The Washington Manual Internship Survival Guide (4 page)

The Cochrane Database of Systematic Reviews

•
  
http://thecochranelibrary.net

•
  Reviews, analyzes, and synthesizes the best clinical trials by topics.

•
  Multidirectional links MEDLINE, EBM, and EUCLID full-text.

•
  Subscription required.

PubMed

•
  
www.ncbi.nlm.nih.gov/entrez/

•
  Maintained by the National Library of Medicine.

•
  Allows a user-friendly approach to medical literature with built-in search filters. Free.

ACP Journal Club

•
  
www.acpjc.org

•
  Evidence-based medicine reviews of journal articles.

•
  Subscription required.

Useful Formulae

5

A-a O
₂
GRADIENT

A-a gradient = PAo
₂
– Pao
₂

PAo
₂
= ([Fio
₂
× 713] – PaCO
₂
)/0.8

(all units in mmHg)

•
  Estimate for upper limit of normal in room air (in mmHg) by age = (age/4) + 4.

•
  Causes of increased A-a gradient: V/Q mismatch, intrapulmonary right-to-left shunt, intracardiac right-to-left shunt, impaired diffusion (room air only).

ANION GAP (SERUM)

AG = [Na
⁺
] - ([Cl
^-
] + [HCO
^-
₃
])

([Na
⁺
], [Cl
^-
], HCO
₃
^-
] in mEq/L
)

•
  Normal = 8–12 mEq/L.

•
  See Acid-Base section in
Chapter 18
for differential diagnosis.

ANION GAP (URINE)

UAG = (U
_[Na+]
+ U
_[K+]
) – U
_[Cl−]

(U
_[Na+]
, U
_[K+]
, U
_[Cl−]
in mEq/L)

•
  Normal = slightly positive.

•
  UAG is
negative
in diarrhea-induced nongap metabolic acidosis (
enhanced
urinary NH
⁺
₄
excretion).

•
  UAG is
positive
in distal RTA-induced nongap metabolic acidosis (
impaired
urinary NH
⁺
₄
excretion).

BODY MASS INDEX

BMI = weight/(height)
²

(
weight in kg, height in m
)

•
  <18.5 = underweight

•
  18.5–24.9 = normal weight

•
  25–29.9 = overweight

•
  > 30 = obese

CREATININE CLEARANCE/GLOMERULAR FILTRATION RATE

Estimated (Cockcroft-Gault Formula)

CrCl = [(140 – age) × weight]/[serum Cr × 72]

Multiply by 0.85 for women

(weight in kg, Cr in mg/dL)

Estimated (MDRD)

eGFR = 186.3 × (serum Cr)
^–1.54
× age
^–0.203
× 0.742 (
if female
)

× 1.21 (
if black
)

(eGFR in mL/min per 1.73 m
²
,
Cr in mg/dL)

Measured (24 Hour)

CrCl = (U
_[Cr]
× U
_volume
)/(P
_[Cr]
× 24 × 60)

(Cr in mg/dL, volume in mL, and time in min)

CORRECTED SERUM CALCIUM

Corrected serum Ca = measured [Ca
⁺²
] + [0.8 × (4.0 – measured albumin)]

([Ca
⁺²
] in mg/dL, albumin in g/d)

CORRECTED SERUM SODIUM

Corrected serum Na = measured [Na
⁺
] + [0.016 × (measured [glucose] - 100)]

([Na
⁺
] in mEq/L, [glucose] in mg/dL)

FRACTIONAL EXCRETION OF SODIUM

FE
_Na
= (U
_[Na+]
× P
_[Cr]
)/(P
_[Na+]
× U
_[Cr]
) × 100

(U
_[Na+]
and P
_[Na+]
in mEq/L, U
_[Cr]
and P
_[Cr]
in mg/dL)

•
  FE
_Na
< 1% in prerenal states, early ATN, contrast or heme pigment nephropathy, and acute glomerulonephritis.

