Successful management of severe hypoventilation and hypercapnia in an alpaca (Vicugna pacos) with short‐term mechanical ventilation

Objective – To describe the successful management of an alpaca with severe hypoventilation and hypercapnia, suspected to be secondary to an anesthesia‐related event. Case Summary – A 3‐year‐old, female alpaca underwent a routine eye enucleation under general anesthesia after traumatic globe perforation. Severe hypoventilation and associated hypercapnia developed postoperatively resulting in a severe primary respiratory acidosis. The awake alpaca was supported with positive‐pressure ventilation for approximately 20 hours before successful weaning. Recovery to hospital discharge occurred over the subsequent 5 days with the alpaca regaining apparently normal respiratory function. New or Unique Information Provided – To the knowledge of the authors, this is the first report describing positive‐pressure ventilation of an alpaca in the veterinary literature. In this case of severe hypoventilation, ventilatory support was essential to the positive outcome. As South American camelids continue to increase in popularity there may be an increased demand for high‐quality and sophisticated veterinary care for these animals. Mechanical ventilation can be used to help restore and maintain normal PO₂, PCO₂, and respiratory acid‐base status in alpacas with ventilatory dysfunction.     

Treatment of a dog with severe baclofen intoxication using hemodialysis and mechanical ventilation

Objective: This case report describes the successful management of a dog with coma and respiratory depression due to severe baclofen intoxication. Case summary: A Doberman Pinscher mixed breed dog ingested 500 mg (20 mg/kg) of baclofen. Signs of severe intoxication included coma and profound respiratory muscle weakness. The dog was supported with positive pressure ventilation and treated with one session of hemodialysis. Weaning from the ventilator was achieved within 4 hours of hemodialysis, and recovery from coma occurred over the following 12–36 hours. The dog regained full neurologic function and was normal at discharge following 3 days of hospitalization. New or unique information provide: Severe central nervous system depression and respiratory depression due to baclofen intoxication can be life threatening. In addition to other supportive care, hemodialysis may hasten recovery and ventilatory support may be essential to achieve a positive outcome. With successful treatment, toxicity can be decreased and the associated life‐threatening central nervous system and ventilatory depression can resolve. Prognosis for return of normal function is excellent.     

Desflurane vapor pressure depression

Due to its high vapor pressure and low boiling point, desflurane requires a specially designed, electronically controlled, temperature and pressure compensated vaporizer to regulate agent delivery to the anesthetic circuit. However, if the vapor pressure and boiling point were decreased, desflurane could be used in any conventional variable bypass vaporizer. Raoult's Law states that the vapor pressure of a liquid is proportional to its molar fraction in a solution. Accordingly, propylene glycol was used as a solvent for desflurane, and the physical characteristics of this mixture were evaluated at various molar concentrations and temperatures. Desflurane boiling point increased and vapor pressure decreased as a nonlinear function of dilution, but these changes were less than predicted by Raoult's Law. Using a circle system with a breathing bag attached at the patient end and a mechanical ventilator to simulate respiration, an in‐circuit, nonprecision vaporizer containing 40% desflurane and 60% propylene glycol achieved a 11.5 ± 1.0% (mean ± SD) circuit desflurane concentration with a 5.2 ± 0.4 (0 = off, 10 = maximum) vaporizer setting. This experiment was repeated with a dog attached to the breathing circuit under spontaneous ventilation with a fresh gas flow of 0.5 L min^–1. Anesthesia was maintained for over two hours at a mean vaporizer setting of 6.2 ± 0.4, yielding mean inspired and end‐tidal desflurane concentrations of 8.7 ± 0.5% and 7.9 ± 0.7%, respectively. Within 5 minutes after cessation of anesthesia, the dog was awake, extubated and standing. In clinical practice, propylene glycol may not prove an ideal solvent for desflurane due to its instability in solution and substantial positive deviation from Raoult's Law. However, rather than alter the vaporizer to suit physical properties of anesthetic agents, this study demonstrates that it may also be possible to alter anesthetic agents to suit physical properties of the vaporizer.     

