Respiratory emergencies: postoperative management of respiratory distress (Proceedings)

Patients that have undergone emergency surgery to address respiratory distress are routinely supplemented with oxygen in the early recovery period and are monitored for oxygenation status using physical parameters (respiratory rate, respiratory character, and mucous membrane color), pulse oximetry (SpO2), and, when practical, arterial blood gases (PaO2). Clinical signs of hypoxia (increased respiratory rate, abnormal respiratory character, and pale, cyanotic, or "muddy" mucous membranes), low SpO2 (less than 96%), and low PaO2 (less than 80 mmHg) indicate continued use of supplemental oxygen. Oxygen therapy is continued if normoxia cannot be achieved when the animal is breathing room air, and positive-pressure ventilation with positive end-expiratory pressure may be necessary if normoxia cannot be achieved with administration of 100% inspired oxygen. Monitoring is not limited to the above mentioned parameters. All critically ill respiratory patients are evaluated at periodic intervals by assessing attitude, pulse rate and quality, and capillary refill time, and by performing thoracic auscultation. Invasive and/or noninvasive arterial blood pressure is monitored in patients with potential (or existent) hemodynamic instability. Intakes (parenteral fluid therapy and oral intake) and outputs (urine, emesis, and defecation) are monitored. Because of potential pulmonary compromise in certain respiratory distress patients intravenous fluid therapy must be performed judiciously to prevent volume overload; therefore, central venous pressure monitoring is employed.

Management Of Tracheostomy Tubes

Supplemental oxygen during recovery can be achieved through a small tube (8 french) placed into the lumen of the tracheostomy tube. The oxygen flow rate should be nearly half of what is required with intranasal oxygen administration because oxygen is delivered directly into the trachea, making the trachea an oxygen-rich reservoir. Upon recovery from anesthesia the need for supplemental oxygen is based on the oxygenation parameters listed above.

Tracheostomy tube hygiene is extremely important because of the risk of iatrogenic respiratory infection and the possibility of acute fatal obstruction due to accumulated respiratory tract secretions. Immediately after surgical placement and for the first several hours tracheostomy tubes require constant vigilance and hourly removal of intraluminal secretions. Around-the-clock observation and care are mandatory. Preferably, the tube in place is one with an inner cannula that can be temporarily removed for cleaning and sanitizing and then replaced. Small tracheostomy tubes (such as in toy dogs and cats) do not have inner cannulae; therefore, clean (ideally, sterile) soft suction catheters are inserted down these small tracheostomy tubes to clear the tubular lumens of secretions.

Strict adherence to asepsis cannot be overemphasized in tracheostomy tube maintenance. Unfortunately, it is rarely practical to use sterilized equipment at each tube cleaning session, but sanitization is possible. Use a 0.05% chlorhexidine solution to soak (and clean) tracheostomy tube components and suctioning accessories, but be sure to rinse with sterile saline any component that may come in contact with, or drip onto, respiratory tract tissues. Wear examination gloves when providing tracheostomy tube care, and remember to periodically cleanse the peristomal skin with warm 0.05% chlorhexidine solution. Scrub solutions are avoided to prevent contact of soap with respiratory epithelium.

Humidification of the airway is important to decrease the viscosity of respiratory secretions and facilitate their removal. Humidification is achieved by instillation of 2 to 3 ml of sterile isotonic saline solution into the trachea at the end of each tube cleaning session. If humidification is not sufficient to prevent respiratory tract dessication and development of viscous secretions, aerosol therapy can be performed.

When it is determined that the tracheostomy tube is no longer needed anchoring sutures and umbilical tapes are cut, the tube is extracted, and the resultant open wound is allowed to heal by second intention. The patient may continue to breathe through the stoma for several days until sufficient wound contraction occurs.

Postoperative Care After Tracheal Resection/Anastomosis

Intranasal oxygen administration is recommended in the early recovery period and is continued based on individual patient needs which are determined as described above. Likewise, postoperative monitoring is performed as described above.

Monitoring for dehiscence of the anastomotic suture line is by physical examination. The obvious clinical sign of a leaky tracheal anastomosis is subcutaneous emphysema, particularly with cervical tracheal disruption. Pneumomediastinum, detected by thoracic radiography, may be present when the intrathoracic trachea is the source of leakage; however, pneumothorax, a more life-threatening condition, could develop with intrathoracic tracheal anastomosis discontinuity because the mediastinum is perforated during surgical dissection. Pneumothorax can be diagnosed radiographically, but observing altered respiratory character and detecting hyper-resonance on thoracic percussion should prompt thoracocentesis to confirm the suspicion in dyspneic animals. Patients with intrathoracic tracheal anastomosis should have an intra-operatively placed thoracic tube present during the early recovery period. This tube is in place to monitor for pneumothorax during recovery, but is usually removed within a few hours after thoracotomy; therefore, subsequent suspicions of pneumothorax due to tracheal anastomotic dehiscence will require confirmation by thoracocentesis followed by thoracic radiography.

