Chapter Outline
Difficult Situations Within Hospitals 321
Remote Anesthesia 321
Major Accidents And Disasters 321
The Battlefield 322
Nuclear Biological Chemical (NBC) Capability 324
Equipment For Other Battlefield Anesthetic Techniques 324
Abnormal Ambient Pressures 324
Developing Countries 325
“District Hospital”-based Anesthesia 325
Draw-over Apparatus 325
Supplemental Oxygen 326
Ventilators Suitable For Developing Countries 326
The provision of anesthesia in modern, well-equipped operating rooms is dependent on sophisticated electronic equipment that requires an uninterrupted supply of both electricity and compressed gases. Such equipment is not readily transportable, although it may be moved within a hospital facility. There are many locations throughout the world where anesthesia is administered to facilitate surgery, examinations, or other forms of treatment outside this generally accepted “safe” environment.
The following are examples of locations and situations away from hospital operating rooms where anesthesia may be required, and where simpler or alternative means of providing anesthesia may need to be employed:
- ▪
Within hospitals away from operating rooms:
- –
Emergency department
- –
Radiology department (MRI, CT, interventional radiology) (See Chapter 23 );
- –
Radiotherapy department
- –
Cardiac catheterization and electrophysiology laboratories
- –
Endoscopy suite
- –
Intensive care unit
- –
Coronary care unit (e.g., for cardioversion)
- –
Psychiatric unit (e.g., for electroconvulsive therapy)
- –
- ▪
Site of an accident or major disaster
- ▪
The battlefield
- ▪
Developing countries:
- –
Hospitals, medical centers
- –
Self-contained visiting surgical teams
- –
All of these situations are remote from the relatively safe, comfortable, and familiar operating room anesthetic environment, and the following problems may be encountered to a greater or lesser degree:
- ▪
Lack of continuous electricity supply
- ▪
Lack of continuous supply of oxygen and nitrous oxide
- ▪
Difficulty with storage of drugs and equipment
- ▪
Difficulty in transport and supply of drugs and equipment
- ▪
Lack of maintenance of equipment
- ▪
Lack of skilled assistance
- ▪
Lack of control of environment
- ▪
Financial restrictions
Where possible, on grounds of safety, patients should be transferred to medical facilities capable of providing the appropriate level of care. For example, electroconvulsive therapy for psychiatric patients with severe aortic stenosis and depression would be better managed (from their cardiac status) in the operating suite of the main hospital rather than in a room off the psychiatric ward. Nonessential surgery should not be undertaken at the site of a major disaster or on the battlefield, and the use of local, regional, or sedative techniques should be considered where appropriate.
The overriding principle in providing anesthesia under any of these conditions should be to use a simple, safe technique, familiar to the practitioner. To reduce complexity and prevent the potential administration of a hypoxic gas mixture and reducing the need for scavenging (and for many other well-rehearsed reasons), there is a case for avoiding the use of nitrous oxide entirely. Training and practice in such techniques are invaluable for the time when they may be required. Even within a modern operating room environment, a “difficult situation” may arise due to failure of a sophisticated electronic anesthetic workstation, a major power cut with failure of back-up generators or a disruption to piped gas supply. The use of total intravenous anesthesia (TIVA) and a self-inflating bag with a separate oxygen cylinder, combined with practical clinical monitoring, will allow adequate and safe anesthesia in such a situation, and a flashlight may be the most essential item of additional equipment.
Difficult Situations Within Hospitals
Sites away from the operating rooms often have anesthetic equipment that is used only occasionally. Piped oxygen and suction facilities may be absent. The equipment in such areas must be maintained and checked adequately, with basic monitoring meeting the standard recommended by the American Society of Anesthesiologists. All modern anesthetic machines in use in the United States should be incapable of delivering a hypoxic mixture. There must be immediate access to resuscitation equipment and drugs, and a means of summoning additional assistance (i.e., telephone or intercom). The anesthesiologist and his or her assistant should have sufficient experience and be familiar with both the environment and the equipment.
Some specific problems posed to patients, medical attendants, and equipment within particular areas are listed below. More detailed discussion of equipment considerations for MRI, CT, and radiotherapy suites can be found in Chapter 23 .
Radiology Departments
- ▪
Ionizing radiation risk
- ▪
Long procedures (e.g., coiling of intracerebral aneurysms)
- ▪
Low levels of lighting
- ▪
Restricted access to patient or patient’s head
- ▪
There may be a requirement to stop ventilation briefly to prevent image blurring.
Radiotherapy Suites
- ▪
Intense ionizing radiation requiring patient isolation from the medical attendants
- ▪
Closed-circuit television or glass-liquid-glass window to view patient causing color and image distortion
- ▪
Multiple frequent treatments over a few weeks
- ▪
Radiotherapy applicators may obstruct access to the patient’s head
Magnetic Resonance Imaging (MRI)
- ▪
Intense magnetic field with the ability to cause equipment made of ferromagnetic material to be attracted at projectile velocity into the scanner. There is, however, a rapid decrease in field strength with distance.
- ▪
Electrical inductance—potential thermal injury from electrical conducting leads
- ▪
Electromagnetic interference leading to equipment malfunction (e.g., syringe drivers)
- ▪
Noise from vibration of switched gradient coils—ear protection for patients
- ▪
Theoretical risk of hypoxia if quenching of the superconducting magnets with cryogenic gases (usually helium) occurs. Quenching may occur as a fault condition or be initiated for emergency shutdown of the magnet.
These factors pose risks to patients and potential occupational hazards to staff. Patients and staff must be screened before access is granted to an MRI scanner to exclude ferromagnetic implants such as aneurysm clips or pacemakers. Anesthetic equipment taken into the vicinity of the MRI scanner must be MR-compatible.
