Monitoring the Critically Ill Patient Part II
Harold Davis Jr., BA, RVT, VTS (Emergency and Critical Care)
The hallmark of critical care is monitoring, reevaluation, and assessment. Once you have completed these three steps you must then act on your findings. It is not acceptable to ignore any negative findings in hopes that they will go away. It is also helpful to monitor as many parameters as possible in regards to a particular body system. By monitoring several parameters you will be able to get a better handle on the respective system. The, pulmonary, central nervous system, fluids in and fluids out, and body temperature will be the major thrust of this discussion.
It is important to monitor the trends of parameters. One particular measurement is more meaningful when compared to previous measurements. The trends should tell you if a patient is improving or deteriorating. An important part of critical care is the recording of trends thus methods of charting these trends will also be discussed.
The normal breathing range is 8 - 20 breaths per minute (BPM). The breathing rate alone does not provide you with much information regarding the pulmonary system, therefore, the quality of breathing should be considered as well.
Eupnea is a normal ventilatory nature and rate. We will define normal ventilatory nature as a tidal volume of 15 ml/kg (normal tidal volume is 10 - 20 ml/kg). Bradypnea is a slow rate without regard to tidal volume. Tachypnea is a fast rate with out regard to volume. Apnea is the absence of any ventilatory effort.
Bradypnea and apnea may be caused by intracranial space occupying lesions, drug induced, hypo- or severe hypercapnia and medullary respiratory center dysfunction. Tachypnea may be caused by hypoxia, hypercapnia, hyperthermia, pain and metabolic acidosis.
Auscultation should be performed in a quiet room. The entire lung field should be ausculted and all abnormal lung sounds should be localized and characterized. Crackles during late expiratory or the early inspiratory phase are indicative of bronchopulmonary disease (pulmonary edema). Expiratory wheezes are due to asthma. Pleural effusion can be characterized by muffled lung sounds. Localized areas of dullness may be caused by atelectasis or lobar consolidation while generalized dullness may be caused by pneumothorax.
Mucous Membrane Color
Cyanosis may be indicative of severe hypoxia, when it occurs it is usually later in the disease process. For cyanosis to occur, 5 g/dl of un-oxygenated hemoglobin must be present. If anemia is present cyanosis may not be seen. Other differentials to consider when cyanosis is seen include: methemoglobinemia and peripheral stagnation of blood flow during shock. In these two instances pulmonary function and PaO2 may be normal.
Blood Gas Analysis
One of the best ways to assess pulmonary function is through arterial blood gases. Blood gases tell us about the patient's ability to ventilate and oxygenate. Blood gases measure the partial pressure of carbon dioxide (PaCO2) and oxygen (PaO2) in the blood. Blood gas measurements are performed on a blood gas analyzer, this is an expensive piece of equipment to maintain, however, recently a new inexpensive portable pH and blood gas analyzer has been developed. The I-STAT7 a a blood analyzer may be financially and technically feasible for use in private practice. An alternative to owning an analyzer is to take the blood sample to the nearest human hospital; perhaps arrangements can be made wherein they will run the sample for a minimal fee.
PaCO2 measures the patient's ability to ventilate. The normal PaCO2 is 40 mmHg with a range of 35 - 45mmHg. A PaCO2 less than 35 mmHg (hypocapnia) is indicative of hyperventilation (excessive elimination of CO2). A PaCO2 less than 20 mmHg may lead to decreased cerebral blood flow leading to cerebral hypoxia. A PaCO2 greater than 45 mmHg (hypercapnia) is indicative of hypoventilation (decreased elimination of CO2). A PaCO2 greater than 60 mmHg may be associated with hypoxemia if the patient is breathing room air. When a PaCO2 reaches this level, ventilator therapy may be required. Hypercapnia may be caused by CNS disorders, pleural filling disorders, abdominal or thoracic restrictive disorders and pulmonary parenchymal disease.
PaO2 measures the patient's ability to oxygenate the blood. The normal range is 90 - 100mmHg. A PaO2 less than 60 mmHg is considered hypoxemic and therapy may be started at this point. Some causes for hypoxemia include hypoventilation, ventilation perfusion - mismatch, right to left shunt and diffusion impairment.
Collection of a blood sample for blood gas analysis entails percutaneous puncture of an artery such as the dorsal pedal or femoral artery. The sample is collected in a heparinized coated syringe being careful not to introduce air or applying excessive negative pressure, both of which can affect your PaO2 measurement. Once the sample is collected the artery is held off for a few minutes. Air bubbles are expelled from the syringe and the syringe is corked and placed in a ice water bath. Blood gas samples may stay in a ice water bath for several hours before metabolism alters the pH or blood gas values.
