Kirby's Rule of 20: the veterinary nurse's critical patient checklist part 2

As veterinary medicine is continuously evolving, so are the expectations for the level of patient care. In the veterinary emergency and critical care setting, patient care checklists can be utilised to optimise patient care quality and standards. Check-lists create a step-by-step process of evidence-based interventions and procedures that help prevent medical oversights (Berenholtz et al, 2002; Fulbrook and Mooney, 2003).

Kirby's Rule of 20 is a checklist created by Rebecca Kirby, DVM, DACVIM, DACVECC that includes 20 patient parameters that should be evaluated daily in critically ill patients. Kirby's Rule of 20 was created as a reminder for veterinarians and veterinary nurses to examine the status of critically ill patients, including organ systems involved, clinical parameters, diagnostic parameters, and treatment goals in order to optimise patient survival (Kirby, 2017). Following the Kirby's Rule of 20 checklist allows veterinary nurses to assess the overall clinical picture of a patient (taking a holistic approach), implement critical thinking skills, elevate the quality of patient care, set standards for patient care, and decrease morbidity and mortality which results in improved patient outcomes (Berenholtz et al, 2002; Fulbrook and Mooney, 2003).

The patient parameters in the Kirby's Rule of 20 check-list are:

• Fluid balance
• Albumin and oncotic pull
• Electrolyte and acid–base
• Mentation
• Heart rate, rhythm and contractility
• Blood pressure
• Body temperature
• Oxygenation and ventilation
• Red blood cells (RBCs) and haemoglobin
• Coagulation cascade
• Renal function
• Gastrointestinal motility and integrity
• Nutrition
• Glucose
• Immune status and antibiotics
• Wound healing and bandages
• Drug dosage and metabolism
• Pain control
• Nursing care
• Tender loving care.

To allow enough detail for each parameter, part 2 will focus on the physiology, clinical application, and monitoring of patient parameters 6–10.

Blood pressure

Blood pressure is another assessment of cardiac function because it is reflective of appropriate cardiac output and systemic vascular resistance (Schumacher, 2016). Cardiac output refers to the driving force of systemic blood flow and is dependent on heart rate and stroke volume (amount of blood pumped during each heartbeat) (Farry and Norkus, 2019). Systemic vascular resistance refers to the opposition of blood flow through peripheral circulation (Sullivan, 2017).

Blood pressure refers to the force exerted by blood on the arterial wall and is a key determinant of appropriate tissue perfusion and tissue oxygenation delivery (Sullivan, 2017). The two blood pressure measurements that result from pulsatile blood flow during the cardiac cycle are systolic and diastolic. The systolic measurement signifies the pressure during contraction of the heart muscle and the diastolic measurement signifies the pressure when the heart muscle is between beats (relaxed) (Scalf, 2014; Schumacher, 2016). The mean arterial pressure (MAP) indicates the timing of the driving force throughout the cardiac cycle, taking into consideration that the duration of systole is typically one-third of the cardiac cycle while the duration of diastole is typically two-thirds of the cardiac cycle (Sullivan, 2017). The MAP value of measurement is an approximated value that is calculated based on the systolic and diastolic values.

Blood pressure assessment is indicated in patients that have a disease process that could affect tissue perfusion. In critically ill patients, hypotension is a primary concern as it develops secondary to a disease process as a reduction in systemic arterial blood pressure as a result of cardiovascular dysfunction (Cooper, 2015). Hypotension is defined as a systolic pressure less than 80 mmHg or a MAP less than 60 mmHg (Sullivan, 2017). The three general causes of hypotension include reduction in preload (hypovolaemia, severe dehydration, oedema, cavitary effusions), reduction in cardiac function (i.e. myocardial dysfunction, cardiogenic shock, severe acidosis/alkalosis, toxin exposure), and reduction in systemic vascular resistance (distributive shock states) (Cooper, 2015).

Blood pressure monitoring involves measurement of blood pressure by either indirect (non-invasive) or direct (invasive) means. The indirect methods of blood pressure measurement include oscillometric or Doppler technique in which individual values are obtained (Figure 1). When using indirect methods, it is important to use the appropriate cuff size (approximately 40% of the limb circumference) as well as use the same limb for each measurement to ensure consistency and accuracy of results (Williamson and Leone, 2012). The direct method of blood pressure measurement is performed from direct arterial catheterisation in which values are constantly recorded second by second (Cooper and Cooper, 2012) (Figure 2). Regardless of the monitoring modality, trends in blood pressure readings are more important than a one-time measurement and should be assessed in consideration with the rest of a patient's parameters and disease process (Darbo and Page, 2017).

