Ccm Formula Sheet 2003

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Critical Care Medicine Information Sheet 2003

Respiratory Critical Care1. Measurement of Hypoxemia

a. Alveolar-arterial oxygen difference (A-a gradient)i. A-a gradient = PAO2 - PaO 2

ii. A-a gradient = [(PB - PH20) (FIO2) - PCO2 / R] - PaO2iii. A-a gradient = [713 (FIO2) - PCO2/ 0.8] - PaO 2iv. A-a gradient = [713 (FIO2) - 1.25 (PCO2)] - PaO2

v. A-a gradient:1. On room air normal always < 25

2. On 100% FIO2on mechanical ventilation normal 1003. Formula for determining normal A-a gradient based on

age:

4. Normal A-a gradient = [Patient age + 4] / 4

b. PaO2/FIO2ratioi. PaO2off blood gas / FIO 2ii. Normal > 200

iii. Useful trend to follow when patient on mechanical ventilation;results affected less by changes in FIO2then when using A-a

difference to monitor hypoxemia.

c. PAO2: PaO2ratio (A.K.A. A/a ratio)

i. Same as for B.3ii. PaO2off ABG

iii. PAO2calculated from known FIO 2and measured PCO 2off ABGwhere, PAO2 = 713 (FIO 2) - 1.25 (PCO2)

iv. Normal PaO2/ PAO 2 0.8

d. Normal PaO2corrected for age in patients with normal Lungs:

i. Arterial PaO2 = 100 - (0.4 X age in years)

2. Oxygen Saturation (Oxygen Dissociation Curve Determinants)

Shift Right ( affinity, P50, delivery) Shift Left ( Affinity, P50, delivery)Acidosis Alkalosis

Hypercapnea HypocapneaHyperthermia Hypothermia

Elevated RBC MCHC Reduced RBC MCHC

2,3 DPG 2,3 DPGAbnl Hgb (ss) Abnl Hgb (fetal, meth, sulf)

Exercise Carbon monoxide

Propranolol


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3. Ventilator Equations and Adjustments:a. Minute ventilation = tidal volume (liters) X respiratory rate (# per

minute) (normal < 10 liters/min)

b. Adjusting ventilator rate:

i. Desired f = [(actual f) (actual PaCO2)] / desired PaCO2

c. Adjusting tidal volume:i. Desired VT= [(actual PaCO 2) (actual VT)] / desired PaCO2

d. Adjusting FIO2:i. Desired FIO2 = [(actual FIO 2) (desired PaO2)] / actual PaO2

e. Static pulmonary compliance (Cst):

i. Cstat = V T exhaled / P plat- PEEPii. Normal = 50-100 cm H2Oiii. Stiff noncompliant lung < 50 cm H2O (example ARDS)

iv. Highly compliant non-stiff lung > 100 cm H2O (example COPD)

f. Pressure generated to overcome airway resistance:

i. P aw = PIP - P plat

g. Mean airway pressure:i. Mean P aw = K (PIP - PEEP) (T 1/ TCT) + PEEP

1. This equation shows the relationship of PIP, PEEP and

time on mean airway pressure.

h. Bohr Equation (VD/ V T):i. VD/ V T = PaCO2- P ECO2 / PaCO 2

4. Strategies to reduce auto-PEEP in bronchospastic patients on mechanicalventilation.

a. Controlled ventilation: sedation paralysis as needed.b. -agonist, Ipatropium, steroids, magnesium sulfate, aersolized

lidocaine.c. Increase peak inspiratory flow rate (70-120 Liters / min).d. Reduce tidal volumes (5-8-ml/kg)--[permissive hypercapnea].

e. Reduce respiratory rate [permissive hypercapnea].i. Permissive hypercapneaadd sodium bicarbonate drip if

arterial pH < 7.20 and titrate the drip to maintain arterial pH >7.20.

ii. Add extrinsic PEEP (never more than 10 cm H20) to counteract

intrinsic PEEP (auto-PEEP).


