"
"
The importance of basic hemodynamic monitoring of
neurocritical patients comes from the goal of maintaining brain
autoregulation. Brain autoregulation and other biological signals
are the variables to be monitored by using biomedical sensors.
Complications that may occur in neurocritical patients (e.g.,
sepsis, dehydration, post-cardiac arrest status) make
hemodynamic monitoring of greater importance.
The goals of hemodynamic monitoring in neurocritical care
units are to assess the magnitude of physiological derangements
in critically ill patients and to institute measures to correct the
imbalance.
The following steps should be taken to reach these goals.
Although our review of data may be helpful, the attending
physician should decide what to use and when to use it. Menu to
work with for proper patient management:
1. Pulse oximeter (SpO2) is regarded as one of the most
important advances in critical care monitoring. SpO2
provides a continuous non-invasive method to measure
arterial oxygen saturation, and should be used on every
neurocritical patient. The absorption spectra of both
neurocritical patients comes from the goal of maintaining brain
autoregulation. Brain autoregulation and other biological signals
are the variables to be monitored by using biomedical sensors.
Complications that may occur in neurocritical patients (e.g.,
sepsis, dehydration, post-cardiac arrest status) make
hemodynamic monitoring of greater importance.
The goals of hemodynamic monitoring in neurocritical care
units are to assess the magnitude of physiological derangements
in critically ill patients and to institute measures to correct the
imbalance.
The following steps should be taken to reach these goals.
Although our review of data may be helpful, the attending
physician should decide what to use and when to use it. Menu to
work with for proper patient management:
1. Pulse oximeter (SpO2) is regarded as one of the most
important advances in critical care monitoring. SpO2
provides a continuous non-invasive method to measure
arterial oxygen saturation, and should be used on every
neurocritical patient. The absorption spectra of both
oxyhemoglobin and deoxyhemoglobin and the
characteristics of pulsatile blood can thus be determined.
SpO2 is accurate to within ± 2% for saturations >70%. SpO2 is
widely used in monitoring patients who have a variety of
neurological conditions (Adams 1997), and calculations
made from the processed signals provide estimates of the
tissue or venous and arterial blood and provide an estimate
of the amount of oxygenated hemoglobin and the percent
saturation of hemoglobin by oxygen SaO2, which is not the
same as the PaO2 (partial pressure of oxygen) in the blood
(Adams 1997). The PaO2 and SaO2 measurements of
oxygenation are related through the oxyhemoglobin
dissociation curve. Importantly, SpO2 is a measure of
arterial oxygenation saturation, not arterial oxygen tension
(PaO2). Given the characteristics of the oxygen dissociation
curve, large fluctuations in PaO2 can occur despite minimal
changes in SpO2. In addition to its inability to measure PaO2,
SpO2 provides no measure of ventilation or acid-base status.
Therefore, it cannot be used to determine pH or arterial
carbon dioxide tension. Significant increases in arterial
carbon dioxide can occur with normal readings in SpO2.
Although useful for arterial oxygen saturation, SpO2 should
not be assumed to provide information about ventilation.
Studies have shown that to assure a saturation of 60 torr
(8.0 kPa), an SpO2 of 92% should be maintained in patients
with light skin, whereas 94% saturation may be needed in
patients with dark skin. Oxygenation is considered
adequate if the arterial oxygen saturation is above 95%. The
majority of these patients are placed on positive end
expiratory pressure (PEEP) at 5cm H2O (Curley 1990).
Also, for patients with manifestations consistent with
hypoxemia (e.g., tachycardia, hypotension, anxiety, and
agitation) there is a time delay in pulse oximeter to express
fluctuation in SpO2. Again in hypothermia, low CO2, and
vasoconstriction secondary to drugs or peripheral hypoxia
characteristics of pulsatile blood can thus be determined.
