Abstract
Although routine pre-operative laboratory testing is firmly established in anesthesia practice, common themes to emerge from the literature are that blood tests are inconsistently applied, consistently overused, and routine testing rarely changes anesthetic management.
Pre-Operative Laboratory Testing
Although routine pre-operative laboratory testing is firmly established in anesthesia practice, common themes to emerge from the literature are that blood tests are inconsistently applied, consistently overused, and routine testing rarely changes anesthetic management.1
In the post-disaster environment, the availability of laboratory testing may range from nothing at all to a full laboratory service offering testing comparable to a modern hospital in a high-income country.2 Minimum standards for disaster medical assistance teams (DMATs) mandate the availability of urinalysis, blood glucose, and rapid detection malaria tests, where applicable.3 However, the increasing availability of portable, robust, and simple to use point-of-care (PoC) testing devices, including Hemocue (AB, Ängelholm, Sweden), iStat (Abbott, Libertyville, IL, USA), and ePoC (Alere, Waltham, MA, USA) mean that access to measurement of hemoglobin, renal function, electrolytes, and others is more readily available.
Rationale for Laboratory Tests
For a peri-operative laboratory investigation to be worthwhile, there should be a reasonable chance that the result will alter the management of the patient, whether through onward referral for further investigation, altering the anesthetic technique, or postponing/cancelling the procedure. Surgery taking place in the aftermath of a disaster is likely to be of an urgent nature, options for anesthesia more limited, and the risks of not operating more significant.
Anesthetists working in disaster medical teams are frequently involved in the management of acutely ill medical patients, and some blood tests – for example arterial blood gases (ABGs) in assessing hypoxia or hypercarbia in a patient with respiratory distress – can also have value in treating patients and assessing response.
In short, the anesthetist working in a disaster environment must remain flexible and be comfortable proceeding without information they may be used to having in their usual environment. However, in recognizing that the use of good clinical acumen is paramount, in certain circumstances targeted laboratory investigations might be useful. Some examples are outlined below.
General Considerations When Selecting Equipment
Many parts of the world most at risk from sudden-onset disasters are also prone to extremes of weather and challenging conditions. Heat, cold, humidity, precipitation, dust, sand, and other factors can all affect the performance of equipment leading to inaccurate results and risking patient harm. Limits of performance and robustness are important when selecting equipment. Other considerations include any requirement for a cold chain to store testing cartridges.
It is vital that equipment is properly maintained, particularly in view of the conditions in which it may be employed. Quality control and maintenance standards according to the manufacturers’ recommendations are mandatory and should not be ignored because the equipment is used intermittently or infrequently, or because of a feeling that “something is better than nothing.”
Specific Laboratory Tests
Hemoglobin
Hemoglobin can be estimated using a fingerprick test on cheap, simple color comparison cards.4 Modern electronic devices such as those mentioned above use either single- or multi-test blood cartridges, or make non-invasive transcutaneous measurements (Pronto-7, Masimo Corp., Irvine, CA, USA).
With the increased trauma load after a natural disaster, the ability to measure hemoglobin concentration can help guide the appropriate use of intravenous fluids and blood products. Measuring hemoglobin may also help in managing obstetric hemorrhage and non-disaster-related trauma, both of which are common presentations to DMATs in the aftermath of a disaster. It is worth considering that in some low- and middle-income countries (LMICs) 25% of the population may be chronically anemic, including around 50% of young children and 40% of women.5 The burden of anemia is particularly high in areas where diseases such as malaria and hookworm are endemic.
Urea, Creatinine, and Electrolytes
There are likely to be limited indications for peri-operative electrolyte testing in the setting of a disaster. However, in patients with crush injuries, such as after an earthquake, rhabdomyolysis may result in both acute kidney injury and profound hyperkalemia. Pre-operative optimization might include the use of intravenous fluids, insulin/dextrose, inhaled beta-2 agonists, and calcium, with ongoing treatment and monitoring intra- and post-operatively.
