhemoglobin.)

What does the solubility coefficient of 0.03 mL/L/mm Hg in the oxygen delivery equation signify?

• 0.03 mL of O₂ dissolves in 1 L of water when the PO₂ is 1 mm Hg at normal body temperature (37°C)

Manipulation of what factors can increase oxygen delivery?

• Greatest increase of oxygen delivery with increasing hemoglobin content and SaO₂; can also increase oxygen delivery by raising CO by increasing either HR or stroke volume

What is the equation for oxygen extraction ratio?

• O₂ER = VO₂/DO₂

• Usually expressed as a percentage; the normal value is 0.25 to 0.3 or 25% to 30%

Treatment for ventricular fibrillation/pulseless ventricular tachycardia:

• 1 shock (monophasic 360 J; biphasic, 100–200 J); cardiopulmonary resuscitation with additional countershocks if shockable rhythm obtained; epinephrine 1 mg IV and repeat every 3 to 5 minutes, or vasopressin, 40 units IV (to replace the first or second dose of epinephrine); consider amiodarone (300 mg IV), lidocaine (1–1.5 mg/kg), magnesium (1–2 g IV); if no shockable rhythm, revert to asystole/pulseless electrical activity algorithm

Treatment for asystole/pulseless electrical activity:

• Verify with lead rotation; epinephrine 1 mg IV and repeat every 3 to 5 minutes, or vasopressin 40 units IV (to replace the first or second dose of epinephrine); consider atropine 1 mg IV every 3 to 5 minutes, up to 3 doses; if shockable rhythm, revert to ventricular fibrillation/ventricular tachycardia algorithm

Treatment for an unstable patient with bradycardia (HR <60 bpm):

• Transcutaneous pacing; if transcutaneous pacing not immediately available, give atropine 1 mg and epinephrine 2 to 10 mg/min

In which patients with atrial fibrillation is anticoagulation unnecessary?

• Patients who had atrial fibrillation for <48 hours

What is the treatment for atrial fibrillation with hemodynamic instability?

• Cardioversion and anticoagulation

What is the treatment for atrial fibrillation without hemodynamic instability?

• Rate control (amiodarone, calcium channel blockers, β-blockers, digoxin) and correction of the underlying cause (fluid overload, electrolyte imbalance, MI, hypoxemia, acidosis, PE); anticoagulation

Formula for anion gap:

• Na⁺ − (Cl⁻ + HCO₃⁻)

What is the normal range for the anion gap?

• 10 to 14

What is the "10 for 0.08" rule of acid base balance?

• The pH falls by 0.08 for every increase of PaCO₂ by 10 mm Hg

What pH, PaCO₂, and bicarbonate will you see with a pure respiratory acidosis?

• ↓ pH; ↑ PaCO₂; normal bicarbonate

What pH, PaCO₂, and bicarbonate will you see with a pure metabolic acidosis?

• ↓pH; normal PaCO₂; ↓ bicarbonate

What pH, PaCO₂, and bicarbonate will you see with a pure respiratory alkalosis?

• ↑ pH; ↓ PaCO₂; normal bicarbonate

What pH, PaCO₂, and bicarbonate will you see with a pure metabolic alkalosis?

• ↑pH; normal PaCO₂; ↑ bicarbonate

What is the 35-45 rule of blood gas values?

• pH = 7.35 to 7.45 corresponds to pCO₂ = 35 to 45

What is the most common cause of postoperative renal failure?

• Hypotension

What laboratory results suggest a prerenal cause of acute renal failure?

• BUN/Cr ratio >20, fractional excretion of sodium (FENa) <1%, urine Na⁺ <20 mEq/24 h, urine osmolality >500 mOsm

What is the formula for the FENa?

• (Urine sodium × plasma creatinine/plasma sodium × urine creatinine) × 100

What does a FENa <1.0 % indicate?

• Prerenal cause of renal failure, from decreased renal blood flow

What does a FENa >3.0 % indicate?

• Intrinsic kidney damage (acute tubular necrosis, severe obstruction of both the kidneys)

What are indications for dialysis?

• Fluid overload, metabolic acidosis, hyperkalemia, poisoning, uremic coagulopathy, uremic encephalopathy

What are the advantages of intermittent hemodialysis over continuous renal replacement therapy?

• Lower cost, lower risk of systemic bleeding, facilitates transport for other interventions, more suitable for severe hyperkalemia

What are the advantages of continuous renal replacement therapy over intermittent hemodialysis?

• Better fluid control, better hemodynamic stability, fewer cardiac arrhythmias, improved nutritional support, better pulmonary gas exchange

What are the disadvantages of intermittent hemodialysis over continuous renal replacement therapy?

• Availability of dialysis staff, inadequate fluid control, inadequate dialysis frequency, inadequate nutritional support, more difficult hemodynamic control, potential complement activation by nonbiocompatible membranes, not suitable for patients with intracranial hypertension

What are the disadvantages of continuous renal replacement therapy over intermittent hemodialysis?

• Greater cost, greater vascular access problems, higher risk of systemic bleeding, long-term immobilization of patient, more filter problems (clotting, rupture)

How does acute adrenal insufficiency present?

