Table of Contents
- Clinical Monitoring
- Invasive Monitoring
- Invasive Blood Pressure Monitors
- Central Venous Pressure
- Pulmonary Arterial Pressure
- Trans-esophageal Echocardiography (TEEC)
- Sensory and Motor Potentials
- Electroencephalography (EEG)
- Bispectral index (BIS)
- Electrocorticography (ECoG)
- Fetal Heart Monitor and Uterine Contraction Monitor
Clinical patient monitoring during any type of anesthesia includes assessment and recording of arterial pulse, blood pressure, ventilation and oxygen saturation (by observing the color of the patient’s skin and mucous membranes and correlating with pulse oximetry values) at regular intervals. A vigilant provider continuously observes the patient, anticipates problems and corrects them promptly.
Monitors, or devices which can record patient’s parameters without having to be placed inside the body, include blood pressure cuff, pulse oximeter, electrocardiogram, temperature probe, oxygen analyzer and carbon dioxide analyzer (capnograph).
Invasive monitoring is useful to observe and maintain adequate hemodynamic status in an anesthetized patient. This helps to ensure adequate tissue perfusion, prevents organ dysfunction and death. It is especially important in high-risk patients, patients undergoing cardiac, neurosurgical or lengthy surgical procedures, or when major blood loss during surgery is anticipated.
Monitors required for high-risk patients include:
- Invasive blood monitors: for blood pressure, central venous pressure and pulmonary arterial pressure
- Intracranial pressure monitor
- Trans-esophageal echocardiography (TEEC);
- Sensory and motor potentials
- Fetal heart monitor
- Uterine contraction monitor
- Cerebral monitors (BIS, cerebral oximetry) – transcranial cerebral oximetry is a non-invasive technique of detecting cerebral oxygenation.
Invasive Blood Pressure Monitors
Hemodynamic monitoring involves measuring the systemic and the pulmonary arterial and venous pressures and the cardiac output. To facilitate this, either a central line or an arterial line has to be introduced in the patient’s body.
Central line is introduced through the internal or external jugular veins or through the femoral and subclavian veins. It can be difficult to insert a central line in morbidly obese patients, in patients with thyromegaly or anatomical abnormalities.
Arterial line: invasive blood pressure measurement is conducted by placing a cannula in any peripheral artery, e.g., radial, brachial, dorsalis pedis or the femoral artery. The cannula is flushed with normal saline–heparin to prevent clotting. It is connected to a transducer device which converts the mechanical energy of diaphragmatic movement with arterial pulsation to electrical energy and displays it as a blood pressure reading on the monitor.
Disadvantages of invasive blood pressure monitoring are:
- Thrombus or hematoma formation
- Accidentally injecting drugs through the arterial line.
Central Venous Pressure
The central venous pressure (CVP) measures the right atrial and vena cava blood pressure directly. It helps to assess the fluid status and right ventricular function of the patient.
A multi-lumen catheter is introduced through the internal or external jugular vein or the subclavian vein. The tip of the catheter is located in the lower one-third of the superior vena cava, while the proximal end is connected to a pressure monitoring device.
The catheter is also used for transfusion of fluids, drugs which cause thrombophlebitis, parenteral nutrition and venous blood tests.
Pulmonary Arterial Pressure
A balloon-tipped Swan-Ganz catheter is used to measure the pulmonary arterial, right atrial and left ventricular pressures. It helps to assess left ventricular and cardiac function.
Intracranial pressure monitor
It is important to measure intracranial pressure in patients with head injury, hydrocephalus, intracranial tumors, cerebral edema and encephalopathies.
Monitoring intracranial pressure helps to detect and intervene early in case of elevated pressure, thereby maintaining the ideal cerebral perfusion pressure. If the intracranial pressure is maintained within the normal range for 48 to 72 hours, or if the patient shows signs of neurological improvement, then the intracranial pressure monitoring can be withdrawn.
Trans-esophageal Echocardiography (TEEC)
TEEC is an endoscope-guided ultrasound transducer which is threaded through the esophagus to obtain dynamic images of the chambers of the heart and the valves as well as cardiac function. It is useful to assess the intra-operative as well as immediate post-operative cardiac status in high-risk patients.
Sensory and Motor Potentials
Intraoperative monitoring of sensory and motor potentials is used to assess the neural pathways. The sensory potentials assess the ascending sensory tracts for integrity, while the motor potentials assess the integrity of the descending motor pathways. Intraoperative monitoring helps to prevent iatrogenic nervous system injury. Constant levels of the anesthetic drugs have to be maintained while recording these potentials.
EEG is a sensitive indicator of changes in the cerebral perfusion. It is used for intraoperative monitoring during carotid endarterectomy and aneurysmectomy as it can detect changes in cerebral perfusion when the carotid artery is clamped. EEG is also useful to monitor cerebral perfusion in patients with hypothermic circulatory arrest during cardiac surgery.
Bispectral index (BIS)
BIS is an algorithmic index based on EEG parameters, and it measures the depth of general anesthesia. The BIS monitor provides a single number between 0 to 100. Appropriate level of anesthesia is indicated by a BIS value ranging between 40 and 60.
ECoG is used during surgeries for the treatment of seizures. During these surgeries, entire regions of the cortex responsible for causing the seizures have to be resected. ECoG provides a map for the resection by indicating lesion margins which are occasionally undetectable with inspection or neuroimaging.
It is important for the anesthesia provider to adjust doses of the anesthesia drugs during deep anesthesia as most anesthesia agents suppress the seizure spikes and may interfere with the monitoring ability of the ECoG.
Fetal Heart Monitor and Uterine Contraction Monitor
Fetal heart monitoring is indicated for non-obstetric surgeries during pregnancy. Intraoperative fetal heart monitoring helps to identify any factors (anesthesia agents, oxygenation, etc.) adversely influencing the well-being of the fetus and to position the patient and assess oxygen requirements.
In pre-viable fetuses, ultrasound monitoring of the fetal heart rate before and after the surgery is advisable. Simultaneous electronic fetal heart rate and uterine contraction monitoring before and after completion of the procedure is essential in a fetus considered viable.