Medical Comorbidities in Elective Surgery

Introduction

A comorbidity is any additional condition simultaneously present in a patient who has the index disease under study. Because intracranial arteriovenous malformations (iAVMs) are usually diagnosed when patients are relatively young (typically around the age of 40 years), the presence of severe or multiple comorbidities is less likely than in some other patient populations. Nevertheless, since AVM surgery is most often performed on an elective basis, it is important to maximize control of all medical comorbidities before the surgical procedure. Although there is a lack of data specific to the perioperative management of medical comorbidities in iAVM surgery, recommendations can be adapted from the principles and practices of general neurosurgical and general perioperative management. This chapter reviews the current best practices to ameliorate the effects of medical comorbidities in patients undergoing elective iAVM surgery.

Comorbidity Rating Scales

Various indices exist to help quantify the degree of comorbidity or functionality a patient has, including the Charlson Comorbidity Index, the Karnofsky Performance Status (KPS), and the American Society of Anesthesiologists (ASA) Physical Status Classification System. Data suggest that these scales may predict neurosurgical morbidity and mortality. Worse KPS scores and worse ASA physical status classification predict early (≤ 30-day) morbidity of intracranial tumor patients. A poor score on the Charlson Comorbidity Index may predict mortality of patients undergoing elective intracranial aneurysm intervention. While it is likely that more comorbidities could increase the risks of elective surgery in iAVM patients, no comorbidity index study has focused specifically on them. Nevertheless, we postulate that elective iAVM surgery in patients with multiple, severe, uncontrolled, medical comorbidities should be approached with caution, whereas surgery in young patients without comorbidities is likely to be medically very safe.

Preoperative Optimization

All patients who plan to undergo elective iAVM surgery should undergo a preoperative anesthesia assessment a few weeks prior to surgery to ensure that all comorbidities are identified and managed, to plan for appropriate and safe anesthesia, and to allow for identification of and planning for any potential medical problems that might arise postoperatively. In this assessment, it is mandatory to review the patient’s entire prior medical and surgical history, medications, allergies, and previous surgical procedure outcomes, and previous anesthetic outcomes as well as examine the patient, conduct necessary tests, and review the surgical treatment plan and possible complications. In selected patients with significant comorbidities, specialists, such as neurology, cardiology, or pulmonary medicine colleagues, should be consulted to ensure optimal comorbidity management.

Cardiovascular Disease

Craniotomy can result in blood pressure fluctuations, arrhythmias, electrocardiographic abnormalities, myocardial ischemia, and heart failure. These can occur due to central neurogenic effects on the myocardium and the autonomic nervous system or due to worsening of concurrent medical conditions. Preexisting cardiovascular disease, both symptomatic and asymptomatic, should therefore be identified in AVM patients about to undergo surgery. Patients with cardiovascular symptoms or known cardiovascular disease should undergo electrocardiography, echocardiography, and sometimes stress testing and other investigations as per established guidelines.

Patients who are already being treated with beta-blockers should continue on these medications, and perioperative beta-blockade should also be used in patients with a positive stress test undergoing major vascular surgery. However, in the absence of cardiac disease, perioperative beta-blockade is not recommended; although it can prevent nonfatal myocardial infarction, it can increase the risks of hypotension, bradycardia, stroke, and death. Other cardiology medications should generally be continued. Statins have been shown to improve perioperative cardiac outcomes; hence, they should be continued in patients already taking them.

Respiratory Disease

The respiratory system should be evaluated and optimized preoperatively to ensure adequate oxygenation and ventilation intra- and postoperatively. Any pulmonary disease should be preemptively treated before surgery because a neurosurgical procedure can cause pulmonary disease exacerbation. Also, after neurosurgery, patients can develop respiratory complications such as aspiration of gastric contents, pneumonia, exacerbation of bronchospasm/asthma/chronic obstructive pulmonary disease (COPD), respiratory failure requiring reintubation, pulmonary embolism, and neurogenic pulmonary edema. It is important to identify those individuals at risk so that these complications can be prevented.

Inquiring about smoking history should be part of the preoperative evaluation, and patients who smoke should be strongly encouraged to stop, because active smoking is a risk factor for worse neurosurgical outcome. Smoking worsens measures of cardiovascular function such as maximal exercise capacity and endothelial vasodilatation. Interestingly, even a brief period of smoking cessation may be of benefit. Cessation of cigarette smoking should begin at least 6–8 weeks prior to surgery, as this period of abstinence is associated with improvement in both pulmonary function and overall perioperative morbidity.

A history of asthma or COPD should lead to an assessment of the patient’s level of disease control. This should include frequency of use of short-acting beta-2 agonists, use of glucocorticoids, exploration of any history of asthma hospitalization, emergency department visits, intubation, and any recent symptoms of a respiratory tract infection or wheezing. If asthma or COPD are found to be not well controlled, the patient should be referred to a pulmonologist for control optimization prior to surgery.

A history of obstructive sleep apnea (OSA) is also associated with an increased risk of perioperative adverse events such as perioperative hypoxia, reintubation, arrhythmia, and intensive care unit admission. Sedation, anesthesia, opioids, and rapid eye movement sleep rebound have been shown to cause worsening of OSA in the perioperative period specifically leading to perioperative complications. Clinical OSA symptoms include daytime somnolence, excessive snoring, and fragmented sleep. The STOP questionnaire is a validated screening tool for OSA and can be used as part of the preoperative assessment to identify patients with OSA. Additional information on the patient’s body mass index, age, neck circumference, and gender can increase the detection of OSA. There are also specific groups of patients, such as those with obesity, acromegaly, or Cushing’s disease, who have a high incidence of OSA and in whom screening should be particularly stringent. If a patient is found to have OSA, the ASA guidelines on the perioperative management of patients with OSA should be followed to decrease their perioperative risk.

Lastly, as with all preoperative patients, an assessment of the airway must be performed. Consideration can be given to the laryngeal mask airway as a less stressful option for the patient, specifically with respect to cardiovascular stress, but currently, this option is rarely used in cranial surgery, and endotracheal intubation is typically preferred by the anesthesiologist.