Introduction

Intraoperative cardiopulmonary resuscitation (CPR) is a skill that most anesthesiologists are experts at and are frequently called upon to perform. CPR usually follows cardiac arrest, which itself is a very serious event that has multifactorial causes. Some events leading to CPR are associated with anesthesia and some are related to the patient’s coexisting disease, trauma, and other factors. In this chapter, we will look at intraoperative CPR and cardiac arrest as it occurs mainly in neurosurgical as well as in other patients in the operative period.

Incidence, Morbidity, and Mortality

Being under general anesthesia is not without risks. In fact, sometimes it could be life threatening. However, it is the safest place where immediate and intensive resuscitation could be applied if needed. Cardiac arrest during anesthesia has a reported incidence of 0.01%–0.34% in adults undergoing noncardiac surgery. Intraoperative cardiac arrest (IOCA) is a feared intraoperative catastrophe that ends up in a significantly high mortality rate. The incidence of IOCA is extremely variable among the different studies. It is reported to occur at around 0.5–9.6 per 10,000 anesthetics. ^, In 1950, the incidence of IOCA was documented to be as high as 7.1 per 10,000 with a 30-day mortality rate of 63%. ^, By the year 2001, the incidence declined to as low as 0.05 per 10,000.

In a major study looking at operating room morbidity and mortality in Japanese hospitals, the incidence of cardiac arrest during surgery was 7.15 per 10,000 cases. The population studied was composed of 2,363,038 patients, so it was quite large. Major causes of cardiac arrest were massive hemorrhage and human error. In another large study at a major medical center, 35% of cardiac arrests were also due to hemorrhage, 44% due to cardiac causes, and 21% to other factors. Fortunately, survival rates were high in such patients because patients were under the care of physicians who have immediate access to a multitude of drugs and defibrillation equipment. The two studies showed survival rates approaching 50%. Furthermore, when the cause of arrest was anesthesia related, survival rate approached 80% ( Table 43.1 ).

Survival From Intraoperative Cardiac Arrest

If we take a closer look at the causes of IOCA, anesthesia is the least likely factor to cause IOCA and has the highest survival rate after resuscitation. Patients under anesthesia be it general or regional are under continuous surveillance and monitoring. The operating room is considered an intensive care setting where patient care is delivered very closely for the duration of the surgery. In fact, the incidence of anesthesia-related cardiac arrests has been declining since the introduction of the pulse oximeter in 1986. Perhaps the enhanced monitoring tools played a major role in decreasing the incidence of cardiac arrest due to respiratory causes. In addition to pulse oximetry, the introduction of capnography as well as the use of disconnection alarms and low-pressure alarms decreased the incidence of IOCA by increasing the likelihood of recognition of the arrest. Moreover, it is well known that witnessed cardiac arrest has the best survival rate. Thus, when CPR is preformed within 1 min of the circulatory arrest, the likelihood of survival and return of spontaneous circulation is ninefold higher. Patients who experience IOCA have higher survival rates since they are promptly diagnosed in less than 5-min interval and therefore advanced cardiac life support (ACLS) protocol is initiated in a timely fashion.

In 1954, Breecher et al. published the first investigation about anesthesia-related mortalities. The study was a pioneer in specifying the causes of death attributed to anesthesia alone within a 5-year period in 10 different hospitals. It was evident that anesthesia-related complications were multifactorial. A combination of underestimation of the preoperative risk along with human error, misjudgment, and poor medical condition of the patient may certainly lead to decompensation and failure.

Predictors

Several contributing factors that are not related directly to anesthesia exist and can be used as predictors of IOCA. To begin with, high American Society of Anesthesiologists (ASA) physical status is a significant predictor of IOCA even after adjusting for comorbidities like heart disease, cerebrovascular disease, renal disease, diabetes, and preoperative sepsis and shock. Multiple studies have shown that patients with ASA greater than or equal to 3 have 92%–96% chance of experiencing IOCA ( Table 43.2 ). Furthermore, another significant indicator of IOCA is the degree of functional capacity of the patient. According to Goswami et al., decreased functional capacity can be due to advanced age, limited cardiopulmonary reserve, or deconditioning. The urgency of surgery plays an important role in risk stratification. Urgent cases with significant hemodynamic instability have a very high mortality rate with a threefold higher frequency of cardiac arrest reported. It was observed that 60% of all cardiac arrests occurred in patients having emergency surgery. By their nature, emergent surgeries limit adequate preoperative preparation and assessment and consequently lead to higher incidence of IOCA. For instance, it is impossible to optimize a patient presenting with a ruptured aortic aneurysm, a perforated viscus, ischemic limb, or acute intracranial hematoma with impending risk of herniation.

