Preanesthetic Evaluation of Neurosurgical Patients

Introduction

A routine preanesthetic evaluation is a process that includes clinical assessment, risk stratification, and optimization before surgery. The primary aim of the preanesthetic evaluation is to reduce the perioperative morbidity and mortality. This involves many steps, which include:

1.
Establishing rapport with the patient and family, explaining the process of surgery, anesthesia, and recovery.
2.
Reviewing the past medical, surgical, personal and family history and history of medication allergy and the lists of current medication.
3.
A through general and clinical examination focusing on cardiopulmonary system and nervous system.
4.
Review of investigations and to assess whether further investigations or multidisciplinary care is needed, which would help to improve the patient condition.
5.
Risk-stratifying the patient for perioperative morbidity and mortality using clinical and laboratory data for the proposed surgical procedure.
6.
Optimization of the patient using the risk reduction strategies.
7.
To plan the type of anesthesia after assessing the risk/benefit of each anesthetic technique for that particular procedure.
8.
Utilization of best available resources to maximize the safety, to reduce the morbidity and mortality, and to speed up the recovery by providing adequate postoperative pain management.
9.
Getting an informed consent after explaining the risk and benefits of anesthesia technique and the need for invasive monitoring, blood transfusion (if applicable), and its associated risks.

Preanesthetic evaluations should be performed well ahead of the surgical procedure especially for high-risk patients [American Society of Anesthesiologists (ASA) grades 3 and 4] thereby allowing time for preoperative optimization, which has been shown to reduce the perioperative morbidity and mortality. Patients with ASA grades 1 and 2 can undergo preoperative evaluation either on the day of surgery or the day before surgery. ASA classification of physical status is a universally accepted grading system to stratify the patient’s preexisting health condition. Although it was not designed for outcome prediction, there has been a good correlation between the grading and perioperative morbidity and mortality.

Most patients undergoing neurosurgical procedures will have an underlying medical comorbidities such as diabetes, hypertension, ischemic heart diseases (IHD), obstructive sleep apnea (OSA), and chronic obstructive pulmonary disease (COPD), or bronchial asthma and seizures. These medical conditions require more intense scrutiny than the pathological process to prevent perioperative morbidity and mortality. Each neurosurgical procedure carries its inherent risk and requires specific preoperative evaluation and optimization. So, during the preoperative evaluation both patient- and procedure-related factors should be kept in mind and optimized accordingly.

Preoperative Evaluation of Patient-Related Risk Factors

In this section, the preoperative evaluation of patient-related risk factors focusing on cardiac and respiratory conditions, OSA, diabetes, and hypertension are discussed.

Preoperative Evaluation of Cardiac Risk in Neurosurgical Patients

Most neurosurgical procedures are considered to be intermediate- to high-risk surgeries. Patients with cardiac diseases undergoing neurosurgical procedure can have aggravation of cardiac dysfunction due to the systemic effect of raised intracranial pressure (ICP) (tumor, head injury) or catecholamine surge [in subarachnoid hemorrhage (SAH)] or autonomic dysfunction (Parkinson disease, cervical myelopathy, and brainstem lesion) leading to increased morbidity. Long-standing hypertension and diabetes are common in patients undergoing carotid endarterectomy and spine surgery, and these patients are more prone for IHD. Identification of cardiac risk associated with each neurosurgical procedure provides information to both the patient and the surgeon, which in turn helps them to understand the benefit vs. risk of a procedure. Cardiac interventions even before the surgery in certain high-risk cases decreases the perioperative morbidity and mortality.

Risk Assessment Tools for Estimating Cardiac Risk

There are various risk assessment tools available to assess the cardiac risk in patient undergoing neurosurgery. These tools use the information obtained from the history, physical examination, electro- and echocardiogram, and type of surgery. The various tools are given below.