SpO2 is accurate to within ± 2% for saturations >70%. SpO2 is
widely used in monitoring patients who have a variety of
neurological conditions (Adams 1997), and calculations
made from the processed signals provide estimates of the
tissue or venous and arterial blood and provide an estimate
of the amount of oxygenated hemoglobin and the percent
saturation of hemoglobin by oxygen SaO2, which is not the
same as the PaO2 (partial pressure of oxygen) in the blood
(Adams 1997). The PaO2 and SaO2 measurements of
oxygenation are related through the oxyhemoglobin
dissociation curve. Importantly, SpO2 is a measure of
arterial oxygenation saturation, not arterial oxygen tension
(PaO2). Given the characteristics of the oxygen dissociation
curve, large fluctuations in PaO2 can occur despite minimal
changes in SpO2. In addition to its inability to measure PaO2,
SpO2 provides no measure of ventilation or acid-base status.
Therefore, it cannot be used to determine pH or arterial
carbon dioxide tension. Significant increases in arterial
carbon dioxide can occur with normal readings in SpO2.
Although useful for arterial oxygen saturation, SpO2 should
not be assumed to provide information about ventilation.
Studies have shown that to assure a saturation of 60 torr
(8.0 kPa), an SpO2 of 92% should be maintained in patients
with light skin, whereas 94% saturation may be needed in
patients with dark skin. Oxygenation is considered
adequate if the arterial oxygen saturation is above 95%. The
majority of these patients are placed on positive end
expiratory pressure (PEEP) at 5cm H2O (Curley 1990).
Also, for patients with manifestations consistent with
hypoxemia (e.g., tachycardia, hypotension, anxiety, and
agitation) there is a time delay in pulse oximeter to express
fluctuation in SpO2. Again in hypothermia, low CO2, and
vasoconstriction secondary to drugs or peripheral hypoxia
all increase bias, imprecision, and response time for
hypoxic episodes, so we proceed to the next step.
2. Arterial blood gas analysis is widely available in hospitals
and offers direct measurements of many critical
parameters (pH, PaO2, PaCO2). Arterial blood gas analysis is
among the most precise measurements of oxygen tension
and pressure that will reflect tissue oxygenation (García
2011).
3. Non-invasive automated blood pressure devices are
frequently used to obtain non-invasive, intermittent blood
pressure measurements. Measurements of systolic and
diastolic pressure to calculate the mean arterial pressure
(MAP) is mandatory to calculate the cerebral perfusion
pressure. These devices are less accurate in critically ill
patients as well as in those with secondary brain injury.
These less accurate readings can distract the attention of
the caregiver. The evaluation of blood pressure will be
significantly affected by the use of vasopressors. Therefore,
the numeric reading may reflect vasoconstriction in spite
of decreasing perfusion with adequate blood pressure.
4. Invasive blood pressure monitoring for continuous
monitoring and recording of the arterial pressure via an
arterial catheter is preferable to the use of an automated
blood pressure device in hemodynamically unstable
patients (García 2011). The radial artery is most commonly
cannulated because of its superficial location, relative ease
of cannulation, and in most patients, adequate collateral
flow from the ulnar artery. Other potential sites for
percutaneous arterial cannulation include the femoral,
brachial, axillary, ulnar, dorsalis pedis, and posterior tibial
arteries. Possible complications of intra-arterial
monitoring include hematoma, neurologic injury, arterial
embolization, limb ischemia, infection, and inadvertent
intra-arterial injection of drugs. Intra-arterial catheters are
not placed in extremities with potential vascular
insufficiency. However, with proper selection, the
hypoxic episodes, so we proceed to the next step.
2. Arterial blood gas analysis is widely available in hospitals
and offers direct measurements of many critical
parameters (pH, PaO2, PaCO2). Arterial blood gas analysis is
among the most precise measurements of oxygen tension
and pressure that will reflect tissue oxygenation (García
2011).
3. Non-invasive automated blood pressure devices are
frequently used to obtain non-invasive, intermittent blood
pressure measurements. Measurements of systolic and
diastolic pressure to calculate the mean arterial pressure
(MAP) is mandatory to calculate the cerebral perfusion
pressure. These devices are less accurate in critically ill
patients as well as in those with secondary brain injury.
These less accurate readings can distract the attention of
the caregiver. The evaluation of blood pressure will be
significantly affected by the use of vasopressors. Therefore,
the numeric reading may reflect vasoconstriction in spite
of decreasing perfusion with adequate blood pressure.