Indication,management, and outcome of brachycephalic dogs requiring mechanical ventilation

Objectives – To evaluate the frequency, and need for mechanical ventilation (MV) in a population of brachycephalic dogs (BD) compared with non‐BD. Also, to describe the pre‐MV abnormalities, ventilator settings used, the cardiovascular and pulmonary monitoring results and complications encountered in the same BD population. In addition, we sought to identify factors associated with successful weaning and describe outcomes of BD requiring MV. Design – Retrospective observational study (1990–2008). Setting – University Small Animal Teaching Hospital. Animals – Fifteen BD managed with MV. Interventions – None. Measurements and Main Results – Signalment, indication for MV, ventilator settings, arterial blood gas values, duration of MV, complications, and outcome were recorded for each patient enrolled in study. BD were more likely to receive MV than non‐BD (P=0.036). Out of the 15 dogs that fulfilled the inclusion criteria 7 (47%) underwent MV for impending respiratory fatigue, 6 (40%) for hypoxemia and 2 for hypercapnea. The most common underlying disease was aspiration pneumonia. Duration of MV ranged from 2 to 240 hours (median 15 hours). Seven patients were weaned (47%). Seven dogs had a temporary tracheostomy tube and 5 of them (71%) were weaned. Dogs that were weaned had a significantly greater preweaning trial PaO₂/FiO₂ ratio than those that were not (359 ± 92 versus 210 ± 57 mm Hg, P=0.025). No significant difference for weaning success between dogs with and those without a tracheostomy was detected (P=0.132). The discharge rate was 27% (all from the respiratory fatigue group). Conclusion – Among all dogs admitted to ICU, BD were more likely to receive MV than non‐BD. Aspiration pneumonia was frequently identified as the underlying cause of respiratory compromise. The survival rate for BD undergoing MV was not markedly different from previous studies. Weaning of BD from MV may be facilitated by employing preemptive strategies such as performing tracheostomy tube placements.     

Ventilatory support of the critically ill foal.

Critically ill foals often have respiratory failure and benefit from respiratory support. Conventional mechanical ventilation using modem mechanical ventilators is easily adapted to foals. Establish-ing ventilator settings is a dynamic process aided by constant monitoring of blood gas values, end-tidal carbon dioxide, airway pressures, respiratory volumes, airway resistance, and respiratory compliance. Early weaning is as important as timely initiation of ventilation.     

Clinical use of positive-pressure ventilation in the horse

Positive-pressure ventilation is used to provide improved ventilatory support during anesthesia in the horse. Because of the horse's size and the physiologic changes it undergoes during anesthesia, however, the use of positive-pressure ventilation does not always provide the improvement seen in smaller species. Careful attention to respiratory rate, inspiratory pressure, and I:E ratio minimizes the negative aspect of IPPV on the cardiovascular system. The goal of future ventilatory techniques will be to improve oxygenation without cardiovascular compromise and to do so at a reasonable cost to the client.     

Cardiovascular and respiratory measurements in awake and isoflurane-anesthetized horses

Circulatory and respiratory function was monitored in nonmedicated, spontaneously breathing horses (n = 7) immediately before, during, and 1 hour after 85 +/- 4.1 (X +/- SEM) minutes of constant 1.57% isoflurane in O2 anesthesia. Comparison of values during anesthesia with those obtained while horses were awake revealed a significant (P less than 0.05) decrease in arterial blood pressure that was related to a slight, but insignificant, decrease in cardiac output and peripheral vascular resistance. Although isoflurane anesthesia and recumbency resulted in a significant (P less than 0.05) decrease in stroke volume, cardiac output did not decrease significantly because heart rate tended to increase. Isoflurane and recumbency also significantly (P less than 0.05) increased PaCO2, peak expiratory gas flow, total expiratory time, and PCV and significantly decreased PaO2, minute expired ventilation, and the ratio of peak inspired to expired gas flow. Differences imposed by isoflurane anesthesia were reversed by 1.5 hour after anesthesia.     

Successful ventilatory management of post‐anesthetic airway collapse and hypoxemia in a dog

Abstract Objective: To report a life‐threatening complication (airway collapse) associated with a common procedure (anesthesia) and to describe its successful management. Case Summary: A dog without pre‐existing signs of respiratory disease developed hypoxemia and severe atelectasis in the post‐anesthetic recovery period and was demonstrated, by bronchoscopic examination, to have severe airway collapse. Mechanical ventilation was used to re‐expand collapsed lung units and to prevent re‐collapse. A ventilation strategy designed to minimize airway and alveolar trauma was used. The dog was successfully weaned from the ventilator and made a full recovery. Unique Information Provided: Acute, severe hypoxemia due to airway collapse occurred in the post‐operative period in a dog with no signs of pre‐existing respiratory disease. The dog was successfully managed with short‐term mechanical ventilation. High frequency jet ventilation was used for a diagnostic bronchoscopy.     

