Preparation for General Anesthesia
Safe and efficient anesthetic practices require certified personnel, appropriate medications and equipment, and an optimized patient.
Minimum requirements for general anesthesia Minimum infrastructure requirements for general anesthesia include a well-lit space of adequate size; a source of pressurized oxygen (most commonly piped in); an effective suction device; standard ASA (American Society of Anesthesiologists) monitors, including heart rate, blood pressure, ECG, pulse oximetry, capnography, temperature; and inspired and exhaled concentrations of oxygen and applicable anesthetic agents. Beyond this, some equipment is needed to deliver the anesthetic agent. This may be as simple as needles and syringes, if the drugs are to be administered entirely intravenously. In most circumstances, this means the availability of a properly serviced and maintained anesthetic gas delivery machine. An array of routine and emergency drugs, including Dantrolene sodium (the specific treatment for malignant hyperthermia), airway management equipment, a cardiac defibrillator, and a recovery room staffed by properly trained individuals completes the picture.
Preparing the patient The patient should be adequately prepared. The most efficient method is for the patient to be reviewed by the person responsible for giving the anesthetic well in advance of the surgery date. Preoperative evaluation allows for proper laboratory monitoring, attention to any new or ongoing medical conditions, discussion of any previous personal or familial adverse reactions to general anesthetics, assessment of functional cardiac and pulmonary states, and development of an effective and safe anesthetic plan. It also serves to relieve anxiety of the unknown surgical environment for patients and their families. Overall, this process allows for optimization of the patient in the perioperative setting. Physical examination associated with preoperative evaluations allow anesthesia providers to focus specifically on expected airway conditions, including mouth opening, loose or problematic dentition, limitations in neck range of motion, neck anatomy, and Mallampati presentations (see below). By combining all factors, an appropriate plan for intubation can be outlined and extra steps, if necessary, can be taken to prepare for fiberoptic bronchoscopy, video laryngoscopy, or various other difficult airway interventions.
Airway management Possible or definite difficulties with airway management include the following:
• Small or receding jaw
• Prominent maxillary teeth
• Short neck
• Limited neck extension
• Poor dentition
• Tumors of the face, mouth, neck, or throat
• Facial trauma
• Interdental fixation
• Hard cervical collar
• Halo traction
Various scoring systems have been created using orofacial measurements to predict difficult intubation. The most widely used is the Mallampati score, which identifies patients in whom the pharynx is not well visualized through the open mouth. The Mallampati assessment is ideally performed when the patient is seated with the mouth open and the tongue protruding without phonating. In many patients intubated for emergent indications, this type of assessment is not possible. A crude assessment can be performed with the patient in the supine position to gain an appreciation of the size of the mouth opening and the likelihood that the tongue and oropharynx may be factors in successful intubation.
High Mallampati scores have been shown to be predictive of difficult intubations. However, no one scoring system is near 100% sensitive or 100% specific. As a result, practitioners rely on several criteria and their experience to assess the airway.
In addition to intubation during surgery, some patients may require unanticipated early postoperative intubation. A large-scale study of 109,636 adult patients undergoing nonemergent, noncardiac surgery identified risk factors for postoperative intubation. Independent predictors include patient comorbidities such as chronic obstructive pulmonary disease, insulin-dependent diabetes, active congestive heart failure, and hypertension. Severity of surgery is also an identified risk factor. Half of unanticipated tracheal intubations occurred within the first 3 days after surgery and were independently associated with a 9-fold increase in mortality.
When suspicion of an adverse event is high but a similar anesthetic technique must be used again, obtaining records and previous anesthetic records from previous operations or from other institutions may be necessary.
Other requirements The need for coming to the operating room with an empty stomach is well known to health professionals and the lay public. The reason for this is to reduce the risk of pulmonary aspiration during general anesthesia when a patient loses his or her ability to voluntarily protect the airway. • Published guidelines recommend that solid food (including gum or candy) should be avoided for 6 hours prior to the induction of anesthesia.
• Clear fluids (ie, water, Pedialyte, or Gatorade ONLY; no other liquids) should be avoided for 2-4 hours prior to the induction of anesthesia.
Patients should continue to take regularly scheduled medications up to and including the morning of surgery. Exceptions may include the following:
• Anticoagulants to avoid increased surgical bleeding
• Oral hypoglycemics (For example, metformin is an oral hypoglycemic agent that is associated with the development of metabolic acidosis under general anesthesia.)
• Monoamine oxidase inhibitors
• Beta blocker therapy (However, beta blocker therapy should be continued perioperatively for high-risk patients undergoing major noncardiac surgery.)
Recent catastrophes under anesthesia have focused attention on the interaction between nonprescribed medications and anesthetic drugs, including interactions with vitamins, herbal preparations, traditional remedies, and food supplements. Good information on the exact content of these supplement preparations is often hard to obtain.