Circulation

Circulation

A continuous assessment of adequate circulatory function to ensure adequate circulation is essential during the administration of anesthetics. Circulation can be evaluated without instruments by observing the mucous membrane and capillary refill time and simple palpation of peripheral arterial pulse, using equipment such as blood pressure cuff, stethoscope, and electrocardiogram.

Mucous Membrane

Mucous membrane color is usually most easily assessed at the gingiva. Pale mucous membranes may indicate blood loss or anemia or may result from poor perfusion. Purple or blue mucous membranes indicate cyanosis, a shortage of oxygen in the tissues. Cyanosis during anesthesia is usually the result of respiratory failure or upper airway obstruction and must be addressed immediately.

Capillary Refill Time

Capillary refill time is the rate of color return to a mucous membrane after the application of gentle pressure and reflects tissue perfusion. Pressure on the mucous membranes compressed the small capillaries and blocks blood flow to that area. When the pressure is released, the capillaries rapidly refill with blood and the color returns, provided the heart is able to generate sufficient blood pressure. A prolonged capillary refill time (> 2 sec) may indicate hypotension resulting from excessive anesthetic depth or circulatory shock. Capillary refill time is usually prolonged in patients in whom the systolic blood pressure is less than 80 mm Hg. Patients suffering from this degree of hypotension will usually feel cold and have pale mucous membranes. Other factors that may cause prolonged capillary refill time or poor perfusion include hypothermia, vasodilatation and cardiac failure.

Surgical Blood Loss Estimation

One of the most important and difficult tasks of the anesthetist is to continually monitor and estimate blood loss. Although estimates are complicated by occult bleeding into the wound or under the surgical drapes, accuracy is important to guide fluid therapy and transfusions. The most commonly used method for estimating blood loss is measurement of blood in the surgical suction container and visually estimating the blood on surgical sponges and laparatomy pads. A fully soaked sponge (4 x 4) is said to hold 10 mL of blood, whereas a soaked laparatomy pad holds 100-150 mL. More accurate estimates are obtained if sponges and laparatomy pad are weighed before and after use (particularly during pediatric procedures). Use of irrigating solutions complicates estimates, but their use should be noted and some attempt made to compensate for them. Serial hematocrits or hemoglobin concentrations reflect the ratio of blood cells to plasma, not necessarily blood loss; moreover, rapid fluid shifts and intravenous replacement affect measurements. Hematocrits may be useful during long procedures or when estimates are difficult.

Heart Rate

Can be counted by palpating the superficial temporal, carotid, or radial artery. Count the pulse for 15 seconds and multiply it by 4 for the pulse rate per minute. For a patient with irregular rhythm, counting should be for full minute. Heart rate should be documented every 5 minutes. The patient's heart rate should be monitored continuously by electrocardiograph (ECG); heart rate reading from a pulse oximeter, and/or precordial/esophageal stethoscope. The precordial or esophageal stethoscope allows simultaneous assessment of the patient's heart and lungs.

Electrocardiograph

It is an essential monitor that records the electrical activity of the heart and helpful in identification of arrhythmias or cardiac arrest, as well as detection of myocardial ischemia and electrolyte abnormality (Figure 2.5). During surgery heart rate and rhythm can be affected by anesthetic agents, surgical stress and direct manipulation of the heart. Changes in both rate and rhythm can have profound effects on blood pressure and over all perfusion. In the operation room, the ECG is monitored by either a three or five lead system. Lead II is most frequently monitored. This usually provides a good view of the P wave, which is helpful in determining the rhythm Precordial lead V5 is often monitored because it is sensitive for the detection of ischemia in the ST segment. It is estimated that 95% of the ischemic events can be detected using lead II and lead V5.

Position of electrodes for a 3-lead ECG: (Figure 2.5B)

NOTE: the electrodes are generally colour coded;

Red - right arm / shoulder

Yellow - left arm / shoulder

Green - lower left chest

Tachycardia may indicate many things. For example, it may indicate the need for additional fluids, excessive blood loss, or light anesthesia. Bradycardia may be caused by traction on certain organs. This reflex is called a vagal reaction. Hypoxia or an anesthetic overdose may also cause bradycardia or tachycardia. Whenever there is a change in heart rate (Table 2.4), you should always check the patient's ventilation and oxygen status to be certain that these are satisfactory.

Table 2.4 Range of Heart Rate

Figure 2.7 Sinus tachycardia	Figure 2.8 Sinus Bradycardia
Figure 2.9 Premature ventricular contraction/PVC

• Sinus tachycardia (Figure 2.7)- see for hypoxia, hypovolemia, then make anesthesia deep
  
• Sinus bradycardia (Figure 2.8)- search for causes, if the surgeons are manipulating the vagus nerve communicate with them; if perfusion is adequate observe if the BP is affected (going low) give Atropine 0.5-1mg IV, monitor closely
• Premature ventricular contraction/PVC (Figure 2.9): common during anesthesia, it could be due to hypoxia, light anesthesia. Identify the cause and mange accordingly. If you can't resolve with treatment of hypoxia and deep anesthesia and BP is affected consider Lidocaine 1mg/kg IV
• Ventricular tachyarrhythmia- Ventricular tachycardia (Figure 2.10) and Polymorphic ventricular tachycardia consecutively (Figure 2.11A). Rate is above 150/min, it could be pulse less or with pulse. Search for possible causes, ABC evaluation and care, if there is pulse administer Amiodarone 150mg over 10minute; or lidocaine 1mg/kg. if pulse less cardioversion if available.

• Ventricular fibrillation- no QRS complex, figure of EKG looks like the picture below, no pulse palpable in the carotid- management ABC, CPR, if defibrillator is available defibrillation
  

• Asystole (Figure 2.11B)- there is no electrical activity, EKG figure (QRS) =flat. Check leads are attached properly, check for carotid artery pulsation, if no pulse- stop surgery, check ABC, start CPR 30compression:2breath(30:2)(see ACLS module 9 for detail)
  

Artifact (Figure 2.12): Several forms of interference can make waveforms difficult to interpret, such as artifact from patient movement. The waveforms created from patient movement may be mistakenly interpreted as ventricular tachycardia, which is the reason to remember to always assess the patient.

Blood Pressure

Blood Pressure: a sphygmomanometer is most commonly used to determine arterial blood pressure during anesthesia. A sphygmomanometer consists of an inflatable rubber bladder with in unyielding cuff that is wrapped around the upper arm. As the bladder is inflated it applies even pressure circumferentially around the upper arm and compresses the brachial artery. Although blood pressure can be determined by a variety of techniques, the standard is auscultation of korotkoff sounds via a stethoscope over the brachial artery. The sounds are generated as the pressure in the cuff is decreased and blood flow returns in the artery. In a nosy operation room, oscillometry is more frequently employed to determine blood pressure. This technique makes use of small oscillations in the pressure of the inflated cuff as the pressure is decreased. When the systolic pressure equals the cuff pressure the magnitude of oscillation increases suddenly.

Blood pressure should be taken every 5 minutes for stable patients. More frequently if the patient's blood pressure is unstable. The blood pressure cuff's width should be one-third to one-half of the distance between the elbow and shoulder. An age appropriate cuff should be used. If the blood pressure cuff is too large for the patient, then your reading may be lower than the actual blood pressure. If the blood pressure cuff is too small, your readings will be higher than the patient's actual blood pressure (Table5.2).