•
  Not valid when diuretics have been given.

FRACTIONAL EXCRETION OF UREA

FE
_urea
= [(U
_[urea]
× P
_[Cr]
)/(P
_[urea]
× U
_[Cr]
)] × 100

(all units in mg/dL)

•
  FE
_urea
< 35% in prerenal states.

•
  Not affected by diuretics.

MEAN ARTERIAL PRESSURE

MAP = [SBP + (2 × DBP)]/3

OSMOLALITY (SERUM, ESTIMATED)

Calculated serum osm = (2 × [Na+]) + ([glucose]/18) + ([BUN]/2.8)
([Na
⁺
] in mEq/L, [glucose] and [BUN] in mg/dL)

OSMOLAL GAP

Osmolal gap = measured S
_osm
– calculated S
_osm

•
  Causes of increased osmolal gap: decreased serum water, hyperproteinemia, hypertriglyceridemia, and presence of unmeasured osmoles (e.g., sorbitol, glycerol, mannitol, ethanol, isopropyl alcohol, acetone, ethyl ether, methanol, and ethylene glycol).

RETICULOCYTE INDEX

Reticulocyte index = [measured reticulocyte count × (measured Hct/45)]/maturation factor

Maturation factor = 1 + (0.5 × [(45 – Hct)/10])

•
  Good marrow response = 3.0–6.0

•
  Borderline response = 2.0–3.0

•
  Inadequate response = <2.0

MEDICAL EPIDEMIOLOGY

•
  The letters in the following refer to a standard 2 × 2 table presented in
Table 5-1
.

•
  
Sensitivity:
The percentage of patients with the target disease/condition who have a positive result [A/(A + C)]. The greater the sensitivity, the more likely the test will detect patients with the disease. High-sensitivity tests are useful clinically to
rule OUT
a disease (SnOUT) (i.e., a negative test result would virtually exclude the possibility of the disease).

•
  
Specificity:
The percentage of patients without the target disease/condition who have a negative test result [D/(B + D)]. Very specific tests are used to confirm or
rule IN
the presence of disease (SpIN).

•
  
Positive predictive value
(PPV): The percentage of persons with positive test results who actually have the disease/condition [A/(A + B)].

•
  
Negative predictive value
(NPV): The percentage of persons with negative test results in which the disease/condition is absent [D/(C + D)].

•
  
Number needed to treat
(NNT): The number of patients who need to be treated to achieve one additional favorable outcome; calculated as 1/absolute risk reduction (ARR), rounded up to the nearest whole number.

•
  
Number needed to harm
(NNH): The number of patients who, if they received the experimental treatment, would lead to one additional person being harmed compared with patients who receive the control treatment; calculated as 1/absolute risk increase (ARI).

Patient and Staff Relations

6

WORKING WITH ANCILLARY STAFF

•
  Give specific directions and use your judgment, but also give others a chance to make suggestions and solve problems. Effective use of ancillary staff can greatly increase your efficiency (see
Table 6-1
).

•
  A compliment for a job well done goes a long way (others are overworked too), and you will be remembered when you need help. When someone performs exemplary work, let his or her supervisor know.

•
  Criticize in private. When done, offer only nonjudgmental and constructive feedback.

•
  Regard ancillary staff as fellow members of the patient care team; they are often “bothering” you out of concern for the patient and not to harass you. They have valuable insight that often proves important in patient care.

•
  Make efforts to let team members know the plan can save you phone calls and increase sleep.

REFERRING A PATIENT

•
  When referring a patient to the ED or another physician, or transferring a patient, always make a courtesy call first.

•
  Pertinent information includes the following:

•  Who you are.

•  Patient identification information.

•  Succinct history of the problem.

•  Supporting lab data.

•  Suggestions for further evaluation.

•  Likely disposition of the patient.

•  A contact number where you or someone covering for you can be reached for questions or follow-up information.