Management Of Thoracostomy Tubes

Once a thoracostomy tube is in place efforts must be made to prevent iatrogenic introduction of air. Ideally, the thoracostomy tube will be interfaced with a continuous suction unit. These units have a safety mechanism, the water seal, that prevents atmospheric air from entering the patient if there is a disconnection from the suction source. However, a hole in the thoracostomy tube or in the tubing between the patient and the continuous suction unit, or a loose connection between the thoracostomy tube and the tubing connecting it to the suction unit, will permit introduction of atmospheric air into the patient's pleural space. Fortunately, the water seal provides a means of monitoring for this situation. The water seal should not routinely bubble. Bubbling in the water seal indicates that the suction unit is pulling in air. That air is either atmospheric air being pulled into the tubing or air produced by ongoing pneumothorax. In the latter case, air bubbling indicates successful management of pneumothorax until the abnormality causing the pneumothorax is corrected and the bubbling stops. Bubbling due to a leak in the system between the patient and the suction unit must be ruled out by inspection of the tubing and connections because, if iatrogenic introduction of air into the pleural space is occurring, the patient's life could be in jeopardy in a matter of seconds. Tubes that are not attached to continuous suction units are monitored by periodic manual aspiration with a syringe. Care must be taken to avoid excessive suction pressure which could injure the lungs. Iatrogenic introduction of air is avoided by proper knowledge and use of connectors, tubing clamps, and three-way stopcocks.

Thoracostomy tubes must also be monitored to prevent premature dislodgement. Naive reliance on friction sutures that anchor the tube may result in premature removal. Likewise, bandages may provide a false sense of security because as a loose bandage slips it may actually pull the thoracostomy tube with it. Physical restraint (such as an Elizabethan collar) and sometimes chemical restraint (tranquilization) will be necessary to prevent premature dislodgement in active patients. If the animal's activity creates doubts as to the ability to prevent premature dislodgement assess the true need for the tube, and remove the tube if it is not serving a useful and necessary purpose. Controlled removal is less likely to create complications than the traumatic removal associated with the animal dislodging the tube.

Tube removal can be uncomfortable; therefore, analgesia is warranted. The author instills local anesthetic (typically a 9:1 solution of 2% lidocaine:sodium bicarbonate) in the subcutaneous tissues and musculature, including the intercostal space, surrounding the tube. The local block will not totally eliminate discomfort because the tube will traverse sensitive pleural surfaces on the way out. Interpleural bupivacaine can be used to obviate the intrathoracic component of the discomfort. The skin around the tube is cleansed with chlorhexidine scrub, the friction sutures are cut, the tube is clamped, and gentle traction is applied to effect removal. It is important that the tube does not tear lung tissue on the way out. Lung damage could occur if excessive suction was applied to the tube immediately prior to removal. Therefore, inject 4 to 5 ml of air into the tube immediately prior to removal to ensure that no lung tissue has been sucked into the tube. Air injection should not be necessary as long as no suction is applied to the tube after instillation of interpleural bupivacaine.

Postoperative Care After Diaphragmatic Herniorrhaphy

Postoperative care of patients after diaphragmatic hernia repair encompasses the respiratory and general monitoring described in the introduction as well as interventions common to animals after abdominal surgery, such as enteral nutritional support via jejunostomy tubes. Hemodynamic monitoring is also important, particularly in acutely operated cases because of previously reported high mortality in the first 24 hours after the inciting trauma. Actually, advances in critical care applied to postoperative diaphragmatic hernia patients are probably responsible for the lower mortality rates we see with these patients today compared to what has been previously reported.

Diaphragmatic herniorrhaphy patients have thoracostomy tubes in place for the first few postoperative hours to allow removal of residual pneumothorax and provide for slow re-expansion of residually atalectic lungs. These tubes exit the abdomen instead of an intercostal space and, conceivably, could be mistaken for a feeding tube. Clear labeling of the thoracic and feeding tubes should be performed to avoid serious mistakes such as administration of liquid diet into the thoracic cavity. Thoracostomy tube removal is painful because there is no easy way to use local anesthetic techniques to ameliorate the discomfort associated with peritoneal stimulation as the tube traverses the abdominal cavity. Giving a dose of buprenorphine (0.005 to 0.02 mg/kg IV, IM, or SC) 10 to 15 minutes prior to tube removal may help in this regard. In the author's experience patient tolerance for removal of this type of thoracic tube is high as long as local anesthetic is used interpleurally and subcutaneously around the tube, buprenorphine is given, and traction on the tube is gentle and steady.

Analgesic Medication

Preemptive analgesia is commonly practiced today, and is particularly useful in respiratory patients because early prevention of pain typically means less need for potent analgesics which could contribute to respiratory depression. As such, analgesic administration should begin before the end of the anesthetic episode, preferably as part of the pre-anesthetic drug regimen. Although there are multiple acceptable analgesic regimens for postoperative respiratory distress patients, most can be managed with either buprenorphine (dogs and cats) or morphine (dogs). Currently, the most common postoperative analgesic protocol used by the author is buprenorphine given as a constant rate IV infusion (0.04 mg/kg/day) for the first 12 to 36 hours until a switch can be made to an oral nonsteroidal anti-inflammatory drug or tramadol. Morphine is often chosen when the majority of the pain is somatic (musculoskeletal) in origin, such as with head and neck surgery (tracheostomy) and thoracotomies. Morphine is most commonly given as a constant rate IV infusion (0.1 mg/kg/hr). As an adjunct to opioid analgesia, or to minimize the amount of opioids used, lidocaine (20 mcg/kg/min) may be used (dogs only) as a constant rate IV infusion for the first 12 to 24 hours. When given together for infusion, buprenorphine (or morphine) and lidocaine may be mixed in the same bag of fluids, typically normal saline or the maintenance crystalloid solution being used for fluid therapy.