Body temperature

Body temperature is a measurement of the body's ability to maintain normal thermoregulation and is part of routine patient parameters. Animals maintain their temperature within a range called the ‘set point’, which is determined by the thermoregulatory centre in the hypothalamus (Scalf, 2014). When an animal's temperature rises or falls out of this range, the body reacts by increasing or decreasing the core temperature in an attempt to return to the set point in order to maintain a balanced thermoregulatory system (Farry and Norkus, 2019). In response to rises and falls in body temperature, thermoreceptors sensed within the central and peripheral nervous system stimulate either heat production or heat dissipation (Farry and Norkus, 2019). Dysregulation of the body's normal thermoregulation, such as hyperthermia and hypothermia, can lead to severe systemic consequences.

Hyperthermia is defined as an elevation in body temperature that occurs when heat production or external heat input exceeds heat loss (Babyak and Backus, 2019). Hyperthermia can be further categorised as either pyrogenic (as a result of an endogenous or exogenous pyrogen) or nonpyrogenic (as a result of the environment). During hyperthermia, the hypothalamus signals mechanisms to decrease the temperature by initiating vasodilation, decreasing heat production, and stimulating heat dissipation through conduction, convection, radiation, and evaporation (Wehausen, 2017).

Hypothermia is defined as a reduction in body temperature that occurs when heat loss exceeds heat production (Babyak and Backus, 2019). Hypothermia can be further categorised as primary (as a result of accidental environmental exposure) or secondary (as a result of alteration of endogenous factors within the body). During hypothermia, the hypothalamus signals mechanisms to increase the temperature by initiating vasoconstriction, decreasing heat loss, and stimulating heat production through piloerection, shivering, and sympathetic excitation (Wehausen, 2017).

Fluctuations in body temperature can result in cardio-vascular, neurologic, respiratory, and metabolic systemic consequences and therefore temperature abnormalities need to be closely monitored (Scalf, 2014). Temperature is most accurately monitored via rectal thermometer in a conscious patient and via oesophageal thermometer in an unconscious patient, with any fluctuation being reported to the veterinarian (Schumacher, 2016). Critically ill patients with abnormal body temperatures should also be frequently assessed for additional peripheral perfusion parameters (such as mentation and heart rate).

Oxygenation and ventilation

Normal pulmonary function involves the exchange of oxygen (O₂) and carbon dioxide (CO₂) through the processes of ventilation and oxygenation. Ventilation is the process of appropriate gas exchange within the alveoli across a blood-gas barrier (Scalf, 2014). During ventilation, O₂ is inhaled and diffuses from the alveoli to the capillary blood supply, then CO₂ diffuses from the capillary blood supply to the alveoli and is exhaled (Farry and Norkus, 2019; Reminga and King, 2017). Oxygenation is the process of O₂ being diffused from the alveoli, bound to haemoglobin, dissolved in the bloodstream, and delivered to bodily tissues (Farry and Norkus, 2019; Reminga and King, 2017).

Pulmonary function can be compromised in critically ill patients for a variety of reasons, and assessing respiratory parameters is vital.

Ventilation monitoring involves patient assessment parameters as well as diagnostic instrumentation. Patient parameters used to assess ventilation include respiratory rate (number of breaths per minutes), respiratory effort (work of breathing), and the character of respirations. The chest should be auscultated to determine the respiratory rate and determine if there are any irregularities detected (such as wheezes or crackles). Diagnostic monitoring of ventilation includes capnography (end tidal CO₂ (ETCO₂)) and/or venous blood gas analysis. Capnography is a minimally invasive method of measuring the exhaled level of CO₂ (in intubated patients). The ETCO₂ monitor uses an infrared sensor to directly measure patient CO₂ levels, with normal range being 35–45 mmHg (Barter, 2012). Hypoventilation is defined as an ETCO₂ greater than 60 mmHg and hyperventilation is defined as an ETCO₂ less than 35 mmHg (Schumacher, 2016). A venous blood gas analysis allows for interpretation of a patient's ventilation status through measurement of CO₂ levels in the blood (total CO₂ (TCO₂) value) (Barter, 2012; Hopper, 2015) (Figure 3).