Other post-disaster situations where electrolyte measurements may provide useful information peri-operatively include in outbreaks of diarrhoeal illness, in malnourishment, in acute kidney injury due to severe sepsis, or in patients who present late with gastrointestinal obstruction.
Blood Glucose
The burden of non-communicable diseases, including type 2 diabetes, is increasing worldwide, across low-, middle-, and high-income countries. Many patients remain untreated or under-treated. Poorly controlled diabetes leads to poor wound healing and secondary infection, necessitating repeated trips to the operating theatre. This in turn results in significant use of limited resources and a poor outcome for the patient.
Modern blood glucose monitors are small, easy to use, and inexpensive, and provide the ability to monitor (thus facilitating control of) blood sugar levels in the peri-operative period. This may lead to fewer procedures, improved wound healing, and reduced morbidity.
Arterial Blood Gas Analysis
Arterial blood gas (ABG) analysis is included in many PoC devices and provides information on the acid–base state of the patient, as well as the oxygen-carrying capacity of the blood. pO2, pCO2, and pH (or H+ concentration) are standard tests and give the most useful information. They may be supplemented by serum lactate and other measurements.
The use of ABG analysis in selected surgical cases may help to inform decisions on medical and surgical management, fitness for surgery, prognosis, and futility and palliation. The presence of extreme metabolic acidosis in a patient being considered for laparotomy in a facility with no critical care facility may prompt transfer to another facility or palliation on the grounds of futility. Such decisions will rely on the combination of results with the clinical condition of the patient, the diagnosis, and the capability of the health care facility (for example the presence of an intensive care capacity in a type 3 facility).
ABGs may also be of use in the assessment and management of non-surgical patients with respiratory distress or metabolic derangement from systemic illness.
Coagulation Testing
Traditional coagulation tests such as prothrombin time (PT) and activated partial thromboplastin time (APTT) are some of the most over-ordered peri-operative investigations in high-income countries. These tests were developed to monitor specific anticoagulant therapies, and may not give an accurate picture of in vivo blood clotting.
The advent of viscoelastic PoC coagulation tests with easy to use cartridge systems has made “whole of coagulation” testing both user-friendly and somewhat more transportable, and has the potential to help peri-operative decision-making in the disaster setting. Clotting abnormalities, for example those due to low platelet numbers (or poor platelet function), can be corrected by transfusing either whole blood or, where available, fractionated blood products. Conversely, the ability to exclude medical bleeding through whole of coagulation testing may help in determining when bleeding is surgical in nature and requires a return to the operating theatre. Whilst still likely to be confined to the most sophisticated of DMAT laboratories at present, devices such as ROTEM (Tem International GmbH, Munich, Germany), TEG (Haemonetics Corp., Braintree, MA, USA), and Sonoclot (Sienco Inc., Arvada, CO, USA) may become more widely available to DMATs, particularly those dealing with trauma patients, in future.
Blood Transfusion
Introduction
Providing safe blood transfusion is challenging in the field hospital or disaster medicine setting. In 2013 the WHO released specific guidelines for the capabilities of DMATs, including blood transfusion services.3 Inpatient surgical teams must provide “basic blood transfusion” (level 2 DMATs) or “enhanced blood transfusion” services (level 3 DMATs). This section outlines the major issues that must be considered regarding austere transfusion, reviews the basic physiology of transfusion medicine, and offers some of the possible approaches and techniques for providing transfusion in the field. Anesthesiologists are the clinicians most likely to be involved in transfusion and are well placed to take a lead role in the oversight of such a service.
Related posts:
Chapter 5 – Inhaled Anesthetics and Draw-Over Devices in Disaster Response
Chapter 4 – Total Intravenous Anesthesia in Disaster Medicine
Chapter 15 – Chemical and Radiologic Exposures in Trauma and Disasters
Chapter 16 – Pain in Disasters
Chapter 12 – High-Altitude Physiology and Anesthesia
Chapter 21 – Operation Tomodachi: Anesthetic Implications
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