4. Invasive blood pressure monitoring for continuous
monitoring and recording of the arterial pressure via an
arterial catheter is preferable to the use of an automated
blood pressure device in hemodynamically unstable
patients (García 2011). The radial artery is most commonly
cannulated because of its superficial location, relative ease
of cannulation, and in most patients, adequate collateral
flow from the ulnar artery. Other potential sites for
percutaneous arterial cannulation include the femoral,
brachial, axillary, ulnar, dorsalis pedis, and posterior tibial
arteries. Possible complications of intra-arterial
monitoring include hematoma, neurologic injury, arterial
embolization, limb ischemia, infection, and inadvertent
intra-arterial injection of drugs. Intra-arterial catheters are
not placed in extremities with potential vascular
insufficiency. However, with proper selection, the
complication rate associated with intra-arterial
cannulation is low and the benefits can be important.
5. A Foley catheter, for monitoring of urine output on an
hourly basis or for 24 hours, is a simple and important tool
to monitor volume status of the patient besides renal
perfusion and function. The hourly urine output is a cheap,
simple and indirect method of assessing adequacy of
cardiac output and tissue perfusion.
6. A temperature probe is also indicated for purposes of
monitoring core temperature.
7. Continuous monitoring of volume status and other
parameters:
If the patient is hypotensive, a fluid supplement with 1-2
liters Ringer’s lactate for 30-60 minutes is reasonable.
Subsequent fluid management should be based upon urine
output and maintaining central venous pressure between 5
and 10 mmHg. Monitor potassium, sodium, glucose and
arterial blood gases every 4 hours. Especially if there is
respiratory embarrassment at initial evaluation,
measurement of hematocrit, magnesium, blood urea
nitrogen, creatinine, calcium, liver function tests, urine
analysis, prothrombin, partial thromboplastin times and
phosphate levels are mandatory. If hematocrit is below
30%, transfuse cross-matched blood (Amin 1993).
8. Common indications for central venous cannulation:
measurement of mean central venous pressure, large bore
venous access, administration of irritating drugs and or
parenteral nutrition, hemodialysis, placement of a
pulmonary artery catheter.
Placement of a pulmonary artery catheter is indicated to
obtain direct and calculated hemodynamic data that cannot
be obtained through less invasive means (Sakr 2005).
The goal for all critically ill patients is to provide
adequate oxygen for cellular use through suitable oxygen
consumption, which is variable between tissues, and the
changes of the basal or active metabolic rate for each cell.
cannulation is low and the benefits can be important.
5. A Foley catheter, for monitoring of urine output on an
hourly basis or for 24 hours, is a simple and important tool
to monitor volume status of the patient besides renal
perfusion and function. The hourly urine output is a cheap,
simple and indirect method of assessing adequacy of
cardiac output and tissue perfusion.
6. A temperature probe is also indicated for purposes of
monitoring core temperature.
7. Continuous monitoring of volume status and other
parameters:
If the patient is hypotensive, a fluid supplement with 1-2
liters Ringer’s lactate for 30-60 minutes is reasonable.
Subsequent fluid management should be based upon urine
output and maintaining central venous pressure between 5
and 10 mmHg. Monitor potassium, sodium, glucose and
arterial blood gases every 4 hours. Especially if there is
respiratory embarrassment at initial evaluation,
measurement of hematocrit, magnesium, blood urea
nitrogen, creatinine, calcium, liver function tests, urine
analysis, prothrombin, partial thromboplastin times and
phosphate levels are mandatory. If hematocrit is below
30%, transfuse cross-matched blood (Amin 1993).
8. Common indications for central venous cannulation:
measurement of mean central venous pressure, large bore
venous access, administration of irritating drugs and or
parenteral nutrition, hemodialysis, placement of a
pulmonary artery catheter.
Placement of a pulmonary artery catheter is indicated to
obtain direct and calculated hemodynamic data that cannot
be obtained through less invasive means (Sakr 2005).
The goal for all critically ill patients is to provide
adequate oxygen for cellular use through suitable oxygen
consumption, which is variable between tissues, and the
changes of the basal or active metabolic rate for each cell.
