Monitoring the critical patient (Proceedings)

For a technician, the daily assessment of their critical care patients often begins with rounds. After receiving a brief verbal history and synopsis of presentation, diagnostics, and treatments a tech is ready to take over the care of that patient. Of primary importance is an initial hands on assessment of each patient. Only then will a tech be ready to monitor each patient according to its individual needs.

Recently there has been a list generated that discusses monitoring 20 items to assess critical patients each day. Many of those parameters will be included, but the primary body systems of cardiovascular, respiratory, neurologic, metabolic, and urologic systems will be discussed primarily. Due to limited time, the depth of this presentation will be very brief since each of those systems would require a book chapter to adequately cover the material. It is difficult to put these items in order of priority as the nature of a critical care patient is to change moment by moment. Rather a technician has to maintain a global eye on the patient to assess for not only the primary complaint, but also remote area body systems that may not be directly related to the illness or injury.

Cardiovascular system

Each patient should be evaluated for heart rate, pulse rate and quality, mucous membrane color, and capillary refill time.

• Both bradycardia and tachycardia diminish cardiac output

• If bradycardia <40-60 bpm- perform a blood pressure to ensure adequate tissue perfusion

• Causes of bradycardia-drugs, pain, vagal reflexes, AV blocks, hyperkalemia

• Tachycardia rates >180 big dogs, >200 little dogs, >240 cats

• Causes of tachycardia-shock, hypovolemia, pain, hypoxemia, hyperthermia, sepsis, heart disease

• Palpate pulse rate and quality while auscultating the heart

• Pulse deficit indicates heart arrhythmia

• Estimate appropriate stroke volume

• Thready pulse indicates poor cardiac output

• Bounding pulse may indicate septic shock (vasodilation conditions)

• MM should be pastel pink color and moist

• Red injected color can indicate sepsis, hyperthermia, hypertension, carbon monoxide poisoning

• Pale/white indicates varying degrees of anemia or vasoconstriction

• Blue (cyanotic) equals lack of oxygen saturated hemoglobin and cannot be seen until Pa02<50

• Brown indicates acetaminophen toxicity

• Yellow indicates liver disease, bile duct obstruction, hemolysis, prior oxyglobin transfusion

• Dry/tacky membranes equal dehydration

• Prolonged CRT (>2seconds) can occur from hypovolemia, hypothermia, poor cardiac output, pain

• Rapid CRT can occur during sepsis, hyperthermia, or drugs (inhalation anesthesia)

An electrocardiogram is a staple of critical care monitoring and technicians should become accustomed to evaluating every ECG tracing for abnormal heart rhythms. Any patient that exhibits irregular rhythm and increased or decreased heart rate upon physical exam should be monitored several times a day.

• ECG does not assess patient for myocardial performance, cardiac output, or blood pressure

• Perform tracings on still patient in right lateral recumbency and evaluate in same systematic steps

• Determine heart rate

• Evaluate rhythm as regular, regularly irregular, or irregularly irregular

• Identify the P, QRS, and T waveforms

• Evaluate the PR and QT intervals and inspect ST segment for elevation or depression

• Rhythm disruptions commonly caused by electrolyte abnormalities, hypoxemia, effusions, and pain

Arterial blood pressure should be monitored several times a day on critical patients by either indirect or direct methods as appropriate for the severity of disease. Arterial blood pressure is the product of cardiac output, vascular capacity, and blood volume. If one of those factors is abnormal, neurohumeral reflexes will alter the others to maintain normal pressure.

• Indirect measurements include sphygmomanometer, Doppler, or oscillometric methods

• Width of cuff should equal 40% circumference of patient limb and fit snugly

• If cuff is too loose pressure will be erroneously high, and vise versa- too tight will be erroneously low

• First audible return of sound is systolic pressure using a Doppler

• Oscillometric method uses mathematical calculations and interpretations of intracuff and limb blood volume changes to determine systolic, diastolic, and mean pressures

• All indirect methods are least accurate when pressures are low and during vasoconstriction

• Direct measurement is most accurate and requires catheterization of an artery

• Measuring devices can be common supplies or manufacturer ready transducer

• Transducer must be at heart level to set zero reading

• Normal systolic, diastolic, and mean ABP are 100-160, 60-100, and 80-120mmHg respectively; variations between dog and cat and pressures between animal to animal will vary

• Hypotension causes, systolic < 60 -hypovolemia, poor cardiac output, or vasodilation

• Hypertension, mean pressure > 140mmHg, can cause retinal detachment, excessive cardiac work, and increased intracranial pressure

Central venous pressure is a critical monitoring tool especially useful for assessing a patient's response to fluid therapy, possible fluid overload, or in conditions such as renal, cardiac, or pulmonary disease and during septic shock.