Remote Anesthesia
Anesthesia for MRI, radiotherapy, and some radiological procedures may necessitate the anesthesiologist and the bulk of the anesthetic equipment being remote from the patient. This may be either to ensure all ferromagnetic equipment is outside the magnetic field or to remove anesthetic personnel from ionizing radiation.
- ▪
TIVA may be employed using long infusion lines on pumps, which must be able to cope with the increased resistance to flow caused by the increased length. This usually means setting to maximum the pressure limit for sensing an occlusion.
- ▪
Although sedation may be sufficient for some patients, the airway may need to be secured with a laryngeal mask airway (LMA) or tracheal tube.
- ▪
Intermittent positive pressure ventilation through a long co-axial breathing system, such as a 9.6 to 10 m Bain circuit and Nuffield Penlon series 200 ventilator, has been shown to provide safe anesthesia. With this system, there is an increase in the static compliance in proportion to the length of the tubing. This is caused by expansion of the breathing hose and compression of the volume of gas during positive pressure ventilation and will result in a lower tidal volume being delivered than is set on the ventilator. This is insignificant in adults. In children, if a Newton valve is used, the ventilator becomes a pressure generator, and the increased resistance and compliance of the long system results in the pressure delivered being significantly less than that selected (23% less with a 10 kg child). This compares with a 6% to 11% reduction when using a long rubber Ayre’s T-piece.
- ▪
The capnography signal is delayed due to the length of the sampling line but provides a guide for adjustment of the tidal volume.
Major Accidents and Disasters
These may occur in any part of the world at any time and are by definition unexpected. All medical services should have a plan to deal with major disasters. A typical approach is to have a mobile medical team that can be rapidly deployed to the disaster site and a receiving hospital capable of dealing with the retrieved casualties. In the event of the number of casualties overwhelming the initial response, there should be a means of either escalating the number of teams or hospitals deployed. In developing countries, there may be a need to seek international assistance. Many countries have teams available for worldwide deployment at short notice. Particular problems encountered include:
- ▪
Unfamiliar territory
- ▪
Unfriendly environment
- –
Extremes of hot and cold and altitude, even in normally temperate climates
- –
Dark, wet, cramped conditions
- –
- ▪
Unfamiliar injuries
- –
Blast and crush injuries
- –
Delayed extrication
- –
- ▪
Risk to rescuers:
- –
Nuclear, biological, or chemical incidents
- –
Terrorism
- –
Fire, explosion risk
- –
Continuing disaster (e.g., earthquake)
- –
Unstable buildings
- –
The predominant anesthetic contribution to a major disaster is resuscitation and stabilization before transfer to the receiving medical facility. Exceptionally, to aid extrication of casualties, amputation of trapped limbs may be required. This is best achieved using ketamine, either intravenously or intramuscularly. Equipment for intubation, self-inflating bag, fluid, and cannulas for intravenous fluid resuscitation should be available. Oxygen and Entonox (mixture of nitrous oxide 50% and oxygen 50%) should be used cautiously in such conditions because they support and accelerate combustion of flammable materials, and although the latter has excellent analgesic properties, it may not be suitable in very cold conditions or in the presence of a head injury or pneumothorax.
The Battlefield
Mobile field hospitals are deployed as close to the battlefront as safety will allow and receive casualties who may have had pressure dressings applied and airways secured in the field, or possibly have had first-aid treatment at a battalion aid station or equivalent. In addition to military casualties from both sides of the conflict, there are frequently civilian casualties, which may include children. This poses a problem if pediatric equipment is not available. Large numbers of casualties may arrive simultaneously and require triage on arrival. In some, immediate surgery is required as part of the resuscitation process. Some of the features of military anesthesia are as follows:
- ▪
Equipment must be portable and durable
- ▪
Oxygen cylinders or concentrators are usually readily available
- ▪
Cost constraints for drugs and equipment are minimal
- ▪
Resupply can often be difficult, especially if supply lines are cut or the area of operation is a truly austere and hostile environment with little existing infrastructure
Electricity is required for lighting, monitoring, suction, heating, and refrigeration (for blood storage and some drugs) and usually will be supplied from generators that must be of sufficient power to cope with maximum demand. Vital equipment should have an independent battery back-up to allow for continued use in the event of power failure. Sensitive equipment should have surge protection to limit voltage spikes from erratic power supplies.
Draw-over anesthesia is the most suitable inhalational technique for use in the field. It can be employed for both spontaneous and controlled ventilation, is not dependent on compressed gases, and requires only light portable equipment. The basic equipment required comprises:
- ▪
Nonrebreathing valve
- ▪
Self-inflating bag
- ▪
Low-resistance vaporizer
- ▪
Means of giving supplemental oxygen (T-piece, length of tubing to use as oxygen reservoir and source of oxygen [i.e., cylinder or concentrator]).
The Ohmeda Portable Anesthesia Complete, or PAC ( Figure 24–1 ), is the draw-over vaporizer currently in use by the U.S. military. The PAC is a calibrated, temperature compensated, flow-over, low resistance vaporizer, which is designed for use in austere environments where economy of size and simplicity are essential. It is designed for use with nonrebreathing type of circuits and is classified as “agent nonspecific,” although it is generally used with isoflurane. It is important that when using the PAC the dial setting is not relied upon as an absolute indicator of the true vaporizer output. Gas analyzers can be used to determine actual vaporizer output. The difference between the dial setting and true output varies based on ventilation or ventilator type, and minute ventilation. In the combat environment often simply verifying that anesthetic gas is being delivered by quickly sniffing the end of the circuit is all that is possible. IV adjuncts and monitoring physiological parameters can then help ensure proper depth of anesthesia.