Thus, the type of surgery is another contributing factor to IOCA. Newland et al. showed that patients undergoing vascular, thoracic, spine, and upper abdominal surgeries have a higher incidence of IOCA. It is also noted that the length of the surgery increases the incidence of IOCA. The longer the surgery, more than 180 min, the higher risk of having a cardiac arrest due to increased incidence of hemodynamic changes and fluid shifts. The timing of the surgery is noted to be significant in raising the incidence of IOCA. Urgent cases are more likely to occur during the night when the resources of getting help are limited.

Cause of Intraoperative Cardiac Arrest

The two main causes for IOCA can be divided into respiratory or cardiovascular compromise. Hypoxia seems to be the most frequent direct cause of anesthesia-related complications. It is encountered not only upon induction of anesthesia but also after tracheal extubation. It is the responsibility of the anesthesiologist to secure the airway. The anesthetist should be providing adequate ventilation and oxygenation for the patients especially upon induction of anesthesia. Hypoxia and hypoxemia are considered to be among the avoidable causes of cardiac arrest. According to the ASA Difficult Airway Algorithm, failure to ventilate or intubate should be addressed with the use of laryngeal mask airway or video-assisted technologies for securing an adequate airway and preventing hypoxemia ( Table 43.3 ).

Another important cause of IOCA is nonoptimal management of intraoperative hypotension. Multiple cases of IOCA were attributed to anesthetic overdose with inadequate fluid resuscitation in a hemodynamically unstable patient. Many deaths were found to be the result of inadequate blood management and underestimation of the degree of the blood loss. Blood loss is considered to be one of the major causes of IOCA that is related to the surgical complications and techniques. However, failure to estimate the magnitude of the anemia with subsequent hypotension ends up in a state of hypovolemic shock and possible postoperative myocardial infarction in patients with coronary artery disease. In a study by Zuercher et al. hypovolemia from blood loss and hyperkalemia from transfusion of stored erythrocytes were considered the most common causes of IOCA. Thus, when the lethal triad of acidosis, hypothermia, and hypocoagulability associated with massive transfusion is attained, the possibility of IOCA increases.

Fluid overload, on the other hand, in patients with chronic renal failure can cause acute pulmonary edema followed by cardiac arrest. Whether the anesthetic technique was general or spinal, maintaining hemodynamic stability before surgical stimulation seems to be one factor that is partially related to anesthesia.

Another cause for IOCA in a healthy patient is an adverse drug reaction. The use of succinylcholine is not without risks. Hyperkalemia as well as direct vagal stimulation like the stimulation of the oculocardiac reflex in ophthalmic surgeries might be behind IOCA during induction of anesthesia. Anaphylaxis is a life-threatening situation in which if the cause is not identified it could eventually end up in cardiac arrest.

Medication-related cardiac arrests share in common the fact that they cause cardiovascular depression. A small dose of propofol or dexmedetomidine may precipitate asystole upon induction of anesthesia due to profound hypotension and vasodilation. Dexmedetomidine is a selective α2 agonist that results in severe bradycardia and is associated with IOCA in elective neurosurgical cases. Inhalational agents including sevoflurane, isoflurane, and desflurane can also contribute to the development of asystole when given in high concentrations. Remifentanil is a very potent opioid that causes severe bradycardia and hypotension, even though it has a very short half-life. β-Blockers including metoprolol are responsible for multiple cases of IOCA especially in patients with undiagnosed pheochromocytoma. ^, A significant number of neurosurgical patients receive phenytoin infusion as part of their medical regimen to control seizures. The use of common vasoactive medications places the patient at risk of asystole due to drug–drug interaction. For instance, Berry et al. described a sudden IOCA due to potential interaction between phenytoin and ephedrine. Fortunately, most medication-related arrests are successfully treated to complete recovery. ^,

Cardiopulmonary Resuscitation Quality

High-quality CPR during cardiac arrest is critical. The American Heart Association guidelines define this as:

• 1.
  

  At least 100 compressions per minute

  
  
• 2.
  

  Chest compressions of at least 2 inches in depth

  
  
• 3.
  

  Complete chest recoil between compressions

  
  
• 4.
  

  Minimization of interruptions to compressions.

Cardiac Arrest and Cardiopulmonary Resuscitation in Neurosurgical Patients

Cardiac arrests and their management in neurosurgical patients is an area that is poorly understood and defined. Standard ACLS algorithms cannot always be deployed in neurosurgical patients. Sometimes the protocols are not feasible, and at other times it is not even appropriate. For example, management of cardiac arrest and defibrillation in one of the various patient positions other than supine needs attention to the underlying cause ( Table 43.4 ).

Table 43.4

Factors in CPR in Neurosurgical Patients

• Before starting CPR: • check adequate ventilation • check adequate oxygen delivery • check acute blood loss event • check delivery of excess anesthetics or vasoactive drugs • During CPR, drug doses may have to be modified to account for various factors • Chest compressions may have to be done in various patient positions • CPR may have to be done in various positions

 

CPR , cardiopulmonary resuscitation.

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