Monitoring and Management During Anesthesia
During surgical anesthesia, various factors such as the surgical condition or comorbid diseases, anesthesia methods and drugs, surgical trauma and blood loss, and changes in body positioning may exert different degrees of impact on physiological functions, potentially posing life-threatening risks in severe cases. For this reason, changes in physiological functions during anesthesia require close observation and monitoring. Proactive measures should be taken to prevent significant physiological disturbances. If such disturbances occur, early detection and timely intervention are critical to minimizing severe complications.
Respiratory Monitoring and Management
Respiratory function is the most easily affected during anesthesia. General anesthesia may lead to varying degrees of respiratory depression, while a high spinal blockade during neuraxial anesthesia may impair respiratory muscle strength and cause severe respiratory depression. Factors such as the use of anesthetic adjuvants, surgical positioning, and coexisting respiratory diseases also have a significant influence on respiratory management during anesthesia. Maintaining normal respiratory function through appropriate airway management techniques is a crucial aspect of anesthetic care.
Normal respiratory function is defined by the maintenance of arterial partial pressure of oxygen (PaO2), arterial partial pressure of carbon dioxide (PaCO2), and arterial pH (also influenced by metabolic factors) within their normal ranges. These parameters are the primary indicators of adequate respiratory management. For patients with spontaneous breathing, the type of breathing (thoracic or abdominal), as well as its amplitude, frequency, and rhythm, should be observed. Additionally, the color of the patient’s lips, mucous membranes, skin, and surgical site bleeding should be monitored to detect potential airway obstruction, hypoxia, or carbon dioxide retention. During anesthesia, continuous monitoring of oxygen saturation (SpO2) is required.
For patients under general anesthesia with controlled ventilation, parameters such as tidal volume, respiratory rate, airway pressure, and end-tidal CO2 concentration (PETCO2) should be monitored. Arterial blood gas analysis may also be performed if necessary to ensure normal respiratory function.
Circulatory Monitoring and Management
Maintaining stable circulatory function and satisfactory organ perfusion is a critical task in anesthetic management during surgery, as changes in the circulatory system directly impact patient safety and postoperative recovery. Routine monitoring during anesthesia includes heart rate, blood pressure, and electrocardiograms, with blood pressure, heart rate, pulse rate, and other parameters measured and recorded at intervals of 5 to 10 minutes. Important surgical milestones, blood loss, fluid intake, transfusion volume, urine output, and the use of vasoactive medications should also be documented.
For major surgeries where significant hemodynamic fluctuations are anticipated or in patients with severe cardiovascular or cerebrovascular conditions, advanced hemodynamic monitoring methods such as direct arterial blood pressure monitoring, transesophageal ultrasound, or continuous cardiac output monitoring may be employed if necessary.
Possible causes of circulatory dysfunction during anesthesia include pathophysiological changes due to the patient’s underlying diseases, as well as the effects of anesthetic agents, surgical trauma, changes in body positioning, intra-abdominal pressure from laparoscopic procedures, or blood loss. When circulatory dysfunction occurs, identifying the underlying causes and contributing factors is important. Accurate assessments of blood volume, cardiac function, and vascular resistance are necessary to provide targeted treatment.
Maintaining adequate and effective circulatory blood volume during anesthesia is particularly important, as hypotension is often linked to absolute or relative hypovolemia. It is necessary to account for factors such as cardiac function, renal function, preoperative fasting, dehydration, intraoperative blood loss, and perioperative fluid loss when replacing fluids. Setting up necessary circulatory monitoring measures helps guide intraoperative fluid therapy.
Inadequately deep anesthesia may cause a physiologic stress response, leading to elevated blood pressure and increased heart rate, while excessively deep anesthesia may suppress myocardial contractility, induce peripheral vasodilation, and reduce vascular resistance, ultimately causing hypotension. Timely adjustment of anesthetic depth based on the patient’s condition and surgical requirements is thus essential to maintaining circulatory stability.
Various types of shock, including hypovolemic shock (e.g., caused by significant blood loss), obstructive shock (e.g., acute pulmonary embolism), distributive shock (e.g., septic shock), and cardiogenic shock (e.g., acute myocardial infarction), may occur during surgery. In cases of acute severe hypotension, factors such as the patient’s medical history, surgical circumstances, anesthetic interventions, and hemodynamic monitoring results should be considered to promptly identify the underlying cause and implement appropriate treatment. In situations where necessary, vasoactive drugs may be administered to support circulatory function, ensure perfusion of vital organs, and reduce the adverse effects of hypotension on the body.