• Cardiovascular collapse unresponsive to fluids and pressors

How much steroids should a patient be on preoperatively to have presumed hypothalamic-pituitary-adrenal axis suppression?

• 20 mg of prednisone or equivalent per day for 3 weeks or longer

How much perioperative steroid supplementation should you give a patient with hypothalamic-pituitary-adrenal axis suppression undergoing a moderate operation (open cholecystectomy, lower extremity revascularization)?

• 50 to 75 mg/d of hydrocortisone equivalent for 1 to 2 days

How much perioperative steroid supplementation should you give a patient with hypothalamic-pituitary-adrenal axis suppression undergoing a major operation (colectomy, cardiac surgery)?

• 100 to 150 mg/d of hydrocortisone equivalent for 2 to 3 days

How much perioperative steroid supplementation should you give a patient with acute adrenal insufficiency?

• 100 mg of hydrocortisone IV Q6 to 8 hours tapered as the patient's condition stabilizes

What steroid can you give to treat suspected acute adrenal insufficiency without interfering with the rapid adrenocorticotropic hormone (ACTH) stimulation test?

• Dexamethasone

How do you interpret the results of the rapid ACTH stimulation test?

• Normal response if baseline cortisol doubles, if baseline cortisol is >34 μg/dL, or incremental increase >9 μg/dL in patients with a baseline cortisol level between 15 to 34 μg/dL. (Note that most recent surviving sepsis guidelines suggest that the ACTH stimulation test not be used to identify the subset of adults with septic shock who should receive hydrocortisone. Instead, steroids should be empirically administered to septic patients with hypotension that is refractory to fluid and vasopressor infusion).

What is the role of α-1 receptors?

• Vascular smooth muscle constriction, gluconeogenesis, glycogenolysis

What is the role of α-2 receptors?

• Venous smooth muscle constriction

What is the role of β-1 receptors?

• Myocardial contraction and rate

What is the role of β-2 receptors?

• Relaxes bronchial smooth muscle, relaxes vascular smooth muscle, insulin secretion

What is the role of dopamine (DA) receptors?

• Relaxation of renal and splanchnic smooth muscle

What is the site of action of intermediate dose (4–10 μg/kg/min) dopamine?

• ++β1, +α1 (increase inotropy with some vasoconstriction)

What is the site of action of high dose (>10 μg/kg/min) dopamine?

• +++ α-1 agonist (marked arteriolar vasoconstriction increasing afterload)

What is the site of action of epinephrine?

• Low-dose β1 and β2 (↑ contractility, ↑ vasodilation) and high-dose α1 and α2 (vasoconstriction)

What is the site of action of norepinephrine?

• Low-dose β1 (↑ contractility) and high-dose α1 and α2 (vasoconstriction)

What is the site of action of vasopressin?

• V-1 receptors: vasoconstriction of vascular smooth muscle

• V-2 receptors: water reabsorption in the collecting ducts of the kidney

• V-3 receptors: mediate release of von Willebrand factor and factor VIII

What is the site of action of phenylephrine?

• α1 (vasoconstriction)

What is the site of action and effect of dobutamine?

• β1 (5–15 μg/kg/min) and β2 agonist (>15 μg/kg/min), ↑ inotropy, ↑ chronotropy, ↓ SVR

What is the site of action and effect of isoproterenol?

• β1 and β2 agonist, ↑ inotropy, ↑ chronotropy. ↑ vasodilation of skeletal and mesenteric vascular beds, extremely arrhythmogenic

What is milrinone?

• A phosphodiesterase inhibitor that causes vasodilation, vascular smooth muscle relaxation, and leads to ↑ cAMP → ↑ calcium flux → ↑ myocardial contractility

Which cardiovascular drug is an arterial and venous dilator: nipride or nitroglycerine?

• Nipride is an arterial and venous dilator; nitroglycerine is predominately a venodilator.

What is the treatment for cyanide toxicity?

• Inhaled amyl nitrite then IV sodium nitrite followed by thiosulfate

What is atrial natruretic factor?

• A vasodilator that is released from the atrial wall with atrial distension that inhibits sodium and water resorption in the collecting ducts

What are the criteria to diagnose systemic inflammatory response syndrome (SIRS) in an adult?

• 2 or more of the following criteria present: body temperature <36°C or >38°C, HR >90 bpm, respiratory rate (RR) >20 breaths/min or PaCO₂ <32 mm Hg, white blood cell count <4000 cells/mm³ or >12,000 cells/mm³ or >10% bands

What is the most potent stimulus for SIRS?

• Endotoxin (lipopolysaccharide-lipid A)

What happens to insulin and glucose with early Gram-negative sepsis?

• ↓ Insulin, ↑ glucose, impaired utilization

What happens to insulin and glucose with late Gram-negative sepsis?

• ↑ Insulin, ↑ glucose, insulin resistance

What is the early sepsis triad?

• Confusion, hyperventilation, respiratory alkalosis

What is the P/F ratio?

• The ratio of PaO₂ to FiO₂

What is the diagnostic triad of ARDS?