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5. Protocol for Mechanical Ventilation in patients with early ARDS.

a. Controlled ventilation: sedation paralysis as needed.b. Use lower tidal volumes for the baby lung seen in ARDS (e.g., 5 - 8

ml/kg of ideal body weight and maintain plateau pressure 35 cm

H2O). This is a lung protective strategy designed to prevent overdistention of normal alveoli and to reduce pulmonary and systemicinflammation caused by volume and/or pressure induced over

distention of the alveoli (alveolar volume/pressure trauma). [JAMA.1999; 282:54-61; Amato NEJM 1998; 338:347-354; ARDS NetworkTrial NEJM 5/00]. Studies show that in large groups of ARDS patients,

the lower inflexion point on the pressure volume curve ranges from(mean) 12.6-13.6 2.8-3.9 (SD). For this reason, initially set PEEP at12-15 cm H2O or set PEEP at 2-3 cm H2O higher than the lowerinflection point on the pressure volume curve. This is a lung protective

strategy to prevent repetitive opening and closure of alveolar units

sheer trauma. [JAMA. 1999; 282:54-61, Amato NEJM 1998;338:347-354; ARDS Network Trial NEJM 5/00].

c. Respiratory rate is adjusted to < 10 -15/min.d. Permissive hypercapneaadd bicarbonate drip if arterial pH < 7.20 and

titrate drip to maintain arterial pH > 7.20.e. The standard inspiratory to expiratory ratio of 1:2 should be used;

however, in some cases Pressure Control Ventilation with inverse ratio

ventilation [I:E ratios of 1:1; 1.5:1; or 2:1] may be required. Be awarethat hemodynamic instability may occur during inverse ratio ventilation

especially in patients with pre-existing heart disease. A reduction inpreload caused by high intrathoracic pressure occurs. Therefore, a

physician must always be present at the bedside during initiation ofPCV or when making a change to inverse ratio ventilation.f. Any patient on mechanical ventilation who develops a pneumothorax

should have a chest tube placed. Prophylactic chest tubes may bejustified in some patients.

g. Be aware that the development of pneumomediastinum or

subcutaneous air signals that the patient is at high risk for developing apneumothorax. A standard CXR does not always show the

pneumothorax (it may be located anteriorly). If a patient ishemodynamically stable, a CT scan of the chest will demonstrate apneumothorax. Rule of thumb: In unstable patients, if in doubt as to

whether or not a pneumothorax is present, place a chest tube.h. Calculation of idea body weight (Kg) for use in determining tidal

volume settings:i. Ideal body weight (kg) males = 50 + 0.91[Height (cm) 152.4]ii. Ideal body weight (kg) females = 45.5 + 0.91[Height (cm)

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6. Differential Diagnosis for Failure to Wean From Mechanical Ventilationa. WEANS NOW:

i. W- Work of breathing = NIF, VC, Tobin Index (frequency / TV),

BICORE machineii. E - Endotracheal or tracheotomy tube size.

1. Note: Airway resistance is related to diameter and lengthof the breathing tube. Airway resistance may be

decreased by using a larger diameter tube and/or ashorter breathing tube.

iii. A- Acid/base; abdominal distention; atelectasis;

anxious/agitated; alkalosis.1. Note: metabolic alkalosis shifts oxygen hemoglobin

dissociation curve to the left and impairs the CNSrespiratory drive.

iv. N - Nutrition and electrolytes (Mg 2+, PO4, K+)

v. S - Secretions due to sinusitis; bronchitis; pneumonia;

aspiration; CHF (systolic or diastolic dysfunction); TE fistula; GEreflux; aspiration.vi. N - Neuromuscular status. Neuromuscular disease;

neuromuscular blockers; steroids; aminoglycosides; endocrine(hypothyroid).

vii. O- Occult obstruction (bronchospasm)

1. Consider: -agonist; ipatropium, steriods, leukotrieneinhibitors, theophyline

viii. W- Wakefulness. Is the patient over sedated? Is the patient

able to follow commands and participate in his/her care?

Cardiovascular Critical Care1. Hemodynamic monitoringa. Normal Values:

i. Cardiac output = 4-8 liters / minute

ii. Cardiac Index = CO / BSA = 2.2 - 4.0 l / m2 / miniii. Stroke Volume = CO / heart rateiv. Cardiac Output = Heart rate X stroke volume (1/min)

v. Right atrium pressure = 0-8 mmHgvi. Central venous pressure (CVP) = 0-8 mmHg

vii. Pulmonary artery systolic (PAS) = 15-30 mmHgviii. Pulmonary artery diastolic (PAD) = 5-12 mmHg

ix. Mean pulmonary artery pressure (MPAP) < 20 mmHgx. Pulmonary artery wedge pressure (PAOP or PCWP):1. < 6 = dehydrated

2. 6-15 = normal3. 18-20 = mild congestion4. 20-25 = moderate congestion

5. 25 = severe congestion


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xi. Body surface area (m2) = [(height (cm) x weight (kg)) /3600] Where means take the square root of the number inbrackets

b. Essential Formulae:

i. Mean arterial pressure (MAP):1. MAP = 1/3 (AP systolic - AP diastolic) + AP diastolic2. MAP = normal > 70

