Body Fluid Compartments

Kidneys = homeostasis of volume, pressure, composition of blood

Ins and Outs
  
60:40:20 rule   60% of body weight = total water; 40% intracellular: 
20% extracellular (= 15% interstitial fluid + 5% plasma)

Kidneys - 1 million nephrons per kidney

glomerulus - has two arterioles in series; afferent and efferent arterioles

Kidney functions

• filtration
• secretion
• reabsorption

• endocrine functions
• renin (enzyme) - long term control of blood volume/pressure
• EPO - stimulated by Hypoxia-inducible factor (HIF-1)
• Calcitriol - active form of Vitamin D

Regulation of Body Fluid Levels

• water moves by osmosis between inside and outside of cells - sodium is the most important "osmolyte"
• water moves by Starling forces between inside and outside of capillaries - this includes osmosis due to colloid osmotic pressure difference

Calculating the volume of fluid compartments

Uses definitions of concentration (C), amount (A), and volume (V)

C = A/V  A = CV   V = A/C     for substances trapped in a compartment; i.e., Amount in = Amount after dilution.   Amount in = VinCin  =  Amount after = VaCa

Va = ViCi/Ca     
Example:  1 mg of Evans blue dye is dissolved in 1 ml saline and injected into a patient's vein.  After 10 minutes, a sample of the patient's blood is taken and the Evans blue concentration if found to be 0.1 mg/L plasma.  
Va = ViCi/Ca  = 1mg = 0.1 mg/L = 10 L

Plasma osmolality calculated from sodium, glucose, and BUN  (2 x Na is good approximation)

normal values:  Na = 140; glucose = 100; BUN = 20.

osmolality = 2x140 + 100/18 +20/2.8 = 280 + 5.5 + 7.1 = 292.6

Increased pleural fluid - pleural effusion

increased pleural fluid - pleural effusion

• altered Starling forces
• decreased lymph flow

evaluation of pleural effusion

• sample fluid if pt. has infection (e.g., pneumonia) - thoracentesis

atelectasis mimics pleural effusion (blockage of left main-stem bronchus)

neurovascular bundle is under rib.  needle should go just above rib.

NEJM medical procedures website

Pleural fluid studies

pH low in pts. with high tumor burden

cyology to look for malignant cells

transudate (pressure/oncotic forces) or exudate (capillary damage, inflammation)

• exudate
• pleural fluid protein/serum protein > 0.5
• pleural fluid LDH/serum LDH >0.6
• inflammation of the lung or pleural space
• top 3 causes
• infection
• parapneumonic effusion
• drain when pH < 7.2, pus, glucose <60, LDH > 1000  High LDH indicates cell or tissue damage
• Tuberculosis pleural effusion - immunologic reaction to TB mycobacteria.  high lymphocytes.
• pulmonary embolism
• tend to be blood tinged
• may be transudates
• malignancy 
• blood tinged pleural effusion, high lymphocytes
• other
• collagen vascular disease (lupus, arthritis)
• subdiaphragmatic inflammation
• drug reactions
• hypothyroidism
• asbestos exposure
• pleural fluid chemistry
• lymphocytosis - TB, malignancy, chylothorax (rupture of thoracic duct = increased lymphatic fluid)
• eosinophilia - blood or air in pleural space (mechanism unknown), parasitic or fungal infections, prior asbestos exposure.
• low pH (<7.2) - malignancy, esophageal rupture, parapneumonic effusion
• pleural fibrosis
• undrained blood or effusion in pleural space

• transudate
• increased pulmonary capillary pressure (left side heart failure)
• increased bronchial capillary pressure (right side heart failure)

pleural effusion (NEJM article)

Pulmonary Emboli; Pulmonary Hypertension

Pulmonary Hypertension when PAP > 25 mm Hg at rest

symptoms

early = none

after right heart starts to fail

lower body edema

RUQ pain or fullness (liver swollen)

sob on exertion

weakness, fatigue

direct signs

• increased or palpable P2
• systolic ejection murmur

indirect signs

• signs of RV hypertrophy
• para-sternal heave (lift)
• right sided S4
• increased atrial "a" wave
•  
• signs of RV failure
• tricuspid regurgitation (due to hypertrophy)
• "v" wave from tricuspid regurgitation 
• right sided S3
• peripheral edema

Diagnosis of pulmonary hypertension

direct measure of PAP

Swan Ganz

indirect measure of PAP

echo Doppler

Etiologies of Pulmonary Hypertension

Pathophysiologic

• chronic increase in flow = remodeling
• increase in pulmonary vascular resistance (e.g., hypoxia)
• increase in pulmonary venous pressure (Left heart failure)

Classifications of Pulmonary Hypertension (Dana Point 2008)

• Pulmonary Arterial Hypertension

• idiopathic (young women)
• weight loss drugs

• PH due to left heart failure
• PH with lung disease/hypoxia
• Chronic pulmonary thromboemboli

Workup

liver function tests, echo, CXR, V/Q scan

Treatment

drugs - NO pathway, endothelin pathway, prostacyclin pathway

NO works but patients get tachyphylactic in 1-2 days

PDE5 inhibitor

prostacyclins = vasodilator (gold standard for patients with severe pulmonary HTN)

anticoagulation

atrial septostomy - create a shunt

transplant - heart and lung

Pulmonary Embolism

risk factors

classic = Virchow's triad = stasis, hypercoagulability, endothelial damage

new = acquired or congenital

clinical signs

pleural friction rub (infarcted tissue)

ECG changes: tachy, right axis, RBBB, S1Q3T3

ABG: low PO2, low PCO2

Well's Criteria to determine whether or not DVT and/or PE

Tests for PE

• D-dimer = crosslinked fibrin   (clotting always includes fibrinolysis).  sensitive but lots of false positives = not specific since d-dimers occur in inflammation, malignancy, pregnancy, recent surgery.
• Ultrasound of legs.  clot in legs often means clot in lungs.  negative test does not rule out PE.
• V/Q scan - radioactive xenon for ventilation scan.  microspheres for perfusion.  looks for areas that are ventilated but not perfused.  no risk for renal damage.
• CT scan
• timed bolus of IV contrast to light up  pulmonary arteries.  more senstive and specific than V/Q.  lifetime increase in lung cancer risk with 1 CT scan = 1 in 1000.
• Pulmonary angiography (not used currently)

Treatment for  PE

• anticoagulant meds - heparin or low MW heparin
• remove aggravating cause
• thrombolysis (TPA) clot busters  (mostly for severe cases, hypotension, heart strain = risk of cerebral hemorrhage)
• IVC filters for pts. with LE DVT.