Anesthetic Management of Anemia
Choice of anesthesia will depend on the severity and type of anemia, extent of physiological compensation, concomitant medical conditions (e.g. lung and heart problem), type and nature of procedure (lower abdomen, extremity...) and anticipated blood loss. The main anesthetic considerations in chronic anemia are to minimize factors interfering with O2 delivery, prevent any increase in O2 consumption (shivering, fever) and to optimize the partial pressure of O2 in the arterial blood (Table2.2). The following measures need to be diligently adhered to in the perioperative period, while giving either general anesthesia or regional anesthesia
Spinal anesthesia is preferred for lower abdomen and limb surgery, if the acute volume status is corrected, as they are associated with reduced blood loss. However, spinal anesthesia is fraught with imminent dangers of hypotension; it is advisable to use vasoconstrictors to sustain blood pressure.
Avoidance of hypoxia
- Preoxygenation is mandatory with 100% O2.
- Oxygen supplementation should be given in the peri- and postoperative period.
- Maintenance of airway is important to prevent fall in FiO2 due to airway obstruction, difficult intubation, etc. Hence measures and expertise to secure a definitive airway should be available immediately.
- Spontaneous ventilation technique is suitable only for short procedures. High FiO2 (40-50%) is administered to overcome effects of hypoventilation. High concentration of volatile agents depresses both the myocardium as well as ventilation resulting in an undesirable decrease in O2 flux.
- Aggressively treat and avoid conditions that increase the O2 demands like fever, shivering, acute massive blood losses leading to an acute drop of Hgb below 7 gm/dL
Minimize drug-induced decreases in cardiac output (CO)
- Intravenous induction of anesthesia should be slowly titrated to prevent precipitous fall in CO.
- Careful positioning of the patient to minimize position associated volume shifts.
- Mild tachycardia may be physiological and should not be confused with light anesthesia
Table 2.2 Important Points on Techniques of Anesthesia
- In elective surgery aim is to have the preoperative Hgb as close to 10 gm/dL as possible. A minimum of 8gm/dL should be aimed at. A relatively fit patient with chronic anemia may cope surgery with a Hgb as low as 7gm/dL whereas a patient with cardiac disease who may have a reduced cardiac output would not. The acceptable Hgb level will depend on the type of surgery, the patient’s general condition and the expected blood loss.
- In patients with Hb less than 5gm/dL operate only in emergencies where surgery is life saving, e.g. massive intra-abdominal bleeding.
- Blood should be given as soon as it is available.
- These patients have minimum oxygen reserve. Hypotension or hypoxia can cause cardiac arrest. The possibility of high output cardiac failure must be considered.
- Transfuse or treat to correct anemia preoperatively one unit of blood raise 1gm of Hgb .
- Avoid excess pre-operative sedation.
- Oxygenate before induction.
- Avoid myocardial depressants. Use ketamine instead of thiopentone and inject slowly.
- Use small doses of drugs.
- Have a good IV line in progress before you start.
- Use a high oxygen concentration.
- Intubate and ventilate except for very short procedures.
- Replace blood loss carefully with whole blood or packed cells.
- Keep the patient warm and warm IV fluids.
- Extubate only when the patient is making a strong ventilatory effort.
- Give the patient oxygen in the post-operative period – up to 100% O2 if the patient is shivering.
Intraoperative monitoring: Monitoring should be aimed at assessing the adequacy of perfusion and oxygenation of vital organs. It should include routine monitors like electrocardiogram, blood pressure, Temperature monitoring, pulse oximetry, urine output and serial Hgb and Hematocrit values can guide us to monitor ongoing blood losses.