Controlled Hypotension
In certain circumstances, controlled hypotension is employed during anesthesia to achieve specific clinical goals. These may include reducing vascular tension to facilitate surgical procedures (e.g., for patent ductus arteriosus or intracranial aneurysm surgeries), minimizing bleeding in the surgical field for improved visibility and reduced blood loss (e.g., for spinal or posterior fossa surgeries), or controlling excessively elevated blood pressure to prevent cardiovascular complications (e.g., myocardial ischemia or acute pulmonary edema). Controlled hypotension involves reducing arterial blood pressure to a predetermined level using medications and/or anesthetic techniques.
Lowering blood pressure carries the potential risk of reducing blood flow to vital organs such as the brain, heart, and kidneys, potentially leading to hypoxia and organ dysfunction. Therefore, appropriate indications and blood pressure control standards must be strictly observed. Enhanced monitoring is essential during controlled hypotension to maintain normal intravascular volume, tissue perfusion, and oxygen supply to critical organs within physiological ranges.
Patients with severe organ diseases (e.g., heart disease, hypertension, cerebral ischemia, liver, or renal dysfunction), disturbances in acid-base balance, hypovolemia, shock, or severe anemia are contraindicated for controlled hypotension. Increasing the concentration of isoflurane can achieve short-term hypotension as it significantly reduces peripheral vascular resistance with minimal effects on myocardial contractility. For longer durations of blood pressure reduction, vasoactive drugs such as sodium nitroprusside, nitroglycerin, or nicardipine may be used in combination with anesthetic techniques. The impact of patient positioning on blood pressure should also be carefully considered.
For patients with normal preoperative blood pressure, it is generally recommended that systolic blood pressure not fall below 80 mmHg, or that mean arterial pressure (MAP) is maintained between 50 and 65 mmHg. Alternatively, a reduction of no more than 30% from baseline blood pressure may serve as the standard, with adjustments made based on surgical field bleeding and other intraoperative factors.
Monitoring and Management of Body Temperature
Body temperature is a critical vital sign, making intraoperative temperature monitoring necessary. Pediatric patients are more prone to temperature abnormalities during surgery due to immature temperature regulation centers and relatively larger body surface area. Hyperthermia can accelerate metabolism and increase oxygen consumption, potentially leading to severe issues such as metabolic acidosis and febrile convulsions.
Hypothermia can slow drug metabolism, resulting in reduced anesthetic tolerance and an increased risk of excessive anesthetic depth, leading to circulatory depression and prolonged recovery time after anesthesia. Hypothermia may also increase the likelihood of cardiovascular complications, potentially causing severe outcomes such as ventricular fibrillation. Additionally, hypothermia impairs coagulation function, increases blood loss, heightens the risk of wound infection, and delays wound healing. Factors such as low operating room temperatures, unheated intravenous fluids, cold washing solutions for surgical fields, and large surgical exposure areas significantly raise the likelihood of intraoperative hypothermia.
Common methods of intraoperative temperature monitoring include nasopharyngeal temperature measurement. In certain situations (e.g., during cardiopulmonary bypass), central temperatures such as esophageal or rectal temperatures are monitored. Frequently used warming measures during surgery include thermal blankets, forced-air warming devices, and fluid warmers.
Certain surgical procedures require induced hypothermia to specific levels in order to decrease metabolic activity and preserve or temporarily pause cellular function. Mild hypothermia (32–35°C) is suitable for patients undergoing brain resuscitation or neurosurgical procedures, as it allows for longer periods of cerebral circulation arrest, reduced intracranial pressure, and attenuation of cerebral edema. Moderate hypothermia (26–31°C) is often used in short cardiac surgeries or major vascular surgeries requiring arterial trunk occlusion for the preservation of distal organ function. Deep hypothermia (below 25°C) is typically combined with cardiopulmonary bypass for the execution of complex intracardiac surgeries.
Other Considerations
For patients not under general anesthesia, it is important to monitor changes in consciousness and mental status during the procedure. Severe hypotension and hypoxemia may present as agitation, apathy, or even loss of consciousness. Toxic reactions to local anesthetics may cause symptoms such as heightened mental excitation, with severe cases leading to seizures.
The monitoring and management of blood electrolytes, acid-base balance, blood glucose levels, and coagulation function are also critical during anesthesia. Additional specialized monitoring techniques may be required based on the type of anesthesia and surgical needs. These include anesthetic depth monitoring, neuromuscular blockade monitoring, recurrent laryngeal nerve function monitoring, and sensory and motor evoked potential monitoring.
Monitoring and Management During the Anesthetic Recovery Period
In the anesthetic recovery period, the physiological effects of surgery and anesthesia on the patient may not be fully resolved. During this time, respiratory and circulatory functions often remain unstable, and protective reflexes may not yet be fully restored. The potential risks during this period are comparable to those in the anesthesia induction phase. Therefore, adequate management of the postanesthesia care unit (PACU) is of significant importance.