End-tidal partial pressure of CO2 as an estimate of arterial partial pressure of CO2 during various ventilatory regimens in halothane-anesthetized dogs

The correlation between end-tidal partial pressure of CO2 (PETCO2) and arterial PCO2 (PaCO2) was studied in six halothane-anesthetized dogs maintained under four different ventilatory regimens: (A) spontaneous breathing; (B) assisted positive-pressure ventilation; (C) intermittent manual inflation; and (D) ventilator-controlled breathing. For procedures A, B, and D together, there was a strong correlation between PETCO2 and PaCO2 (r = 0.8) that was highly significant at P less than 0.0001 for PETCO2 values between 31.3 and 61 mm of Hg. In spontaneous and controlled breathing, PETCO2 is representative of PaCO2 and provides a useful noninvasive tool for monitoring the patient maintained under general anesthesia. Furthermore, data suggest that any ventilatory support of the anesthetized patient markedly improves blood gas and acid-base status compared with that of the unsupported, spontaneously breathing animal.     

Indications, management, and outcome of long-term positive-pressure ventilation in dogs and cats: 148 cases (1990-2001)

OBJECTIVE: To determine outcome of positive-pressure ventilation (PPV) for 24 hours or longer and identify factors associated with successful weaning from PPV and survival to hospital discharge in dogs and cats. DESIGN: Retrospective case series. ANIMALS: 124 dogs and 24 cats that received PPV for 24 hours or longer. PROCEDURES: Medical records were reviewed for signalment, primary diagnosis, reason for initiating PPV, measures of oxygenation and ventilation before and during PPV, ventilator settings, complications, duration of PPV, and outcome. Animals were categorized into 1 of 3 groups on the basis of the reason for PPV. RESULTS: Group 1 patients received PPV for inadequate oxygenation (67 dogs and 6 cats), group 2 for inadequate ventilation (46 dogs and 16 cats), and group 3 for inadequate oxygenation and ventilation (11 dogs and 2 cats). Of the group 1 animals, 36% (26/73) were weaned from PPV and 22% (16/73) survived to hospital discharge. In group 2, 50% (31/62) were weaned from PPV and 39% (24/62) survived to hospital discharge. In group 3, 3 of 13 were weaned from PPV and 1 of 13 survived to hospital discharge. Likelihood of successful weaning and survival to hospital discharge were significantly higher for group 2 animals, and cats had a significantly lower likelihood of successful weaning from PPV, compared with dogs. Median duration of PPV was 48 hours (range, 24 to 356 hours) and was not associated with outcome. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that long-term PPV is practical and successful in dogs and cats.     

Strategies for mechanical ventilation

With the advancement of veterinary critical care medicine, an increasing number of veterinary patients are being supported with positive-pressure ventilation. Animals with potentially reversible ventilatory failure (PaCO2 > 60 mmHg) caused by neuromuscular disease or pulmonary parenchymal disease or with pulmonary parenchymal disease causing hypoxemia (PaO2 < 60) despite supplemental oxygen are candidates for ventilatory support. The equation of motion for the respiratory system is defined and is used to describe the potential interactions between the patient and the ventilator. Commonly used modes of ventilation are described in terms of control and phase variables. The intent of this report is to aid clinicians in choosing an optimal ventilatory strategy for each patient that will best achieve the desired physiologic goals with minimal detrimental side effects.     

Ventilatory failure and successful management for a dog with severe cervical meningioma

A 12-year-old intact male mongrel dog with a weight of 22 kg was referred with a complaint of progressive tetraparesis. Cervical myelography revealed an intradural-extramedullary mass at the second cervical vertebra. After computed tomography (CT) under general anesthesia, the patient showed dyspnea and cyanosis caused by insufficient movement of the chest wall. Positive pressure ventilation was therefore initiated. Hemilaminectomy and partial mass removal were performed 12 hr after the CT. The mass was histopathologically diagnosed as meningioma. Gradual weaning from the mechanical ventilation lasted for 80 hr after the operation. The patient eventually recovered from the ventilatory failure and the tetraparesis at approximately 6 and 14 days after the operation, respectively.     

Anesthetic equipment fault leading to hypercapnia in a cat

Spontaneous ventilation during positive pressure ventilation was observed in a 4-year-old DSH cat maintained under general anesthesia with isoflurane delivered with a nonrebreathing system. This was accompanied by an increase in heart rate and blood pressure. On investigation, neither an inadequate plane of anesthesia, nor hypoxemia, nor hyperthermia was present. The nonrebreathing system was replaced and the hypercapnia resolved. A defect in the inner fresh gas delivery tube of the Bain system was identified. A simple and quick test is described which can be performed to verify the integrity of the inner tube of the Bain breathing circuit.     