1.
Revised Cardiac Risk Index ( Lee’s ) tool : This is the most commonly used tool and was originally published in 1999; it has been used to assess the risk for >15 years. It uses six factors such as high-risk surgery, history of IHD, congestive heart failure (CHF), cerebrovascular diseases, diabetes or insulin, and presence of high creatinine to estimate the cardiac risk. Using the aforementioned predictors, the estimated risk of cardiac death, nonfatal cardiac arrest, and nonfatal myocardial infarction (MI) following the elective surgical procedure are 0.4% [95% confidence interval (CI): 0.1–0.8] if there is no risk factor and 1.0% (95% CI: 0.5–1.4) if there is one risk factor. The risk increases to 2.4% (95% CI: 1.3–3.5) and 5.4% (95% CI: 2.8–7.9) if there are two and three or more risk factors, respectively.
2.
American College of Surgeons-National surgical Quality Improvement Program (ACS-NSQIP) universal surgical risk calculator : This surgical risk calculator model is a Web-based tool consisting of 20 patient factors such as body mass index (BMI), age, sex, ASA classification, functional status, prior cardiac history, and so on. The calculator then provides a risk of a major adverse cardiac event for the patient. This model had excellent performance for mortality, morbidity, and six additional complications. Limitations of this tool are that it is more cumbersome and its external validity is still questionable.
3.
Gupta myocardial infarction/cardiac arrest (MICA) - NSQIP database risk model : This risk model uses the following five factors to assess the risk of perioperative MI and cardiac arrest. They are (1) type of surgery, (2) dependent functional status, (3) abnormal creatinine, (4) American Society of Anesthesiologists’ class, and (5) increased age.

Assessment of Functional Capacity

Assessment of patients functional capacity is the next step in cardiac evaluation, expressed in metabolic equivalents (METs). One MET is defined as 3.5 mL of O ₂ uptake/kg/min in a sitting position, which is a resting oxygen uptake. Duke activity state Index is one of the most frequently used scales to assess the functional status. Ability to take care of oneself, such as eating, dressing, or using the toilet is considered 1 MET. Walking up a flight of steps or a hill or walking on level ground at 3–4 mph is considered as 4 METs. Participating in strenuous sports such as swimming, singles tennis, football, basketball, and skiing is equivalent to >10 METs. Ability to do an activity that requires >4 METs indicates good functional activity. Assessing the functional capacity in patients with walking disability such as paraplegia or hemiplegia can be done by using bicycle or arm ergometry stress testing. After determining the cardiac risk and functional capacity, one can follow the multistep algorithm provided by the American College of Cardiology (ACC) and American Heart Association (AHA) for determining the need for further preoperative cardiac evaluation before proceeding with surgery. Refer ACC and AHA 2014 guideline for details.

Indication for Cardiac Testing During Preoperative Evaluation

Electrocardiogram ( ECG ): All patients with cardiac problems such as IHD, arrhythmias, valvular heart diseases (VHD), and peripheral arterial diseases should obtain a baseline ECG to compare the changes that occur during the perioperative period. Patients with neurological problem such as raised ICP or SAH have underlying cardiac dysfunction, they often need baseline ECG.

Echocardiography : It is indicated to assess the ventricular function in symptomatic patients (dyspnea or heart failure), patients with VHD, and patients with past history of previously documented cardiac dysfunction with no assessment within 1 year.

Stress echocardiography : Although there is a correlation between the degree of MI and the prognosis, there is no evidence that prophylactic revascularization at the time of surgery improves outcomes. So, further cardiac evaluation (stress echocardiography or 24-h ambulatory monitoring) is only indicated in patients with known IHD with recent deterioration.

Evaluation of Pulmonary Risk in Patients Undergoing Neurosurgical Procedure

The incidence of perioperative pulmonary complications (POPCs) are high in patients with preexisting lung (obstructive, restrictive) diseases. Perioperative hypoxia and hypercapnia not only affect the cardiorespiratory status but also can aggravate the existing neurological illness. Neurosurgical patients are more prone to pulmonary complications because of low Glasgow Coma Scale (GCS) score (tumor, head injury, seizure, SAH), lower cranial nerve dysfunction in posterior fossa tumors or cranio vertebral junction anomalies causing aspiration pneumonia, or the presence of a high cervical or thoracic spine lesion causing cord compression leading to restrictive lung diseases.

POPCs contribute significantly to overall perioperative morbidity and mortality in the neurosurgical population. According to the NSQIP report, POPCs are the costliest of all postoperative medical complications (including cardiac, thromboembolic, and infectious) and resulted in the longest length of hospital stay. POPC is defined as any pulmonary disease or dysfunction that is clinically significant or adversely affects the clinical course of the patient. They are (1) atelectasis, (2) infection including bronchitis and pneumonia, (3) prolonged mechanical ventilation (>48 h), (4) respiratory failure, (5) exacerbation of underlying chronic lung disease, and (5) bronchospasm.

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