3. MAP < 70 = shock in the majority of patients.

ii. Mean pulmonary artery pressure:

1. PAP mean= 1/3 (PA systolic - PA diastolic) + PA diastolic

ii i. Systemic vascular resistance (SVR)1. SVR = [MAP CVP / CO] x 80 (nl = 700 - 1400 dynes

- sec - cm-5)

a. Where MAP = mean arterial pressureb. CVP = central venous pressure

c. CO = cardiac outputd. 80 = Conversion factor used to convert wood

units to dynes - sec - cm-5

iv. Pulmonary vascular resistance (PVR)

1. PVR = [PAP mean - PCWP / CO] x 80 (nl < 200 dynes -sec - cm-5)

a. Where PAP mean = mean pulmonary artery

pressure

b. PCWP = pulmonary capillary wedge pressurec. CO = cardiac outputd. 80 = conversion factor used to convert wood

units to dynes - sec - cm-5

c. Hemodynamic monitoring (short form) calculation

i. Theoretical, calculated, end-pulmonary capillary oxygencontent (CcO2), assuming 100% hemoglobin saturation withoxygen:

1. CcO2= 1.39 (Hgb)

ii. Total arterial oxygen content (CaO2):1. CaO2= 1.39 (Hgb) (SaO 2)

iii. Total venous oxygen content (CvO2)1. CvO2= 1.39 (Hgb) (SvO 2)

iv. Arterial venous oxygen content difference (AVDO2)1. AVDO2= CaO 2- CvO 2(nl < 5)


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v. Oxygen delivery (DO2in ml/min)

1. DO2= CO (CaO 2) (10)

vi. Oxygen consumption (VO2 in ml/min)

1. VO2= CO (AVDO 2) (10)

vii. Intrapulmonary shunt fraction (QS/QT). AKA: arterial-venousadmixture (nl < 10%)

1. Qs/QT= CcO 2 - CaO 2 / CcO 2- CvO 2

viii. Extraction ratio (nl 22 32%)

1. VO2/ DO 2

ix. Caloric requirements (kcal/24 hours):1. 7.1 (VO2)

x. Crude method of estimating intrapulmonary shunt fraction inpatients on mechanical ventilation who are on 100% FIO 2:

1. Normal PaO2~600-650 mmHg2. For every drop in PaO2 of 100 mmHg from the normal

corresponds to a 5% shunt.

3. Example: PaO2 = 230 mmHg on 100% FIO2corresponds to an estimated 20% intrapulmonary

shunt.

2. Adverse consequences of PEEP

a. Elevation in airway pressure; increased risk of barotrauma.b. Decreased venous return to right heart decreased rightventricular preload decreased cardiac output.

c. Decreased left ventricular filling (preload) decreased cardiacoutput (due to increased PA, PVR, and RV afterload).

d. Direct compression of heart by overextended lungs thus limiting LVfilling decreased cardiac output.

e. Decreased LV output due to PEEP induction of increased RVafterload with subsequent RV distention and bulging ofintraventricular septum into LV cavity (causes LV diastolic

dysfuntion).

3. Beneficial effects of PEEP:a. Increases FRC improves / prevents atelectasis.b. Decreases work of breathing by reducing hypoxemia.c. Reduces LV preload and afterload.d. Improves hypoxemia by:

i. Recruiting atelectatic alveoli and increasing FRC


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ii. Redistribution of lung H2O from alveolar space into theinterstitium

iii. Improving static lung complianceiv. Decreasing intrapulmonary shunting.

e. May be used to counter the effects of intrinsic (auto) PEEP.

f. Peep at or above the lower inflection point on the pressure volumecurve has a protective effect on the lungs in patients with ARDS.

g. Special note: PEEP does not prevent the development of ARDS.