Oxygen delivery to tissues and organs responds to many
local systemic variables to keep cellular homeostasis.
Pulmonary artery balloon flotation catheter insertion may
be necessary for full assessment of these parameters, and of
evaluation of determinants of cardiac output and the
oxygen content of circulating blood, on which oxygen
delivery is dependent. In the presence of positive pressure
ventilation with PEEP, central venous and pulmonary
artery occlusion pressures may be falsely elevated and need
to be interpreted with caution. The fluid challenge is the
only way to interpret Central Venous Pressure (CVP) or
Pulmonary Artery Occlusion Pressure (PAOP).
Assessment of the determinants of cardiac output will
proceed as follows:
a. Heart rate and rhythm assisted by pulse oximeter and
electrocardiogram.
b. Preload assessed right and left heart; right heart
through neck vein distension, liver enlargement and
central venous pressure assessment; left heart through
dyspnea on exertion, orthopnea, arterial blood
pressure; pulmonary artery occlusion pressure and
arterial pressure through waveform analysis (Sakr
2005).
c. Afterload assisted by mean arterial blood pressure and
systemic vascular resistance; contractility can be
assessed by ejection fraction and echocardiography.
As discussed earlier, the goal of hemodynamic monitoring in
neurocritical care units is to assess the magnitude of
physiological derangements in critically ill patients and to
institute measures to correct the imbalance. Basic hemodynamic
monitoring consists of clinical examination, invasive arterial
monitoring, central venous pressure monitoring, hourly urine
output, central venous oxygen saturation and echocardiography.
Dynamic indices of fluid responsiveness such as the pulse
pressure variation and stroke volume variation can guide
local systemic variables to keep cellular homeostasis.
Pulmonary artery balloon flotation catheter insertion may
be necessary for full assessment of these parameters, and of
evaluation of determinants of cardiac output and the
oxygen content of circulating blood, on which oxygen
delivery is dependent. In the presence of positive pressure
ventilation with PEEP, central venous and pulmonary
artery occlusion pressures may be falsely elevated and need
to be interpreted with caution. The fluid challenge is the
only way to interpret Central Venous Pressure (CVP) or
Pulmonary Artery Occlusion Pressure (PAOP).
Assessment of the determinants of cardiac output will
proceed as follows:
a. Heart rate and rhythm assisted by pulse oximeter and
electrocardiogram.
b. Preload assessed right and left heart; right heart
through neck vein distension, liver enlargement and
central venous pressure assessment; left heart through
dyspnea on exertion, orthopnea, arterial blood
pressure; pulmonary artery occlusion pressure and
arterial pressure through waveform analysis (Sakr
2005).
c. Afterload assisted by mean arterial blood pressure and
systemic vascular resistance; contractility can be
assessed by ejection fraction and echocardiography.
As discussed earlier, the goal of hemodynamic monitoring in
neurocritical care units is to assess the magnitude of
physiological derangements in critically ill patients and to
institute measures to correct the imbalance. Basic hemodynamic
monitoring consists of clinical examination, invasive arterial
monitoring, central venous pressure monitoring, hourly urine
output, central venous oxygen saturation and echocardiography.
Dynamic indices of fluid responsiveness such as the pulse
pressure variation and stroke volume variation can guide
decision making for fluid resuscitation. Cardiac output is
traditionally measured using the pulmonary artery catheter; less
invasive methods now available include the pulse contour
analysis and arterial pulse pressure derived methods. It is
essential to determine whether the hemodynamic therapy is
resulting in an adequate supply of oxygen to the tissues
proportionate to their demand. Mixed and central venous
oxygen saturation and lactate levels are commonly used to
determine the balance between oxygen supply and demand
(Walley 2011).
traditionally measured using the pulmonary artery catheter; less
invasive methods now available include the pulse contour
analysis and arterial pulse pressure derived methods. It is
essential to determine whether the hemodynamic therapy is
resulting in an adequate supply of oxygen to the tissues
proportionate to their demand. Mixed and central venous
oxygen saturation and lactate levels are commonly used to
determine the balance between oxygen supply and demand
(Walley 2011).
ليست هناك تعليقات:
إرسال تعليق