Oxygenation monitoring involves the use of diagnostic instrumentation, which includes pulse oximetry (oxygen saturation (SpO₂)) and arterial blood gas analysis. Pulse oximetry is a non-invasive method to measure the oxygen saturation of haemoglobin — the pulse oximeter collects data from passing red blood cells (Ayres, 2012). The pulse oximeter monitor uses red and infrared light to scan capillaries to assess if red blood cells are saturated or unsaturated, however, the degree of saturation can vary (one O₂ molecule per haemoglobin versus four O₂ molecules per haemoglobin) (Ayres, 2012). The pulse oximeter then averages these findings to produce a percentage of saturation, which should be greater than 95% (Ayres, 2012). A SpO₂ reading of less than 95% is indicative of hypoxaemia, and a SpO₂ of less than 90% indicates severe hypoxaemia (Reminga and King, 2017). While pulse oximetry is a reasonable option for oxygenation monitoring, the ‘gold standard’ is arterial blood gas analysis. An arterial blood gas analysis allows for interpretation of a patient's oxygenation status through measurement of arterial oxygen content (PaO₂) (Scalf, 2014; Hopper, 2015) (Figure 4). A concept regarding a patient's oxygenation status is the oxyhaemoglobin dissociation curve. The oxyhaemoglobin dissociation curve depicts the relationship between oxygen haemoglobin saturation (SpO₂) and partial pressure of oxygen (PaO₂) in a sigmoid curve (SpO₂ and PaO₂ are directionally but not linearly related) (Reminga and King, 2017; Scalf, 2014). The curve is determined by haemoglobin's affinity for oxygen (how readily haemoglobin acquires and releases oxygen molecules) (Figure 5) (Babyak and Backus, 2019). The most important clinical application of this SpO₂/PaO₂ relationship is the difference between normoxaemia and hypoxaemia; small changes in SpO₂ correlate with large changes (roughly four times) in PaO₂.

Red blood cells and haemoglobin

Red blood cells (RBCs) are mainly composed of haemoglobin (Hgb) molecules, and each Hgb molecule comprise an iron atom bound to four heme subunits (Linklater and Higgs, 2017). Each haemoglobin molecule can carry four oxygen molecules and is responsible for transporting oxygen throughout the circulatory system. Adequate RBC and haemoglobin levels are essential to delivering oxygen to bodily tissues (Scalf, 2014).

A decrease in RBCs can become life-threatening because of impaired perfusion and poor tissue oxygenation (Lin-klater and Higgs, 2017). The most common RBC or Hgb disorder in critically il patients is anaemia. Anaemia occurs when there is a reduction of the total circulating RBCs and is the cause of a decrease in the oxygen-carrying capacity of the blood (Bays and Foltz, 2019). Common causes of anaemia include blood loss, RBC destruction, decreased RBC production, or insufficient haemoglobin production (Bays and Foltz, 2019).

When anaemia is present, the body will trigger compensatory responses to increase oxygen delivery to tissues, which include increasing production of RBCs and/or Hgb, increasing blood flow, and increasing the oxygen unloading capacity from Hgb (Linklater and Higgs, 2017). Factors that can cause a variation in the body's oxygen delivery during anaemia include the underlying disease process, the acuteness of onset, and the ability for the body to initiate compensatory mechanisms (Scalf, 2014).

Monitoring for RBCs and Hgb involves assessment of the six perfusion parameters and packed cell volume (PCV). The six perfusion parameters (mentation, heart rate, pulse rate, mucous membrane colour, capillary refill time, extremity temperature) are used to assess the systemic effects of hypoxia within the circulatory system as a result of a compromised ability of RBCs and Hgb to deliver oxygen to tissues (Scalf, 2014). PCV is the volume of RBCs in blood and correlates with the number of RBCs available for tissue oxygenation (Linklater and Higgs, 2017). When considering the use of blood component therapy, a patient's PCV value should be taken into consideration along with patient parameters that are indicative of hypoxia (altered mentation, weakness, tachycardia, tachypnoea, pallor, prolonged capillary refill time) to determine the need (Bays and Foltz, 2019).