4. Nitroprusside Informationa. Thiocyanate toxicity

i. Most common in patients with renal failure.

ii. Thiocyanate level < 10 mg/dl considered safe.iii. Manifest as: fatigue, muscle weakness, nausea, vomiting,

confusion, seizures, coma.iv. Treatment: hemodialysis

b. Cyanide toxicityi. Use of nitroprusside for > 3 days.ii. Most common with severe liver failure.

iii . Manifest as severe lactic acidosis.iv. Treatment:

1. IV sodium nitrate

2. IV thiosulfate3. IV vitamin B12

Critical Care Acid-Base:2. Stepwise approach:

a. Determine electrolyte and ABG values concomitantly.b. Compare the calculated and measured plasma HCO3concentration

to rule out laboratory error using H+ = 24 (PaCO2 / HCO3) wherenormal H+ = 40 and corresponds to a normal pH = 7.40. Anincrease in H+results in a lower pH and vise versa.

c. Compute anion gap (Na (Cl + HCO3).d. Calculate degree of compensation (see below).

e. Compare the change in plasma sodium and chloride concentration;anion gap and bicarbonate concentration; chloride and bicarbonateconcentration.

3. Determinants of compensation:a. Metabolic acidosis:i. PaCO2= 1.5 (HCO 3) + 8ii. PaCO2= last two digits of pH

iii. PaCO2= 1.0 1.5 per 1 mEq/L HCO 3


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b. Metabolic alkalosis:i. PaCO2= 0.9 (HCO 3) + 9

ii. PaCO2 = 0.5 1.0 mm per 1 mEq/L HCO 3

c. Respiratory acidosis and alkalosis (acute acid-base changes based

on PCO2and HCO 3):i. H+=0.8 (PaCO2)ii. For every or of PCO 2by 1 = pH by 0.008iii. For every or of HCO 3 by 1 = pH by 0.015

d. Estimate of baseline PCO2in patients with Acute RespiratoryAcidosis:

i. Estimated baseline PCO2= 2.4 (admission measured HCO 3 22)

4. Increased anion gap metabolic acidosis

a. Anion gap = Na+

- [Cl-

+ HCO 3-

] = Normal < 15i. Differential Diagnosis (MUD PIES):

1. M- Methanol2. U - Uremia

3. D - DKA4. P - Paraldehyde

5. I- Ischemia (lactic acidosis); INH6. E - Ethanol; ethylene glycol7. S - Salicylates

5. Normal anion gap metabolic acidosis

a. Differential diagnosis (HARD UP):i. H - Hyperalimentationii. A- Acid Ingestion; Addisons; hypoaldosteronism;

acetazolamide, aldactoneiii. R - RTA; early renal failure

iv. D - Diarrhea; diuretics (e.g., spironolactone, diamox)v. U - Uretosigmoidostomyvi. P - Posthypocapnea; pancreatitis

6. Differentiating acidosis in alcohol ingestion:

Substance Target OsmGap Ketones Breath Acidosis Urine

Ethanol Liver +++ 0Methanol Eyes 0 --- +++

Ethylene glycol Kidney 0 --- +++ Oxalatecrystals

Isopropyl + 0Alcoholic ketoacidosis N + +


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7. Osmolar Gap:a. Osmolar gap = [measured osmolality] [calculated osmolality]

b. Osmolar gap = normal < 10

c. Calculated osmolality = 2 [Na

+

] + [glucose / 18] + [BUN / 2.8]d. Differential Diagnosis of increased osmolar gap:

i. Lactic acidii. Ethylene glycol

iii. Ethanoliv. Isopropanolv. Methanol

e. If osmolar gap > 25 think ethylene glycol and methanol.f. You will generally see an anion gap > 20 and an osmolar gap > 25

in ethylene glycol and methanol poisoning.

8. Osmolar gap and ingestion of an unknown alcohol-glycol:

Osm Normal pH No acetone Ethanolacetone Isopropanol

Acidosis Methanol

Ethylene glycol9. Calcium relationship to albumin

a. Corrected calcium = observed calcium + 0.8 (4.0 - albumin)

10. Water/salt balance:

a. Fractional excretion of Na+

i. FENA = [(Urine Na

+

) (Plasma Cr) / (Plasma Na

+

) (Urine Cr)]X 100

b. Water deficit (L) = [(0.6) (wt in kg) ((Observed Na+/ 140) 1)]

i. Infuse of deficit over 24 hours then the remainder over thenext 2-3 days.

Critical Care Nutrition1. Energy (kcal/gram)

a. Lipid = 9.1 kcal/gramb. Protein = 4.0 kcal/gram

c. Glucose = 3.75 kcal/gram

2. Ideal body weight (kg) males = 50 + 0.91 [Height (cm) 152.4]

3. Ideal body weight (kg) females = 45.5 + 0.91 [Height (cm) 152.4]4. Short form basal energy expenditure (BEE) equation:

a. BEE (kcal/day) = 25 x wt (kg)b. Stress factors

i. Burns:


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Ccm Formula Sheet 2003

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