Developments in management of the newborn foal in respiratory distress 2: Treatment

New developments in therapy for foals in respiratory distress are discussed. Therapy is based on preservation of the foal's life by maintenance of a patent airway, resuscitation with fluids and warmth, provision of humidified oxygen to raise the fractional concentration of inspired oxygen sufficient to avoid hypoxia and provision of ventilatory support when hypercapnia becomes critical. Ventilatory support described includes assisted and controlled ventilation, positive end expiratory pressure, continuous positive airway pressure and intermittent mandatory ventilation. The aims of these techniques are discussed together with their associated indications, disadvantages and complications. Secondary therapy includes coupage, airway hygiene, drug therapy and stress management. Knowledge of equine neonatology is limited in comparison with human neonatology. More information in basic physiology and pharmacology relating to equine neonatology is needed and the efficacy of various modes of therapy must be evaluated.     

Respiratory mechanics in Standardbred horses with sub-clinical inflammatory airway disease and poor athletic performance

The aim of this study was to investigate and quantify respiratory mechanical dysfunctions in Standardbred horses with both poor performance and bronchoalveolar lavage fluid cytology characteristic of inflammatory airway disease (IAD). A control group of healthy Standardbred horses was compared. Respiratory mechanics and breathing pattern were examined at rest and during hyperventilation induced using a rebreathing method. At rest, respiratory mechanics and breathing pattern were superimposable in both groups. In IAD horses, rebreathing increased ventilation, with larger tidal volumes and lower respiratory frequencies. During hyperventilation, IAD animals showed frequency-dependent dynamic lung compliance, and had greater viscous lung resistance and rate of dynamic work of breathing. As IAD alters pulmonary mechanics, the ventilatory load increases and horses requiring significantly higher energy for breathing may suffer restrictions in their athletic performance. This rebreathing method permits early evaluation of respiratory mechanical dysfunction in poorly performing horses with sub-clinical IAD.     

Evaluation of Elevent, a ventilator manufactured in Czechoslovakia for controlled ventilation during inhalation anesthesia in dogs]

Controlled breathing during halothane inhalation anesthesia was tested experimentally in fifty clinically healthy test dogs. In the first group the breathing regime was evaluated when a new Czechoslovak electronic ventilator Elvent was used in the course of 120-minute anaesthesia in 10 dogs. In the second group controlled ventilation was used in 40 dogs in the course of 180-minute anaesthesia with an administration of pipecurium as muscle relaxant. In the course of these experiments a total of 28 parameters was investigated to evaluate the effects of the given breathing regimes on the dog organism. An evaluation of the dynamics of changes in the target parameters indicated that the following model of ventilation programme with these parameters was the best: breathing rate 15-20 breaths per min., per-minute breathing capacity 1.5-3.5 l per min., breathing capacity from 0.15 to 0.25 l, inspiration length 0.8 to 1.2 s and twofold expiration length.     

A technique to depress desflurane vapor pressure

OBJECTIVE: To determine whether the vapor pressure of desflurane could be decreased by using a solvent to reduce the anesthetic molar fraction in a solution (Raoult's Law). We hypothesized that such an anesthetic mixture could produce anesthesia using a nonprecision vaporizer instead of an agent-specific, electronically controlled, temperature and pressure compensated vaporizer currently required for desflurane administration. ANIMAL: One healthy adult female dog. PROCEDURE AND RESULTS: Propylene glycol was used as a solvent for desflurane, and the physical characteristics of this mixture were evaluated at various molar concentrations and temperatures. Using a circle system with a breathing bag attached at the patient end and a mechanical ventilator to simulate respiration, an in-circuit, nonprecision vaporizer containing 40% desflurane and 60% propylene glycol achieved an 11.5% +/- 1.0% circuit desflurane concentration with a 5.2 +/- 0.4 (0 = off, 10 = maximum) vaporizer setting. This experiment was repeated with a dog attached to the breathing circuit under spontaneous ventilation with a fresh gas flow of 0.5 L minute(-1). Anesthesia was maintained for over 2 hours at a mean vaporizer setting of 6.2 +/- 0.4, yielding mean inspired and end-tidal desflurane concentrations of 8.7% +/- 0.5% and 7.9% +/- 0.7%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Rather than alter physical properties of vaporizers to suit a particular anesthetic agent, this study demonstrates that it is also possible to alter physical properties of anesthetic agents to suit a particular vaporizer. However, propylene glycol may not prove an ideal solvent for desflurane because of its instability in solution and substantial-positive deviation from Raoult's Law.     

