Postoperative hypertension is
usually present by the time the patient arrives in the intensive care unit. It occurs in 30-60% of the cardiac patients. It is defined as mean arterial pressure of greater than 105mm Hg or a 20mm Hg, increase from the preoperative base line arterial pressure. Systolic hypertension is more common especially in the elderly patient population. The prevalence of systolic hypertension is particularly apparent after aortic valve surgery. The release of an aortic valve gradient may exert more stress on the peripheral circulation that was originally protected by the critical aortic stenosis before the surgery.
Risks
The risks of uncontrolled hypertension could include intracranial bleeding, disruption of suture lines, aortic rupture, mediastinal bleeding, and/or acute myocardial infarction or ischemia. It may also place undue burden on already compromised myocardial function. Persistent hypertension could also cause changes in the vein graft lining that could eventually lead to graft closure or premature atherosclerosis.
Causes of Hypertension
As mentioned else where in the book, post -operative cardiac patients may experience wide swings in their autonomic nervous system functions. High levels of epinephrine, and norepinephrine, and Vasopressin have been detected in these patients, as well as an elevated activity of the rennin-angioplasty system. Certain reflexes originating from the heart and blood vessels could also cause the blood pressure to rise. However, it is worth mentioning here that most cardiac patients have high levels of catecholamine, whether they develop hypertension or not. So, there must be a high population of those, who under the high catecholamine influence have a tendency to develop hypertension. Epinephrine is released as a result of the stimulation of the adrenalmudullary system, while norephinephrine, a neurotransmitter, is released from the sympathetic nerve endings. Infusion of norepinephrine leads to significant hypertension due to adrenergic vasoconstrictions. Norepinephrine levels have been found to be elevated 2-4 times above normal in hypertensive patients following cardiac surgery. Hence, hypertension often responds to lessening the sympathetic stimulation. Patients' blood pressure may spontaneously improve following extubation and appropriate levels of sedation. Patients who have been on Beta-blockers in the pre-op period have been found to have hypertension in the post-op period. It may be related to the withdrawal of the medications in the immediate postoperative phase.
Clinical Features
Significant elevation of the blood pressure may be associated with an increase in the systemic vascular resistance, and some times a slight decrease in the cardiac output.
Antihypertensive Medicines
Nitroprusside
infused intravenously could provide an excellent control of blood pressure. The drug can be titrated to keep the mean arterial blood pressure at or above 70mmHg. While the starting dose is 0.5 mcg/kg/min, the average dose is 1 to 2 mcg/kg/min. Nitroprusside has a tendency to dilate normal coronary blood vessels and cause a coronary steal in patients with severe coronary artery disease. Hence, caution must be exercised when using heavy doses of nitroprusside to control hypertension. Reflex tachycardia may be noted when you reach 4mcg/kg/min rate. You also need to monitor the thyocyanate and cyanide levels. Patients have a tendency to develop metabolic acidosis, which can worsen intra pulmonary shunting in patients with compromising pulmonary functions by the inhibition of hydroxyl vasoconstrictions in the pulmonary vessels. Excessive reduction in diastolic blood pressure could also reduce coronary blood flow and thus increase myocardial ischemia. To avoid some of these side effects you should consider the use of intravenous nitroglycerine.
Nitroglycerine
administered intravenously has advantages over nitropressude. One such is that it does not cause hypoxia or myocardial ischemia. Patients with congestive heart failure respond very well to nitroglycerine, which reduces pulmonary filling pressure. You can start the intravenous drip at 0.5mcg/kg/min and titrate up to 1.2 mcg/kg/min to achieve adequate blood pressure control.
Beta-blockers
work well in patients with heightened sympathetic function, high levels of norephinephrine, and a hyper dynamic cardiac state. Presently, there are several beta-blockers that are available that can be used intravenously. However, most of them have a short duration of action. As soon as the patient is exhibited, you can try 50-100mf of atenolol once or twice daily. Both will adequately bring down the blood pressure. The real problem arises when the patient undergoes abdominal vascular surgery such as AAA repair. The patient may have an NG tube for several days and is unable to take any medications by mouth. Even in such patients we have advocated the use of beta-blockers through the NG tube with adequate control of the blood pressure. By clamping the NA tube for an hour or so, we can still expect some benefit in bringing the blood pressure down. However, beta-blockers alone may not be able to do the job. Since, most cardiac surgery patients are volume overloaded, judicious uses of the diuretics could add to the beneficial effects of the beta-blockers.
Vasotec IV
TSS patches
, in those patients who could not take pills by mouth for several days due to the presence of an NG tube, could be another alternative to reduce the blood pressure. TTS patches come in 0.1,0.2,and 0.3 mg patched, and are applied one weekly.
Since we use multiple drugs in the general population, we could try the same approach. We need to be a little creative. Using a combination of
1. Nitropaste
2. TSS patches
3. Beta-blockers through the NG tube
4. IV diuretics, 5.
We should be able to adequately control the blood pressure even in those who are NPO for several days after cardiac surgery. Patients who cannot be exhibited for several days would also pose similar challenges and hence the above recipe could provide multiple drug approach toward the better control of hypertension.
Once the patient is exhibited then we can use the usual pre-op medicines the patient was receiving to control hypertension.
Ultra short actions of beta-blockers can be given as a continuous infusion without a significant reduction in cardiac functions. IT also does not cause intrapulmonary shunting as an infusion. The dosage can be titrated to maintain adequate mean arterial blood pressure of 70mmHg.
Lobetolol
can be given orally or intravenously. It is given in 10mg doses and the dosage can be increased to 40mg IV. It causes a reduction in heart rate and blood pressure. IT also can be administered intravenously as a continuous drip at 2 mg/min to control hypertension. However, it may have a tendency to decrease the heart rate and cardiac index without significantly lowering the systolic vascular resistance. That might signal predominant beta blocking effects over the alpha blocking effects.
Calcium channel
blockers
administered intravenously can be used for treatment for hypertension. However, they have not attracted much attention from the team of people who deal with cardiac surgery patients. Intravenous infusion, though popular among neurosurgeons for control of hypertension, is not considered the first line or even the second line of drug when it comes to treating hypertension in cardiac surgery patients. Intravenous Cordarone though useful for the control of ventricular rate in patients in the presence of arterial fibrillation with rapid ventricular response, is regularly used for control of hypertension. I personally have never used cord ozone IV for treatment of hypertension.
Using a combination of drugs that reduce the
peripheral vascular resistance, reduce the contractility of the left
ventricle, and reduce the volume expansion in for those patients where the
maximum dose of one drug to fail to bring down the blood pressure. In
those patients we could consider using:
-Nitrates to reduce venous return and resistance
-Beta-blockers to reduce contractility
-Diuretics to reduce volume overload.
After extubation, patients generally feel better. The blood pressure may spontaneously improve with extubation and pain control. Hence, we need to titrate down intravenous infusion once the patient becomes more comfortable and less irritable. However, those who were hypertension before surgery need long acting medicines to maintain their blood pressure. They can be resumed on the pre-surgery regimen through a reduced dosage and gradually wean off the intravenous blood drip as the blood pressure gradually comes down. We should be able to switch over to oral pills and discontinue the intravenous therapy within 24 hours after the initiation of the oral medications.
