Anesthesia and Monitoring of the Thoracotomy Patient

During intrathoracic surgery the negative pressure that normally exists in the thoracic cavity and is necessary for lung expansion is disrupted by surgery. Therefore, these patients need to be provided with positive pressure ventilation. This can be done manually, which can be very labor intensive for the anesthetist, or by the use of a mechanical ventilator, which is recommended. Usually normal tidal volumes of 15-20 mls/kg are acceptable. Peak inspiratory pressure (PIP) is normally limited to 15-20 cm H2O. In some cases where there is significant pressure on the diaphragm from enlarged abdominal organs or in the case of a diaphragmatic hernia, higher pressures may be needed to deliver adequate tidal volumes. Respiratory rates of 8-12 breaths per minute as usually adequate. It is important to maintain adequate tidal volumes to help prevent atelectasis. The use of capnography to monitor the adequacy of ventilation is ideal. ETCO2 levels should be maintained at 35-45 mm Hg. Thoracotomy patients will often de-saturate at some point during the procedure so a plan for dealing with this complication should be made. Desaturation can occur at any time during surgery but can often occur just after induction during the surgical prep depending on the lesion and the condition of the patient. If it is a case of pneumo/chylo/hemo thorax, a thoracocentesis or aspiration of existing chest tubes usually helps saturation return to acceptable levels. If possible, the affected side of the chest should be put down. Ideally respiratory compromised patients should be placed in sternal recumbency but this is also not practical for surgery. Very often turning a patient onto its back for surgical prep can have catastrophic results. Patients can actually arrest when they are flipped into dorsal. If at all possible, prep these patients “side to side,” build an incline on the surgery table so that the head remains higher than the tail. The use of positive end expiratory pressure (PEEP) can be extremely helpful in treating desaturation during surgery. PEEP can be applied manually or with PEEP valves which are commercially available in various sizes. Monitoring ventilation on thoracotomy patients under anesthesia can be done a number of ways. Ventilation is assessed in terms of rate, rhythm, and tidal volume. First of all, a good look at the patient’s chest excursions should be done to evaluate for quality and effort. Auscultation of the lungs should be performed prior to sedating or anesthetizing any patient. Normal lung sounds should be heard on both sides of the chest. Any abnormal sounds should be investigated prior to moving forward with anesthesia as anesthetic drugs can depress respiration and ventilation and may worsen existing problems. Mucous membrane color should be assessed regularly. The tongue and gums should be pink. Any change in color, especially blue or purple tingeing can indicate hypoxemia. Respirometers can be used to measure tidal volume and minute volume. Expired gas passes through oblique slits, which creates circular gas flow in a chamber, causing rotation of a doublevaned rotor. The rotor is coupled via a set of linkage gears to a display indicator dial and needle. Accumulated minute volume is recorded and each breath’s tidal volume can be viewed. The respirometer measures volume in one direction only. Flow can be calculated by averaging recorded volumes over time. Respirometers may be especially helpful during recovery to ensure that the patient is ventilating well enough to be removed from support. Apnea or respiratory monitors detect the movement of gas through the proximal end of the endotracheal tube. They