Page 277 - Clinical Application of Mechanical Ventilation

Monitoring in Mechanical Ventilation 243

VITAL SIGNS

Vital signs (heart rate, blood pressure, respiratory rate, and temperature) can pro-
vide very useful information on the overall condition of a patient. During me-
chanical ventilation, changes in vital signs often indicate changes in the patient’s
cardiopulmonary status.

Heart Rate

In the intensive care unit, heart rate assessment is readily available on the electro-
Normal adult heart rate cardiograph (ECG) monitor. High and low alarms can be set on the monitor to
is between 60 and 100/min.
warn of tachycardia and bradycardia.

Tachycardia. Tachycardia in adults is defined as a heart rate higher than 100/min.
During mechanical ventilation, some conditions that may increase a patient’s
Tachycardia may be
caused by hypoxemia, hypo- heart rate are hypoxemia, pain, anxiety and stress, fever, drug reactions, and
volemia, pain, anxiety and myocardial infarction. Tachycardia can alert the clinician to blood volume or car-
stress, fever, drug reactions,
and myocardial infarction. diac output deficits. Increase in heart rate must be evaluated as part of the larger
picture as it can be secondary to extreme conditions ranging from hypovolemia
to anxiety.

hypoxemia: Deficiency of oxygen Bradycardia. Bradycardia in adults is defined as a heart rate lower than 60/min.
in blood; low PaO 2 . Bradycardia often occurs with vagal stimulation during endotracheal suctioning.
Preoxygenation is often necessary to minimize the occurrence of arterial desatura-
tion and arrhythmias (e.g., premature ventricular contraction) during suctioning.
Since arterial desaturation occurs in as little as 5 sec during suctioning, hypoxia
hypoxia: Deficiency of oxygen
in tissues. and cardiac complications can happen rather rapidly. When arrhythmia or brady-
cardia occurs, endotracheal suctioning must be stopped and 100% oxygen should
be provided to the patient immediately (Burton et al., 1997).
Bradycardia, if it appears together with a low cardiac output, can be ominous and
may suggest a decrease in coronary blood flow. Table 9-1 outlines the conditions
that affect the heart rate.

Blood Pressure

Continuous blood pressure monitoring in the critically ill patient is usually done via
an indwelling arterial catheter interfaced with a pressure monitor. The most common
insertion site for the catheter is the radial artery. Other sites include the brachial,
femoral, popliteal, and dorsalis pedis arteries.

Hypertension. Hypertension, higher than normal blood pressure, may be caused
Fluid overload, vasocon-
striction, stress, anxiety, and by acute or chronic patient conditions. Acute conditions such as fluid overload,
pain may lead to hypertension. vasoconstriction, stress, anxiety, and pain may lead to hypertension. Patients
who have a history of congestive heart failure (CHF), cardiovascular disease, or
polycythemia may develop hypertension, which can become a complicating factor
during mechanical ventilation.

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