Monitoring
During the recovery period, primary attention should be given to the patient's consciousness, respiratory and circulatory status, and any possible complications related to surgery or anesthesia. Routine monitoring includes electrocardiography (ECG), blood pressure, respiratory rate, and oxygen saturation (SpO2), with recordings made every 5–15 minutes. Patients undergoing major surgeries, whether under general or regional anesthesia, typically receive supplemental oxygen postoperatively. For patients with underlying pulmonary diseases, or those undergoing thoracic or upper abdominal surgeries, emphasis on monitoring and managing respiratory function is necessary. In patients recovering from general anesthesia, awareness should be paid to the degree and rate of regaining consciousness; for patients under neuraxial anesthesia, it is crucial to monitor the recovery of sensory and motor functions in the blocked regions.
Management of Delayed Emergence Following General Anesthesia
Delayed awakening is often caused by residual effects of general anesthetic agents, including inhalation and intravenous anesthetics, muscle relaxants, and narcotic analgesics. It may result from excessive anesthetic depth or prolonged drug metabolism and clearance due to the patient’s pathophysiological conditions such as advanced age, hepatic or renal dysfunction, or hypothermia. Additionally, postoperative complications that occurred during anesthesia (such as electrolyte imbalances, cerebral hemorrhage or thrombosis, hypothermia, hyperglycemia or hypoglycemia, or sepsis) may lead to altered levels of consciousness. Even after excluding anesthesia-related causes, various degrees of consciousness impairment might persist in affected patients.
Regardless of the underlying cause of delayed awakening, measures should aim at maintaining circulatory stability, ensuring adequate respiratory function, and providing sufficient oxygenation. For patients who remain unresponsive for an extended period after surgery, further investigation into the cause is necessary, followed by targeted treatment.
Maintaining Airway Patency
In the early postoperative period, incomplete recovery of consciousness and residual muscle relaxation can result in upper airway obstruction. Risk factors such as pre-existing pulmonary conditions, obesity, advanced age, smoking history, intraoperative airway manipulation, prolonged prone positioning during surgery, thoracic and upper abdominal surgeries, administration of high doses of opioid analgesics, and effects of residual neuromuscular blockade may increase the incidence and severity of upper airway obstruction.
Close monitoring of airway conditions is essential to prevent severe respiratory obstruction that could lead to significant hypoxia. In the event of an airway complication, airway patency and oxygenation need to be ensured. Measures such as jaw thrust, placement of oropharyngeal or nasopharyngeal airways, mask-assisted ventilation, or tracheal intubation may be required. Simultaneously, blood pressure and heart rate should also be closely monitored. Delayed detection and management of airway events can pose a serious threat to the patient’s life.
Maintaining Circulatory Stability
Cardiovascular events such as blood pressure fluctuations, arrhythmias, and myocardial ischemia are relatively common during the recovery period. Changes in body positioning can also affect circulatory dynamics. When cardiovascular events occur, identifying the underlying causes and addressing them promptly is necessary.
Common Causes of Postoperative Hypotension
Common causes include:
- Hypovolemia: Symptoms include dry mucous membranes, tachycardia, and oliguria. Assessment of hemoglobin concentration and hematocrit levels is important to rule out internal bleeding. For refractory hypotension, monitoring parameters such as urine output, direct arterial pressure, and central venous pressure can aid in guiding treatment.
- Impaired Venous Return: Causes may include mechanical ventilation, tension pneumothorax, or cardiac tamponade.
- Reduced Vascular Tone: This may result from neuraxial anesthesia, allergic reactions, adrenal insufficiency, antihypertensive or antiarrhythmic medications, or rewarming-induced vasodilation.
- Cardiac Causes: This category includes arrhythmias, acute heart failure, myocardial ischemia, and pulmonary embolism.
Common Causes of Postoperative Hypertension
Factors such as postoperative pain, bladder distention with urinary retention, delirium or agitation, or nausea and vomiting are frequent contributors.
Hypoxemia and/or hypercapnia may play a role.
Elevated intracranial pressure, hypothermia, or drug errors could also serve as precipitating factors.
Preexisting hypertension, especially in patients who discontinued their antihypertensive medications preoperatively, may contribute to postoperative hypertension episodes.
Common Causes of Postoperative Arrhythmias
Potential triggers include hypoxemia, hypercapnia, pain, electrolyte disturbances (particularly hypokalemia), myocardial ischemia, drug effects, or acid-base imbalances.
Common Causes of Postoperative Myocardial Ischemia
Contributing factors include systemic inflammatory responses, hypoxemia, severe anemia, tachycardia, hypotension, and hypertension.