Page 204 - WSAVA2018
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 25-28 September, 2018 | Singapore
There are several methods of BP measurement:
Doppler ultrasound BP method: usually considered
to be low cost. The Doppler sounds indicate HR
and rhythm. Dysrhythmias will often sound distinctly “different” on a Doppler. Then, you can confirm the type of dysrhythmia with an ECG. To measure BP, a
cuff is placed proximal to the probe on the leg (the cuff width must be 40% circumference of the area to which it is being applied) after that, the cuff is inflated with a sphygmomanometer until Doppler sound disappears, then pressure is slowly released. In theory the pressure at which sound is again heard is the systolic BP. However, research shows that Doppler is not a reliable method for measurement in cats.
Oscillometric BP equipment: This technology is designed to detect oscillations in the cuff pressure that occur with arterial pulsations when the cuff is placed around an area. The monitor is able to electronically measure the pressures and display HR, systolic, mean, and diastolic pressures. Oscillometric BP monitors
do not always give accurate pressures, particularly in patients with extremely slow or fast HRs, dysrhythmias and when they are very small animals, such as cats and dogs <10 kg; Again: Cuff width should be 30-40% of limb circumference. Only buy BP a monitor if research is available to prove the accuracy of that particular brand and model. Not all monitors are the same.
Direct (intra-arterial or invasive) BP monitoring technique: This is the most accurate method available.
It is considered the “gold standard” for BP measurement and is the preferred method when exact measurements are important. For this technique, a catheter is inserted into a peripheral artery (most commonly, the dorsal- pedal artery or the femoral artery). Then the catheter is connected to an electrical transducer via a fluid filled extension set and the transducer is then connected
to the monitor. The transducer then converts the mechanical energy of a pressure wave into an electrical signal that is displayed on the monitor screen as a waveform and as a numerical display of systolic, diastolic, and mean BP, and HR. The resultant waveform on the oscilloscope screen gives an indication of contractility, vasoconstriction or vasodilation, and volume status
of the patient. For instance, myocardial contractility
is indicated by the rate of upstroke of pulse pressure wave. Stroke volume is indicated by the area under
the systolic ejection phase. Vasodilation is associated with steep down stroke and low dichroitic notch. Vasoconstriction is often described by gradual down stroke and high dichroitic notch. Hypovolemic patients can show exaggerated variations in size of the waveform with respiration (generally just see this with IPPV) and arrhythmias can also be detected as an absent or altered pressure wave form.
Electrocardiography (ECG): Cardiac impulse generation and conduction are assessed electrocardiographically. The sinus node is the site of normal impulse generation, and the typical p”, “QRS”, and “T”-waves are the result of propagation of sinus impulses in the normal, orderly sequence of atrial and ventricular depolarization and repolarization. The appearance of the normal cardiac waveform varies with the choice of lead orientation, but the morphology of electrocardiograms is directly related to the site of impulse generation, and/or the route of impulse conduction.
Remember: ECG provides only HR and rhythm; A normal ECG does not indicate adequate cardiac output or tissue perfusion. Patients with significant arrhythmias identified on ECG (i.e., ventricular premature contractions or ventricular tachycardia) should have BP measurement performed to determine if tissue perfusion is adequate. MONITORING THE RESPIRATORY SYSTEM
The respiratory system is monitored to insure adequate oxygenation and ventilation. Oxygenation is also dependent on adequate cardiac output, lung function, inspired oxygen levels (FiO2), ventilation and hemoglobin concentration.
Capnography (ETCO2): The capnograph or end tidal carbon dioxide (ETCO2) will help you to understand the ventilator status of your patient. The normal range is between 35-45 mmHg. If ETCO2 is higher than 45mmHg the patient is hypoventilating (most common reason under anesthesia). This can also be caused
by equipment failure such as stuck one-way valve or exhausted soda lime (when patient is re-breathing CO2) in a rebreathing circuit or the fresh gas flow is too low in non-rebreathing circuit. If the patient is hypoventilating, you can correct the ETCO2 with intermittent positive pressure ventilation (IPPV); if the equipment is malfunctioning, repair the equipment.
When the ETCO2 is less than 30mmHg your patient
is hyperventilating. This can be cause by: iatrogenic hyperventilation, V/Q mismatch, sampling of dead space, there is a leak in the breathing system, the patients endotracheal tube is disconnected from the anesthesia machine, the endotracheal tube is in the esophagus or perhaps your patient has low cardiac output.References are available upon request

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