Central Nervous System
Like all other systems it is important to establish a baseline when evaluating a body system and then monitor the trends. This is especially true with the central nervous system (CNS), subtle changes can take place that require astute monitoring abilities. Therefore, the patient should be monitored frequently and the results recorded. Any deterioration in the monitored parameters should be brought to the attention of the clinician.
Consciousness may be categorized into four levels. Normal, obtunded, stuporous and coma. An obtunded patient is one who has mild to moderate reduction in alertness and often appears drowsy, but is easily aroused. Stupor is a condition characterized by a deep sleep that is only responsive to vigorous or painful stimuli, once the stimulus is removed the patient returns to its sleep-like state. The comatose patent is totally unresponsive even to painful stimuli. It is a poor sign when a patient moves from a higher level of consciousness to a lower level.
When evaluating posture the concern is for the presence or absence of abnormal posture associated with opisthotonos. Opisthotonos is a form of spasm in which the head is bent backwards and the body bowed forward. The three types of abnormal posture include Schiff-Sherrington, decerebellate rigidity and decerebrate rigidity (each posture has a opisthotonic component). Schiff-Sherrington is due to a severe spinal cord injury. With Schiff-Sherrington, the patient's front limbs are in extensor rigidity and the rear limbs are relaxed. The patient has a normal level of consciousness. Prognosis is poor. Decerebellate posture occurs with severe cerebellar injury. The patient's front limbs are in extensor rigidity while the rear limbs are flexed. The patient has altered mentation. The prognosis is fair for this posture. Decerebrate posture is due to a severe brain stem injury, extensor rigidity is present in both front and rear limbs. The patient is unconscious. The prognosis is poor for this posture. Should any of these postures develop it should be brought to the attention of the Veterinarian.
Normally pupils should be equal in size and have a direct and consensual response to light. If the pupils are fixed in a midpoint position and unresponsive to light a severe midbrain lesion is suspected and the prognosis should be considered guarded. If there are changes in the pupils especially the fixed midpoints a-reflexic, notify the clinician.
There are several breathing patterns that are a result of CNS lesions. They are as follows:
1. Apnea shows medullary dysfunction.
2. Cheyne-Stokes breathing is characterized by cyclic hyperventilation and is attributed to greater than normal delays in the medullary response to changing carbon dioxide levels.
3. Biot's breathing is characterized by cyclic hypoventilation and apnea and is a sign of a serious medullary disturbance.
4. Apneustic breathing may be associated with brainstem disease.
Fluids In And Fluids Out
Urinary output is an excellent reflection of tissue perfusion. If the kidneys are producing urine then the other organs are probably being perfused. The normal urinary output is 1 - 2 ml/kg/hr. Ideally its important to quantitate the urine output. There are several techniques for urinary collection some examples include: Placing a urinary catheter and using a closed collection system, walking your patient and collecting the urine in a bowl, weighing a disposable diaper and placing it underneath the penis or vulva in a recumbent patient obtaining the difference between the wet weight and dry weight, weighing the litter pan pre and post urination and again obtaining the difference for urine output.
In addition to quantitation of urine, it is also helpful to quantitate defecation and emesis, this can provide you with a better picture of your total fluid balance. Weight gains and losses should be monitored on a daily basis if not more frequently. Acute changes in weight are usually a result of fluid changes and not muscle mass.
The fluid losses should be compared to fluid intake, they should just about balance out. Any big discrepancy in the "ins and outs" should be brought to the attention of the clinician.
Core temperature may be monitored by placing a deep rectal or esophageal thermometer. When monitoring the temperature early recognition of hypo or hyperthermia will result as well as trends in the patients status.
The normal temperature for a dog or cat is 101 - 102.5oF. In the neonate the normal body temperature is 7oF above the environmental temperature during the first week of life. By the second week they can maintain their temperature from 98 - 100oF. By the forth week their thermal regulation is mature.
The causes for hypothermia (Temp < 101) include prolonged exposure to a cold environment and peripheral vasoconstriction, causing shunting of blood from the peripheral tissues and GI tract in response to decreased perfusion.
The causes for hyperthermia include, a hot environment with poor ventilation, a response to infection or inflammation, and thermoregulatory dysfunction.
As stated earlier it is important to monitor the trends. To help you keep track of the trends you should use some type of charting system. It need not be an elaborate system but one that will allow you to see all the parameters measured. A critical care patient checklist has been included in these notes to serve as a reminder as to your nursing care considerations when caring for the critically ill patient. A critical patient care checklist has been included. The parameters listed should be monitored as frequently as necessary based upon the patient's condition.
Critical Patient Care Checklist