• CVP's require a central venous catheter placement

• Catheter should terminate in cranial vena cava proximal to right atrium

• Measuring devices may be common supplies or manufacturer ready transducer

• Transducer must be at right atrium level to set zero reading

• Normal value in dogs and cats is 0-5 cmH20 and trends are ultimately important

• Readings of <0, or negative numbers, reflect hypovolemia

• Values of 12-15 cmH20 indicate varying degrees of fluid overload, approaching 20 indicates heart failure, with values >20 present with cardiac tamponade

Cardiac output monitoring requires sophisticated catheters and devices as well as monitoring true oxygen delivery and oxygen consumption. These procedures are not commonly performed. More typically monitored is respiratory function and assessment of lung perfusion and ventilation. These will be discussed next.

Respiratory monitoring

Monitoring the critical patient for respiratory comfort and effectiveness is a large part of a technician's role.

Slow trends or sudden changes in breathing pattern, respiratory rate, or lung sounds are often detected by careful observation. Pulse oximetry is a rapid assessment method while an arterial blood gas analysis is the gold standard for evaluating both ventilation and oxygenation. Additionally performing an A-a gradient calculation (Alveolar-arterial oxygen gradient) or a Pa02/Fi02 ratio will help to assess respiratory function.

• Normal breathing = easy, subtle, with minimal and simultaneous chest and abdomen excursion

• Prolonged inspirations may indicate upper airway obstruction

• Prolonged expirations may indicate lower airway disease

• Pulse oximetry measures the % of hemoglobin that is saturated with oxygen

• Normal value 98-100% SpO2; with 90% approximating a PaO2 value of 60mmHg

• Limitations are considerable-peripheral vasoconstriction, hypothermia, motion, ambient light

• Heart rate reading should equal patient's rate with good waveform present to be accurate reading

• Values <92% warrant 02 supplementation; values <90% warrant more aggressive therapy

• Arterial gas samples may be obtained with percutaneous needle puncture or via arterial catheter

• Arterial partial pressure of carbon dioxide (PaCO2) is measure of ventilatory status

• Normal PaCO2 = 35-45mmHg; feline values slightly lower; values >45 = alveolar hypoventilation and may indicate a need for ventilation as values increase with patient breathing room air

• Hypoventilation often manifests as increased PaCO2 accompanied by decreased PaO2

• Providing oxygen will increase 02 levels but will not alleviate CO2 levels until ventilation increases

• Hypercarbia (hypoventilation) may be caused by airway obstruction or thoracic restrictive condition, central neurologic disease or anesthesia, neuromuscular disease, high cervical spine injury

• Values <35 = hyperventilation; values <20 are dangerous and indicate severe respiratory alkalosis and can lead to cerebral ischemia by excessive vasoconstriction

• Hyperventilation can be caused by diabetic ketoacidosis and midbrain lesions

• Normal Pa02 = 80-100mmHg with patient breathing room air; values <80 = hypoxemia with values approaching 60 requiring oxygen supplementation and/or ventilation therapy

• Hypoxemia may be caused by decreased inspired O2 concentrations, hypoventilation, shunt (ventricular septal defect or large atelectatic lung area), V/Q mismatch (ventilation/perfusion mismatch- pulmonary edema or pulmonary thromboembolism), and diffusion impairment (pulmonary fibrosis)

• A-a gradient = estimate of effectiveness of oxygen transfer while accounting for extent of ventilation

• A-a gradient is calculated from arterial blood gas sample PaCO2 and Pa02 measured values

• A simplified calculation can be done when the patient is breathing room air at sea level

• A-a gradient = [150 – PaCO2(1.1)] – PaO2

• Values less than 10-12 at sea level and breathing room air indicate normal lung function

• Values of 12-20 may be considered mild pulmonary dysfunction

• Values > 20 would be considered moderate dysfunction; values >30 require careful assessment to determine proper therapy

• Arterial PaO2 should be 5 times the % of oxygen breathed (room air 20% x 5 = 100 PaO2)

• Also Pa02/FiO2 ratio can be calculated when patients are receiving supplemental oxygen

• Arterial Pa02 from blood gas sample is divided by fractional inspired oxygen being delivered (PaO2 sampled 200/.4 FiO2 delivered = 500)

• Values <300 indicate acute lung injury; values<200 indicate acute respiratory distress syndrome

Neurologic monitoring

Technicians should monitor patients for normal motor activity, brainstem reflexes, and appropriate level of consciousness. Patients presenting with severe trauma will be difficult or impossible to perform a complete neurologic examination on, but serial examinations are important to monitor for changes in condition.

