Author: Uday Jain MD PhD
ASA Monitor 12 2015, Vol.79, 28-30.
Anesthesia and critical care during disasters and in austere environments requires improvisation.1 –4 Partially trained personnel utilize some techniques, often adequately, yet occasionally dangerously. Triage is essential to prioritize care. Preoperative, recovery and postoperative care is often inadequate. In disasters, casualties exceed resources. Critical resources may be missing. Much of the anesthesia care takes place outside the O.R. Disaster may affect care providers. It is desirable to replenish providers and materials from outside. Surgery may focus on damage control, followed by definitive repair, often at other facilities. Infection control and sanitation are critical. Immunizations, such as for tetanus and pneumococcus, are usually indicated. Proper antibiotic administration is imperative.
Patients: Surgery is often urgent, in younger patients in poor general health. Stabilization of trauma victims is a major task. Surgical patients may suffer from various infectious diseases and their serious sequelae. Hypovolemia is common due to blood loss, low fluid intake, perspiration, diarrhea and vomiting. Patients may be sensitive to anesthetics because of hypovolemia, sepsis, lack of prior exposure to alcohol and drugs, fatigue, poor health and malnutrition. Clear fluids are encouraged up to two hours before surgery and again after surgery. Rare fresh donor blood must be used quickly after donation. Anesthetics usually drop blood pressure, often critically. Maintaining adequate BP is critical. Pressors are often required.
Supplies and Equipment: It is necessary to optimally utilize limited drugs and supplies, some of them unfamiliar and some employed for uncommon indications. I.V. fluids may be in short supply, and I.V. catheters may be utilized for drug delivery without being connected to an infusion. If there is no I.V., drugs can be administered via intramuscular (IM), subcutaneous (SQ), nasal or oral routes.
Compact, inexpensive battery-operated monitors, defibrillators and medication pumps exist but may not be available. It may be necessary to check, and possibly assemble, modify and repair equipment.5 One monitor may be used for several patients by monitoring intermittently. Pulse oximeter checks cardio-respiratory function and helps minimize hypoxia as well as O2 utilization.
As mechanical ventilators may not be available, spontaneous ventilation is preserved, if possible. Sterilization facilities for surgical equipment can also be utilized for anesthesia equipment. Reusable supplies are preferred over disposable ones. Often utilized are bag-valve-mask or Mapleson D Bain circuit and reusable supraglottic airway. Lighted stylet may be utilized for difficult or regular intubation.6
Anesthesia Machines: Some are transportable in a case, some others do not require compressed oxygen. A 100 ml flow through a universal vaporizer (e.g., Copper Kettle or Vernitrol) delivers 1 percent anesthetic if vaporizer plus diluent flow equals 2.5 l/min for sevoflurane (MAC 2.0 percent), 5 l/min for isoflurane (MAC 1.11 percent) or halothane (MAC 0.77 percent), or 3 l/min for enflurane (MAC 1.66 percent).7 Desflurane is not suitable. As a fail-safe mechanism is usually not present, to avoid high inhaled concentration, the vaporizer should be kept off until diluent and vaporizer flows are on.
Intravenous Anesthetics: They are more likely to be available than inhalational anesthetics and apparatus. If there is no I.V., many drugs can be administered SQ, IM, nasal or orally. The dose is higher and latency is longer through the alternate routes. Oral/parenteral diazepam is widely available internationally.
Analgesics: Acetaminophen (paracetamol), non-steroidal anti-inflammatory drugs (NSAID), gabapentin and pregabalin are suitable. Morphine can be administered I.V., IM, SQ, orally and rectally. Meperidine (pethidine) is popular because of its high oral efficacy. Codeine is a weak oral or parenteral analgesic. Other available opioids may include fentanyl and congeners, hydrocodone, oxycodone, hydromorphone and oxymorphone.
Ketamine: When administered through I.V., IM, oral or nasal routes, it works in three to five minutes and produces profound and lasting analgesia. Depth of anesthesia may be difficult to assess as patients may move, open eyes and speak. Secretions due to ketamine can cause laryngospasm. Glycopyrrolate should be considered for reducing secretions. Protective airway reflexes are mostly preserved but there is a risk of aspiration. Ketamine is relatively contraindicated in recent head trauma and increased intracranial pressure.
Ketamine causes nausea and vomiting. Emergence may be prolonged and with hangover. Postoperative dysphoria is reduced by utilizing smaller doses or infusions and by propofol or benzodiazepines. S-isomer is more potent and has fewer side effects. It is available in Europe but not in the U.S. Ketamine is safe in malignant hyperthermia and porphyria.
Total Intravenous Anesthesia: In a healthy patient, ketamine infusion may be started at 40 mcg (Kg.min) and fentanyl infusion at 0.03-0.05 mcg/ (Kg.min). Awakening from sufentanil infusion is faster than from fentanyl infusion. Equal milligrams of propofol and ketamine infusion can be combined for infusion. The same number of micrograms of fentanyl can be added.8
Reversal: If post-anesthesia care is inadequate, for rapid recovery after a procedure, flumazenil IV 0.1-0.2 mg over 15 seconds may be utilized for partial reversal of benzodiazepines. If necessary, an additional 0.2 mg may be administered at 60 second intervals to a maximum of 1 mg. For opioid reversal, naloxone 0.5 mcg/Kg I.V., IM or SQ may be utilized. It may be repeated after two to three minutes. Naloxone dose should be minimized to maintain partial analgesia while regaining spontaneous ventilation. A muscle relaxant should be utilized only if necessary, and its reversal is usually needed.
Regional Anesthesia and Analgesia: Busy anesthesia providers may administer nerve blocks while others monitor and follow the patients. Combinations of anesthetics may be suitable. Neuraxial block, proximal or distal extremity blocks, local infiltration, I.V and inhalational anesthesia may be combined.9 Single-shot or continuous spinal or epidural that can be lateral is suitable for abdominal and lower-body surgery. Spinal tetracaine with epinephrine provides long duration and strong motor block. If hyperbaric local anesthetic is not available, preservative-free, low-concentration local anesthetics available for peripheral nerve block can also be utilized for hypobaric spinal anesthesia. For arm surgery AXIS block, i.e., axillary first then interscalene block, is suitable. Chronic catheters are difficult to manage but may be suitable is some situations. Infiltrate local anesthetic deep up to fascia, then wait 10 minutes. Local anesthetics may also be installed in peritoneum, pleura and open wounds.
Epinephrine may prolong and potentiate motor and sensory blocks. However, durations of action of ropivacaine and levo-bupivacaine are not prolonged. Epinephrine reduces systemic absorption of the local anesthetics, permitting use of greater amounts. Maximum utilized concentration of epinephrine is 5 mcg/ml (1:200,000). Adding 1 ml bicarbonate to 10 ml of lidocaine hastens onset of nerve block by three to five minutes and reduces pain on injection.
Local Anesthetic Toxicity: Reported incidence of seizures after regional anesthesia is less than 1 in 1,000.10 More serious complications are rare with lidocaine. Benzodiazepines and hypnotics reduce seizures. Compared to CNS toxicity, CV toxicity is more lethal and occurs at higher doses (lidocaine-7.1X, bupivacaine-3.7X). Lidocaine plasma concentration peak may be delayed by hours after administration.
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