Monitoring anesthetized dental patients: the five-parameter approach

Monitoring anesthetized dental patients: the five-parameter approach

Mar 01, 2010

Clients frequently express concern about the anesthesia their dogs or cats need for professional oral evaluation and care. Often, tooth-by-tooth assessment results in a treatment plan that requires many hours of anesthesia. Constant monitoring of the patient's physiological status is critical to a consistently positive outcome.

The American College of Veterinary Anesthesiologists (ACVA) recommends monitoring circulation to ensure the following things happen: blood flow to tissues is adequate; enough oxygen concentration is in the patient's arterial blood; and the patient's ventilation is maintained. ACVA also recommends, for legal purposes, maintaining an anesthetic record of significant events and trends in monitored parameters. Furthermore, a responsible individual, aware of the patient's status, must be available at all times during anesthesia and recovery, according to ACVA recommendations.

Monitoring is accomplished through subjective methods (e.g., clinical appearance) and objective methods (e.g., electronic systems). During anesthesia, the patient should have minimal jaw tone and no palpebral reflex. The femoral pulse should be palpable, and the perfusion time should be two seconds or less. Breathing during balanced anesthesia should be even and regular.

Anesthetic complications may be detected by electronic monitors before being recognized by a trained clinician. In these situations, seconds count. Often, the advanced warning system can head off problems before they become critical or do long-term damage. Thus, these systems provide better patient outcomes, reduce stress during the procedure and may help minimize overall procedure time.

Figure 1: An ideal monitoring system checks for blood pressure, ventilatory status, oxygenation of hemoglobin, temperature, and heart rate and rhythm.
An ideal electronic monitoring system checks for the following: blood pressure, ventilatory status, oxygenation of hemoglobin, temperature, and heart rate and rhythm (Figure 1).

Blood pressure (BP)

Ensuring the proper perfusion of the patient's vital organs is paramount in anesthetic procedures. Since perfusion is affected directly by anesthetic depth and blood volume (i.e, hydration), continuous BP monitoring to avoid hypotension is critical. A recent human study concluded that two of the three causes of death up to a year after non-cardiac surgery can be attributed to anesthetic depth and duration.1 While the gold standard for continuous BP monitoring is direct arterial pressure, it is highly invasive, which renders it impractical in clinical practice.

Three noninvasive, indirect BP methods include Doppler, plethysmography and oscillometric. Doppler does not allow for continuous, hands-free monitoring of BP trends, and it delivers a reading only on systolic pressure. Plethysmography has never been validated against direct pressure in both anesthetized dogs and cats. This leaves the oscillometric method as the best choice. Since there are veterinary-specific oscillometric BP monitors that have proven to be accurate and reliable in anesthetized dogs and cats, these are becoming the standard, just as we saw 20 years ago in human medicine.

For best results, the technician should set the oscillometric BP monitor's high and low alarms to warn of trouble, cycle the readings automatically every three to five minutes, and focus on cuff selection and placement. As a rule of thumb, the cuff diameter should be 40 percent of the circumference of the patient's limb. A cuff should be placed on the limb so it is snug and at heart level.

Normal readings for anesthetized dogs and cats are:
> systolic, 90 to 150 mm Hg;
> diastolic, 40 to 60 mm Hg; and
> mean, 60 to 90 mm Hg.

Figure 2: A variety of treatments may help return blood pressure to normal.
Treatment of hypotension includes decreasing the plane of anesthesia, administering fluid or increasing the rate of fluid administration, and giving an inotrope (e.g., dopamine or dobutamine by intravenous infusion to effect). If these treatments are ineffective, administration of hypertonic saline (5 mL/kg), blood or hetastarch usually will return the blood pressure to normal (Figure 2).