Physiologic Monitoring Of the Surgical patient Flashcards
(18 cards)
The point of critical oxygen delivery (DO2crit)
Represents the transition from supply independet to supply dependent oxygen uptake and is increased in sepsis
- Microcirculatory derangements such as those seen in sepsis, will shift this point higher. Below a critical threshold of oxygen delivery, increased oxygen extraction cannot compensate for the delivery deficit; hence oxygen consumption begins to decrease
Least ifluenced by an underdamped or overdamped intra-arterial blood pressure monitoring system
Mean arterial pressure
- Underdamped
- systolic pressure is overestimated
- diastolic pressure underestimated
- Overdamped
- systolic pressure is underestiamted
- diastolic pressure woll be overestimated
Regarding ECG monitoring in the ICU
Lead V4 is the most sensistive for dd=etecting perioperative ischemia
- to detect 95% of the ischemic episodes, two or more precodial leads were necessary. Thus, continuous 12-lead ECG monitoring may provide greater sensitivity than 3 lead ECG
Preload
- It is approximated by the left ventricular EDP as estimated with pulmonary artery occlusion pressure(PAOP)
- for the right ventricle,central venous pressure approximates right ventricular end diastolic pressure
EDP
- The raltionship between EDP and preload is exponential
- determined by both volume and compliance of the ventricle
- The relationship between EDP and end diastolic volume (EDV) can be changed with pharmacologic agents
- EDP is often used as a surrogate for EDV because it is easier to approximately n the clinical setting
The end systolic pressure volume line
- The slope will become steeper if contractility is increased
- small changes in preload and or afterload will result in shifts of point defining end of sytole
- These end systolic points on the pressure versus volume diagram describe a straight line, known as the end systolic pressure volume line
The thermodilution technique for determining cardiac output
- influenced by respiratory cycle due to changes in blood temperature QT
- The relationship used by thermodilution technique for caculating QT is called the Stewart-hamilton equation
QT = [V x TB - TI ) x K1 x K2] / fTB (t) dt
- V = volume is the blood of the indicator injected
- TB = temperatutre of blood
- TI = is the temperature of the indicatior
- K1 = constant that is the function of the specific heats of blood
- K2 = empirically derived constant
- fTB (t) dt is the area under the time temperature curve
True the fractional saturation of hemoglobin in mixed venous blood (SVO2)
- It will decrease with worsening heart failure
- It will decrease with worsening anemia
- It will decrease with fever
The Fick equation for cardiac output can be rearranged as follows
CVO2 = Cao2 -VO2/QT
Subnormal vaues of SVO2 can be caused by a decrease in QT (due to heart failure or hypovolemia)m a decrease in Sao2 (due to intrinsic pulmonary disease), a decrease in Hgb (anemia) or an increase in metabolic rate (due to seizures or fever)
Surviving Sepsis Campaign, the initial resuscitation of sepsis-induced hypoperfusion
- The goals of resuscitation be met within the 6 hours of management
- should include of the following
- CVP 8 to 12 mm Hg
- MAP >65 mm Hg
- urine output>0.5 mL/kg/h
- ScVO2 of 70%
- SVO2 of 65%
Noninvasive methods of measuring cardiac output
- Allow for continuos measurement of QT
-
Impedance cardiography
- noninvasive
- provides a continuous readout of QT
- does not require extensive training
- not sufficiently reliable
- poor correlation with thermodilution
-
Pulse contour analysis
- comparable in accuracy to standard PAC thermodilution methods
- less invasive (transcardiac catheterization is not needed)
- non invasive photoplethysmographic measurements of arterial pressure
Using pulse pressure variability to determine preload responsiveness
- is a better predictor of preload responsiveness than CVP
- PPV
- defined as the difference between the maximal pulse pressrue and the minimal pulse pressure divided by the average of these two pressures
- Atrial arrhythmias can interfere with the usefulness of this technique
Strategies for increasing oxygen delivery in mechanically ventialted,critically ill paients
- Increasing Sao2 by increasing inspiratory time
- Sao2 in mechanicaly ventilated patients depends on the
- mean airway pressure
- fraction of inspiredoxygen
- SVO2
- Inreasing Sao2
- increase mean airwaypressure by increasing PEEP or inspiratory time
- FiO2 can be increased to a maximum 1.0 by decreasing the amount of room air mixed with the oxygen supplied to the ventilator
- SVO2 can be increased by increasing Hgb or Qt or decreasing oxygen utilization (muscle relaxant and sedation)
True regarding airways pressures
- Bronchospasm will cause increased peak pressure with relatively normal plateau
- Pnuemothorax will cause increased peak and plateau pressures
- Plateau pressure isindependent of airways resistance
The peak pressure measured at the end of inspiration is is a function of the tidal volume, the resistance od he airways, lung chest wall compliance, and peak inspiratory flow.
- If both Peak and palteau are increased then the underlying problem is a decreased in compliance in the lung/chest wall
- pneumothorax, hemothorax, lobar atelectasis, pulmonary edema, pneumonia, acute respiratory distress syndrome.
- When peak is increased but plateau is relatively normal
- the primary problem is an increase in airway resistance, such as occurs with bronchopasm, use of a small caliber endotracheal tube or kingking or obstruction of a small caliber endotracheal tube
Causes increase in end-tidal CO2
- Reduced minute ventilation
- Increased metabolic rate
Decreased in end-tidal CO2
- obstruction of sampling tubing
- loss of ariway
- disconnection or obstruction
- ventilator malfunction or a marked decrease Qt
- If ventilator is working normal
- cardiac arrest
- massive pulmonary embolism
- cardiogenic shock
- hyperventilation
Monitoring of intracranial pressure
- GCS <8 with an abnormal CT scan
- Severe TBI in a patient older than 40 years and sytolic blood pressure less than 90 mmHg, unilarteral or bilateral posturing
- Fulminant hepatic failure with coma and cerebral edema on CT
- Patient swith acute subarachnoid hemorrhage with coma or neurologic deterioration, intracranial hemorrhage with intraventricular blood, ischemic middle cerebral artery
- global cerebral ischemia or anoxia with cerebral edema on CT scan.
Currently accepted uses of transcranial Doppler
TCD measurement of middle and anterior cerebral artery blood flow
- Diagnosing vasopasm after subarachnoid hemorrhage
- Confirm brain death after clinical examination in patients under the influence of CNS depressants
- Confirming brain death after clinical examination in patients with metabolic encephalopathy
Regarding jugular venous oximetry in patients with TBI
- It requires placement of a catheter in the jugular bulb
Changes in jugular venous oxygen saturation (SjO2) reflect changes in the difference between cerebral oxygen delivery and demand
- Decrease in SJO2 reflects cerebral hypoperfusion
- SjO2 cannpt detect decrease in regional cerebal blood flow if overall perduson is normal or above normal
- Increase in SJO2 reflects hyperemia
Monitoring local brain tissue oxygen tension (PbtO2) in patient swith severe TBI
Has been shown to lower mortality when compared with ICP monitoring alone
- Standard of care for patients with severe TBI includes ICP and CPP monitoring
- Early detection of brain tissue ischemia despite normal ICP and CPP
- PbtO2
- Normal : 20 to 40 mmHg
- Critical levels : 8 to 10 mmHg