Cardiopulmonary effects of halothane anesthesia in cats

The cardiopulmonary effects of 2 planes of halothane anesthesia (halothane end-tidal concentrations of 1.78% [light anesthesia] and 2.75% [deep anesthesia]) and 2 ventilatory modes (spontaneous ventilation [SV] or mechanically controlled ventilation [CV]) were studied in 8 cats. Anesthesia was induced and maintained with halothane in O2 only, and each cat was administered each treatment according to a Latin square design. Cardiac output, arterial blood pressure, pulmonary arterial pressure, heart rate, respiratory frequency, and PaO2, PaCO2, and pH were measured during each treatment. Stroke volume, cardiac index, and total peripheral resistance were calculated. A probability value of less than 5% was accepted as significant. In the cats, cardiac output, cardiac index, and stroke volume were reduced by deep anesthesia and CV, although only the reduction attributable to CV was significant. Systemic arterial pressure was significantly reduced by use of deep anesthesia and CV. Respiratory frequency was significantly lower during CV than during SV. Arterial PO2 was significantly decreased at the deeper plan of anesthesia, compared with the lighter plane. At the deeper plane of anesthesia, arterial PCO2 and pulmonary arterial pressure were significantly lower during CV than during SV. The deeper plane of halothane anesthesia depressed cardiopulmonary function in these cats, resulting in hypotension and considerable hypercapnia. Compared with SV, CV significantly reduced circulatory variables and should be used with care in cats. Arterial blood pressure was judged to be more useful for assessing anesthetic depth than was heart rate or respiratory frequency.     

Cardiovascular and respiratory effects of inspired oxygen fraction in halothane-anesthetized horses

Anesthesia of equids is associated with pulmonary dysfunction. Cardiovascular and respiratory effects of inhalation anesthetic agents and duration of anesthesia have been studied, using oxygen as the carrier gas. To our knowledge, the effects of inspired oxygen have not been determined. We studied the cardiovascular and respiratory effects of 2 inspired oxygen fractions (0.30 and greater than 0.85) in 5 laterally recumbent, halothane-anesthetized horses. Mean systemic arterial blood pressure, cardiac output, central venous pressure, pulmonary arterial pressure, arterial pH, and arterial base excess were similar in horses of the 2 groups during 4 hours of anesthesia at constant end-tidal halothane concentration. End-tidal partial pressure of CO2, arterial partial pressure of CO2 and O2, and alveolar-to-arterial O2 tension difference were greater in horses exposed to the higher oxygen concentration. On the basis of the data obtained, we suggest that greater hypoventilation and ventilation/perfusion mismatch occur when horses are breathing high-oxygen fraction. Arterial partial pressure of O2 was not different between the 2 groups of horses after they were disconnected from the anesthesia circuit and allowed to breathe room air. Horses recovered from anesthesia without complications.     

Respiratory disease in neonatal cloned calves

Background: Numerous clinical abnormalities occur in cloned calves during the neonatal period. Objectives: Describe respiratory diseases affecting cloned calves. Animals: Twenty‐five cloned Holstein calves. Methods: Retrospective clinical study of the cloned calves born at the Veterinary Teaching Hospital, Saint‐Hyacinthe, QC. Results: Records of 31 cloned calves were reviewed. Twenty‐five records were included. Four stillborn calves and 2 calves euthanized at birth were excluded. Twenty‐two calves suffered from respiratory diseases. Nineteen calves received intranasal oxygen treatment (INO). They were tachypneic (78 breaths per minute) and 5 of them were hypoxemic (PaO₂ < 55 mmHg). Two of 19 calves remained hypoxemic despite INO. Thirteen calves were weaned from INO after a median of 70 hours and were discharged at a median of 5 days of age. Nine calves required ventilatory support: 3 from birth and 6 after INO. Five were successfully weaned from the ventilator after a median of 32 hours and were discharged at a median of 8 days of age. Three calves died and 1 was euthanized because of respiratory disease. Necropsy revealed atelectasis, pulmonary congestion, and alveolar damages. Conclusion and Clinical Importance: Respiratory disease occurs frequently in cloned calves. The most frequent abnormality is hypoxemia because of V/Q mismatch. It is possible to successfully support these calves by INO and mechanical ventilation.