• Capillary wedge pressure <18 mm Hg, x-ray of chest with bilateral infiltrates, ratio of PaO₂ to FiO₂ <200

What does the classic chest x-ray in a patient with ARDS look like?

• Bilateral fluffy infiltrates

What concentration of oxygen leads to oxygen toxicity?

• FiO₂ >60% for 48 hours

What are the main causes of carbon dioxide retention?

• Increased dead space ventilation, hypoventilation, increased carbon dioxide production

What is total lung capacity (TLC)?

• Lung volume after maximal inspiration; TLC = forced vital capacity (FVC) + residual volume (RV)

What is FVC?

• Volume of air maximally exhaled after maximal inhalation

What is RV?

• Lung volume after maximal exhalation

What is tidal volume?

• Volume of air with normal inspiration and expiration

What is functional residual capacity (FRC)?

• Lung volume after normal exhalation, FRC = expiratory reserve volume (ERV) + RV

What is ERV?

• The volume of air that can be forcefully expired after normal expiration

What is inspiratory capacity?

• The maximal amount of air that inspired from the FRC

What is the FEV1?

• The forced expiratory volume after maximal inhalation in 1 second

What is PEEP?

• Positive end expiratory pressure, positive pressure maintained at the end of a breath that keeps alveoli open

What is normal "physiologic" PEEP?

• 5 cm H₂O, postulated to be the normal pressure caused by the closed glottis in a nonventilated patient

What are the presumed advantages of PEEP?

• Prevention of alveolar collapse/atelectasis, decreased shunt fraction, improved gas exchange, increased pulmonary compliance

What are the side effects of excessive PEEP?

• ↓ Preload leading to decreased CO, barotrauma (pneumothorax), increased intracranial pressure, decreased compliance, decreased gas exchange, fluid retention

What is dead space?

• The portion of inspired air that does not participate in gas exchange (large airways/endotracheal [ET] tube)

What increases dead space?

• Underperfusion (PE, pulmonary artery vasoconstriction, low CO), overventilation (excessive PEEP, emphysema)

What is shunt fraction?

• Portion of pulmonary venous gas that does not participate in gas exchange

Name some clinical situations that can cause increased airway resistance:

• Airway/ET tube obstruction, ARDS, bronchospasm, congestive heart failure (pulmonary edema), mucus plug

What 2 conditions must you worry about in a patient with low urinary output and increased peak airway pressures?

• Abdominal compartment syndrome, tension pneumothorax

How can you manipulate ventilation to decrease pCO₂?

• Increase minute ventilation

How can you increase PO₂ in a ventilated patient?

• ↑PEEP, ↑FiO₂

Why does increasing the FiO₂ in a patient with a high shunt fraction has minimal effect on the arterial PO₂?

• If >50% shunt fraction, the oxygenated blood is already at maximal oxygen absorption hence the minimal effect

What is minute ventilation?

• Total lung ventilation per minute

• Tidal volume × RR

• Can be measured by expired gas collection for a period of 1 to 3 minutes

What is the normal range of minute ventilation?

• 5 to 10 L/min

What is CPAP mode on the ventilator?

• Continuous positive airway pressure: patient breathes on their own with continuous positive pressure delivered during inspiration and expiration with no volume breaths given by the ventilator

What is pressure support ventilation?

• A mode that overcomes the resistance of the ventilator circuit to decrease the work of breathing; the ventilator only delivers pressure during an initiated breath

What is IMV mode on the ventilator?

• Intermittent mandatory ventilation: patient can breathe on their own above the mandatory rate without assistance from the ventilator, otherwise the ventilator will deliver a mandatory breath at the predetermined rate

What is SIMV mode on the ventilator?

• Synchronous intermittent mandatory ventilation: delivers a mandatory breath synchronously with the patient's initiated breath; if the patient does not initiate a breath, the ventilator delivers a predetermined mandatory breath

What is A-C mode on the ventilator?

• Assist-control ventilation: the ventilator "assists" the patient by delivering a breath when the patient initiates a breath, otherwise the ventilator takes "control" if the patient does not initiate a breath and delivers a breath at a predetermined rate.

What medications can be delivered through an ET tube?

• Narcan, atropine, vasopressin, epinephrine, lidocaine (NAVEL) along with acetylcysteine, albuterol

What parameters are evaluated when deciding to extubate a patient on the ventilator?

• Awake, alert patient able to protect airway (absence of correctible comorbid conditions (afebrile, no significant electrolyte abnormalities), no evidence of myocardial ischemia, HR ≤140 bpm, normotensive without vasopressors or with minimal vasopressor support), RR <35, PaO₂ ≥60 mm Hg on FiO₂ ≤40% to 50% and PEEP ≤5 to 8 cm H₂O, pCO₂ <50 mm Hg, tidal volume >5cc/kg, minute ventilation <10 L/min, negative inspiratory pressure <−20 cm H₂O, pH >7.25, rapid shallow breathing index (RSBI) ≤105

What adjustment should you make to the diet/total parenteral nutrition (TPN) in a patient with hypercapnia, a respiratory quotient >1.0, and difficulty getting off of the ventilator?

• Decrease the amount of carbohydrates in the diet/TPN; carbohydrates have the highest CO₂ production