• Note any abnormal pain, gait, reflexes, paresis, or rigidity present

• Patients in deep shock may not respond appropriately-stabilize patient first

• Monitor for peripheral nerve injuries and anal or bladder innervations before repairing fractures

• Perform serial evaluations of deep pain to monitor spinal cord injuries

• Withdrawal reflex may still be present despite severe spinal cord damage-animal must show pain

• Monitor for slow or absent pupillary light response, unilateral or bilateral miosis or mydriasis, and reduced oculocephalic reflexes to assess brainstem reflexes

• Generally- constricted pupils, slow pupillary response, and slow physiologic nystagmus carry a better prognosis than dilated and unresponsive pupils (fixed and dilated indicates brain stem lesion)

• Mentation should be evaluated for appropriate response to stimuli

• Monitor head trauma patients for bleeding from nose, ears, or ocular hemorrhage; also bradycardia or hypotension

Metabolic monitoring

Technicians are frequently responsible for performing serum blood evaluations or other bedside monitoring and to report back to the clinician with any alarming abnormalities.

• Glucose monitoring is fast and easy bedside test

• Hyperglycemia may occur in stressed cats, diabetic pets, head trauma, early sepsis

• Hypoglycemia may occur in young toy puppies, portosystemic shunts, insulinoma, liver disease, sepsis, or addisons disease

• Hypoglycemia may cause- weakness, ataxia, seizures, coma

• Albumin is frequently measured in critical patients to estimate and protect colloid oncotic pressure

• Hypoalbuminemia may occur in protein losing enteropathy and nephropathy, generalized vasculitis conditions, hypercoagulable conditions, chronic liver disease, peritonitis, severe burns, or starvation

• Hypercalcemia may occur in neoplasias, renal failure, hyperparathyroidism, addisons disease, or vitamin D rodenticide toxicosis

• Hypocalcemia may occur in eclampsia, renal failure, hypoalbuminemia, GI malabsorption, pancreatitis, hypoparathyroidism , post- thyroidectomy in cats, ethylene glycol or citrate toxicity

• Hypocalcemia may cause- panting, weakness, ataxia, tremors, seizure, tetany, vomiting, arrhythmias

• Calcium solutions must be given IV, diluted, and slowly

• Hypernatremia may occur in dehydration, diabetes insipidus, or salt toxicity

• Correction must be slow (0.5mEq/hr) or risk cerebral edema; isotonic and hypotonic fluids to treat

• Hyponatremia may occur in addisons disease, diuretics, burns, psychogenic polydipsia

• Correction must be slow; NaCl or hypertonic saline to treat

• Hyperkalemia may occur in renal failure, ruptured bladder, urethral obstruction, and addisons

• Clinical signs are weakness, paralysis, arrhythmias, collapse, and death

• Treatment may include bicarb, insulin & dextrose, and calcium gluconate to protect heart

• Hypokalemia may occur in renal disease, diuretics, vomiting, diarrhea, anorexia, K+ deficient fluid therapy and is common in hospitalized pets

• Clinical signs are weakness, anorexia, vomiting, polydipsia, polyuria, and ventroflexion in cats

• Treatment is K+ supplementation in fluids; must not exceed 0.5mEq/kg/hr

• K+ can be used in subQ fluids, but <30mEq/L due to tissue irritation

• Hyperchloremia occurs during metabolic acidosis through diarrhea losses or prolonged administration of NaCl as maintenance fluids

• Hypochloremia commonly results from vomiting, foreign body obstruction, pancreatitis, diuretics

• Treatment is fluid therapy (NaCl) to replace volume deficits

Urologic monitoring

There are many indications to monitor urine output in critical animals. It is a great indicator of tissue and renal perfusion. Urine production can be measured by free catch of urine, weighing urine soaked diapers, or by placement of a urinary catheter. Other parameters of excretory function include protein/creatinine ratio, BUN, creatinine, potassium, and phosphorus.

• Urine output expected at 1ml/kg/hr but can vary from 0.5-2ml/kg/hr

• When weighing diapers-subtract tare weight of dry diaper; and 1g = 1ml urine output

• Specific gravity has wide range; generally 1.015-1.030; increases with dehydration; cats higher

• Dilute urine occurs in renal insufficiency, diuretics, addisons, cushings, diabetes

• Measurement of urine protein/creatinine ratio is helpful if proteinuria present; normal value <1.0

• Values to 10 indicate urinary tract inflammation; higher indicate glomerulonephritis, amyloidosis

• BUN is an estimate of glomerular filtration

• Renal azotemia does not occur until dysfunction of 75% of nephrons

• Prerenal azotemia occurs with dehydration, hypovolemia, hemorrhage, heart failure, sepsis

• Postrenal azotemia occurs with urethral or ureteral obstruction or ruptured bladder

• Increases of BUN - GI hemorrhage, dehydration, catabolic states, high protein diets, hypotension

• Decreases of BUN – liver dysfunction, low protein diets, diuresis

• Creatinine is a product of muscle metabolism and is excreted through the kidneys

• Increases of creatinine, both prerenal and postrenal, occur in similar situations as above (BUN)

• Hyperkalemia occurs in postrenal obstruction and acute renal failure

• Hypokalemia occurs in anorexia, vomiting

• Hyperphosphatemia occurs when GFR decreases

• Low phosphorus diets are appropriate for pets with acute renal failure