Coagulation

The haemostatic system is a complex physiologic pathway dedicated to protecting the body from blood loss from the vascular system on damage (Scalf, 2014). The process of coagulation has been described in the traditional cascade model and using the cell-based model.

The traditional cascade model involves two phases of coagulation: primary and secondary. Primary haemostasis occurs at the site of tissue injury when von Willebrand factor binds to collagen and platelets to form platelet aggregation and clots. Secondary haemostasis follows primary and involves coagulation factors interacting through a mutual, sequential activation of the intrinsic and extrinsic pathways. Secondary haemostasis is often described with the ‘water-fall’ or ‘cascade’ model because the intrinsic pathway (within the bloodstream) and extrinsic pathway (outside the blood-stream) leads to thrombin activation (conversion of fibrino-gen to fibrin) in order to stabilise the platelet clot (Bays and Foltz, 2019).

The cell-based model involves three overlapping phases of coagulation: initiation, amplification, and propagation. Initiation occurs when tissue injury exposes tissue factor to plasma factor VII, which leads to cross-linked fibrin formation. Amplification occurs as a the result of small amounts of thrombin activating platelets to bind coagulation factors to the surface of the cells. Propagation occurs when the coagulations factors are bound to the platelet cell surface and are able to convert large amounts of prothrombin to thrombin, so that sufficient conversion of fibrinogen to fibrin is activated (Linklater, 2017).

Coagulation is monitored using patient parameters for signs of haemorrhage (heart rate, respiratory rate, mucous membrane colour, capillary refill time) and laboratory values (prothrombin time (PT) and partial thromboplastin time (PTT)). Critically ill patients with a known or suspected co-agulopathy should be routinely examined for clinical signs of bleeding, which include mucosal haemorrhage (for example oral or genital), ocular haemorrhage (such as hyphaema), integumentary haemorrhage from injection/insertion sites (such as haematoma formation), integumentary petechia (Figure 6), integumentary ecchymosis, gastrointestinal (such as haematemesis, haematochezia), renal (such as haematuria) (Bays and Foltz, 2019; Scalf, 2014). Laboratory values related to coagulopathy include PCV, complete blood count, manual blood smear for platelet count, and clotting times (Linklater, 2017).

Conclusion

Veterinary nurses are the patient's primary caregivers and are involved in monitoring critical patients. Utilising the Kirby's Rule of 20 patient checklist provides an organised method for veterinary nurses to thoroughly assess the critical patient parameters of blood pressure, body temperature, oxygenation and ventilation, RBCs and haemoglobin, and the coagulation cascade. Having a thorough understanding of each of these patient parameters enables veterinary nurses to prioritise patient needs by assessing the overall clinical picture to elevate the standards for quality patient care.

KEY POINTS

• Kirby's Rule of 20 is an established, evidence-based patient checklist that can be used by veterinary nurses in the emergency and critical care setting to assess the overall clinical picture of critically ill patients, implement critical thinking skills, and elevate the quality of patient care.
• Blood pressure reflects appropriate cardiac output and systemic vascular resistance, meaning it is a peripheral indicator of appropriate cardiac function. Blood pressure assessment is warranted is critical illness that could affect tissue perfusion and can be monitored through indirect and direct methods.
• Body temperature is a measurement of the body's ability to maintain normal thermoregulation. Fluctuations in temperature (hypothermia, hyperthermia) result in systemic consequences and require close monitoring.
• Oxygen and ventilation status are components of normal pulmonary function: ventilation is the process of appropriate gas exchange while oxygenation is the process of oxygen diffusion and delivery to bodily tissues. Changes in a patient's oxygenation or ventilation can have severe respiratory effects and necessitate close monitoring.
• Red blood cells (RBCs) are composed of haemoglobin molecules and are responsible for transporting oxygen throughout the circulatory system. Disruption of RBC or haemoglobin levels can result in a reduction in oxygen-carrying capacity and warrants close monitoring.
• Coagulation is a component of the haemostatic system, which is responsible for protecting the body from blood loss from the vascular system. Critically ill patients can have disease processes that result in coagulopathy and require close monitoring.